Modern Welding 1635636868, 9781635636864

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Designed to help today's welding programs provide students with the skills and knowledge required for entry-level employment Aligned with AWS SENSE Level I and Level 11 certification criteria.

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Be Digital Ready on Day One with EduHub EduHub provides a solid base of knowledge and instruction for digital and blended classrooms. This easy-to-use learning hub delivers the foundation and tools that improve student retention and facilitate instructor efficiency. For the student, EduHub offers an online collection of eBook content, interactive practice, and test preparation. Additionally, students have the ability to view and submit assessments, track personal performance, and view feedback via the Student Report option. For instructors, EduHub provides a turnkey, fully integrated solution with course management tools to deliver content, assessments, and feedback to students quickly and efficiently. The integrated approach results in improved student outcomes and instructor flexibility. Flamingo Images/Shu«e,stoda,111,._

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Experiments provide opportunities to apply knowledge gained from the chapter to further explore the world of welding.

TOOLS FDR STUDENT AND INSTRUCTOR SUCCESS EduHub EduHub provides a solid base of knowledge and instruction for digital and blended classrooms. T his easy-to-use learning hub provides the foundation and tools that improve student retention and facilitate instructor efficiency. For the student, EduHub offers an online collection of eBook content, interactive practice, and test preparation. Additionally, students have the ability to view and submit assessments, track personal performance, and view feedback via the Student Report option. For instructors, Edu Hub provides a turnkey, fully integrated solution with course management tools to deliver content, assessments, and feedback to students quickly and efficiently. The integrated approach results in improved student outcomes and instructor flexibility. Be digital ready on day one with EduHub! • eBook content. EduHub includes the textbook in an online, reflowable format. The interactive eBook includes highlighting, magnification, note-taking, and text-to-speech capabilities. • Video Clip Library. EduHub includes a video clip library containing 30 video clips. These clips include demonstrations of common welding and thermal cutting processes. • Lab Workbook content. EduHub includes all of the assessments contained in the printed Lab Workbook in digital format: chapter review questions (with auto-grading capability) and lab activities. • Interactive activities. EduHub provides engaging activities to help students master the technical vocabulary, concepts, and procedures presented in the textbook.

Student Tools Student Text Modern Welding is a comprehensive text that provides curriculum support for a col lege-level welding program. The textbook is an exciting, full-color, and highly illu strated learning resource. It is available in print or online versions.

Lab Worl(boob: The Lab Workbook combines review questions and activities that relate to the content of the textbook chapters. Questions designed to reinforce the textbook content help students review their understanding of the terms, concepts, theories, and procedures presented in each chapter. Jobs provide an opportunity to apply and extend knowledge gained from the textbook chapters. T he Jobs are completed in the welding lab with instructor guidance and supervision.

Instructor Tools LMS Integration Integrate Goodheart-Willcox content in your Learning Management System for a seamless user experience for both you and your students. Contact your G-W Educational Consultant for ordering information or visit www.g-w.com/lms-integration.

Instructor Resources Instructor Resources provide all the support needed to make preparation and classroom instruction easier than ever. Available in one accessible location, you will fi nd instructor resources , Instructor's Presentations for PowerPoint®, and assessment software w ith question banks. These resources are avail able as a subscription and can be accessed at school, at home, or on the go.

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Instructor Resources One resource provides instructors with time -saving preparation tools such as answer keys, chapter outlines, editable lesson plans, and other teaching aids.

Instructor's Presentations for PowerPoint® Instructor's Presentations for PowerPoint" provide a useful teaching tool when presenting the lessons. These fully customizable, richly illustrated slides help you teach and visually reinforce the key concepts from each chapter.

Assessment Software with Question Banks Administer and manage assessments to meet your classroom needs. The following options are available through the Respondus Test Bank Network: • A Respondus 4.0 license can be purchased directly from Respondus, which enables you to easily create tests that can be printed on paper or published directly to a variety of Learning Management Systems. Once the question files are published to an LMS, exams can be distributed to students with results reported directly to the LMS gradebook. • Respondus LE is a limited version of Respondus 4.0 and is free with purchase of the Instructor Resources. It allows yo u to download question banks and create assessments that can be printed or saved as a paper test.

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EXPERT AUTHORS TRUSTED REVIEWERS 100 YEARS OF EXPERIENCE

EMPLOYABILITY SKILLS · TECHNICAL SKILLS · ACADEMIC KNOWLEDGE · INDUSTRY RECOGNIZED STANDARDS

by

Andrew D. Althouse Technical-Vocational Education Consultant Member, American Welding Society

Carl H . Turnquist Career Education Consultant Member, American Welding Society

William A. Bowditch Career Education Consultant Portage, Michigan Member, American Welding Society Member, Association for Career and Techflfcal Educati,pn

Kevin E. Bowditch Welding Engineer Specialist Subaru of Indiana Automotive, Inc. Lafayette, Indiana Member, American Welding Society Member, Association for Career and Technical Education

Mark A . Bowditch Member, American Welding Society Member, Association for Career and Technical Education

Publisher

The Goodheart-Willcox Company, Inc. Tinley Park, IL www.g-w.com

Copyright © 2020 by The Goodheart-Willcox Company, Inc. P1-evious editions copyright 2013, 2004, 2000, 1997, 1992, 1988, 1984, 1980, 1976, 1970, 1967 All rig hts reserved. No part of this work may be reproduced, s tored, or transmitted in any form or by any electronic or mechanical means, including information s torage and retri eval systerns, without the prior written pern,ission of The Goodheart-\lV-illcox Company, Inc. Manufactured in the United States of America. Library of Congress Catalog Card Nun1ber 2018032044 ISBN 978-1-63563-686-4

2 3 4 5 6 7 8 9 - 20 - 23 22 21 20 19 The Good heart-Willcox Company, Inc. Brand Disclaimer: Brand names, con1pany names, and illustrations for products and services included in this text are provided for educationa l purposes only and do not represent or imply endorsenwnt or recon1mendation by the author or the p ublisher. The Good heart-\-Villcox Company, Inc. Safety Notice: The reader is expressly advised to carefu lly read, understand, and apply a ll s.1fety precaut·ions and warn ings described in th is book o r that might also be ind icated in undertaking the activities and exercises described herein to min imize risk of personal inju ry or injury to others. Common sense and good judgment shou ld a lso be exercised and applied to help avoid a ll potential hazards. The reader shou ld a lways refer to the appropriate manufacturer's technical information, directions, and recommendations; then proceed wi th care to follow specilic equipmen t operating instructions. The reader should understand these notices and cautions are not exhaustive. Th e publisher makes no warranty or representation whatsoever, e ither expressed o r implied, including but not li mited to equ ipment, procedures, and applications described or referred to herein, their quality, performance, merchantability, o r fitness for a particular p urpose. The publisher assumes no responsibi lity for any changes, errors, or om issions in this book. The publisher specifica lly disclaims any liabi lity whatsoever, including any d irect, ind irect, incidental, consequential, special, o r exemplary damages resu lting, in whole or in part, from the reader's use or reliance upon the information, instructions, procedures, warnings, cautions, applications, or other n,atter contai ned in this book. The publisher assumes no responsib ility for the activities of the reader. The Goodheart-Willcox Company, Inc. Internet Disclaimer: TI1e Internet resources a nd listings in this Goodheart-Willcox Publis her product are provided solely as a convenience to you. These resources and listings were reviewed a t the tin1e of publication to provide you with accurate, safe, and appropriate information. Goodheart-\'lillcox Publisher ha s no control over the referenced websites and, d ue to the dynamic nature o f the Jnternet, is not responsible or liable for the content, products, or peiformance of li nks to othe r websites or resources. Goodheart-Willcox Publisher makes no representation, e ither expressed o r implied , regarding the content of these websites, and such references do not constitute an end orsement or recommendation of the information or content presented. It is your responsibili ty to take a lI protective measures to gua rd against inappropriate content, v iruses, or other destructive e lements. Cover Image Credit: zilber42/Shutterstock.com.

l ibrary of Congress Cataloging-in-Publication Data Names: Althouse,Andrew D. (Andrew Dan iel), 1895-1980 au thor. I Tu rnquist, Carl H. (C~rl Harold), 1910- au thor. I Bowd itch, William A., author. I Bowditch, Kevin E., author. I Bowditch, Mark A., a uthor. Title: Modern welding / by Andrew D. Althouse, Carl H. Tun,quist, William A. Bowdi tch, Kevin E. Bowditch, ~1ark A. Bowditch. Description: 12th edi tion. I Tin ley Park, TL : The Goodhea rt-Willcox Company, Inc., (2020) I lncludes index. I Revised edition of Modern welding/ by Andrew 0 . Althouse ... [etal. ). 2013. Identifiers: LCCN 2018032044 I ISBN 9781635636864 Subjects: LCSH: Weld ing. I Metals. Oassification: LCCTS227 .A369 2020 I DOC 6n.5/2-reakmedta/fstock.com

What's New? This edition of Modern Welding includes updated content and coverage of new welding topics in order to align the textbook \.Vith both SENSE Level I and Level II standards. In addition, organization of the arc welding sections of the book has been improved. In this edition, gas tungsten arc 'A7elding material is presented in its own section. Coverage of flux cored arc welding has been expanded as well. Chapter 31, Procedure and Welder Qualifications, has been greatly expanded and revised. A Quick Reference table of contents has been added. The Quick Reference I.is ts useful tables of information that students will likely need to reference repeatedly as they learn to ,.veld. The listed tables help students with tasks such as selecting the proper electrodes, determining proper 1nachine settings, and setting gas flow rates. The entries in the Quick Reference are divided into sections based on welding process. End-of-chapter questions have been divided into three headings. "Know and Understand" questions test recall of subject matter, "Apply and Analyze" short-ans"Arer questions ask the student to describe, explain, compare, differentiate, etc., and "Critical Thinking Questions" require deeper thinking and engage higher-order thinking skills. In addition, an "Experiment" has been added to the end of each d 1apter. These experi1nents encourage students to further explore \.Velding concepts with hands-on activities. This edition also includes new feahlres. E111ployability features have been added in several chapters to provide in forn1ation pertaini11g to seeking employ1nent and succeeding in a career. Pro Tip features call out work practices and advice. The Nonstandard Tenninology fearnres differentiate between AWS-approved terminology and the nonstandard teru1s often encountered on the job.

Color Code Many of the drawings in Mcxl.ern Welding are color coded for quick identification of the components shown. By comparing the color of a component in a drawing to the following color code key, the student can detern1.ine the function of the co1nponent. In figures, travel angles a re sho,.vn in red and work angles are shown in black to help differentiate between these in1portant angles.

How to Use the Key Colors are used throughout Modern Welding to help show the flow of different gases and to indicate various 1naterials or equipn1ent features. The following key shows what each color represents. Gases Oxygen Fuel gas

high-pressure high-pressure

0

~

low-pressure

Shielding gas (1) high-pressure

low-pressure

Shielding gas (2) high-pressure Air

Weld Base metal or plastic Molten metal or plastic Welding rod Weld bead or surfacing material Flame, arc, or plasma

□ □ □ □

Electrode Flux Slag Fumes Direction or motion

high-pressure

□ □ □ ~

•

~

D

low-pressure low-pressure

~

vacuum

D D D

Welding machines/equipment Wires , leads, graph curves Water

Other Materials Special features, materials, or components not otherwise color-coded

□

VII

Brief Contents Part 1 Welding Fundamentals 1 Safety in the Welding Shop .... . . ...... ...... 3 2 Print Reading ..... . .......... . ........... 25

Welding Joints, Positions, and Symbo ls ...... 37 4 Welding and Cutting Processes . . . . ......... 69 3

Part2 Shielded Metal Arc Welding 5

Shielded Metal Arc Welding Equipment and Supplies ....... . . . ..... . .. 103

6

Shielded Metal Arc Welding...... . ........ 127

16 Soldering . ....... . . . . . ..... .. ... . ..... . . 433

17 Brazing and Braze Welding .. . . . . . . . ...... 457

Part7 Resistance Welding 18 Resistance Welding

Equip1nent and Supplies ..... . ... . . . ...... 485 19 Resistance Welding .... .....•.....•...... 513

Parts Special Processes 20 Special Welding Processes ................ 535 21

Part3 Gas Metal and Flux Cored Arc Welding 7 GMAW and FCAW Equip1nent and Supplies ....... ...... ... . . 169 8 Gas Metal and Flux Cored Arc Welding ..... 195

Part4 Gas Tungsten Arc Welding 9

Gas Tungsten Arc Welding Equipment and Supplies ..... . ............ 241

1O Gas Tungsten Arc Welding ..... . . . . . . .. ... 263

Part 5 Plasma Arc Cutting 11

Plasma Arc Cutting . .......... ... ........ 301

Part 6 Oxyfuel Gas Processes

Special Ferrous Welding Applications ......... •. .... . .... 563

22 Spedal Nonferrous Welding Applications . ........ •. . . . ...... 583 23 Pipe and Tube Welding ................... 603 24 Spedal Cutting Processes .. . . . . . . . ........ 637

25 Underwa ter Welding and Cutting.......... 657 26 Automatic and Robotic Welding .... ....... 677

27 Metal Surfacing ... . ...... . ....... •. ... .. 697

Part9 Metal Technology 28 Metal Production, Properties, and Identification . . . .............. ... .... 719 29 Heat Treatment of Metals .......... . . ... .. 745

Part 10 Professional Welding 30 Inspecting and Testing Welds.............. 767

Proced ure and Welder Qualifications ....... 791 32 The Welding Shop . . ..................... 825

31

12 Oxyfuel Gas Welding Equipment and Supplies ..... . . . . . . . ...... 321

33 Getting and Holding a Job in the Welding Industry ... ... ... .. • ...... 845

13 Oxyfuel Gas Welding........ ... . . . . ...... 353

34 Technical Da ta .... . . . ...... . . . . . ........ 857

14 Oxyfuel Gas Cutting Equipment and Supplies . .......... . ...... 395

Glossary ............................... 871

15 O>..-yfuel Gas Cutting ... . . ....... . . . ...... 409

Index ... . . ... ......... .. . . .. ......... .. 893

VIII

Contents Part 1 Welding Fundamentals .... . .... . . 2 Chapter 1 Safety In the Welding Shop. . ... . . . . .... . . . .. .. .3

1.1 1.2 1.3 1.4

1.5 1.6 1.7 1.8

Accidents ............... . . . ............ . 3 General Shop Safety ..................... 4 Safety in t he Welding Environment ....... 11 Oxyfuel Gas Welding and Cut ting Safet y .................... . . 16 A rc Welding and Cutting Safety .......... 19 Resistance Welding Safety ............... 21 Safety around Welding Robots ........... 22 Spedal Welding Process Safety ........... 22

Chapter 2 Print Reading . .. . . . ... . . .. ... . . . ... . .... . ... 25

2.1 Types of Dra~vings ..... . . ... ...... . ... . . 25 2.2 Orthographic Projection . ................ 26 2.3 Using a Working Drawing ... .......... . . 29 2.4 Types of Lines Used on a Drawing ........ 32 2.5 Drawings Made to a Scale ............. . . 33 2.6 The Title Block ......................... 33

Chapter 3 Welding Joints, Positions, and Symbols . . . . . . . 37

3.1 3.2 3.3 3.4 3.5 3.6 3.7

Basic Weld Joints ...... . ................ 37 Types of Welds ....................... . . 42 Joint Geometry ........ . . . .......... . ... 44 Welding Positions . ... ...... . . . ... . . . ... 45 The Welding Symbol. .. . . . . . ...... . . . . . . 48 Review of Welding Symbols ......... . . . . 62 Electrode Angles ...... . . . . . ........ . ... 62

Chapter 4

4.7 Solid-State Welding Processes ............ 91 4.8 Other Welding Processes .............. . . 97

Part 2 Shielded Metal Arc Welding .... . 102 Chapter 5 Shielded Metal Arc Welding Equipment and Supplies .. . . . . . ........ . . . .. 1 03

5.1 Shielded Metal Arc Welding Station . . .... 103 5.2 Arc Welding Power Source Classifications ....... . ................ . 104 5.3 Constant Current Power Sources......... 104 5.4 Arc Welding Power Source Specifications ......................... 108 5.5 Welding Leads ........ ...... ....... ... 109 5.6 SMAW Electrodes ..................... 112 5.7 Carbon and Low-Alloy Steel Covered Electrode Classification ......... 114 5.8 Nonferrous Electrode Classifications ..... 119 5.9 Electrode Care ........................ 120 5.10 Power Source Remote Controls ......... . 121 5.11 Weld-Cleaning Equip1nent. ............. 121 5.12 Shields and Heln1ets . . ..... .... ... ... . . 122 5.13 Special Arc Welder Clothing ............ 124

Chapter 6 Shielded Metal Arc Welding . . ... .. . . . . . ... . . 127

6.1

6.2 6.3 6.4 6.5

Welding and Cutting Processes . . . ........ . . . . 69

4.1 4.2 4.3 4.4 4.5 4.6

A rc Welding Processes .................. 71 Oxyfuel Joining Processes .. . ............ 76 Oxygen Cutting Processes ............... 79 Resistance Welding Processes ............ 82 A rc Cutting Processes ................... 86 Spedalized Arc Welding Processes ....... 89

6.6 6.7 6.8 6.9

6.10

Direct Current (DC) Arc Weld ing Fundamentals .... . .. ... . . . 127 Alternating Current (AC) Arc Welding Fundamentals .......... . . . 131 Selecting an Arc Welding Machine . . . . . . . 132 Inspecting an Arc Welding Station ....... 134 Safety, Protective Oothing, and Shieldi ng ......... . ............... 135 Starting, Stopping, and Adjusting the Arc Welding Po,,ver Source for SMAW . .. . 136 DC Arc Blow .......................... 145 A re Welded Joint Designs ............... 147 SMAW Welding Techniques ............ 150 SMAW Safety Review .................. 165

IX

Part 3 Gas Metal and Flux Cored Arc Welding . . ... . .. .168 Chapter 7 GMAW and FCAW Equipment and Supplies ... 169

7.1

Gas Meta l A.re Welding (GMAW) and Flux Cored Arc Welding (FCAW) Welding Stations ...................... 169 7.2 Arc Welding Power Sources for GMAW and FCA\1\1 . ....... . . . ..... . 172 7.3 Wire Feeders Used with GMAW/ FCAW .. 174 7.4 GMAW/FCAW Shielding Gases . .. .. . . . . 176 7.5 The GMAW/ FCAW Welding Gun. . ...... 180 7.6 GMAW and FCAW Electrode W ire . .. . . . . 185 7.7 Smoke Extracting Systems ... . . . . . . . .... 191 7.8 Filter Lenses for Gas-Shielded Arc Welding.. 192 7.9 Protective Clothing .. . ...... . ... . ...... 192 7.10 Safety Review ......................... 192

Chapter 8 Gas Metal and Flux Cored Arc Welding . ...... 1 95

8.1 Gas Meta l Arc and Flux Cored 8.2 8.3 8.4 8.5 8.6 8.7 8.8 89 8.10 8.11

8.12 8.13 8.14 8.15 8.16 8.17

Arc Welding Principles ................. 196 Metal Transfer ........................ 196 GMAW and FCAW Power Sources ....... 202 Setting Up the GMAW/FCAW Station .... 202 Preparing Metal for Welding .. . ......... 218 Electrode Extension .................... 219 Welding Techniques ................... 220 Running a Bead . . .............. . ...... 221 Shutting Down the Station ............ . . 224 Welding Joints in the Flat Welding Position ............. . .... 224 Welding Joints in the Horizontal Welding Position ............ 226 Welding Joints in the Vertical Welding Position ............... 229 Welding Joints in the Overhead Welding Position . . ..... .. .... 231 Automatic GMAW and FCAW .... . ...... 232 Gas Metal Arc Spot Welding .. . ....... . . 233 GMAW/ FCAW Troubleshooting Guide ... 233 GMAW and FCAW Safety ............ . . 235

Part 4 Gas Tungsten Arc Welding . .... . 240 Chapter 9 Gas Tungsten Arc Welding Equipment and Supplies . . . . .... . . . . . ..... . . 241

9.1 The Gas Tungsten Arc Welding Station ... 241 9.2 Arc Weld ing Power Sources for GrAW ... 242 X

9.3 Shielding Gases Used with GTAW ....... 246 9.4 Electrode Leads and Hoses Used for GrAW .......... .. ..... 249 9.5 GTAW Torches ................. . ...... 250 9.6 Tungsten Electrodes ........ . .......... 253 9.7 Filler Meta ls Used with GTAW . .. . . . .... 258 9.8 Filter Lenses for GTAW ................. 259 9.9 Protective Clothing .................... 259 9.10 Safety Review ... . .......... . .......... 260

Chapter 10 Gas Tungsten Arc Welding . . . . .. . . ..... .. . .. 263

10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15 10.16

Gas Tungsten Arc Welding Principles .... 264 GTAW Power Sources .................. 268 Setting Up a GrAW Station ... . ....... . . 269 Preparing Metal for Welding . . . . ... . .... 281 Methods for Starting the Arc .. .. . . ...... 282 Gas Tungsten Arc Welding Techniques ... 283 Shutting Down the GTAW Station ....... 284 Welding Joints in the Flat Welding Position .. .... . • . •..... . . . 284 Welding Joints in the Horizontal Welding Position ..... .. ..... 288 Welding Joints in the Vertical Welding Position ............ .. . 290 Welding Joints in the Overhead Welding Position .......... . . . 291 Welding Stainless Steel and Aluminum ... 292 Se1niautomatic Welding .......... . ..... 294 Automatic and Mechanized GTAW ...... 294 GTAW Troubleshooting Guide . ......... 295 GTAW Safety ... . . . .... ... . . . . ........ 296

Part 5 Plasma Arc Cutting ....... . .... . 300 Chapter 11 Plasma Arc Cutting . .. . .. . . . .. ......... ... .. 301

11.1 Plasma Arc Cutting Principles .... . ...... 301 11.2 Plasma Arc Cutting Equipment and Supplies . . ....... . ...... 302 11.3 Plasma a nd Shielding Gases ..... • ...... 305 11.4 Setting Up the PAC Station....... . .... . . 308 11.5 Safety Equipment... ...... . ............ 308 11.6 PAC Cutting Procedures ......... . ...... 310 11.7 Plasma Arc Gouging ........ • .......... 316

Part 6 Oxyfuel Gas Processes . ... . ... . 320 Chapter 12 Oxyfuel Gas Welding Equipment and Supplies... 321

12.1 Co1nplete Oxyfuel Gas Welding Outfit. ... 321 12.2 Oxygen Supply ....................... . 322

12.3 12.4 12.5 12.6

U.7 12.8 U.9 12.10 12.11

Acetylene Supply ..... . ................ 329 Pressure Regulator Principles ........... 333 Welding Hoses ....... . ................ 339 Flashback Arrestors and 01ec k Valves ..... . . . ... . .... . ... . . 342 Oxyacetylene Torch Types .............. 343 Welding Tips... . . . ...... . ....... . . . ... 345 Welding Goggles and Protective Clothing ................ 347 Torch Lighters and Econontizers ......... 348 Oxyfuel Gas Welding Supplies .......... 349

Chapter 13 Oxyfuel Gas Welding . . . . . .... . . . ... . .... . . . 353 13.1 Introduction to Oxyfuel Gas Welding .................. 354 13.2 The Oxyfuel Gas Welding Outfit ... ... ... 358 13.3 Welding Preparation ....... . ........... 368 13.4 Oxyfuel Gas Welding Procedu res .... . . . . 375 13.5 Welding Positions ..................... 382 13.6 Welding Thick Metal. . . . . ............ . . 385 13.7 Appearance of a Good Weld ............ 387 13.8 Safety in Oxyfuel Gas Welding .......... 389

Chapter 14 Oxyfuel Gas Cutting Equipment and Supplies . . . . . . ......... .. ... 395 14.l Complete Portable Oxyfuel Gas Cutting Outfit ..... . . . . . ...... . . . . . 395 14.2 OFC Cutting and Cylinder Safety ..... . . . 396 14.3 Regulators for Oxyfuel Gas Cutting ... . . . 397 14.4 Cutting To rches ...... . ...... . ......... 397 14.5 Torch Guides.......... . . . ........ . . . . . 403 14.6 Multiple Torches . . . . . . . . . ... . ...... . . . . 406

Chapter 15 Oxyfuel Gas Cutting . . . . . .. . . . . . . . . . . .. ... . . 409 15.1 The Heat of Combustion of Steel. ........ 409 15.2 Oxyfuel Gas Cutting Process ............ 410 15.3 Cutting Outfit .... . . . . . ...... .. .... . . . . 410 15.4 Using a Cutt ing Torch .. . . . . . ...... . . . . . 413 15.5 Cutting Steel with an Oxyfuel Gas Cutting Torch.............. 419 15.6 Automatic Cutting .... . ........ . . . ..... 427 15.10 Safety in Oxyfuel Gas Cutting ........ . . . 430

Chapter 16 Soldering . . . . . . . . . . . .. ... . ... . . ...... . . . . . . 433 16.l Solde1·ing Principles and Advantages ..... 434 16.2 Soldering FiUer Metals . ................ 435 16.3 Soldering Fluxes ....... . . . . . ........ . . . 439 16.4 Soldering Procedures ...... .. .......... 441 16.5 Soldering Methods .... . . . ............ . 446 16.6 Special Soldering Procedures for Non-Copper A Uoys . . . . ............ . 452

16.7 Testing and Inspecting Soldered Joints ...... . ................. 454 16.8 Rev iew of Soldering Safety Practice . ..... 454

Chapter 17 Brazing and Braze Welding . . . . . . . ...... . . . .. 457 lZl Brazi11g and Braze Welding P rinciples ... . ................. 458 1Z2 Joint Designs for Brazin g and Braze Welding .................... 458 1Z3 Cleaning Base Metals Prior to Brazing or Braze Vleld ing ....... . .... 462 1Z4 Brazi11g and Braze Welding Fluxes . . . . . . . 462 1Z5 Brazing Filler Metals ... . ............... 465 1Z6 Brazi11g and Braze Weld ing Processes .. . . 468 1Z7 Brazing or Braze Welding wit h Various Alloys ... . ..... . . ..... .... 473 1Z8 Controlled-Atmosphere Brazing Furnaces . . . . . . . . . .. ..... . . . . . . 479 1Z9 Heat-Resistant Brazed Joints ............ 480 1Z10 Rev iew of Brazing Safety Practices . . . . . . . 480

Part 7 Resistance Welding . ........... .484 Chapte r 18 Resistance Welding Equipment and Supplies ... ....... . ... . ..... 485 18.l Electric Resistance Welding Machines .... 486 18.2 Transformers.......... . ......... . . ... . 487 18.3 Force Systems ........ . ................ 489 18.4 Conh·ollers ........... . ............... 491 18.5 Contactors ..................... . ...... 494 18.6 Resistance Welding Electrodes .... . . .... 495 18.7 Electrode Holders ..... . ... . ........... 499 18.8 Spot Welding Machines . . . .......... . . . 500 18.9 Projection Welding Equipment . ......... 505 18.10 Seam Welding Machines .......... . ... . 505 18.11 Flash and Upset Welding Machines . ... . . 506 18.12 Special Resistance Welding Machines .... . . ..... .. .. .. . .. . 508 18.13 Care of Resistance Welding Equiprnent... . . . . ..... . .... . .. 508

Chapter 19 Resistance Weldi ng ...... . ... .. ....... . ..... 513 19.1 Principles of Resistance Welding..... . .. . 513 19.2 Resistance Spot Welding (RSW) . . ....... 514 19.3 Projection Welding (PW) ............... 527 19.4 Resistance Seam Welding (RSEW) .. . .... 527 19.5 Flash Welding (FW) . . . . . . .... . . . ....... 528 19.6 Upset Welding (UW) ... . ... . .......... . 530 19.7 High-Frequency Resistance Welding ..... 531 19.8 Review of Resistance Welding Safety .. . . . 531

xi

Part 8 Special Processes . ..... ... . . .. . 534 Chapter 20 Special Welding Processes. ................. 535

20.1 20.2 20.3 20.4 20.5

Special Welding Processes ... .. .. . . ..... 535 Arc Welding (AW) Processes ..... . ... . .. 536 Solid-State Welding (SSW) Processes ..... 547 Other Welding Processes .... . . . . . ...... 554 Review of Safety................ . .. .... 560

Chapter 21 Special Ferrous Welding Applications .. ...... 563

21.1 Ferrous Metals and Alloys .............. 563 21.2 Welding Mediun1and High-Carbon Steels .............. . . 564 21.3 Welding Steel Alloys . . ...... . ... . ...... 565 21.4 Welding Chrome-Molybdenun1 Steels .... 568 21.5 Welding Precoated Steels ...... . . . . . .... 568 21.6 Welding Ma raging Steels ...... . . .. . . ... 569 21.7 Welding Stainless Steels ..... . . . . . ...... 569 21.8 Welding Dissi1ni lar Ferrous Meta Is ...... 576 21.9 Welding Cast Iron . . . . ...... . . . . . . . .... 577

Chapter 22 Special Nonferrous Welding Applications. . . .. 583

22.1 22.2 22.3 22.4 22.5 22.6 22.7 22.8 22.9 22.10 22.11

Nonferrous Metals and Alloys . . . . ...... 583 Alw11inum .................... . ...... 583 Welding Aluminum .......... . . . ...... 584 Welding Magnesiun1 .............. . ... . 590 Welding Copper and Copper Alloys...... 591 Welding Titanium ..................... 594 Welding Nickel-Based Alloys .. . . . ...... 597 Welding Zirconium .............. . . .. .. 598 Welding Beryllium ............. . ...... 598 Welding Dissi1nilar Meta Is ........ . ..... 598 Welding Plastics . . . . . . ...... . . . . . ...... 598

23.11 Code Requiren1ents ............. • ..... . 632 23.12 Welding Plastic Pipe ............ . .... . . 633 23.13 Review of Safety in Pipe and Tube Welding .......... . ...... 633

Chapter 24 Special Cutting Processes .................. 637

24.1 24.2 24.3 24.4

Air Carbon ATc Cutting (CAC-A) . . . . .... 637 Exothermic Cutting .................... 643 Oxygen Lance Cutting (OLC). . ... . ...... 649 Shielded Metal ATc Cutting and Go uging (SMAC) . ... . . . .... 651 24.5 Laser Bean1 Cutting (LBC) .............. 652 24.6 Water Jet Cutting . ... . .......... . ...... 653 24.7 Safety Revievv ......................... 653

Chapter 25 Underwater Welding and Cutting . . . ......... 657

25.1 Development of Underwater Welding .... 657 25.2 D3.6M Underwater Welding Code . .. . . . . 659 25.3 Welding Equipment for Underwater Welding ... ..... . . . . .... 660 25.4 Wet Welding .... . .......... . ... . ...... 661 25.5 Hyperbaric (Dry) Welding Undervvater ............ . ...... 663 25.6 C rack Repairs .. . ....... . ..... . . . ...... 666 25.7 Underwater Cutting ............ . ...... 666 25.8 Divi ng Operations ........... . . .•. ..... 671 25.9 Jobs in Underwater Welding ..... . ...... 673 25.10 Safety . . ....................... . . . .... 674

Chapter 26 Automatic and Robotic Welding. . . . . . ........ 677

26.1 26.2 26.3 26.4 26.5

Chapter 23 Pipe and Tube Welding . . . . . . .... . . . . . . ... .. . 603 23.1 Types of Pipe ... . .............. . ...... 604 23.2 Types of Tubing . . ........... . ......... 610 23.3 Prepai-ing Pipe Joints for Welding. . ...... 611 23.4 Welding Pipe Joints with SMAW ......... 618 23.5 Welding Pipe Joints with GMAW and FCAW ........... . .... 623 23.6 Welding Pipe Joints with GTAW . . . . . .... 625 23.7 Welding Tube Joints ,-vith SMAW . . . .. ... 629 23.8 Welding Tube Joints ,-vith GTAW and GMAW ....... . ........ 630 23.9 Heat Treating Pipe and Tube Welded Joints . .......... . .... 631 23.10 Inspecting Pipe and Tube Welds .. . ...... 631

xii

Advantages of Automatic Welding ....... 678 Feedback Controls . . ...... . ............ 678 Automatic Welding Processes . .......... 683 Introduction to Robots ...... . .......... 684 Safety Practices in Automatic and Robotic Welding .... . .... 694

Chapter 27 Metal Surfacing . . ...... . . . ... . . . . . ...... . .. 697

2Zl 27.2 2Z3 27.4 2Z5 2Z6 2Z7 27.8

P1inciples of Surfacing ........... . ... . . 698 Selection of a Surfacing Process... . ...... 699 P1inciples of Flame Spraying ......... . .. 704 Electric Ai·c Spray Surfacing . . ... . ...... 710 Detonation Flame Spraying ...... • . . .... 711 Plasma Arc Spraying Process. . . . . . ...... 711 Surface Preparation .. . ......... ..... ... 713 Selecting Thermal Spray Surfacing Material .............. • ...... 714 27.9 Testing and Inspecting Thero1a l Surfacings ............. ... . . .. 714 2Z10 Review of Surfacing Safety ... . ... . ...... 715

Part 9 Metal Technology . ..... . .. . .. . . 718 Chapter 28 Metal Production, Properties, and Identification . .............................. 719

28.1 28.2 28.3 28.4 28.5 28.6 28.7 28.8 28.9 28.10

Manufacturing Iron and Steel .... . . . . . . . 719 Iron and Steel ......................... 722 Ph ase Diagrams ... . . . . .......... . . .... 725 Iron-Carbon Phase Diagram ........... . 726 Identification of Iron and Steel. .......... 729 Nonferrous Me tals ..... . ............... 738 Special Metals .... .. ... . .. .. .... . . ... . . 740 Hard Surfacin g Metals . . . .... ....... . . . 741 Soft Surfacing Metals . . ..... ........ . .. 741 Revievv of Safety ....... . . . ............ . 741

Chapter 29 Heat Treatment of Metals . . .. . ........ ...... 745

29.l 29.2 29.3 29.4 29.5 29.6 29.7 29.8 29.9 29.10 29.11 29.12

Purposes of Heat Treatment ... ... . . .. . . . 745 Carbon Content of Steel . . .. . . . .... . . . . . 748 Crystalline Structure of Steel ......... . . . 749 Heat Treating Processes . . . . . ........ . . . 751 Hardening Steel ... ..... ..... .. ...... .. 755 H eat Treating Tool Steels . . . . ...... . . . . . 758 Heat Treating A Uoy Steels .. .......... .. 758 Heat Treating Cast Irons . . . . . ........ . . . 758 Heat Treating Alu1ni num . . .. ......... . . 759 Heat Treating Copper .. . .............. . 760 Temperature Measurements ... ... . ..... . 760 Review of Safety ....... . . . . . . .... . . . . . . 762

3L3 31.4 31.5 31.6

Procedure Qualification Record ......... 797 Welder Performance Qualifications ...... 799 Methods of Testing Specilnens ... . . . ... . 801 Filling Out and Reading a Welding Procedure Specification .... . . . .. 811 31.7 Filling Out and Reading a Procedure Quali1ication Record . ..... . .. 815 31.8 Filling Out and Reading a Welder Perfonnance Qualification Test Record .. . 816

Chapter 32 The Welding Shop . .. ....... .. .... ..... . .... 825

32.l 32.2 32.3 32.4 32.5 32.6 32.7 32.8

Welding Shop Design .... ... ....... .... 825 Welding Shop Equipment.............. . 826 Welding Shop Tools ... .... . ........ . .. . 837 Welding Shop Supplies . . .......... . . . . . 837 Weld Test Equipment . ...... . ......... . 840 Repair of Welding Equipment ...... . ... . 840 Welding Shop Policy ................... 840 Review of Safety..... . . . . . .......... . . . 841

Chapter 33 Getting and Holding a Job in the Welding Industry. . . . . ........ . .... 845

33.l The Future of the Welding Industry ...... 845 33.2 Welding Occupations and Required Education .... . ..... ...... 846 33.3 School Subjects Suggested for Success . . . . 846 33.4 Qualities Sought by Entployers .......... 849 33.5 Finding and Keeping a Job . ...... . ... . . . 850

Chapter 34 Technical Data . . .. ..... .. . ..... ... .... . .... 857

Part 10 Professional Welding . . .... . ... . 766 Chapter 30 Inspecting and Testing Welds. ......... .. . .. . 767

30.1 30.2 30.3 30.4

Nondestructive Examination (NDE) . . . Destructive Tests ...... ...... ..... . . Laboratory Methods of Testing Welds . Review o f Safety....... . .. ..... . ... .

. . . 767 . . . 777 . .. 782 . .. 788

Chapter 31 Procedure and Welder Qualifications....... . . 791

31.l Welding Codes ......... ... ......... .. . 791 31.2 Welding Procedure Specifications ... . . . . . 796

34.1 34.2 34.3 34.4 34.5 34.6 34.7 34.8 34.9 34.10 34.11 34.12

Codes and Standards .................. 857 Inverter Arc Welding Power Sources . . . . . 858 Fla1ne C haracteristics ..... . ...... ... . .. 860 Properties of Metals . ... . ............... 861 Stresses Caused by Welding ............ 862 Sheet Metal Gages ... . . . ... ...... . . . . . . 862 Drill Sets and Sizes ......... .. ... . ..... 862 Tapping a Thread .. . . . . . ... .. .......... 863 The SI (Metric System) ............. .... 864 Temperature Scales and Conversions . . . . . 866 Safe ty Data Shee ts (SDS) . ............... 866 Measuring Length . . . . . . ... . ...... . .... 868

Glossary . . ................ . . . ............. 871

Index .... . . . . . ............ . .......... . . . . . 893

XIII

Quick Reference General Information Filter Shades for Welding and Cutting ... . ...... 8 Welding Positions .... . ............ . . . ....... 46 ANSr/ AWS Standard Welding Symbols . ....... 49

Shielded Metal Arc Welding Welding Lead Current Capacity ... . ... . ...... 110 SMAW Carbon Steel Electrodes ... . .......... 114 SMAW Lo,-v-Alloy Steel Electrodes ........... 115 SMAW Electrode Designations ......... . .... 116 Low-Hydrogen Electrodes. . ...... . . . . . ...... 118 E60:XX Electrode Required Amperage ... ...... 139 E70XX Electrode Required A 1nperage .. . ...... 139 Effect of Cw·rent, Arc Length, and Travel Speed on Beads ..... . . . ...... 143

Gas Metal Arc Welding GMAW Recommended Electrodes .... . . . .... 186 GMAW Electrode Designations ... . . . . . ...... 186 GMAW Deposition Rates............. . ...... 197 Spray Transfer Transition Currents ... .. .. . ... 200 Approximate Machine Settings . . . . . ... .. .. . . 204 GMAW Shielding Gases ............. . ...... 209 Short Circuiting ... . . .. ......... . . . ...... 211 Spray Transfer. . . . . . .......... . . . . . ...... 211 Selection Based on Base Material .. .. ...... 214 Flow Rates ........ . .............. .. ..... 214 Effect of Current, Arc Length, and Travel Speed on Beads .............. 222 GMAW Troubleshooting Guide ... . ...... ... . 234

Flux Cored Arc Welding FCAW Electrode Designations ...... . . . ...... 189 Approximate Machine Settings .............. 205

xiv

Gas Tungsten Arc Welding GTAW Gas Nozzle Sizes ........... . . . ...... 253 Tungsten Electrode Color Codes . ... . . . ...... 254 Recommended Fi.lier Metals for GTAW ....... 258 GTAW Recommended Settings for Carbon Steel-DCEN . ...•. .. .. ..... 275 GTAW Recommended Settings for Stainless Steel- DCEN ....... . ...... 275 GTAW Recommended Settings for AJumlnu1n-AC and l-iF ............ 276 GTAW Shielding Gases and Current .......... 277 GTAW Electrode Cu1Tent Ranges . .... . ...... 279 GTAW Troubleshooting . . ........ . . . ........ 296

Plasma Arc Cutting Suggested Orifice and Shielding Gases . . .. . .. . 307 Suggested Settings for Carbon Steel .. . .. . .... 311 Suggested Settings for Stainless Steel . . . ...... 311 Suggested Settings for Aluminum. . . . . . ...... 311

Oxyfuel Gas Welding and Cutting Oxyacetylene Welding Para n1eters and Settings ......... • ...... 362 Oxyacetylene Cutting Parameters .. . ......... 413 Brazeable Metals and Conditions for Brazing ...... . ..... ... .. 463 Brazeable Metal Combinations and Filler Metals .. .................... 465

Resistance Welding Recommended Spot Weld Settings for Low-Carbon Steel. ........ .. . . ...... 520 Aluminum Spot Welding Variables . . . ........ 525

Feature Contents Employability Decision Making and Problem Solving..... . ... . ............ . .......... . . . . . ............ . . . .. 30 Applying for a Job .. ....... ....................... ..... .... .. . ...... . ................ . . . .. 72 Evaluating Job Offers ............ . ..... . ....... . . . . . ........ . ... . . . ....................... 134 Communication and Welding Terms .. ..... .. . • . . . . . . . . . . . . •. • . • ... . . . ... . . . ........ . ...... 309 Preparing for a Job Intervie,,v ................................ . ............................. 498 Aptitudes and Abilities ..... . ... . ...... . . . . . ............ . . . ..... . ... . . ... . ............ . . . . 607 Staying Safet)' Co11scious ... . .............. . ....... . .... . ....... . ... . . ................ . ... 678 Teamwork ....................................... . ........•....... . ..................... 746

Procedures Preparing a GMAW or FCAW Outfit .......... . .... ......... . .......... . . . .............. . ... Removing a Bird's Nest ...................... • ..... . .... . . . . . .... . . ....................... Shutting Down a GMAW/FCAW Station ............. . ........ . ....... . ..................... Shutting Down a PAC Station ....................... . ........ . .................. . .......... Moving Gas Cylinders . ..... . . . . . ...... . . . . . ............ . . . ..... . ... . . ................ . . . . Assembling an Oxyfuel Gas Welding (or Cutting) Outfit .... . . . . . ....... . . ... . ............ . ... Checking a Regulator for Leaks . . . ........ . .............. . ... • ... . . . . . ... . . ............ . . .. Checking Cylinder-to-Regulator Connections for Leaks ....... . . . ....... . . ............. . ...... Checking Hoses and Hose Fittings for Leaks .............. . ... . ... . ......................... Turning On an Oxyacetylene Welding or Cutting Outfit ....... . .......... . . . . . . . .......... . . . . Lighting and Adj usting a Welding Torch Fla1ne .............. . .......... . . . .............. . . . . Shuttin g Down an Oxyacetylene Welding Outfit ........... . ... . ... . ......................... Lighting and Adjusting an Oxyacetylene Cutting Torch ... . . . . . . • . • . . . . . . ... . . . .... . ... . ... ... Shutting Down a Cutting Torch .............................. . ..... . . . ..................... Producing a Soldered Joint with a Torch.. . ... . ............ . . . ..... . ... . . ... . ............ . ... Steps for Brazing . ... ....... . . . ........ . . . . . ....... . ........ . ....... . . ... ... ...... . ... . ... Brazing Alun1inum ............................... . ........ • ....... . . .......... ... ... . .. . Using a Controlled-Atmosphere Brazing Furnace ... ... . ........ • . .. • ......................... Shielded Metal Arc Welding Stainless Steel. .......... . ........ . ... . ....... . . ................ Uphill Welding (Pipe) ............................. ..... . . . ... . . . ....................... .. Downhill Welding (Pipe).... . ... . ........ . . . . .. .... . ........ ....... . . . ... ...... ..... ...... Setting Up Exotherinic Cutting Equipment . .......... ... . . . . ... . . ... . . . . . ................. .. Adjusting and Lighting a Wire-Feed-Type Flarne Spraying Gun ...... . ... . . . .. .. ... .. . ..... . . . . Annealing Steel. ............. . ............................. . ....... . ..................... Normalizing Steel. ............. . .............. . ................ . ... . . ... . ............ . ... Quenching and Tempering Steel .................... . ...... .. . ....... . . ................ .. .. Thern1a l Stress Re lieving Steel ... . .... ... . . . . ... . ... . ........ . ... . . . ... ....... .... . . . . . . . . . Spheroidizing High-Carbon Steel ............... . ... . ........ • ... . ... . ..................... H eat Treating a Cold Chisel . .......... . ... . . ....... . ... . .... . . . . . ... . ........ ... ..... . . ... Performing a Liquid Penetrant Inspection .. . ........................... . ... . ............ . . . .

203 208 224 316 327 360 361 361 362 363 366 367 414 417 449 47{) 476 480 571 619 619 648 709 752 753 754 754 754 755 773

1

Welding Fundamentals

, • ~

•

.

•

Safety in the Welding Shop Nederman, Inc.

Learning Objectives After studying this cl1apter, you will be able to: • Identify common causes of accidents. • Recognize health and safety hazards in the ,,velding shop or other work environments and take appropriate meastues to prevent accidents and injuries. • Select and properly use safety equipn1ent appropriate to ,,vorlvaste Occupational Safety and Health Adn1inisb·a tion (OSHA) personal protective equipment (PPE)

23

positive-pressure respirators Resource Conservation and Recovery Act (RCRA)

safety data sheets (SDS) safety inspection work envelope

Review Questions Ans,ver thefollmving questions using the infon11atio11 in the chapter. Know and Understand 1. All of the following are physical factors that may be involved in shop accidents, except: __ A. equipment failure B. time of day C. poor attitude D. lack of housekeeping. 2. True or False? If necessary, a welder can douse his or her entire body using a safety shower or only the face and eyes using a special sink designed to flush the eyes in an en1ergency. 3. Recommended filter lens shade numbers for shielded metal arc welding range from _ _ A. 3 to5 B. 4 to 8 C. 9 to 12 D. 10 to 14 4. A document that provides important safety infom1ation about a che.1nical or substance used in the workplace is referred to as a(n) - - ' A. ANSI B. PPE C. SDS

D.RCRA

5. True or False? Negative-pressure respirators are recom1nended for filtering out toxic fumes. 6. True or False? A CO2 arc welding shielding gas can break down in the welding arc and fonn carbon monoxide. 7. Federal regulations for the legal storage, treatment, and disposal of hazardous waste are provided by the _ _ A. Resource Conservation and Recovery Act B. Occupational and Health Administration C. National Fire Protection Association D. An1erican National Standards Institute

8. True or False? Hot metal parts in the shop can be picked up by hand if the worker is wearing leather gauntlet gloves. 9. Fires fueled by gasoline or oil would be extinguished with a _ _ fu·e extinguisher.

A. Type A B. Type B C. Type C D. Type D 10. Which s tatement about a secon d degree bum is

false? A. B. C. D.

Ice s hould be app lied to the burn. The bun1 involves blistering. Cold compresses can be applied. A doctor should be seen for treatment.

Apply and Analyze

1. Leather gloves wj th gauntlet-type cuffs and a flame-retardant lining are recommended for welders to protect against what hazards? 2. Describe three welding situations in which a positive-pressure respirator should be \¥Om. 3. When working in a confined space, a welder should post a fellow worker outside the confined space. Explain tJ1e reasons for doing this.

4. Describe arc flash and the precautions that n1ust be taken to protect a welder from arc flash. 5. Explain the purpose of a safety light curtain in a robot's v,rork cell.

Crit ical Thinking

1. Explain how a welder's a ttitude affects con1p lia nce with safety rules, housekeeping, and the wearing of appropriate PP E. 2. Search the OSHA websi te fo r safety and health topics pages regarding welding, cutting, and brazing. Topics include confined spaces, fire safety, hazard comn1unication, occupational noise exposure, PPE, and others. Choose a topic and prepare a concise summary of the information contained on the safety and health topic page. Experiment

1. Search the s hop for materia ls that have a Safety Data Sheet (SDS). Find one that is dangerous and make a listing of its h azardous ingredients and che,nicals. Also, learn all of the known health effects and symptoms related to exposure to this material. What is the p1oper first-aid treatment for exposure?

Copynghl Goodheart-Willcox Co Ince

Print Reading

Blend 1mages/Stwttarstoe1vs the weld to penetrate as deep as required by the engineer or \,veld designer. A groove joiJ1t allows the welder to reach the b otto1n of the 1-veld joint. The groove angle must b e large enough to allo,~r the electrode or torch tip to reach n ear the bottom of the joint However, if the groove angle is too large, filler metal and the ½'eider's time are wasted. This increases the cost of m a king a weld. See Figure 3 -12A. A properly designed J-g roove or U-g roove joint also decreases the groove dimensions while allowing ad equate space for ""elding. See Figure 3-12B.

3.3.2 Joint Alignment The alignment of a joint before ,-velding is important. In the shop, the a lignment of the weld joint is often referred to as fit-up. A ragged edge or an ed ge that is

C Goodh9aJt-Wlllcox Publlsh91

Figure 3-11 . Comparison of stringer and weave beads. A- A stringer bead in progress on a square-groove butt joint. The bead width is two to three times the metal thickness. B- A weave bead in progress. The torch tip and weld pool are moved from side-to-side in the direction of the arrow. C-The crescent motion is a pattern used for creating a weave bead. The bead width is seldom greater than 3/4"-1 " (19 mm- 25 mm).

A

Various torch or electrode movement patterns can be used when making a \>veave bead. The crescent 1notio11, shown in Fig u re 3-l l C, is a comn,only used pattern.

3.3 Joint Geometry The American Welding Society defines joint geo1netry as the shape and dimensions of a (weld) joint, in cross section, prior to welding. Joint geometry is gen erally detennined b y a welding engineer or designer. The assembly desig n and the clin,ensions of a joint depend on the metal thickness and shape and on the load requirements of the p a rts. The parts are prepared

B Goodhoatt•Wi/lcox Publisher

Fi gure 3-12. Compare 70° and 90° groove angles. A- A 70° groove angle requires less filler metal and time to weld than a 90° groove angle. The shaded area represents the differences. B-Look at the two joint designs. The root of the weld can be reached easily in both, however, less filler metal and welder time are required to complete the U-groove joint. Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 3 Welding Joints, Positions, and Symbols

45

not cut straight is hard to weld. See Figure 3-13. Edges to be welded must be straight and cut to exact size. Parts of a weldment should be properly aligned and held in position during the ,,velding operation. Tack welding is usually adequate to hold parts during welding. A tack iveld is a small \>veld used to hold pieces in a lignment. Parts can also be held mechanically during the "\ovelding operation using clamps, jigs, and fixtures. See Figure 3-14.

3.3.3 Penetration A completed ,,veld joint must be at least as strong as the base metal. The weld mus t penetrate deeply into the base metal to be strong. Penetration is the depth of fusion of the ,,veld below the surface. Total (100"/o) penetration occurs when a ,,veld penetrates through the entire thickness of the base n1etal. Generally, total penetration is required only on a butt joint. The edges of thick metal m ay need to be machined, arc cut, or flame cut to achieve 100"/o penetration. Thick 1netal also may have to be welded from both sides of the joint.

Bossoy Tools North America

Figure 3-14. Various clamps are used to position and hold

3.4 Welding Positions

parts to be welded.

Welders of ten mus t weld in a variety of positions. Welds may be made in the flat, horizonta l, vertical, or overhead welding positions. On drawings, welding positions a re often abbreviated in the tail of the ivelding symbol as F, H, V, and 0.

Welding positions are detennined by the positions of the we ld axis and weld face. The weld axis is an imaginary line running lengthwise through the center of a completed weld. As defined earlie1; the weld face is the exposed surface of a co1npleted weld on the s ide on which the welding was done. See Figure 3-15.

Weld lace

A

B C3oodhean-Wilfcox Putiisher

Figure 3-13. Examples of poorly prepared base metal

edges, which are difficult to weld and result in a weak or defective weld joint. A-Edges are ragged. B-One edge is not cut straight, which changes the width of the joint. Copvrighl Goodheart-WIilcox Co, Inc

Weld axis Goodnoart-Wlllcox Publisher

Figure 3-15. The weld axis is an imaginary line running lengthwise through the center of the weld. The weld face is the exposed surface of the finished bead.

46

Modern Welding

The An1erican Weld ing Society refers to welding positions with a number and letter combination. See Fig ure 3-16. Groove joints in the flat, horizontal, vertical, and overhead positions are referred to as lG, 2G, 3G, and 4G, respectively. Fillet joints in the flat, horizontal, vertical, and overhead position are designated as 1F, 2F, 3F, and 4 F, res pectively. AWS designations for pipe welding positions are lG, 2G, 5G, and 6G.

3.4.1 Flat Welding Position Welds 1nade on a groove joint in the 1G flat ioelding position must meet these conditions:

• The weld axis n1us t be within 15° of horizontal. See Figure 3-17. • The weld face is within 30° of horizontal. • The weld is made from the upper side of the joi.J1t.

3.4.2 Horizontal Welding Position Groove welds made in the 2G horizoutal 1velding position must meet these conditions: • The weld axis mus t be within 15° of horizontal. • The weld face must be bet\veen 80°- 150° or 210°-280°. See Fig ure 3-18. Angles are measured clockwise with 0° at the bottom.

Five Basic Weld Joints in Four Welding Positions Butt Joint

Corner Joint

Edge Joint

T-Joint

Lap Joint

Flat

1G

1G

1G

1F

1F

Horizontal

2G

2G

2G

2F

2F

Vertical

3G

3G

3G

3F

3F

4G

4G

4F

4F

~

§

:

Overhead

4G

\

;,.,

'

\..

GoodheBrt·WU/cox Publisher

Figure 3-16. Each of the five basic weld joints may be made in four different welding positions. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 3

Welding Joints, Positions, and Symbols

47

Weld axis

~ / Horizontal

15° upfrom~~ ~ - - ~ ~ horizontal to 15° down

A

y

Weld axis

Horizon

Weld face Weld :ls ~

o•-30•

l

B

face _

/

Horizontal

0°- 30° [

C Goodheart•Wi/Jcox Publishe,

Figure 3-17. Specifications for the AWS 1G (flat groove welding) position. A-The weld axis must be within 15° of horizontal. B and C-The weld face must be within 30° of horizontal.

Face View

End View 150°

15• up

210°

l-

o· ,,...;:----

210°- 280°

Horizontal

Weld axis

!

-

15° down ,-...._,_ 280° Weld face

A

B GoOdhearr.WJncox Publisher

Figure 3-18. Specifications for the AWS 2G (horizontal groove welding) position. A- T he weld axis must be within 15° of horizontal. 8-An end view (View B) with the weld shown in blue. The weld face must be within 80°-150° or 210°- 280°. All angles are measured clockwise with 0 ° at the bottom. Copvrighl Goodheart-WIilcox Co, Inc

48

Modern Welding

3.4.3 Vertical Welding Position

Face View

A weld on a groove joint in the 3G vertical tvelding position must meet either of these sets of conditions: Condition A • The weld axis is 80°- 90° from horizontal. • The weld face is between 0°-360° from horizontal. See Figure 3-19A.

I

_ - Weld I axis 0'-90

Weld axis

Weld face

Condition B • The weld axis is 15°-80° fro,n horizontal. • The weld face is vvithin 80°- 280° fron1 horizontal. • The weld is 1nade fron1 the upper s ide of the joint. See Figure 3-19B.

End View

£1::D.......... ,.._. 0°-360°

3.4.4 Overhead Welding Position Welds n1ade on groove joints in the 4G overhead 1.veldi11g positio11 are made under these conditions: • The weld ax is is between 00-80°. • The weld face is between 0°- 80° or 280°- 360°. • The weld is made from the lower side of the joint. See Figure 3-20.

A Face View

~ Weld axis

1s -so 0

3.5 The Welding Symbol The welding symbol described in this section ,~1 as developed by the American National Standards Institute (ANSI) and the A 1nerican We lding Society (AWS). It is described in detail in the publication ANSI/AWS A2.4, Standard Syn1bols for Welding, Brazing,

Weld face

and Nondestructive £xa111inalion. The entire symbol, with all of its numbers and other symbols, is called the welding symbol See Figure 3-21. Welding sy mbols a re used on drawings of parts and assemblies that are joined together by ,~1elding. A welding syn1bol may appear in any view on the dra,,v ing. Whenever two or more pieces a re joined by ~ 1eld ing, the assembled item is called a lueld,nent. When the pieces of a weldment are assembled, the lines along which their edges and su rfaces come in contact are called joints. The dra,,ving of a weldment seldom shows ho,,v the edges are to be prepared or how the completed weld appears. The drawing shows only how the parts come together and what type of joint they form. Occasionally, wh en an unusual or very complex \,v eld joint is to be made, a detail drawing of the joint is drawn, with the joint preparation and weld shape sho,,vn and dimensioned, Refer to Fig ure 3-1 for the types of welded joints and the types of welds used on the various joints. A complete ,,velding symbol provides all the information needed to create a specific ,,veld on a weld1nent.

0

Horizontal ~

End View

_c:2:)_ B Goodhean·Willcox Publisher

Figure 3-19. Specifications for the AWS 3G (vertical groove welding) position. A vertical weld must meet either of the followin g sets of conditions. A-The weld axis must be between 80° and 90° from horizontal. Look at the End View. The weld face may be rotated from 0°-360°. B- The weld axis is 15°- 80° from horizontal. Look at the End View. The weld face must be within 80°-280°. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 3

Welding Joints, Positions, and Symbols

Face View

49

End View

ap•

Weld axis "'-,

"

Weld axis

I

Weld race

A

B

0° (360°) Go0\1eld metals at very high speeds. Because the equipment is large and expensive, it is used only where other processes cannot do the job. The rnachine uses a filarnent that emits (gives off) elech·ons. These streams of electrons are controlled (focused and concentrated) by electromagnets called a tnag11etic l ens. The electron beam is generated in much the same \~ray as in old CRT-type television sets.

Insulator

B E3

Air inlet

/

~

IJ Filament Bias Anode

Electron Beam Optical View Vacuum Movement

□

Molten Metal

Vacuum bypass valve

Optical mirrors

Q

Opticalviewing system

End View of Weld Welding chamber

Deflection coil

---

' I

Electron/ beam f Base

metal Workpiece (metal being welded)

To vacuum t - - - - - - - L - -- - - - - - --, system

-- -- -

,.

Base metal movement under the beam

GOofned length of the electrode and work I eads. Goodhoart~WiUcox Publisher

Figure 5-9. Arc welding lead recommendations. Cables are listed from largest diameter to smallest. 4/0 (0000) size is the

largest diameter. As the lead size number increases, the cable diameter decreases. Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 5

DIN connections also use a quick disconnect tnethod, Figure 5-12. Adapters are available to connect the twist-style and DIN terminals. Terminals are connected to the leads by the following methods: • Mechanical. • Soldering. • Brazing. [n the case of alurni num cables, it is claimed that it is best to clamp the aluminum to the electrode holder and to the other terminals. However, the cable can be successful ly aluminum-brazed to either aluminum connections or copper connections. Twisting of the cable, especially at the connections, should be avoided. The cable may separate fron1 its tenninals if this is done. Mechanical connections must be tight and clean. Soldering and silver brazing of connections must be done properly. lt is necessary to make co,nplete connection of the cable and connector to allow the electrical current to flow over the entire soldered or brazed surface area. Good workpiece lead and electrode lead connections are important. The v-1orkpiece lead can be fastened to the welding bench or table by means of a lug or insulated terminal. This method is practical when welding can be done on a welding table. Frequently, the vvorkpiece lead must be moved on a regular basis or fastened to the article being welded, due to its size or location. A spring-loaded clainp isco1nn1only used to connect the workpiece lead to the iten1 being welded. AC-clamp can also be used. See Figure 5-13. It is so1netin1es difficult to use a clamping device on a metal fabrication. Care must be taken to avoid marring finished surfaces. A magnetic workpiece lead terminal,

Shielded Metal Arc Welding Equipment and Supplies

111

A

Lenco/NLC

B

Lenco/NLC

Clamps connect the ground cable to the item being welded. A-A spring-loaded clamp for the workpiece lead. B-C-clamp for the workpiece lead.

Figure 5-13.

Figure 5-14, permits quick and secure fastening of the workpiece lead to the weldment. This makes it easy to cl1ange the position of the ground to obtain better arc characteristics and does not injure or mar the article to be welded. The workpiece lead is either soldered or mechanically fastened to a permanent n1agnet or an elechumagnet ground device. The operator can easily position the magnetic grounding device on most ferrous (iron) surfaces.

Lenco/NLC

of DIN connectors. Those labeled A, B, D, and E are cable end connectors; C is a panel receptacle, and F and G are cable connectors with a hose barb for air--cooled torches.

rweco, a dN/sion of Thormadyn& Indus.tries. Inc.

Figure 5-12. A variety

Copvrighl Goodheart-WIilcox Co , Inc

Magnetic workpiece connectors can be turned on and off and are used to connect the workpiece lead to the items being welded.

Figure 5-14.

112

Modern Welding

5.5.2 Electrode Holders The electrode holder is the part of the arc welding equiptnent held by the operator during we lding. The electrode holder holds the electrode. Many different styles and models are available, but they all have similar characteristics. The electrode lead is usually fastened to the electrode holder by means of a mechanical connection inside the electrode handle. Solid brass or copper inside the handle conducts the electrical current from the lead connection to the lower jaw. The outer handle is made of an insulating material. The outer ha11dle has high heat resistance. Electrode holders are built to produce a balanced feeling when held in the operator's hand. There should be a good balance with the cable draped over the operator's arn1, and with an average length electrode in the holder. Severa l methods are used to clamp the electrode in the holder. The rnost com 1non styles of e lectrode holder have a pinch-type construction and include a spring to produce the necessary pressu1·e. See Figure 5-15 and

Figure 5-16. Electrode holders come in different sizes. They are designed to hold different diameter electrodes and to carry different amounts of welding current. Select the smallest size that can handle the electrode diameter and c urrent that \\rill be used. A smaller size is more comfortable for the welder to hold and manipulate.

The area of the elecbooe holder that contacts the eJectrode should be clean. Periodically clean the contact area with a wire brush, steel wool, or other suitable means.

5.6 SMAW Electrodes Shielded metal arc welding electrodes have a solid metal wire core and a thick flux covering (coating). SMAW electrodes aTe identified by the ~vire diameter and by a series of letters and nutnbers. These letters and numbers identify the metal alloy and the intended use of the electrode. The co1nmo n SMAW electrode wire diameters are 1/16" (1.6 mm), 3/32" (2.3 rrun), 1/8" (3.2 mm), 5/32" (4.0 mm), 3/16' (4.8 mm), 7/32" (5.6 mm), 1/4" (6.4 mm), 5/16' (7.9 rnm), and 3/8" (9.5 mm). They a re available in lengths up to 18" (46 cm). The most frequently used length is 14" (36 cm). Electrodes are usually purchased in 50 lb (22.7 kg) packages. Small packages, down to 1 lb (.5 kg) or 5 lb (2.3 kg), are available for small jobs or home u se. Electrodes 1nay be packaged in cardboard cartons or in hermetically sealed (airtight) metal cans. SMAW electrodes are produced in accordance with AWSspecifications for welding on various n1etals and alloys. See Figure 5-17. Covered electrodes serve many purposes in addition to adding filler metal to the 1nolten weld pool. The additional functions of the covering are discussed in the next section. Dampness, usually due to moisture absorbed from the air, destroys the effectiveness of most electrode coverings. Dampness introduces hydrogen into the weld, which can cause cracking or brittleness in some welded metals. Ma ny welding procedures require that electrodes be thoroughly dried prior to use. This is done in spectally built drying ovens. See Figure 5-18.

Goodhoatt•Willcox Puti/shor

Figure 5-15. A SMAW electrode holder rated for 200 amperes.

AWS Specifications for SMAW Electrodes

Release lever Replaceable

copper or brass socket copper toll over bare wires

J~ia s .,...,.;;.a:~ Allen screw Allen wrench

Curved cable pressure plate Goodhean-wtltcox Publisher

Figure 5 -16. An exploded view of a SMAW electrode

holder. Note the insulated handle and the parts required to connect the welding lead to the electrode holder.

ANSI/AWS specification number

Metal and alloy

A5.1

Carbon steels

A5.3

Aluminum and aluminum alloys

A5.4

Corrosion-resistant steels

A5.5

Low alloy steels

A5.6

Copper and copper alloys

A5.11

Nickel and nickel alloys

A5.t3

Surfacing electrodes

A5.15

Cast iron Goodhea,. WIiicox Publisher

Figure 5-17. AWS specifications for SMAW electrodes. Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 5

Shielded Metal Arc Welding Equipment and Supplies

113

The tune it takes for an e lectrode to pick up 1noisture from the air varies from t hirty minutes to four hours, depending on the electrode. This time period is known for each electrode. Welders, therefore, take only enough electrodes from the oven to last for this moistlu·e-exposure time limit. Electrodes 111ust be handled carefL1Uy to prevent breaking the flux coating. Many ,velding procedures do not permit an electrode to be used if the flux coating is chipped. Elect1:ode dispensers are sea led to keep the electrodes dry. The dispenser is also tough enough to prevent physical damage to the electrodes. See Figure 5-19.

-.

~

5.6.1 Electrode Covering Fundamentals

·Pho9nix Ptoducts Co., Inc.

Figure 5-18. Three types of electrode drying ovens. The large gray oven designed for shop use holds up to 350 lb of 18" electrodes. The two yellow units are portable and can be easily moved to the job site for field welding. The square portable oven holds 50 lb of 18" electrodes, and the round unit holds 13 lb.

The covering on an SMAW electrode is called flux. The flux on fhe electrode performs many different functions: • Producing a protective gas around the weld area. • Providing fluxing elements and deoxidizers. • Creating a solid coating that protects the weld from oxygen as it cools. • Establishing electrical characteristics. • Adding iron powder and alloying elements. ---Flexible atmospheric seal in opening

Belt--~ _ _ _ Feed

lever

Hmm~•lo d"sspenses. new'"electrode throu h the to seal Gui/co Gui/co A B Figure 5-19. Electrode dispenser. A-This welder is wearing a loaded dispenser. B-With the top closed, the dispenser is sealed. Moving the lever feeds a new electrode through the top seal.

Copvrighl Goodheart-WIilcox Co. Inc

114

Modern Welding

During the arc process, some of the flux covering changes to a reducing gas, such as carbon n1onoxide (CO) or hydrogen (H). These gases, as they surrow1d the arc proper, prevent air frorn coming in contact ,¥ith the 0101ten metal. They prevent oxygen in the air fron1 combining '"'ith the molten metal. However, the gases usually do not protect the hot rnetal after the arc leaves that area of the weld. The covering also contains special fluxing ingredients that reruove impurities frorn the rnolten metal. Irnpurities are floated to the top of the molten weld pool As the electrode flux coating residue cools, it fo1ms a coating of material over the \>veld called slag. The slag prevents the air from contacting the hot metal. The slag covering also allows the weld to cool 1nore s lowly and helps prevent a hard, brittle weld. When welding is performed with AC, the current changes direction and actually stops 120 times per second. To maintain an arc as the current changes direction, ingredients are added to the cove1ing of the electrode to a·eate an ionized gas. This ionized gas allows good arc stability when welding with AC. The flux covering on a shielded metal arc elech·ode also contains alloyi11g elements. These alloying elements are added to the weld pool as the covering is melted. Iron powder and iron alloys can be added to the coverings of steel electrodes. These electrodes deposit metal into the weld at a faster rate than s tandard electrodes. Certain coverings on steel electrodes are designed to be low in hydrogen. Hydrogen causes low ductility and cracking in certain cases. The use of low-hydrogen electrodes helps to eliminate these problems. A good flux-covered electrode in the hands of a skilled welder will produce a weld that has excellent physical and chern ical properties.

5. 7 Carbon and Low-Alloy Steel Covered Electrode Classification A large variety of carbon and low-alloy steel electrodes

are available. The composition of the flux coating on the electrodes varies considerably, and electrodes must be selected based on the planned use of the electrode. To ensure that different manufacturers' electrodes produce the same quality welds, the An1erican Welding Society has developed a series of identifying number classifications for SMAVV electrodes. The carbon and low-alloy steel electrode classification. 1111111ber has four or five digits. In addition, low-alloy steel electrodes have a suffix. See Figure 5-20 and Figure 5-21.

SMAW Carbon Steel Electrodes AWS classification

Type of covering

Capable of producing satisfactory welds in position shown"

Type of CUITentb

E60 series electrodes

E6010

High cellulose sodium E6011 High cellulose potassium E6012 High titania sodium E6013 High titanla potassium E6020 High iron oxide E6022< High iron oxide E6027

High iron oxide, iron powder

F, V, OH, H

DCEP

F, V, OH, H

ACorDCEP

F, V, OH, H

AC or DCEN

F, V, OH, H

AC or DC, either polarity ACorDCEN AC or DC, either polarity ACorDCEN

H-fillets F

H-fillets, F

E70 series electrodes

E7014 E7015 E7016 E7018 E7024 E7027

Iron powder, ti1ania Low hydrogen sodium Low hydrogen potassium Low hydrogen potassium, iron powder Iron powder, titania

High iron oxide, iron powder E7028 Low hydrogen potassium, iron powder E7048 Low hydrogen potassium, Iron powder

OH, H

AC or DC, elther polarity DCEP

F, V, OH, H

ACorDCEP

F, V, OH, H

ACorDCEP

H-fillets, F H-fillets, F

AC or DC, either polarity ACorDCEN

H-fillets, F

AC or DCEP

F, OH, H,

AC or DCEP

F,

V, OH, H

F, V,

V-down

a. The abbreviations, F, V. V-dowl\ OH, H. and H-fillets irxticate the welding posltloos as IOIIOWS: F = Flat H = Horttontal H-flllets - Hortzontal 1111ets V-oown - vertical oown v = ver11ca1 } f'orelectrodes3/16" (4.Smm)arxt under, eiccepl H = 0/ertead 5132" (4.0mm) and unclerforclasslflcaftons E7014, E7015, E7016, and E7018. b. The te,m DCEP refers lo direct current, eleclrode positiw (DC ieverse polanty). The te,m DCEN reters to alrect current electrode negatNe (DC s1ra1git polanty).

c. ElectrOdes of tile E6022 classmcauon are ror slngle-pass welds. Reproduced with P9tmlssion from tho American Wr.Jdfng Society, Miami, FL

Figure 5-20. AWS A5.1/A5.1M, Table Electrode Classification for SMAW.

1, Carbon Steel

Copyr!ghl Goodhear1-Wlllcox C-0 . Inc.

Chapter 5

Shielded Metal A rc Welding Equipment and Supplies

115

SMAW Low-Alloy Steel Electrodes

AWS classification•

Type of covering

Capable of producing satisfactory welds in positions shownb

Type of current"

E70 series-Minimum tensile strength of deposited metal, 70,000 psi (480 MPa) E7010-X E7011-X E7015-X E7016-X E7018-X

High cellulose sodium High cellulose potassium Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

E7020·X

High iron oxide

F, V, OH, H F, V, OH, H F, V, OH, H F, V, OH, H F, V, OH, H { ~-fillets { ~-fillets

E7027-X

Iron powder, Iron oxide

DCEP AC orOCEP DCEP AC or DCEP AC orDCEP AC orOCEN AC or DC, either polarity AC orDCEN AC or DC, either polarity

E80 series-Minimum tensile strength of deposited metal, 80,000 psi (550 MPa) E8010-X E8011-X E8013-X E8015-X E8016-X E8018-X

High cellulose sodium High cellulose potassium High titania potassium Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

F, V, OH, H F, V, OH, H F, V, OH, H F, V, OH, H F, V, OH, H F, V, OH, H

DCEP AC orDCEP AC or DC, either polarity DCEP AC orDCEP AC or DCEP

E90 series-Minimum tensile strength of deposited metal, 90,000 psi (620 MPa) E9010-X E9011·X E9013-X E9015-X E9016-X E9018-X

High cellulose sodium High cellulose potassium High titania potassium Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

F, V, F, V, F, V, F, V, F, V, F, V,

OH, OH, OH, OH. OH, OH,

H H H H H H

DCEP AC orDC EP AC or DC, either polarity DCEP AC orOCEP AC orDCEP

E100 series-Minimum tensile strength of deposited metal, 100,000 psi (690 MPa) E10010·X E10011·X E10013-X E10015-X E10016-X E10018-X

High cellulose sodium High cellulose potassium High tltania potassium Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

F, V, F, V, F, V, F, V, F, V, F, V,

OH, H OH, H OH, H OH, H OH, H OH, H

DCEP AC orDCEP AC or DC, either polarity DCEP AC orDCEP AC orOCEP

E110 series-Minimum tensile strength of deposited metal, 110,000 psi (760 MPa) E11015-X E11016-X E11018-X

Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

F, V, OH, H F, V, OH, H F, V, OH, H

DCEP AC orOCEP AC orDCEP

E120 series-Minimum tensile strength of deposited metal, 120,000 psi (830 MPa) E12015-X E12016-X E1 2018-X

Low hydrogen sodium Low hydrogen potassium Iron powder, low hydrogen

F, V, OH, H F, V, OH, H F, V, OH, H

DCEP AC orDCEP AC orDCEP

a. The letter suffix 'X" as used in this table stands for lhe suffices A1 , 81, 82, elc. (see A!1,lre 5-46) and designates the chemical composition of the deposited weld metal. b. The atl:>revlatlons F, V. OH, H, and H-fillets Indicate welding posmons as follows: F = Flat H = Honzontal; H-fillets = Hortzontal aneis. For electrodes 3/16" (4.8 mm) and under, except 5'32" (4.0 mm) and under for classifications V • 1/ertlcal } OH • Overhead EXX15-X, EXX 16-X, and EXX18-X. c. OCEP means electrode poslbve (reverse polarity). OCEN means electrode negauve (straight polanty). Roprodc.x:ed with permission from tho Amor/can WDlding Soc,cty, Miamf. FL

Figure 5-21. AWS A5.5/A5 .5M, Table 1, Low Alloy Steel Electrode Classification for SMAW

Copvright Goodheart-WIilcox Co, Inc

116

Modern Welding

The meaning of the digits in the AWS dassification number is shown in Figure 5-22. The letter E preceding the four- or five-digit number (EXXXX) indicates a welding electrode used in arc welding. The first two or three digits of the four- or five-digit number (E60XX or ElOOXX) repr esent the nlini.mun1 tensile strength of the fi l.ler 1netal. That is, 60 1neans 60,000 psi (410 MPa) and 100 means 100,000 psi (690 MPa). The value 60,000 psi (po w1ds per square inch) may also be shown as 60 ksi. The letter k represents 1,000 lb (one kilopound), so 60 ksi (kilopounds per square inch) is the same as 60,000 psi (pounds per square inch). Tensile stre11gtl1 is the 1naxi1num p ull stress, in pounds per square inch or megapascals (newtons per square millimeter), that a specimen will ,,v ithstan d. The chem ical composition o f the steel wire used in E60XX and E70XX electrodes is exactly the same. The added strength of the E70XX series comes from the alloys in the flux coatings. Each n1anufacturer has its own compounds for the coverings. Therefore, even though electrodes from different 1nanufacturers h ave identical classification numbers, their tensile strengths may be slightly different. The classification number indicates the minimum tensile s trength of the filler

metal. All electrodes produced wi th the sa1ne classification meet the AWS s tanda1·d and the minin1um requirements for the weld. The tensile strength 1nay be g iven in the ns-Ivelded or the stress-relieved condition. See the electrode manufacturer's specification to de termine under what cond ition the indicated tensile sh·ength occurs. As-Ivelded means without postheating. Stress-relieved means the weld has been given a heat h·eatinent after ,.,,elding to relieve stress caused by the welding process. The second digit from the right indicates the recom1nended position of the joint that the electrode is designed to ~veld. For example, an EXXlX electrode can be used to weld in all positions, whereas EXX2X electrodes are for 1 ,velding in the flat or horizontal welding position only. An EXX3X is used for flat position only, and an EXX4X e lectrode is recommended for flat, ho1izontal, ovethead, and vertical downl1ill 1,velding. A11 EXX2X elect.rode deposits more weld a1etal thru1 a sinula r size EXXlX electrode. The right-hand dig it indicates the po'l'.rer supply (AC, DCEN, or DCEP), the type of covering, and the presence of iron po~vder or low-hydrogen chru:acteristic (or both).

SMAW Electrode Designations

E 601 0

--

E

E 80 -1 6-82 --

= Electrode

Minimum Tensi le Strength 60, 70, 80, 90

'

100, 110, 120, etc. Welding Poslllo ns

= All Postllons 2 = Flat and H orizontal Fillet 1

3

= Flat Only

4 = Flat, Hori zontal, Overhead, or VerticaI Down Coating and Po larity 2 digits: See Figure 5-20 Suffix number _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __. Letter/Number: See Figure 5-23 Goodhoart-WH/cox Publisher

Figure 5-22. SMAW electrode designations.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 5

The last two digits need to be looked at together. The two digits give the welder information on the electrode covering, current to use, and position to use the electrode. See Figures 5-21 and 5-22, which show the type of elech·ode covering, position the electrode is designed for, and the type of current to use for various carbon and low-alloy steel electrodes. Some elech·ode numbers have a Jetter and number after the normal four or five digits, such as E7010-Al or E8016-82. The letter and nu mber con,bination, or suffix, is found in classifications of low-alloy steel electrodes. See Figure 5-23. The suffix indicates the chemical con1position of the deposited weld meta l: • A indicates a carbon-1110Jybdenum steel electrode. • B indicates a chromium-molybdenu.1l1 steel electrode. • C indicates a nickel steel electrode. • D indicates a manganese-molybdenum steel electrode. The final digit in the suffix indicates the chemical composition under one of these broad chemical classifications. The exact chemical composition can be obtained fro1n the e lectrode 1nanufacturer. The letter G is used for all other low- alloy electr odes with minimum values of molybdenum (0.20% mini.1num); chromium (0.30% miniJnu1n); manganese (1% minimum); silicon (0.80% minimum); nickel (0.50% minimum); and vanadium (0.10% minin1wn) specified. Only one of these elements is required to meet the alloy requirements of the G classification.

Composition of AWS Suffix Numbers ·A1

1/2% Mo

-81

1/2% Cr, 1/2% Mo

-82

1 1/4% Cr, 1/2% Mo

-83

2 1/4% Cr, 1% Mo

-C1

21/2% Ni

-C2

31/4% NI

-C3

1% NI, .35% Mo, .15% Cr

-01 and 02

.25- .45% Mo, 1.25-2.00% Mn

-G

.50 min Ni, .30 min Cr, .20 min Mo, .10 min V, 1.00 min Mn, .80 min SI (Only one of the listed elements Is required for the G classification.} Goodheart•Willcox Publish11r

Figure 5-23. The approximate chemical composition of suffix numbers of the AWS Electrode Numbering System.

Copvrighl Goodheart-WIilcox Co. Inc

Shielded Metal Arc Welding Equipment and Supplies

117

An example of a complete e lectrode classification is E8016-B2:

E-Indicates electrode. SO-Indicates tensile strength (80,000 psi or 80 ksi). 16--lnd icates a lo~v-hydrogen, potassium coveting used with AC or DCEP. I -Indicates an all-position e lectrode. B2- Indicates that the deposited metal d,emical composition is a lo,-v-aUoy chromium-molybdenum steel ,vith 1.25% clu-omiLun and 0.50% molybdenum. Manufacturers imprint AWS nu1nbers on the covering material near the grip end for identification. See Figure 5-24.

5.7.1 Low-Hydrogen Electrodes Hydrogen has harmful effects on alloy steels. It causes a low-ductility weld and underbead cracking. This is caUed hydrogen e111brittle111ent or ltydroge11 cracking. Ductility is the ability of a material to be formed, bent or stretched without cracking. Good ductility is desired in a weld. Low-lzydrogen electrodes deposit minimal hydrogen in the weld. The low-hydrogen condition is obtained by using a special covering in the EXXXS, EXXX6, or EXXX8 category. These electrodes have special sodium, potassium, or iron powder coverings. The deposited metal has excellent tensile strength and ductility. It is exceptionally clean, as can be seen by X-ray inspection. Low-hydrogen electrodes are classified as EXX15, EXX16, EXX18, EXX28, or EXX48, depending on which criteria they meet in AWS 5.1, Specification for

Carbon Steel Electrodes for Shielded Metal Arc Welding.

Ooodhean-Willcox Publisher

Figure 5-24. These electrodes show the identifying numbers placed on the covering.

11 8

Modern Welding

These electrodes produce welds with a tensile strength of 70,000 psi or higher. They are used on low-carbon, lo,-v-alloy, and hardenable steels. The slag is very fluid. Good flat or convex beads are easily obtained. Figure 5-25 sho~vs the composition and application of some low-hydrogen electrode coverings. These special coverings contain practically no organic material. Recommended arc welding machine settings for these electrodes are shown in Figure 5-26. Low-hydrogen electrodes should be dried by baking at 250°F {120°C) before use. If they have been exposed to the atmosphere for an appreciable period, they should be re-baked at 500°F to 700°F (260°C to 370°C) for one hour. This baking removes any moisture that may be in the coating. The electrodes are then stored at 250°F (l20°C) until they are used.

5.7.2 Carbon and Low-Alloy Steel Iron-Powder Ele ctrodes

the an1ount of 6ller n1etal deposited. See Fig ure 5-27. Much higher currents can be used to produce welds faster. The addition of iron powder a lso produces more easily cleaned welds, less spatter, and better bead shapes.

Iron Powder Electrode Deposition Electrode classification

Iron powder content Amount deposited

E6012

E7018

E7024

E7028

0%

24%

39%

45°/o

8 lb/hr

9 lb/hr

78%

100%

4.5 lb/hr 5.5 lb/hr

Deposit efficiency increase over E6012

0%

22%

Goodhcart•W1/lcax Publisher

Figure 5-27. The effect of using iron powder in electrode

The addition of iron powder to the covering of SMAW electrodes changes the arc behavior and greatly increases

coatings. Note the change in the amount of fille r metal deposited per hour. The deposit efficiency increase is based on the deposition rate of an E6012 electrode.

Low-Hydrogen Electrodes Right-hand digit 5

Covering compositions

Low-hydrogen sodium type.

This is a low-hydrogen electrode for welding low-carbon alloy steels. Power shovels and other earthmoving machinery require this rod. The weld files or machines easily. Use DCEP only.

Same as "5" but with potassium salts used for arc stabilizing.

It has the

Iron powder (low-hydrogen), flat position only. Iron powder plus low-hydrogen sodium covering.

For low-carbon alloy steels, use DC or AC.

E7015 6

E7016 8

E7028 E8018

Application ( use)

same general application as (5) above, except II can be used on either DCEP or AC.

Similar to (5) and (6) DCEP or AC. Heavy covering allows the use of high-speed drag welding. AC or DCEP may be used. Goodh6all•WJ/l cox Publish91

Figure 5-25. Low-hydrogen electrode compositions and applications.

Current Settings for Low-Hydrogen Electrodes Electrode diameter

Amps (flat)

Amps (vertical and overhead)

Volts

1/8"

140- 150 170- 190 190-250 260- 320 280-350 360-450

120- 140 160-180 200-220 Not recommended Not recommended Not recommended

22- 26 22- 26 22-26 24-27 24-27 26-29

5/32" 3/16" 7/32" 1/4"

5/16"

Goodhearc-Willcox Publisher

Figure 5-26. Recommended current settings for using low-hydrogen electrodes to weld in flat, vertical, and overhead positions. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 5

The arc obtained is smooth and steady. You may use about 25% more current , vith the EXX18 ironpowder electrode, and as much as 50% more current with the EXX24 and EXX27 iron-po,vder e lectrodes, because of their heavy coverings. Electrodes 1,vith a h igh iron-powder content (39% and above) in their coverin g produce a weld pool so fluid that only flat position welding or horizontal fillet welds are practical. Electrodes with high iron-po,vder content have a nun1ber 2 before the last digit: EXX2X.

5.7.3 Corrosion-Resistant Steel Electrodes Corrosion-resistant steel electrodes are often caUed stainless steel electrodes. The specification that covers these electrodes is AWS AS.4, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding. Th ese electrodes are used to ,veld the different stainless steels, which are corrosion-resistant. Stainless steel base metal and electrodes contain chro1niu.m, or chromium and nickel, plus other elements.

119

5.7.4 Covered Electrodes for Cast Iron Cast iron can be arc welded with cast-iron, nickelbased, copper-based, or mild steel a rc ~velding electrodes. AWS A5.15, Specification for Welding Electrodes and Rods for Cast Iron contains more information on cast-iron 1velding electrodes. A cast-iron electrode designated ECJ is used to weld gray cast iron. Another elech·ode, ESt, is a mild steel electrode that is also used to weld cast iron. Four nickel-based electrode classifications used to weld cast iron are ENi-CI, ENiFe-CI, ENiCu-A, and ENiCu-B. These are all covered in theAWS A5.15 specification. The nickel-based electrodes contain from 45% to 98% nickel, depending on their designation. They a lso contain s1nall percentages of iron, carbon, silicon, manganese, sulfur, and copper. These electrodes produce a fairly ductile weld on cast iron. Copper-based e lectrodes for cast iron are designated ECuSn-A, ECuSn-C, and ECuAl-A2. The ECuSn-A and ECuSn-C copper tin electrodes contain tin plus s1nall amounts of phosphorus, a luminum, and/or lead. The elech·odes are more than 90% copper. These electrodes are covered under the AWS A5.6 Specifica-

tion for Copper and Copper-Alloy Electrodes for Shielded lvletal Arc Welding. These electrodes are used for more

Pro Tip Refer to the current AWS AS.4 specification for a complete listing of all the AWS classification numbers for corrosionresistant steel electrodes. This specification also specifies the chemical composition of each classification of electrode. The following is a listing of son1e conunon corrosionresistant steel electrodes. The three numbers represent a type of stainless steel. The letter E stands for electrode. The letter L after the three nu1nbers is a very-Iowcarbon version of the electrode. Some electrodes have major alloying elements listed following the threedigit nun1ber. Exatnples are Ni for nickel a nd Mo for molybdenum. E308 E310 E309 E309L E309Mo E312

Shielded Metal Arc Welding Equipment and Supplies

E316 E316L E317L E320 E320LR E347

E349 E410 E410NiMo E630

These electrode numbers are sometimes followed by a two-digit suffix. Examples are F320- 15 and F31016. The -15 electrode is used with DCEP. The -16 electrode is used with AC or DCEP. Both -15 and -16 electrodes are low-hydrogen electrodes. Electrodes up to 5/32" (4.0 mm) in size can be used in all positions. Electrodes 3/16" (4.8 mm) and larger are used only in the .flat or horizontal-fi Uet welding positions. Copvrighl Goodheart-WIilcox Co. Inc

of a brazing application than a welding application on cast iron. When welding cast iron, it is not desirable to melt a lot of the base m etal.

5.8 Nonferrous Electrode Classifications The American Welding Sodety has produced the following specifications for nonferrous electrodes: • AWSA5.3, Specification for Ali1111inu111 and

Al1111iin11111-Alloy Electrodes for Shielded Metal Arc Welding. • AWS A5.6, Specification for Copper and Copper-Alloy Electrodes for Shielded Metal Arc Welding. • AWS A5.ll, Specification for Nickel and NickelAlloy Welding Electrodes for Shielded Metal Arc Welding. The designations of all nonferrous electrodes include letters that identify the e lectrode's major alloying ingredient. The letters are abbreviations for chemical elements as follows: Al- a luminum Cr-chronuum Cu-copper Fe-iron Mn- manganese

Mo-molybdenum Ni-nickel Si- silicon Sn-tin

120

Modern Welding

There are three a/11111i 11u111 electrodes in the AWS AS.3 specification. They are the EllOO, with an aluminum content of 99°/o; the E3003, with an aluminum content of about 96.7%; a11d the 84043, with approximately 92.3°/o aluminum content. The copper-based electrodes range in copper content fro1n about 69% to 99'1/o. ECuNi is the exception, with copper content of about 62%. It also contains up to 33% nickel, with the remainder n1ade up of other elen1ents. The AWS classifications fo r copper-based e lectrodes are as follows: ECu ECuSi ECuSn-A

ECuSn-C ECuNi ECuAl-A2

ECuAl-B ECuNiAJ ECuMnNiAJ

The nickel-based electrodes contain from 59% to 92% nickel. Their exact chemical composition can be found in AWS AS.11. The eight AWS c lass ifications are as follows: ENi-1 ENiCu-7 ENiCrFe-1 ENiCrFe-2

ENiCrFe-3 ENiCrFe-4 ENiMo-1 ENiMo-3

5.9 Electrode Care

Low-hydrogen electrodes are often stored in an oven, Figure 5-28. Electrode manufacturers may recommend a storage te1nperature, often 220°F-350°F (105°C-175°C), to keep the elech·odes fron1 absorbing moisture (hydrogen). If lo,.v-hydrogen elec trodes are exposed to the atn1osphere for too long, they pick up hydrogen. It is best to remove from the oven only the quantity of electrodes tha t can be used before the end of the exposure time li.n1it. Different e lectrode types have different time limits for exposure. Most low-hydrogen SMAW elech·odes can be reconditioned if they exceed thei.r exposu re time lin1it. R econditioning involves placing the electrodes in an oven for a period of time at a temperature that is higher than that used for storage. For exa mple, electrodes can be reconditioned by heating them at 575°F (300°C) for one hour. Always check \.Yith the manufactw·er or the original packaging for reconditioning recomn1endations. Some electrodes have a limit of how many times they can be reconditioned. The best plan is to remove from the oven only a quantity of electrodes that can be used before the exposure time limit. Electrodes that are not properly stored and handled can produce poor-quality or defective welds. This cru1 lead to rework or scrap, which costs time and money.

Follow the electrode manufacturer's recon1mendations regarding proper ampere settings, electrode h andling and storage, welding position, and other procedures. lf an electrode is used beyond its ampere rating, it v.1 ill overheat. The covering \\rill crack, ruining the electrode. The excess current will also cause considerable spattering of the 1nolten 1neta I.

J

[ 1'22

Caution

Store and handle SMAW electrodes carefully to protect the coating from damage or cracking. Electrodes are sold in cardboard boxes, tubes, or metal cans, depending on the quantity purchased. Often there is a resealable plastic bag i.nside the container. The packaging identifies the electrode type and diameter and keeps the electrodes safe. The packaging should be resealed after each time electrodes are removed. Small quantities of electrodes are sold in r esealable plastic bags. For most electrodes, keeping them in their original packaging is recommended.

•••• •••• • ••• •••

Goodhean-Wlllcox PublWPer

Figure 5-28. An electrode drying oven is used to remove

moisture from the electrode covering before use.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 5

Shielded Metal Arc Welding Equipment and Supplies

121

5.10 Power Source Remote Controls

5.11 Weld-Cleaning Equipment

Welders work on a variety of joints and materials with varying metal thicknesses. They use different electrodes and weld in various positions. AlJ these variables require changes in welding current. Often the welding machine is at a distance fro1n where the welding is being done. The welder may be welding on a structw·e or pipeline and the machine is on a truck or support equipment. Several n1anufacturers provide re,note control devices that may be kept near the operator for convenient control of the machine. See Figure 5-29. These remote devices a llow the welder to adjust the cu rrent without changing the controls on the front of the machine itself. This eliminates the time required to walk back and forth to the welding machine. T he result is more time welding. Also, better welds are produced since the welder can make small current adjusttnent to 111eet the requiren1ents of the weld joint, metal thickness, and position.

Base metals in weldments must be deaned prior to welding. It is difficult to weld dirty or corroded surfaces, and doing so v.1iU resuJt in poor-quality welds. Many types of equipment and tools have been developed to clean joints and ,,velds. Cleaning can be done with a disk grinder, rotary wire wheels, and hand tools such as chipping hammers and wire brushes. Nonferrous metals can be chemically deaned, especially in production welding situations. The amount and size of the welding done usually de termines the kind of c leani ng needed. To prevent inclusions in the finished weld, the slag that covers each weld bead must be removed before the next weld bead is laid. The slag on the fina l bead must aJso be removed before the weld can be inspected or painted. This slag coating can be removed with a rotary wire ,,vheel or by tapping the slag with a pointed hammer called a chipping ham1ner.

Miller Bect.ric Mfg. Co.

Figure 5-29. A remote amperage adjuster. With this device, a percentage of the amperage range set on the power supply can be adjusted remotely.

Copvrighl Goodheart-WIilcox Co, Inc

122

Modern Welding

fflwarning When removing slag, always wear approved safety glasses. Slag will fly in all directions and can cause eye injuries.

Chipping han'\illers a re often double-ended, as shown in Figure 5-30. One end is shaped like a chisel for general ch ipping. The other end is shaped like a pick, for reaching into comers and narrow spaces. Another type of chipping hammer is shown in Figure 5-31.

Welding heltnets are available with an autodarkening filter lens, Figure 5-32. When no arc is present, this lens is fairly clear. A welder can see through the lens to view the weld joint and position the electrode. Once the arc is struck, the lens instantly changes to a dark filter lens. There is no need to raise or lower a helinet w ith an autodarkening lens. H elmets without an autodarkening lens have a fixed shade number. The helme ts have a tens ion adjustment that keeps the heliue t up, Figure 5-33.

5.12 Shields and Helmets Special equipment must be ,,vorn to protect skin surfaces, such as the hands, face, and eyes during arc welding. An arc 1veldi11g he/111et protects the face and eyes. It is mounted and supported on the head. Headbands on the helmets are adjustable.

The Uncoln Bectric Compa.ny

Figure 5-32. An autodarkening arc welding helmet. A welder can see through the lens. Once the arc is struck, the lens instantly changes to the set lens filter number.

LencoJNLC

Figure 5-30. A variety of chipping hammers.

Atlas Woldi1g Accossorios, Inc.

Figure 5-31 . A combination wire brush and chipping hammer.

Jackson ProdUC1.s

Figure 5-33. An arc welding helmet. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 5 Shielded Metal Arc Welding Equipment and Supplies The tension is adjusted so a slight nod of the head a llows the helmet to rotate down over the welder's face. After the welder has positioned the electrode over the joint in preparation for welding, a slight nod of the head causes the helmet to fall into place. The welder then stii.kes the arc. The intense light of the •,velding arc allows the welder to view the joint, the electrode, and the arc. When welding is romplete, the welder lifts the helmet to the raised position. A handheld welding shield is sometimes used by observers like inspectors, foremen, or instructors. See Figure 5-34. An aperh.u-e or opening a t the level of the eyes p rovides visib iJity. Two n1ain s izes are 2" x 4 1/4" (51 mm x108 mm) and 51/4"x41/2" (133mm x 114mm). A filter lens is set into the opening. A filter len s p rotects the eyes frorn ultraviolet and infrared rays of the welding arc. A filter lens can be autodarkening or a fixed-value filter lens. Different lens shade nun1bers are requ ired for different types of welding. Figure 5-35 lists recommended shade numbers. Most autodarkening lenses can be adjusted to different lens shade numbers. Traditional filter lenses are made to a se t shad e number. They do not change from clear to dark. However, the filter lens in the helmet can easily be replaced with a different strength filter lens as needed.

123

Recommended Lens Shades for Arc Welding Process

Lens shade number

SMAW (shielded metal arc welding} up to 5/32" (4mm} electrodes 5/32"-1/4" (4mm-6mm) electrodes > 1/4" (6mm) electrodes

10 12 14

GMAW (gas metal arc welding) and FCAW (flux cored arc welding) < 160amps 160-250 amps > 250 amps

11 12 14

GTAW (gas tungsten arc welding) < 50amps 50-150 amps > 150amps

10 12 14 GOOdhean-WIIJCOX PvtJlsher

Figure 5-35. Suggested lens shade numbers for various

a rc welding applications.

Place a dear plastic or glass cover plate in front of and be· hind the expensive filter lens. Cover plates are inexpensive and protect the filter lens.

Safety glasses are always worn under the welding helmet. Flns/1 goggles are safety glasses with a #1 to #3 lens. Flash goggles protect the \.ve lder's eyes from arc flashes from behind the welder. The safety glasses protect the eyes when the helmet is raised during setup or chipping tasks. The Occupational Safety and Health Act (OSHA) requires a hard hat to be worn with the arc welding helmet on construction s ites. A combination welding helmet and hard hat is shown in Fig ure 5-36. Lens Safety helmet (hard hat)

Welding helmet

Jackson Products Jackson Products

Figure 5-34. A handheld welding helmet. Copvrighl Goodheart-WIilcox Co, Inc

Figure 5-36. An arc welder's helmet used in combination

with a safety helmet (hard hat).

124

Modern Welding

Fresh a ir is fed into so1ne helinets through a hose. The constant d elivery of fresh air protects the welder from ha rmful fumes. The fresh air also increases the comfort of the v.relder. Helinets that fil ter the air or provide clean air that the welder breathes are also available. Refer to Fig ure 5-37.

5.13 Special Arc Welder Clothing While an arc weld is in progress, the molten flux and the metal itself somet imes spatter for a considerable distance a round the joint being welded.

The operator 1nust, therefore, be protected from the danger of being burned by these hot particles. C lothing items, including a jacket, apr on, cape, leggings, and g loves, are made o f leather. They are re ferred to as leathers. See Fig ure 5-38. Clothing ,,vorn while welding, other than the leathers mentioned, should be of heavy n1ateria l such as cotton or wool. All clothing should be carefully inspected to eliminate any place ,-vhere the metal may catch and burn. Open pockets are dangerous. Thin clothing permits infrared and ultraviolet rays to penetrate to the skin. If the skin is not properly protected, the operato r w iJ I become "sunburned." Easily ignited materials, such as butane cigarette lighters and ite1ns that can ignite or melt plastic combs and pens, should not be carried by the operator ,~,hile ,,velding. When performing welds in the overhead welding position, welders should wear a jacket or cape to protect their shoulders and arms. They should wear a cap or a special hooded arc helmet to protect their head and hair. The operator should also wear high-top shoes or boots. Frequently, steel-toed shoes or boots are required. Pants worn by the welder should not have cuffs. Cuffs can catch burning particles as they fall. Gloves must be worn to cover the hands and wrists and to prevent "sunburn."

The Lincoln Electric Comp\1 ith GMAW, FCAW elech·ode wire is manufactured to specilications written by the An1erican We.ld.ing Society. Fig ure 7-37 lists the AWS specilications for FCAW electrodes. Figure 7-38 lists a few common FCAW electrodes used to weld various types of steel base 1netals. Flux cored "''ire is made by first rolling flat strip steel into a U shape. The U-shaped area is filled w ith prepared granLtlar flux and alloying ele1uents. After filling, the metal is closed and rolled into a round shape. This closing and rolling compresses the flux material. The tubu lar wire is then passed through dra,-ving (fonning) dies. This further compresses the granular flux and forms a perfectly round form of an exact d.iameter.

AWS Specifications for FCAW Electrodes Base metal

AWS specification number

carbon steel

A5.36

Low-alloy steel

A5.36

stainless steel

A5.22

Cast iron

AS.15

Nickel alloys

AS.34 Goodheart•W11/cox Pubhsher

Figure 7-37. AWS FCAW electrode specifications.

FCAW Base metal

Recommended electrodes

GMAW Electrodes for Aluminum

carbon steel

E70T-1, E71T-1, E70T-2

GMAW electrodes are available for welding alu1ninum. Aluminum alloys are designated with a four-digit number for non-cast aluminum. Examples of typical alwninun1 alloy numbetS a re 5052, 5056, 6061, and 6063. GMAW electrodes use this same four-digit numbering system.

Low-alloy steel

E80T1-B2, E80T1-Ni2

Stainless steel

E308T-3, E308LT-3, E316LT-3,E347T-3 GOO 250 amps GTAW (gas tungsten arc welding)

fflwarning An air-purifying respirator does not remove toxic fumes and should not be used for protection in a closed, confined, or contaminated area.

< 50amps

10

50-150 amps > 150 amps

12 14 Go0et

Figure 7-44. A guide to the correct welding lens shade for various welding processes and applications.

7.8 Filter Lenses for Gas-Shielded Arc Welding Because of the clearer atmosphere arow1d the arc, the operator n1ust use arc welding lenses with a darker shade to reduce eye fatigue and prevent possible eye darnage. Most helmets for gas metal arc welding have a clear cover lens and a filter lens. Sometimes there is a clear cover lens on the inside of the helmet, as well. It is crucial that all these lenses be clean. Fig ure 7-44 Lists recomn1ended shade numbers for gas tungsten, gas metal, and flux cored arc welding.

7.9 Protective Clothing Leather clothing provides the v.1elder with the best protection. Ho,,vever, heavy wool or cotton can also be worn. Cotton may be treated to reduce its ability to burn. Dark clothing should ah,vays be worn because it reduces the reflection of light behind the helmet. Clothing worn while welding should have no cuffs or open pockets, since these can collect sparks. Leather gloves should be worn. Chapter 1, Safety in the Welding Shop, includes additional information on clothing recomn1ended for arc v.relding.

7.10 Safety Review When using GMAW or FCAW equipment, follow all the safety precautions normally used with arc welding equipment. These include the follov.1 ing: • Elech·ical connection leads should be in good condition and tight. They should be protected from accidental damage from shop hc1ffic_ • To prevent fumes and contaminated air from reaching the welder's face during welding, adequate ventilation and filtration equipment n1ust be used. In sorne welding conditions, it is necessary to use a pmified air breathing apparatus. • Proper clothing should be worn to prevent burns from hot metal and ultic1violet and infrared rays. • Flammable materials should not be car1ied in pockets. Pockets should be closed and cuffs roUed do,.vn to prevent hot metal from going into thein. • Ah,vays v.rear a welding helrnet with the proper number filtering lens for the type of welding being done. • Shielding curtains should be placed around all jobs so workers in the area are protected from arc flashes.

Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 7

Summary • Gas metal arc welding (GMAW) is a welding process in which an arc is struck between a consun1able metal electrode and the metal workpiece. The weld area is protected by a shielding gas. • In the flux cored arc •,velding (FCAW) process, the ~veld is shielded from atmospheric contamination by one of two methods. FCAW-S primariJy relies on fluxing materials in the electrode to remove oxygen and nitrogen from the weld pool. Some shielding gas is formed f1·om vaporizing the flux materials in the electrode core. FCAW-G uses a shielding gas, like GMAW, to keep the abnosphere out of the weld area. Some shielding gas is formed by the vaporizing flux in the electrode core. • A GMAW station and an FCAW-G welding station use the same equipment, including a constantvoltage DC arc welding power source. • Wire feeders consist of a coil-mounting device; a set of drive rolls; and an adjustable, constant-speed motor to turn the wire drive rolls. Wire feeders can have two or four drive rolls. Drive rolls can have one of three groove designs. • Mixtures of a1·gon and carbon dioxide; mixtures of argon and oxygen; 100% carbon dioxide; and a h·iple gas mixture of helium, argon, and carbon d.ioxide are used ,,vith GMAW to weld carbon steel, low-alloy steel, and stainless steel • Gas1netal arc welding guns are usually air-cooled. Continuous welding, welding at amperages above 300A with argon shielding gases, or welding at amperages of 600A or above require the use of water-cooled guns. • A contact tip is the part of a welding gu11 that transfers the electrical current from the gun to the electrode wire. The contact tip must be 1·eplaced when it weai·s. • Nozzles fit on the end of GMAW and FCAW-G guns to direct shielding gas to the weld area. • GMAW electrode wire is usually a continuous solid electrode wire. A second type is a meta l cored electrode wire. • Flux cored electrode wire is tubular with different core ingredients. The material in the flux core adds alloying elements, provides deoxidizers and denitrifiers, produces a slag to protect the weld metal as it cools and other functions. • The AWS identification system for GMAW and FCAW electrode wires includes a designation for each electrode that provides essential i.nformation about the electrode to the welder, such as tensile strength, composition, usage and other information. Copynglll GOOdhear1-w1nco~ CO Irie

GMAW and FCAW Equipmen t and Supplies

193

• The GMAW and FCAW processes generate smoke. Welding with CO2 creates some toxic carbon 1nonoxide and ozone. To prevent breathing gases or fumes, a welding gun equipped with a built-in fume extJ-actor can be used. A large fume extractor systen1 can also be used.

Technical Terms Select the icons to access Drill and Practice activities. adapter liner nozzle contact tip dash number power pin denitrifier purge switch deoxidizer reactive gas flow meter regulator gas-shielded flux cored sell-shielded flux cored arc ,,velding (FCAW-G) al'c welding (FCAW-S) slope inch switch inert gas spool gun jog switch

Review Questions Ansiver the fo/101ving questions using the infonnation provided in this chapter.

Know and Understand 1. True or False? The arc welding power source used for GMAW and FCAW produces a constant voltage. 2. GMAW power sources have a sloping voltage curve. The curve should slope _ _ per 100A when carbon dioxide (CO2) gas is used. A. 4Vto5V B. 3V to 4V C. 2V to 3V D. 1.5V to2V 3. Which of the follov.ring is not a standard drive roll groove design? A. A-groove. B. U-groove. C. V-groove. D. Knurl-groove. 4. Which of the following drive roll designs is used with FCAW electrode wire? A. A-groove. B. U-groove. C. V-groove. D. Knurl-groove.

5. Increasing the wire feed rate in GMAW or FCAW increases the _ _ in the circuit. A. voltage B. slope C. current D. inductance 6. The FCAW process most con1monly uses which type of shielding gas? A. Carbon dioxide. B. Argon. C. Argon with 2% oxygen. D. Argon with 10% carbon dioxide. 7. During gas metal arc welding of steel with 100% argo n, w1de.rcutting can occur. Wl1at gas is often added to argon to prevent undercutting? A. Helium. 8. Nitrogen. C. Carbon dioxide. D. Hydrogen. 8. What shielding gas is used to weld aluminum vvith GMAW? A. Argon. B. Nitrogen. C. Carbon dioxide. D. Argon with 2% oxygen. 9. Which of the following statements about an ER90S-B3 elech·ode is false? A. It can be used as both an electrode and a fiUer rod. B. Its tensile strength is 90,000. C. The composition is chromium-molybdenum. D. It is a cored electrode. 10. True or Fnlse? An E90T5-B3 electrode can be used in all welding positions. 11. True or False? When an FCAW elecb·ode is being fed through the wire feed mechanism, care must be taken not to flatten or crush the flux cored wire. 12. Which of the following is not a fw1ction of flux in an FCAW electrode? A. Add deoxidizers. 8. Add hydrogen. C. Form a slag covering. D. Add arc s tabilizers. 13. Which of the following is a metal cored electrode wire? A. ER70S-6. 8. ER70C-6. C. ER70M-6. D. E70T-6. 14. A number _ _ filter lens is recornn1ended for GMAW welding of steel with a cw·rent of 200A. A. 10 8. 11 C. 12 D. 14

15. A number _ _ filter lens is recommended for FCAW welding steel with a current of 300A. A. 10 8. 11 C. 12 D. 14 Apply and Analyze

1. What is the difference in the electrode wire used in GMAW and FCAW? 2. What is the difference in the way FCAW-S and FCAW-G protect the weld? 3. How does a constant voltage power source selfadjust to maintain a constant arc length when the \.velding gun is moved closer to the work? 4. What is the purpose of the inch switch on the \.Vi.re drive control panel? 5. What shielding gases are used for FCAW-G ? 6. List two precautions to be taken when storing gas cylinders. 7. Why is maintaining the proper arc length critical when carbon dioxide is used for GMAW? 8. Why is a pull-type gun used for alunlinum electrode ,vire? 9. What do the letters "ER" at the beginning of a GMAW electrode designation mean and ho"" can such an electrode be used? 10. What electrodes are commonly recommended for the following? A. GMAW welding of stainless steel. B. FCAW welding of low-alloy steel. C. GMAW welding of carbon steel. Critical Thinking

1. Compare SMAW to FCAW-S when welding in the field. Identify at least one advantage and one disadvantage of each process. 2. Think of an industry in your area that uses welding, such as building, mining, equipment fabrication, pipeline, oil and gas, energy, agriculture, and automotjve. Which process, GMAW, FCAW-G, or FCAW-S, do you think is most widely used in that industry? Why? Experiment

1. Judge the amount of smoke produced by GMAW, FCAW-G, and FCAW-S. H ave one person weld with GMAWand observe the a1nount of smoke produced. Repeat having the same person \.Veld FCAW-G and then FCAW-S. Copynghl Goodheart-Willcox Co Ince

Gas Metal and Flux Cored Arc Welding ESAB WelcJ/ng and Cut11ng Products

Learning Objectives After studying this chapter~ you will be able to: • Contrast GMAW metal transfer methods, considering arc cha racteris tics, weld characteristics, and out-of-position welds. • Select the proper arc welding machine, wire feeder, shielding gas, flow rate, contact tip, nozzle size, and ,,velding wire type to produce an acceptable ,~,eld. • Identify the different shielding gases used for GMAW and explain how they affect the shape and penetration of the completed ~1elds. • Properly assemble and adjust all the equipment required to produce an acceptable weld using the GMAW and FCAW processes. • Make accep table welds on aU types of joints in all positions using GMAW. • Make accep table welds on all types of joints in the flat and horizontal positions using FCAW. • Identify potential safety hazards associated ,,vith the GMAW and FCAW processes and describe proper safety procedures.

he gas metal arc welding (GMAW) process uses a solid or metal cored welding wire that is continuously fed into the weld pool. The welding ,~•ire is consumed and beco1nes the filler n1etal.

T

Flux cored arc welding (FCAW) is very sunilar to gas metal arc welding, but w,like GMAW, it uses a fluxfilled welding wire. GMAW has a 1,vide range of applications due to several factors. The continuous development and refinement of constant voltage power sources and wire feeders has 1nade GMAW more effective to use. GMAW is easy to learn, especiaUy if a welder has already lea1ned a different welding process. GMAW equipment is relatively low in cost. Also, GMAW deposits rnore weld metal in lb/ hr (kg/hr) than the SMAW and GTAW processes. The low purchase cost, the ability to weld continuously, and the abiHty to deposit weld n1etal faster make GMAW an attractive choice for welding. GMAW can produce hlgh-quality welds on most rnetals commonly used in ma nufacturing, inc luding carbon and alloy steels, stainless steels, aluminum, magnesium, copper, and o thers. GMAW can also be perforrned easily in all welding positions. GMAW is performed in almost a ll industties and is used in most robotic arc welding applications. It is also ~videly used on farm and home applications. FCAW is a popular welding method that is used in many indus tries, including structural welding. It has the adva ntages of both GMAW and SMAW. Like GMAW, FCAW includes the abilit y to weld continuously and to deposit weld 1ne tal faster. FCAW and GMAW are a lso easy processes to learn. Like SMAW, FCAW includes the addition of alloying and fluxing elements in the electrode.

195

196

Modern Welding

FCAW can be done with shielding gas. Gas-shielded FCAW is known as FCAW- G. Because FCAW- G uses a shielding gas, it is frequently used inside a building where there are no cross winds to disrupt the shielding gas. FCAW can also be done without shielding gas. This is known as FCAW-S. The FCAW-S flux cored electrode does less to protect the weld frotn the atmosphere. The flux in the electrode wire does a better job at removing oxygen and nitrogen from the weld pool. FCAW-S is tnore co1nn1only used outdoors on construction sites. Any cross wind will not affect the weld quality.

8.1 Gas Metal Arc and Flux Cored Arc Welding Principles Gas metal arc welding is a quick and easy process that produces quality welds. GMAW is usually performed with solid wire electrodes. FCAW uses flux cored welding wires. See Figu re 8-1. A shielding gas or gas mixture must be used with GMAW. GMAW is nearly ah,vays performed ,-vitl1 direct cun·ent electrode positive (OCEP) current. Direct current electrode negative (DCEN) is rarely used for gas metal arc welding, but has a limited u se for surfacing. A straight AC output current is not produced for GMAW or FCAW. However, a variable polarity wavefor1.n is possible witl1 an inverter power source. The variable wave combines the penetration of DCEP with a higher deposition of DCEN. It can be used on tl1inner steel and aluminum base metal. It differs from normal AC in tl1at

the positive and negative portions of the output \Vave are not balanced. For every pound of solid GMAW ,~relding wire used, 92%- 98'1/o beco1nes deposited weld 1netal. About 82°/o-92% of flux cored arc welding wire is deposited as ,,v eld metal. As a compadson, SMAW deposits 60%-70"/o of tl1e welding wire as weld 1netal. Son1e spatter does occur in tl1e GMAW processes. FCAW- G has some spatter. FCAW-S has higher levels of spatter. Very little stub loss occurs when continuously fed wire is used. There are very thin glass-like islands over tl1e weld bead after gas metal arc welding. No heavy slag is created because tl1e ,~reld area is sh ielded by a gas. FCAW produces a slag covedng. Some of the flux i..n the FCAW forms a gas arow1d the weld area Some of the flux forn1s a slag that covers the weld. A welder can spend more time on the welding task with a continuously fed wire process. This improves the cost efficiency of GMAW and FCAW. The GMAW process can be adapted to a variety of job requireinents by choosing the correct sh.ielding gas, electrode size, and welding parameters. Welding parameters include voltage, travel speed, and wire feed rate. The arc voltage and wire feed rate determines the filler metal transfer metl1od.

8.2 Metal Transfer 1"1etal transfer is the transfer of molten filler metal from the electrode to the vveld pool, either by tl1e short circuiting metl1od or by transferring metal across the arc.

Gas Metal Arc Welding (GMAW)

Flux Cored Arc Welding (FCAW)

Wire motion

Wire motion

t

t i --

Shielding gas

- -1--

Electrode -

-

Gas noule

Shielding - -1-- gas (if used) - Contact tip

contact tip

r

rr,

( rr (( '(

r

'

r

'""')

)~)l))

-

(((

~1"')

Flux cored electrode

r,;r;-,

'

Gas nozzle {II used) I

J

:-'I ...)l) '\

)

\ Goodhoart~WiUcox Publisher

Figure 8 -1. Cutaway views of GMAW and FCAW gas nozzles and electrodes. If shielding gas is not used with FCAW, no nozzle is required. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 8 Gas Metal and Flux Core d Arc Welding The various methods of h:ansfer deposit .□1etal at different rates, Figure 8-2. Methods of transferring metal across the arc include the following: • Globular transfer. • Spray transfer. • Pulsed spray transfer. Short circuiting, globular transfer, spray transfer and pulsed spray transfer will eacli be discussed in the next four subheadings.

Metal short-circuits to weld pool

197

Pinch force squeezing off droplet Pinch force

Shielding gas ---- - envelope (

8.2.1 Short Circuit GMAW (GMAW-S) Short circuit gas metal arc welding (GMAW-S) is used with relatively low welding currents. Welding current, which is controlled by the wire feed speed, is lov.rer for short circuiting transfer than any other transfer method. Thus, short circuiting b:ansfer is particularly suitable for thin meta.l sections. Short circuiting h·ansfer is also useful for filling large root gaps or gaps between poor-fitting parts. Short circuiting transfer can be used in all positions. All position welds are made easily because there is no metal h·ansfer across the arc. The weld pool cools and solidifies rapidly using the short circuiting a1·c. Short circuiting transfer results in low heat input into the base metal. Since GMAW- S has a small weld pool and lo\~' heat input, it is used to weld in the overhead or vertical welding position. In short circuiting transfer, the arc is terminated or goes out when the electrode touches the molten weld pool. Surface tension from the weld pool pulls the 1nolten metal from the end of the electrode into the pool. A pinch force is an electrical force around the electrode that squeezes the molten end of the electrode. The co1nbined effects of surface tension and the pinch force separate the molten metal from the electrode. This separated portion of the electrode flows into the weld pool and flattens out. See Figure 8-3.

GMAW Deposition Rates Metal deposited GMAWmethod

Short circuiting Globular Spray Pulsed spray

lb/hr

kg/hr

2-6 4-7 6--12 2-6

0.9-2.7 1.8- 3.2 2.7-5.4 0.9-2.7 Goodheart-Willcox Publisher

Figure 8-2. The approximate rate at which carbon steel

filler metal is deposited with various GMAW methods. Copvrighl Goodheart-WIilcox Co. Inc

A

B

Wire nears another short circuit

Arc reignites

,. C

('

D Goodnearr-lVlllcox Pu/II/Mer

Figure 8-3. The sequence of metal transfer during the short

circuiting transfer method. A- The welding wire short- circuits lo the weld pool. There is no arc at this point. B-A magnetic pinch force squeezes off a droplet of molten electrode metal. C- The welding arc reignites. D-The electrode nears another short circuit condition and the process repeats itself. Once the molten metal from the electrode is separated from the electrode, the current jumps the gap between the new end of the electrode and the weld pool, reestablishing the arc. The arc melts the base metal and the end of the electrode. The continuously fed electrode again touches the molten pool and the process repeats . The process of shorting the electrode to the ¼ 1ork repeats about 20 to 200 tin1es per second. The pinch force, whicli acts to separate the end of the electrode, is created by current flowing through the electrode. Arc voltage, the slope of the power source, and the circuit resistance determine the strength of the pincli force. These factors-voltage, slope, and resistance-also affect the welding current. If a 150A current is set on the arc welding machine, the amperage may rise rapidly to the maximun1 output of the 1nacliine when the electrode short circuits; that could be 500A or more. An inductance circuit is built into the arc welding u1ach.ine to control and slo¼' do\,vn any rapid rises in current.

198

Modern Welding

l11ducta11ce is the property i.n an electric circuit that slows down the rate of the current change. Increasing inductance in a welding machine slows down the increase of the welding current. Decreasing the inductance increases the rate of change of the "velding current. Current rises too rapidly when too little inductance is used. The n1axin1um current will be high. The pinch force is so great that the molten metal at the end of the electrode explodes, resulting in a great deal of spatter. Current does not dse fast enough when too much inductance is used. The molten end on the electrode is not heated sufficiently because the n1aximum current is too lo,,v. An ideal short circuiting transfer rate and pinch force can be obtained by properly balancing the inductance and slope. Shielding gas also has an effect on short circuiting transfer. Carbon dioxide (CO2) can be used as a shielding gas for short circuiting transfer of carbon and low-alloy steels. CO2 produces greater peneh·ation but creates mo1-e spatter than an inert shielding gas. Mixtures of argon and CO2 are often used because they provide a good combination of improved penetration with minimal spatter. Welding stainless steel ~vith short circuiting transfer usually requires a mix of three gases. A typical mixture is 90% helium, 71/2"/oargon, and 2 1/2% CO,. Inert shielding gases are required for all nonferrous base metals. Nonferrous base metals are those in which iron is not the main element. This includes all metals except steels, steel alloys, and cast irons. Adding heliu1n to argon increases the penetration. Mixtures containing only argon and helium are used only on nonferrous base metals.

Transfer (ST'f'&). MiUer Electric Manufacturing Company calls their process Regulated Metal Deposition (RMD™). Figure 8-4 shows the current duri11g a short circuit cycle of the modified short circuiting transfer process.

Peak lime --1--1 r-----1 -

Peak current

Pinch current"'Tall-out speed Background current

I

I

! 111! A

B

A

C

B

D

! A

E

C

D

E

Modified Short Circuiting Transfer Advancements in inverter power source technology have made modification of the short circuiting transfer process possible. Inverter welding machines can alter or modify the current output of the power supply. This ability aUows an inverter power so11rce to be used for modified short circuiting transfer. The power source uses feedback information to determine when to change the current from a 101,v background current to a high peak current and to a near zero current. Peak current is necessary to establish the arc after a short circuit. 8ackgro1111d c11rre11.t 1uaintains the arc and is significantly less than the peak current. The average of these t,,vo nurents is less than the current value set during the standard short circuiting process covered earlier. This results in less heat introduced into the weld joint and significantly reduced spatter. Different power source manufacturers have their own names for this modified process. The Lincoln Electric Company calls their process Sw·face Tension

The Uncoln ETecutc company

Figure 8 -4. The graph at the top of this figure shows the changes in the welding current during a single ST-re short circuit. The high-speed photos in the center of the figure correspond to the points in the graph above. The graph at the bottom of the figure shows the changes in voltage and current and their effects on the electrode, arc, and weld pool. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 8 Gas Metal and Flux Cored Arc Welding At point A, the lo\~1er background current is £101,ving. The arc melts the end of the wire and the base metal. Just as the electrode shorts to the base metal at point B, the power source reduces the current to near zero. There is no arc. After the short occurs, the cu1-rent increases. At point C, the current is increasing to create the pinch force, v.1hich necks down the welding v.1i.re. A very important pa1t of this process is that just as the molten end of the electrode is about to separate, the current is again reduced to a very lo\,v level at point D. The surface tension of the molten weld pool pulls the molten droplet off the end of the electrode and into the weld pool. There is very little current flowing when the rnolten droplet separates from the electrode. This low current prevents the end of the electrode fron1 exploding or creating spatter. After the droplet leaves the end of the electrode, the current ina·eases to the peak current amount. The peak cw·rent is shown as point E in Figure 8-4. Dw·ing this peak current period, the weld pool is very fluid. The high current helps the weld pool flow out to the toe of the weld. Finally, Point A shows a new droplet forming on the end of the electrode; the process is repeating. One complete short circuit cycle is con1pleted and a new one begins. This process is repeated 20 to 200 times per second.

8.2.2 Globular Transfer Globular metal transfer occurs when the weldingcw·rent is set sHghtly above the range used for the short circuiting metal transfer. In the globular metal transfer process, the metal transfers across the arc as lru·ge,

Irregular large droplet forming

Droplet may short-circuit when It falls

Shielding gas envelop::e:----l

199

irregularly shaped drops. See Figure 8 -5. The drops a1·e usually larger than the electrode diameter. Drops form on the end of the electrode. Each drop grov.1s so large that it falls from the electrode due to its own weight. If the shielding gas contains a high percentage of inert gas, the drops fall sh·aight into the weld pool. lf the shielding gas contains a high percentage of CO2, the drops travel across the arc in random paths, creating spatter. To minimize spatter, a lower arc voltage, whid1 produces a shorter arc length, can be used. However, too short of an arc voltage allows large drops to contact the base metal before the drops separate from the electrode. The resulting short circuits cause the drops to explode, creating a lot of spatter. One way to minimize spatter when using CO2 is to increase the cwTent slightly. This creates a deep weld pool that is lower than the surface of the surrounding metal. This is referred to as a buried arc. Using a bw·ied arc, most of the spatter is contained within the deep weld pool With a buried arc, a combination of globular and short circuiting transfer occurs. Deeper penetration occurs with a buried arc. The globular transfer method can be used to create welds faster than the short circuiting transfer method, Fig u re 8-2. Welds produced with globular transfer are sufficient quality for many applications. However~ because of the excessive spatter and nonuniform metal deposition, this transfer method is not capable of producing truly high-quality welds. Short circuiting and spray transfer are preferred transfer methods. Because the molten metal falls into the weld pool due to gravity alone, this method of transfer can be used only in the flat position.

Droplet may fall erratically and cause spatter

Spatter

Buried rue helps to contain droplet to reduce spatter

Deep weld pool

Arc

Goodhoart4Villcox Publisher

Figure 8-5. GMAW globular metal transfer. Drops fall erratically and cause spatter. Nole that the buried a rc may help

contain the drops lo reduce spatter. Copvrighl Goodheart-WIilcox Co, Inc

200

Modern Welding

8.2.3 Spray Transfer

Stage 2

Stage 1

Spray transfer gas metal arc welding requires current and voltage settings higher tha n those required for globula r t ransfer. Spray transfer occurs when very fu1e droplets of metal form at the tip of the welding wire. The droplets t ravel at a h igh rate of speed directly through the arc stream to the weld pool. See Figure 8-6. Spray transfer takes place on ly when the shielding gas contains a hig h percentage of argon. To ,-veld nonferrous metals and alloys, use 100°/o argon shielding gas. A shielding gas mixttu·e containing at least 80% a rgon is required for spray trans fe r on carbon or lowalloy s teels or stain less steels. Before spray transfer can occur, the welding mac hine's curre nt setting mus t be set high eno ug h. The current mu st be a bove the tra11sition curre11t, which is the current required for the transfe r me thod to change fro1n glo bular to spray tra ns fe r. The transition current varies with the electrode diameter, the composition of the electrode, and the leng th of electrode ex tension (the a1nount that the end of the welding wire sticks out beyond the end of the contact tip). The trans ition current increases as the electrode d ia mete r increases and deo·eases as the electrode extends fa rther from the contact tip. The

Shielding gas envelope

Wire

necks down

Metal droplets

Arc

Goo ,__..7

Stubby gasket

-

Collets

Handle-textured

Collet body/ gas lens

I

_ _J

I Handle-smooth

Noz.zles

0

Power cable adapter

Ame11Can TO/Ch Tip co.

Figure 9-15. The various parts in a typical water-cooled GTAW torch, and how they fit together. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 9

Gas Tungsten Arc Welding Equipment and Supplies

End caps Nozzles

Collet bodies

251

Stubby end caps

Collets

I Electrode

\

Insulators

-

Gas lens collet

Torch body Amor/can Ton:h Tip Co.

Figure 9·16. Different sizes of nozzles, collets, and collet bodies available for a typical GTAW torch.

Figure 9-17 shows some of the torch parts as they \1/0ttld

be assembled. There are two basic torch designs: • Torch es designed f or general access. These

torches usually use a long electrode and have a long cap. They also use standard collets, collet bodies, and nozzles. Refer to Figure 9-13. • Torches designed for work in areas where space is limited . These torches are called stubby or stubs because they use a very short electrode and have a very short cap. They also use stubby collets, stubby collet bodies, and stubby nozzles. Refer to the right torch in Figure 9-14. There are variations of the ge neral access design. These variations allow a \,velder to select different parts for the torch to customize it for specific jobs.

Goodheart-Wilfcox Publisher

Figure 9-17. A gas-cooled GTAW torch.

9.5.1 Collets, Collet Bodies, and Gas Lenses Tungsten electrodes are held in a collet, Figure 9-18. The collet is held by a collet body. The col/et body contacts and centers the coUet and transfers the electrical current to the collet. The collet, in turn, transfers the electrical c urrent to the electrode. The collet body is threaded into the end of the torch. Examples of collet bodies are shown in Figure 9-16 and Figure 9-17. Collet bodies are made for a single size of collet. If a different diamete r electrode \,viii be used, both the collet and the collet body need to be changed. The func tion of the collet is to firmly hold the electrode and make an electrical connection to it. Collets are made with va rious inside dia1neters. Copvrighl Goodheart-WIilcox Co , Inc

•

GoOdhean-Wtncox Publlst'ler

Figure 9-18. Two copper GTAW collets.

252

Modern Welding

A collet 1nust be selected to match the diameter of the electrode being used. A collet is installed into the top of a torch assembly, Figure 9-19. To n1ake a coUet tight arou nd the electrode, the cap is tightened. Tightening the cap forces the collet against the collet body, which squeezes the col let. The i.ns ide diameter of the coUet decreases, firmly gripping the electrode. A collet body •,vith a gas lens can be useful to a welder. The gas lens n1akes the shielding gas exit the nozzle more as a column than as a turbulent stream that spreads out after exiting. See Figure 9-20. The column of gas provides better gas coverage farther from the nozzle than a turbulent stream. This allows the electrode to stick out farther for visibility and for better access to the weld area. A gas lens is a series of stainless steel ,,vire mesh screens. The collet body 1,vith gas lens is installed in the torch in place of a standard coliet body. A different gas lens is required for each different electrode diameter. Different nozzles 1nust be used with gas lenses because a gas lens has a larger diameter than a standard collet body.

9.5.2 Nozzles Gas nozzles direct the shielding gas over the tungsten electrode. The nozzle also directs the shielding gas over the weld area. Nozzles must withstand very high temperatures because they are so dose to the arc Different nozzle designs are available to meet the requirements of different welding jobs. Most commonly, nozzles are ,nade from a ceraJnic material. Other materials include metal-jacketed ceramics, metal, and fused quartz.

Ceramic, nozZle

CK Work/wide, Inc.

Figure 9-20. The torch at the right has a gas lens installed. The gas flow from the conventional GTAW nozzle on the left is turbulent and dissipates more rapidly.

One end of a gas nozzle must attach to the end of the torch. The nozzle is usuaUy threaded onto the torch assembly, but the thread size and design vary somewhat among dilierent manufacturers' torches. TI1e exit e nd of the GTAW nozzle is more s tandard. The exit diameter is identified with a number. The number is the exit diameter measured in 1/16' (1.6 1n.1n) increments. A number 6 nozzle thus has a diameter of 3/8" (9.6 mm): 6 x 1/16" = 6/16" or 3/8" (6 x 1.6 1nm = 9.6 min) A number 8 nozzle diameter is 1/2" (12.8 mm): 8 x 1/16" = 8/16" or 1/2" (8 x 1.6 mm= 12.8 mm)

Goodheart-WIiicox Publisher

Figure 9-19. A copper electrode coll et being installed in a GTAW torch. The electrode and electrode cap are installed next.

Nozzle ex.it diameters must be the correct size for the job. If they are too small, they will not allov., the shielding gas to cover the weld area. They cannot be too large, or the velocity of the gas coining out will be too slow and will easily be blovvn away. A high velocity and a small diameter is also not good because air may be caught up iJ1 the turbulence a nd conta1ninate the weld area. Selecting the correct size nozzle is important. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 9 Gas Tungsten Arc Welding Equipment and Supplies Factors such as accessibility of the \,veld area affect selection of the nozzle. Note the different nozzle styles shown in Figure 9-15, Figure 9-16, and other figures in this chapter. See Figure 9 -21 for suggested nozzle size for a given electrode diameter.

The chencical cotnposition of tungsten electrodes, from the AWS AS.12 specification, is shown in Figure 9-22. Le tters and numbers used in tungsten electrode classifications are i.nterpreted as fol.lows: E~lectrode W-tungsten P-pure Ce--ceria La-lanthana Th-thoria Zr-zirconia

9.6 Tungsten Electrodes The folJowing types of e lectrodes are used in gas tungsten arc welding: • Pure tungs ten. • Tungsten with 2% thoria (thorium oxide). • Tungsten with 0.15% to 0.40% zirconia (zirconium oxide). • Tungsten with 2% ceria (cerium oxide). • Tungsten with 1% or 1.5°/o lanthana (lanthanum oxide).

Electrodes are referred to as follows: EWP-Pure tungste11 EWTh-Thoriated tungsten EWZ- Zirconiated tungsten EWCe--Cer iated tungste n EWLa- Lanthanated tungsten

Nozzle Sizes Electrode diameter

Suggested nozzle size Qn)

in

mm

(in)

Nozzle #

.010 .020 .040 1/16 3/32 1/8 5/32 3/16 1/4

.25 .50 1.00 1.6 2.4 3.2 4.0 4.8 6.4

1/4 1/4 3/8 3/8 1/2 1/2 1/2 5/8 5/8

4 4 6 6 8 8 8 10 10 Goodheart•Wilfcox Publisher

Figure 9-21. A table of suggested nozzle sizes for use

with vario us electrode dia meters.

253

l■,Nole Tungsten electrodes not covered in the preceding list are designated EWG. Pure tw1gsten electrodes are the least expensive. These electrodes are used only with AC welding. Pure tu ngsten electrodes carry less current than alloyed electrodes. Pure tungsten electrodes can split or break down and cause inclusions (tungsten) in the weld if used with excessive current. Electrodes with thoria added carry rnore cu.rrent than pure tungsten or zirconia electrodes. It is easier to strike an arc and maintain a stable arc with l:horia electrodes.

Tungsten Electrode Compositions Percent Tungsten min. percent (by difference)

Ceria (Ce02)

Lanthana (La 20 3)

Thoria (ThOJ

Zirconia

(ZrOJ

Total other elements or oxides, max.

EWP

99.5

-

-

-

-

0.5

EWCe-2 EWLa-1.5 EWTh-1 EWTh-2 EWZr-1 EWG

97.3 97.8 98.3 97.3 99.1 94.5

1.8 - 2.2

-

-

-

-

1.3 - 1.7

-

-

0.8-1.2 1.7 - 2.2

-

-

0.15 - 0.40

0.5 0.5 0.5 0.5 0.5

AWS classification

-

-

-

-

Not Specified Feproduced with fJ6rmlssion from tho Amtuicsn Walding Society. Miami. FL

Figure 9-22. ANSI/AWS A5.12/A5.12M:2009 (ISO 684 8:2004 MOD), Table 1, Chemical Composition Requirements for Tungsten Electrodes for Arc Welding and Cutting. Copvrighl Goodheart-WIilcox Co, Inc

254

Modern Welding

These electrodes have a greater resistance to tLtngsten contamination of the weld Electrodes with thoria added are usually used only with direct current. Z irconia added to tungsten e lectrodes g ives the e lectrode qualities which fall some"vhere between pure tungsten and tw1gsten w ith thoria ad ded. Tungsten electrodes with zircon ia are the best e lectrode to use when AC welding aluminum or magnesium. They minimize tu ngsten inclusions compared to pure tungsten electrodes. For this reason, tungsten e lectrodes with zirconia are used for high-quality applications. Electrodes w ith ceria or lanthana a re similar to e lectrodes w ith thoria. They can be used ,-vith AC o r DC. They promote a stable arc and easy arc starting. Si.nee these electrodes are identical in appearan ce, the type of e lectrode is identified by an AWS color code. A color band is painted near one end of the electrode, or a color is painted on the end of the electrode. See Figure 9-23.

Tungsten Electrode Color Codes AWS classification

Defined

Color

EWP

Pure tungsten

Green

EWCe-2

2% Ceria

Gray

EWLa-1.5

1.5°/o Lanthana

Gold

EWLa-2

Blue

EWTh-2

2% Lanthana 2% Thoria

Red

EWZr-1

0.15o/o-0.40% Zirconla

Brown

EWG

Other

Sky Blue

A

ooocinean-w111co• Pull/1$1,er

B

Diamond Ground Products Inc.

Tungsten electrodes are available in dian1eters of 0.010'; 0.020'; 0.040': 1/16': 3/32'; 1/8'; 5/32", 3/16'; and 1/4" (0.25 mm, 0.51 mm, 1.02 mm, 1.59 mm, 2.38 mm, 3.18 m m, 3.W 1nm, 4.76 n1.m, and 6.35 1nn1). The 1nost common electrode length is 7" (175 mm). Other lengths are available.

9.6.1 Preparing a Tungsten Electrode for GTAW The correct type and diameter of tungsten electrode 1nust be selected in order to perform a successful gas tungsten arc weld. The preparat ion o f the tungsten electrode is important, especially in precision and h ighly critical welding applications. The type of welding mad, ine used is a factor in electrode selection. Pure tungsten or zirconiated electrodes are used for AC welding ,-vith sine wave AC machines or with conventional square-wave 1nachines. A ball, or hemisphere, needs to be formed on the end of the electrode prior to welding. The ball shape is beneficial because it increases surface area at the tip of the electrode, allowing AC to flow more easily and reducing current rectification See Fig ure 9-24. lantha.nated electrodes also "''ork fairly well for AC welding. To form a ball or hemisphere, set the current on the power source to DCEP. Strike an arc on a clean piece of copper. Copper does not melt easily and does not contaminate the electrode easily. Increase the current until the end of the e lectrod e melts and forins a ball about the same diameter as the electrode. This process can also be done using AC cu1Tent. Once the proper s ized ball is fo rmed, break or stop the a rc. To obtain full current capacity from a pure tungsten, zirconium tungsten, or lanthanum h mgsten electrode for use ,-vith AC, do no t grind the electrode to a point.

Kocsis Sandor/Shuttorstook.com

Figure 9-23. A- AWS tu ngsten electrode classification,

description, and color code are listed. 8- Tungsten electrodes with their color bands.

Figure 9-24. A GTAW torch with a balled tungsten

electrode for AC welding. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 9

Fonn a ball the san, e size as the electrode dian,eter on the end of the electrode prior to welding. See Figure 9-24. This ball may be up to one and one-half times the size of the electrode dia1neter, but should never exceed that Limit. A ball larger than one and one-half times the electrode diameter may melt off and fall into the weld. If the ball on the end of the tip is 1nuch larger than the electrode diameter, the current may be set too high. Electrodes used with AC can be ground to a taper so a sn,aller ball forms on the tip. A tapered and balled tip reduces the current capacity of the electrode when used with AC. For AC welding with a square-wave inverter power source, a different composition and preparation of the electrode is recommended. Use a 2°/o ceriated electrode, or as a second choice, a 2% thoriated electrode. Grind the electrode to a point. Then, slightly blunt the electrode by grinding a flat on the end of it. AC welding with square wave inverter power source produces quality welds with a tapered and blunted electrode. This configuration will give you 1nore control of the arc. DC welding is done with thoriated, ceriated, or Janthanated tungsten electrodes. Grind these electrodes to create a taper that is two to th.ree times the dian,eter of the electrode. There will be a point at the end of the taper, but a point is not good for welding. Blunt the point as described in the previous paragraph. The blunted flat on the end of the electrode should be about onequarter of the electrode diameter. Refer to Figure 9-25.

Gas Tungsten

Arc Welding Equipment and Supplies

255

Grind electrodes in a lengthwise direction. The grinding marks on the tapered area must run lengthwise to ensure the best arc characteristics. Always wear safety goggles \-vhen grinding.

Special grinding wheels must be used for grinding tapers on tungsten electrodes. Different tungsten electrodes can be ground on the same grinding wheel, but a wheel used to prepare tungsten electrodes should not be used to grind steel, aluminum, and other base 1netals. Particles from these other metals ,vould remain on the grinding wheel and become embedded in the tungsten. If contruninated, a tungsten electrode cannot 1naintain a ,,veil-defined and controllable arc. Keeping the electrodes free from contamination is essential. Grinding ,,vheels n,ade of s ilicon carbide or a luminum oxide are often used. Other grinding wheel materials are used in industry and welding shops. Rough grinding of an electrode should be done on an 80-grit grinding wheel. The finish grinding shou.ld be done on a 120-grit or finer wheel. Figu re 9-26 shows a welder grinding an electrode on a grinding wheel.

Correct D

)

\I__ _ _ _ _ _ _ _ _ _ _ __ . ._

t

Lengthwise grinding marks.

~~ _

1-

20 - ...

Correct D

Pointed for DCEN welding

t

t

1-----= -

I.

I

l

2-3D 1/4D

.1_ D

t

Wrong

1~ 2D ~

b,-------~ Rotary grinding marks. This causes arc wandering and restricts current flow. Goodhoalt•Wfllcax Publisher

Figure 9-25. An electrode used for DC welding is ground

to a taper two to three times the diameter of the electrode. The end is blunted. The point of the tapered tip should be centered on the electrode. Grind marks should run lengthwise on the electrode for better arc control. Copvrighl Goodheart-WIilcox Co, Inc

Goodh9art•Willcox Publishor

Figure 9-26. The correct position for grinding a tungsten

electrode. The grinding marks on the taper must run lengthwise on the electrode.

256

Modern Welding

Grinding wheels made of diamond or Borazon"' (cubic boron nitride) mounted in a tungsten grinding machine produce the best ground surface on a tungsten electrode. These grinding wheels s hould be used when the welds must meet high quaUty standards.

See Figure 9-27. Different dia1neter electrodes can be ground and different angles can be set. The equipment is also used to cut elecb·odes to length or remove a contantinated end fron1 the electrode.

Insert to - - - - notch electrode

Insert to ..,,..__ _ _ blunt end

A

Insert lo grind electrode

Diamond Ground Products Inc.

Grinding wheel is located behind faceplate

Diamond GrOl.lld Products Inc. C Figure 9-27. Preparing tungsten electrodes. A-Equipment with a diamond grinding wheel. B-Notching used to cut the electrode to length or to remove a contaminated end. C-Precision grinding the desired angle on an electrode.

B

Diamond Ground Products Inc.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 9

!'warning Tungsten dust should not be inhaled. This is especially true with thoriated tungsten, because thorium is a low-level radioactive material. To prevent grinding dust from getting into the air, a dust extractor should be installed on the grinding wheel. A dust mask can be worn. Always wear safety glasses when grinding.

Problems occur if the wrong electrode is used for a welding application. If a thoriated electrode is used ,~•ith AC, the electrode initially forn1s a ball on the end. Dw·ing the welding process, the ball breaks do,,vn quickly and forms a nu1nber of small projections at the tip. See Figure 9-28C. These projections cause a wild ,,vandering of the arc. Therefore, thoriated electrodes should be used only for direct current GTAW. A pure tw1gsten e lech·ode used with AC is sho"vn in Fig u re 9-280 . The amperage in this case was too high. The ball on the end has begun to melt and bend to one s ide. With continued use, the ball nught have fallen into the weld and contaminated the ~•eld. Excessive current may also cause tungsten electrodes to split near the end.

I

Gas Tungsten Arc Welding Equipment and Supplies

257

A pure tungsten e lectrode that was grou11d to a point and used with DCEN is shown in Figure 9-28E. Note the small ball formed at the tip. Pointing of pure tungsten electrodes is not reco1nmended. The small ball formed at the tip may n1elt off and fall into the weld. Tungsten electrodes of any type must be protected fron1 conta n1ination. The electrode should not be touched to the base metal, weld metal, or filler metal when it is hot. See Figure 9-28F. Such contamination prevents the e lectrode fro1n emitting or receiving e lectrons effectively and must be removed. One way to re.move the contamination is to break off the tip of the electrode a nd reshape it The hot tungsten electrode and metal in the weld ru·ea can be contrurun ated by oxygen and nitrogen in the air and by ai rbor11e dirt. To prevent this contamination, a shielding gas is allo,.ved to flow over the electrode and the weld area after the arc is stopped. The timing of this sh._ieldi.ng gas postflow is set on the arc welding machine's panel. The electrode in Figure 9-28G was contruninated by the air. The black surface of the electrode indicates that the shielding gas did not have sufficient postflow time to protect it. An electrode contaminated by oxidation must be properly reconditioned before reuse, or the oxides will fall from the electrode into the weld.

•

'•

A

B

C

D

E

F

G MIiier Etecrr/C Mtg.

Figure 9-28. The appearance of several properly and improperly used tungsten electrodes. A-Pure tungsten electrode with a ball or hemisphere. 8-Thoriated electrode ground to a point. C-Thoriated electrode used with AC. D- Pure tungsten electrode used with excessive amperage, AC . E- Pure tungsten electrode ground to a point. F-Tungsten electrode contaminated by a welding rod. G-Tungsten electrode contaminated by air.

Copvrighl Goodheart-WIilcox Co, Inc

c;o.

258

Modern Welding

The electrode must be g round to re rnove the conta rnination or broken off behind the contamination. The altered electrode must then be regro und or shaped before use. Tungsten electrodes are available in sizes from 0.010" to 1/4" (0.25 1nm to 6.4 mm). The most frequently used length is 7" (175 1n1n). Each dian1eter and type of electrode is capable of carrying a maximum amperage that varies wifu fue current, polarity, and shielding gas used.

9.7 Filler Metals Used with GTAW Because gas tungsten a rc \,velding is appropriate for alrnost all weldable 1neta ls, a wide range of filler me tals is used. See Figure 9-29. A letter and number combi11ation ide ntifies each filler n1etal. Each filler metal sta rts w ith the le tters E and R. The E stands for electrode. The R stands for rod. The same alloy filler n1etals can be used to \>Veld w ith GMAW; they fu nction as the electrode in GMAW welding. In GTAW, the filler metal is a filler rod, not a n electrode. Carbon steel, lo\,v-alloy steel, and stai nless steel filler metals have the san,e designation as those used for GMAW. A three-dig it nun1ber identifies the staiitless steel alloy in stainless steel filler metal. Aluminum filler metal h as a four-digit number that identifies the alloy.

Recommended Filler Metals for GTAW Base metal

Recommended filler metal

Fil.le r 1neta ls for titan ium, copper, magnesium, nickel, and zirconium use letters to identify the major alloying elements. The letters are follo,,ved by a number. You have to look up the electrode designation to properly determine the alloy contents. For example, ERTi-1, ERTi-2, and ERTi-5 are all titanium filler me tals. You need to look at a chart to de ternune the ac tual alloy contents. Figure 9-30 lists the American Welding Society (AWS) specification s that cover filler me tals, consumable inserts, and shield ing gases used fo r GTAW. Fille r metal is available in various diameters, with common diameters ranging from 1/ 16"-5/32" (1.6 m.m-4.0 mm). The fille r metal ca n be purchased in precut leng ths, u sually 36" (915 mm). Filler metal is also available in continuous coils for semiauto matic, 1nechanized, or auton1aticwelding operations. GTAW with continuous coil filler metal requires a wire feeder a nd a me thod to guide the filler metal to tile weld pool. See Figure 9-31.

AWS Specifications AWS specification number

General content of booklet

AS.7

Copper alloys

AS.9

Stainless steel

A5.10

Aluminum alloys

A5.12

Tungsten electrodes

A5.14

Nickel alloys

A5.15

Cast iron

Aluminum

ER1100, ER4043, ER5356

A5.16

Titanium alloys

Copper and copper alloys

ERCu, ERCuSi-A, ERCuAI-A 1

A5.18

Carbon steel

Magnesium

ERAZ61A, ERAZ92A

A5.19

Magnesium alloys

Nickel and nickel alloys

ERNi-1 , ERNiCr-3, ERNiCrMo-3

A5.21

Surfacing alloys

Carbon steel

ER?OS-2, ER?OS-6

A5.24

Zirconium alloys

Low-alloy steel

ERSOS-82, ER80S-D2

A5.28

Low-Alloy steel

Stainless steel

ER308, ER308L, ER316, ER347

A5.30

Consumable inserts

Titanium

ERTl-1

A5.32

Shielding gases Goodhean-W/1/cox Pub/ls.her

Zirconium

ERZr-2

Figure 9-30. AWS fill er metal, electrode, and gas GOOdhearr-WfHCOt Pvl:J/lsher

Figure 9-29. Recommended filler metals for gas tungsten a rc weldi ng of differe nt base metals.

specifications. The material covered in the listed A5 publications are for GTAW, GMAW, and PAW unless otherwise indicated.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 9

Gas Tungsten Arc Welding Equipment and Supplies

259

Figure 9-32 shows the effect of an autodarkening lens. Recommended lens shade numbers for gas tungsten arc welding are shown in Figure 9-33.

9.9 Protective Clothing

CK l'\t>rfdwide. Inc.

Figure 9-31. Two models of GTAW power sources with an automatic wire drive to provide filler metal to the weld pool during the welding process. Note the wire guide tube.

Clothing can a lso be made of heavy wool or cotton. Cotton n1ay be treated to reduce its ability to burn. Always wear dark clothing to reduce reflection of light behind the helmet. The heat ge nerated in GTAW is less than SMAW, GMAW, or FCAW. Leathers are usually not worn for GTAW. Leather g loves should be worn duringGTAW. The leather gloves for GTAW are much thinner than those used for SMAW, GMAW, or FCAW. Welders manipulate the GTAW torch in o ne hand and feed filler metal w ith the other hand. The gloves must be thin enough to allo~v the welder to perform both of these functions effectively.

Recommended Lens Shades for GTAW

9.8 Filter Lenses for GTAW Because of the clear at1nosphere a round the arc, the operator must use a dark fi lter lens to reduce eye fatigue a nd prevent eye damage. Most helmets for gas tungsten a re we ldi.ng have a clear cover lens over an autodarkening or fixed filter lens. Sometimes a clear cover lens is also used on the inside of the helinet. It is cr ucial that a ll these lenses be c lean.

-~-~MAN

A

{

AUTO

~

. ---

SHADE

Hn e

10 1 1 .

~

13

..... ·-- ·

150 amps

14

Figure 9-33. A guide to th e correct welding lens shades forGTAW.

SHADE HU .

XL

tl'(,r....

Lens shade number

Go0ving, or atteinpts to flo"'' in the reverse direction. Therefore, check valves prevent the reverse flow of gases through the torch, hoses, or regulators (see Figure 12-39). Figure 12-40 shows a check valve in the opei1 and closed positions and depicts how the check valve works. Flashback arrestors h ave the following safety features built in: • A reverse-flow check va lve. This valve stops any flow of gas in the wrong direction. • A pressure-sensitive cut-off valve that cuts off gas flow if an explosion or fla1ne occurs. • A stainless s teel filter that s tops the flame. • A heat-sensitive check valve that stops the gas flow i.f the arrestor read1es 220°F (104°C). Some flashback arrestors automatically reset after a flashback. Others must be manually reset before they can be put back into service. Some flashback arrestors now have a red a la.rm indicator to show when a flashback has occurred.

GOO EQ1Jlpmen1

Reducing Flame (Excess LP gas with oxygen) For heating and soft soldering or silver brazing.

Sm/II> EQ!Jlpmonr

Neutral Flame (LP gas with oxygen) Temperature 4579 ° F (2526 ° C). Fo r brazing light material.

Sm/II> EQ!Jlpmont

Oxidizing Flame (LP gas with excess oxygen) Temperature 5300 ° F (2927 ° C). For fusion welding and heavy braze welding.

Smiill EqtJlpment

Figure 13-4 . Note the differences between different types of ox ygen-LP gas flames.

Copvrighl Goodheart-WIilcox Co, Inc

358

Modern Welding

A neutral oxyacetylene welding flame produces a temperature of approximately 5589°F (3087°C). A neutral oxypropane flame reaches 4579°F (2526°C). Oxidizi11g fla1nes produce slig htly higher te1nperatures. The temperatures required to melt various metals are listed in Figure 13-5. Steel, for exa1nple, melts a t 2800°F (1538°C). An oxyacet ylene welding flame is the hottest oxyfuel gas flame. It is hot enough to melt co1nmon metals easi ly and quickly. Acetylene is generally the only fue l gas used for ~velding. Propylene gas is used for preheating, cutting, torch brazing, flame spraying, and flame hardening. Propane is used for preheating, soldering, and brazing. Natural gas (methane) is generally used for hea ting, cutting, soldering, and brazing. Hydrogen gas is used in welding nonferrous metals and in some brazing operations. Dirt in a welding flame may come from d irty equipment. Good quality gases should always be used for welding and cutting.

outfit consists of t he oxygen and fuel gas cyli11ders; the regulators, hoses and hose fitti ngs for each gas, and a ,.velding torch. Gases from the cylinde rs flo,,v thro ug h the regulators, iJ1to the hoses, and on to the torch. Fig ure 13-6 shows a complete oxyacetylene gas welding outfit. A ivelding station includes the ,,velding outfit plus a ,,veldi11g table, holding fixtures, ventilation, and possibly a booth. Figu res 13-7 and 13-8 show speci a l weld ing tables where ,.velding can be practiced under ideal conditions. Notice tha t the tables are equipped with holding fixtures. T he n1ost common ty pe of oxyfue l gas welding torch is the positive-pressure torch. A positivepressw·e torch normally operates at a pressure of 1 psig to 10 psig (7 kPa to 70 kPa), depending on the torch tip size. The oxygen and fuel gas working press1u·es a re usually the same when welding with this type of torch.

13.2 The Oxyfuel Gas Welding Outfit Before the procedures used to make a good oxyfue l gas weld are discussed, it is in1po rtant to kn ow the welding equipment required, its HmHations, and its proper u se. Basically, the oxyfuel gas ,.velding

Melting Temperatures for Common Metals Melting temp. Metal

Aluminum Brass (yellow) Bronze (cast) Copper Iron. gray cast Lead Steel (.20%} SAE 1020 Solder (50-50) Tin Zlnc

•F

·c

1215 1640 1650 1920 2200 620 2800 420 450 785

657 893 899 1049 1204 327 1538 216 232 418 Goodh9art♦Wlltcox

Pubhsh9T

GoodhBan-Willcox Publish9r

Figure 13-5. Melting temperatures of some common

Figure 13- 6. A portable oxyacetylene gas welding and

metals.

c utting station.

Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 13 Oxyfuel Gas Welding

359

Before using an oxyfuel gas welding or cutting outfit for the first time, make sure you understand how to operate the equipment: 1. Learn the proper ways to assemble the outfit and prepare the station for use. 2. Learn how to check the entire outfit for any gas leaks. 3. Learn the proper method of turning on the oxyacetylene outfit and Hghting the tord1. 4. Learn how to adjust gas flows to produce a neutral flame. 5. Learn the proper method of shu tting down the equipment. The proper procedures for handling the torch and selecting the size tip to use depend on several factors. These factors are the type of weld desired, the kind of metal used, the thickness of the metal, and the shape and position of the metal. These topics \,v ill be covered later in this chapter.

Fixture _,,.-,r for vertical, horizontal, and overhead welding practice Bench top

13.2.1 Assembling an Oxyfuel Gas Welding Outfit Goodhean·Willcox Publisher

Figure 13-7. A well-planned welding table. Note the

built-in stool and the fixture for holdi ng work in various welding positions.

Proper assembly, care, and security of the oxyfuel gas welding outfit is necessa ry for its safe and effective use. Care must be taken when assembling the various threaded fittings. When tightened, the fittings n1ust not leak. The fittings are generally made fro1n soft metal, such as brass.

[ujcautian Do not overtighten fittings, or the threads may be damaged.

fflwarning Petroleum-based oil, grease, and soap contain flammable material. Petroleum-based products must not be used to lubricate any part of a cutting or welding outfit. These materials could ignite and cause a fi re.

GoocJ11eau-Wllfcox PUbliSfler

Figure 13-8. A well-designed bench enables a person

to practice welding in any position and at various heights. A-Clamp used for holding weldments in the flat, horizontal, vertical, and overhead positions. 8-Height adjustment that enables positioning of a weldment at various heights above the bench.

Copvrighl Goodheart-WIilcox Co, Inc

An oxyfuel gas cutting outfit is assembled in the san1e manner as an oxyfuel gas welding outfit, since oxyfuel gas cutting and welding equipment is e ssentially the san1e. The main differences between the cutting and welding outfits are in the oxygen regulator and the torch. Aside from the torch and the oxygen regulator, the assembly of the oxyfuel gas outfit is the same for both cutting and we.l ding.

360

Modern Welding

Procedure Assembling an Oxyfuel Gas Welding (or Cutting) Outfit 1. Securely fasten the oxygen and fuel gas cylinders to a wall, column , or hand truck in the vertical position. Chains or steel straps are commonly used to fasten the cylinders. See Figu re 13-6. Safety caps may be removed after the cylinders are safely secured. 2. Clean the oxygen and fuel gas cylinder outlets before attaching the regulators. The cylinder opening is cleaned by quickly opening the cylinder valve slightly, then closing it. This is called cracking the valve. Cracking allows some of the high-pressure gas to blow through the valve opening to remove dirt and other particles. The following image shows a cylinder valve being opened. Do not point the cylinder outlet toward people in the area. Flames or sparks must not be present when you open the fuel gas or oxygen cylinder valves . If cylinder valves are damaged or leaking, do not use the cylinders. Return defective cylinders to the supplier.

4. Attach the fuel gas hose to the fuel gas regulator and attach the oxygen hose to the oxygen regulator. A fuel gas hose should be red for easy identification. A groove is machined around the nuts used on fuel gas hoses. Fuel gas hose connections have left-handed threads. An oxygen hose is green, and the nuts do not have a groove. Also, oxygen hose connections, like those of the oxygen regulator, have right-handed threads. These characteristics make the hoses easy to distinguish. A flashback arrestor should be installed between the regulator and the hose. After the hoses have been hand-threaded onto the regulators , tighten the nuts with a proper size open-end wrench so they are snug and leakproof, as shown in the following image.

BOC

Goodh••r~Wi/lcox Publishw

3. Attach the regulators to the cylinder outlets. The regulators should be threaded onto the cylinder nozzles by hand, as shown in the following image. The regulator nuts should then be tightened with a regulator wrench or a proper size open-end wrench so they are snug and leakproof. The oxygen regulator nut has right-handed threads and can only be threaded onto oxygen cylinders, which also have right-hand threads. Large, commercial fuel gas cylinders have left-hand threads. This is a safety precaution that prevents a welder from being able to screw an oxygen regulator onto a fuel gas cylinder.

5. Before the hose is attached to the torch, the hose should be blown out or purged. With the regulators attached, open the cylinder valves . Make sure you are standing to the side of the regulator gauges, as shown in the following image. Then, gently open and close the regulator valves-first the fuel gas regulator, then the oxygen regulator. This brief purging clears the hoses. A check valve should be installed between the hose and the torch body. Where pipe threads are used, they should be sealed with pipe-thread sealing compound (such as a glycerin and litharge paste) or Teflon- tape.

BOC

Goodhoart-Willcox Publishor

(Continued) Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 13

6. Attach the welding torch (or cutting torch) to the hoses. The torch inlet fittings have right-hand and left-hand threads to match the regulators and hoses. Attach the green oxygen hose to the torch's oxygen in let fitting and the red fuel gas hose to the torch's fuel gas inlet fitting. After tightening by hand, use a wrench to seal the connections as shown in the following image. Be careful not to overtighten the nuts. For additional safety, flashback arrestors or check valves may be installed between the torch and hoses.

Oxyfuel Gas Welding

361

Checking Regulators The high-pressure valve under the regulator diaphragm opens and closes to control the working pressure. A leaking regulator valve allows pressure to r ise uncontrollably rnside the regulator. The regulato r or low-pressure gauge may burst if there is excessive pressure below the diaphragm. Check regulators for leaks immediately after setting the working pressure.

Procedure Checking a Regulator for Leaks 1 . Turn on the welding or cutting outfit.

Goodhean•Willcox Publlshor

7. Select the proper size torch tip and place it into the torch or into the torch tube. Tighten it securely.

2. Close both torch valves. 3. Carefully watch the acetylene and oxygen low-pressure gauges. The pressure readings should remain constant. A leaky regulator valve is indicated if the gauge pressure continues to rise. Immediately close the cylinder valves and shut off the outfit. 4. Replace the leaking regulator. 5 . Send the bad regulator out for repair.

Checking Cylinder-to-Regulator Connections

13.2.2 Checking for Gas Leaks After completing the welding equipment assembly, test for gas lea ks using a nonpetroleum-based soap solution. Leak testing must be done after a cylinder or any part of the welding outfit is replaced. The reromm ended procedure to test for leaks is to put a soap and water (soapsuds) solution on the outside of the joints suspected of leaking. A flame or oil of any kind should never be used lo lest for leaks. Petroleum-based products can spontaneously combust in the presence of oxygen. To test for leaks, tw·n the regulator scre,~rs out all the way, open the cylinder valves, and slowly build up 5 psig to 14 psig (35 kPa to 97 kPa) of pressure in the regulators and hoses by slo,.vly turning the regulator screws iJ1 (cloc~-vise). Then, apply the soap solution to a II joints. U there are any leaks, bubbles will form at the leak point. If a leak is discovered, note the location of the leak and then tightly c lose the cylinder valves. Open the hand valves on the torch and wait for the pressure gauges on both the acetylene and oxygen regulators to read zero. Next, turn the adjushng screws on both the acetylene and oxygen r egulators all the ~vay out. Finally, lightly close b oth h and valves on the torcl1. Do not use the system until the leaking joints are repaired. After the parts have been replaced or repaired, be sure to perform another leak test before lighting the torch. Copvrighl Goodheart-WIilcox Co, Inc

Cylinder-to-regulator fittings can be checked for leaks by intentionally trapping pressurized gas between the regulator and cyUnder. A d ecrease of press ure on the high-pressure gauge indicates a leak This test must be made on b oth the oxygen and acetylene systems as follows:

Procedure Checking Cylinder-to-Regulator Connections for Leaks 1. Turn on the outfit. Note the pressure on the high-pressure gauge. 2. Close the regulator by turning the adjusting screw counterclockwise. Close the cylinder valve. Highpressu re gas is now trapped between the regulator and cylinder valve. 3 . The high-pressure gauge reading should remain constant. If it drops , there is a leaking connection between the regulator and the cylinder. Check the fitting for tightness. Check for leaks using soapsuds and repeat steps 1 and 2. If a leak is still indicated, the cylinde r outlet fitting may be bad. If so, return the cylinder to the vendor. 4. Try the regulator on another cylinder and repeat steps 1, 2, and 3. If there is still a leak, the regulator fitting itself may be bad.

36 2

Modern Welding

Checking Hoses and Hose Fittings Gas leaks in the hoses or fittings between the regulators and the torch valves will show as a pressure drop on the low-pressure gauge. Gas must be trapped between the regulator and the torch valves to perform this test. The procedure used to test the oxygen and acetylene hoses and fittings is as follows:

Procedure Checking Hoses and Hose Fittings for Leaks 1. Turn on the outfit.

2. Close the torch valves. 3. Note the reading on the low-pressure gauge. 4. Close the regulator with the adjusting screw. 5. The low-pressure gauge reading should remain constant. If the pressure drops, there is a leak in the hose or fittings. Locate it using nonpetroleum-based soapsuds.

13.2.3 Handling Fuel and Oxygen Cylinders Safely Welding cylinders are safe when properly handled. They can be very dangerous if they are i1nproperly handled. Cylinders should never be dropped or

tipped over. The cylinder safety cap, which encloses and protects the cylinder valve, should always be screwed into place when the cylinder is not in use, or when it is being moved . A cylinder truck should be used to move a cylinder. The cylinder must be properly secured so that it cannot tip o r fall off the truck. Avoid storing or using cylinders in extremely hot locations. High te1nperatures may cause the cylinder pressure to reach dangerously high levels. Check local community building and fire codes to ensure that cylinders are used and stored according to those codes.

13.2.4 Selecting a Welding Torch Tip of the Correct Size Selection of the correct size welding torch tip is primarily dependent on the 111etal thickness of the base metal being ,velded. Torch tip size is designated by a nu1nber stamped on the tip. The tip size is determined by the size of the orifice (opening). The orifice size detennines the amount of fuel gas and oxygen fed to the flame. The orifice, therefore, determines the a 1nou nt of heat delivered fron1 the torch to the base metal: the larger the orifice, the greater the amount of heat generated. With a positive-pressure tord1, the tip sizes shown in Fig ure 13-9 should provide satisfactory results for oxyacetylene welding.

Oxyacetylene Welding Parameters and Settings Oxygen

Metal thickness

Size• welding tip orifice

Welding rod diameter

Psig pressure

1/32" 1/16" 3/32" 1/8" 3/16" 1/4" 5/16" 3/8" 1/2"

74 69 64 57 55 52 49 45 42

1/16" 1/16" 1/1 6" or 3/32" 3/32" or 1/8" 1/8" 1/8" or 3/16µ 1/8" or 3/16" 3/16" 3/16"

1 1 2 3 4 5 6 7 7

Acetylene

Cu ft/hr 1.1 2.2 5 .5 9.9 17.6 27.5 33 44

66

Psig pressure

Cu ft/hr

Welding speed ft/hr

1 1 2 3 4 5 6 7 7

1 2 5 9 16 25 30 40 60

20 16 14 12 10 9 8

·Note 1he Up orl!IQ, slze as shown Is the rumber c:tlll size. These recoflYTlendallons are apprcoc!male. The torch manuracti.er'S recanmendatlons shOuld be careluly Jolbwed. Goodhoatt•Wlllcox Publisher

Figure 13-9. A table showing the relationships between welding tip size, gas pressures, welding rod diameters, and

metal thickness fo r oxyacetylene weld ing.

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Chapter 13

l f the torch tip orifice is too s1na ll, not enough heat is available to b1ing the metal to its melting temperature. If the torch tip is too large, poor welds result for the fo llowing reasons: • The ,veld is made too fast. • The ,velding rod melts too quickly and the weld pool is ha rd to control. • The a p pearance an d quality of the weld bead a re gen era lly poor. There is no s tandard system of numbering welding torch tip sizes. Manufacturers have the ir own numbering systems. For this reason, tip size instructions in this text are g iven in o rifice "number drill size." Nu1n ber dr ills form a series of drills in g rad uated d iameters, numbered 1 through 80. The diameter of a Number 1 d rill is 0.2280" (5.79 mm). Th e diame ter of a Num ber 80 drill is 0.0135" (0.34 1nm). The la rger the number, the smaller the drill d iameter. Manufacturers of welding tips s upply charts explaining how their numbering system corresponds to standard number drill sizes. Once a ,velder becomes familiar w ith the o peration of a certa in manufacturer's to rches and n umbering syste1n, it is seld om necessary to refer to orifice number d rill sizes.

13.2.5 Turning On an Oxyacetylene Welding or Cutting Outfit The procedure for turning onan oxyacet ylene \\ 7elding outfit is nearly identical to turning on an oxyacetylene cutti ng outfit. O ne d ifference, regarding the oxygen cutting lever, is expla ined below Step 9 of the following procedure. The cylinder, regulator, and torch valves must be turned on in a specific sequence in order to be used safely. Before lighting an oxyacetylene flame, the oxygen and acetylene syste1ns must be purged. Purging is the process of passing the correct gas through the entire system to remove a ir or undesirable gases. Purging ens ures that the correct gas is flowing in the appropriate regulator, hose, and torch passage. P urg ing is done by allowing ace tylene to flo.v through the acetylene hose and oxygen to flow through the oxygen hose for a short period of time. If the following steps a re carried o ut, the system will be properly purged an d ready to light. Follow these steps to turn on an oxyacetylene welding or cutting outfit:

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Procedure Turning On an Oxyacetylene Welding or Cutting Outfit 1. Visually check the torch, valves. hoses, fittings , regulators, gauges, and cylinders for damage. Be sure to check that the oxygen and acetylene torch valves are closed by tuming them clockwise (to the right). Also, ensure that the oxygen and acetylene cylinder valves are closed by tuming them to the right. If any of the pressure gauges have a reading above zero, the outfit was not properly shut down or there is a leak in the system. Before proceeding, go through the steps of shutting down the system and ensure that all gauges read zero.

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2. Make certain the regulators are closed (or "off") before opening the cylinder valves. This prevents damage to the regulators and gauges. Close the regulators by turning the regu lator adjusting screws on the oxygen and acetylene regulators c ounterclockwise (to the left). Continue to turn the screws counterclockwise until they feel loose. Be careful not to tum them too far, however, or they will fall off. Again , ensure all gauges read zero.

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(Continued)

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3. Stand to one side of the regulators as you open the cylinder valves. A regulator or gauge could burst, causing severe injury. Slowly open the acetylene cylinder valve by turning it counterclockwise about 1/4 to 1/2 turn. This provides enough acetylene flow for most purposes. If the valve is not equipped with a handwheel, use the proper size wrench for the cylinder valve. Leave the wrench in place so that the valve can be closed quickly in case of an emergency. 4. Slowly tum the oxygen cylinder valve counterclockwise until it is fully open (the valve may leak if it is not fully opened). Remember that cylinder pressure can be 2200 psig (15200 kPa). A rapid flow of high-pressure gas could rupture the regulator diaphragm or gauges. At this point in the process of turning on the outfit, the cylinder pressure gauge on both regulators show a reading.

The correct working pressure depends on the tip size used. Refe r to Figure 13-9 for a table showing the recommended pressure in relation to the tip orifice size.

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7. Close the acetylene torch valve, as shown in the following figu re. Check the acetylene regulator for possible leaks.

5. Turn the acetylene torch valve one-half tum counterclockwise. Goodhean-Willcax Publisher

8. Open the oxygen torch valve one-half to one turn counterclockwise.

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6. Set the correct working pressure on the acetylene regulator gauge by turning the acetylene regulator adjusting screw clockwise (to the right) until the low-pressure gauge shows the correct working pressure, as shown in the following figure.

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(Continued)

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9. Turn the oxygen regulator adjusting screw clockwise until the desired working pressure is obtained.

GOOtlhea,1-IVIIICOX Pu/JI/sher

GOOdhean-WfJICOX PubllShet

1■,Note

Figure 13-10. When turning on an oxyacetyl ene cutting out fit, depress the cutting torch lever while setting the working pressure.

13.2.6 Regulator Gauge Readings

When turning on an oxyacetylene cutting outfit, the cutting torch oxygen valve (lever) should also be open while the oxygen cutting pressure is set. See Figure 13-10. After setting the working pressure, release the oxygen cutting lever. 10. Close the oxygen torch valve, as shown in the following figure. Check the oxygen regulator for leaks. Remember that the preceding steps for turning on the oxyacetylene cutting or welding outfit must be performed in the correct order to purge the system properly prior to lighting the torch.

After adjusting the desired p ressure o n the regu la to r low-pressure gauge, the torch valve is closed. There is a slig ht rise in the pressure on the low-pressure gauge. The p ressure reading rises and stops. This is normal. The flowing pressure (dynamic pressure) is a lways lower than the pressure tha t exists when the torch valve is closed (sta tic pressure). If the low-pressure gauge reading continues to rise (creep) after the torch va lve is turned off, this indicates a leaking regulator nozzle and seat. Turn o ff the cylinder valve imme diately or the low-pres sure gauge may receive the fu ll cy linder pressure, w hich w ould cause the gauge to rup ture. If a continuous rise (creep) occurs, replace the regulator or have it repaired before using the station agai n. Ad d itional regulator safety information is presented later in this chapter.

13.2.7 Lighting and Adjusting the Flame of a Welding Torch

Goer

Figure 13-12. A left-handed person braze welding a T-joint using correct torch and filler metal angles for forehand welding. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 13 Oxyfuel Gas Welding as s hown in Figure 13-13A The angle at "vhich the torch is held can also be measured fro1n the surface of the major \Vorkpiece to the torch axis. Therefore, the travel angle in Figure 13-13A could also be described as an angle of 45°-55° off the surface.

A

369

The luo1i angle is the angle between a line perpendicular (90°) to the major workpiece and a plane determined by the centerline of the torch tip and the •,veld axis. When the tord1 tip is held perpendicular to the major workpiece, the work angle is 0°, Figure 13-13B. The angle at which the torch tip is held can also be measured from the surface of the major workpiece to the centerline of the torch tip. In this case, the work angle in Figure 13-13B could be described as an angle of 90° off the surface. When using the foreha nd welding n1ethod, the torch tip points forward in the direction of h-avel. The travel angle for forehand ,,velding can also be called the push angle. In backhand welding, the torch tip points back toward the weld bead that has been completed, which is opposite the direction of travel The travel angle for backhand welding can also be called the drag angle. For forehand welding of fillet "velds, the torch is held at a work angle of 15° to 75°. The angle depends on the tip size used, metal thickness, and other welding conditions. A 30° to 45° "vork angle is typical. For groove 1,velds, the torch is typically held at a 0° work angle. For both groove and fillet welds, the torch is held at a travel angle of 30° to 60°. The angle depends on the tip size used, 1netal thickness, and other welding conditions. A 35° to 45° angle is typical. See Figure 13-14.

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Top view

Weld pool

\ ,,..._____.-"; Torch Up

Side view

B Goodheart-Willcox Publisher

Figure 13-13. Creating a continuous weld pool. A- Front view with torch tip held at a 35°-45° travel angle. The 35°-45° travel angle may vary, depending on the amount of heat required. B- Left side view with torch tip held at a o0 wor1< angle, which is an angle of 90° off the suriace of the workpiece. The 0° work angle keeps the heat equal on both sides of the centerline. Copvrighl Goodheart-WIilcox Co, Inc

Ooodheau•Willcox Publisher

Figure 13-14. Recommended to rch angle, direction, and

flame distance from the metal for running a continuous weld pool in the flat welding position. The torch is held at a travel angle of 35°- 45°.

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Modern Welding

In forehand weldiJ1g, the flame spreads over the work ahead of the weld. This preheats the metal before it comes under the high-temperature flame. The tip of the welding torch should be moved sBghtly as the weld progresses. This movement helps distribute heat and keeps the center of the weld pool from overheating. A weaving ,notion, oscillating n1otion, or circular motion can be used. Figure 13-15 shows different torch motions commonly used by welders. Regardless of which pattern is used, the cone of the fla .me should never go outside oi the weld pool The tip of the inner flame cone should be about 1/16" (1.5 mm) to 1/8" (3 nun) above the metal. See Figure 13-14.

13.3.2 Running a Continuous Weld Pool Before attempting a weld of any kind, it is recommended that a beguu1ing welder practice running a continuous lveld pool. Once described by the term "puddling," running a continuous weld pool is the creation ru1d conb·ol of a molten pool of metal that is carried a long the sean1 of the parts to be ,,velded together. By watching the appearance of the weld pool carefully, an experienced welder can tell the following about a weld: • The arnount of weld penetration. • The torch adjustment ru1d heat provided. • How and when to move the torch. • When and how often to add filler metal.

The size (diameter) of the weld pool is in proportion to its depth. The welder may judge the depth, or penetration, of a weld by watching and controlling the size of the pool of molten rnetal. On very thin metal, the penetration (or depth of the weld pool) is greater, in proportion to the ~vidth, than with thicker metal. The appearance of the surface of the pool indicates the type of flame coming from the torch. A neutral flame, when melting a good grade of n1etal, creates a smooth, glossy ,\reld pool The edge of the pool away from the torch has a small bright incandescent spot. This spot n1oves actively around the edge of the pool. If this spot is oversized, the flame is 1wt neutral. If the weld pool bubbles and sparks excessively, an oxidizing flame is in use. A poor quality and/or dirty rnetal also sparks as it is being welded. If the flame is excessively carburizing, the weld pool has a dull and dirty (sooty) appearance. The tip of the inner cone of the torch flame must be held within the boundru·y of the weld pool at all times. A correctly adjusted flao1e prevents the oxygen in the atn1osphere fi·om coming in contact with and oxidizing the sw·face of the pool. The hottest area of the flame is 1/16' to 1/8" (1.5 mn1 to 3 1nm) from the end of the inner flame cone. See Figure 13-16. If the weld pool sinks or sags too far, indicating too much penetration, lower the angle of the torch or increase the speed of movement rather than dra,,v the torch away from the surface. Figure 13-17 shows a continuous weld pool in progress.

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Figure 13-15. Common types of torch movement patterns used for oxyfuel gas welding. All motion must remain within the size of the weld pool.

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A

A

Section A-A Goodheart-Willcox Ptlblisher

...

Figure 13-18. Weld pool procedure. This shows a partially completed exercise piece. Note the penetration. The welder has obtained unifom, width and has carried the weld pool in a straight line. The penetration is unifomi.

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Direction of travel 1/16" to 1/8" (1.5 mm to 3 mm)

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493

Alternating current is supplied at 60 hertz. AC controllers monitor and make small adjustments 60 times per second. MFOC controllers use an inverter to change the 60 hertz AC into DC and then divide the DC into 1000 or more time intervals. Therefore, an MFDC controller can make small adjustments to the ,.velding current 1000 or more ti1nes per second. This is one advantage of an MFDC controller. A second advantage is a smaller transformer. As the frequency of the current increases, from 60 hertz to 1000 hertz, the size of the transformer needed to convert the current decreases. MFDC transformers are often the size of a toaster, making the transformer more portable and allowing it to be placed near the resistance welding macltine. This is very important for robotic welding.

u

0 Vitched on and off at specified times during a resistance welding cycle. The voltage in the p1imary circuit is so high that it would cause arcing across a mechanical-type switcl1. Therefore, electronic silicon-controlled rectifiers (SCRs) are used as contactors (switches) in the prin1ary circuits of welding controllers. An SCR is a heavy-duty diode. See Figure 18-14. It allows current to flow in one direction only. Two SCRs are used in ead1 circuit that requires switching. One conducts current during the positive half of the AC cycle, and the other conducts during the negative half of the AC cycle. See Figure 18-15. When the controller sends a signal to the gate side of one SCR, it allovvs current to flow, but only d uring this half of the AC cycle. When the polarity changes in the AC cycle, this SCR stops conducting. A second SCR is needed to perform the same function during the opposite half of the AC cycle. Using h,vo SCRs allows the current to be switched on and off as needed during both half waves of the AC cycle. A welding controller using SCRs is shown in Figure 18-16.

Anode

Cathode

(+ charge}

(- charge)

Workpiece

- x--

Goodho.an-WiI/cox Publisher

Figure 18-15. Two SCAs in an AC circuit. This allows c urrent to be turned on and off as needed during both the positive and negative halves of the AC cycle.

rrent coll

Gate Goodheart-WIiicox Publisher

Figure 18-14. The symbol for a silicon-controlled rectifier (SCA) as used on electronic circuit drawings. The SCA allows current flow in only one direction.

Weari-WIIICOt PVOIISl>ef

Figure 18-18. The firing of the two SCRs is controlled by the controller, whi ch sends a signal to the firing circuit to allow the SCRs to conduct current.

LORS Machilory, Inc.

Figure 18-19. A variety of electrodes, electrode holders, caps , adaptors, and electrode removing and dressing tools. Note the large, round electrode used for seam welding.

100% Heat

50% Heat

80% Heat

20% Heat

Goodhoart-WiJtcox Publisher

Figure 18-17. The p ercent heat setting changes the point at which the current begins to flow in each cycle. The higher the percent heat setting, the longer the current flows in each cycle. Current is flowing only during the shad ed portions of each cycle. Copvrighl Goodheart-WIilcox Co, Inc

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Some spot welding electrodes are rnade up of two pieces. The two pieces are called the electrode cap and the sh ank or adaptor shank. Electrode caps come in six different designs, as shown in Figure 18-20. The most common shape is the B style or domeshaped cap. The electrode caps can be male or female, as shown in Figure 18-21. The advantage of an electrode cap and shank is the electrode cap can be changed frequently without changing the sh ank. A shank 1nay be bent like a one-piece electrode. Every spot welding electrode has a certain diameter for the majority of its length. This large part of the electrode is the e lectrode dia n1eter. The e lectrode dia111eter is the major diameter of the electrode and must be large enough to carry the force and the ,.,velding c w·rent. To\,vard the end of the e lectrode th at contacts the parts to be \•v elded, the shape of the electrode may change to a s1naller area or diameter. The end of the electrode is called the electrode face. The electrode f ace is the flat part of the electrode that contacts the work

Shank

Taper

Taper fits

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-

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Female cap

Nonstandard Terminology

The nonstandard terms tip, electrode tip, welding tip, and cap are often used to refer to the electrode cap. Most electrodes and electrode caps are water cooled. There is a hole do\,vn the center of the electrode. A flexible water tube is placed inside the electrode. The end of the water tube is cut at a 45° angle. The cooling wate1· flows through the tube and into the cavity of the electrode, ,,vhi.ch cools the electrode and the electrode's face.

Goodhean-Wlllcox Pub1Jsh9r

Figure 18-21 . Two-piece electrode cap and shank. The

electrode caps may be male or female and are held on the shank by a taper fit. The water in the cooling tube is constantly flowing to achieve the cooling effects on the electrode. The path of the rooling water through a bent electrode is shown in Figure 18-22. Figure 18-23 shows electrodes up close.

Clooc/hean-W/1/cox Puo/iSl>er

Figure 18-20. The six common cap designs for spot welding. The letter designations A-Fare those used by the Resistance Welding Manufacturing Alliance.

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Group A materials are copper-based alloys. These alloys have good electrical and thermal (heat) conductivity, with in1proved hardness and wear qualities. Group B n1aterials are refractory meta I al.loys. The electrical and thermal properties of matelials in this group are not as good as those of the Group A alloys. However, Group B materials have extren1ely high melting temperatures and high compressive strength and wear resistance. Group Care specialty materials. Alloys in Group A and Group Bare further categorized into different classes within these groups based on their physical and electrical properties. The information in the following sections can be used as a guide for ordering or purchasing resistance welding electrodes. Each Group and Class has an electrical conductivity percentage. Conductivity is a 1neasure of how well a material passes electrical current. The conductivity scale used is the International Annealed Copper Standard (!ACS). In this scale, annealed copper has a conductivity of 100%. The conductivity of other materials is co1npared to the conductivity of a1mealed copper and shown as a percentage.

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Resistance Welding Equipment and Supplies

Hollow cooling water tube

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Figure 18-22. The cooling water path through a bent electrode. Notice the end of the water tube is cUl at a 45° angle.

CMW, Inc.

Figure 18-23. A straight electrode, an electrode cap, and

a bent electrode with wate r tube.

18.6.1 Electrode Materials The Resistance Welding Manufacturing Alliance (R¼IMA) recognizes three groups of n1aterials used for resistance welding electrodes. They are designated Group A, Group B, and Group C.

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Group A, Copper-Based Alloys Group A consists of copper-based alloys. The most common materials used for resistance welding electrodes are Group A, Class 1 and 2 alloys. These two types of alloys have the best conductivity and good hardness. They are also the least expensive and most widely available. The characteristics and uses of Group A alloys are as follo,¥s: Class 1. These a Lloys have the highest conductivity (80%) among alloys used for resistance welding electrodes. Electrodes made fron1 these alloys are recommended for spot welding galvanized steel, aluminum alloys, magnesium alloys, brass, and bronze. Gass 2. These alloys have high conductivity (75'¼) and good hardness. Electrodes made of these n1aterials ru·e recommended for high production spot and seam welding clean mild steel, low-alloy steels, galvanized and coated steels, stainless steels, and nickel alloys. Alloys in this class ru·e the most commonly used materials for resistance welding electrodes and electrode caps. Class 3. These aUoys have higher strength and hardness than Class 2 alloys, with 45% conductivity. Electrode shanks are often 1nade from Class 3 alloys. Electrodes made from alloys in this class are recommended for projection welding and for flash welding. They are also recommended for resistance welding stainless steel.

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Preparing for a Job Interview A job interview gives you the opportunity to learn more about a company and to convince the employer that you are the best person for the position. The employer wants to know if you have the skills needed for the job. Adequate preparation is essential for making a lasting, positive impression. Here are some ways to prepare for the interview. • Research the employer and the job. Know the mission of the employer and specifics about the job. Also, try to learn what the company looks for when hiring new employees. • List the questions you want answered. For example, do you want to know if there is on-the-job training? • Decide what to wear. Dress appropriately, usually one step above what is worn by your future coworkers. For instance, casual clothing is acceptable for individuals who will do manual labor or wear a company uniform. If applying for a supervisor position, casual pants, not jeans, and a collared shirt are appropriate. Always appear neat and clean.

Class 4. These are hard, hig h-strength alloys. These alloys are recommended for electrodes a nd electrode s hanks used in special applications where the forces are extremely high a nd the wear is severe. Special flash, upset, an d projection welding electrodes are m ade fron1 these materia ls. The conductivity of these alloys is only 20%. Class 5. These alloys a re used chiefly as castings. Specia I electrodes, e lectrod e s han ks, and rig id parts of a welding machine's seconda ry a re cast using these alloys. Th ey have hig h m echanical strength. The electrical conductivity of these a lloys is only 15%.

Group B, Refractory Metal Alloys Materia ls in Group B contain or a re made fro m refractor y n1etals. A refractory metal has a very high melting p oint, above 3600°F (2000°C), and is very hard a nd dense. T he two refracto ry me tals used in Group Bare tu ngsten and molybdenum. In Class 10, 11, and 12 alloys, tungsten is alloyed with copper, with tungsten being the 1najor e lement present.

• Practice the interview. Have a friend or family member interview you in front of a mirror until you are happy with your responses. • Know where to go for the interview. Verify the address of the interview location and plan to arrive at least 10 minutes early. Good preparation will make you feel more confident and comfortable during the interview. Be pol~e. friendly, and cheerful during the process. Answer all questions carefully and as completely as you can. Be honest about your abilities. A prospective employer may ask you to take employee tests. This may include a welding test. Some employers administer tests to job candidates to measure their knowledge or skill level under stress. You can ask those who have completed similar tests what to expect. Since all employers support a drug-free workplace, most will likely require you to take a drug test if hired. After the interview, send a letter to the employer within 24 hours, thanking him or her for the interview. If you get a job offer, respond to it quickly. If you do not receive an offer after several interviews, evaluate your interview techniques and seek ways to improve them.

The cha racteristics an d uses of the refractory alloys in Classes 10-14 are as follows: Class 10. These a lloys have the best conductivity (45%) of the Group B a lloys. They are recomme nded for facings for projection vvelding elech·odes and flash weld ing electrodes. Classes 11 and 12. These alloys a re ha rder tha n the materials in Class 10. They are used when exceptional v\lea r resis tance is required. Classes 13 and 14. These classes of materia ls consist of commercially p ure tw1gsten and molybdenum, respectively. Elect1·odes mad e fro1n these n1ateria ls a re used to weld nonferrous metals that have ver y high electrical cond uc tivity.

Group C, Specialty Materials Group C a lloys are a combination of coppe r a nd s1na ll aLnounts of a luminu1n oxide, 1.1% or less. The addition of a luminum oxide strengthens the copper microstructure. The term used for these alloys is d ispers ion-streng thene d cop per. This g ro up has

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higher ha rdness at e levated te1nperatures and different properties compared to Group A alloys. Class 20. These alloys consist of a powdered combination of copper and stnall a1nounts of a luminum oxide. The electrode face of these electrodes does not widen out or deform as much as Class 1 and Class 2 electrodes. Dispersion-strengthened copper electrodes ai-e used on galvanized and galvannealed coated steels. Electrode caps made from Group C stick less to these coated steels. CMW. lnc.

18.7 Electrode Holders Resistance welding elech·odes and adaptors are held by electrode holders. The holders are clamped into the ends of the movable welding arm and the stationary arm. Most electrode holders are water cooled. The electrode holders hold the electrode in proper position, carry the welding current, and provide the elech·ode with water cooling. The water tube runs down the center of the e lectrode holder and continues

Snap ring

Coupling

into the electrode. See Figure 18-24. Typical electrode holders are sho,"'n in Figure 18-25. On n1ost spot welding machines, elech·ode holders are adjustable for length and position. In general, the electrode holder should be adjusted to the shortest length at whid1 the weld metal can be easily inserted.

Return spring 0-ring seals

Ejector head

Figure 18-24. Electrode holder. Note the water tube that carries cooling water to the electrode.

Ejector tube

Self-adjusting water tube

i-- - - - - - - - - Barrel length - - - - - - - - --

0-ring seal Ejector tube

Self-adjusting water tube

Ejector button ruua1oy Producrs. Inc.

Figure 18-25. Cross section of two electrode holders.

Copvrighl Goodheart-WIilcox Co, Inc

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Modern Welding

Electrode holders are 1nade of a copper alloy that provides good conductivity and rigidity. Some examples of electrodes and electrode holder combinations ai-e shown in Figure 18-26. The electrode or adaptor can be attached to the electrode holder in the following t11ree ways: • Taper fit. • Threaded. • Straight shank. A tapered fit is the most common means of attaching an electrode and electrode cap, especially for highproduction spot welding. Replacing electrodes and electrode caps is quick and easy when a tapered fit is used. Some electrode holders have an ejector tube or knock-out bar, which is used to loosen tapered shanks

and electrodes. On equiptnent without a knock-out bar, a set of pliers or various special tools are used to ren1ove the electrode or electrode cap. The preferred taper in the resistance welding industry is the RWMA taper. When written, the taper specification is preceded by RW, such as RWS taper. A larger taper number means the 1najor dia1neter is larger. RW tapernu1nbers progress in order from #3 to #7. A threaded attachment is used \.vhen high welding forces are required. T he straight shank electrode or adaptor is mechanically connected to the holder by a separate co upling or collar.

18.8 Spot Welding Machines Spot "''elding machines are the most common resistance \>Velding machines. Spot welding machines are made in a great variety of sizes, from sn1all bench units to extremely large welding 1nachines. Small bench models may be used to spot weld electronic components, denta l braces, and various n1edical devices. A benchtop resistance welding machine is shown in Figure 18-27. Custom-designed resistance welding n1achines like those shown in Fig ures 18-28 and 18-29 have multiple sets of electrodes. They are capable of producing many spot welds quickly on large and s n1all sheet n1etal products, such as automobile body parts, refrigerator cabinets, and computer frames. This greatly r educes production time, ensures quality and accuracy, and lowers operating costs. S01ne resistance welding machines are portable. Portable machines will be covered in a later section.

B

Welding machine Welding controller

Servo drive controller

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Tuffaloy Products, Inc.

Figure 18-26. Different types of electrodes and electrode

holders can be combined to meet a job requirement. A-An offset holder on top and paddle-type holder on bottom. B- A straight holde r on top and an offset holder on bottom, both with bent electrodes. C-A universal holder on top and close-coupled holder on bottom. D- Paddle-type holders on top and bottom.

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AMADA MIYACHI AMERICA , I nc.

Figure 18-27. A benchtop resistance spot welding setup.

The welding machine has a servo motor force system, which requires a controller. Copyr!ghl Goodheart-WIiicox C-0 Inc,

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.r== ..

LORS Machinery. inc.

Figure 18-28. Special resistance welding machine designed for welding stiffeners onto elevator door panels. Programmable welding and motion control pennits variable weld gun sequencing in pairs and auto-indexing of the worktable.

Tay/()r·Winie/11 Technobgies, Inc.

Figure 18-29. This custom-designed , semiautomatic, multi-gun resistance workstation is able to complete 20 different spot welds on an assembly within five seconds.

The basic purpose of the spot welder is to make a spot weld (a fused nugget) between two or more lapped pieces of n1etal The size of the spot weld is controlled by Copvrighl Goodheart-WIilcox Co. Inc

changing the welding va1iables. The variables in resistance spot welding are as follows: • Current. • Time. • Force. • Electrode face diameter. • Welding machine. Consider the following when selecting a welding machine: • The power (KVA) rating. • The type of pressure system . • The di1nensions of the operating area. • How energy is obtained. Select a machine with a KVA rating and pressure systen1 for the required welding. These ~vere discussed earlier in thjs chapter. The operating area has two dimensions. These are called the throat depth and the throat height. Throa.t depth is the distance from the center of the electrodes to the frame of the \Velding machine. The throat depth limits how far frotn the edge of a part a weld can be made. Select a machme with a throat depth to accept the p arts being welded. The throat dept h should be kept to a 1n inimu1n. As the throat depth increases, the

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power needed to create a weld increases. Throatheigl,t is the distance between the welding arn1s when the electrodes are closed. The maximum height of the parts that can be ,~•elded is limited by this di1nension. The throat height is usually adjustable. Throat depth and throat height are shO¼'n in Fig ure 18-30.

•

Nonstandard Terminology

Throat depth is often referred to by the nonstandard term

ham spacing. Resistance spot ,.velding n1achines can be subcategorized based on their input power requirements: • Single-phase madunes. • Three-phase madunes. • Stored energy machines.

•• ••

AU resistance spot welding machi11es demand a lru·ge cu1·rent for a very short period of time. The single-phase machine, the most common type, is connected to one phase of the electrical supply. The large d emand for electrical energy by the single-phase machine can cause a drop in the line voltage of the one phase. lf several sing le-phase resistance welding machines are all connected to the same phase and are all turned on at once, a large drop of voltage can affect other mad1ines (welding and nonwelding) on the same phase. This decrease in voltage on the one phase causes ai1 inlbalance in the power system. Use of multiple three-phase or stored energy machines does not result in this type of imbalance.

Three-phase resistance spot iuelding n1.achines draw energy from each of the three phases of the electrical supply equally. Three-phase machines are more complex and contain many more con1ponents than single-phase machines. A three-phase machine has three primary and three secondary transfo1mer windings as sho¼•n in Figure 18-31. Because of the additional electrical requirements and increased size, a three-phase resistance welding machine is more expensive than a single-phase inachine. There are a few "vays that manufacturers improve the performance of their single-phase and three-phase machi11es. One is by converting the output of the secondary winding from AC to DC. This is done by passing the output or secondary AC through a diode bridge rectifier. The output of a bridge rectifier is DC. The advantage of secondary DC is that it eliminates reactance. Reactance is the resistance to the flo,,v of AC. Primary

Secondary

DC / bridge ___ ..I.. _':c~if~e~ I I

I

I I I I I

Workpiece I

Welding transformer Taylor-Winfield Techno!Ogies, Inc.

Figure 18-30. Throat depth and throat height measurements on a press-type resistance spot welding machine. The throat height is measured with the electrodes touching one another (power off).

Goodhean-WIIICOJ< Pul)lisher

Figure 18-31. The electrical circuit drawing for a

three-phase resistance welding machine. This three-phase machine has three transformers. This schematic has a DC bridge rectifier to change the output from AC to DC. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 18 Resistance Welding Equipment and Supplies

It can be a problem when the dirnensions of the operating area are large and when there is a lot of iron inside the operating area. This occurs wh en welding on a large it:em. Welding ,-vith DC eli1ninates this problern. The three-phase schematic in Figure 18-31 rectifies the output from AC to DC. A second improvernent that rnanufactu rers can offer is the ability to weld with mid-frequency DC. The prin1ary current is ch anged to mid-frequency AC. The use of a higher frequency prirnary power allows the use of a smaller transformer and a corresponding reduction in the cost and size of the equipment. The secondary rnid-frequency AC is passed through rectifiers to ch ange it from AC to DC. The result is equipment that is smaller and h as DC o utput. The process of creating mid-frequency cur rent requires an inverter. Principles of inverter power sources are discussed in Chapter 34, Technical Data. Stored energy resista11ce spot 1veldi11g nzacliines have special elechical characteristics. A stored energy spot ,-velding machine gets the energy needed for welding from the service lines at a re latively slow rate. This energy is stored as it is drawn. Once it has reached the desired level, it can be released at a high rate for welding. Because it takes the energy at a slow rate from the service line and stores it, a stored energy machine does not cause a voltage drop in the service lines. There are two types of stored energy resistance spot ,~•elding machines: • Electrostatic (capacitor-type). • Electrochemical (battery-type). An electrostatic resista11ce spot welding 111achine is the most common type of s tored energy machine. It operat:es by storing electrical energy in a capacitor. Energy is released by the capacitors when it is needed to weld. This type of machine is also called a capacitor discharge resistance iuelder. The use of capacitors to store electrical energy enables the welding machine to have a smaller transforn1er. When the power source is no t on, prirnary energy is sent to the capacitors to recharge them for the next weld. An electrocl,e,nical resistance spot1veldi11g 111acfti11e stores energy in a set of batteries. Energy is released from the batteries to make a weld. This type of n1achine is limited to welding thin rneta l and s1nall d iameter w ires. Stored energy machines, both electrostatic and electroch e1nica l, are commonly used for precision welding of small items. These n1achines are small and are usually used on metal thicknesses of less than 0.03" (0.8 mm). Large capacitor discharge machiJ1es are also avaiJable for special applications on thicker metals. Copvrighl Goodheart•Wlllcox Co, Inc

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18.8.1 Portable Spot Welding Machines A portable resistance spot welding n1achine has four main parts: • A portable weldin g gun 1,vith electrode holders, electrodes, and a force mechanism. • A welding transforrner. • An electronic contactor and controller. • Cables and hoses to bring power and cooling water to the welding n1achine. A portable spot welding machine is sh own in Figure 18-32. 1l1ey are often referred to as PSW (portable spot welding) guns. Portable spot ,-velding guns are used to make spot welds on weldments that are too large to bring to a fixed welding 1nad1 ine. As ivith other resistance welding equipment, the main parts of the system- the transformei~ ,velding arms, and electrodesare water cooled to remove excess heat. Since portable welding guns are heavy, they are hung by cables from an overhead support. They are count:erba lanced to lighten their ,-veight and 1na ke it possible for a ~•elding operator to manipulate the gun.

~Overhead support Handles

Water cooling , hoses '-,..

Fixed upper electrod

'\. Rotational mount °"4 '-4_

_

Movable lower electrode __

LORS Machlne,y. Inc.

Figure 18-32. A portable resistance spot welding gun.

This unit is suspended from overhead, relieving the operator of its weight. The gun can be rotated into any welding position.

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Th is arrangen1ent 1na.kes them very easy to n1ove to the weldn1ent. It also allows the gun to move from weld to weld and into a variety of positions. Their range of move1nent is li1nited only by t he length of the overhead support and the length of the power cable and ,.,,ater cooling hose. The disadvantage of long power cables is that they require a higher secondary voltage. Some portable spot welding guns have transformers in the gun. This type of gun is called a tra11sg 1111. Several h-ansguns are shown in Figure 18-33. Transguns

reduce the need for long secondary cables. They are often mounted on robots to perform spot welding tasks. Transguns can also be used in handheld and fixture welding applications. Portable spot ,.,,eJding guns and transguns are designed to do specific jobs. They are used to assemble sheet metal parts in a variety of industries. The automotive industry uses transguns mounted on robots. Resistance welding controllers and robot conh·ollers work together for precision spot welding operations. See Figure 18-34.

Movable electrode arm

Resistance welding controller

Servo motor I

I Transformer Shunt Water cooling supply and return lines

Flxed electrode arm I I

Robot controller Robot teach pendant

•

II 0

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, CenrerLlne (Windsor) Lim/red

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Wldlng Technology Corp-0,adon

Figure 18-33. Three transguns that are designed to be

Figure 18-34. A resistance welding controller cabinet

mounted onto robots. These all have serw-driven force systems. The parts of the transgun are labeled in the top view.

mounted on top of a robot controller to simultaneously operate a robot and a portable welding gun. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 18

18.9 Projection Welding Equipment Projection welding equipment is similar to the equipment used in spot welding. In projection welding, one of the pieces to be welded has one or n1ore small projections pressed into it. The current passes through the projection and forrns a weld between the two me tal pieces. Projection welding is used to accurately place the welds on parts that are in high production. A press-type or rocker-type welding machine can be used for projection ,.velding. If there is only one projection .veld, electrodes with a flat face can be used in either type of machine. Ji more than one projection weld is being made, special flat plates called platens are used as the •,velding n1achine electrodes. The two pieces of base metal are placed together between the platens, and they touch only at the projections or bumps. Higher forces and currents are required to make multiple projection welds using platens, becau se current flows through m ore than one weld area. The platen is a large, generally flat surface through which welding current flows. The upper platen is movable. The lower platen is adjustable, but once adjusted, it remains stationary. An air cylinder forces the upper platen against the lower platen. Figure 18-35 shows a large press-type resistance welding rnachine equipped with two platens.

Tayto,.Wfnbeld Tectmologtes. Inc.

Figure 18-35 A large press-type resistance welding machine equipped with two platens used for projection welding. Copvrighl Goodheart-WIilcox Co, Inc

Resistance Welding Equipmen t and Supplies

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18.10 Seam Welding Machines A sean1 weldi11g1nachine is a special type of resistance welding machine. Seam welding uses two copper a Uoy wheels as electrodes. These circular electrodes press the two pieces of meta] together and roll slowly along the seam. Current is passed between the electrodes and the work continuously or at timed intervals.

•

Nonstandard Terminology

Circular electrodes are often referred to by the nonstandard terms wheel electrodes and welding wheels.

A seam welding machine h as the following parts: • A frame, which contains the trans former and tap switch. • Secondary connections to the electrodes. • Circula r electrodes. • A stationary lower electrode arin. • A movable upper electrode arm. • An air cylinder and ram to apply required force. • An electrode drive mechanisn1. The frame, air cylinder, and ram are similar to those used on a press-type welding machine. The electrode drive 111echanism can be one of tv.10 types: • Gear drive. • Knurl diive or friction drive. A gear drive turns the center of the circular electrode at a constant speed. Usually only one circular electrode is driven by the gear drive; the second circular electrode rotates freely. As the drive electrode wears do,vn, the welding speed will decrease unless the drive s peed is increased to con1pensate for the smaller drive electrode. A knurl or friction drive uses a small roller that contacts the outer edge of the circular electrode. The small roller rotates and drives the circular electrode at a constant speed. With a knurl or friction drive, the welding speed remains constant as the electrodes wear. On some machines, only one circular electrode is di·iven by the knurl or friction drive roller. On other machines, both circular electrodes are driven by knurl or friction drive rollers. There are three types of seam welding machines. The circular electrodes can be parallel to the front of the machine (transverse seant); perpendicular to the front of the machine (longitudinal sea1n); or a combinatio n of the two (universnl). A universal machine can be used to make both longitudinal and transverse seam welds. Universal machines come with two lower a1·ms

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that can be interchanged as needed. One is designed to make longitudinal seam welds. The other is designed to make lateral seam ,,velds. The single upper a rm and circular e lectrode can be rotated as required. See Figure 18-36. A sea1n welding machine is controlled by a prog rammable welding controller. Current can run constantly to make a continuous seam, or it can be timed to make overlapping spot welds or spot welds at a uniform spacing. Pneumatic (air) or servo motor force systems are used to apply required force to the electrodes. The pressures required are not exh·e,nely high. The details of the upper electrode operating mechanism on a universal seam welding machine are shown in Figure 18-37. The metal parts being sea,n welded and the c.i rculai· electrodes can get very hot. It is usually necessary to cool the electrodes and the weldme nt. Two or more flexible tubes are positioned to deliver a steady flow of water directly to where the circular electrodes contact the metal being welded. At least one tube directs water to each electrode. See Figure 18-38.

Down stroke adjustable stop nut Upstroke adjustable stop nut

:1

- . _ Head support casting Anti-friction mounted "meehanlte" ram Low-inertia head actuating rod

18.11 Flash and Upset Welding Machines

Roller

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Flasl, welding is a process used to weld the ends of metal rods, rails, beams, and other shapes together.

-

Rolling diaphragm

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Hinge pin /

Low-Inertia head balancing spring

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'-.__i_7 . .. ,.

Taylor•Winfield Technologies, Inc.

Figure 18-37. Air-operated upper electrode of a universal seam welder. It is used to raise and lower the upper roller and apply the correct welding pressure.

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cir~l\'8~ electrbde

Flexible tubing

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H20 supply lar etectrOda

GoodhOart•WiUcox Publisher

SClaky. Inc., suOSl(lia1yo1 Phlllip.s servt>e 1n~s111es

Figure 18-36. A large universal seam welding machine.

Figure 18-38. The electrodes of a seam welder are cooled by a flow of water. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 18

Many products are flash we lded. Examples Lndude automobile wheel rims, chains, aircraft landing gear, structural engine components, railroad rails, and a luLni11um and steel wheels for agricultural app(jcations.

18.11.1 Flash Welding Machine Operation To perl01m a flash weld, the parts are secured in special damps or fixtures. The fixtw·es that hold the parts also serve as the electrodes and carry the electricity to the two parts. One fixture is fixed and one is movable. After securmg the pru·ts, the operator starts the welding process. The entire process is controlled by a weldmg controUer and takes seconds to complete, rather than the fraction of a second required for most resistance spot welds. While the parts are separated, voltage is applied. See Figure 18-39. The movable part advances slowly toward the stationary part. The parts initially contact over small irregular areas. High weldmg current passes between these small areas and quickly melts them. Flashing occw-s. Flashing is expulsion of the molten metal. TI1e movable part is continuously moved slowly toward the stationary part. After a lot of flashmg, the entire slu-face area of both parts Ls molten and the metal just behind the n1olten surfaces is at a forging temperature. Metal at a forging temperature is still solid but is soft enough to be □1a1Jeable or reshaped. At this point in the process, a large force is applied to the movable part. This forges the two pa.its together. Parts are brought together slowly. Arcing melts the ends of both pieces.

Resistance Welding Equipment and Supplies

The outside surfaces are upset or raised as the softened material is forced together. After a very brief cooling period, the clamping fixtures open and the welded assernbly is removed. New parts are loaded and the process is repeated. No cleaning of parts is required prior to flash welding.

18.11.2 Upset Welding Machine Operation Upset 1veldi11g is another resistance welding process that joins two pieces of metal over the entire area of surface contact. The process is similar to flash welding. Upset we lding is used to join the butt ends of rods, ba1-s, strip, and tubing. The heat is obtained from resistance to the flow of electric current through the entire area of surface contact. Force is applied before heating is started and is maintained during the heating period. At the end of the heating period, a large force is applied to upset the 1netal at the joint. The metal cools and forms a weld. The finished ,.veld has an enlarged area at the joint. See Fig ure 18-40. This enlargement, or upset 1netal, is usually ground down so the weld area is the same size as the original metal. An upset welding machine uses the same type of transformer as a spot welding machine. The electrodes on this type of machine also serve clamping dies or vises. One die is movable and one is fixed. An important difference between upset welding and flash welding is that the surfaces in upset welding

The movable piece is forced into the stationary piece under high pressure.

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The pieces are held stationary until the weld joint cools.

• Goodheart-Willcox Publisher

Figure 18-39. A flash weld being made. Metal is clamped to form joint prior to welding

Joint area heats up due to resistance

Molten metal at joint forced together under pressure

Upset metal cools to form weld

ii

• Goodheart-Willcox Publisher

Figure 18-40. A joint being upset welded. Notice the enlarged, or upset, metal area at the weld joint. Copvrighl Goodheart-WIilcox Co, Inc

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Modern Welding

must be cleaned and are usually n1ad1ined just prior to welding. Machining produces a clean surface with no irregularities.

Two pneumatic force systems

Two welding machines

Welding controller

18.12 Special Resistance Welding Machines There are nuinerous specially designed resistance welding machines available. These machines are variations of one or 1nore of the machin e types already discussed in this chapter. Two examples of these special machines are the cross-wire welding machine and the parallel gap welding machine. Cross-ivire resistance welding machines are press-type machines. Wires are crossed and held beneath a s ing le electrode or 1nultiple electrodes. See Figure 18-41. The current passes between wires where they cross. A resistance spot weld is created where the wi.res cross. A strong ,,velded joint is produced. Parallel gap resistance spot welding is a variation of spot \\relding that allows spot welds to be made from o ne side only. It .is used on 1netal up to .015" (0.38 mm) thick. Two parallel electrodes are mounted in a small resistance welding 1nachine, as shown in Figure 18-42. The upper arms and electrode holders each hold an electrode. Current passes from one electrode, through the pa1ts being ¼relded, to the other e lectrode. Force systems can be manual, pneumatic, or servo. The programmable controller can be an AC transformer or a stored energy type. A capacitor discharge power supply is often used with very low energy, measured in watt seconds.

Two parallel electrodes AMADA MIYACHI AMERICA. Inc.

Figure 18-42. A parallel gap resistance spot welder. Two side-by-side welding machines each have one electrode, which are parallel to each other. The force on each electrode is set independently.

Parallel gap resistance spot welding can be used to repair electronic circuits. Electronic circuits may be built on ceramic- or fiberglass-base boards. Brea ks occasionally occur in the copper trace circuits on expensive electronic circuit boards. They cannot be repaired by the norn1a l spot welding process, because fiberglass and ceramic do not conduct electricity. Spot welding can be used to weld a bridge over the gap in the h-ace. Parallel gap resistance spot ,,velding a llows the spot ¼reld to be made from one side. See Figure 18-43. Figure 18-43A sho,.,vs how the parallel gap resistance spot welder ""ould make a r epair weld on an electronic circuit board. The same equipment is used to weld a tab onto small batteries, Fig ure 18-43B. The welding current does not go through the battery. The Cllrrent contacts only the surface of the battery where the resistance weld is formed.

18.13 Care of Resistance Welding Equipment Sommer Met.a/craft

Figure 18-41. Cross-wire resistance welding machine. Cross-wire welding is used to make products like fence panels, shopping carts, shelving, and display racks for re tail stores.

The main areas of maintenance for resistance welding equipment are as follows: • Mechanical. • Electrical. • Pneumatic. • Water-cooling. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 18 Resistance Welding Equipment and Supplies

Resistance spot weld Fiberglass or ceramic

Repair Electrodes trace

i +

Broken copper or gold trace Material less than .015 in (.38 mm) thick

B AMADA M/YACHI AMERICA, Inc.

Figure 18-43. A-A parallel gap resistance spot welding

repair. The broken original trace is bridged by another conductor and spot welded from one side. 8 - A tab is welded onto a battery during the process of making a battery pack. Mechanical maintenance consists of the following: • Lubrication. • Checking 1noving parts for wear. • Checking welding electrodes are properly aligned. • Checking the force applied by the electrodes against the base metal being welded. • Checking mechanical safety devices, such as guards and machine mounting. Maintenance manuals should be consulted to determine the exact procedures and specifications to be used on a particular machine. Electrical n1aintenance consists of the following: • Checking ail electrical connections. • Checking prilnary voltage and cw·rent. • Checking secondary voltage and current. • Checking, cleaning, and installing fuses, switches, ai1d relays. • Checking for loose connections and failing shunts, which are a frequent source of trouble. Troubleshooting may require the use of a voltmeter or an oh1nmeter. Additional tools and equipment may be needed to make a complete analysis of the electrical equipment. Copvrighl Goodheart-WIilcox Co, Inc

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!'warning Use ex1reme caution when working with resistance welding machines. The high currents and voltages used in resistance welding can cause death. Follow proper lock-out and tag-0ut procedures. Whenever working on the secondary of a welding machine, make sure the machine is off. The circuit should also be turned off. Work on the primary side should only be performed by skilled electricians. If work must be done on the primary, disconnect the machine from the electrical power. Disconnect the circuit breaker. Whenever a machine is turned off or a circuit is disconnected to perform maintenance work, proper lockout, tag-out procedures must be followed for worker safety. Lock-out, tag-out procedures consist of locking the machine or breaker in an "off" position. The lock will be identified or tagged with the person's name who is responsible or owns the lock. This precaution prevents someone from turning the power back on and possibly killing the person repairing the welding machine. All maintenance and repair work should be performed by a person knowledgeable in electrical circuits and power. Pneumatic maintenance consists of the following: • Checking pressw·e. • Checking for leaks. A water-cooling circuit is an iinportant co1nponent of a resistance welding machine. The1mometers, pressure gauges, and flow meastu·ements are necessary for checkup purposes. An adequate supply of cool water should be provided to each welding roach.me, at a minimum of 30 psi (210 kPa) Iine pressure. Cooling ,~rater shou Id be at a temperature less than 85°F (30°C). Be certain that the water hose connections are tight. The welding transforiner, the SCR 111ounts, the electrode holder, and the electrodes are water cooled. On smaller machines, however, these components are typically not water cooled. Use electrode holders that can pass at least 1.5 gallons of water per n1i11ute (5.7 1pm). Make sw-e the water inlet hose is connected to the electrode holder inlet. TI1e water tube inside the electrode holder must extend to the electrode to keep the electrode cool. The end of the water tube is cut at a 45° angle. Seam welding electrodes and the work should be sprayed with cooli11g water. The water should be directed at the point where the circular electrodes contact the work. The water hoses should be free of any deposits that might reduce water flow. Make sw-e none of the hoses or connections leak, since water in the machine could cause an electrica1 short.

Summary • The resistance metals have to the flow of electrical current creates heat. Resistance welding uses this to create a weld. The most con1mon resistance welding process is resistance spot ,,velding. • The parts of a typical resistance ,,velding machine include the frame, transformer, force system, controller, welding arms and electrodes, and foot pedal. • A resistance welding transformer lo\>\1ers the supplied voltage and increases the s upplied current. Input voltage a nd current are called primary voltage and primary current, while output voltage and c urrent are called secondary voltage and secondary current. • The rated duty cycle is the maximum duty cycle that the welding machine can operate at without overheating dming a one-minute period. • Resistance welding transfonners have a KVA rating that is based on the capacity of the input, or pritnary, cit·cuit. • A t ransformer has two electrical coils, primary and secondary. Each coil consists of a single conductor, or ,,vinding, wrapped around an iron core. • In resistance welding, there are three main n1ethods of applying force to the electrodes or to the base n1etals: pneumati.cs (air), electric servo motors, and mechanical leverage. • A programmable electronic welding controller is used to control the welding operation. Required current and tunes are set in the controller. Force may be set in the controller. • Three titne settings are required to complete a resista1tce weld: squeez.e time, weld time, and hold time. • Dynamic weld resistance monitoring is the process of measurmg the contmuously changmg resistance of a ,,veld while it is being tnade. The controller can make adjustments based on this to ensure the weld is a good weld. • High current must be switched on and off at specified ti1.nes dLu·ing a resistance welding cycle. A pair of silicon-controlled rectifiers (SCRs) functions as a contactor in the primary ci1·cuit of welding conh·ollers.

• Resis tance welding electrodes conduct current to the surfaces of metals to be welded. An electrode n1ust be a good electrical and thermal conductor, have good n1echan ical strength and hardness, and have a minimum tendency to alloy with metals bemg welded. • Electrode holders hold the electrode in the proper position, carry the welding current, and provide the electrode with water cooling. Electrode holders are adjustable on most spot welding machines. • The size of a spot weld is rontrolled by changing welding variables, mcludmg current, time, force, and electrode face. When selecting a welding 1uachine, consider the dimensions of the operating area, the KVA rating, and the type of pressure system. • Resistance spot welding machines may be smglephase, three-phase, or stored energy n1achines. • Portable spotweldmg (PSW) guns are used to make spot welds on weldn1ents that are too large to bring to a fixed welding machine. PSW guns with transformers in the gun are called transgtu1s. • In projection weldmg, one of the pieces to be welded has one or more small projections pressed mto it. 11,e current passes through the projection and forms a weld between the t wo metal pieces where they touch. • Seam weldmg uses two copper alloy wheels as electrodes. There are three types of seam weld ing macl1i11es: transverse seam, longitudmal seam, and universal. • Flash welding is a process used to weld the end s of metal rods, rails, beams, and other shapes together. • Mamtenance areas for resistance welding equipment include mechanical, electrical, pneumatic, and water cooling.

Technical Terms Select the icons to access Drill and Practice activities. electrode diameter capacitor discharge resistance welder electrode face conductivi ty electrostatic resistance cross-wire resistance spot welding machine welding flash welding dynamic weld resistance flashmg monitoring hold tiJ.ne electrochemical resistance KVA (kilovolt-an1pere) spot weldi11g n1achme rating

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Chapter 18

laminated core off time parallel gap resistance spot welding reactance resistance welding resistance welding schedule seam welding machine silicon-controlled rectifier (SCR) squeeze time

step-do,.vn transformer stored energy resistance spot welding machine tap three-phase resistance spot ,.velding macltine throat depth throat height trans ratio transgun upset welding weld time

Review Questions Answer the falloiving questions using tl,e infor111alio11 provided in this chapter. Know and Understand 1. True or Fnlse? Resistance welding requires low

an1perage and high voltage electrical energy. 2. True or False? A step-down transformer lowers the supplied voltage. 3. True or False? Step-down transforn1ers have Lnany secondary windings. 4. What is a typical duty cycle rating for a L"esistance welding machine? A. 10"/o duty cycle. B. 20% duty cycle. C. 50% duty cycle. D. 80o/o duty cycle. 5. For resistance welding, the duty cycle is based on a _ _ period. A. one-min.ute B. two-minute C. five-minute D. ten-1ni.nute 6. True or False? The KVA rating of a resistance welding transformer is based on the output of the secondary circuit. 7. Which of the following is not a variable in resistance welding? A. Cw,ent. B. Electrode face. C. Lubrication. D. 11me.

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Resistance Welding Equipment and Supplies

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8. True or False? Servo motor force systems are more accurate than pneumatic systems. 9. The time required for the electrodes to close on the workpiece and apply the proper force is the _ _ ti1ne. A. squeeze 13. weld C. hold D.off 10. True or False? Resistance welding electrodes should resist conducting heat. 11. RWMArecogni.zes three groups of n1aterials for resistance welding electrodes. Group A includes A. refractory 1netal alloys B. copper-based alloys C. specialty materials D. galvanized steel alloys 12. Reactance is - -A. a measw·e of how ,veil electrical current passes through a material B. the expulsion of molten metal C. an increasing curient D. the resistance to the flow of AC 13. Which type of machine is used for projection welding? A. Seam 1,velding machine. B. Cross-wire resistance welding maclune. C. Parallel gap resistance welding machine. D. Press-type welding machine. 14. Which type of machine uses two copper alloy circular electrodes? A. Seam welding machine. B. Cross-wire resistance welding machine. C. Parallel gap resistance welding 1nachine. D. Press-type welding machine. 15. True or False? The surfaces being welded in flash welding do not need to be cleaned.

Apply and Analyze 1. What happens to the voltage and to the current when it goes through a step-down transformer? 2. Describe two ways to increase the current on a resistance welding machine. 3. What is required to make an SCR conduct cw-rent?

4. How do throat depth and throat height limit the size of the pieces that can be welded by a resistance spot welding machine? 5. What is the advantage of using a stored energy 1nachine? 6. What are the main parts of a seam 1,velding 1nachine? 7. When sean1 welding, what is the advantage of using a knurl or friction drive, rather than a gear diive? 8. List t,vo processes that use the following procedure: T1,vo metals are brought together and heated by passing electrical current through them. When they have been heated, a large force is applied to join the pieces. 9. Why is parallel gap resistance spot welding used to repair electronic circuits? 10. What parts of a resistance welding machine may be water cooled?

Critical Thinking 1. RSW and GMAW can both be used to make a 1/4" (6 mm) spot weld. What is an advantage and a disadvantage of each process? (An advantage of one may be a disadvantage of the other.) 2. Force is a variable in resistance welding. If you 1nake a good weld with a set force and then make a second weld with double the amount of fot-ce, do you think the second weld will be larger and stronger or smaller and weaker than the fi.rst weld?Why?

Experiment 1. Determine the minimum and maximum times available on a weld controller. Record the 1ninimllln nu1nber of cycles or 1nilliseconds that can be set for squeeze time, weld time, and hold time.

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Resistance Welding Dmttry XaJmovsky!Slluttersiock.com

Learning Objectives After studying this chapter~ you will be able to: • Describe the variables involved in producing an acceptable resistance weld. • Describe and be able to set or measure such items as transformer tap setting, percent heat, and electrode face diameter. • Select the electrode face dian1eter, current, electrode force, and weld time to make a quality weld. • Set up a resistance spot welding machine. • Make good quality resistance spot welds in mild steel. • Visually inspect and peel test a spot weld to determine its quality. • Describe how feedback control and dynamic weld resistance monitoring can be used to produce good quality resistance welds. • Identify the safety hazards involved with resistance welding and describe tnethods to reduce or eliminate these hazards.

esistance welding is based on the fundan1ental principle that when an electrical current is passed through a metal, friction caused by resistance to this electrical flow heats the rnetal. The majority of the heat is developed where the two pieces of metal to be welded are in contact. Very high

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te1nperatures result fro1n applying sufficient current. Welding occurs when these temperatures reach the fusion (melting) temperature of the metal. The tertn resistance 1velding refers to a variety of welding applications, including spot welding, projection welding, seam welding, and upset welding. Resistance ~velding is fast. There is very littl.e distortion of the metal, and the process can be accurately controlled. Because of these qualities, resistance welding is well suited to all fortns of auto rnatic production activities.

19.1 Principles of Resistance Welding When two pieces of metal are in contact, the area where they touch has a high resistance to the flow of electrical current. Due to surface roughness, the pieces of metal to be welded are never in perfect or complete contact. Heat is generated when an electrical current is passed across the metal surfaces. When enough current is used, the metal s urfaces heat until they become n1olten. Two pieces that are pressed together while their surfaces are molten will fuse into one piece when cooled. The welding current produced by resistance welding n1achines can be either alternating current (AC) or direct current (DC). DC is more commonly used today. DC offers better heating control than AC. Since DC has no waveform (unlike AC), DC produces a steadier heating of the weldment. Therefore, creating

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a resistance vveld schedu le that does not result in expulsion is much easier. Expulsion is the unwanted forcing out, or expelling, of m olten metal dw·ing a resistance welding process. O ther advantages of DC include shorter weld times and lower required cw·rent to achieve an acceptable weld nugget. DC machines a re also best used for joining thick n1etal p ieces. An AC resistance welding machine is basically an electric transformer. It is powered by an alternating current circuit. Resista nce ,.velding requires very high current (high amperage) at a relatively low voltage. This requires the resistance welding machine to have a step-d oivn h·ansfonuer. Figure 19-1 shows an e lementary AC electric circuit for a resistance welding machine. A DC resistance 1.velder is an AC machin e that converts the AC output to DC.

19.1.1 Types of Resistance Welding There a re severa l types of welding processes and equipment based on the resistance welding principle. Some o f the more common types and their abbreviations a re listed below: • Resistance spot welding (RSW). • Projection ,.velding (PW). • Resistance seam welding (RSEW). • Flash welding (FW). • Upset welding (UW).

Primary winding

I Off-on / switch

19.2 Resistance Spot Welding (RSW) One way to join sheet metal parts is to drill holes a nd fasten the parts together w ith mechanical fasteners, s uch as rivets, machine screws, or sheet metal scre,.vs. Another vvay to join sheet n1etal parts is to spot vveld them together. Although more than n.vo pieces of metal can be spo t welded together, two pieces are most commonly joined. Rarely are four or more pieces vvelded together at one t ime. Spot welding is the most common resis tance welding process. The process cons ists of overlapp ing tvvo pieces of metal and clamping them between two electrodes. A current is passed bet1.veen the two electrodes. A s1nal 11nolten spot is forn1ed where the 1neta l pieces contact each other between the elect rodes. After the current s tops, the electrodes continue to h old the metal, allowing the s pot of molte n rnetal to solidify. The tvvo pieces of metal are fused together by a spot weld or 1veld nugget. Fig ure 19-2 sh ows a diagram of spot welds. Cross sections of va rious spot weld nuggets are shown in Figu re 19-3.

Secondary winding

Transformer

AC

AU of these operations use resistance to create the heat for welding. H ovvever, the machines used and the metal preparation are different.

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Electrodes

s

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Soft iron core

Goodhearr-Wlllcox Pul)lisher

Figure 19-1. A basic resistance spot welding machine electrical circuit. Note that the primary winding has many more turns than the secondary winding. This is a step-down transformer.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 19

Spot welds

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Resistance Welding

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CRS .047"

Nugget

_____ b(, ._____.,I_________. I

Ooodhean-Willcox Putilsher

Figure 19-2. These two pieces of metal have been

A

overlapped and spot welded in two places. Note the nugget where the fusion takes place between the two pieces.

In resistance spot ,.velding, there are five variables that must be controlled. These variables are as follows: • Amount of current • Leng th of ,.veld time. • Amount of force applied. • Electrode face diameter. • Type of welding machine. The time required to ma ke a spot weld is d ivided into three separate timing period s. These timing periods are: • Squeeze time- The time required for the electrodes to close o n the 1neta l and apply the proper force. • Weld time--The time that the cur rent flows and heats the metal. • Hold time--The period after the current s tops w hen the pressure is still applied. The hold time allows the molten m etal spot to solidify. At the end of the hold time, the applied force is released. These three times make up one weld sequence, or a resistance welding schedule. Each of these times is set on the controller o r control pan el. The times are set in numbers of cycles or hertz. One cycle, or one hertz (Hz), is 1/60 of a second. On som e welding equipment, tiines a re set in 1nilliseconds. One n1illisecond is 1/1000 of a second.

Copvrighl Goodheart-WIiicox Co, Inc

Ta'YfOr-Winfield Technologies. Inc.

Stainless .042"

B

Taytor-WinlitJld Technologtes, Inc.

Aluminum .042"

C

Taytor-Wln«•ld T•clmologl•s. Inc.

Figure 19-3. Magnified cross sections of resistance

spot welds in various metals. A- Cold-rolled steel (CRS). 8-Stainless steel. C-Aluminum.

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Modern Welding

The a1nount of current is a"n in1porta11t variable. The amount of current used can be changed in one of the following ways depending on the controller: • Change the transformer tap setting on the welding machine. • Change the percent heat setting on the welding mad1ine controller. • Change the current set value. The transforrner tap setting is used to make large changes in the current settings. A given transformer tap setting has a range of currents" Tovarythecurrentwithin a given range, some controllers require the desired current to be set. On other types of conh·ollers, the percent heat setting is set. The higher the percent heat setting, the higher the current (as measured in amperes). For exan1ple, a given transformer tap setting may supply between 9000A and 15,000A. Because 12,000A is right in the middle of the current range, a 50"/o heat setting is required to obtain 12,000 amps. So1ne controllers allow the desired current output to be set in amperes (amps or A). If 12,000 amps is required for welding, this value is entered or set.. The controller uses electronic feedback to n1onitor the process and provide the desired current output. To operate a spot welding n1achine, the operator must carefully and safely clean the electrodes, turn on the cooling water, and set the tap switch on the transformer to the correct current setting. The \,velding operator 1nust also set the times and percent heat on the controller, and set the desired force on the electi-odes. Resistance spot welding machines are shown in Figures 19-4 and 19-5. These machines have a pneumatic (air) force system. There is a valve to turn on the air and a regulator to adjust the air pressu1·e. There is a valve to turn on the cooling water. Both machines have a foot pedal to start the ,,veld operation. To perforin a weld or a series of welds, the welding operator places the pieces to be v.relded on the lower (stationary) electi-ode. When the operator steps on the foot pedal or pushes the starting S\~ritch, the electrodes come together and a weld is made. If a series of welds is to be made, the operator moves the part to each nevv weld location, presses the foot pedal or pushes the start button, and makes a new v.reld. This process continues until the correct number of welds are made. On larger parts, the operator uses a portable spot welding gun and moves the gun to the desired location on the part. The parts are often held in location by jigs and clan1ps" On automated equipment, parts are loaded into a jig. Parts are clamped into position using manual damps or

Air-pressure regulator

Water cooling hoses

Foot pedal ACRO Automaoon Sysaems, Inc.

Figure 19- 4. This spot welding machine uses a

pneumatic electrode force system" The controller is at the right of the welding machine. Note the foot pedal start switch at the lower right. At the left side of the welding machine, just above the hose connections, note the colored balls. The movement of these balls indicates that cooling water is flowing. automated clainps. The welding operator steps back into a safe area, away from any automated moving equ ipn1ent, and presses the start button. Then, the welding sequence begins. Each "velding gun makes the weld or welds it is program111ed to 1nake" At the end of the sequence, the pieces have been welded. Clamps are undamped. The welded assembly is removed. New pieces are loaded into the jig and the sequence is started again" Robotic resistance welding is similar. Parts are loaded into a jig and clamped. The welding operator steps to a safe working area and presses the stru·t button to begin the welding sequence. A programmed robot ,,vith a spot welding gun moves to a programmed weld position.

Copyr!ghl Goodheart-WIiicox C-0" Inc,

Chapter 19

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I

Tap switch

Air-pressure regulator

Foot pedal Vfsr,a fndusrlaJ Produc11;, Jnc.

Figure 19-5. The welding operator places the bracket being welded between the electrodes, and then presses the foot pedal to start the weld sequence.

See Figure 19-6. A weld is made. The robot moves the weld gun to each additional weld point until all progra,n med welds are 1nade. The robot returns to its home position ,.vhen the welding sequence is oomplete. The clamps on the jig unclamp. The welded assembly is reinoved. The ,.velding operator loads new parts and the process is repeated. On an assembly line, welded parts are not unloaded by the operator. They are picked up by automated shuttle equipment or another robot and moved to the next welding s tation. Additional welds are made at each welding station. Some resistance welding machines use two palm switches to start the welding cycle. Palm s,.vitches are pushed by hand. Both palm switches 1nust be pushed to stait a weld With this setup, there is no danger of the ,,veldi.ng operator getting a hand caught between the electrodes.

Copvrighl Goodheart-WIilcox Co. Inc

Welding gun

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Robot

""

xieyutang/Shuttersrock.com

Figure 19-6. A robot using a welding gun to make resistance spot welds on parts held in a fixture.

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Modern Welding

The dual paln1 switches can be used to satisfy some Occupational Safety and Health Administration (OSHA) requirements.

19.2.1 Spot Welding Machines Many components and systems make up a resistance spot ,-velding machine. The following a re the three basic n1acrune designs: • Rocker arm 1nachines. • Press-type machines. • Portable machines. A resistance welding 1nad1ine's components consist of a transformer, a force system, and u1ovable and stationary electrode arms. The parts of a portable spot \Nelding machine are labeled in Figure 19-7. Spot welding 1nachines use dilierent types of force systems. These force systems are described in detail in Chapter 18, Resistance Welding £q11ip111e11t and Supplies. The following are the different types of force systems: • Pneumatic (air) pressure. • Servo n1otor. • Mechanical leverage. Pneumatic force systems are most commonly used in manual spot ,-velding. Force on a pneumatic system is set by manually adjusting an air regulator. Usually, one set force is used in a pneumatic force system. This force is used for all welds made.

Servo n1otor force systems are widely used i.n automated spot ,velding and on automobile assembly lines. See Figure 19-8. Servo force systems are more accu.rate and repeatable. Another advantage of a servo force system is the desired force can be changed for each different weld. This gives greater control than possible "vith either pneumatic or mechanical leverage force systems which only use one force for all welds.

xieyulang/Shuttcrstock.com

Figure 19-8. An automotive welding line. The weld guns use servo motor force systems. An accurate and repeatable force from a servo motor system can be set and changed for every weld.

Pneumatic force cylinder

Movable electrode arm

Fixed electrode arm

Handle

CentorUno (Windsor) Limitod

Figure 19-7. A portable spot welding machine, or PSW gun. This gun hangs from an overhead support. The operator moves the gun to the desired weld location and starts the welding process by pulling a trigger on the handle. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 19

Mechanical leverage force systems are prirnarily used on small, detailed welding applications that use lo~v welding forces. Force is n1anually adjusted. One force is set on a mechanical leverage force system for welding. Spot welding machines are electronically controlled. They are classiEied according to the way the primary circuit is powered. There are three types: • Single-phase macl1ines. • Three-phase 111achines. • Stored energy machines. Additional information about these three types of spot welding 1nachines is presented in Chapter 18, Resista11ce Welding Eq11ipn1ent and Supplies. Spot welding machines are selected for specific jobs based on their basic design, force syste1ns, and types of electrical inputs and outputs. Two other factors are also considered: the KVA rating and duty cycle. KVA stands for kilovolt amperes, or thousands of watts. KVA is a measure of the power, or heating potential, of a welding machine. A 150KVA machine can produce 150,000 W of power or heat. KVA ratings vary from 10KVA to over 150KVA. Duty cycle is the percentage of time, in a oneminute period, that a welding n1achine can have current flowing through the secondary circuit without overheating. A 50°/o duty cycle indicates that the welding n1achine can safely be used with weld current flowing for 30 seconds in each one-minute period. The most common duty cycle is 50%. Each of these factors is i111portant when identifying or selecting a spot ,,velding machine. There is no one machine that is best for all applications. Each machine has advantages and disadvantages. Select the best machine for a specific job. The most common spot welding machines are automatically controlled, single-phase machines that use a servo n1otor force system. Pneumatic force systems are common in sheet metal shops and autobody repair businesses. Presstype, rocker arm, and portable rnachines are all con1monly used in industry. Portable spot welding (PSW) guns are popular in welding sheet metal fabrications, such as autornobile bodies, appliances, and enclosures for electronics. The transformer may be built into the gun or it may be separate. The tin1ing and current are set on the weld controller. The function of the controller is to execute the resistance weld schedule, as explained in Chapter 18, Resistance Welding Equip111ent and Supplies. The controller is not part of the welding machine; it is separate. The welding operator selects the place to weld and positions the nonmoving electrode against the metal. Copvrighl Goodheart-WIilcox Co, Inc

Resistance Welding

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The operator then pulls the trigger (start switch) and the controller executes the preset weld schedule. The elech·odes separate when the weld is complete. The operator n1oves the PSW gun to the next weld location and repeats the process.

19.2.2 Spot Welding Setup Spot welding setup involves selecting the proper resistance welding machine for thejob. ln 1nany industries, the equipment for a given job is selected or specially designed by the engineering group. Special tooling is al.so designed to hold and clamp parts to be welded. In sheet metal shops and job shops, the operator deter1nines which of the available equipment will best perform the desired welding task. Once the resistance \,velding machine has been selected, fow· other variables must be determined. These variables are the electrode face diameter, electrode force, ,veld time, and weld CUITent. Once these are decided, they must be installed or set on the welding machine and the controller. When setting up a spot welding machine for a specific job, select the best electrode holders, adapters, and electrodes. Detennining whi.c h holders, adapters, shanks, and electrodes to use often depends on the parts being welded. Next, instal I the selected parts onto the welding machine. Figure 19-9 Lists the recommended electrode face diameters for spot welding different gages of rnetal. Electrode caps are made in six basic shapes, as shown in Chapter 18, Resistance Welding Equipment and Supplies. The rnost comn1on electrode cap design is the dome, foUowed by pointed and radius designs. These caps are designated types B, A, and F, respectively. These are good general-purpose electrode designs. T he flat design, type C, is used when welding on a surface that should remain cosmetically appealing. The flat faces do not dent the su.rface of the welded parts as much as other designs. An offset design, type D, is used to weld on narrow flanges. Each of these electrode cap designs is available with different electrode face diameters. Choose the best cap design with the correct face dian1eter. Align the electrode holders, adapters, shanks, and electrodes so the two electrode faces are parallel and centered on each other. The remaining variables of force, welding time, and current must now be set. Figui e 19-9 provides recommended values for spot welding low-carbon steel. Class A welds have the largest fused area, or weld nugget, and they have the highest sh~ngth. Class A welds require the highest electrode force and welding current. Class B and Class C welds require less elech·ode force and less welding current, but longer welding times.

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Modern Welding

Recommended Practices for Single-Pulse Spot Welds in Low-Carbon Steel Data common to all classes of spot welds Thickness of thinnest outside piece

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.010 (0.25) 1/2 .021 i0.53) 112 .030 (0.76) 1/2 .036 (0.91) 112 112 .048 (t22) .060 (1.52) 112 .075 (1.91) 5/8 .090 (2.29) 5/8 .105 (2.67) 5/8 .120 (3.05) 5/8 Weldina setuo

Weld time Thickness of thinnest outside (single piece pulse)

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Amps " Dw" Inch "C" Inch " L" Inch Pounds (acorox.) (accrox.) Pounds 1/8 1/4 4 4,000 .13 235 200 3/8 3/16 6,100 3/8 7/16 6 .17 300 530 3/16 7/16 8,000 8 400 .21 1/2 980 1/4 3/4 112 10 500 9,200 .23 1,350 1/4 7/8 9/16 12 660 10,300 .25 1,820 1/4 1-1/16 5/8 14 800 11 ,600 .27 2,350 1-3/8 11/16 5/ 16 21 1,100 13,300 .31 3,225 1,300 .34 5/16 1-5/8 3/4 14.700 25 4.100 13/16 29 1,600 16,100 .37 5 ,300 3/8 1-1 3/16 1,800 17,500 6,900 3/8 2 7/8 30 .40 for best cualitv Class "B" welds Weldin a setuo for best aualitv Class "C" welds Minimum Weld Minimum Net Diameter tension time Diameter tensionelectrode Weld of fused shear (single Electrode Weld of fused shear current" zone force current• zone strength force strength pulse)

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thickness cycles Inch (mm) (60 Hz) .010 (0.25) .021 (0.53) .030 (0.76) .036 /0.91) .048 (1.22) .060 (1.52) .075 (191) .090 (2.29) .105 (2.67) .120 (3.05)

5 10 15 21 24 29 36 44 50 60

Pounds 130 200 275 360 410 500 650 790 960 1,140

Amps

" Dw" Inch

(approx.) 3,700 5,100 6,300 7,500 8,000 9,000 10,400 11,400 12,200 12,900

(approx.) .12 .16 .20 .22 .23 .26 .30 .33 .36 .39

Pounds

Cycles (60 Hz)

Pounds

200 460 850 1,230 1,700 2,150 3,025 3,900 5,050 6,500

15 22 29 38 42 48 58 66 72 78

65 100 135 180 205 250 325 390 480 570

Amps " Ow" Inch (approx.) (approx.) 3,000 .11 3,800 .14 4,700 .18 5,600 .21 6,100 .22 6,800 .25 7,900 .28 8,800 .31 9,500 .35 10,000 .37

Pounds 160 390 790 1,180 1,600 2,050 2,900 3,750 4,850 6,150

• starting values shown are based on eocpertence of member companies 1. Minimum spacing shown for welding of two pieces. Increase spacing by 3>% when we Icing three pieces. Smaller minimum spacing requires higher current • rype Of steel: SAE 1008-1010 • Materta.l should be free from scale oxides, pain~ grease, and heavy 011. • Table Is for a 3:1 maximum rauo 01 thl m est piece. and a max.imlfll s1ae1

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Aluminum Goodhean·Willcox Publisher

Figure 19-22. Weld schedule used for aluminum. The forge force is applied during the hold time.

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19.2.5 Feedback Control and Dynamic Weld Resistance Monitoring To improve the quality of spot welding, including projection and seam welding, feedback control and monitoring systems are used. A 1nonitoring system measures and displays the welding variables. Limits can be set for certain variables, such as welding current and weld time, and an alarm is issued if the value is outside of the set limit. Equipment can be set up to s top 1naking additional welds until the alarm is cleared. The ,,.,elding operator must determine why an alarm occurred a nd take the necessary steps to prevent the fault from reoccurnng. As explained in the previous chapter, some equipment has dynain ic weld resis ta nee monitoring. Dynamic weld resistance n1onitoring measures the resistance of the \¥eld as it is being made. The controller compares the actual measured resistance to a known resistance of a good weld As the weld is being made, the controller adds or reduces current to the weld so its measured resistance 1natches the resistance curve of a known good weld. When the weld is complete, it is known to be a good ,veld.

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Stainless Steel Goodhoan-Wlllcox Publisher

Weld schedule used for stainless steel. A stainless steel weld is tempered by applying additional heat after the cool time. Figure 19-23.

Feedback controls can a lso be set to adjust welding variables. The feedback controller manges the welding variables electronically to maintain constant weld quality. One example is a constant current welding controller. Feedback controls monitor the current and voltage and make small changes to maintain a constant output current. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 19

Va.riables that can easily be monitored include primary and secondary voltage, primary and secondary cu1Tent, and cable resistance. Other variables can also be monitored. Using the voltage, current, and Ohm's law, the resistance of the weld can be calculated using the formula R = VII (R = resistance, V = volts, and l = curre nt).

19.3 Projection Welding (PW) Projection welding requires projections or bumps on one of the pieces of metal. The projections are accurately formed in precise locations by a special set of dies when the part is manufactured. See Figure 19-24. The raised portions on one piece of 1netal are pressed into contact with ano ther piece of me tal. Figure 19-25 shows a projection weld setup. Pressure is applied on a projection. Th en current is passed through the two pieces. Since the projection contact area is small, the current is concentrated on that a rea. The point heats and forms a spot weld.

Resistance Welding

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An advantage of projection welding is that it locates the .velds at certain desired points. Also, several spots can be welded at the same time. Projection studs and nuts, like those Ln Figure 19-24, are often welded with standard electrodes. Some studs and nuts require an electrode with a hole to accept the ci1·cular part of the stud or nut. When projections are present on larger parts, specialty electrodes are used to weld them. The specialty electrodes must be designed to contact al I the projections on the parts. The specialty electrodes are inserted into custom-designed holders and attached to platens (flat plate electrodes) on the resistance ,,velding n1ach ine. The large flat s urface of the platens ensures that pressure is evenly distributed to all of the projections. The cost of the tooling, required to fabricate the special electrodes and their holders, makes this welding method practical only when high production is planned.

19.4 Resistance Seam Welding (RSEW) Resistn11.ce sea n1 1ueldittgproduces a continuous or an intermittent seam. The weld is usually near the edge of t,,vo overlapped metals. Two circula r electrodes travel over the metal and c urrent passes between them. The current heats the two pieces of metal to the fusion point. See Fig ure 19-26.

Copper alloy

electrode wheels ~ The Ohio Nut and Bolt Co.

Figure 19-24. A variety of nuts, studs, and pins with

projections stamped into the parts. The projections locate where the weld will be made.

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Before welding

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Figure 19-25. A schematic drawing of metal before and

after projection welding. Some of the depression formed by the stamped projection remains on the top surface of the finished weld. Copvrighl Goodheart-WIilcox Co, Inc

Goodhoart•Willcox Publisher

Figure 19-26. A schematic drawing of metal being seam

welded.

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Modern Welding

The current ca n be continuous or intennittent. Continuous cw·rent produces a continuous seam. Inte11nittent current produces spots that can be tin1ed to overlap. Either type of cun·ent can produce a leakproof lap joint for use with gases and liquids. Continuous and overlapping seam vvelds are shown in Figure 19-27. Another fonn of seam ,¥elding is called butt sen111 ?velding. lt is used to ,¥eld a longitudinal seam in pipe. Electric current heats the edges of the metal to a molten condition just before it passes beh¥een a set of rollers. The two rollers press the pipe edges together, and the metal is welded. The rollers also hold the welded joint in position while it cools to a safe temperature. This resistance ,¥elding method uses high-frequency cwTent to h eat the metal Figure 19-28 shows a long itudinal sea,n weld being made on a pipe. A seam welding machine must have a higher duty cycle than a spot welding machine. A machine that produces a continuous sea.in or an overlapping sean1 1nust be rated at a 100% duty cycle.

Overlapping spots

Continuous seam

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End view Goodhean-Wil/cox Publisher

Figure 19-27. This sketch shows metal that has been

seam welded. A seam weld is made with circular electrodes. If the current to the electrode is turned off and on, a se ries of overlapping spots forms the seam. An uninterrupted flow of current to the electrodes forms a continuous seam.

19.5 Flash Welding (FW) Flash welding is a resistance welding process generally used to weld butt joints in mo pieces of metal. The end surfaces of the two pieces are not cleaned o r machined. The parts are held in two clamps. One clamp is stationary; the other is movable. See Figure 19-29. The h"lo clamps also serve as the electrodes. They pass the electrical current to the parts to be flash welded. When the weld process is started, the butt ends of the h"lo pieces are brought into light contact. Heat for ,¥el ding

is created when a high current is passed fro1n one piece to the other. The high resistance of the uneven contacting surfaces causes these areas to h eat and quickly melt away. Nov.r there are s1nall gaps betv.,een the two parts. Arcs form at these points initially, and as more metal is melted, the arcing spreads to cover the entire surface to be welded. This action is called flashing. See Fig ure 19-30. During the arcing period, the prui:s are brought together slowly as some mate1ial is consumed or melted away. Point of welding

Welded ~

pe travel

Electric - -...... current .,......,

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GoOdnean-WIIICOX PUl)lisne,

Figure 19-28. High-frequency resistance welding used to weld the longitudinal seam on a pipe or tube during production. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 19

Resistance Welding

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Out/in

Alignment maintained by water-cooled dies with alloy inserts

i

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Piston

-

Insulation prevents "flash" or dirt reaching transformer

In/out

Pneumatic cylinder

Goodheart·WIIICOJC Publisher

Figure 19-29. Schematic drawing of a resistance flash welder. The heated stock is forced together rapidly by a pneumatic (air) cylinder.

The entire surface area to be \,velded becornes n1olten. The current is stopped ,,vhen the surfaces are completely molten and the material behind the surfaces is at a forging ternperatw·e. Then, a very high pressure is applied. The parts are squeezed together, forci11g some of the molten, uooean metal on the contacting surfaces outward. The softened rnaterial beltind the surfaces is upset or enlarged. The parts fuse together and are held in position for a sho1t time to allow them to cool. After the weld is cornpleted, the clarnps are released and the parts removed. Figure 19-31 shows two pieces of metal after they have been flash welded.

Taytor--WtnlielrJ Teellnologtes, Inc.

Taytor-lVinDold Tochnologios , Inc.

Figure 19- 30. Low-carbon steel rings being welded using a flash welding machine. Copvrighl Goodheart-WIilcox Co, Inc

Figure 19-31. Angle iron that was flash welded. The upset areas on the parts were removed by a trimming tool in the welding machine. This trimming occurs while lhe parts are hot.

530

Modern Welding

Flash welding is a fast operation. Two pieces of 1/2" (13 mn1) stock can be flash welded in about 5 seconds. Two pieces of l" (25 mm) stock can be completely flash welded in about 12- 15 seconds. No metal cleaning or special preparation is requjred prior to flash ,~•elding.

19.6 Upset Welding (UW) Upset welding is a resistance welding process in which two pieces of meta.I are secured in separate clamps. One clamp is stationary; the other is movable. The clamps a re electrodes and carry current to the parts being ,.velded. Meta.I to be upset welded must be very clean and properly aligned. The clamps and the

electrical wiring of a n upset weld ing machine are shown in Figure 19-32. In upset welding, two pieces are forced together, and a large current is passed fro1n one c la 1np to the other. The metal between the two clamps is heated. A majority of the heat is concentrated at the place w here the two metal pieces toud1. The ends of the metal are heated to the fusion (melting) temperature. After reacrung the fusion temperature, the two pieces are forced together (upset) under high p ressure. This upsetting occurs while the current is flowing and after the current is twned off. The metals join together and become one piece. After a short cooli,ng period, the clamps are released and t he part is removed from the welder. Figure 19-33 shows the fina.l upset weld.

Heated region

,..------r--------------1------ --------------------1-----

----~--------------i-----...-------------------~----' V Base metal

Stationary clamp _ _ ___...,.

Secondary winding

t Primary windings

Variable - - - - transformer control

Goodhoart~WiUcox Publisher

Figure 19-32. A diagram of an upset welding mach ine, showing transformer primary and secondary windings and a clamping mechanis m. Only the reg ion between the clamps is heated. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 19

Upset

53 1

19.8 Review of Resistance Welding Safety

_l

GoOd/Jeafl•Wlllcox Publisher

Figure 19 -33. A completed upset weld. Note that the diameter of the rod is increased {upset) in the area of the joint.

19.7 High-Frequency Resistance Welding When exh·emely high-frequency current flo,,vs through a conductor, it flows at or near the surface of the metal aJ1d not th_rough the entire thickness. This phenon1enon of high-frequency electricity has been used to weld sections as thin as 0.004" (0.10 mm). lo,,v-arn perage current with frequencies as high as 500,000 Hz (cycles per second) is used. This highfrequency current heats the surface of the metal. When pressure is applied to force the metal parts together, an excellent fusion ,,veld occurs at the surfaces of the parts. This process is used to ~veld longitudinal sean1s in pipe, as s hown in Figu re 19-28. This method has been used to weld copper to steel and alloy steel to carbon steel. It can also be used to weld exotic metals in an inert gas ahnosphere. The electronic equipment needed for high-frequency resistance welding is complicated. Special training is required to beco1ne a competent technician for n1aintaining, adjusting, and servicing these machines.

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Resistance Welding

Resistance welding and resistance welding equipment, if properly handled, are very safe. The greatest resistance welding dangers come from the following: • Electri cal s hock and other electrical hazards. • Cuts from sharp metal edges. • Burns from hot metal and from flying sparks or molten metal. • Crushing injuries caused by the high forces exerted by the electrodes. All operators of resistance welding equipment must lvear safety glasses, face shields, or Hash goggles. There may be some flying sparks or "flash" throlvn from the jointbeing welded Protective clothing, lvhich includes long-sleeve shirts and pants, is necessary. The welding voltage across the electrodes is very low, b ut the secondary current is very high. The primru·y ciJ·cuit wiring should be handled only by qualified e lectricians. All resistance welding equipment should be grounded. Naturally, an y sw-face being welded is very hot. Ahvays wear protective gloves to handle the materials being welded. Gloves also protect hands against sharp sheet metal edges. Resistance welding inachines apply great force to the parts being welded. There is always d anger of injury if the operator's hand or fingers should accidentally be caught between the electrodes as they come together on the work. Safety, including using proper lock-out, tag-out procedures, should always be used to minimize the risk of personal injury when the machine starts to operate.

Summary • Resistance welding is based on the fundamental principle that when an electrical current is passed through a metal, friction caused by resistance to this electrical flovv heats the 1netal where the two pieces of metal to be welded are in contact. • Resistance welding requires very high current (high amperage) at a relatively low voltage. This requires the resistance welding machine to have a step-down transformer. • Spot welding consists of overlapping two pieces of metal, clamping them between two electrodes, and passing current between the two electrodes. A s1nall molten spot fonns and then solidifies. The two pieces of metal are fused together by a spot weld or weld nugget. • Spot welding machines are selected for specific jobs based on their basic design, force systems, types o.f electrical inputs and outputs, KVA rating, and duty cycle. • When setting up a spot welding machine for a specific job, select and install the appropriate electrode holder, adapters, and electrodes. Determining which holder, adapters, shanks, and electrodes to use often depends on the parts being welded. • After the welding current and time are set, saa1ple welds are made to test and fine-tune the settings. Welding test samples involves welding the base metals together, tearing the pieces apart, exa1ninLng the weld quality, and then adjusting the current or time setting as necessary. • If parts to be welded do not weld, this is called weld separation, or ,~eld peel. If there is no weld or there is a weld nugget that is too small, more current or time is required to increase the weld nugget size. • Spot welding aluminum differs from welding mild steel Significantly more current for shorter times are needed to spot weld alu1ninu1n co,npared to mild steel. • Stainless steel requires less time to weld than mild steel. Stainless steel cools rapidly and forms n1artensite. To improve the properties of martensite, the finished weld is te1npered. • Projection welding requires projections or bumps be for1ned on one of the pieces of metal to be joined. P1·essure is applied to the projections. Then, current is passed through the two pieces.

• Sea1n welding produces a continuous or a11 intermittent seam. The weld is usually near the edge of two overlapped 111etals. Two circular electrodes travel over the metal and CUJ·rent passes between them. • Flash welding is a resistance welding process generally used to weld the ends of two pieces of metal. The end surfaces of the two pieces are not cleaned or machined. • In upset welding, t,~o pieces are forced together, and a large current is passed from one clamp to the other. The ends of the metal are heated to the fusion (melting) ten1peratuJ·e. Then, the two pieces are forced together (upset) under high pressure. • Resistance welding dangers come from electrical shocks and other electrical hazards; cuts from sharp 1netal edges; burns from hot 111etal, flying sparks, or molten metal; and crushing injuries caused by high forces exerted by the electrodes.

Technical Terms Select the icons to access Drill and Practice activities. blowhole forge force butt seam welding pinhole current analyzer projection welding dressing resistance seam 1,velding expulsion transformer tap setting weld nugget expulsion weld force gauge weld peel

Review Questions A11s,oer tlte fol/01ui11g questions 11si11g tlte infornmtion provided in this chapter. Know and Understand 1. What are the three times that make up a resistance welding schedule in the order that they occw·? A. Weld ti.1ne, hold time, squeeze titne. B. Hold time, \veld time, squeeze time. C. Squeeze time, weld time, hold time. D. Hold ti1ne, squeeze time, weld time. 2. The tenn pneu111aHc 1neans _ _. A. operated by spring pressu1:e B. operated by oil pressure C. gear-operated D. operated by air pressure 3. True or False? The flat electrode face design is the most commonly used. GOOd heart-Wll!Wx Co Inc

Refer to Figure 19-9 to answer questions 4-6.

Apply and Analyze

4. What current is required to resistance spot weld two pieces of 0.060" (1.52 mm) mild steel and obtain a Class A weld? A. 6800 amps. B. 9000 amps. C. 11,600 an1ps. 0. 17,500 amps. 5. What weld time is required to obtain a Oass B weld when resistance spot welding a 0.036" (0.91 n1n1) piece to a 0.090" (2.29 mm) piece? A. 10 cycles. B. 21 cycles. C. 44 cycles. D. 60 cycles. 6. To weld a piece of 12 gage metal to a piece of 14 gage metal, what welding force, time, and cw-rent give the best quality weld? A. 1600 pound force, 29 cycle 1,veld time, 16,100 amps. B. 1100 pow1d force, 21 cycle ,,veld time, 13,300 amps. C. 960 pound force, SO cycle weld time, 12,200 amps. D. 300 pound force, 6 cycle weld time, 6100 amps. 7. True or False? The electrode force on a pneun1atic force system is changed by adjusting a regulator. 8. True or False? A spot weld that squirts out molten metaJ is called a blowhole. 9. True or False? "Dressing an electrode" lneans reshaping an electrode. 10. _ _ describes metal that was not successfully welded together. A. Weld peel B. Weld nugget C. Expulsion D. Flashing 11. Tr11e or False? Spot 1,velding aluntlnum uses the same a1nount of current as spot welding 1niJd steel. 12. True or False? A sean1 welding mad,Jne uses an intermittent current to produce a seam ""ith overlapping spots. 13. True or False? A seam welding machine must have a lo,,ver duty cycle than a spot welding machine. 14. Which type of resistance welding is used to weld a longitudinal seam in pipe? A. Projection ,,velding. B. Flash ¼'elding. C. Upset we lding. D. Butt seam ,,velding. 15. True or False? High-frequency current is used to weld thin sections of metal.

1. What is the basic principle of resistance welding? 2. What does a step-down transformer do? Refer to Figure 19-9 to answer question 3.

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3. Using a portable spot welding gun that has a maxim tun available force of 600 pounds to join t'\ovo 0.060" (1.5 n11n) pieces of meta], what is the best quality weld that can be made? What welding force, ti.tne, and current give the best quality weld? 4. After setting up the conditions in question 3 and making a weld, suppose the weld still fails with weld separation or weld peel. What h,vo settings might need to be increased to i.tnprove the weld quality? 5. What is forge force and why is it used ¼1 hen spot welding aluntlnum? 6. What is tempering and why is it used when spot welding stainless steel? 7. What are two advantages of projection welding? 8. List three causes of a blowhole or pinhole in a weld. 9. What are two advantages of flash ,velding? 10. What are the dangers associated with resistance welding?

Critical Thinking 1. While n1aking sample welds, you find the weld nugget needs to be larger. Explain how to adjust each of the following to make a larger ¼'eld nugget: ClllTent, weld ti.tne, and weJd force. 2. The electrode face diameter is a variable in RSW. What would happen to the weld quality if the electrode face diameter was changed from 1/4" (6 n,m) to 5/16" (8 mm), with no other changes made to the equipn1ent?

Experiment 1. Set up a resistance spot welding machine to weld two pieces of 20 or 18 gage carbon s teel. InstaJ l the proper electrodes. Set the proper force and weld tin1e. Set the ,veld current to 4000A. Make two "velds. Separate the pieces and 1neasure the weld nugget diameter. Increase the current to 5000A and repeat the test. Increase agai.t, to 6000A and 7000A. Continue i.t,creasing the current until there is expulsion or you reach 14,000A. Make a graph 1,vith the weld current on the horizontal axis and the weld nugget diameter on the vertical axis. What conclusions can you make from the graph?

Special Processes

Special Welding Processes Process W9ldlng Sysmms, Inc.

Learning Objectives After study ing this chapte r~ you will be able to: • Identify special v,elding processes by their AWS abbreviations. • Describe the principles of and equipment used in specia l arc welding processes. • Describe the principles of and equipment used in sol id-state welding processes. • Describe the principles of and equipment used in other welding processes (electroslag welding, electron beam ,,velding, and laser beam welding). • Take appropriate safet y precautions when performing special welding processes.

eneral classifications of we lding include unusual or special methods that have been developed for joining rnetals together. Some of these special processes n1elt the base n1etal. Some processes do not melt the base m etal but still weld or join the materials together. Many of these methods are hig hly specialized. Some are patented and can be used only with the permission of the patent o,.vner. Other welding methods have been developed as special adaptations of standard oxyfuel gas, arc, or resistance welding processes.

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20.1 Special Welding Processes Three of the main American Welding Society classifications of welding processes are arc welding, oxyfuel gas •..velding, and resistance welding. Welding is

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much broader than these three main g roups. There a re many special ,,velding processes. Son,e processes fall into the three main ,,velding process classifications; others do no t. The s pecial processes that are not included in the three main welding classifications fall under the classifications of solid-s tate ,,velding (SSW) a.nd other welding. Review Figure 4-1. Many of the welding processes that a re considered special are used regularly in industry. The following are special welding processes. Arc Weldin g (AW) Processes • Submerged arc welding (SAW). • Electrogas welding (EGW). • Narrow g roove welding (not a process separately recognized by AWS). • Arc stud welding (SW). • Plasma arc ,,velding (PAW). Solid-State We lding (SSW) Processes • Cold welding (CW). • Explosion v.relding (EXW). • Forge 1,velding (FOW). • Friction welding (FRW). • Friction s tir welding (FSW). • Ultrasonic welding (USW). Other Welding Processes • Electroslag welding (ESW). • Electron beaJn welding (EBW). • Laser beam welding (LBW).

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536

Modern Welding

20.2 Arc Welding (AW) Processes When most people think of welding, they think of arc welding. The four main arc welding processes are shielded 1netal arc, gas metal arc, flux cored arc, and gas tungsten arc welding. In these processes, an arc is struck between an electrode and the base 1netal. The same is true for the special arc welding processes covered in this chapter. The heat of an electric arc is used to n1elt the parts to be joined.

20.2.1 Submerged Arc Welding (SAW) S11btnerged arc welding (SAW) involves striking an arc between a consun1able electrode and the base metal while the end of the electrode is buried in a granular flux. See Figure 20-1. The electrode is continuously fed to the weld. Granular flux is placed in front of the weld pool and completely covers the ,,veld joint and the weld pool. The arc melts both the base metal and the electrode. The heat of the arc also 1nelts some of the flux. The flux adds alloying elements to the weld pool and also removes irnpurities from the weld pool. As the Aux and iinpurities cool, they form a slag covering over the weld. This slag covering protects the weld as it cools.

The SAW process is used to weld the following metals: • Carbon steel. • Low-alloy s teel. • Stainless steel. • Chromium-molybdenum s teel. • Nickel-based alloys. Some submerged arc ,,velding n1achines can produce s ingle-pass welds on square butt joints up to 1/2" (13 mm) in thickness and fillet welds with up to 3/8" (10 mm) legs. Thicker plates can be ~velded in a single pass by preparing a groove butt joint. Common electrode sizes used with submerged arc welding range fron1 1/16" to 1/4" (1.6 mn1 to 6.4 mm). Typical currents range from 300A to 1000A for automatic SAW with a single electrode and a DC power supply. Higher currents are required when more than one electrode is used. SAW can be done ¼7ith either an AC or a DC power source. Usually, a constant voltage (CV) power source is used. A constant current (CC) power source is preferred for welding with largediameter electrodes. A typical sub n1erged arc welding 1nachine, Figure 20-2, has a power-operated carriage. The carriage can be used on a standard track or a te1nplate track, or the 1netal being welded ca n be mounted on a carriage and moved under the welding head. A variable-speed motor controls the travel speed.

AC or DC+ - electrode - - - - - - - - - - - - - -

Welding electrode

Ground Solidified flux

• Direct,on · of Welding •

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L-- - Welding "flux" tube

V-groove if required

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Base metal Weld backing if required

Weld metal Granulated flux / Workpiece

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Figure 20-2. A submerged arc welding outfit with all components labeled including a flux delivery system and wire feeder.

A hopper feeds granular flux to the joint just ahead of the a1·c. T his flux protects the electrode, arc, and weld pool from ox idatio n. T he heat generated by the arc melts the adjacent flux g ranules. As the flux solidifies, it covers the weld with an airtigh t slag that protects the weld fro1n ox ida tion until it cools. The slag covering is easily removed with a chipping hammer. A completed weld bead with excellent contour is revealed. See Figure 20-3. The unn1elted Au x

•

granules can be used again. In some applications, special equipment vacuums up the unused flux and feeds it back into the hopper. See Figure 20-4. The constant voltage or constant current power supply controls the welding voltage and current. The voltage and current are displayed on 1neters, a voltmeter and an ammeter. The operator can monitor the meters to verify that the voltage and current are within conh·ol limits or between the allowed high and low values.

•

•

Th& Lincoln El9CtflC Company

The Lincoln Elecuic Company

Figure 20-3. View of a completed submerged arc weld. The slag is easily removed to reveal a clean, high-quality weld.

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Figure 20-4. A submerged arc weld on pipe. Flux is b eing applied in front of the electrode. Unmelted flux is returned to the hopper by a vacuum pickup.

53 8

Modern Welding

SAW is an efficient arc ,~relding process. There is no visible arc, no spatter, no loss of electrode material, no shielding gas is used, and the ,,velds are of high quality. Submerged arc welding is excellent for production jobs like ships, bridge decks, plates, and pipes that require long, thick weld seams. See Figure 20-5. Consuniable electrodes (electrodes that melt and become part of the weld) are furnished in large coils. Variable speed electric motors control the electrode feed speed. The controls for the process are mounted on the welding outfit, as shown in Fig ure 20-2. Submerged arc welding can be done using semiautomatic, mechanized, or automatic welding equipment. In each case, the welding operator must set the ,,vire feed speed, travel speed along the joint, the voltage or amperage (depending on the type of power

source), a.nd the electrode extension, These are the same valiables as in gas metal arc welding. For automatic or mechanized SAW, the operator must initially align the rnetal to be ,.velded ,.vith the electrode and welding head. SAW is most frequently done with 1nechanized equipment. The welding gu.n is driven along a searn by an electric motor attached to a beam or along a track. The operator must align the welding head with the weld seam prior to starting the weld. SAW is most often done with a single electrode. More than one electrode may be used if the finished weld must be ~ride, filling a deep groove ,.veld, ,.velding a large fillet weld, or higher welding speeds are desired. Large welds c,u1 be completed quickly using this 1nethod. When two or n1ore electrodes are used, they are usually arranged in a tandem position, as shown at the top of Figure 20-6.

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•

' The Uncoln Electric Company B Figure 20-5. Submerged arc welding is well-su ited for large-scale construction and fabrication projects. A- A SAW weld in progress on bridge construction project. B- Using SAW to weld a joint on a long steel plate.

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111e u ncorn Electric compaf11

Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 20 Special Welding Processes / Power source

Multiple power connection tandem position

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539

20.2.2 Electrogas Welding (EGW) The elect rogas welding (EGW) process is an arc welding process that is theoretically capable of v>1elding sections of metal of virtually any thickness. In practice, EGW is used to make welds on thicknesses ranging from 3/8" (10 mm) up to about 4" (100 mn1). These welds can be n1ade in one pass without an edge preparation. See Figure 20-7. The EGW process is used almost exclusively to weld butt joints in the vertical welding position. However~ T-joints, V-groove joints, and double V-groove joints are also ,,velded. The equipment required to produce an electrogas ,,veld is simiJar to that used for GMAW or FCAW and includes the following: • A DC power source for each electrode used. • One or more solid or flux cored elech·odes and electrode guide tubes. • One or more wire feeders. • Water-cooled backing shoes. • Shielding gas (if a solid electrode is used).

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Guide rollers Series connection transverse position

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Plate 1

Flux cored electrode Molten weld meta-:.1..__ Solidifying _ _ weld metal Solidified ---r metal

Gas shielding Water ~ ~ - - r Gccilirculation

Goodh981t•Wl/lcox Publishor

Three different ways to use multiple electrodes in submerged arc welding. Figure 20-6.

Plate 2 SAW is usually done in the flat welding position. ltis not normally used to weld joints horizontally, vertically, or oved1ead, but can be used to n1ake horizontal fillet welds. On other types of out-of-position welds, the loose, g1-anular flux and molten metal ,-vould not stay in place. The flux remaintng over the completed weld acts as a heat insulator. As a result, the weld remains very hot for some time after it is completed. To avoid btu·ns or fire hazards, be sure to follo,-v a ll safety precautions. Approved goggles, gloves, and clothing should be worn. Good ventilation is necessary.

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connections completed \-1181d

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Cutaway drawing of an electrogas weld in progress. The shoes are water-cooled and are moved up as the weld proceeds. A s hielding gas or flux cored electrode is used to protect the molten metal from oxidation. Figure 20-7.

540

Modern Welding

Solid electrodes can b e used with a shielding gas fed into t he joint area. Self-shielding flux-cored electrodes a lso can be used. If self-shielding electrodes are used, no additional shielding gas is required. Water-cooled backing shoes are mounted on each s ide of the weld joint. They act as barriers that keep the n1olten weld metal from flo,,ving out of the joint. The shoes move up,,vard as the weld proceeds from the bottom to the top of the joint. Depending on the thickness of the joint, one or more flu x-cored e lectrodes are fed into the weld pool simultaneously. Standard wire drive units move the electrodes through wire guides do·,vn to the weld surface. The electrogas welding process is started by initiating the a rc on a s tar ter block that is tacked to the bottom of the joint. The cooling water and s hielding gas (when used) begin to flow as the arc is struck. If a preflov.1 time is set into the madune, the water and shielding gas (when used) begins to flow before the arc is struck. To ensure an equal distribution of heat fron1 the arc(s), the e lectrodes may be oscillated (moved from side-to-side) within the joint by oscil lating equipment. A carbon d ioxide (CO2) or an argon-carbon d ioxide (Ar-CO2) mix tw:e is used as a sh.ielding gas w ith solid electrodes. Electrode diameters of 1/16: 5/64': 3/32': or 1/8" (16 1nm, 2.0 mm, 2.4 mm, or 3.2 mm) can be used. A consumable or nonconsumable e lectrode guide can be u sed in electrogas welding. The consumable guide addsS¾- 10°/4 of the filler metal to the weld.

ch ange to the GMAW welding process, AWS does not recognize this as a separate process. However, special equipment is required to deliver the welding w ire and s hie lding gas to the bottom of a deep, narrow v.1eld joint. The advantage of narrow groove welding is that it saves materials an d tune. However, some special equipment is required .

•

Narrow groove we lding is sometimes referred to by the nonstandard term narrow gap welding .

Nonnal-width V-g1uove, U-groove, and bevel-groove joints provide enough space for a welder to move an electrode (such as a SMAW electrode) from one side of the groove to the other. This helps ad1ieve good penetration into the side walls of the groove. There is n ot en ough space in a narrow groove joint to allow the ~velder to 1nan ipu late the e lectrode s ide-to-side. In narrow groove welding, the first weld pass is made at the root of the ,,veld. Multiple additional v.reld passes are made to fill the iveld joint. GMAW 1nust be used because slag from other welding processes cannot be cleaned fro111 the narrow gap. A proble1n with nar row g roove we lding is lack of penetration into the sid e walls. In order to obtain penetration into the walls of a n a1Tow g roove joint, the a1·c and e lectrode must oscillate, or move from one side of the joint to the other. A few methods are u sed to direct the arc to the side walls. One method is to bend the e lectrode into a wave fonn as it is fed into the joint. See Figure 20-9. Another method is to use two electrodes that are twisted a round each o ther before being fed into the joint. With this 1nethod, the arc occurs in a circular manner as the electrode melts. See Figure 20-10.

20.2.3 Narrow Groove Welding Narro,v groove iveldi11g was developed to v.1eld thick sections with a g roove that is 111uch narrower than normal. See Figure 20-8. T he welding process is gas metal arc welding (GMAW). Because t here is no

SMAW

Nonstandard Terminology

Narrow Groove

SAW I

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-9mm-16mm Goodhoart~WiUcox Publisher

Figure 20-8. A comparison of the weld joint preparation for SMAW, SAW, and na rrow groove welding. Note that the

narrow groove joint requires less weld metal to fill the groove. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 20

Arc stud welding is a welding process that quickly

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20.2.4 Arc Stud Welding (SW)

Oscillations to bend electrode

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Special Welding Processes

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• Goodh••n•IVillcox Publlshor

Figure 20-9. A method used to bend the electrode wire into a wave form and guide it into the weld joint. The wire oscillates across the weld pool as the weld progresses.

Wire guide

and efficiently welds stud s, nuts, pins, hooks, brackets, and other fastening devices to plates and other s1.trfaces. The process permits studs or nuts to be attached to a structure without piercing the 1netal. Arc stud ,-veldingeliminatesthe need to drill or punch holes in the main structure. This "no hole" advantage of stud welclli1g saves the work of 1nechanically fastening an object to the main structure using bolts, rivets, or screws. An arc stud welding system, shown in Figure 20-11, includes the following: • Po,..ver supply. • Arc stud ,-velding gun. • Cables. • Studs. • Feed system for automated systems. • Shielding gas supply for welding aluminum and some other □1etals. Power supplies can be one of the following: • Inverter power source. • DC power source, trans former-rectifier. • Capacitor discharge power source. Arc stud welding guns are one of the following types: • Servo motor di;ven weld head. • Clutch action weld head. Stud feeder

Power source Weld cable

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Backing bar Goodheart-Willcox Publisher

Figure 20-10. Two wire electrodes are twisted before being fed into the weld pool to create an arc that circulates in the weld groove.

Another method is to use a bent contact tip that rotates left and right and directs the arc from side-toside as the weld travels a long the joint. A final method is to use two electrode "vires. Each is directed toward one side wall of the joint. Copvrighl Goodheart-WIilcox Co. Inc

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""'

Orifice

T he arc used in PAW can be a transferred or a nontransferred arc. See Figure 20-19. A transferred arc is created be tween a n egative electrode (DCEN) and a positive workpiece. The a re fo rins bet,veen the electrode and the base metal, as is the case with o ther forms of arc welding. A nontra n sferred arc is an arc between the negative elec trode and a positive constricting nozzle. With a n ontransferred arc, the workpiece is n ot a part of the elec trical circuit.

Constricting orifice length

Electrode setback

545

Transferred

_ _ _ Orifice gas passage

L

I-

j_ Shielding gas

t

dlamete~,-------Ba-s_e_metal _ _ _ _ _ __,,~

1

Torch standoff Gooer

Figure 20-21. Variables to be used when plasma arc welding stainless steel.

Copyr!ghl Goodheart-WIiicox Co Inc,

Chapter 20

20.3 Solid-State Welding (SSW) Processes The American Welding Society defines solid-state 1veldi11g as follows: "A group of welding processes that produce coalescence by the application of pressure without melting any of the joint components." Coalescence 1neans to g rovv together. Solid-state welding processes join metals with the application of force. These processes do not use an arc, a bea1n of energy, a flan1e, or res istance to heat metal. These processes can be done when the metal is cold, warm, or hot. However, the temperature does not exceed the n1elting points of the n1etals. The 1netal to be joined is heated (if necessa1y) to a point where the pieces can be forced together without fracturing. No fi ller metal is needed. The American Welding Society recognizes the follo,,ving as solid-state welding processes: • Coextrusion welding (CEW). • Cold welding (CW). • Diffusion welding (DFW). • Explosion welding (EXW). • Forge welding (FOW). • Friction welding (FRW). • Friction stir vvelding (FSW) • Hot pressure welding (HPW). • Roll welding (ROW). • Ultrasonic ,.velding (USW). The most com1non of these processes are covered in the follo,,ving sections.

20.3.1 Cold Welding (CW) The theory of the cold 1veld ing (CW) p1:ocess is that pressure at the surface creates fusion only a few molecules deep. This is sufficient to hold the material together and provide good strength. T his room-teinperature pressure welding process works best on soft, ductile n1etals like a luminum and its alloys; copper; and alloys of cadm iu1n, nickel, lead, and zinc. No heat is needed. Both butt and lap joints can be made with this process. Two dissimilar metals can be joined. Applications of cold welding include butt welding aluminum, copper, gold, silver, and platinum wires together. Cold welding is an upset process, which is a process that forces 1netal fro1n the joint area until clean n1etal from each piece contact each other. Diameters as sn1a ll as .0025" (.06 mn1) up to .50" (13 mn1) can be cold welded. Lap welding includes electrical

Copvrighl Goodheart•Wlllcox Co. Inc

Special Welding Processes

547

connections in whic h an alum.inu1n wire can be cold welded to a copper terminal. In CW, cleaned metal pieces are forced together under considerable pressure. The ductility of the 1netals produces a thin but true fusion condition. Where the metals are pressed together, enough pressure must be applied to reduce their thickness to about o nefourth of the original thickness. Aluminum, when welded by this process, has a tensile strength of up to 22,000 psi (150 MPa). Figure 20-22 shows typical cold welded lap joints. The metals to be joined by cold welding must be carefully prepared. Oxides a nd other contan1inants must be completely removed. A wire wheel, turning at a high speed of about 3000 ft/1nin (15 m/sec), is satisfactory for cleaning 1netals to be cold welded. This method is better than chemical methods because residual solvents often 1·emain on the metal surface after cheinical cleaning. The design of the tool for imposing pressure on the metals is important. Dies 1nust be designed to compensate for the va1ying hardness of the metals. For example, for cold welding a lap joint of aluminum to copper, the tool must have twice as 1nuch contact against the softer aluminu111.

,

~ .

- . .·

/.

•· • · -Fu'sion

••

• area .

Kelsey-Hayes Co.

Figure 20-22. Samples of cold-welded parts. The welds are aluminum to aluminum. Notice the large indentation of the surface.

548

Modern Welding

Cold welding tools can be either hand-, pneurnatic-, or hydraulic-powered. Figure 20-23 shows a hand-operated oold \>\7eld:ing tool. Typical hand-operated tools can weld alum inum up to a combined thickness of 0.080" (2 111111), or copper to 0.060" (15 mm). Figure 20-24 shows a pneumatically0powe1ed unit. Weld times to oomplete a oold weld are usually less than one minute. It does take time for the molecules to be fo1ced together and multiple upset operations to be oompleted. The result is a strong "''eld. The strength of a oold weld often is greater than the strengths of the individual metals being welded. When cold welding, the operator should wear gloves, a face shield or safety goggles, and approved clothing.

20.3.2 Explosion Welding (EXW) Meta ls have been successfully welded with the energy from an explosion, using a process called explosion welding (EXW). This process is very dangerous. It should be perfonned only by explosive experts. Special permits must be obtained from local, state, and federal authorities before this type of work can be done. The most common application of explosion welding is to forn1 plates with cladding welded over the entire area. Cladding is a covering of a different 1naterial over a base material. Very different metals can be explosion welded together. Metals that are not oompatible for welding can be welded using this solid-state welding process. BWE Ltd.

Figure 20-24. A pneumatic-operated cold

weld machine. This machine is foot-pedal-operated. It can weld aluminum up to .25" (6.35 mm) and copper up to .20" (5 mm). Weld preparation is not required. As an example, a cladding of titanium can be ,~relded

BWE Lttl.

Figure 20-23. A hand-operated,

battery-powered cold weld machine that can cold weld aluminum wire .080" (2.0 mm) diameter and copper wire .047" (1.2 mm) diameter. Weld preparation is not required.

to a mild steel plate. Alunlinum plate can be welded to steel. EXW is the only process that can join these over a large area. Another application where dissimilar metals require joining is the welding of transition joints used in the cryogenic (very low te1nperature) industry. Explosion welding is used to join a large sheet of material to another large sheet over the entire stuface area. Often the base metals are thick, with the thinner metal being 1/4" (6 mm) thick and the other piece n1easuring 1" (251n111) to 1nany inches thick. The n1etal to be explosion welded is not set up as a butt joint; it is arranged as a lap joint. An example is to weld an 8' x 20' (2.4 1n x 6.0 1n) piece to another piece the sa1ne size over the entire surface area. The result is one piece 8' x 20' (2.4 m x 6.0 m) of two oftendissiJnila r metals. This plate can be further processed Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 20 Special Welding Processes by rolling or n1achining to make the d esired Knished product. This application has a low cost material, like mild steel, covered with a very high cost metal, like stainless s tee l or titan ium. The res ult is a lov.rer overall cost material with desired properties on one sid e. To prepare an explosion weld, the metals to be welded are g round very flat on the s ide to be welded. The plates are set up parallel to each other with a small designed gap between the plates. A protective material is placed over the metal, a nd then the explosive is placed on the metal surface. See Figure 20-25. When detonated, the explosion forces the plates together at high velocity. A jet action removes son1e material from the plate surfaces and provides an instant cleaning action. Th e force of the explosives causes sw·face ripples in the 1netal. These ripples lock, or weld, the two metals together. Preparation of this process takes time, due to the safety concerns related to handling explosives. O nce the explosive is detonated, the welding process is completed almost instantly. After being welded, the plates can be ro!Jed to stra ighten and further rolled to reduce the thickness. Explosion welding can successfully weld steel to stainless or alloy steel; a luminum to steel or stainless steel; copper to s teel, stainless steel, or a luminum; titanium to steel or stainless steel; and many other metal combinations. These could n ot be welded wi th other welding processes. This highly specia lized and d angerous weld ing process is to be done o nly by experts ,,vith knowledge and experience. Many special permits are required.

549

No one is a l lowed to be near the process at the rune of detonation. Safety glasses an d ear protection must be worn when working around explosion welding.

20.3.3 Forge Welding (FOW) Forge ,,velding (FOW) is the oldest me thod of fusing two pieces of metal together. This t ype of welding requires considerable skill on the part of the forge welder, also called a blacks,nith. Forge welding is used to effectively join pieces of solid bar stock toge ther. The pieces of n1etal to be forge welded are heated in a blacksmith's forge (see Figure 4-24). Metal to be welded is heated to a white lzeat, just short of the rapid oxidizing or burning point. A blacksmith usually swages (enlarges) the ends to be joined. They are then placed together over an anvil so the surfaces can be forced against one another by pounding with a hammer. The pressure of the hammer blows fuses the two pieces together. See Figure 20-26. To speed their work, n1oden1 blacksmiths typica lly perforn1 this type of welding using power hammers or presses.

Ends are first swaged

A

B White hot

Explosive material

t( ~

Cladding

•

Hammer

C Base metal

Fusion starts in the center

t C ,K◄-Hammer D

Partially fused area GoOd/JtJatt•WIIICox PutJ#1S/JQ(

Figure 20-25. The top drawing shows the setup for an

explosion weld. When the explosive material is detonated, the cladding is forced against the lower plate with a lot of force. A jet action cleans the surface of each piece ahead of the impact The weld is completed almost instantly. See also Figure 4-23. Copvrighl Goodheart-WIilcox Co, Inc

E

Completed weld Ooodhearr-Willcox Plltiisher

Figure 20-26. The steps used in forge welding.

550

•

Modern Welding

Nonstandard Terminology

Forge weld ing is sometimes referred to by the nonstandard terms hammer welding or blacksmithing.

A forged weld, when done correctly, has every quality of the original metal. Forge welding is still used today to produce c us to1n-1nade knives, swords, hammers, and various tools, as well as antique hardware and utensils. Blacksmithing is alive a nd well in the United States and around the world. There will always be a demand for custom-made forged and forge welded products. See Figure 20-27.

Le,ne, Vadim lShurrers,oclt.com

Figure 20-27. An assortment of custom-made knives and tools made with forge welding techniques.

20.3.4 Friction Welding (FRW) Friction generates heat. If I\NO surfaces are rubbed together, enough heat can be generated to fuse the parts together. Friction welding (FRW) is based on this principle. A friction weld is prepared by mounting the pieces to be welded in a chuck or fixture. One fixture is stationary; the other spins. For this reason, friction welding is also referred to as rotary friction ,uelding. The pieces to be welded are brought together under pressure. Friction between the parts raises the temperatw:e to a welding heat. After a preset time, the spinning part s tops. The parts are then forced together. See Fig ure 20-28. After being allowed to cool, the friction vveld is complete, and welded pa1ts are removed from the machin e. The welding process is completed in about 15 seconds. The progression of a fricti on weld is shown in Figure 20-29. Figure 20-30 sho,,vs con1pleted friction welds. Weld s treng th of a friction weld is the same as that of a forged weld.

ManutacttN/ng Tochnology, Inc.

Figure 20-28. A friction weld in progress. One part is rotated at a high speed while pressed against the stationary part. The resulting friction heats the parts, but neither part melts. After the parts are red hot, the spinning part stops and the two pieces are forced together, creating a forged weld.

GOOean-WlflCOX PuC/iSher

Figure 20-29. The steps in friction welding two rods of 1" (25 mm) mild steel. The rod at the left is rotated at a high speed while the rod at the right is held stationary. The rods are then forced together. The friction creates enough heat to make a sound butt weld. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 20 Weld

Special Welding Processes

551

Weld

Manu1act1vlng Tec1mo1ogy. inc. B Figure 20-30. Completed friction welds. A-Steel yokes are welded to steel shaft using friction welding for this drive shaft application. 8-Friction welding is used to join nickel-based heat-resistant steel to medium carbon steel for manufacturing turbochargers.

A

Manutacwrlng Tec~no/Ogy, Inc.

Parts to be welded are mounted in a machine that often look s like and functions like a lathe. See Fig1tre 20-31. For safet y, a sliding door is dosed to isolate the welding operator from rotating parts inside the FRW 1nachine. Once started , the process controller completes the ,.velding process. In friction welding, the spinning part of the chuck is driven by a motor. The s pinning part is 1nade to rotate

while the metal pieces are in contact. A small constant pressure is applied, causing the 1netal to heat. Once the heating is complete, rotation is s topped, and a great force is applied along the axis to join the surfaces. The proces.s is similar to upset or flash welding, but friction is used to generate the heat, not e lectrical current. Most friction welding is done to weld ferrous parts. FRW is also wel l-suited for joining dissimilar 1naterials

Manulacruring Technology. Inc.

Figure 20-31. This friction welding machine welds engine valve stems made from two dissimilar metals. Friction welding can eflectively join different materials that are impossible to join using other techniques. Copvrighl Goodheart-WIilcox Co. Inc

552

Modern Welding

to mild steel in production. Aerospace, au tomotive, agricultural, oil field, and ntllitary industries use friction v.relding to join similar and dissimilar metals. No protective atmosphere is re9uired , w hic h saves a significant amount of time and material Friction welding is a clean and e fficient welding p rocess. Son1e n1ad1ining n1ay be needed to reD1ove flared metal around the •..veld joint. Safety glasses m u st be worn, which is a standard requiren1ent in most metal fabrication industries. Parts will be very hot when welding is completed. Approved clothing and g loves a re required.

20.3.5 Friction Stir Welding (FSW) In friction stir welding (FSW), parts to be welded are placed on a backing plate and securely clamped in place. A special rotating tool is used to ma ke the weld. This tool h as a w ide shoulder that contacts the metal surface and a probe or pin that protrudes into the part. See Figu re 20-32. As the tool rotates, it generates heat through friction and pressure. Enough heat is generated to plasticize (soften) the b ase 1netal, but n ot enough to liquefy it. Th e rotating tool mi xes together the material from each base metal. Material flows from the leading edge of the tool and cools as it leaves the traiJ ing edge. Figure 20-33 s hows a butt joint in progress using a friction stir welding machine. Friction stir welding was initially developed to weld a lun1inum. Most commercia l applications are on aluminum parts in industries such as aerospace, shipbuilding, and automotive. Copper, magnesium, lead,

Manuf:,c,uring Technology, Inc.

Figure 20-33. A friction s tir weld in progress.

zinc, and titanium have also been friction stir welded. Friction stir welding of low and high strength steel can also be done, b ut it is not as popttlar as aluminum and other softer metals. Butt joints a re the most conunon joint design welded with FSW. Ho,¥ever, other joint designs can be friction stir welded, as sh own in Figure 20-34. Friction stir welding produces excellent high-9uality ,velds and high-strength joints with minimal distortion. FSW is an automated, repeatable process. Joint preparation is nunimal Welds can be made on a.luminum fJ·om .07" to 2.95" (1.7 mm to 75 mm) thick. Material thickness mu st be controlled closely w hen making 100"/o penetration welds to prevent defects. The 1ned1anical properties of the completed '\>velds are very good. Sample bend and tensile test coupons are shown in Figure 20-35.

Downward force

~ Leading llllr edgeof the tool

A

Tool shouldei

zone

Trailing edge of the tool

Profiled probe TWI

Figure 20-32. A shouldered tool with a protruding probe

or pin is made to rotate and travel along th e joint to be welded. The metal is plasticized due to the heat from friction and applied pressure. Materials from each side of the weld joint are mixed together by the stirring action.

TWI

Figure 20-34. Joint designs. A-Joint designs possible

with friction stir welding. 8-Examples of completed welds. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 20

Special Welding Processes

553

Welding tip

I

. '

.

.

:

Anvil-like

base

100mm

r TWI

Figure 20-35. Friction stir welds show very good bend test results (top). Tensile test samples (bottom) show that the material fractures in the heat-affected zone.

20.3.6 Ultrasonic Welding (USW) In 11ltrasonic 1veldi1zg (USW), metals are clamped together under pressure and high-frequency vibrations are introduced into those metals tlcrough a welding tip or so11otrode. The vibrations, at frequencies above those hwnan beings can hear, break up the surface films and cause the solid 1netals to bond tightly together. This happens without the use of heat and without melting the metal Careful cleaning of the metals is not necessary. The low clamping pressure reduces deforn1ation. USW equipment contains one or n1ore transducers that convert high-frequency electrical power into mechanical vibration at the same frequency. The welding frequency is usually between 10,000 Hz (cycles per second) and 75,000 Hz. The metals to be ~velded are positioned between the transducer and a small anvillike base, Figure 20-36. In addition to the transducers, a coupling system trans1nits the mecl1anical vibration to the welding tip and into the metals being joined. As a production tool, ultrasonic welding is used to weld fine wires, semiconductors, foils, batteries, and microcircuits. An ultrasonic wire ,-velding machine can be used to splice stranded wire. See Figure 20-37. Battery assembly using ultrasonic welders has beco111e an important nev.1 process for battery n1anufacturers worldwide. Ultrasonic welding has several advantages. There is no heat distortion in the parts. No fluxes or filler metals are required. Thin sheets can be welded to thick sections. Copvrighl Goodheart-WIilcox Co. Inc

sonot>ond Ulrrasontos. Inc.

Figure 20-36. An ultrasonic spot welding machine. This machine uses high-frequency vibrations to weld nonferrous similar or dissimilar metals without added heat, current, or consumables.

Sonobond Ulua.sooics. Inc.

Figur e 20-37. An ultrasonic wire welding machine. This machine can splice stranded wire up to 100 sq. mm and tinned wire up to 60 sq. mm, creating a solid-state metallurgical bond with minimal electrical resistance.

554

Modern Welding

The pressures used are less, and the welding tin1es shorter, than those used in resistance welding. Many types of metal can be joined together or to other metals. The maximu n1 thickness that can be "''elded is 0.10" (2.5 mm) for aluminum and 0.040" (1 mm) for harder materials. The equipment can be operated by semiskilled personnel with mini mal trai ning. Operators should wear safety glasses and other personal safety equipment as required by the working environment.

20.4 Other Welding Processes Otlierivelding processes are those that do not 1neet the definition for oxyfuel gas welding, arc welding, resistance weldi ng, or solid-state welding. These processes are listed in Figure 4-l The most common of these processes are explained in the following sections.

20.4.1 Electroslag Welding (ESW) The electroslag ivelding(ESW) method was developed to weld very thick sections or joints. The ESW process eli1ninates the need for multiple passes and for bevel-, V-, U-, or J- grooves. Metal thicknesses up to 30" (76 cm) have been welded with this process. The ESW process is used to weld joints in a vertical welding position. Figure 20-38 shows a diagram of an electroslag welding operation. Equipment for ESW includes the follo,-ving: • DC power source. • One or more electrodes and elech·ode guide tubes. • One or more wire feeders and oscillators. • Backing shoes (molds). • Flux hopper and distribution tube or flux-filled electrode wire.

0

Flux hopper

0 Horizontal drive Direction of motion

Wire

Molten slagMolten weld metal Water system/ ' Work->-1

Copper shoe

0

Vertical drive Power leads

Power source

Goodhoart~WiUcox Publisher

Electroslag welding operation showing the flux hopper, electrode wire feed, shoes, and the vertical rail on which everything moves as the weld progresses. Figure 20-38.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 20 Special Welding Processes Before t he weld is started, a starter block is tacked to the bottom of the joint. U-shaped braces are tacked across the joint to hold it together while welding is being perfonned. The electroslag process is started by producing an arc between the electrode(s) and the joint bottom. Flux is added from a hopper or fluxfi lled electrode wi re an d forms a layer of 1nolten slag. The arc is no longer needed once a large layer of slag has formed. Since the arc is used only for start ing the process, ESW is not considered to be an a rc we lding process. The resistance to electrical current flow through the molten slag creates the heat necessary to melt the electrode(s) and base 1netal and to keep th e weld pool molten. The electrodes are either solid wire or flux cored. Flux-cored w ires are required if there is no separate flux supply system. The process is fast and requires no edge preparation of the metal. More than one electrode can be used, wh ich permits a thick joint to be we lded faster. See Figu.re 20-39. Water-cooled copper shoes cont ain the 1nolten metal and slag. As the weld is made, the shoes move up the joint. The weld is co1npleted in one pass. Butt joints, T-joints, corner joints, and other types of joints can be n1ade with this process. See Figure 20-40. Welds in butt joints are most contmon. Specially shaped shoes are required for T-joints and corner joints. Mul tiple special shoes are required for some joints.

Butt Joint I I

I I

...

Wire feed rolls and oscillating mechanism mounted on carriage that rises automatically as weld fills the joint Plates In vertical positlon

Face plate #1

Consumable electrodes ---..::::::Molten,_ _ __ slag

Water-cooled copper shoes confine molten slag and weld metal

Molten weld metal Weld metal

Completed weld Goodhoan~~Villcox Publishor

Figure 20-39. A cutaway view of the e lectroslag we lding process. In this application, three flux-filled electrodes are used. The molten slag floats above the weld metal and prevents oxidation.

Corner Joint I I I I I I)

T-Jolnt

--

Edge joint

T-joint

555

Cross weld

I I I

,.c- _

-

-

--

'

--

·/

I I

_ ......,_

l Ooodheart·Willcox Plltiisher

Figure 20-40. Several joint designs used for electroslag welding. The weld and depth of fusion are also shown. Copvrighl Goodheart-WIilcox Co. Inc

55 6

Modern Welding

The extreme heat produced by the 1nolten slag and metal in the weld causes the base metal to melt away from the original joint gap, as shown in Figure 20-41.

20.4.2 Electron Beam Welding (EBW) In e lectron bean1 welding (EBW ), a concenh·ated h igh -energy bean, of h igh-velocity electrons 1nelts the 1ne tal to be welded. The parts to be ,,v elded a re p laced ver y close together, a lmos t touching. The edges to be we lded 1nust be very straight. If the joint is proper! y prepared, an electron beam can 1nake a complete pene tra tion weld in a 10" (250 mm) thick steel plate. See Fig ure 20-42. Electron beam we lding is also very fast. Steel that is 0.25" (6 mm) thick ca n be we lded at a rate of over 200"/m in (5 m/min). A diagram of the principa l parts of a n electron beam gun is shown in Figure 20-43. Current is p assed through a tungsten filament that emits electrons. This part is kn own as the e111itter o r cathode. After leaving the emitter, t he electrons pass t hrough the bias electrodes, which shape the beain. Elec h·on s a re then accelerated towa rd the anode, whic h has a positive charge. A voltage difference between the emitter and the anode can vary between 25,000 V- 200,000 V. This is known as the accelerating voltage. An electromagnetic lens focuses the electron beam. A cutaway view of an electron beam welder is shown in Figure 20-44.

PTR-Precisbn Technologies. Inc.

Figure 20-42. A cros s section of an electron beam weld.

Note how narrow the weld is in relati on to the thickness of the base metal.

- Emitter {cathode)

- Grid

(bias cup)

--j

r-

A. J oint gap

+ Anode

Beam current

+

control voltage

C

-I

-

Highvoltage supply

I+

•

-

Magnetic focusing lens

D. Direction of weld travel

F· Width of weld free

Magnetic deflection coil

C. Surface

I

z-,

of weld

I

■

- Electron beam

Goodhean•Willcox Publisher

Figure 20-41. A macrograph (1.Sx) of a manganese

molybdenum steel joint welded by electroslag process. Note how the base metal melts away from th e edges of the original joint gap.

Target PTR•Preoisbn Technologies, Inc.

Figure 20-43. The basic parts of an electron beam welder. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 20

Special Welding Processes

557

High-voltage cable

Second-stage pumping line Column valve

Lead shrouding (typical)

Column diffusion pump

Upper housing

To holding pump

High-voltage - -cable socKet and Insulator Center housing - - Electron gun assembly

--

First-stage pumping line Orifice assembly - ----1 External airjet _ _ __,

~ Gun access door Beam alignment coil Focusing coll Lower housing Upper orifice Middle orifice Lower orifice PTR-Preclsbn Technologies, Inc.

Figure 20- 44. A cutaway of a nonvacuum electron beam welder.

Electron bea1n welding is usually done in a vacuurn. [n a high vacuum, there are no particles in the air to interfere with the electron beam. In a partial vacuum, there are son1e particles, 1,vhich causes the electron beam to spread out. In a pa1tial vacuum, the parts to be welded must be closer to the source of the electrons to maintain a high energy density. Lo1g Soelery, Miami, FL

Figure 21 -14. Recommended filler metals for welding wrought and cast austenitic stainless steels. The electrode designation can be followed by a -15 or -16 to indicate the currents with which the electrode can be used. Both -15 and -16 are low-hydrogen electrodes. From AWS Welding Handbook, 8th edition , Volume 4, Table 5.15. Copvrighl Goodheart-WIilcox Co, Inc

576

Modern Welding

Argon is the shieldi.ng gas used for 111anual GfAW. Helium or a helium/argon mixture is used for automatic GfAW. This is done to take advantage of the greater heal input and penetration possible with heliu1n shielding gas. The root of the weld should be protected from oxidation with an inert gas during welding. For GMAW, argon 1-vith 1°/4, to 2% oxygen is used. Argon and helium mixtures can be used to produce higher heat input to the ,-veld. In the flat position, the spray transfer method is preferred. Short circuitiJ1g or pulsed-spray transfer is used for 1,velds in other positions.

21 .7.6 Carbide Precipitation (Sensitization) The inherent corrosion-resistance of austenitic stainless steel makes it an excellent, cost-effective material for long-tenn applications in many industries. However, joining austenitic stainless steel presents unique challenges, especially with GTAW. The biggest challenge is carbide precipitation. Another d1alle11ge is distortion. Carbide precipitation refers to the separating (precipitation) of carbides at grain boundaries in a stainless steel oJ· other alloy. A carbide is a chentlcal compound of carbon combined ,,v ith another element. When carbide precipitation occurs, the metal becomes prone to intergranular corrosion when it is exposed to a temperature range called the sensitizing te1nperature. In this sensitizing temperature range, a corrosive at1nosphere results, which causes serious i ntergranular damage. Carbide precipitation is also referred to as

sensitization. The chromiun1 and carbon in austenitic steel are drawn to the boundaries or pulled out of the material during the arc 1-velding process. When these elements separate, they react with the atmosphere, resulting in corrosion and discoloration of the material. This unwanted separation and chemical reaction occw·s when the material is heated (or sensitized) in the range of 800°F to 1400°F (425°C to 760°C). Therefore, the ,-veld zone temperature should be kept below 800°F (425°C). Alternatively, a shielding gas can be used to keep the elements from reacting with the atmosphere. Austenitic stai11Jess steel beco111es stra,-v-colored when. welded properly Carbide precipitation cru1 be easily detected because the metal turns black. Therefore, the color of the metal should be carefully 1nonitored. Material that turns blue or purple indicates possible carbide precipitation. The three main causes of carbide precipitation are too much heat, a travel speed that is too slow, and inadequate shielding gas. Proper travel speed must be

mai11tained to prevent too inuch heat in the ,,veld zone. The correct type and amount of shieldh1g gas helps prevent carbide precipitation. Pure argon provides the best results for thin austenitic stainless steel. When austenitic stainless steel is welded with GTAW, a gas lens should be used. A gas lens replaces the collet body in a standard GTAW torcl1. The lens piece is made of brass and copper and layered with stainless steel mesh screens. The gas lens distributes the shielding gas evenly around the weld pool to protect against carbide precipitation. For full-penetration welds, shielding gas must cover both the front and the back of the ,-veld (or the top side and the bottom side). To prevent carbide precipitation, both sides of the weld must be protected from elements in the atmosphere. A high-temperature solution heat treatment, commonly called sol11tio11-a1111eali11g, is used to 1ninimize carbide precipitation and intergranular corrosion. After welding, the metal is heated to a temperature of 1950°F to 2050°F (1050°C to 1120°C) and then water cooled or air cooled.

21.8 Welding Dissimilar Ferrous Metals Many iron and steel fabrications require welding together metals of different compositions. Examples are welding stainless steels to 101-v-alloy steels, lowalloy steels to carbon steels, a:nd nickel-based alloys to stainless s teeI. The composition and the properties of each metal must be known prior to welding. Du1·ing welding, the composition of the weld pool changes due to the intermixing and dilution of the various alloying elements in each base 1neta L. The fi Uer 1netal tnust be chosen carefully so the resulting alloy in the weld is at least as strong as the weakest of the base metals. The welding parameters must be control.led to ensure that the solidified weld metal n1eets physical and chemical requirements. The filler metal or electrode 1nust be selected to properly 1nix with the base metals being welded ru,d produce a high-quality weld. Controlling the dilution in the welds and weld zone is an iinportant consideration. Quite often, a small 1-veld pool must be maintained to minimize dilution. Multiple stringer beads instead of a 1-vide weave bead are often used to fill a weld joint in order to mi.ni1nize dilution. If dissimilar 1netals have melting temperatures within about 200°F (95°C) of each other, normal 1-velding procedures can be used, and no difficulties

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Chapter 21

norinally occur. Ho1,vever, if the melting te mperature diffe rence is greater than this, welding becomes more d ifficult. It may be necessary to weld a layer of a metal \,vith an intennediate melti ng tempera tu re onto the face of the metal w ith the higher melting tem perature in a process is called buttering. Buttering allo\,vs a weld to be made between two metals of closer melting temperatures. If one of the metals requires preheating, it must be p reheated independently and in isolation fron1 the second piece. Post\,veld heat treatment of dissimilar metals also can be a problem, if one piece requires a treatment different from the other. Another solution to the problem of joining dissimilar metals is to braze them. Brazing can be done at temperatu res that do not melt either part of the joint. When there is no melting of the h-vo base metals, there is no d ilution or intermixing of the two n1etals. However, brazed joints are wea ker than welded joints.

Special Ferrous Welding Applications

577

form at the weld boundaries, and high-ca rbon 1n a.rtensite also tends to form. Both of these are brittle and have very low strength. Weld ing also produces high stresses in this brittle n1etal. Ductile and n1alleable cast irons are easier to weld. Gray cas t iron is cooled slowly an d forms graphite in a fl ake form as it cools. It is brittle and lacks ductility. v\lhen gray cast iron is broken, the exposed metal is gray i n appearance. Gray cast iron ca n be a rc welded using a nicke l or nickel alloy electrode such as ENi-CI, ENiFe-CI, ENiFeMn -CI, ERNi-CI, or ERNiFeMn-CI. The nickel con tent in the fi ller meta l perinits the weld to move or "creep" after welding, relieving stresses and preventing cracks. N ickel-bearing filler metals, being less brittle than the cast iron base rnetal, also make the completed weld easier to machine. Pure i ron filler metal, which conta ins very low-carbon content, can also be used. Ca rbon from the base inetal is diluted in the weld area by the pure iron filler metal and creates a Jess brittle weld. Specification AWS A5.15 descr ibes cast-iron e lectrodes and their recommended uses. Gray cast iron can also be braze welded s uccessfully. Wlzite cast iron forms when cast iron cools very rapidly. The high carbon content remains throughout the microstructure. As a result, the cast iron is brittle and has virtually no ducti lity. It is considered unweldable. The fractured end of white cast iron has a white appearance. Preheating of cast iron produces slower cooling rates. Posh-veld heating slows the cooling rate and reduces the amoun t of hard.ness in the weld and heataffected zone. See Figure 21-15 for reconunended preheat and interpass temperatures for welding cast iron .

21.9 Welding Cast Iron Cast iron contains between 1.7% and 4.P/o carbon, w hich makes the metal brittle. There are four types of cast iron: • Gray cast iron. • White cast iron. • Malleable cast iron or malleable iron. • Nodular or ductile cast iron. All cast irons are difficult to weld because they contain a great deal of carbon. Welding temperatures and an uncontrolled cooling rate can produce undesirable microstructures in the metal. Carbides tend to

Cast Iron Welding Preheat Temperatures Welding process

Type of cast iron

Matrix micro-structure

-

Gray

Arc

Oxyacetylene

•F

·c

•F

·c

70-600

21-315

800- 1200

430-650

Malleable

Ferrilic

70-300

21- 150

800-1 200

430-650

Malleable

Pearlitlc

70-600

21-315

800-1200

430-650

Ductile

Ferritic

70-300

21-150

400-1200

200-650

Ductile

Pearlitic

70-600

21-315

400-1200

200-650 GoOvrought B. extruded C. ferrous D. alloyed 2. All of the following are acceptable methods of cleanmg alummum, except: A. dippmg in a degreaser, then rinsing m water B. soaking in acetone, then air drying C. dipping in denatured alcohol, then rinsmg in water D. brushing with a stainless steel wire brush 3. The major alloying ele1nent in a SXXX series alloy JS_~

A. manganese B. magnesiwn C. s ilicon D. zinc 4. Alummum is usually welded usmg ___ A. GMAW ru1d SMAW B. oxyfuel gas weldit1g C. resistru1ce welding D. GMAW ru1d GTAW 5. True or False? Thoriated tw1gsten elech·odes are recon11nended forGTAW with AC. 6. True or False? DCEN welding cur1·ent produces a cleaning action on aluminu,n.

7. Which of the following is not used for welding thin sections of aluminum with the GMAW process? A. A push-pull wire feed systen1. B. Spray transfer or pulsed spray transfer. C. Preheating of the base metal. 0. Direct curre nt electrode positive. 8. Which of the fo llowing stateu1ents about magnesium is false? A. Magnesium oxidizes rapidly when heated to its n1elting point. B. Magnesium changes color prior to n1elting. C. AC is generally used for welding magnesium. D. Magnesium alloys with zin c added can be spot welded. 9. True or False? The heat in a copper weld leaves the "veld faster than the heat in a steel weld. 10. True or False? Deoxidized copper is comparatively easy to weld. 11. True or False? Phosphor bronze is most commonly ,,velded with the GMAW and GTAW processes. 12. True or False? The electrodes and filler metal used for welding brass contain zinc. 13. For welding titanium with the GTAW process, ·,vhat type of electrode and current is used? A. A pure tungsten or 2°/o thoriated tungsten electrode with AC. B. A pure tungsten or 1% lanthanated tungsten e lectrode with DCEN. C. A2% thoriated tungsten or 2% ceriated tungsten electrode ""ith DCEN. 0. A 2% ceriated tungsten electrode with OCEP. 14. True or False? Zirconium is welded in a 100% inert gas atmosphere. 15. True or False? Thermoplastics can be repeatedly heated and reformed.

Apply and Analyze 1. What filler n1etal should be used to obtain the best strength and ductility when welding a piece of 5052 aluminum to a piece of 3003 aluminum? See Figure 22-2. 2. Which two filler metals produce the best strength when used to ,veld two pieces of 6061 aluniinum together?

3. Wl1y is a backing strip used when aluminum is welded? 4. Explain why using a square-wave power sow·ce set to provide much more DCEN than DCEP is beneficia I for welding alu minu1n. 5. Why does a weld in oxygen-bearing copper have less strength than the base 1netal? 6. What shielding gas should be used for welding 3/8" (9.5 mm) copper? 7. What can cause titaniu1n to beco1ne brittle? 8. What elern·ode motion is used for GTAW of titani u1n to overco1ne tlie s luggish ,veld pool? 9. What welding processes can be used to weld steel to copper? 10. How is plastic heated during welding?

Critical Thinking 1. Suppose you are working in the automobile industry and mass-producing various plastic car parts. What are two advantages of selecting thermoplastic base materials instead of ferrous or nonferrous metals? 2. You have been assigned to select the best a luminum alloy base materials and filler 1netal. for an important p roject. All s ix key characteristics of the welds (ease of welding, strength of joint, ductility, corrosion resistance, reco1nn1ended for service at sustained temperatures above 150°F, and color match) must have an A rating. Using Figure 22-2, give your reco n1mendation for one combination of base and filler metals tha t meets the criteria. Note: While most combina tions do not meet the criteria, there are multi ple combinations found on the chart that do.

Experiment 1. Weld identical aluminum butt joints using 1 /8" (3.2 rnn1) or less base 1netal with and without a 300-series stainless steel, removable backing ship. Compare the results. Conduct the experiment again using a n a lwninum alloy backing strip that is welded in place and becomes part of the joint. Record the results.

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Learning Objectives After studying this chapter~ you will be able to: • Describe the differences between a pipe and a tube. • Identify a variety of pipe and tube fixture tools. • Describe consumable inserts, backing rings, and backing tape. • Describe the procedures for welding pipe or tubing with SMAW, GMAW, FCAW, and GTAW welding processes. • Describe different pipe weldi ng passes. • Use one or more welding processes to weld pipe and tube. • Identify the code or standard used for highpressure applications and that used for lowpressure applications. • Na n1e severa l nondestructive exarnination methods used to determine pipe and tube "veld quality.

ipes and tubes a re used to carry gases and liquids fro□1 one poi nt to another. Pipes of various sizes can carry oil and natural gas thousands of miles from the sow·ce to the user. Pipes are used in many industries to carry fluids around a facility. Tubing carries refrigerants in refrigerators and a ir conditioners; gasoline, oil, and brake fluids in a utomobiles; and water a nd natu ra l gas in homes.

P

A pipe is a hollow cylinder with a thick wall. The pipe wall is thick enough and strong enough to carry high-pressure fluids. The wall of a pipe is generally thick enough for threads to be cut into the wall. Pipes can be assen1bled 1nechanically with threaded joints or with compression fittings. Figure 23-1 shows two types of rnechanical pipe butt joints. Pipes can a lso be welded or joined with a brazed or soldered coupling. Weldable pipe mate1ia ls include carbon steel, sta inless steel, a luminum, o ther metal, a nd plastic. Pipes have a round cross section.

Threaded Joint

Compression Joint

Threaded coupling

Packing

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Figure 23-1. Mechanical pipe butt joints.

60 3

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Modern Welding

A tube is a hollow condujt with a relatively thin wall. A tube's cross section can be round, square, hexagonal, oval, or aLnost any other shape reqwred. A tube's walls are too thin to be threaded. Tubing can be assembled vvith n1echarucal connectors, or it can be welded, soldered, or brazed. Figure 23-2 shows pipe a nd tube butt joints joined by welding, brazi ng, and soldering. A hollow str11ct11ral section (HSS) is used in the construction of buildings and othe r structures. Hollow structure sections can be round, rectangular, or square. The wall truckness is thick like a pipe. HSS can ha nd le high loads and are used as s truc tural elements, such as columns and beams. The steel used for HSS is a higher strength material than 1nost pipe 1naterials. Mu ltiple welding processes are used to ,,veld pipe and tubes, including SMAW, GMAW, FCAW, and GTAW. Other processes can be used. When arc welding pipe, five welding variables must be set and controlled to produce a quality arc weld: • Electrode type and diame ter. • Machine settings: • CU1-rent setting (SMAW and GTAW). • Voltage and wire feed speed (GMAW and FCAW). • Arc length. • Travel angle. • Travel speed. The first two variables a re specified by a welding procedure sp ecification (WPS). A WPS specifies how to prepare the pipe and what electrode and CU1-rent

Welded joint

(voltage) to use. A skilled welder will know the electrode type, electrode diameter, and c urrent setting to use for a pipe welding job. The next three variables are a ll ski.II related. Arc leng th, travel angle, and travel speed are all controlled by the welder. Using proper techruque 1,vill produce a quality ,-veld. Using poor or improper ted1njque will produce a poor weld joint with ,-veld defects. The welder must direct the a rc to penetrate into the root of the weld, the pipewalJs, a nd the previous weld passes. Stringer and weave beads are used in pipe welding.

23.1 Types of Pipe Pipe is made from many types of m eta l and plastic. Different materials a re used for different purposes. Pipe is found in many industries. It is used for petroleum, chemical, and drilling pipelines; gas lines; water supply systems; and water drainage systems, including se,-vers; and consh·uction. Large oil drilling rigs, both onshore a nd offshore, are built using pipe as the s tructura l me1nbers. Three methods are used to fabricate pipe, producing seamed, seamless, and cast pipe. Seamed pipe is fabricated by rolling plate into a cy)jnder. The sea,n is vvelded using SAW or high-frequency resistance •,velding. Seamless pipe is fabricated from solid bar stock that is heated to the plastic state and drawn through special dies. Seamless pipe has considerably more strength than sean1ed pipe and can withstand a higher pressure. Cast iron pipe is seamless pipe formed or cast ina mold.

Brazed or soldered joint

Brazed or soldered joint

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Figure 23-2. Cross sections of pipe and tube butt joints joined by welding, brazing, and soldering. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 23

Pipe and Tube Welding

605

and wall thickness. Generally, as a pipe's non1inal size increases, the wall thickness also increases. The schedule number indicates the wall thickness. Schedule nu1nbers for carbon steel pipe include 5, 10, 40, 80, and 160. Schedule nunlbers for stainless s teel pipe include SS, 105,405, and 80S. As the schedule number increases, the wall thickness increases. Schedules 40 and 80 are common pipe schedules. A given size pipe, such as 8" pipe, can be manufactured with 1nany inside dia1neters and wall thicknesses. Refer to Figure 23-3 for examples. The nominal size may be 8", but the actual inside diameter will change depending on the schedule, which c hanges the wall thickness.

23.1.1 American National Standards Institute (ANSI) Pipe Schedules The American National Standards Institute (ANSI) pipe schedule is used to designate pipe. The size of a pipe is specified by its nominal pipe size and a schedule number. TI1e no1ninal size is silnply an industry standard number that approxi1nates the inside diameter of a schedule 40 pipe. For pipe diameters up to 12': the no1nina.l pipe size is roughly the same as the pipe ID. For pipe diameters 14" and above, the noowal pipe siz.e is the same as the pipe OD. A chart, like the one shown in Fig u re 23-3, can be used to determi11e a pipe's inside diameter (ID), outside dian1eter (OD),

Standard Pipe Schedule Pipe schedule wall thickness (in)

Pipe Nom. size (in)

OD (in)

5

1/8

0.405

1/4

55

10

105

40

405

80

805

160

0.035

0.049

0.049

0.068

0.068

0.095

0.095

0.540

0.049

0.065

0.065

0.088

0.088

0.119

0.119

3/8

0.675

0.049

0.065

0 .065

0.091

0.091

0 .126

0. 126

1/2

0.840

0.065

0.065

0.083

0.083

0.109

0.109

0.147

0.147

0.187

3/4

1.050

0.065

0.065

0.083

0.083

0.113

0.113

0.154

0.154

0.218

1

1.315

0.065

0.065

0.109

0.109

0.133

0.133

0.179

0.179

0.250

1 1/4

1.660

0.065

0.065

0.109

0.109

0.140

0.140

0 .191

0 .191

0.250

1 1/2

1.900

0.065

0.065

0.109

0.109

0. 145

0.145

0 .200

0.200

0.281

2

2.375

0.065

0.065

0. 109

0.109

0.154

0.154

0.218

0.218

0.343

2 1/2

2.875

0.083

0.083

0.120

0.120

0.203

0.203

0 .276

0.276

0.375

3

3.500

0.083

0.083

0.120

0.120

0.216

0.216

0.300

0.300

0.437

4

4.500

0.083

0.083

0.120

0.120

0.237

0.237

0.337

0.337

0.531

5

5.563

0.134

0.134

0.258

0.258

0.375

0.375

0.625

6

6.625

0.134

0.134

0.280

0.280

0.432

0.432

0.718

8

8.625

0.148

0.148

0.322

0.322

0.500

0.500

0.906

10

10.750

0.165

0.165

0.365

0.365

0.500

0.500

1.125

12

12.750

0.180

0.180

0.406

0.375

0.593

0.500

1.312

14

14.000

0.250

0.188

0.437

0.375

0.687

0.500

1.406

16

16.000

0.250

0.188

0.500

0.375

0.750

0.500

1.593

values are per ASME/ANSI 836.10. Welded and Seamless Wrought Steel Pipe and ASME/ANSI B36.19. Stainless Stce/ Pipe. For a nominal pipe s12e. as me scnedule increases, tne pipe wan thlcKness Increases. Pipe OD, ID, and wall lhlcKness may vary sllghU/ fran lhese values because of tolerances and manufacturing methods. SChedlles 5, 10, 40, 80, and 160 are !Or cartJon steel pipe. Schedlles 5S, 10s, 40S, and sos are for s1alnless sleel pipe. Goodheatl·Willcox Pul:Jisher

Figure 23-3. The standard pipe schedule shows the nominal pipe size, OD, and wall thickness for common carbon steel and stainless steel. As the pipe schedule number increases, the wall thickness increases. Copvrighl Goodheart-WIiicox Co. Inc

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Modern Welding

A determining factor in selecting pipe schedules is the purpose of the pipe. As the pipe schedule and wall thickness increase, the pipe is able to withstand h igher pressures and loads. Pipes with a higher schedule number are used for high-press ure applications and heavy s tructural loads. There are three types of pressure piping systen1s: • Lo w-pressure pi ping. Used for water, noncornbustible chemicals, and other nonhazardous materials used in industry. • Medium-pressure piping . Used for corrosive or flammable chemicals, low-pressure s team heat, or waste disposal. • Hig h-pressure piping . Used for high-press ure steain, gases, and fluids, radioactive n1aterials, fired or unfired boilers, offshore oil rigs, and other heavy-duty applications. There are pipe specifications and materials establish ed by the American Petroleum Institute (API) and ASTM Jnte1national. Figure 23-3 Lists ava ilable sizes for fetTOUS pipe.

23.1.2 Hollow Structural Sections (HSS) Tubular rnaterial, known as hoUow structural sections (HSS), can also be used for structural applications in buildings, race car roll cages, and other s tructures. HSS can be round, square, or rectangular. They are used as beams, columns, trusses, or other pieces in a building or structure. These structural pieces do not carry liquids or gas. They are the main pieces of steel in a building and carry the loads in a building or stiucture. The Steel Tube Institute lists the following benefits of HSS: • Aesthetic appeal (looks good). • High strength-to-weight ratios. • Uniform strength. • Cost effectiveness and recyclability. Examples of the use of HSS for structures include airport terminals and sports arenas. Bo th often u se HSS 1nen1hers for their expansive roofs or do1nes. O th er uses of HSS in buildings include entryways and colun1ns and beams. See Fig ure 23-4. HSS rounds are specified by their OD and wa ll thickness. Both are ~vritten with three decimal places. Examples of HSS ro unds are HSS4.000 x 0.237, HSS6.625 x 0.280, and HSS8.625 x 0.375. The size starts with HSS, which stands for hollow structural section. Then the true outside diameter and the wall thickness are listed. Square and rectangular HSS sections have three values. Examples are 4 x 2 x 1/4, 14 x 6 x 5/16, and 8 x 8 x 1/2, which is a square s ince both sizes are 8. Multiple ,vall thicknesses are available in every size.

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Figure 23-4. Roof made with hollow structural sections (HSS).

Di rnensions in the United States are in inches. ln other countries, the dimensions are in millimeters. Exa1nples of metric rectangula r and square HSS a re HSS400 x 250 x 14 and HSS150 x 150 x 10. Wall thickness will vary from 1/8" to 1/2" for round HSS and from 1/8" to 5/8" for square and rectangular HSS. For reference, an 8" schedule 40 pipe has a wall thickness of .322': which is about 5/16". An 8" schedule 80 pipe has a wall thickness of 1/2". Most HSS are rnade to ASTM ASOO. A new ASTM specification for HSS was released in 2013. This new specification is ASTM A1085. ASTM A1085 s teels have higher yield and tensile strengths than A500 steel. They also have a required minimum impact strength. There is no impact sti·ength requiren1ent for A500 steel. Welding of HSS s tee l is covered by structural welding requirements. ·T ue most common is AWS D1.1

Str11cturnl Welding Code- Steel.

•

Nonstandard Terminology

Hollow stru ctural sections are often incorrectly referred to as tubing. The wall thicknesses of HSS are much greater than tubing. Referring to HSS as pipe is also incorrect because HSS can be shapes other than round.

23.1.3 Materials Used in Pipe Materials used in pipe include the following: • Carbon steel. • High-yield-strength steel. • Wrought iron. • Chron1e-molybdenum. • Stainless steel. • Nonferrous rnetals. • Plastic. Copyr!ghl Goodheart-WIiicox C-0 Inc,

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Carbon steel pipe is the n1ost used material in piping systenlS today. Car bon steel pipe is pop ular due to its lov.r cost and welding and forming prope11ies. Carbon s tee l pipe can have tensile strengths up to 70,000 psi, which 1nakes it compatible for low-, medium-, and highpressure piping. High-yield-strength steel pipe was developed for highpressure transmission pipelines. High-yield-strength steel pipe is a lighter weight than carbon steel pipe, making it suitable for long cross-cow1try pipe Ii nes. Wrought iron pipe is widely used for undergro w1d, maritin1e, cond ensate, and radiant heating piping. Wro ug ht iron pipe has a surface that is easily galvani zed or p ainted. C hrome-molybdenun1 pipe has high-tem pera ture streng th and to ughness. When fa bricating th is type of pipe, specia l welding procedures, annealing, and postweJd heat treatment are required . Sta inless s teel pipe has applications where corrosive materials are present. Corrosion-resistant pipe is used in the chemical and food processing industries. Stainless s teel and nicke l pipes are used in lowtemperature applications to hold and process liquid carbon dioxide, liquid oxygen, liquid nitrogen, and even liqu id helium. Temperat ures in t hese applications can run as low as -452°F (-269°C), the te mperature of liquid helium. Nonfe rrous pipe can a lso be used for extreme high- or low-temperature situatioru. The most common nonfe rrous pipe tnate riaJs a re nickel, a lumin um, copper, titaniu m, ru1d t heir alloys. Nickel a lloys have registered names, such as Hasteloy and Inconel. Coppe r a nd brass pipe are used for \-\later an d refrigerant applications.

Pipe and Tube Welding

607

Plastic pipe is often used to ca.rry natural gas at low pressures. It is also used to carry highly and mildly corrosive chemicals at Jow pressures. Plastic pipe is used in low-pressure waler syste1ns, including ho1ne and irrigation systems.

23.1.4 Methods of Joining Pipe Pipes can be joined together or to fittings using the following me thods: • Pipe threads. • Flange fitiings. • Weld ing. • Adhesives (for plastic p ipe). Pipe parts tha t are connected by threads or flange fittings can be separated. Pipe parts that are welded and plastic pipe parts that a re ad hesively bonded cannot be sepa ra ted. To assemble pipe using threads, the ends of pipe and a variety of fittings are thread ed using the National Pipe Tapered Threa.d (NPT). As the pipe and fitting are screwed together, they get tighter because of the taper in the th reads. The threaded joint is air- a nd watertight \-\lhen properly asse1nbled. A flange fitting is attached to a pipe at one end and has a wide, flat collar on the other end. Flange fitt ings a re asse mbled to a pipe using th reads or by welding. The flange on t he fitting has several holes in it. To connect two pipes with flanges, a sealing gasket is placed be tween the mati ng fl anges. Bolts a re placed into the holes and the flanges are drawn tight to compress the gasket. Flanged joints are easily disassembled by re1novi ng the bo lts.

Aptitudes and Abilities Spending a lifetime-or even a few years-in a career for which you are not suited can be frustrating, to say the least. As you are considering your future career, take into account your aptitudes and abilities. An aptitude, or natural talent, is an ability to learn something quickly and easily. Are some of your subjects in school much easier than others? Knowing this can help determine some of your talents. You may not be aware of all of your aptitudes if you have never been challenged to use them.

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A school counselor can give you an aptitude test to help reveal your strengths. Abilities are skills you develop with practice. As you prepare to handle a new responsibility, you will learn that it requires certain skills. Can you develop those skills with practice? For example, can a person who is afraid of heights become a good roofer? Can someone lacking finger dexterity learn to manipulate precision tools? You may be able to develop different skills, so find out what you can do well.

608

Modern Welding

Welding is the 1nost popular 111ethod of per111anently joining pipes. The advantages of welding pipe are n eah1ess, compacmess, quickness, and low cost. A va riety of fittings that can be used to join pipes by welding ru:e shown in Figure 23-5. Pipe welding can be performed using SMAW, GMAW, FCAW, GTAW, and SAW processes. The 1nost common process used for pipe welding is shielded metal arc welding. Pipes can also be joined by flash weld ing and friction welding. Chapter 18, Resistance Welding Equip111ent a11d Supplies, and Chapter 19, Resistance Welding, discuss these processes. Oxyfuel gas welding of pipe is not done co1nmercially because it is slo,.v and inefficient. Pipe welding is an advanced welding skill. Th e techniques required for welding plate still apply to pipe ,velding. Welding angles, electrode manipulation, current and voltage settings, and h·avel speed a re all si_milar. What D1akes pipe welding more difficult is the challenge of maintaining the co1Tect work and travel an gles •,vhile welding around a circular joint. To create qua ljty weld beads, the pipe welder must

constantly ch ange the position of the e lectrode, gun, or torch in relation to the curving joint. This requires great body control and skill. The 1nost co111.mon joiJ1t in pipe \Ve Iding is the single-V-groove butt joint. The position of the pipe and joint to be welded can vary greatly. The most common position or orientation for a pipe weld is with the pipe horizontal and the joint vertical. The American Welding Society (AWS) refers to this position as the SG position. The pipe is stationary for the SG position. A 5G pipe joint requires the v.relder to weld in the overhead, vertical, and flat welding positions. See Fig ure 23- 6. For the 1G positio n, the p ipe is a lso horizontal, but it is rotated as the weld is made so the welder always welds in the flat (lG) position. The AWS pipe we lding positions are shown in Figure 23-7. In the 2G position, the pipe is vertical. The g roove weld is in the horizontal position. The pipe is at a 45° angle for the 6G position. A 6G welder qualification test is the most challenging of all pipe positions.

Pipe Joint Fittings go reducing

3 R elbows

elbows

45° and go

Crosses

Concentric reducers

0

90° elbows

go elbows 0

180° returns

Ts

Laterals

Shaped nipples

Sleeves

Saddles

11 l

0

go elbows

45° elbows

180° returns

Eccentric reducers

Caps

Lap joint stub ends

Welding rings

Expander flanges

Venturi expander flanges

0

ri u~-)) -~

·~_) GoodhBalt•WIIICOX Publ!sh9f

Figure 23-5. Pipe joint fittings. Such fittings are commercially made in various sizes and thicknesses of s teel and steel

alloys. The edges are generally beveled and ready for welding. Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Chapter 23 Pipe and Tube Welding

60 9

FIiiet Welds in Pipe

;x/ I

.'

'

~

·r

~

l l '\

•

Goodhean-\Villcox Publishe, /

Figure 23-6. This welder is arc welding in the overhead

I

45 °

position. The pipe is in the 5G position.

2F - Horizontal

1F - Flat (rotate)

I

Groove Welds In Pipe

.

~

-

(

-

'"'

I;::

,

I

.

L

1G - Rotated flat

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,

2G - Horizontal

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~ .. '

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,r

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5G - Multiple (not rotated)

,.

)

I

2FR - Horizontal (rotate)

, •

,

,c__ _ _ _ _ _

4F - Overhead

/

H

/

6G - Multiple (not rotated)

Adap;ed w,th permJ.SSJon from the Am91ican Wekllng Socl8ty, Miami. FL

Figure 23-7. AWS position designations for groove welds in pipe. AWS A3.0:2010, Figures 17 and 19, Welding Test Positions and Their Designations tor Groove Welds in Plate and Pipe.

Fillet welds are also produced on pipe. These are n1ade if a pipe butts up against a plate or a socket fitting is used. Welding techniques for a fillet weld on pipe are the same as a fille t weld on plate. A fillet weld on pipe can be .made in the lF, 2F, 2FR, 4F, SF, and 6F positions. See Figure 23-8. Adhesives are often used to join plastic t ubing a nd pipe. The resu lting joints are watertight and have adequate strength and reliabi lity ,,vhen the adhesive is properly applied.

Copvrighl Goodheart-WIilcox Co. Inc

/

/

/

/

/

/

5F - Multiple (not rotated)

6F - Multiple (not rotated)

Adapted with permission horn the American Welding Society. Miami. Fl

Figure 23-8. AWS position designations for fillet weld joints in pipe. AWS A3.0:2010, Figures 18 a nd 20, Welding Test Positions and Their Designations tor Fillet Welds in Plate and Pipe.

61 O

Modern Welding

23.2 Types of Tubing Tubing is made from steel, copper, alwninum, brass, or plastic. In automobiles, aircraft, refrigerators, and air conditioners, tubing is used for moving fluids. Tubing is also an excellent choice for transn1itting forces in hydraulic systems. Tubing is available i n flex ible (soft) or rigid (hard) forn1s. If a change in direction is necessa ry, f lexible t ubing can be easily bent to the shape needed . Rigid tubing, like pipe, requires the appropriate fittings to change its direction. Tubing is measured and specified by its outside diameter (OD). For instance, a 1/4" tube measures 1/4" on i ts outside d iameter, and a 1" tube rneasures 1" on its outside diameter. Tubing is available in different strengths and is manufactured in sea1nless and seamed forms. Seamless tubing is made by piercing a piece of metal heated to the plastic state and drawing that meta l through a die and over a rnandrel. A rnandrel is a metal rod with a tapered head that forms the in ner diameter of the tubing during the dra,,ving process. Rollers rnay be used to force the heated metal over the mandrel, as shown in Figure 23-9. Seamed tubing is produced by rolling flat stock into a cylindrica l or other shape form, then welding the seam. The joint formed at the seam is normally a butt joint. Resistance sean1 welding is often used to weld a sean1ed tube. After welding, some tubing is further processed and dra,,vn over a mandrel. Drawn over mandrel (DOM) welded tubing has the best rnechanical properties, surface fi nish, and dimensional accuracy. DOM tubing is used on the most demanding applications. Tubing s tandards have been established by ASTM, ASME, Society of Automotive Engineers (SAE), Steel Tube Institute, and the U.S. Government (military or MIL specifications). Tubing is available in the following cross-sectional shapes: • Round. • Square. • Rectangular. • Hexagonal. • Octagonal. • Oval. • Irregular (various shapes).

Start of operation

Po1Nered roller

Mandrel

Heated rod Seamless tubing being formed

Various steps in operation

Changing size of tubing

Mi;higwi seamless Tube co.

Figure 23-9. Forming seamless tubing from a solid rod.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 23

Pipe and Tube Welding

61 1

23.2.1 Methods of Joining Tubing Tubing can be joined by the following methods: • Med1anical compression or flared fittings. • Mechanical quick disconnect fittings or couplers. • Soldered fittings. • Brazed fittings. • Welding. • Adhesives. Mechanical connechons are used for tubing designed to be separated. Welding and other permanent joining methods are used to permanently join tubing. Compression fittings and flared fittings are used on s mall-diameter copper or steel tubing. Both types of fittings use a threaded nut and threaded fithng. As the threaded nut is tightened over the tube and onto the fitting, it forms a tight seal. The fittings are easily assembled and disassembled. Compression fittings can be used on relatively low-pressure systems Hke fuel and water lines. Flared or double-flared fittings are used with higher-presSl.lre systems. They are fow1d on automotive brake fittings, hydraulic systems, and refrigeration lines. Quick disconnect couplers are sp1ing-loaded, gasketed fittings tha t enable quick assembly and dismantling of tubing systems without loss of fluid. Quick disconnect fittings are often joined to tubing by threads. Figure 23-10 shows a quick disconnect coupler. Soldered connections and brazed co11nectio11s are assembled •,vith fittings similar to those shown in Figure 23-5. The inside dia me ter of a solder or braze fitting is made slightly larger than the outside diameter of the tubing. This allows space for the soldering or brazing filler metal that joins t he assembly. The soldering or brazing filler me tal is applied to the heated joint and drawn into the fitting by capillary action. The filler metal fonns a thin fi lm, joining the tube and fitting by adhesion. Soldered or brazed connections can be used on seamed and seamless tubing and on small-diameter copper, brass, or bronze pipe. SMAW, GMAW, FCAW, and GTAW processes can be used to join tubing. The welding of tubing is discussed later in this chapter.

Copvrighl Goodheart-WIilcox Co, Inc

GOO\1ay from the weld pool, leaving a hole. This tendency is called Jwt shortness. Metals that exhibit hot shortness n1ay need s upport during welding. Backing rings can provide this support.

A

Robvon Bae/ring Ring Co., Inc.

C

Rol>VOn Bae/ring Ring co.. Inc.

B

Robvon Backing Ring Co.. Inc.

D

Robvon Bacl(ing Ring Co.• Inc.

Figure 23-22. Backing rings can be used to space the root opening and support the weld pool. A- A backing ring is inserted into one piece of pipe. 8-The backing ring is pressed against the root face. C-The second piece of pipe is placed into position, pressing the root face against the spacer pins. D-The two pieces of pipe are aligned and properly spaced by the backing ri ng. Copvrighl Goodheart-WIilcox Co, Inc

618

Modern Welding

If a permanent backing ring is not acceptable for the application, a backing tape may be used. Backing tape is fiberglass or ceramic material on an adhesive tape. The backiJ1g tape is applied to the root side of t11e weld. Backing tape does not become part of the welding joint during welding. Backing tape helps control the depth of root penetration. See Figure 23-23.

23.3.5 Tacking Pipe and Tube Joints Tack welds are necessary to hold the sections of pipe in place prior to welding. It is very important that the proper techniques be followed, including using the keyhole method. Tack welds should have complete penetration. Skill and care must be followed while tacking because poor tack welds are often the cause of discontinuities and defects in the final weld. Four tack welds are recoD1mended. The tacks should be evenly spaced around the pipe. When a position on a pipe is being described, the end view of the pipe is referred to like a clock face. Twelve o'clock is at the top, six o'clock at the bottom, nine o'clock to the left, and three o'clock to the right. The four tack welds are made in the three, six, nine, and twelve o'clock locations. Tack welds should be 1/2"-3/4" (13 mm-19 mm) long. Size depends on the diameter of pipe, the WPS, company standard, or welder preference. After the joint is tack ,-velded, each tack weld should be ground with a narrow wheel grinding disk. Any high reinforcement is removed. Each end of the tack weld is tapered approximately 1/4" (6 mm) as shown in Figure 23-24. Grinding thins t11e tack weld at the ends. Feathering is the process of using a grinder to thin a tack ,-veld or the end of a weld stop. Feathering allows complete and proper fusion of the root pass into the pipe and t11e tack weld.

Radius edges

GOotJheafl-Wl"COI( Publisher

Figure 23-24. A 1/2"- 3/4" (12 mm- 19 mm) tack weld with a keyhole that has been feathered. Feathering removes any excessive reinforcement. It also thins out the start and end about 1/4" (6 mm). This allows the welding root pass to obtain good fusion into the tack.

23.4 Welding Pipe Joints with SMAW SMAW is used to join pipe. Welding pipe ,-vith SMAW takes skill and practice. Piping can be horizontal (SG), vertical (2G), or at an angle (6G). Cross-country pipelines and a lot of industrial piping is welded in the 5G position. A pipe joint in the SG position can be welded in one of t"vo ,-vays: uphill or downhill. The directions are sho,,vn in Figure 23-25.

23.4.1 Uphill Welding Upl1ill 1veldit1g, sometimes referred to as vertical up, is done by starting the weld at the bottom, or six o'clock, position and n1oving upward to the top of fue joint, or twelve o'clock position. Once the "veld reaches the twelve Uphill

Centering line

Downhill

Gas release

holes

-

Ceramic weld backing is centered on pressure sensitive coated aluminum foil

I Welded from one side only Gunca lntornational Lid.

Figure 23-23. Ceramic backing tape is placed on the root side of the weld to control penetration.

Goodhean·Wilfcox Publisher

Figure 23-25. Uphill welding begins at the bottom of the pipe and progresses up the pipe to the top. Downhill welding begins at the top of the pipe and progresses toward the bottom. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 23

o'clock p osition, the 1,velde r returns to the six o'clock position and completes the "veld pass by h·aveling up the other side of the pipe. Uphill \,velding produces better penetration and requires fe,~•er passes to cornplete than a joint with the same groove angle welded downhill Fewer passes are required because uphill welding is done at a s lower pace. A larger weld pool is used. Uph ill welding is used on thicker-walled pipe, high-pressure pipe welds, and HSS structural \>\1elding. The electrode dia n1e ter for each pass in a pipe weld is specified by the WPS. Electrode selection for the root pass is based on the root face in the gToove. Figures 6-15 and 6-16 can be used as a reference for selecting the proper electrode diameter for the root pass. As an example, ii the root face is 1/8" (3.2 mm), a me tal thickness of 1/8" (3.2 mm) should be used to look up the proper electrode size. Amperage will be on the lower end of the suggested range. A com1non electrode for the root pass on carbon steel pipe is the E6010. Techniques for uphill groove welding on pipe a re similar to uphill groove welding on plate. The root pass is a stringer bead. No t much side-to-side motion is required except '"'hen there is a poor fit-up or a wide root gap. Proper pipe prepa ration, alignn1ent, and tacking wiJJ p revent poor fit-up and gaps. For uphill welding on pipe, use the following procedure:

Procedure Uphi II Welding 1 . On the root pass, strike the arc in the center of the tack at the bottom of the pipe joint. Start welding uphill. 2. As you leave the tack, develop a keyhole, melting both pipes. Maintain a short arc length. Use a forward and back motion of the electrode. This is the whip and pause technique used on plate. 3. Move the electrode forward to advance the keyhole. As the keyhole opens, move the electrode backward over the weld pool. Watch the keyhole. Do not let it get too big and do not let it fail to form or close up. The whip and pause motion allows you to control the heat. 4. If the keyhole is too large, move forward quickly and spend slightly more time with the electrode over the rear part c:A the molten weld pool. Another technique is to reduce the electrode travel angle doser to 0°. Also, increase travel speed slightly to put less heat into the weld. If you are having difficulty reducing the keyhole size, stop welding. Wait a minute and let the pipe cool slightly. Then restart. 5. If the keyhole is too small, spend slightly more time at the front of the weld pool and wait for the keyhole to open up. Spend less time over the weld pool. Another technique is to increase the travel angle to 10°- 20° drag. This puts more arc action into the root and keyhole. Also, decrease travel speed. Copvrighl Goodheart-WIilcox Co, Inc

Pipe and Tube Welding

619

23.4.2 Downhill Welding Doiv11/1ill ivelding, sometimes called vertical doivn, sta rts at the twelve o'clock position a nd rnoves downward to the six o'clock position. DownhiU welding is used on thinner-walled pipe, with a wall thickness less than 1/2" (13 1nm), and specifically on c1uss-country petroleum pipeline welding. Downhill welding requires a faster travel speed than uphill welding. The API Standard 1104, Welding of Pipelines and Related Facilities requires downhill welding. All downhill passes are performed with an E6010, E7010, or E8010 electrode. These are fast-freezing electrodes. The weld pool in a \>veld made with a fast-freezing electrode solidifies q uickly.

Procedure Downhill Welding 1 . On the root pass, strike the arc in the middle of the tack weld at the top of the pipe. Start moving downhill. This wil be a stringer bead. There should not be much movement of the electrode. Some movement may be required if a joint has a poor fit-up or a wide root opening. 2. Maintain a short arc length. When downhill welding with the SMAW process, weld rapidly to prevent the molten s lag from rolling into the weld pool. 3 . Stay on the leading edge of the weld pool. Penetration is less when welding downhill than when welding uphill. This is why a smaller root face and root opening are used. 4. Downhill pipe has a 60° groove angle. You can drag the coating of an E6010 or any EXX10 electrode on the groove angle to control the a rc length. More weld passes are required to fill the joint when downhill welding than uphill welding pipe with a similar wall thickness.

23.4.3 Pipe Weld Passes Pipe welds require several different weld passes. These include the root pass, intermediate passes, and cover pass. Weld passes are shown and labeled in Figure 23-26. Intermediate passes

Cover pass

Root pass Goodhoart•Willcox Publisher

Figure 23-26. The specific names for the various pass es

in a pipe weld.

620

Modern Welding

A powered grinder v,rit h a grinding wheel or with wire brushes may be used beh\1een each weld pass. The grinder is used to remove all slag and to knock do\>\711 any high spots in the completed weld pass. Ji high spots remain, slag could get trapped in the next weld pass, which is unacceptable.

Root Pass The first pass is the root pass. The root pass must have complete penetration. The root pass is usually 111ade with an E6010 electrode because it produces good penetration. To obtain complete penetration, the keyhole method is used. The keyhole can be seen and heard when properly formed. When welding with a keyhole, the arc blo,vs through the keyhole and echoes inside the pipe, creating a uJtique sound. When ,~rel ding over a tack weld or if the keyhole closes up, the sound will not be heard. Chapter 6 explains the keyhole method. Figure 23-27 shows the keyhole on an open butt joint weld. Root reinforcement, the amount of penetration on the inside of the pipe, should be about 1/16" (1.5 mm). This applies whether welding uph i.11 or down hill. Whenever you restart a weld bead on the root pass, start by cleaning the partially completed pass. Then, strike the arc 3/8" (10 m,n) back on the existing bead. Always strike the arc in the groove of the weld joint, not on the pipe surface. Move the arc forward over the keyhole. Push the electrode into the keyhole to melt the keyhole to the root side. Move the electrode to the back of the weld crater to melt into the crater. Then, start moving forward again. This tecl1nique will prevent a lack of fusion, a lack of penetration, and a lack of fill at the point of restarting. An important consideration in pipe welding is the angle at which the welding operator

holds the electrode. ln pipe welding, the electrode 1uust be continuously repositioned. v\lhether the ,velder is welding uphill or downhill, the electrode should have a 90° work angle and a 00-10° drag travel angle. See Figures 23-27 and 23-28 for electrode angles used on a typical SG uphill root pass. An E7018 electrode can be used for the root pass when a backing ring is used. The root pass with a backing ring must melt into the root face of both pieces of pipe and into the backing ring. After the root pass is completed, the slag must be removed. The root pass is paJtially ground out to remove any crown in the bead and to remove and prevent slag from getting trapped in the following passes. Proper grinding to remove slag and crown is an important step. Figure 23-29A shows a completed root pass. The root pass is sometimes done with GTAW to produce the highest quality weld possible. Modified short circuiting transfer GMAW may also be used to weld the root pass.

Intermediate Passes The second pass or layer requires more current than the root pass. It must fuse well with the root pass and with the pipe wall. The second pass or layer must also melt out any s lag rernaining after the root pass has been cleaned. The second pass should be welded as soon as possible after the root pass is completed, usually within five minutes of completion of the root pass. A chippiJ1g hammer, wire brush, or grinder should be used to remove all slag after the second pass is completed.

Keyhole Goodhoatt•Willcox Publishor

Figure 23-27. When a butt joint is welded in pipe, the electrode work angle is 90°.

Goodhoatt-Willcox Publisher

Figure 23-28. Side view of an SMAW uphill root pass. The work angle is 0° and the travel angle is 0 °-10°. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 23

A

GoOdhean-Wi!Jcox Pu~isnor

8

Pipe and Tube Welding

621

GoodhearHVillcox Publisher

Figure 23-29. A multiple-pass pipe weld. A-This pipe has a root pass, one intermediate pass, and the start of the first cover pass. 8- Three beads make up the cover passes on this schedule 80 pipe. The two intermediate passes have not yet been covered at the top of the pipe. All intermediate and cover passes were welded using an E7018 electrode. This pipe was welded using six passes.

For uphiJI welding, a sa,all Z-weave or circular motion of the electrode can be used to direct the arc to the edges of the root pass. Pause s lightly at each side of the weave. This melts the pipe side ,-valJ and any trapped slag. This small weave motion will flatten out the weld pool. An uphill second pass n1ay be welded ,-vith an E6010, E7010, E8010, or E7018 electrode, depending on the WPS. For downhill welding, a straight stringer bead or a ve1y small side-to-side motion is used. The whip and pause method helps to control the ,,veld pool. It is often necessary to stop, replace the electrode, and restart the weld during a pass. Start by cleaning the partially completed pass. Then, strike the arc 3/8" (10 011n) in front of the weld crater from the last electrode. Move the electrode and arc to the rear of the existing crater. Pause and allow the arc to melt into the crater. One technique is to 1nove the electrode in a half circle around the rear of the crater to n1elt the entire crater area. Once the weld pool develops and has n1elted into the existing crater, s tart 1noving forward. Failure to properly restart causes welding defects. Intermediate passes are used to fill a weld joint. Several intern,ediate passes ,nay be required. The nu1nber of Copvrighl Goodheart-WIilcox Co, Inc

intermediate passes depends on the pipe diameter and pipe schedule. Each intermediate pass must fuse (melt) into the previous weld passes and into the pipe walls. To prevent slag inclusions, each pass must be cleaned prior to welding the next pass. A chipping hammer and a wire brush or po,ver grinder with a wire wheel can be used. Some welding procedures require a grinding ,-vheel to remove slag. A stringer bead or a ,veave bead can be used for welding uphill on intermediate passes. AZ-weave technique is con,monly used. A stringer bead or a slight sideto-side or weave 1notion is used for welding downhill on intermediate passes. The ,,veld pool is smaller in downhill welding than in uphill welding.

Cover Pass The final pass o r layer is the cover pass. This pass is used to cover the weld joint. The top edge of the groove must be melted about 1/16" (1.5 mm). See Figure 23-29B. The cover pass or passes must have a min.i1num of 1/32" to less than 1/8" (1 1nm to 3.0 1nm) buildup above the pipe. There must be good fusion into a ll previous weld passes and into the pipe wall and pipe surface. A weaving 1no tion can be used to

622

Modern Welding

produce a wide bead for uphLI I welding.Stringer beads with some side-to-side motion are used for downhill welding. Some specifications do not allow large \Vires inside the pipe. The bar must be large enough for the materia l to be cut. Burning bars are available in .540" (13.7 mm),

Ooodheart-lVillcox Publisher

Figure 24-11. A fire triangle. All three sides of the triangle

must be present for a fi re to continue burning. The exothermic process has the right combination of fuel and oxygen and, after initial ignition, generates heat to maintain the process. Copvrighl Goodheart-WIilcox Co, Inc

Oreg Caln Of Oxytance, Inc.

Figure 24-12. End view of a bundle of burning bars.

A number of alloy wires are crimped inside of a steel tube or lance. The alloy wires are being inserted into the steel tubes.

644

Modern Welding

.635" (16.1 mm), .675" (17.1 mm), .840" (21.3 mm), .922" (23.4 11101), and 1.05" (26.7 mm) dia1neters and in lengths of 5'3" (1.6 m), 7' (2.1 m), and 10'6' (3.2 m). A bw·ning bar holder is required for exothermic cutting. The holder has an oxygen control valve and a thermal shutoff device. See Figure 24-13. An important internal ele1nent is the rubber g rommet that holds the tube in place and prevents oxygen leaks. The bent or crimped end of the burning bar is inserted into the holder, and the grom1net seals the connection. Cutting with an exothermic burning bar requires high volumes of high-pressure oxygen. Oxygen pressure is often 90 psi-150 psi (620 kPa- 1000 kPa). The volume of oxygen required is 25-100 ft3/min or 15006000 ft3 /hr (700 lpm-2800 1pm). This extremely high flow cannot be achieved from a s ingle tank of oxygen or a single De\var flask of liquid oxygen. A manifold of multiple cylinders can be used for short duration cuts. For extended cuts, 1nultiple Dewar flasks connected to an evaporator a1·e needed. See Figure 24-14. A high-volume oxygen regulator and properly sized oxygen hose are required to d eliver the necessary oxygen to the cutting process. Figure 24-15 bsts suggested oxygen pressures and flow rates.

Oxygen control valve

Greg Cain ct Oxytanca. Jnc.

Figure 24-13. A burning bar or oxygen lance is inserted through an internal rubber grommet in this holder to prevent oxygen leaks. The flow of oxygen is controlled by the control valve or handle.

Greg Cain ct Oxytancc, Inc.

Figure 24-14. An evaporator with four Dewar flasks of liquid oxygen. This system can produce the required 25 ft 3/min - 100 ft3/min (700 lpm-2800 1pm) of oxygen required for long cuts with a large diameter burning bar.

Recommended Bar Sizes and Flow Rates for Exothermic Cutting Buming bar size

Operating pressure (psi)

Bar OD

Pipe size

Minimum

Maximum

.540" .625" .675" .840" .922" 1.05"

1/4" pipe 5/8" tube 3/8" pipe 1/2" pipe No pipe size 3/4" pipe

90 90 90 90 90 90

150 150 150 150 150 150

Oxygen flow rate

20 elm @ 90 psi 25 elm @ 90 psi 30 cfm @ 90 psi 55 elm @ 90 psi 60 elm @ 90 psi 70 cfm @ 90 psi

30 elm @ 150 psi 40 elm @ 150 psi 45 cfm @ 150 psi 70 cfm @ 150 psi 75clm@ 150psi 90 elm @ 150 psi Grog Cain d Oxylanco, Inc.

Figure 24-15. A table of suggested oxygen pressures and fl ow rates for exothermic cutting using burning bars and oxygen lance cutting. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 24 Special Cutting Processes

A standard oxyfuel torch is required. Most often, an oxyacetylene cutting torch is used. The purpose of the cutting torch is to heat the end of the burning bar to start or ignite the burning process. Once the burning bar is ignited, the cutting torch is no longer used. Once the equipn1ent is asse1nbled, a safety d 1eck is performed. A soap and water solution is used to check all oxygen connections for leaks. Equipment needs to be rechecked for leaks any tin1e a part of the system is changed, such as tanks of oxygen, the holder, or hoses. Any connection point that is changed must be rechecked for leaks. A leak check should also be done when equipment has not been used overnight or for a longer period of time.

645

A

Grog Cain ol Oxytance, Jno.

B

Greg Cain ot Oxytance. tnc.

(a.a] Caution Do not use high pressure oxygen if any leak is found. Fix all leaks and recheck prior to using the equipment. Personal safety equipment including goggles, a weldi ng h elmet, an aluminized Ke vlar jacket, alum inized Kevla r leggings, an apron, a nd gloves must be worn. Exoth ermic cu tting creates a lot of sparks, especially durin g a p iercing operation . Workers, as well as t he cutt in g equipment and surro unding a reas, must be protected against h ot pa rticles. Airsupplied or air -purifying b reathing protection is also r ecommended .

24.2.2 Cutting and Gouging with a Burning Bar Starting a cut with a burning bar is easy. The operator gets in position to cut and an assistant heats the tip of the bwning bar with a standard cutting torch. As soon as the tip of the burning bar reaches its kindling te1nperature, the burning bar operator slo,,vly opens the oxygen control valve. The burning bar ignites and the operator is ready to begin cutting. The oxyfuel cutting torch is not needed after the burning bar is ignited. Figure 24-16 shows the end of a burning bar before and after the oxygen is turned on. It is better to start on an edge with the burning bar at an angle. As the cut progresses, the operator brings the burning bar up to a near vertical position and then 1noves the burning bar into and out of the kerf in a sa,-ving motion. This action ensures complete peneh·ation and also forces all of the slag out of the kerf.

Copvrighl Goodheart-WIilcox Co, Inc

Greg Cain Of Oxytanoe. Inc. C Figure 24-16. Igniting a burning bar. A- An oxyacetylene

cutting torch heats the end of the burning bar to its ignition temperature. Oxygen is not flowing through the bar at this point. B- Once the ignition temperature is reached, the oxygen is slowly turned on. C-Oxygen is flowing at the correct rate. The burning bar is ready to begin cutting.

646

Modern Welding

Pro Tip Keep the burning bar touching the metal you are cutting. The tip of the burning bar should be almost into the molten cut. Do not try to maintain a tip distance as you would with an oxyfuel torch. For piercing applications, the burning bar is held perpendicular to the metal being pierced. The bwning bar must be kept in the center of the desired location and n1oved in and out of the hole constantly. The faster the burning bar is moved in and out of the cut, the cleaner ilie completed hole and the smaller the hole will be. Because burning bars are easy to use and cut so quickly, they are used in demolition projects as well as everyd ay jobs in power plants, paper mills, steel miJls, and petrochemical pla nts. See Figu re 24-17. In steel mills, burning bars are used to cut large sections of sa·ap down to a size that can be put in furnaces to ,nanufactu re new steel. This operation is ca lled scrap processing. Foundries use burning bars to remove unwanted parts fron1 castings. A casting that has cooled down v.rould need to be preheated for a long time in order to be cut with a different cutting process. Frozen pins in heavy equipment are removed very e ffectively v.rith burning bars. Such pins can be four or more inches in diameter. A hole is pierced in the center of the pin. Neither the pierce nor the cut should extend to the outer edge of the pin. After the small hole is pierced, the burning bar is used to enlarge the hole to two to three inches in diameter. When the pin cools, it contracts in diameter. Since the pierced and cooled pin is slightly smaller than ilie bore (hole) it

Greg Cain rl Oxyfance. Inc.

Figure 24-17. An exothermic burning bar being used to cut through a 24" (61o mm) thick shaft.

was frozen into, the pin can be re1noved ,~riiliout da111aging the bore. Although an oxyfuel torch is not needed for exothermic cutting, it can be used to assist the exothermic cutting of some nonferrous materials, including copper and brass. These metals conduct heat away from the cutting area. T hey do not oxidize Like s teel, which adds additional heat as it oxidizes. The addition of heat from the oxyfuel torch increases the cutting speeds on 111ateria ls that do not oxidize easily. The metal being cut does not have to be cleaned before cutting. Paint, insula tion, and rust do not create any problems for burning bars. Burning bars can be used in many applications including cutting concrete, cutting refractory (resistant to extreme heat) material, cutting laminated plate, and underwater cutting. Safety equipment including goggles, face shield or helmet, aluminized Kevlar jacket, aluminized Kevlar leggings, apron, and gloves should be worn. Breathing protection is also recommended.

24.2.3 Exothermic Cutting Rod Equipment An exothermic cutting rod is a smaller type of burning bar and operates on the same principle. To operate, the correct co1nbina tion of fuel (cutting rod), heat, and oxygen must be present. Once these three elements are present, the chemical reaction of oxidation continues until o ne of the three is no longer present-the rod (fuel) is burned up, the oxygen is shut off, or ilie ten1perature in the chemical reaction is reduced belovv the kindling temperature. Because the chemical reaction is the same, these smaller cutting rods burn at ilie sa1ne tip temperature as the big burning bars. The limiting factors fo r the smaller rods are the volume of molten metal and the volume of oxygen. However, the smaller rods can pierce very thick metal alinost as fast as the big burning bars. Cutting rods a re useful for piercing smaller dia1neter pins or piercing s1naUer diameter holes in plate for plate-cutting applications. The equipment required to cut wiili exoiliermic c utting rods is shovvn in Fig u re 24-18 . It includes tl1e following: • A specifically designed handheld rod holder. • Exoiliermic cutting rod s. • A copper striker plate. • A 12-volt battery. • An oxygen supp.ly with pressure regulator. • An oxygen hose. • Welding cables to the holder and ilie striker plate. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 24

Special Cutting Processes

647

Oxygen regulator

/

Oxygen cylinder

Exothermic rod

Oxygen hose

12V / battery Copper striker plate

(+)

(-) Sroco. Inc.

Figure 24-18. An exothermic arc cutting outfit.

The exothennic rod holder consists of a collet, a seal, and a control valve. The collet secures the rod in the holder and conducts the electricity to the rod for ignition. The rubber seal prevents oxygen from leaking around the base of the rod. The control valve gives the operator precise flow control during the cut. There are several variations of exothern1ic cutting rod. A cutting rod can be a combination of an outer tube filled with smaller tubes, an outer tube filled ,,vith wire, or a rolled form that has slits in it for the oxygen to flow through. All of the different designs have two things in common-they each provide a precise weight of n1etal, and the openings are sized to al.low a precise volume of oxygen to flow through them. Tubular designed rods have a crimp on the holder end to hold the inner tubes or wires in the outer tube. See Figure 24-19. Cutting rods are available in 3/16" (4.8 mm), 1/4" (6.4 ntn1), 3/8" (9.5 mm), and 1/ 2" (12.7 n11n) dian1eters. Rod lengths are 18" (460 mm), 24" (610 mm), 36' (910 mm), and 48" (1.2 m).

Copvrighl Goodheart-WIilcox Co. Inc

Broco, Inc.

Figure 24-19. Several exothermic electrodes. The crimping holds the exothermic wires in place in the copper-coated outer tube. These electrodes can be bent to get at hard-to-reach places.

648

Modern Welding

The exothermic cutting process is used for a wide variety of applications, such as demolition, n1aintenance and repair of heavy equipn1ent, and breaching operations by firefighters and the 1nilitary. The equip1nent is lightweight and can be carried in a portable case or a backpack by rescue workers, Figure 24-20. Aside fro1n a small battery used to start the reaction, no welding po,,ver source is necessary for this exothermic process. Another advantage is that it leaves no caibon deposits on the base metal.

Cutting _ _~ rod holder

Cuttlng rod

/

Procedure Setting Up Exothermic Cutting Equipment The following steps must be performed in preparation for making an exothermic cut or gouge: 1. Connect the oxygen regulator to a high-pressure oxygen cylinder. (Only pure oxygen can be used for exothermic cutting.) 2. Connect the oxygen hose from the rod holder to the oxygen regulator. 3. Set the oxygen pressure to the rod manufacturer's recommended pressure. 4. Turn the oxygen on and check for leaks. Turn oxygen off after checking. 5. Connect the welding lead from the holder to the positive terminal(+) of the battery. 6. Connect the welding lead from the striker plate to the negative terminal (-) of the battery. 7. Insert the exothermic rod in the holder. Make sure the rod goes through the collet and through the rubber seal. Tighten the collet nut to secure the rod. 8. Tum the oxygen on and check for oxygen leaks around the collet nut. Never use a cutting system that is leaking oxygen. Tum the oxygen off when you are done.

GrBg C.ln

a OxytancB, Inc.

Equipment required for exothermic cutting with cutting rods fits into a portable carrying case. The 12-volt battery is not shown. Figure 24-20,

Broco, Inc.

24.2.4 Cutting and Gouging with an Exothermic Rod The pressure and volume of the oxygen flowing through the rod determines the thickness of 1naterial that can be cut and the speed of the cut. Oxygen pressure is usually set between 30 psi-150 psi (210 kPa-1000 kPa), depending on the rod dian1eter, the thickness of 1naterial to be cut, and the type of cut being performed. For a 3/8" (9.5 mm) dia1neter rod, oxygen pressure of 40 psi-90 psi (275 kPa-620 kPa) and a flow rate of 4 ft3-8 ft3/min (110 lpm-220 1pm) are used for most cutting and gouging operations. To ignite the rod, slowly drag the rod across the copper striker plate to heat the tip of the rod, Figure 24-21. While the rod is arcing, slowly depress the oxygen control valve. As soon as the rod ignites, move it away from the striker plate and to the work.

Igniting an exothermic rod by striking it on the copper plate. The sparking means it is lit.

Figure 24-21 .

The rod continues to burn as long as oxygen is flowing through it. The temperature at the tip of the rod is about 7600°F (4200°C). During cutting or gouging, keep the tip of the cutting rod in the molten area of the cut. The oxygen blows the molten metal out of the cut. To end a cut, release the oxygen lever. Oxygen stops flowing, and the exothermic process stops. A rod that is not consumed can be reignited. The cutting rod is consumed as a cut is made. As the rod gets very short and burns through the crimp, the internal rods are blown out of the outer tube. The cutting process stops. Release the oxygen lever. Install a new cutting rod into the holder. Ignite the rod on the copper striker plate and resume cutting. Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 24

To gouge, hold the exothe1mic rod at an 80°- 85° travel angle or 5°-10° off the surface. Move the cutting rod to the start of the gouge position. Metal "vill quickly be re1noved. As soon as the desired depth is reached, start moving for,vard. See Figu_re 24-22. Maintain the desired depth of gouge. The rod can be moved from side to side to n1ake a wider gouge.

Special Cutting Processes

649

When cutting, you tnay need to n1ove the rod into the kerf to cut through a thick piece of base metal. A travel angle of 0° to 45° can be used to do this. To pierce a hole through metal, hold the cutting rod 90° to the base metal surface. Squeeze the oxygen control lever. Quickly n1ove the electrode in and out to deepen the hole until the hole is pierced through the plate. A piercing operation should only take a few seconds. Move the cutting rod around in a circular motion to enlarge the dia1neter of the hole. Always wear all safety recommended s afety equipment when cutting, gouging, or piercing w ith cutting rods.

fflwarning Remember during piercing that the molten metal sprays upward until the hole goes through the bottom of the base metal. Keep your face away from the hole.

A

Greg Cain ot oxy,ance, Inc.

8

Greg Cain ot Oxytance. inc.

C

Greg Caln ot oxy,ance. inc.

Figure 24-22. Gouging with an exothermic cutting rod to remove a 3/4" (19 mm) fillet weld. A-Beads in a 24" (600 mm) long fillet weld to be removed by gouging. B-The weld is gouged with a travel speed of about 1" (25 mm) per second. Notice the 80°-85° travel angle. C- The gouge is nearly complete. Copvrighl Goodheart-WIilcox Co. Inc

24.3 Oxygen Lance Cutting (OLC) Oxygen lance cutting (OLC) is si1nilar to exothern1ic cutting with a bu ming bar. Oxygen lance cutting was developed before burning bars. In this process, the ferrous material to be cut is preheated with an oxyacetylene torch. Once the material is hot enough to support oxidation (burning), a hollow tube is place d over the area to be cut or pierced. High-pressure, h.ig h-volun1e oxygen is delivered to the cut. The oxygen bums away, or cuts, the ferrous base metal. Unlike exothermic cutting, OLC often requires continuous addition of preheat from an oxyacetylene cutting torch. A burning bat~ once started, does not need an additional source of heat. With a standard oxyfuel gas cutting torch and tip, the preheating flan1es and the oxygen £or cutting are co1nbi.ned in one torch. The maxi.J.num thickness of material that a regular handheld cutting torch is able to cut is about 24" (610 mm). The performru1ce of a handheld torch is completely dependent on the volume of preheat gas and oxygen. Cutting very thick material requires a very high volume of oxygen. Steel a few feet (or a few meters) thick can be cut ,-vith the OLC process. Generally, two people are required to perform the cutting. One person keeps the metal at the kindling temperature with the cutting torch. The second person controls the oxygen lance. In other situations, oxygen lance cutting can be performed \o\rithout a preheating torch. One example is metal being cast into ingots in a steel mill The metal coming out of the caster is ah-eady red or white hot.

650

Modern Welding

When the casting needs to be cut off, the oxygen lance operator heats the tip of the lance pipe by placing the tip against the hot casting. Once the tip is hot enough, the oxygen control valve is opened. The oxygen lance and the steel start to burn. Oxygen lance cutting is used to cut risers from large castings. It can also be used to cut through thick pieces of steel in scrapping operations and is used in steel mills. The oxygen lance pipe is consumable and burns up dw·ing the lance cutting operation. Lance pipe ran ges fro1n 1/8" (3.2 mm) to 11/2" (40 mm) in diameter. Piercing small holes in thick plate requires a pipe only 1/8" (3.2 mm) or 1/4'' (6.4 mm) in diame ter. These sn1aller dian1eter lance pipes vary in length hum 4' (1.2 m) to 10' (3.0 m). Opening a tap hole in a 100 ton ladle of steel in a steel mill can require a 1" (25 mm) pipe that is 21' (6.4 m) long.

•

Nonstandard Terminology

Oxygen lance cutting is sometimes referred to by the nonstandard term oxygen lancing.

24.3.1 Oxygen Lance Cutting Equipment The following equipment is required for oxygen lance cutting operations:

• An oxyfuel cutting torch outfit to provide the preheat for lance cutting. The thickness of the metal to be cut and the type of cutting deter1nines how large the oxyfuel cutting torch needs to be. A torch \,Vith a small rosebud tip can be suffident to pierce a hole in 10" plate. A very large torch is required to cut 5 or 6 linear feet of 24" thick material. If constant preheat is required, use a special long torch with a straight head. The tord1 body, head, and tip are alJ in a straight line. This type of torch can be several feet long and have a tip size that can use up to 20 ft3 of oxygen per minute (1200 cfh or 560 1pm). • An oxygen system capable of supplying the required volume of gaseous oxygen. Oxygen flow depends on the lance pipe size and the thickness of metal being cut. For very high flow rates, muJtiple Dewar flasks of liquid oxygen and an evaporator are necessary.

• A heavy-duty, high-flow regulator capable of maintaining the required pressure and volume. • An oxygen hose of appropriate inside diameter (ID) and l ength, complete with fittings. Because the volume and pressw-e of oxygen is the most important aspect of oxygen lance cutting, the ID of oxygen hose is a·itical to efficient operation.

• An oxygen lance holder with a thermal shutoff and an oxygen control valve. The oxygen lance holder is the same holder used for cutting with a burning bar. • An adequate length of 1/8" (3.2 mm) or larger

lance pipe that has been cleaned for oxygen service. Pipe must be long enough to penetrate the desired thickness. It must a lso be long enough to permit consumption of the pipe as the cutting progresses.

• Safety equipment, including goggles, helmet, alu.minized Kevlar jacket, aluminized Kevlar leggings, apron, and gloves. Breathing protection is also recommended.

!'warning Considerable sparking accompanies the oxygen lance cutting operation. The workers, as well as equipment and surroundings, must be protected against hot particles.

24.3.2 Oxygen Lance Cutting Procedures Use the oxyfuel torch to preheat the edge of the piece. Once the steel reaches a cherry red or white hot temperature, place the tip of the lance pipe wh ere you plan to cut and let the tip of the lance pipe a lso become cherry red or ,~1hite. As soon as the lance pipe is hot, slowly open the oxygen conti·ol valve until the material begins to cut. Generally, the cut is started with the lance pipe at an angle to the metal beh1g cut. As the cut progresses, the oxygen lance is raised to a perpendicular position. The cut is much easier to start and maintain using this technique. See Figure 24-23. Depending on the thickness of the material being cut, preheat may be necessary during the entire operation. For very thick pieces, a spedal oxyfuel torch is needed The preheat tip rnust be large enough that the flame reaches well down into the kerf. As the lance pipe extends down into the cut and is in the presence of pure oxygen, the lance is exposed to very high temperatures. The end of the pipe continually burns away. As the pipe is consumed, lengths of nev.r pipe are added. Oxygen lance cutting, like exothermic cutting, has been used for such tasks as ren1oving frozen pins from paper miU roUs, removing ax les from railroad wheels, and removing very large hinge pins from drawbridges. Pins as large as 12" in diameter and 24" long have been removed front rai Lroad d1-awbridges.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 24 Special Cutting Processes

Preheating torch ------...

Oxygen ----- lance

Arc stream and Covering gas Jet from electrode covering ~ and wire ◄ti.---

651

Steel core (- )

-..'-...

-~

~\" Kerf

t+-- - Kert

Plate (+)

Deeply recessed electrode wire Heavily covered cutting electrode

5°-10° to plate

\

GoOdnean-lVlllcox PulJ/isne,

Figure 24-23. An oxygen lance and cutting torch being

used to cut a piece of thick metal.

GoOdheart•Willcox PuOlisnor

Figure 24-24. A typical gouging operation using an

Oxygen lance cutting can also be used to pierce holes through pieces up to 8' (2.5 m) thick. This makes it possible to pierce holes through thick parts that would be expensive if not in1possible to drill through or n1achine. Oxygen lance piercing can also be used to pierce starter holes in thick pieces of steel for shape-cutting machines. When oxyfuel machine torches need to perform a cut in the middle of a thick plate, a starter hole is needed. The oxyfueJ torch can start a cut on this pierced hole. By piercing a starter hole with an oxygen lance, welders speed up the process and cut down on da1naged tips on their oxyfuel torc hes.

24.4 Shielded Meta I Arc Cutting and Gouging (SMAC) Shie lded n1etal arc cutting (SMAC) is a11 arc process for cutting and gouging n1etal. It is done with the same equipment used for SMAW. A special cutting electrode is recommended, but a regular SMAW electrode can also be used. A tltickly covered electrode with a slow-burning covering is used with this process. Since the covering bums slowly, a deep cup is formed in the end of the electrode. This deep cup and high currents create a high-velocity gas that blows molten metal out of the cut or gouge. See Figure 24-24 . Copvrighl Goodheart-WIilcox Co, Inc

SMAC e lectrode. The electrode is pushed a long the plate. The arc melts the metal and the force of the arc blows the molten metal out of the gouge. The enlarged view shows the deep cup that creates the electrode force. Commercially available cutting electrodes are used with DCEN or AC cw-rent. The ctu-rents are higher than those used for weldi.ng. Fig u re 24-25 lis ts suggested amperages for cutting with SMAC electrodes. E6010, E6012, and E6020 elech·odes are sometimes used as a cutting or gouging electrode. Any electrode can be used with some success as a cutting electrode. Better r esults are obtained with an electrode designed as a shielded metal arc cutting electrode.

Recommended Amperages for SMAC Electrodes Electrode diameter

Amperage

in

mm

DCENorAC

3/32 1/8 5/32 3/16 1/4

2.4 3.2 4.0 4.8 6.4

130-200 150- 250 175-300 20()-600 350-600 Cronatron Wel ding Systems, Inc.

Figure 24-25. Recommended DCEN or AC amperage for cutting or gouging with SMAC e lectrodes.

652

Modern Welding

SMAC electrodes are low carbon. The resulting cut is a clean, carbon-free surface ready for welding. The same SMAC electrode is used to cut steel, stainless steel, cast iron, a lumi11u1n, brass, and other base metals. They are also used to remove hardfacing materials. Typical uses forSMAC include the folJowing: • Bevel plate prior to welding. • Chamfer edges prior to welding. • Gouge out weld d efects prior to rewelding. • Re1nove o ld welds. • Remove frozen bushings. When gouging, the elech·od e angle should be 5° to 10° from the metal s urface. This angle can be va ried as necessary to control the depth of the gouge. The electrode covering touches the base metal s urface and should be pushed a long the gouge line w ithout causing the electrode to short out. See Figure 24-24. Gouge depth should be abou t one-half the diameter of the electrode. To ma ke a deeper or wider gouge, 111a ke additional passes. SMAC elech·odes can also be used to pierce a hole. Hold t he electrode at a 90° angle to the base meta l and strike the arc. Be aware that molten metal is ejected out of the hole. Use a straight up-and-down or pecking motion of the electrode to pierce through the plate. SMAC is seldom used commercially because other cutting a nd gouging methods a re cheaper and rnore efficient. SMAC has applications, usually w hen a better method is not available. One advantage is it uses the sa,ne welding power source used for SMAW. One concern is that if a lot of cutting or gouging must be done, the power source duty cycle n,ust be ra ted to support the high current and long operation tin,es.

• Compared to other cutting processes, LBC has lower noise and fwne levels. • The equipment is us ua lly automated, so highly rep roducible cuts can be made.

1■,Note The fundamental principles of laser beam welding were presented in Chapter 4, Welding and Cutting Processes. Chapter 20, Special Welding Processes, contains a more detailed description of the types of lasers that can be used for cutting.

Oxygen or an ineit gas can be used as an assist gas to reinove n1olten metal fro1n the cut or kerf before it can solidify. The assist gas surrounds the laser beam, as shown in Figure 24-26. Cuts have been made on 1" (25 1nm) carbon steel using the carbon dioxide (CO2) laser. Because the beam spreads out quickly and the laser energy is harder to focus on thicker materials, cuts in material less than 3/8" (9.5 n,m) thick are most con1mon. As the metal thickness increases, the required laser power increases and the cutting speed decreases. Laser cutting a.nd piercing is d one w ith auton,atictype equipment. Because of the precision usually required, the cut i s often computer-progra1nmed. Laser beam

Mirror

Laser beam

24.5 Laser Beam Cutting (LBC) The laser bean1 cutting (LBC) process uses a constant bea1n of concentrated and polarized light to melt a very small area of material to produce a precise cut. The follo,.,ving are advantages of laser beam cutting: • The laser beam generator does not have to be located near the cutting operation. • A laser beam can be deflected by mirrors and can be directed into hard-to-reach a reas. • The metal or other material being cut is not part of the e lectrical ci rcuit. • A laser o·eates an extremely narrow kerf and a s1na II heat-affected zone. • Exh·emely deep, sn1all-dian1eter holes can be cut.

Focusing lens

Gas nozzle/ '-1++1-1 Laser beam /

Gas assist Goodh9an•Wil/cox Publlsh9T

Figure 24-26. A laser beam c utti ng torch with an assist gas system incorporated.

Copyr!ghl Goodheart-WIiicox C-0. Inc.

Chapter 24

lasers can also be used to drill holes in materials. This process, called laser bearn drilling (LBD), provides a n1ethod of drilling ext1·e1nely small diameter holes to exact depths. The drilling laser is norn,ally a pulsed beam. Holes with diameters from 0.0001" to 0.060" (0.0025 mm to 1.5 mm) can be accurately drilled in 1nost 1naterials. Because the depth o f the hole created with one laser beam pulse is usually only six tinles the hole d iameter, many pulses are required to dri ll corn pletely through a 1naterial.

l■rNota Laser cutting and drilling processes have been adapted for use in medical surgery. Laser beams are also used to engrave metals and other materials.

24.6 Water Jet Cutting

Special Cutting Processes

653

nlixing cham ber. The pressurized water tnixes with the abrasive in the mixing chamber prior to exiting the nozzle orifice. Figure 24-27 shows metal being cut w ith a water jet and an abrasive. Dirnensional tolerances of +0.004" (0.102 mm) are possible. The process is easily adapted to robotics where location tolerances can be ±0.002" (0.051 1nm). Water under this high pressure can do extreme damage to a person, so stay far a\vay from the water jet cutting operation and the piping that is carrying the high-pressure water.

24. 7 Safety Review Cutting tnethods discussed in this chapter may involve very high temperatures, high pressures, high cw-rents, and high voltages. Welders must be particula rly a lert for the types of haza rds produced by these conditions. Bu.ms, flying sparks, and electrical shock are ever-present hazards.

Water jet cutting is a process that uses a high-pressure jet of water, ,~1 ith or ,~1 ithout an abrasive added, to cut a wide variety of 1nate1ials. The water jet cutting process competes favorably ,.vith the band saw, oxyfuel gas, plas1na, and laser cutting processes. The following are some 1naterials that have been cut with the water jet process: • 7.5" (191 mm) carbon steel. • Stain less s teel. • Aluminu1n. • 10" (254 mm) titanium. • Plastics. • 0.103" (2.6 mm) circuit board. • 0.05011 (1.3 1nm) rubber. • 0.125" (3.2 mm) wood. • Composites. • Ceranlics. • Stone. • Cardboard. • Rubber-backed carpeting. During the water jet cutting process, water is filtered and its pressw·e raised to between 30,000 psi and 90,000 psi (200 MPa and 620 MPa). The ,.vater flow rate is about 3.5 gpm (13 1pm). The high-pressure water is forced t hrough a sapphire, ruby, or diamond orifice, forrning a high-velocity jet as it exits. The velocity of the water jet depends on the water pressure. When hard materials a re to be cut, abrasives of garnet or a lumi nu1n oxide are often added to the jet of water. The abrasives a re fed from a hopper into a

Copvrighl Goodheart-WIilcox Co. Inc

Example of finished

/

piece

er jet nozzle i ...

~

tngotson~Rand Wat9tJ8t Cutting Syst9ms

Figure 24-27. A water jet cutting apparatus cutting an

intricate pattern. Note the high quality of the complete d cut on the segment to the right.

654

Modern Welding

Reread the review of safety in C hapter 15, Oxyfuel Gas Cutting. In addition, observe the follo,.ving precautions: • Be s ure that all skin is well shielded fron1 arc rays and flying molten metal. Wear approved gloves, helmet, and clothing. Wear fire-resistant garments. Cover pockets, cuffs, and other clothing crevices that could trap sparks. • Due to the great amount of spatter generated in flame- and arc-cutting, be sure your eyes are well -protected. Wear safety glasses and also wear goggles, a face shield, or a welding helmet. • When arc cutting, use a helmet filter plate a shade or n,vo darker than would be used for welding with the sa,ne size e lectrode. A #12-#14 plate is recommended forCAC-A. • Be sure that the area in which cutting operations are performed is \,veil-ventilated to ensure that the welder is working in clean, fresh air at all times. Fumes contain small particles produced from the cutting operations. Use a positive-pressure respirator to prevent breathing contaminated air. • Wear ear protection when plas1na arc cutting, exothermic cutting, oxygen lance cutting, or when using any high-volume gas process. Other workers in the area also need to wear ear protection. • Stand or work only in dty sun·oundings. • When piercing a hole, take precautions to avoid being burned. The molten metal is projected back toward the welder until the hole goes through the metal. • Post a fire watch. A fire watch is a person who has the responsibility to look for fires during and after a welding or cutting operation. • Have an approved fire extinguisher at hand. • Be sw·e that the working area is fireproof. Remove all fla1nmable materials (such as wood, paper, and cloth) from the vicinity or cover them with flame-resistant inaterials. • Be s ure there are no openings in the floor that n1ight allow the s parks to travel to a different level of the structure. • To reduce the possibility of fire, some cutting stations use a ",.vet table." The wet table provides a thin water film under the flame-cutting area. The water quenches the flying sparks.

• Due to the fairly high oxygen pressures carried in cutting hoses, be sure aJI hoses used are in good condition and that all fittings are tight. • Never weld or cut on a container that may have combustible liquid or fumes in it. It can explode! A container that has held combustible liquids must be thoroughly purged prior to being cut. • Use completely insulated elec trode holders. • Wear special protective lenses when working around laser equipment. A person doing a lot of cutting or \,Velding gets wann or even hot, especially when wearing the required protective clothing. A cooling shirt is available that keeps the welder cool, comfortable, and sa fe w hile performing cutting and welding operations. This shut is ,.vom next to the body, and cool liquids are passed through passages in the shirt. See Figure 24-28.

Greg Cain \rater welding.

he demand for welding has expanded from onshore welding jobs to the need to \.veld structures on or under water. Offshore oil platfo1ms and unde1water pipelines are now coJnJnon around the world. These structures require maintenance, repair, and modifications. Special equipment and welltra i.ned underwater welders are needed to address the welding demands on underwater sh·uctures.

T

1■,Note In this chapter, the terms welder/diver and welder refer to an underwater welder.

Welding methods have been developed to allow wet and d r y underwater welding. Wet ivelding is underwater welding where the \~reld joint is completely surrow1ded by wate r. Dry 1.velding is underwater welding where the water is removed from the welding a rea. Dry LLnder\>\rater welding is refer red to as hyperbaric 1.veldi11g. Cutting is also done underwater to prepare an area for welding or for dernolition of a sh·ucture. Different methods are used for these two categories of cutting.

25.1 Development of Underwater Welding Prior to the 1960s, a ll under water \,veldi.ng and cutting was performed as either a means of salvage or as a temporar y repair. Ships and barges could be patched well enough to float and would then be taken to a dry d ock for permanent repairs. Dry docks and other marine facilities were located on coastlines. These facilities could tnake repairs w ithout the use of underwater welding. However, the need for under¼rater welding increased. Processes and equipment to allo\,v underwater welding had to be d eveloped. Early oil d1illing and oil platforms were in very shallow water or near land. In the 1960s, the demand for oil sent o il companies further offshore into deeper water.

657

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Modern Welding

Perinanent platforms were put in place, and it became necessary to develop solid repair procedures to use on these structures. Repair procedw·es were also needed to repair the pipelines that transported the crude oil and natural gas to shore. See Figure 25-1. Since all of these shuctures and pipefu1es ,,vere built to standards or codes, all repairs to the1n also had to meet the same requirements. While the AWS already had a technical committee that addressed welding in 1narine construction, they needed a nevv subcommittee for underwater welding. The D3B Subcommittee for Underwater Welding was formed and tasked with developing a specification for underwater welding. Commercial diving contractors saw the potential for additiona I work so they began developing systems for underwater welding. The demand for offshore structures was forecast to significantly increase, and a specification was needed. One of the first companies to undertake a development program for underwater welding was Chicago Bridge and Iron. They had designed a platform for Saudi Aramco in the Persian Gulf. Before they could install the platform, they had to demonstrate that they could maintain it and repair it if required.

Chicago Bridge and Iron brought together a group of welding engineers and their top welders. This group put together an all-out effort to develop wet welding procedures that could 1neet the requirements of the oil company and the offshore structures. They completed the project and gave the test results to the oil co1npany. The welding procedures they developed were accepted, and the test results from that project became the baseline for the D3.6M Specification for l/11derzvater Welding. As the oil industry expanded exploration further offshore, it rapidly became apparent that the scope of the specification had to be broadened. Not all underv.,ater repairs could be performed with wet welding. Wet welding could be used for structural welds, but were not strong enough or ductile enough to be used to repair pressure piping or pipelines. There was a need to develop underwater welding techniques and systems that could create a dry atn1osphere in which the welding could be performed. Improvements continue today in both wet and dry underwater welding equipinent, electrodes, and processes. The Ohio State University, Colorado School of Mines, and other universities and companies have programs doing research in underwater vvelding.

Cq photo juy/Shuttorstock.com

Figure 25-1. An oil drilling platform. The oil and gas industry drove the need for underwater welding equipment, techniques, and welders. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 25

25.2 D3.6M Underwater Welding Code The current AWS D3.6M Underivater Welding Code covers a ll requiren1ents for welding structures or components under the surface of water. This code covers welding in both wet and dry env ironments. Clauses 1 through 8 address all of the gene ral require1nents for underwater welding. Clauses 9 through 11 contain the special requirements applicable to three specific classes of welds (A, B, and 0). These classes are covered in the next section . The D3.6M specification began as a specification for wet welding but was expanded. ft no,~, includes underwater welds made in a dry habitat (hyperbaric welding) and aligns with other specifications, such as 0 1.1 Structural Welding Code - Steel, API 1104 Welding of Pipelines and Related Facilities, and ASME B31-3 Process Piping Design. The specification was broken down into various subtypes, or classes, of welds. TI1e class of the weld specifies a level of serviceability and a set of required properties. This a llows the cus to1ner to select a repair method based on the sh·ucture's o riginal design. The D3.6M specification also identifies essential variables for underwater welding.

In industry, the term underwater welding usually refers to wet welding. The term hyperbaric welding refers to dry welding.

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nonstructural items to a s tructure. The welds do not carry the load of the main structure or pipe but do carry a secondary load. The welds must not weaken the 1nain structure. ln recent years, there has been a great deal of improven1ent in wet welding electrodes and ¼1elding machines. As a result, Class B welds are n1uch in1p roved. See Figure 25-2. Class O welds, used for pipelines, m ust meet the requirements of a designated code or specification as wel l as the underwater require1nents of 03.6M. Using the specifications for Class O welds, new pipelines have been tied into new platforms in ¼'ater depths as deep as 1,100' (335 m). TI1ese welds were made using conventional welding techniques in a dry habitat. Class O is the most demanding class of underwater welds. Not all materials can be welded in a wet environment. However, with proper engineering ai1d testing, most materials that can be "velded above water can be welded in a dry habitat under,\rater.

25.2.2 Essential Variables There are va riables in all ¼ 7e lding procedures. Son,e are essential variables and some are nonessential variables. An essential variable has a significant effect on the n1echanical properties of a weldn1ent if the variable is changed. A change to an essential valiable requires a new WPS. A nonessential variable, when changed from the approved welding procedure specification, does not require requalification of the procedure.

25.2.1 Weld Classes The three weld classes specified in the D3.6M:2017 Underivater Welding Code a re Class A, Class B, and Class 0. The code does not specify which class is to be used for a given application. The customer must specify which class is required for a project. Class A welds can be made in either a wet or dry environment. These welds are intended to be suitable for applications an d design s tresses compa rable to their counterparts welded on land. This weld class is primarily based on D1.1 Structural Welding Code Steel, with additional essential variables to cover the unique problems encountered in an underwater environment. Class A ¼1elds are specified for constructing or 1·epairing main s truch.u·al members. Class B welds are normally performed in a wet environment. These welds are used for less critical applications in which lower ductility, greater porosity, and other relatively large discontinuities can be tolerated. A typical use for Class B welds is attaching Copvrighl Goodheart-WIilcox Co, Inc

Reiner Eggendor/er tor Oxytance, Inc.

Figure 25-2. A welder making a fillet weld on a pipe

reinforcement, or doubler. Wet welding is a Class B weld per AWS 03.6M code.

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The nonessential variable must be written on the WPS, but no additional testing is required. Procedw·e qualifications are discussed in Chapter 31, Procedure and

Welder Qualifications. One example of an essential variable is the type of electrode. A welder qualified to 1nake a weld on a pipeline using E6013 electrodes cannot change to an E7018 to make a weld. The weld parameters and techniques are different. The welder must pass an additional qualification test using an E7018 prior to welding with this electrode. In underwater welding, there are more essential variables than for welds above water. The essential variables in under1.vater welding address all of the variables involved in welds made above water, as ,veil as the unique require1nents of the underwater envirorunent. In underwater welding, nearly every variable is an essential variable. The D3.6M specification lists all essentia l and nonessential variables. The following are examples of essential variables listed in D3.6M: • Electrode type. • Electrode coating. • Electrode 1nanufacturer (the coating changes). • Electrode diameter. • Welding current and voltage. • Travel speed. • Wet versus d1y welding. • Depth of welding. • Background gas. • Type of base metal being welded. • An increase in the exposure time of fiJler metal at the qualification depth atmosphere. An example of the effect of the depth of welding variable is that son1e welding rods, such as stainless steel, can be used for wet welding at 50' (15 111) but ,vil I not weld at all at 60' (l8 n1). For every procedure, depth limits n1ust be strictly adhered to. A background gns is a gas mixture used to force v.,ater out of an underwater chamber and keep oxygen at a safe level. The background gas mixture changes as the depth increases. The background gas in the chamber affects the weld, so the weld must be qualified using the same background gas that will be used on the job. This 1neans that the background gas in the chamber is an essential variable. If gas tungsten arc welding is being used, the background gas must be compatible with the shielding gas. Essential variables for depth of welding in dry habitats are different because they address backgrow1d gas.

Down to 90' (2.7 m), welding can be perforined in a habitat with compressed air i.n the habitat. Air or other gases are used to force water out of an underwater chamber. The pressw·e used is equal to the pressure of the water outside of the chamber. Gases are compressed as the pressure increases. As the pressure increases, more gas is fit into the sa111e volume of space, including more oxygen. At depths greater than 90' (Zl 1n), the amount of oxygen present increases the possibility of a fire. The allowable depth requirement for compressed air is different &om the a Llowable depth for other gases. To summarize, depth of welding and background gas are key essentiaJ variables in underwater welding.

!'warning Compressed air at depths greater than 90' (27 m) becomes oxygen-enriched and dangerous. For the divers' safety, the habitat is pressurized with a nonflammable or inert gas, such as nitrogen, argon, or helium. Another essential variable that is critical to wet welding is the type and grade of steel being welded. For example, some steels that can be welded above v.1ater with an E7018 welding rod cannot be wet welded with a 70 series welding rod because of their carbon content. Rapid quenching of the welds made on higher carbon steels cause underbead cracking. Higher carbon steels must be v.1et \.Velded v.rith stainless steel or nickel electrodes. Stainless steel and nickel v.1et we lding electrodes are highly sensitive to hydrostatic pressure, so they are used only in v.,ater depths to 50' (15 m). Beyond 50' (15 m), these rods will not we ld . At depths greater than 50' (15 m), higher carbon steels must be dry welded. Many ivelding procedw·e specifications (WPS), v.1elrung procedure qualification records (WPQR), and welder performance qualification tests are required of con1panies perfornting underwater v.1elding. These docu1nents are explained in Chapter 31, Procedure and

Welder Qualifications.

25.3 Welding Equipment for Underwater Welding Most welding machines that are 300 amps or greater and have a 100"/o duty cycle can be used for underwater \.Velding. Di fierent welding machines produce different results on underwater wet welds. Welding equip1nent is installed on a dive barge, boat, or oil platforn1.

Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 25

Recent advances in inverter technology have made weld:ing power sources that produce higher quality wet welds than older model welding machines. These inverter 1nachines produce a quality arc with voltage read:ings in the 22 to 26 volt range. This low arc voltage ensures a controlled short arc length. The combination of short arc length and the higher an1perage associated with the short arc has proven to produce welds with lov., porosity and high ductility. The SMAV.Telectrode holder isa specifical ly designed unit that is insulated to prevent electrical shock. See Figure 25-3. There are no bare metal parts on an underwater SMAW electrode holder.

•

Nonstandard Terminology

Electrode holders designed for underwater use are commonly referred to as stingers. Electrodes for wet underwater weld:ing are coated with waterproofing that prevents the flux from absorbing water. See Figure 25-4. The ,,vaterproofing of

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electrodes is so critica I that the 03.6M Llndenvnter Welding Code specifies that any change :in waterproofing of wet welding electrodes requires that the procedure be recertified and all welder/divers also requaUfy. Electrodes used :in a dry habitat are the same as those used above ,,vater. £7015, E7018, and other SMAW electrodes are used in dry environn1ents. E6010 and E7010 electrodes are not used for underwater weld:ing in a dry habitat because their electrode coatings do n ot provide enough s hie lding gas. GTAW and GMAW equipment, power supplies, torches, guns, shielding gas, electrodes, and filler metal are all the sa1ue as those used above water. GTAW and GMAW are done only in a dry habitat underwater. Thus, the process and equipinent are the same as used above v.rater. As the depth of v.reld:ing increases, the diameter of the elech·ode lead and workpiece lead must increase to n1inimize the cable resistance. This is the same as weld:ing on land as the distance from the power source to the welding s ite increases.

25.4 Wet Welding

Broco, Inc.

Figure 25-3. An underwater SMAW electrode holder.

The holder is well-insulated, with no bare metal areas.

Wet underwater shielded n1etal arc welding is performed directly in the water with no barrier between the arc and the water. For the best mechanical results, wet welding SMAW elech·odes should be 3/32" (2.4 mm) or 1/8" (3.2 mm). Larger electrodes deposit so much metal that they tend to trap more porosity and make v.1elds that are not as ductile as welds n1ade ,,vith smaller electrodes. Also, research and testing have found that when a ,,veld was built-up with multiple passes, the beads on top anneal

Grog Caln of Oxylance, Inc.

Figure 25·4. Underwater SMAW electrodes have special waterproof coatings on the electrodes. The specific coating on

an underwater SMAW electrode is an essential variable.

Copvrighl Goodheart-WIilcox Co, Inc

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the underly ing beads. This anneali11g softens the ,,veld metal and makes it more ductile. Once this was discovered, the D3.6M sp ecification made both the number of beads and the use of anneal mg or temper beads essential variables in the sp ecification. All under,,vater wet welds a re made using the stringer bead technique. The weld pool solid i.fies so fast under\.vater that a weave bead ,,vill trap slag. For the same r eason, a ll vertical welds are made downhill. Most underwater welds are made vvith DCEN. Ho,,vever, new electrodes, mostly stainless steel and nickel, have been developed that requir e DCEP. Mild steel e lectrod es fo r wet SMAW ca n be used to ,.veld a ll materials cont aining up to .40 carbon equivalen t. Carbor1 equivalent (CE) is a formula used to quantify the weldability of a steel. T he formula produces a value tha t takes in to account many alloys found i11 steel. As ca rbon or the carbon equivalent increases, th e weldability of a s teel d ecreases. With a higher ca rbon equivalent, the steel has a greater tendency for cracki11g. A weld in material with a carbon equivalent above .40 t ends to develop u nderbead cracking and normally will not pass a bend test. Stainless steel rods can be used on some material above .40 CE and on stainless base m etals. Nickel welding electrodes are used on higher ca rbon steel and were developed for the US Navy to "veld on submarines and other ships w ith material up to high y ield sh·ength of 100 ks i. Figure 25-5 shows a fillet weld made with a nickel elech·ode.

When perfor111ing underwater weld mg, it is important to keep the arc leng th as short as possible. A rc length is critical to under water welding. Amp and volt settmgs are essentia l variables in an under\.vater welding specification. A longer a rc increases the arc voltage, w hich in turn increases the amount of porosity in the we ld. The best mechanical results are achieved \.vith arc voltage of 22 to 26 arc volts. Rod angle and travel speed are critical for the welder/diver to control. T he steel core of an under\,vater SMAW electrode melts faster than the flux and insulation coating on the electrod e. This is similar to the way an E7018 electrode perfonns above wa te r. The flux and insulation coating are kept in contact with the pipe or part being welded. There is a tiny gas bubble at the tip of the electrode. Too much travel an g le or a travel speed that is too fast disrupts the gas bubble and causes defects i n the weld. When ready to strike the arc, the welder comtnun icates w ith the dive supervisor who is in the dive station on the surface. Th e welder tells the super visor or radio operator to make the knife switch hot. A knife switch, Figu re 25-6, electrically connects the weldjn g leads to the we[djng power source. Making the knife switch fzot means to connect, or close, the switch. Once the knife switch is made hot, the d iver can s tart to weld. The knife switch is kept in the hot(closed) position while the diver is welding. When the diver is not welding, the knife switch is kept in the cold (open) position, cutting off electricity to the electrode. This p rotects the welder from accidenta l shocks.

Grog Caln at Oxytanc•, Inc.

Bay.Teen Jmlus.trlos, Jnc.

Figure 25-5. Fillet weld made with the wet welding

Figure 25-6. A knife switch is a simple and reliable type

technique and nickel SMAW electrodes. Note that each pass was laid down as a stringer bead.

of switch. When the switch is opened, electrical power is cut off to the electrode.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 25

Once the arc is established, the welder 1nust keep a slight pressure on the electrode to keep the flux and insulation coating in contact with the part being welded. This 1naintains a short arc and the small gas bubble at the tip of the electrode. The gas bubble keeps water away from the weld pool. The electrode should be held at a slight drag travel angle of no n1ore than 25°. A constant travel speed must be maintained to produce a quality weld bead. There a re two ways to end a weld bead. 0 ne 1nethod is to draw the electrode away from the weld bead. The arc stops when the distance is too great for the voltage to 1naintain the arc. Once the arc is stopped, the diver tells the dive supervisor or radio operator to make the knife switch cold (open). This keeps the diver safe by cutting off electrical current when no welding is being performed. The problem with this method is that a long arc produces porosity in the weld. The gas bubble at the end of the electrode is broken, and water quenches the weld pool This area must be ground out prior to striking another arc to continue the ~veld bead. A second method to stop a ,,veld bead is for the diver to tell the dive supervisor or radio operator above water to n1ake the knife switch cold when the diver nears the end of the weld or must change electrodes. The dive supervisor or radio operator opens the knife switcl1. This stops the welding current. No porosity is created in the weld pool. The problem ,,vith this method is that the welding circuit is still complete when the knife switch is opened. This causes an arc across the knife switch, which can damage it. Manufacturers are researching and evaluating possible solutions to the arcing proble1n. When performing underwater welding, the diver must be careful not to ground the metal parts of the diving helmet to any part of the welding circuit. For this reason, the knife switch is opened whenever the welder is not welding. When the knife switch is open, no welding current is flowing, which prevents any potential shock. A lighter value filter plate is used to protect the welder's eyes during wet underwater welding. The visibility is poorer underwater, and 90% of UV rays fron1 the arc are filtered out by the water. A shade 5 to shade 9 filter plate is normally adequate, depending on ,,vater clarity.

,■,Note GTAW and GMAW are not done in a wet welding environment.

Copvrighl Goodheart-WIilcox Co. Inc

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25.5 Hyperbaric (Dry) Welding Underwater There are five basic types of dry habitats for underwater welding. Each type has its own advantages. Four of the habitats allo,,v the welder to enter the habitat. These can be large structures. One is very small, so only the welder's arms enter the habitat. Two habitats are accessed from the surface, while the others require the welder to enter from a wet environment.

25.5.1 One-Atmosphere Pressure Vessel In a one-ntmosphere pressure vessel application, the ,-veld project is encapsulated in a chamber with an access tunnel to the surface. This type of welding is called 011e-ntn1osphere dry chan1ber ive/ding. Many pipeline repairs in rivers and shallow water are repaired using this method. With the dry chamber method, a chamber is lowered over a pipeline. It is sealed around the pipe and the water is pumped out. Welders enter the chamber through a trunk that extends to the surface. Any work and welding nonnally done in a fabrication shop can also be performed inside the chamber. See Figure 25-7. There is no depth limit for a one-atmosphere pressure vessel, but in practica I terms, it is used in relatively shallow applications.

25.5.2 Ambient Pressure Chamber An an1bient pressure c/1atn.ber can also be used to create a dry environment for welding. The chamber is set in place on the pipeline or structure and is sealed around the structure and at the high point. Air pressure or a background gas mixture is used to force the water out of the chamber. The diver enters through an entrance that is lower than the botton1 of the welding chamber. Once inside, the diver removes the diving equipment and puts on regular welding clothes. He or she can then perform any task that would be done in a small, above-water welding shop. In this type of systern, the welder/diver may be required to ,,vear a breathing 1nask, depending on the atmosphere in the chamber. An ambient pressure chambe1· can be used at depths of hundreds of feet (hundreds of meters).

664

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Modern Welding

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veowa E.S Special services veoffa ES. Specie/ services H G Figure 25-7. Hyperbaric welding. A-A one-atmosphere habitat being lowered onto an underwater pipe to be repaired. B- People and equipment can enter through the two access holes to the surface. C- lnside of the habitat, an inspector examines the damaged pipe. D- Damaged areas of the pipe are documented. E- A repair sleeve is put in place. F-Welders weld the sleeve to the damaged pipe. G-Completed welds secure the repair sleeve over the existing pipe. H-Completed welds are inspected using dye penetrant.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 25

25.5.3 Open Bottom Chamber An open bottotn cha111ber is a simple chamber that can be set on to p of a pipeline or hung on a structttral n1en1ber of an oil platform. See Figure 25-8. Once the chamber is set in place and any seals around the s tructure are secured, pressurized air or a backgr0Lu1d gas Dtlxture forces water out of the chamber. The diver enters from the bottom, and the diver's upper body is in the dry area. The diver removes his or her dive helmet, puts on a welding hood, and makes the n ecessary welds.

25.5.4 Dry Spot Welding Dry spot welding is an underwater welding method in which the welding takes place in a s n1a ll cha1nber built from Lexan (a plastic), while the welder remains outside the cha1nber. The diver attaches the Lexan box to the weld area. It is open on the botto1n for the diver to place his or her hands inside. Compressed gas is pumped into the box to displace the water. The diver stays in the water and performs the ,veld inside the box. Small r epairs have been m ad e in nuclear spent fuel pools using this 1nethod to perform GTAW welds.

25.5.5 Cofferdam A cofferdan1 is a structure built around the structure being welded. A cofferdan1 is also called a coffer and

Ocoaneedng lntClfnotionBJ. Inc.

Figure 25-8. An open bottom chamber, or bell, has been

placed around a vertical structure where a horizontal piece connects. Water is forced out using air pressure or a background gas mixture. The welder/diver enters from the bottom and welds in a dry environment. Copvrighl Goodheart-WIilcox Co, Inc

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in so1ne parts of the \vorld is know n as a caisson. A cofferdam diverts water around a const ruction project or keep s ,vater out of the working area of a project. The orig inal use of a cofferda m ,vas to divert ,vater around a dam construction project. Cofferdams are used to keep water away from bridge piers, oil platform structures, or the a rea where a ship is being repaired. Steel or wood pillars are driven into the river bed. Sheet metal is often u sed and joined to the vertical pillars. The sheet metal forms a watertight seal. La rge r structures use a combination of \.Vood, sheet metal, and concrete to form the barrier. Once the cofferdam is in place, the water inside it is pumped out. The force of the water pushing on the cofferdam, which increases as the depth of the cofferdam increases, must be accurately calculated. The cofferdam must be designed to withstand these forces. As an example, a cofferdam can be constructed on the rea r of a ship so repairs can be performed on the ship ,vhile it is still afloa t. A reinforced sheet 1netal cofferdam is constructed a round the area to be repaired. Water is pumped out of the cofferdam so the area to be repaired is not in water. See Figure 25-9. The u se of cofferdams is generally not covered under the D3.6M Underiuater Welding Code. Cofferdams are mentioned in parts of the specification for genera 1 information. In most cases, welding in a cofferdam is the satne as vvelding above water. There may be ci1·cumstances in which the material to be welded has water on the opposite side, which can cause the weld and base m etal to be rapidly cooled. In such cases, special tes ting techniques may be required to prove that the weld ,vill n o t fail. Welding in a one-atmosphere p ressure vessel or a cofferdam h abitat is tl1e same as welding above water. The appropriate specification for the welding being perfonned is followed. The D3.6M code is not followed in these applications. The sophisticated design of underwater welding chambers makes the1n essentia lly unde1,,vater fabrication shops. Any job that can be performed on the surface can be p erformed unde1water, w ith the exception of ope rating cutting torc hes. Cutting in one-at1nosphere chambers, ambient pressure chambers, and open bottom cha1nbers is limited to cold cutting methods, like sawing or g ri nding, or plasma or carbon arc gouging. No flammable gases should be introduced into the atmosphere of a habitat under pressure. The three most common welding methods used in habitats today a1-e SMAW, CTAW, and GMAW. Welding with these three processes in a dry underwater habitat is similar to "''elding on the surface. The same electrodes, currents, wire feed speeds, and welding techniques are used. The helmet filter shade is the same as that used above ,vater.

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o ceanee11ng Intelnat!Onal. Inc. B Figure 25-9. Cofferdam in use. A- This cofferdam built onto the rear of a ship keeps water ou t of the working area. The part to be welded to the ship is being lowered into the cofferdam. 8-Welders are welding a part onto the ship below the waterline.

A

Oceaneering lnre,na,IOna/, Inc.

One strange pheno1nenon welde1/divers notice in deep chamber welding with GfAW is the visible flow of argon shielding gas. At extreme depths, helium and oxygen are used to fill the welding chamber. With helium as the background gas in the chambet~ the welder can see the flow of argon shielding gas. Helium is thin and light. Argon is much heavier. The argon corning out of the GrAW torch and flowing in a helium-rich environment looks like oil and water mixing or like oil and vinegar in salad dressing. Welders v.rith a lot of experience in deep hyperbaric welding do not adjust the flowmeter by volume. They hold the cup up to a light background and adjust the flow by visually watd1ing how much argon shielding gas is flowing from the torch head.

25.6 Crack Repairs Repairing cracks in steel with underwater wet ,.velding is much more difficult than performing the same repair above water. Most small cracks are repaired by either grinding out the crack with a hydraulic grinder or chipping out the crack with an RV-4 chipping gun and a gouging chisel The RV in the designation stands for ri11g valve. This valve type is required for use unde1water. The -4 is a size that works well and can be handled unde1,.vater.

For extensive cracks, the damaged area is removed using an underwater carbon arc gouging system. This system is similar to air carbon arc gouging, except that it uses a water jet instead of air to re.1nove the slag. Underwater carbon arc gouging is covered later in this chapter. Carbon arc gouging in a wet environment causes the surface of the base metal to beco1ue hard and irnpregnates it with carbon. When cracks are repaired using the carbon arc method, the diver has to grind anywhere fron11/16" to 1/8" frorn the surface to reinove the carbon and the heat affected zone. When repairing cracks in a dry habitat or hyperbaric d1amber, tJ1e diver uses the nor1nal air carbon arc gouging equipment. Light grinding is required to remove the carbon from the steel surface. Heavy grinding is not required because there is no quenching effect in the dry habitat.

25.7 Underwater Cutting Undei:water cutting falls into two cat:egories. One is cutting in preparation for welding. The second is cutting for den1olition or salvage work. Cutting in preparation for welding must produce a clean cut and leave the metal ready for ,.velding. Cutting processes used to Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 25

prepare metal for vvelding 111ust not create rough surfaces or a high-carbon-content surface. Demolition/salvage cutting does not have these restrictions. Cold cutting methods are used to cut a pipeline or structural me1nber underwater if repair ,,velds are going to be made. Cold cutting methods do not use heat. These methods use auto1nated saws des igned for underwater use. Examples include Wachs guillotine saws, diamond sa,¥s, travel cutters, and p ortable hydraulic lathes. Wachs is a manufacturer of equipment; their Subsea division specializes in underwater cutting tools. These tools produce highly accw·ate cuts that are beveled and read y for vvelding. Carbon arc gouging is a process used to remove a defect in a '"'eld Carbon a rc gouging leaves a highcarbon deposit on the cut area. Also, the a rea is rough. Additional work, often grinding, must be done to remove the high carbon area and smooth rough areas to prepare the base metal fo r additional welding. Undenvater cutting for demolition or salvage includes exothermic cutting and oxygen arc c utting. These processes leave a very rough cut that is extremely hard and brittle, but they are effective at quickly cutting steel underwater. Since the metal will be scrapped, the hard, brittle, and rough edges left by these processes are perfectly acceptable.

25.7.1 Mechanical Cutting Mechanical cutting is used if the finished cut \Viii be part of a repair or construction that requires a precise finish. Pipe o r s tructures that are being prepared for

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welding need an accurate cut to aUow for good part fit up for tacking and welding. A w ide varie ty of mechanical cutting equipment is used in the underwater oil industry. Cutting done with this equipment is normally referred to as cold cutting because the cut is made with saws, 1nilling tools, or high-pressure water. Because cold cutting processes do not use heat, they do not burn the steel being cut. Cold cutting systems for under\vater use are sim ilar to systems used above water bu t are n1odified for the underv.rater environment. The machines are operated by hydraulic pressure. They all require a high-pressure, high-volume hydraulic pump. Any electrical controls used on the land-based versions of these units 111us t be conver ted to mechanical controls for underwater use. The Wachs guillotine saw is a reciprocati ng saw that uses a hydraulic motor to move a large saw blade back-and-forth to ma ke a straight cut on pipe. See Figure 25-10. This type of sa,-v is used for cutting a pipe so a mechanical flange can be attached to each end to repair the pipe. For exa 1nple, if a pipeline is damaged over a length of 150' (50 m), this section must be replaced. Divers wiJl use a guillotine saw to re1nove the 150' (50 m) of damaged pipe. They install a mechanical sealing flange on the ends of the remaining good pipe. Then, they weld a 150' (50 111) piece above water and lower it into the water. They bolt the flanges on both ends of the repair section, and the repair is complete. T his is not a welded repair, but a mechanical repair. The pipe cou ld also be welded, depending on the application.

-

Wac/1s Subsea LLC

Wachs Subsea LLC B Figure 25-10. Guillotine saws. A-A hydraulic reciprocating saw, called a guillotine saw, is used to cut pipe underwater. B-Guilloline reciprocating saw cutting through a vertical pipe column.

A

Copvrighl Goodheart-WIilcox Co, Inc

66 8

Modern Welding

A dian1ond wire saw makes cuts with a ,~,ire that has commercial diamonds embedded in it. A hydraulic control unit continuously drives the wire. The diamonds do the cutting. The result is a very c lean cut that is ready for welding. See Figure 25-11. The Wachs travel cutter is a hydraulic milling machine that is cla1nped onto the pipe that is to be cut. It is capable of making very straight cuts and can be set up with sh·aight saw blades or a combination of a saw blade and a beveling blade. 171is n1acni ne is so accurate that a finished cut can have another pipe fit up to it and welded with no additional preparation. See Figure 25-12. The Wachs travel cutter is used primarily on pipelines or sh1.1ctural members where the repair method is a dry habitat weld and the repair is a full penetration butt joint weld. AJI of the cutting and fitting up of the pipe is completed in the water. A habitat is then set on the pipe, and the fu1al v.reld is performed in the dry habitat. A hydraulic lathe is another cutting tool used underwater. One ring is attached to the pipe to be cut. A second ring with a cutter attached is forced to rotate and cuts the pipe. A beveling tool can also be used. This hydraulic lathe tool can cut and bevel a pipe at the same tiJne. The result of this lathe cutting operation is a very clean and straight cut edge ready for welding. See Figure 25-13. An ROV (remotely operated vehicle) version is shown in Figure 25-14. This unit clamps onto the pipe and then cuts and bevels the pipe. An advantage of an ROV is that it can be driven remotely. The diver does not have to be in the water to place the equipment onto the pipe.

A

B

Wachs SUbs"" LLC

Figure 25-12. A hydraulic milling machine A-This machine

cuts and bevels the end of a pipe in preparation for welding. B-Underwater cutter in use.

Diamond-Impregnated wire Wsd>s Subs ... LLC

Figure 25-11 . A diamond wire saw has industrial

diamonds embedded in a wire. The diamonds cut through the pipe as the wire is continuously fed across or through the pipe.

High-pressure water jet cutting equipment is available but is not used as much as the n1echanical cutting machines. These machines use water and grit that is mixed together into a slurry and pressurized to 50,000 psi (350 MPa). Water jet cuttiJ1g machines can cut layers of steel ,¥ith concrete between the layers. An example is cutting off jacket legs with pilings inside. There is concrete pun1ped in between the pile and the jacket leg. The vvater jet cutting system can be used in situations where it would be dangerous for divers to cut undervvater. This section lists only a few of the most common types of mechanical cutting machines. Numerous other cutting tnachines are used unden,vater. Copyr!ghl Goodheart-WIiicox C-0 Inc.

Chapter 25

Underwater Welding and Cutting

669

Workers should use a co1nmerciaJ diving heJn1et and related equipment when they perform underwater thermal cuttu1g. Cutting should not be performed in SCUBA (self-contained underwater breathing apparatus) diving equipment.

Exothermic Underwater Cutting Equipment

Wadls Subsoa L LC

Figure 25-13. A hydraulic lathe tool is attached to the pipe to be cut. A cutting and optional beveling tool are driven around the pipe to prepare the pipe for welding.

Underwater exothermic cutting is the same process as exothermic cutting above water. The equipment is the san1e with a few exceptions. The cutting rod holder is designed for underwater use and is insulated to prevent electrical shock to the diver. See Figure 25-15. The same holder for underwater exothennic cutting is also used for oxygen arc underwater cutting. Underwater exothermic cutting rods are a lso insuJated. Exothermic cutting can cut tru·ough steel, concl'ete, and any other 1naterial Required equipment includes the follo,ving: • Underwater cutting rod holder. • Welding cable (long enough to reach the job). • Ground cable (with either a workpiece connector or a striker plate). • Oxygen hose--3/8" (9.6 mm) inside diameter recom1nended. • Oxygen cylinders. • High flow oxygen regulator. • Insulated exothe1mic cutting rods. • Po,ver source--12V or 24V DC battery or a DC welding machine capable of 150 amps set on OCEN. • Knife switch. This is above water and used to connect and disconnect the power fron1 the rod holder. • Con11nercial diving helmet. • Dive radio for cornn1unications between the dive station on the su rface and the diver.

Wilchs SUbsea LLC

Figure 25-14. A remotely operated vehicle can be driven onto a pipe. This machine uses a vertical mill and other tools to cut and prepare a pipe prior lo welding and to remove excess weld material from a completed weld.

Exothermic Underwater Cutting Process Current is supplied to the cutting rod tro1n a 12V or 24V battery or a welding po,,ver source. The current is needed to initiate the process, but is not needed to

25.7.2 Thermal Cutting Thermal underwater cutting is performed using two main processes-exothermic cutting and oxygen arc cutting. These processes are siJJi.ilar to those used for thennal cutting above \.vater, but the equipment is slightly different. The cut quality is not good enough for proper fit-up prior to welding. Thermal cutting hardens the cut su1·faces or makes them brittle, conditions that are not accept· able prior to welding. Most underwater thermal cutting is done for demolition, scrap, or salvage operations. Copvrighl Goodheart-WIilcox Co, Inc

oxygen control valve Broc.o, Inc.

Figure 25-15. An exothermic underwater cutting torch and insulated rod.

670

Modern Welding

continue the process once it has started. One advantage of exothermic unde1,.vater cutting compared to oxygen a1-c underwater cutting is the steel does not have to be cleaned prior to cutting. A person on the surface of the water connects the battery or turns on the DC welding power source. The oxygen pressure is set to 100 psi (700 kPa) over the water pressure at the depth the cutting process will take place. Keep il1 mind that water pressure mcreases as the depth increases. This is due to the .veight of the water above pushing down on the water below. When ready, the diver calls for the dive station to make the knife switch hot. The term /Jot means that electrkal current is flowing through it. The diver then strikes an arc and slowly opens the oxygen control valve. As soon as the rod is ignited, the diver instructs the dive station to make the knife switch cold, or turn off the electrical cw-rent. Once an exothennic cutting rod is ignited, it continues to bu111 as long as oxygen is flowing through the rod or until the rod is consumed. See Figure 25-16. The diver keeps the tip of the rod in contact with the steel. The rod is pointed in the direction of travel. The diver pushes the rod in the direction of the cut, and the exothermic cutting rod melts the metal and blows it out of the cut. For steel thicker than 1/2" (13 mm), the diver should reduce the angle, moving the cutting rod more toward vertical. For steel over 1" (25 mm) thick, the rod should be almost perpendicular to the steel being cut.

BtlM Derby, EPIC Divers an Goodh08/t•WIHcox Publisher

Figure 27-6. The proper way to overlap adjacent surfacing beads when 100% coverage is required.

Figure 27-7. A roll surface has been completely covered with a surfacing alloy. Both FCAW and SAW are well suited to make continuous beads. Note the hardfacing stringer beads applied to the arm surface to the right.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 27

Metal Surfacing

703

27.2.3 Surfacing Using the Submerged Arc Welding Process

27.2.4 Surfacing Using the Gas Tungsten Arc Process

The equip1nent is the san1e for both ,,velding and s w·facing with the submerged arc ,,velding process. The electrode ,vire and flux a re ch osen for the surfacing cha1·acteristics desired . C rusher rollers, di·ums, 1nine car wheels, deep hole drill steins, ru1d oth er parts have hardfacing materials applied using the SAW process.

Sw·fac ing can be accom plish ed using the gas tungsten a rc p rocess. The 1neta l to be s urfaced is heated ,vith the GfAW torch and tungsten electrode. Filler "''ire is added to deposit surfacing 111ateria l. The eq uipment should be set up \ pc,,;-iriI not required. Roptoduced whh permission from th9 Am&rlcan We/ding Society, Miami, FL.

Figure 31 · 24. Table showing the type and number of test specimens required and the qualified range of thicknesses. AWS D1.1 /D1 .1M: 2015, Table 4.11, Welder and Welding Operator Qualification-Number and Type of Specimens and

Range of Thickness and Diameter Qualified. Continued. Copvrighl Goodheart-WIilcox Co, Inc

820

Modern Welding

Table 4.11 (Continued) Welder and Welding Operator Qualification- Number and Type of Specimens and Range of Thickness and Diameter Qualified (Dimensions in Millimeters) (see 4.15.2.1) (1) Test on Plate

Qualified Dimensions

Number of Specimens'

Nonu nal Plntc, Pipe or Tube Thickness Qun Iified, nm,

Production Groove or P lug Welds

Nominal

Type o f Test Weld (Appl icable Figures) Gr oove (Fig. 44.Q or 4.21) G roove (Fig. 4 .16, 4.17, or 4.!2)

Groove (Fig. 4 .16, 4.17, or4.!2) Plug (Fig.

4._w

Face Root Side Thickness of Bend• Bend• 1lendb Test Plate, T, (Fig. (Fig. (Fig . mm 4.§.) 4.§.) 4.~

(Applicable Figures)

e1eh

Min.

Max.

(Note c)

-

3

20 max"

l

1

IOVilling to be trained for the position if you lack a specific required skill. It is i1nportant to be a little early 1,vhen you go in for an intervie,~'. You have only one opportunity to create a positive first impression. Be sw·e to look yow· best for a n interview. Dress well, but appropriately. Lf you are interviewing for a welding job, a business suit is not necessary; business casual atti1·e or a nice pair of jeans is sufficient A collared shirt and tie would be appropriate if you are applying for a job as an inspector, foreman, or supervisor. A suit is appropriate if applying for an engineering position. Present a clean and neat appearance.

Do not wear work clothes to an interview unless you are directed to do so by the interviewer. You will not normally be expected to go to work immediately, but you may be asked to complete some performance tests.

852

Modern Welding

Michael

J. Garcia

134 Lincoln Street Wilton, TX 93232

(915) 555-1234 mjgarcia22@e-1na il.com

Career Objective To obtain an entry-level ivelding technician position in the fabrica tion industry.

Professi onal Experience Heavy Metal Welding, Holloton, TX August 2017-present Welder's Helper • Perforn, general shop labor, incl udi ng material cutting and prepara tion with oxyfuel and plasma systems. • Cu t parts to required length on horizontal band savJ. • Tack weld ladder systems with GMAW. • Help " 'elders \s1ith material prep and grinding. May 2016-August2017 Simpson Supply Co., Wilton, TX Parts Clerk • Worked with customers at parts counter, cl1ecked inventory system, and obtained parts. • Conducted daily and monthly inven tory d1ecks. • Gen eral stocking and cleaning throughout store. • Delivered and picked up parts a nd equipment.

Education Associate Degree in Welding Technology May2018 Gardendale Community College • GPA: 3.22/4.0 • Coursework included welding layout and fab1ica tion, SMAW, GMA W, FCAW, and GTA W processes, oxyfuel and plasma cutting. • Obtai ned level one and leve l two welding technology certificates: Entry Level Welder, and Advanced Welder. • Passed AWS ,velder performance qualification test for CMAW /E'CAW and SMAW. • Member AW5 s tudent chapter a t CCC. • Participa ted in SkillsUSA welding completion in high scl100I.

Community Service Habitat for 1-lumanity, volunteer, summers of 2016, 2017, and 2018 Wilton Food Bank, volunteer, 2016-present

References Available upon request.

Goodhoan•WJ/lcox Publish9r

Figure 33-6. A resume can be uploaded to a company's website. A well-written resume will help you get a job interview. Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Chapter 33

After going for an interview, send a thank-you note right away. This can be e-mailed, but handwritten notes cause you to stand out from the cro,-vd. If there are 1nultiple interviews during the hiring process, send a thank-you note each time.

33.5.3 Welding Tests Required of Applicants Employers who hire welders, welding operators, and tack welders often check the applicant's hands-on welding skills. Welding tests are given to applicants by the employer. These welding performance tests can vary from very easy to very difficult. There are two main categories of welding performance tests. These are given by the following two types of co1npanies: • Companies that fabricate products not required to meet a welding code or standard. • Co1npanies that fabricate items required to n1eet codes or standards. Con1panies that fabricate products not required to meet codes or standards usually fabricate less complicated assemblies with simpler designs. However, the employer sbU requires each applicant to prove his or her skills in performing welds. The applicant is usu ally given a typed and illustrated list of welds required fo r evaluation by the employer. The applicant is taken to an area to perform the welds listed on the welding test. The 'vvelding tes t direc tions inc lude the welding process to be used, the type of base metal, the position, the number of welds to be performed, and the size o f the welds. It is common for the applicant to be given a blueprint that has a detailed drawing of a weldment with welding symbols. The applicant is often required to read the drawing and weld a replica of an actual product that the company fabricates. Usually, each welding p erforn1ance test of this type has the visual acceptance criteria lis ted on the test sheet. Companies that fabricate items that require meeting welding codes, such as the AWS D1.1, S f-r11cfural Welding Code-Steel, require a more difficult performance test. The e1nployer is required to give a welder performance qualification test to applicants who are seeking a job requiring them to perform welds covered by a code. These 1nore difficult welder qualification tests may be performed with any v,relding process, in any position, and on many different types of base 111e tal or pipe. Applicants who have taken welder performance qualification tests for one employer are required to take the tes ts again for a new employer. Copvrighl Goodheart-WIilcox Co, Inc

Get1ing and Holding a Job in the Welding Industry

853

Chapte r 31, Proced11re a11d Welder Qunlificatio11s, covers welder performance qualification tests and the different welding positions and types of tests that could be g iven to an applicant.

33.5.4 Factors That Lead to Rejection for Employment In a study, executives from a variety of companies were asked to identify traits, behaviors, or qualities that might cause the1n to reject an employ 111ent candidate. They identified the following factors: • A poor scholas tic record. • Personality flaws. • Lack of goals. • Lack of enthusiasm. • Lack of interest in the business where employment is being sought. • Inability to express oneself. • Unrealistic salary de1nands. • Poor personal appearance. • Lack of maturity. • Failure to get information about the company where employment is sought. • Excessive interest in security and benefits.

33.5.5 Typical Weld Shop Duties The typical duties and responsibilities of a "''elder working in a weld shop include, but are not li:ntited to, the following: • Maintain proficiency in all phases of assigned tas ks, including print reading, 1na terial selec tion, equipment setup, c utting, joint prep, welding, finishing, inspection, and tes ting. • Perform regularly scheduled maintenance on welding equipn1ent and basic tools to 1nai:ntain a safe shop environment. • Conduct a thorough daily cleanup and s urvey of the shop to make sure all equipment and supplies are properly s tored. Clean equipment using appropriate materials. • Exercise proper safety and h ousekeeping skills, an understandiJ1g of occupationa l haza rds, and effective safety precautions. • Continue to learn job-related skills and knowledge through oral instruction and observation. This learning takes place mainly in on-the-job training.

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Modern Welding

• Learn and adhere to company policies regarding equipment and co1nputer usage, operational procedures, and office-related tasks. These tas ks may include properly filling out time cards, inventory reco rds, and other applicable types of recor ds. • Give and receive regularly scheduled evaluations for the pw-pose of advancement, discipline, 1noni.toring perfo nnance, or any other purpose d eemed necessary by the management.

33.5.6 Time Card Records Employers must comply with US D epartment of Labor record keeping laws. The Fair Labor Standa rds Act (FLSA) requires employers to keep records that determine employee earnings. Tin1e cards are used for this purpose and must be acc urate. Time cards are essential for paying hourly workers and must be carefully organized for paycheck acc uracy and record keeping compliance. Hourly employees are responsible for accurately recording all h ours worked, Figure 33-7.

GlJn Jones /Shutte1stock.com

Figure 33-7. In the United Slates, the Fair Labor Standards Act require s employers to keep records that determine employee's earnings. Time cards are used for th is purpose and lo accurately track all regular and overtime hours.

Overtime ho urs a re carefuUy recorded on ti1ne cards so additional overti1ne pay can be accurately calc ulated. In case the Department of Labor needs to inspect time card records, they n1ust be kept open at the workplace or at a central records location. Most companies set a specific time card submiss ion d eadline for each payroU period. For exa1nple, the time card submission deadline may be set for 9:00 a.m. ever y Monday. Not having a specific day and time for e1np loyees o r supervisors to subn1it a ll time cards "vould result in sloppy record keeping that could cause payroll processing to be delayed. Also, time and money are wasted tracking down employees and super visors to determine employee hours. A company policy manual should include a time card policy so all e mp loyees assist in the process of properly n1aintaining records.

33.5.7 Factors That Can Lead to Termination from a Job The following factors can lead to lack of promotion on the job or even to being fired (te1minated) f rom a job: • Poor a ttendance without good reason. • Habitually coming to work late. • Alcohol abuse. • illegal drug use. • Inability to perform the tasks required. • Inability to work as a team member. • Inability to work with peers. • Fighting wi th or making threats to peers or supervisors. • Insubordination to directions from a supervisor. • Talking with others too much and too often. • Lack of respect for o thers. • Lack of respect for o thers' property. • Ahvays making excuses. • Constant complaining. • Inability to n1ake lndependent decisions ,,vi thin the scope of the job.

Copyr!ghl Goodheart-WIiicox C-0 Inc,

Chapter 33

Getting and Holding a Job in the Welding Industry

855

Summary

Technical Terms

• Due to a shrinking workforce and job growth, there is an increasing need for ski Ued welders. • Welding and welding-related careers require varying levels of education. The education i-equired may be high school, trade school, technical school or community college, military training school, trade apprenticeship, or college/ university. • In addition to "velding comses, school subjects that contribute to success in the welding field include print reading and mechanical drafting, elech;icity and electronics, metals shop, physics, mathematics com ses, and computer courses. • Many welding resomces can be accessed on the Internet. Welding companies offer apps ,-vith a variety of helpful welding information. • In the field of welding, e1nployers seek to hire those with a keen ability to carefully follow written and verbal directions. • When screening applicants, employers consider personal traits, academic skills, and personal management skit ls. • Applying for a job generally involves completing a job applicatio n and sub1nitting a resu1ne online. An accurate, complete, and carefully prepared resume is helpful in obtaining a job interview. • Prior to going to an interview, the applicant should learn about the company and the job and practice answering potential questions. • Interviewees should arrive a little early to an interview; dress well, but appropriately; and send a thank-you note after the interview. • Welding performance tests vary in difficulty based on whether the company fabricates products required to meet a welding code or s tandard. • Many factors may lead to rejection for ernployrnent, including a poor academic record, lack of enthusiasm, unrealistic salary demands, and poor personal appearance. • The Fair Labor Standards Act requires employers to keep records that de termine employee earnings. Employees mus t record all hours worked.

Select the icons to access Drill and Practice activities. personal management resume skills tedmical trade physics principles ti.n1 e ca rd reference

Copyng111 Goodhear1-w1nco~

co

Irie

Review Questions A11swer the Jollo,ving q11esf-io11s using the i11for111ation provided in this chapter. Know and Understand 1. Which of the following requires an education

level beyond high school or trade school? A. tool and die welder B. arc welder C. v.relder-fitter D. resistance welder 2. The educational level normally required for a pipe and steamfitter is-~ A university B. trade apprenticeship C. community college D. high school 3. True or False? Welding resomces can be accessed using apps. 4. True or False? Self-confidence is a personal trait sought by employers. 5. Volunteering new ideas and volunteering to do extra tasks demonstrates _ _ A. self-confidence B. dependability C. ability to follow oral instructions D. initiative 6. True or False? Suggesting a new way to perform a job is frowned on by employers. 7. True or False? When in doubt, you should wear work clothes to an intervie"v in case you have to take a welding test. 8. True or False? An employment candidate may be rejected due to lack of maturity. 9. True or False? Typical weld shop duties include performing regularly scheduled maintenance on ivelding equipn1ent. 10. True or False? Frequent tardiness is a factor that can lead to tennination of an ernployee.

Apply and Analyze

1. List two reasons for the expected growth of welding jobs in the United States. 2. Explain why a student should take physics in high school. 3. Wl1at print reading skills are needed by a welder who wants to advance in the field? 4. What skills and kno~vledge can students learn in the metals shop? 5. What resources can be accessed in the AWS online resource library? 6. What four behaviors den1onsb·ate dependability? 7. Explain how to apply on line for a job. 8. Explain how to prepare for a job interview. 9. Describe two welding tests that could be given by a company that does not perform welding per a code or standard. 10. Why do companies need to keep time card records?

Critical Thinking

1. What questions could you ask a potential employer in an interview to show that you have an interest in tl1e job? 2. In what ways would a job applicant with sol.id mathematics skills have an advantage in getting hired over a job applicant with poor math skills? How are .m ath skllJs used by welders? How could you communicate or demonstrate strong math skills in a job interview? Experiment

1. Obtain a print containing all necessary welding information to fabricate a weldment. Suppose a prospective e1nployer gives you this print to look at for the first time in a job interview. Assuming all new hires are required to read and understand the information on this print, 1neet with a fellow \.Velding student to ask and answer a series of questions demonstrating that you possess solid print reading skills for welding.

Technical Data

G&n Jones/S/futtsrstoel\'n as An1erican Society of Testing and Materials. (28) austenite. High-temperature form of steel. It has a face-centered cubic structure. (28) austenitic stainless steels. Steels that contain 16% to 30% chromium, 3°/o to 37% nickel, 2% manganese, and smal I a,nounts of silicon, phosphorus, sulfur, and other elements. (21) automatic cutting. Cutting 1vith automated equipment that requires only occasional or no observation of the cut, and no manual adjustment of the equipment controls. (15) automatic GTAW system. A system that uses feedback signals to adjust the CTAW process to produce a high-quality weld. (10) automatic mode. Mode of operation in which a robotic system performs a program exactly and the program can be repeated over and over. (26) automatic welding. Welding with equipn1ent that needs minimal monitoring and no manual adjustments during the process. (26) axonometric projection. A drawing view in which an object is rotated on any of its three axes relative to a projection plane in order to create a pictorial view. (2)

B backfire. Short "pop" of the torch flaine followed by extinguishing of the flame or continued burning of the gases. (13) background current. Current level that is high enough to maintain the arc but not enough to continue to melt the base metal. (8) background gas. Gas mixture used to force water out of an undef\>\rater chan1ber and keep oxygen at a safe level. (25) backhand welding. Welding technique .in which the tip of the electrode or torch is pointed away from the direction of travel. (3) backing. A plate, ring, strip, or other device placed on the root side of the joint to control penetration of the weld. (6) backing gas. Shielding gas applied to the root side of a weld. (10)

backing ring. A metal ring placed inside a pipe before welding a butt joint. The backing ring ensures complete weld penetration and a smooth inside surface. (23) backing strip. Strip of metal placed at the root of a weld joint to support the molten weld metal and control penetration. (22) backing tape. Fiberglass or ceramic material on an adhesive tape. The tape is applied to the root side of a weld to help control the depth of root penetration. (23) backing weld symbol. A symbol that indicates an addiHonal weld should be made on the root side of the joint to ensure 100"/o penetration. (3) backstep method . Starting the first segment of a ~veld a"''ay from the beginning of the joint, then performing a number of short welds, welding each section back tov.,ard the previous section. (6) backward arc blow. As the magnetic flux intensifies ahead of the electrode, the arc and molten metal are blown back toward the beginning of the weld. (6) balanced wave. Wavefonn that results when the san1e amount of current flo~vs during both halves of the AC cycle. (9) base metal. Metal to be welded, cut, or brazed. (4) basic oxygen furnace. Furnace that uses oxygen to burn off the carbon and impurities in molten metal to produce steel. (28) bell . Chamber used to lower and raise divers into the water. (25) bell-mouthed orifice. A torch tip orifice that is nusshapen and enlarged due to improper cleaning. (14) bend deduction. Value (length) to be subtracted from the total lengths of two legs to account for material loss during a bending operation. Also referred to as setback. (32) bending jig. A device used to conduct a bend test on a sample of a test weld. (31) bends. Condition that occurs when gases dissolved in the diver's blood are not allowed to return to normal prior to returning to atmospheric pressure at the surface. (25) bend test. Common destructive testing method in which a sample of the weld and surrounding base metal is bent and checked for o·acks. (30) beryllium. A commercial metal that is lighter than aluminum and has a fairly high n1elting temperature. (22) bevel angle. The angle between the bevel of the joint and a plane perpendicular to the surface of the base material. (3) Copyr!ghl Goodheart-WIiicox C-0. Inc.

Glossary

bezel. A large th.readed cla1np ring that holds a gauge lens in place. (12) bird's nest. Tangle of welding wire that did not feed properly through the rolls and into the guide tube. (8) blow hole. A hole in one or more pieces of metal being welded, usually referring to a spot weld. (19) body-centered cubic structure. The structure of steel at room temperature, in which there is one ato1n at each corner of a cube and one in the center. (28) bond coat. An intermediate surfacing between the base material and the finished surfacing. (27) bottom time. The time from when a dive begins to when the diver begins to ascend. (25) Bourdon tube. A tube in a pressure gauge that straightens as pressure increases. As it straightens, it operates a geai- and pointer mechan.iSJn. (12) brake press. A n1achi.ne used to bend metal. A punch is located above the metal to be bent, and a die is located below the 01etal to be bent. As the punch and die come together, they contact the meta I and bend it. (32) brass. An alloy consisting chiefly of copper and zinc. (17) brazed connection. Connection made using special fittings that are brazed onto tubing. (23) brazement. An assembly joined by brazing. (17) braze welding (BW). Making an adhesion groove, fillet, or plug weld above 840°F (450°C). The metal is not distributed by capillary action. (17) brazing. Making an adhesion connection using a 1nin.imu1n a1nount of an alloy that 1nelts above 840°F (450°C). The alloy flo,¥s by capillary action between close-fitting parts. (13) Brinell hardness testing machine. Machine that has an indenter built into a press. The indenter is pressed onto the test sample for a given amount of ti1ne, the load is re1noved, and the diameter of the indentation is measured. (30) brittle. Easily fractured. (28) brittleness. Quality of a 1naterial that causes it to develop cracks with only a small degree of bending (deformation) of the material. (28) broach. A tool used to shape a hole. Broacl1ing \¥ires are used to clean welding torch tips and correspond to the diameter of the tip orifice. (12) bronze. An a !Loy consisting chiefly of copper and tin. (17) buildup. The a1now1t that the weld face extends above the smface of the base meta I. (27) buried arc. A weld pool that is lower than the surface of the surrounding metal. (8) burn. To rapidly oxidize. (4) Copvrighl Goodheart-WIilcox Co. Inc

873

burning bar. A pipe 6JJed ,vith special alloyed wires. Once the bar is heated to its kindling temperatui·e, it burns as long as oxygen is forced through the pipe at a sufficient pressure and volu1ne. The burning stops when the oxygen is shut off, the burning bar is consun1ed, or the te1nperature in the chemical reaction is reduced below the kindling temperature. (24) buttering. Surfacing deposit that is applied to provide a metallurgically co1npatible surface for a weld metal to be applied later. (27) butt jou1t. An assembly in 1,v hich the two pieces joined are in the same plane, with the edge of one piece touching the edge of the other. (3) butt seam welding. Forn1 of seam welding in which elech·ic current heats the edges of the metal to a molten condition just before it passes between a set of rollers. The two rollers press pipe edges together, and the metal is welded. (19)

C capacitor discharge resistance welder. The most co1nmon type of stored energy resistance we lding machine. Elect1ical energy is stored in a capacitor and released by the capacitor when it is needed to weld. Also referred to as an electrostatic resistance spot welding nzachine. (18) capillary action . Property of a liquid to move into sn1all spaces if it has the ability to "wet" those surfaces. (16) carbide precipitation. The separating (precipitation) of carbides at grain boundaries in a stainless steel or other alloy. As a result, the stainless steel and other alloys become susceptible to intergranular corrosion when exposed to a temperatme range characterized as a sensitizing te111perature. Also referred to as sensitizing. (21) carbon and low-alloy steel electrode classification numbet Four- or five-digit American Welding Society identifying nu1nber for carbon and low-alloy steel electrodes. (5) carbon equivalent (CE). Formula used to quantify the 1,v eldability of a steel. As the carbon equivalent increases, the weldability of a steel decreases. (25) carbon monoxide (CO). A colorless, odorless, toxic gas that unites readily ,vith oxygen to forin carbon dioxide (CO2). (34) carbon steel. An alloy of iron and controlled amounts of carbon. Also referred to as plain carbon steel and straight carbon steel. (28) carburizing flame. A reducing oxyfuel gas flame in which there is an excess of fuel gas, resu lting in a carbon-rich flame zone beyond the inner cone. (4)

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case-hardening. Adding carbon to the surface of a mild steel object and heat t reating it to produce a hard surface. (29) cast aluminum. Aluminum that is shaped by pouring it into a mold and then solidifying it by cooling. (22) cementite. The compound also kno1,vn as iron carbide (Fe30. It contains 6.67% carbon. (28) center finder. Tool used to find the top and center of a pipe. Used 1,vhen a ligning pipe and p ipe fitti ngs. (23) centerline. A line that marks t he center of a radius, circle, or cylinder. Two centerlines run perpendicular to each other and intersect at the exact center of a circular part or hole. (2) chain intermittent weld. Type of intermittent weld in which the \,velds on either side of the joint begin and end at the same spot. (3) Charpy V-notch. A standard impact test used to measure a material's toughness. (30) check valve. A valve that allows a liquid or gas to flow in only one direction. It closes when flow in the opposite direction is attempted. (12) chemical analysis. Test that determines the chemical rnakeup of a metal. (30) chemical cleaning. Using a solvent to remove oil and grease from parts. (17) chemical corrosion. Deterioration of metal d ue to exposure to corrosive chemicals. (27) chipping hammer. Pointed hammer used to remove s lag £ron1 weld beads. (5) chip test. The removal of a small sample of me ta l with a chisel so that the metal's structure can be ana lyzed. (28) chrome-molybdenum steels. Relatively corrosion-resistant steels that contain from 0.5% to 9.0% chromiurn and from 0.5% to 1.0% molybdenum. They are used \,vhen strength at high temperatures is r equired . Also referred to as chro111e-n1oly steels or Cr-Mo steels. (21) circle-cutting guide. Device that consists of an adjustable-length rod with a cente1· pivoting point and a means of holding the tip. It guides the torch for cutting perfect arcs or circles. (14) cladding. A somewhat thick layer of material applied to a surface to improve resistance to corrosion or other agents that tend to wear away the metal. (27) coalescence. The intermixil1g or growing together of materials into one body \,vhile being welded. (16) code. A document that deals with the design, structure, and loads of a structure. (31) cofferdam. Barrier built around the structure being welded. It diverts water around a construction project or keeps water out of the working area of a project. (25)

coherent. Tenn used to describe \~raves of light that are m-phase and move together. (20) cold welding (CW). Welding process that makes use of h ig h pressure and no outside heat to force n1etal parts to fuse. (20) cold work mg. The bending (deforming) of metal at a ten1perature lower than its recrystallization temperature. (29) collet. The device that fu·mly holds the electrode and transfers electrical current to the e lectrode. (9) collet body. GrAW torch component that contact s and centers the collet and transfers the electrical cu n·ent to the collet. (9) color test. A visual test that identifies categories of metals based on their color. (28) combination AC and DC arc welding power source. Power source that includes a transformer with a DC rectifier, motor- or engine-di·iven generator wit h a DC rectifier, or inver ter. (5) combustibles. Easily ignited materials. (1) commentary. Additional i.nfonnation at the end of AWS D1.1. Commentary is not part of the code, but helps the reader understand the w riters' intentions. (31) complete jomt penetration (CJP). A groove weld where the weld metal complete ly fills the groove thickness. (31) compression fitting. Type of fitting contn1only used on small copper or steel tubmg. A threaded nut is tightened over the tube and onto the threaded fitting to form a tight seal. (23) compressive strength. The greatest stress developed in a rnaterial under cornpression. (28) conductivity. A measure of how well electrical current passes through a material . (18) connector. Insulated terminal on a welding lead that allows the lead to be quickly connected to or disconnected from the welding supply. (5) constant current. Amperage that changes very little in relation to changes in voltage. (9) constant current power source. Arc weldil1g 1nachine that produces a steep output slope. (S) constricting nozzle. The part of the PAC torch that accelerates and concentrates the arc and plasma flow to create a cutting jet. (11) consumable electrode. Electrode that melts and becomes pai·t of the weld. (20) contact tip. The part of a \,velding gun that transfers the electrical current from the welding gun to the electrode wire. (7) continuous casting process. A method of casting metal in an open-ended mold so that metal is fed into and cools in the mold in a continuous form. (28) Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Glossary

continuous weld pool. A n1olten pool of metal that is carried along the seam of the parts to be welded together. (13) contour marker. Tool used to draw a straight li.ne on the outside diameter (OD) of a pipe for pipe preparation. (23) contract. An agreen1ent between the manufacturer or builder of a product and the buyer regarding the way the product will be built. (31) copper-based electrode. Class of SMAW electrodes composed mainly of copper. (5) corner joint. The junction formed by edges of two pieces of n1etal touching each other at an angle of about 90° (a right angle). (3) couplant. A material placed between the transducer and the 1netal test surface during ultrasonic inspection. (30) cover lens. A removable pane of dear glass or plastic used to protect the expensive welding filter lens. (12) cover pass. The final weld pass in a multipass ,.veld. (3) cover plate. Clear plastic or glass plate that is placed in front of and behind the filter lens to protect it. (5) cracking. The action of opening a valve slightly, then closing it i.Jnmediately. Cracking is used to blow out any dust m tl1e valve orifice. (13) crescent motion. Movement of a torch or electrode in a crescent pattern to create a weave bead. (3) critical defect size. The maximum allo,vable size of a discontinuity before it is considered a defect. (30) critical temperatures. The temperatures at which phase changes or structural changes occur in a 1netal. (28) cross-wire resistance welding. A welding technique in which wires are crossed and held beneath a single electrode or 1nultiple electrodes of a specialized weldmg machine. Current passes between wires where they cross and creates a resistance spot weld at that point. (18) crowned. Built up above the surface of the parent ,netal. (13) cryogenic steels. Steel alloys that maintain their strength at very low temperatures. (21) current analyzer. A hand held meter that can use a coi I probe to measure cu rre.nt through resistance ,.velded equipment and weldment. (19) cutting outfit. All equipment required to perform a cut. (15) cutting oxygen lever. Lever on an oxyfuel gas cutting torch that is depressed to control the flo,,v of oxygen from the cutting oxygen orifice. (15) Copvrighl Goodheart-WIilcox Co, Inc

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cutting plane line. A thick line that shows v.1here an object is sectioned. (2) cycle. One complete waveform of alternating current. (5) cylinder (safety) cap. A metal cap threaded onto a cylinder to protect the cylinder valve. (12)

D dash number. Number used at the end of a carbon steel electrode classification to indicate electrode polarity, shielding gas requi.J·ements, etc. (7) defect. An ilnperfection or flaw which, by its size, shape, location, or makeup, makes the part unfit for service. A defect must be repaired. (6) degreasing solvent. A liquid that effectively dissolves grease and oil. (16) denitrifier. Element added to n1ost electrode wires to reduce the porosity in the finished weld. (7) density. The mass of a substance per unit of volu1ne. (28) deoxidized copper. Copper that has had a small amount of silicon added to it, which dissolves any oxides in the 1netal. (28) de oxidizer. Substance that, when added to molten metal, re1noves either free or combmed oxygen. (7) depth of bevel. The depth of preparation for a groove-type jomt (3) destructive testing. The process of testing a sample until it fai ls. It is used to determine the physical properties of a weld and predict its service life. (30) detail drawing. Dra1,ving that shows the shape and size of each small part of an asse1nbly. (2) detail view. View that depicts a portion of the parent working drawi.J1g m much greater detail and typically appears as a callout that allows for enlargement and better visibility. (2) detonation flame spraying. Thermal spraying process that uses controlled explosions of a mixture of fuel gas and oxygen to propel a powdered coating material onto the surface of a \Norkpiece. (27) detonation flame spraying gun. Spray gun that contains a co1nbustion cha1nber i11 which oxygen, a fuel gas, and a charge of surfaci11g materials mix. (27) Dewar flask . A cylinder designed to hold gases that have been reduced in t:emperature until they condense into a liquid. (12) die. A tool used to shape or cut n1etal. (32) diffuser. Device mto which the contact tip threads. The adapter threads into the welding gun. Shielding gas flows through s1naU holes around the adapter. Also referred to as adapter. (7)

876

Modern Welding

diffusion hardening. Surface hardening process that changes the surface of the base metal by causing the base metal to absorb another element that then ha rd ens it. (29) dimension. Size information found on a dra\>v ing. (2) dimension line. A thin liJ1e, broken in the middle to allow the placement of the dimension value, with arro\-vheads at each end. The end points for the arro\-vheads of di·m ension I ines are extension lines. (2) dimetric view. Axonometiic view in which two of the three angles and corners are equal. (2) direct current electrode negative (DCEN). Direct current that flows from the elech·ode to the work. (5) direct current electrode positive (DCEP). Direct current that flows from the work to the electrode. (5) direct current (DC) power source. Machine that produces direct current for welding. (5) discontinuity. Interruption in the normal c1ystalline lattice structure of a metal. (30) distortion. Warping of a part of a structure. (34) dive table. A table that shows the n1aximum time a diver can stay at a given depth. (25) downhill. Welding \-Vith a downward progression. (6) downhill welding. Vertical \-Velding traveling from the top to the botto1n of a joint. Welding a SG pipe weld starting at the top, or twelve o'clock, position and weld downward to the bottom, or six o'clock, position. (23) downslope current. Gradual decrease in current at the end of a weld. (10) drag. A measurement, made in the direction of travel, between the ent1y and exit points of the cutting jet. (15) drag angle. The top of the electrode leads the welding end of the electrode, and the welding arc is pointing back to,vard the weld bead. Also referred to as drag travel angle. (3) drawn to scale. The drawing of an object at a reduced (or in some cases, enlarged) size. (2) dressing. Reshaping of the electrode. (19) droop curve machine. Welding machine that has a steep volt-ampere curve. (5) drooper. See droop curve 1nacltine. (5) dross. Metal that is removed during a cut but becomes attached to the metal surface. (11) dry spot welding. Underwater welding method in which the welding takes place in a small chamber built fron1 Lexan, while the welder remains outside the chamber. (25)

dry welding. Underwater welding .vhere the vvater is removed from the welding area. Also referred to as hyperbaricweldi11g. (25) dua l-flow plasma arc cutting. Plas1na arc cutting in which a shielding gas is used. (11) ductile. Able to be worked without cracking. (28) ductile cast i ron. Cast i.ron that is sin1.iJar to gray cast iron, but differs in the form of the graphite that develops when it is produced. The graphite is in the fonn of spheres, resulting in higher ductility. Formation of spheroidized graphite is aided by adding magnesiwn (Mg). Also referred to as 11odular cast iron. (21) ductility. The ability of a material to be changed in shape without cracking or breaking. (28) ductility. A measure of how much a san1ple stretches or elongates before it breaks. (30) duplex stainless steel. A combination of austenitic and ferritic stainless steels. (28) duty cycle. The percentage of time in a 10-minute period that an arc welding mach.i ne can be used at its rated output without overloading. A resis tance welding machine duty cycle is usually calculated over a one-1ninute period. (5) dynamic weld resistance monitoring. In resistance welding, the process of measuring the continuously changing resistance of a weld while it is being n1ade. The weld controUer compares the measured dynamic \,veld resistance to a known good weld resistance curve. (18)

E economizer. A device that shuts off gas flow and holds an oxyfuel torch when it is not in use. Gas flow is immediately restored ,-vhen the torch is lifted from the cradle. (12) eddy current inspection (ET). Inspection method that uses an AC coil to induce eddy currents into a part. A discontinuity in the part interrupts the flow of the eddy currents. (30) edge joint. A joint between the edges of two or n1ore parallel parts. (3) edge preparation. The shaping of the edges of the joint prior to welding. (3) elastic limit. The greatest stress that can be applied to a structure without causing permanent deformation. (30) electrical resistance h eating. Heating that occ,u·s due to resistance to electrical cw·rent. (29) electric arc furnace. A primary steelmaking furnace that can use scrap steel as the main ingredient. An arc is struck between carbon electrodes and n1etal in the furnace. (28) Copyr!ghl Goodheart-WIiicox C-0 . Inc,

Glossary

electric arc spray method. Metal surfaci11g method in which wire material melted by an arc between two current-carrying wires is sprayed onto the part to be surfaced. (27) electrochemical resistance spot welding machine. Resistance welding machine that stores energy in a set of batteries. Energy is released fron1 the batteries to make a weld. (18) electrode angle. Position of the electrode in relation to the n1aterial being ,.velded. (3) electrode diameter. The width of a cylindrical or tubular electrode. (18) electrode extension. The amount that the end of the welding wire sticks out beyond the end of the contact tip. Also referred to as slickouf. (8) electrode face. The part of the electrode that contacts the "''Ork. (18) electrogas welding (EGW). An arc welding process that uses one or Lnore ,.vire feeders that deposit metal between water-cooled shoes. It is theoreticaUy capable of welding sections of 1netal of virtually any thickness. (20) electrolysis. A chemical change or decomposition created by passing electricity th.rough a solution of the material or through the substance whiJe it is in a molten state. (12) electron bean1 welding (EBW). Focused stream of electrons that heats and fuses metals. (20) electroslag welding (ESW). A process that uses 111olten slag to melt the base metal As the weld progresses vertically, the molten metal, slag, and flux are held in place by water-cooled moving shoes. (20) electrostatic resistance spot welding machine. The most common type of stored energy resistance ,.velding machine. Electrical energy is stored in a capacitor and released by the capacitor "''hen it is needed to weld. Also referred to as a capacitor discharge resistance welder. (18) elongation. The percentage increase in the length of a specimen when it is stressed to its yield strength. (28) essential variable. A variable that has a significant effect on the mechanical properties of a weldment if the variable is changed. (25) etch. Treat with acids to bring out features, such as the grain boundaries and microstructures in the metal. (30) eutectic point. The point on a graph of solidus and liquidus temperatures ,.vhere the alloy begins to melt and completely 111elts at one temperature. (16) eutectoid point. On an iron-carbon phase diagram, the point that occurs at 0.77°/o carbon and at 1341°F (727°Q. When a steel is cooled through this point, only pearlite is formed. (28) Copvrighl Goodheart-WIilcox Co, Inc

877

exit d.iameter. Oian1eter of the nozzle opening closest to the arc. (10) exothermic process. A self-consuming process in ,.vhich fuel wires, once ignited, continue l'O burn as long as oxygen is available to support the burning. (4) explosion welding (EXW). A process that joins metal as powerful shock waves create pressure to cause metal flow and resultant fusion. (20) expulsion. The unwanted forcing out, or expel Ii ng, of molten metal during a resistance welding process. (19) expulsion weld. Resistance spot weld that squirts (expels) molten metal. (19) extension line. The ends or terminal points of a dimensioned line are n1arked solid extension lines. The size of a given line or feature on the object is usually placed between extension I ines. (2) eye of the weld pool. A bright flake of oxide on the surface of the 1.veld pool. (13)

F face-centered cubic structure. The structure of austenite, in which there is one atom at each corner of the cube and also one in the center of each face. (28) face reinforcement. Distance from the top of the weld face to the surface of the base 1netal. (3) fast-freezing electrode. A SMAW electrode where the weld pool solidifies quickly. EXXlO and EXXll are fast-freezing electrodes. (23) feathering. Technique of smoothing the top of the tack weld with a grinder and grinding the start and end of the tack weld. (8) feedback control. Adjustments made to welding variables or mechanical devices (such as robots or positioners) as a result of feedback received by the controller. (26) ferrite. Iron that contains s1nall amounts of carbon. It has a body-centered cubic structure. (28) ferritic stainless steels. Stainless steels that contain fro1n 10.5% to 30'Yo chro111iurn. (21) ferrous metals. Metals and their aUoys that contain large amounts of iron (Fe). (21) field weld symbol. Symbol used when welds are to be made away fro1n the shop. It is a small flag located at the arrow end of the reference line. (3) filler material. Material that is added to a we.Id to build it up. (4) fillet weld. Metal fused i:nl'O a corner formed by two pieces of metal whose welded surfaces are approximately 90° to each other. (3)

878

Modern Welding

fillet weld break lest. Test that requires a fillet weld to be made on one side of a T-joint. The vertical piece is then bent over the ,,veld until the weld fails or is bent flat against the horizontal piece. (30) filter lens. Lens that protects the eyes from ultraviolet, infrared, and visible radiation and are available in a variety of shade intensities. (5) finish symbol. Symbol that indicates the method of finishing, used only when the ~veld is not to remain in an "as welded" condition. (3) firebrick. Heat-resistant brick or stone used to form welding table tops or to provide support to weldrnents. Also used to build a p reheat furnace. (32) fire watch. Person who carefully watches for fires that n1ay start in the area ,-vhere the ,-velding or cutting is done. (1) fitness for service. The concept that a ll welds contain flaws. If the fla"-'S or discontinuities are too large, or there are too many of them, they will affect the performance of the weldment. (30) fixture. Device designed to hold a specific part and accurately locate it during production. Parts are often located in the fixture by pins and held by clamps. Also referred to as jig. (32) flame hardening. Surface hardening process that uses a multiple-tipped oxyfuel flame. (29) flame spraying. Process that sprays pure or aUoyed metals onto a part or assembly. Surfacing or cladding n1aterials are melted in an oxyfuel gas flame and carlied in a flame or gas jet to the surface of the part being surfaced. (27) flange fitting. A fitting that is attac hed to a pipe at one end, and has a wide flat collar on the other end. (23) flange joint. Joint that is formed when the edge of one or more pieces of the joint is bent to form a flange. (3) flared filling. Threaded fittings that are installed over tubing, which is then flared to form a seal with the fitting and hold it in place. (23) flare-groove joint. Joint formed when the flanged edges of one or both pieces are placed together to form a single-flare-bevel or double-flare-V-groove. (3) flash. Impact of elechic arc rays against the human eye. Also, the surplus metal formed at the seam of a resistance ~veld. (4) flashback. A condition in ,-vhich the torch flame burns inside the torch or hoses. (12) flashback arrestor. A type of check valve, usually installed between the torch and ,~•elding hose to preven t flo,-v of burning fuel gas and oxygen mixture back into hoses and regulators. (12)

flash goggles. Safety glasses with a #1 to #3 lens. They protect the welder's eyes from arc flashes h·on1 behind the welder. (5) flashing. Expulsion of n1olten 1netal. Also, the fonnation of elecmc arcs between the closest points in oppositely charged irregular surfaces. (18) flash welding. A process used to weld the ends of metal rods, rails, beams, and other shapes together. (18) flat welding position. Welding position in which the weld axis and iveld face are horizontal. (3) flaw. A discontinuity or change in the normal structure of a n1aterial. If a flaw is larger than an acceptable limit, it becomes a defect. (6) flexible tubing. Tubing that can be easily bent to the shape needed. (23) flow switch. Device used to verify that gas or fluid is flowing through a pipe or tube. (26) flow temperature. The temperature at which all of the elements in an alloy become liquid. (17) flux . Material used to prevent, dissolve, or help remove oxides and other surface contanunants. (12) flux cored arc welding. Welding method in which heat is supplied by an arc between a hollow, fluxfilled electrode and the base 1netal. (4) force gauge. A device used to set the proper force on a spot welding gun. (19) forehand welding. Welding ¼•ith the welding end of the electrode pointing forward in the direction of travel (3) forge force . Additional pressure applied during the hold time to prevent aluminum or aluminum alloys £ro1n cracking ,-vhi le cooling. (19) forge welding. Welding process that joins t wo pieces of metal by heating them to a high temperature and then hammering them together. (4) forging. The process of making metallic shapes by either hammering or squeezing the original piece of metal. The resu Iting shape is a lso called a forging. (4) forward arc blow. Magnetic field forces the molten filler metal to blow inward from the end of the weld joint toward t he center of the work. (6) fractional drill set. Drill set that increases in size in steps of 1/64". (34) fracture test. Identification test that involves breaking a po1tion of metal in two and examining the grain size and color. (28) freehand cutting. Cutting performed without the use of a guide. (14) friction stir welding. A solid-state welding p rocess in which a rotating shouldered tool with a probe or pin moves along a joint, creating heat through friction and pressure. The base 1netal is plasticized and stirred together. The metal is not 01elted. (4) Copyr!ghl Goodheart-WIiicox C-0 . Inc.

Glossary

friction welding (FRW). \l\lelding process iJ1 which the welding heat is generated by revolving one part against another part, under heavy pressure to create friction. (20) front view. Vie,v on an orthographic drawing that shows the most about the overall shape of the object. (2) full anneal. Postweld heat treatment in which the weld area is heated to the full annealing ten1perature. The weldment is then slo,"'IY cooled in the furnace to llOD°F (590°C) and then slowly air cooled. (21) full scale. Dra,"7ing in which an object is dra,~1 n full size. (2) fully active (RA) flux. ComJnonly used soldering Aux that is the rnost active and cleans the best. (16) fumes. Particles suspended in air, often produced by high heat. (1) furnace. An enclosed structure that produces heat by air-fuel gas, electrical induction, or electrical resistance units. (29) fuse plug. A safety plug threaded into a gas cylinder. If the cylinder is subjected to a high temperature, the plug tnelts and allows the gas to escape before enough pressure builds up to burst the cylinder. (12) fusible alloy. An alloy that contains 50% bismuth and is used in soldering operations when the temperature should remain below 361°F (183°C). (16) fusion. lntirnate mixing or combining of rnolten metals. (6)

G galvanizing. The process of coating iron or steel with zinc. (21) gantry. A light, rigid rail and all its mechanisms. Torches are rnounted on it for automatic cuttiJ1g operations. (15) gas lens. A device used in a GTAW nozzle to reduce turbulence in the shielding gas flovv. (9) gas metal arc welding (GMAW). Arc welding using a continuously fed consumable electrode and a shielding gas. Son1eti1nes incorrectly called MIG ,velding. (4) gas-shielded flux cored arc welding (FCAW-G). A flux cored arc \