Manufacturing Process in Canada 9781487576172

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Manufacturing Processes in Canada

Manufacturin g Processes in Canada Eclltecl by

K. C. LIVINGSTON ancl

T. C. GRAHAM

Uniwerslty of Toronto Press

COPYRIGHT, CANADA,

1960

BY UNIVERSITY OF TORONTO PRESS

PRINTED IN CANADA LONDON: OXFORD UNIVERSITY PRESS

Reprinted in 2018 ISBN 978-1-4875-7703-2 (paper)

Preface

for this book was developed by the editors because of the lack of information about manufacturing processes available to students. Existing books were limited to the treahnent of one or two industries. A book was required that would provide a condensed, yet helpful, technical description of a number of industries. It seemed to us that the most definitive sources of the requisite information were the industries themselves. Hence, representatives of sixteen industries were invited to contribute accounts of their manufacturing methods; our aim has been to ensure brief descriptions of the raw materials required, rather full descriptions of the operations used to transform these base materials into the finished product or products, and brief descriptions of the movement of the products to the consumer. Statistical information pertinent to these industries is also included. It is not suggested that these processes are strictly Canadian in nature. They are likely to be found, and perhaps originated, in other countries. What imparts to these contributions a Canadian flavour is the fact that they have been written by men in organizations in Canada representative of the industry of which they are a part. The name of the organization, and the name of the writer commissioned by the organization, appear at the beginning of each chapter. The editors wish to thank Miss J. Forgie, Miss J. Arrowsmith, Mrs. H. Ignatieff, Mrs. G. Black, and Miss B. Martin for their patience in typing the manuscript. Miss M. J. Houston of the University of Toronto Press provided invaluable assistance, advice, and guidance through the many hazards associated with publication. The editors are indebted particularly to the authors and to the officials of the participating organizations who assisted in transforming an idea into reality. K.C.L. T.C.G. September, 1959 THE IDEA

Contents

PREFACE

V

ALUMIN{j'.\f, by I. H. Jenks ( Aluminium Laboratories Limited)

3

BEEF, by G. Moore and T. Hercus ( Canada Packers Limited)

28

BREWING, by R. R. Service ( O'Keefe Brewing Company Limited)

39

BRICK, by the Staff of Toronto Brick Company Limited

57

DETERGE'.'fTS, by F. H . Lehberg (Lever Brothers Limited)

68

FLAT-DRAWN GLASS, by Leo B. Kowal (Canadian Pittsburg Industries Limited)

86

ASBEST0S-'.\-rAGNESIA INSULATION, by the Staff of Canadian Johns-Manville Company Limited

105

moN AND STEEL, by the Staff of the Steel Company of Canada Limited

109

CANADA'S '.'JATI0NAL MAGAZINES, by E. Nymark (Maclean-Hunter Publishing Company Limited)

156

PETR0LEU'.\f, by G. A. Purdy ( Imperial Oil Limited)

166

PULP AND PAPER, by Howard Hart ( Canadian Pulp and Paper Association)

197

by C. J. Coon (The Goodyear Tire and Rubber Company of Canada Limited)

216

RUBBER.

TEXTILES : COTTON, by J. R. Dunkerley (Dominion Textile Company Limited)

232

TEXTILES: wooL, by G. E. Largy (Paton Manufacturing Company Limited)

254

TEXTILES: :MAN-MADE FIBRES, by C. J. Warrington (Canadian Industries Limited)

265

TOBACCO, by

J. M. Keith

( Imperial Tobacco Company of Canada Limited)

WIRE AND CABLE, by the Staff of the Engineering Department, Canada Wire and Cable Company Limited

279 290

M■nufacturing

Processes in Canada

Aluminum BY I. H. JENKS ALUMINIUM LABORATORIES LIMITED

ALTIIOUGH aluminum does not occur free in nature, it is nevertheless very widely found as a constituent of many minerals. It is the third most abundant element in the earth's crust ( 8.05 per cent) and is contained in many rocks, particularly clay, shale, slate, and granites. All aluminum-bearing minerals can not be regarded as ores, since the extraction of the metal is difficult, and for this reason the history of the production of metallic aluminum is little more than one hundred years old. Sir Humphry Davy suspected the existence of the metal but failed in his attempt to separate it from alumina by electrolysis in 1807. It was first isolated in 1825 by the Danish physicist, H. C. Oersted, who heated potassium amalgam with aluminum chloride and distilled the mercury from the aluminum amalgam. In 1827, Frederick Wohler, in Berlin, produced the metal in a similar way using metallic potassium instead of potassium amalgam. In both these experiments the quantity of aluminum produced was minute and impure, and aluminum remained a scientific curiosity until 1854, when Henri SainteClaire Deville improved Wohler's method by substituting sodium for potassium. The use of sodium cheapened the process and improved its efficiency, enabling appreciable quantities of aluminum to be obtained. However, in spite of the improvements that continned to be made in this process, the cost of production remained very high. For many years, attempts were made to electrolyse molten salts of aluminum

but without much practical success until the problem was eventually solved independently by Charles Martin Hall in America and Paul L. V. Heroult in France, both in the same year, 1886. The novelty of the Hall-Heroult process consisted in the use of a fused electrolyte, cryolite, which dissolved substantial quantities of alumina and which was more stable than the latter, so that the alumina could be decomposed electrochemically without affecting the solvent. The process proved both technically sound and commercially practicable, but it took both Hall and Heroult two years to interest business men in its possibilities. In 1888 the first aluminum ingot was poured at Pittsburgh by the Pittsburgh Reduction Company using the Hall process, and in the same year aluminum alloys were first produced in Switzerland by the Schweizerische Metallurgische Gesellschaft ( later the Aluminium Industrie Aktiengesellschaft) under the Heroult patent. Also in 1888 the Societe electrometallurgique frarn;aise was founded to develop the French rights to the Heroult process, and the modem aluminum industry in Great Britain was launched in 1894 with the foundation of the British Aluminium Company Limited. In 1899, the Pittsburgh Reduction Company decided to build an aluminum plant at Shawinigan Falls, Quebec, in order to utilize water power then being developed, and for this purpose a Canadian company was incorporated. This was the Northern Aluminum Company, which became the Aluminum Company

4

MANUFACTURING PROCESSES IN CANADA

of Canada Limited in 1925, and which began in 1926 the construction at Arvida, Quebec, of what was to become the world's largest reduction plant. 1 The basic process as developed by Hall and Heroult has remained unchanged, but as a result of improvements, continuing reductions in the cost of the metal have been effected. The number and variety of applications have increased until they cover almost every branch of human activity, and the output of aluminum is now greater by volume than that of any other nonferrous metal. Production Bauxite mining. The commercial ores of aluminum are those rich in hydrated oxides of the metal and are grouped under the generic term 'bauxite." The grade of bauxite is determined by the percentage of alumina it contains and by the kind and quantity of impurities. In high-grade ores such as those of British Guiana, as much as 60 to 62 per cent of alumina may be present. Iron oxide (Fe20 3 ) and titania (Ti02) are found in varying amounts in practically all bauxites, and compounds of many other elements, including calcium, potassium, and magnesium, may be observed as traces or locally in substantial quantities. Titania is usually present to the extent of 2 to 3 per cent, and is not injurious. European bauxites are commonly high in iron oxide, those of the Western Hemisphere much lower, sometimes less than 2 per cent; as much as 25 per cent can be tolerated, the only disadvantage being that it increases the quantity of waste matter to be handled. Silica, on the other hand, is definitely undesirable, since during processing it forms sodium aluminum silicate, which is lost when filtering, thus decreasing 1Arvida was named for Arthur Vining Davis a colleague of Charles Martin Hall since 'the early days of the Pittsburgh Reduction Company.

the yield of alumina. For this reason bauxite for aluminum production should be low in silica, and in practice the amount present is rarely greater than 5 per cent. However, bauxite containing a larger percentage of silica may be subjected to additional processing allowing recovery of most of the alumina. In the Western Hemisphere the principal sources of bauxite are British and Dutch Guiana and Jamaica. British Guiana has filled the major part of Canadian requirements, although Jamaican bauxite is assuming a share in the supply of Canadian needs, and Dutch Guiana bauxite goes to the United States. In Europe, the chief sources are France, Hungary, Italy, Yugoslavia, and Roumania. In Africa, large undeveloped reserves exist in French Guinea, French Sudan, and Nyasaland, and other deposits on the Gold Coast and in French West Africa are now being exploited. In Asia, extensive deposits of low-grade bauxite are known to exist in China and proved reserves of varying size and quality are to be found in India, the Dutch East Indies, and British Malaya. Australia possesses deposits of lowgrade bauxite. Bauxite occurs in three main forms, blanket, interlayered, and pocket deposits. Blanket deposits are commonly found relatively near the surface in tropical or semi-tropical regions including the Guianas, West Africa, and India. The overlying sediment is usually removed mechanically and the deposits are mined by the open-cut methods. Interlayered deposits, such as those found in France and Greece, represent surface deposits of past geological ages which have been submerged; the outcrops can be quarried by means of open pits, while the deeper bauxite is mined by underground methods. Pocket deposits found in !stria, Dalmatia, and, relatively recently, in Jamaica, represent irregularities in the rock surface upon which the bauxite has formed, and may

ALUMINUM:

5

Fie. 1. Bauxite mining in British Guiana by the open-cut method.

frequently be mined by simple openpit methods. After the bauxite has been mined, it is frequently subjected to preliminary beneficiation treatment before it is transported to the refining plants. The extent to which these processes are employed depends on the nature of the ore and on economic factors. In British Guiana, the ore is mined by the Demerara Bauxite Company by the open-pit method and transported a short distance to the site where it undergoes the preliminary treatment. Here the ore is crushed and washed to remove silica-bearing minerals, and then dried in rotary kilns to reduce transportation and subsequent handling costs. Preparation of alumina. Since the early days of the industry the preparation of pure alumina from the bauxite

has usually been accomplished by the Bayer process. In Jamaica the Bayer process is carried out at a site adjoining the bauxite mines; in Guiana, on the other hand, bauxite is shipped to the site of the reduction plant for refining. In the Bayer process, the bauxite is treated under pressure in digesters with hot caustic solution, generally provided by the proper quantities of soda ash and lime which, by their reaction, produce caustic soda. This in turn dissolves the alumina from the bauxite, forming soluble sodium aluminate; the residue, commonly known as "red mud," contains the iron oxide, titania, and silica. originally present in the bauxite, and is separated from the sodium aluminate· liquor by filtration, or decantation and filtration. Alumina trihydrate ( Al 2 0 3 • 3H20) is then precipitated from the sodium aluminate liquor by agitation

6

MANUFACTURI:-JG PROCESSES IN CANADA

in the presence of a "seed" charge of trihydrate from a previous cycle. The trihydrate is washed to remove soda and calcined in rotary kilns at a temperature of approximately 1000°C to drive off the combined water, producing alumina ( Al203). The alumina contains approximately .5 per cent sodium oxide ( Na20) resulting from incomplete washing of the trihydrate, but this sodium oxide is not regarded as an impurity as it is converted to electrolyte in the reduction cells. The actual impurities, amounting to less than .1 per cent of the alumina, are mainly oxides of iron, titanium, and silicon. Since silica reacts with the sodium hydroxide to form sodium aluminum silicate, which becomes insoluble during the digestion period, appreciable quantities of soda and alumina are lost as a part of the red mud which is filtered out. To permit the use of bauxites containing high percentages of silica, the "combination process" has been developed. The red mud is mixed with limestone and soda ash and sintered (heated to a high temperature) in rotary kilns similar to those used for calcining. The sintered material is then leached with water containing a little caustic soda to produce a solution of sodium aluminate with only a small amount of silica. This solution is fed into the digesters at the beginning of the Bayer process, to react with fresh bauxite and caustic soda. Other operations are the same as in the straight Bayer process. The combination process recovers most of the soda and alumina that would otherwise be lost. Low-grade bauxites containing as much as 15 per cent silica have been economically refined by this method. The process makes available large tonnages of bauxite that previously were considered uneconomical for the production of aluminum. Another process, the Pedersen, has been used successfully in Scandinavia. Low-grade (high-silica) bauxite is smelted with limestone and coke in

large electric furnaces. The iron oxide present in the bauxite is reduced to pig iron-a valuable by-product-while the alumina is converted to an aluminous slag. The slag is pulverized and leached with sodium carbonate solution to dissolve the alumina, and the liquor is separated from the residue by settling and filtration. The solution is treated with flue gases ( which contain a high percentage of carbon dioxide) to precipitate pure aluminum hydrate, and this is washed, filtered, and calcined as in the Bayer process. The yield of alumina from bauxite by the Bayer process depends on the grade of material treated. The yield from high-grade ore may be as much as 50 per cent of the weight of the bauxite. Approximately one-half pound of aluminum can be obtained from each pound of alumina, and therefore approximately four pounds of bauxite are required to produce one pound of aluminum. Reduction. The reduction of alumina, that is, the removal of oxygen from the aluminum oxide, is carried out by the process invented by Hall and Heroult. A bath of fused cryolite containing dissolved alumina is electrolysed by the passage of a direct current between carbon anodes and the carbon lining of the cell, which is itself the cathode. The alumina is decomposed into oxygen and aluminum. The oxygen, liberated at the anodes, combines with carbon and is carried off as carbon dioxide, while the metal sinks to the bottom of the cell from which it is tapped at appropriate intervals. In the electrolytic cell, sometimes referred to as a "pot," are one or more carbon anodes; these are of either prebaked or the self-baking Soderberg type. Pre-baked anodes are made from crushed petroleum or pitch coke, mixed with pitch as binder and pressed into blocks, which are then baked to remove volatile matter. The cathode may be built up of carbon blocks similarly pre-

ALUMlNtJM

7

pared, or it may be formed by ramming of aluminum produced. It will thus be into the steel a hot mixture of coke and seen that the manufacture of anodes pitch which is subsequently baked. The constitutes an important phase of the Soderberg continuous self-baking anode industry. consists of a large rectangular aluminum On top of the bath a solid crust forms, or mild steel casing into which a warm underneath which the electrolyte is held coke and pitch mixture is packed. As in a molten state by the heat created by the electrode becomes baked and ulti- passage of the heavy current which may mately consumed at the lower end vary from 8,000 to as high in recent where it enters the electrolyte, the years as 100,000 amperes. The alumina casing is moved down mechanically, dissolved in the cryolite is continuously fresh sections of the shell being added decomposed at the rate of one pound and the anode mixture being renewed per hour for every 900 amperes. The at the top as required. Provision is made electrical pressure at which the cell for remaking the current connections operates is usually about 6 volts, but as as the anode descends, so that the pro- the concentration of alumina in the electrolyte falls, a point is reached at cess is continuous. The electrolyte, cryolite, is a double which the effective electrical resistance fluoride of sodium and aluminum, of the cell is suddenly increased, so that 3NaF.AlFa. Natural cryolite obtained the pressure required to maintain the from Greenland has been widely used, flow of current may rise as high as 60 but its beneficiation is becoming more volts. This is the signal for the addition complicated as the grade of available of more alumina, placed in readiness ore is lower, and synthetic cryolite of on top of the solid crust, which is high purity for use as an electrolyte is broken to admit it. When sufficient now produced on a large scale in many aluminum has accumulated, it is reparts of the world. The most common moved by ladling or siphoning. The method of preparing artificial cryolite metal is finally cast into ingots weighing consists in treating soda and alumina usually about fifty pounds. The purity with hydrofluoric acid, the latter being is within the range 99.0 to 99.9 per cent, obtained by the action of sulphuric acid and this is referred to as commercial on ftuorspar. In the aluminum industry purity aluminum. it is customary to use the sodium alumiAluminum of very high purity may nate solution from the Bayer process to also be produced. This is obtained by supply the soda and alumina required electrolytic refining in a cell with a for the production of synthetic cryolite. three-layer bath. On the bottom is a To start the operation of the reduc- layer of a comparatively heavy molten tion cell, the anodes are lowered until copper-aluminum alloy which acts as they touch the carbon bottom, and the anode, upon which floats the electropowdered cryolite is packed around lyte ( consisting of a mixture of cryothem. When the current is switched on, lite, fluorides or chlorides, and alumina), sufficient heat is generated to melt the with the top layer of molten aluminum cryolite, the anodes are gradually forming the cathode. During electrolysis raised, and more cryolite is added until aluminum is transferred from the allov the cell is filled to the correct height. layer to the cathode giving metal of Alumina is then introduced and dis- 99.99 per cent purity. solves in the cryolite; aluminum is deAs previously mentioned, the electroposited on the bottom of the cell, and lytic cells operate at about 6 volts, so carbon dioxide is given off at the anodes that for economical operation it is which are gradually consumed at the necessary to connect a number of cells rate of about 1,200 pounds for each ton in series. In modem practice, each line

8

MANUFACTURING PROCESSES IN CANADA

of cells contains from 120 to 150 ( in some recent installations up to 180), to which direct current is fed at up to 850 volts, or more if necessary. The current is supplied by generators driven by water, or by steam turbines, and is usually transmitted to the reduction plants as alternating current, which is converted to direct current in most modem installations by mercury-arc rectifiers. In some new plants, direct current is provided straight to the reduction cells by generators which are driven by diesel engines or internal combustion engines; the latter are fuelled by coal or natural gas. About ten kwh of electricity are used to produce each pound of aluminum and thus the history of the aluminum industry has always been associated with a constant search for economic and adequate power resources. Location of plants. The necessity to locate close to an abundance of water power, or some suitable alternative source of power such as natural gas, has played a very large part in determining the sites of reduction plants. In the United States, until recent years, plants have been grouped close to the power supplied by the Tennessee Valley Authority, the Bonneville Power Administration, or the St. Lawrence River system. In Europe, notably in Italy, France, and Norway, conditions are very favourable for the production of aluminum; in Italy and in France, the sources of raw materials are close to water power, and in Norway many water power stations are near tidewater so that raw materials may be brought in by ocean-going vessels. The chief factor determining the location of the early reduction plants in the province of Quebec has been the abundant supply of hydro-electric power generated on the St. Maurice and Saguenay rivers. Bauxite is shipped from British Guiana and refined to alumina at Arvida. The huge reduction facilities at Arvida now require practically all of the 2,600,000 h.p. generated by the Saguenay River-

Lake St. John system. The main hydroelectric station is Shipshaw and additional generating facilities are located at Isle Malinge, Chute a la Savanne, and Chute du Diable. Other reduction works are located at Isle Maligne, Shawinigan Falls, and Beauharnois. Deep-water handling facilities are provided at Port Alfred close to the reduction plant. Alumina for the Kitimat reduction works is supplied by Alumina Jamaica Limited, which operates the bauxite mines at Mandeville in Jamaica and an alumina processing plant nearby. The alumina is shipped by ocean freighter through the Panama Canal and up the Pacific coast to tidewater at Kitimat. Cryolite, fluorspar, and other raw materials for use in the reduction process also come by ocean transport. The hydro-electric power development known as Nechako-Kemano will have an ultimate installed capacity of 2,400,000 h.p. The installed generating capacity in December 1957 was 1,050,000 h.p.; this is regarded as only an interim stage of the power project and is capable of meeting the demands of the potlines installed to date at Kitimat, which in the present stage ( December, 1957) will produce 186,000 tons of aluminum and in the final stage will be capable of producing 550,000 tons. Alloying The aluminum produced by the Hall-Heroult process is known as commercial purity aluminum and usually averages in purity between 99.5 and 99.7 per cent. It is suitable for many applications but most of it is used in the form of alloys, from which a very wide range of semi-fabricated and finished products are made. One of the prime objects in alloying aluminum is to increase its strength. When properties other than strength need to be enhanced, either super-purity aluminum may be produced by the refining process mentioned previously or commercial purity aluminum may be alloyed

9

ALUMINUM

CHART I BAYER PROCESS FOR PRODUCTION OF ALUMINA

Fuel oil

Demerara bauxite

Lime

Soda ash

~0.0% 60 .0 2.5

CaO

Na2COa

a.o

Ca(OH)2

L.O.1. Al2Oa Fe2Oa SiO2 TiO2

Boilers

t----""' Digestion under pressure

Red mud L.O.1 Al,O, CaO Fe,Oa SiO, TiQ. Na,()

or

4 .5

17%

25

Spent liquor strengthened & recirculated

Separation of red mud (filtration or decantation and filtration)

12

11 16

10 S

Precipitation of alumina hy cooling, agitation & seeding

Alumina trihydrate

10',;,~

Free Bound Al 2O3 Impurities

L-----------1--i

:~2 58 l

Cakination in rotary kiln at high temperature

Calcined alumina H.O Ai2Oa SiO. FeeC>a TiO. Naz()

1.0

99.0 0 .03 0 .03

0.005 0.5

'JO

(Seed)

10

MANUFACTURING PROCESSES IN CANADA

with an ingredient chosen specifically to confer on aluminum the property which is desired. Aluminum itself is a soft, ductile, non-magnetic metal, having a high electrical and thermal conductivity, and an excellent resistance to corrosion. It has a specific gravity of 2.70 and thus is about one-third the weight of iron, copper, or zinc. It has a great chemical affinity for oxygen, and a film of oxide forms spontaneously on any freshly cut or abraded surface. This film is transparent and is relatively inert chemically. Aluminum is an ideal metal to work and may be hot rolled, extruded or forged, cold rolled, pressed, drawn, stamped, bent, or shaped. The aluminum alloys possess many of the properties of the pure metal to a marked degree and, in addition, they exhibit the properties conferred upon them by the alloying ingredient. In general, the use of an aluminum alloy in any application is governed by its ability to provide two or more particular properties. Non-heat-treatable alloys. On subjection to working, most metals harden and increase in strength and it is by this work-hardening process that the strength of "non-heat-treatable wrought alloys" is developed. The effects of work-hardening can be removed and the metal softened by annealing, that is, by heating to about 360°C, depending on the alloy. Thus, the final strength of the non-heat-treatable alloys is governed by the amount of cold work introduced after the last annealing operation. These alloys are usually provided in a range of tempers, the designations of which vary from one country to another. Heat-treatable alloys. The process known as heat treating, which applies to both wrought and cast alloys, develops the strongest class of aluminum alloys. This process takes place in two stages. The first stage, solution heat treatment, makes use of the fact that certain of the alloying elements are substantially taken into solid solution

at a temperature of about 500°C, and can be retained in this state by rapid cooling to room temperature ("quenching") . In the second stage, . called "precipitation treatment" or "aging," these constituents are precipitated throughout the metal in a finely divided state, in which condition they most effectively reinforce the aluminum, making it strong and hard. Some degree of precipitation of alloying constituents follows spontaneously at room temperature after solution heat treatment, and in some alloys the desired effect is attained when a stable condition is reached in about five days, the process being known as "natural aging." These are the "single heat treatment" alloys. Other alloys, however, respond effectively to further heating for some hours to increase precipitation; the actual temperature chosen depends upon the alloy, and may be as low as 100°C or as high as 230°C. This is called "precipitation heat treatment" or "artificial aging," and these "double heat treatment" alloys are available in two alternative conditions: "solution treated only" and "solution treated and aged" ( otherwise described as "fully heat treated"). Before precipitation, the metal is soft and ductile, and hardness and strength increase as precipitation proceeds. For either type of alloy, therefore, the softest condition is immediately after solution heat treatment; but after natural aging a fair degree of ductility remains, and the metal may be formed satisfactorily. After artificial aging, double heat treatment alloys are hard and strong, and offer much greater resistance to deformation. The heat-treatable alloys are usually available in up to eight tempers, the symbols of which once again vary from country to country. COMPOSITION OF ALLOYS

There are two main alloy groups, wrought alloys and casting alloys, and

ALUMINUM

within these two main groupings there are alloy classes according to the alloying ingredient. Some wrought alloys follow: Aluminum-manganese. One per cent to l¼ per cent manganese increases the strength of aluminum with only a slight reduction in ductility. Alloys of this type find wide application where a nonheat-treatable (work-hardening) alloy is required, with greater strength than commercial aluminum together with high resistance to corrosion. Aluminum-magnesium. The addition of magnesium to aluminum confers certain valuable characteristics. These include high resistance to attack, particularly by sea water, improved tensile strength, good fatigue strength, good formability and workability, and slightly lower specific gravity than the pure metal. The useful alloys of this class range in magnesium content from approximately 1 per cent up to as much as 7 per cent. In the range 1 per cent magnesium, they possess good finishing characteristics and excellent appearance, particularly when anodized. Those alloys containing magnesium from 3 to 5 per cent have medium strength and good weldability. Alloys with 5 to 7 per cent magnesium are not in as general use, and although alloys containing more than 7 per cent magnesium have been made their practical application is limited. Aluminum-copper-magnesium-manganese. This group includes the principal strong alloys, in all of which copper is the main alloying constituent, with varying percentages of magnesium and manganese. These alloys are all of the heat-treatable type, and both single and double heat treatment allovs are included. Certain alloys are · fabricated into nearly every type of wrought product, while others find application only in special forms, such as rivets. In sheet form, certain of the alloys are used as "Alclad," that is alloy sheet coated on each side with high purity aluminum to

11

provide increased resistance to corrosive attack. Aluminum-magnesium-silicon. These heat-treatable alloys are generally of slightly lower strength than the alloys of the aluminum-copper-magnesiummanganese group, but they are more readily fabricated and formed, and have a higher resistance to corrosion. They are characterized by stability and excellent formability in the "solution heat treated only" condition. After forming, parts may be given an aging treabnent at a low temperature to increase their strength. The two most widely used alloys in this group contain just over ¼ per cent magnesium, one of them having about ¼ per cent silicon and the other 1 per cent silicon. In the two principal variants of this type of alloy the magnesium content is increased to about 1 per cent with additions of copper ( up to 2 per cent) and manganese or chromium (less than 1 per cent). Aluminum-copper-zinc-magnesium. Of recent development, these are the strongest of all aluminum alloys with a strength/weight ratio superior to that of high-tensile steels. In composition they have up to 8 per cent zinc, up to 4 per cent magnesium, up to 3 per cent copper, and manganese, chromium, and titanium not exceeding 1 per cent, 1 per cent and .3 per cent respectively. These alloys are slightly more difficult to fabricate and form than other highstrength alloys. Any forming has to be undertaken as soon as possible after solution heat treabnent, since natural aging continues for many months. Precipitation heat treabnent is invariably applied. Among cast alloys are the following: Aluminum-silicon. The alloys of this group contain from 2 to 13 per cent of silicon, with and without other alloying elements. They are noted for their excellent foundry characteristics, permitting all types of casting processes. Pressure-tight castings are readily produced.

12

MANUFACTURING PROCESSES IN CANADA

and they possess good resistance to corrosive attack. Without other alloying elements they are used "as cast," and though their tensile strength is relatively low, they have fair ductility and are not brittle. Alloys containing 10 to 13 per cent silicon are improved in structure and properties by the addition of about .1 per cent sodium; this is known as "modification." With the addition of other elements, notably magnesium, improved tensile properties can be developed by heat treatment. Aluminum-copper. The earliest aluminum casting alloys belong to this group. In all cases the presence of substantial amounts of copper makes them susceptible to heat treatment and reduces resistance to corrosion. High strength and good machining qualities are outstanding advantages, and foundry characteristics are good, though inferior to those of the aluminum-silicon group. Aluminum-copper alloys are not suitable for diecastings, and intricate permanent mould castings cannot be produced unless other elements, such as silicon, are present to improve fluidity and reduce "hot shortness" ( weakness at temperatures within the solidification range). Aluminum-magnesium. Alloys of this group combine excellent resistance to marine exposure, high strength and ductility, and good machining qualities. They are not so easily handled in the foundry as other groups, however, and require special treatment to prevent oxidation while casting. A 10 per cent magnesium alloy, heat treated, is one of the toughest of all aluminum casting alloys; with lower magnesium content the presence of silicon is necessary to produce effective response to heat treatment. Fabricating The intention here is to treat fabrication processes of semi-fabricated products. It has not been considered necessary to deal with the production of aluminum powder and alpaste, the pro-

cessing of products secondary to the aluminum industry such as the aluminum chemicals, or the further fabrication of semi-fabricated forms into finished products. These operations entail such manufacturing processes as machining, forming, joining by riveting, welding, brazing, and adhesives, and such surface treatments as mechanical and chemical finishing and anodizing. These last secondary fabricating processes are described in technical terms in a number of handbooks available from the producers of aluminum fabricated products, including the Aluminum Company of Canada Limited. The starting point in the fabrication of all aluminum products is remelting and alloying. Commercial purity aluminum is delivered to the remelting furnaces in the form of ingots or notched bars, and other metals are added to adjust the composition to that of the alloy required. The alloying constituents are supplied in a variety of forms. Commercial purity magnesium and zinc ingot are generally added directly to aluminum, but for other alloying constituents of high melting point, "hardeners." or alloys of aluminum rich in the required alloying ingredient must first be prepared. Such an alloy is 20 per cent copper, 10 per cent manganese, 12 to 20 per cent silicon, 20 per cent nickel_ 10 per cent titanium, 10 per cent chromium and the remainder aluminum. Compared with pure alloying elements, these aluminum alloy "hardeners" have a relatively low melting range, and are therefore more readily taken into solution by molten aluminum. REMELTING AND POURING

The largest furnaces for remelting are of the reverberatory or open hearth type. Charge capacities of 10 to 15 tons are common. Coke, coal, gas, or oil firing may be used, and electric induction furnaces are being used on an increasing scale. When a furnace is

CHART II ALUMINUM FABRICATED PRODUCTS

Aluminium

Rolling ingot

Atomized powder

Forging ingot

Extrusion ingot

Alpaste Sand castings Structural shapes

;\louldings

Die castings

Hammer & press forgings

Penuanent mould castings

Plaster mould castings

Sheet

Bar and rod

Tubing Upset forgings

Screw machine products

Wire

Plate

Cable

Deoxidizing in'got

N'ails

Impact extrusions

Corrugated sheet

Alpaste

Sized aluminium

Powder

Rivets

Circles

Hardener ingot

t---------1

t-----...J

Roll-formed sections & shapes

14

MANUFACTURING PROCESSES IN CANADA

started up, the temperature is brought to the proper level and commercial grade aluminum or suitable equivalent ( with a melting point of about 658°C) is charged gradually into it. In practice, the temperature of the metal is not allowed to exceed about 780°C. The composition of the charge is, of course, carefully worked out, and may comprise aluminum ingot, hardeners, and process scrap of known analysis. The molten metal is stirred, and dross is carefully skimmed from the surface, flux sometimes being added to assist removal of oxide. When castings are the final product, the molten metal may be taken to smaller "holding" furnaces, from which it is transferred by hand ladle into moulds as required, or it may be cast into ingot for remelting later. For rolling and extrusion ingots, it may be tapped into large pots from which it is poured into water-cooled iron moulds, rectangular in cross-section ( for rolling ingots) or circular ( for extrusion ingots), or, more usually, cast by the semi-continuous casting process described below. Before pouring, the metal is usually treated either with chlorine or nitrogen gas, which is bubbled through it by means of a pipe thrust into the pot, or with a degasser supplied in the form of tablets which are plunged beneath the surface. In either case the object is to free the metal from oxide and dissolved gases. Iron pots, ladles, moulds, and other containers of molten aluminum are coated with a protective wash of alumina, lime, etc., to prevent "pick up" of iron by the metal. Pouring temperatures must be closely controlled to · get the best results, and ladles and moulds are preheated. On exposure to air, molten aluminum immediately forms an oxide skin. During pouring it is important to keep this skin intact, in the form of a tube through which the molten metal flows . Otherwise, the· re-

suiting ingot may have substantial inclusions of oxide and dross. In order to reduce turbulence to a minimum, pouring is commenced with the moulds in a position tilted slightly above the horizontal, and as they fill they are gradually rotated to the vertical. Aluminum alloys have high shrinkage on solidification, and this is very marked with pure metal. When the mould has been lowered, with its main axis vertical, it should be full, but as the metal sets, a "pipe" or shrinkage cavity tends to form in the centre at the top, and to avoid this, hot metal is steadily added. This operation is called "heading" or "feeding." Most casting for wrought products nowadays is done by the "continuous casting process" ( actually semi-continuous), in which the metal is poured into a water-cooled mould with a withdrawable base mounted on a hydraulic ram. The sides of the mould are only a few inches deep and are cooled with an abundance of water, usually supplied by water sprays. In the very short time, therefore, that it takes to fill the mould, the metal at the bottom solidifies and contracts away from the sides of the mould. The hydraulic ram supporting the bottom plate is then slowly lowered as the solidified metal comes through the mould, and pouring proceeds continuously until the required length of ingot is obtained. In the latest practice for large-scale production, the metal after fluxing is poured direct from the "holding hearth" of a double-hearth furnace, thus eliminating the handling of pots and increasing the potential volume of metal poured. This semicontinuous casting process is rapid, enables more than one ingot to be cast at a time, and has the advantage that very large ingots ( depending on end product or size) can be produced, which can then be cut up as required. The product is better in quality, having finer constituent size and less segrega-

ALUMINUM

tion as the result of more rapid chilling. Ingots made by this method often have a rougher surface than those derived from the old types of tilting moulds, and "scalping," which consists of removal of the skin in a lathe or a m;!ling machine, is necessary for the strong alloys, and sometimes for others, depending on the use to be made of the ingot. ROLLING SHEET

Rolling ingots usually range in size from 500 pounds or so up to about 1,500 pounds in weight and up to nine inches in thickness, but much larger and much smaller ingots are sometimes rolled. They are placed in a preheating furnace, where they are heated to a uniform temperature of about 480°C and held at this temperature for a minimum soaking period preparatory to hot rolling. Furnaces for this work are commonly heated by gas or electricity, with forced air circulation, and in this country are usually of the "continuous" type, the ingots being put in at one end, conveyed mechanically through the furnace chamber, and discharged at the other end. "Soaking pits" in which the ingots are placed for the soaking period may also be used. In hot rolling, large reductions are possible, since the metal work-hardens comparatively little. Cold working is essential for work-hardened alloys, to attain the desired temper; it also confers a smoother finish and improves the crystalline structure. Even metal which is to be heat treated is therefore cold rolled, and the limit of hot working is set by these considerations as well as by expediency. Aluminum or aluminum alloy ingot is normally hot rolled down to a slab one-quarter inch or less in thickness; this long slab may he sheared into smaller pieces and cold rolled as individual flat sheets down to the finished gauge and size; or the slab may

15

be hot rolled somewhat thinner, and then coiled, annealed, and cold rolled in coils down to the required gauge. If flat sheets are required, the coils are flattened and cut up into the desired lengths. Hot rolling. Mills used for hot rolling are commonly of the single stand "2high"-that is, two work rolls highreversing type, though single stand 3high non-reversing mills have been used. Multistand non-reversing 4-high mills in line with and following one or two reversing 2-high or 4-high mills have been developed for large-scale production. The width of the slab, which remains almost constant during rolling, may be increased by "cross rolling" -that is, passing the slab before it gets too long through the mill with its longer axis parallel to the rolls. Most alloys tend to crack at the edges during hot rolling, so the slab is run up on separately powered roller tables from the hot mill to an "edge trimmer" or rotary shear, which can also be used to slit the slab into two or more strips. To maintain more uniform width of slab, reduce cracking at the edges, and obviate trimming, the latest practice is to use an edge-rolling mill in conjunction with the reversing hot mill. A "slab shear," which cuts the ends square and may also be employed to cut the slab into short lengths for production of flat sheet, is standard equipment. The .final dimensions of the slab and the procedure after hot rolling depend on the product required. It has already been stated that the resistance to corrosion of pure aluminum is superior to that of most alloys. In order to combine the high corrosion resistance of the pure metal with the strength of the stronger alloys, composite sheet. "Alclad," is produced, consisting of a thin coating of pure aluminum on either side of an alloy core. Plates of high purity aluminum are clamped on either side of the scalped

16

MANUFACTURING PROCESSES IN CANADA

Fie . 2. A general view of a modern rod rolling mill.

alloy ingot before preheating, the clamping bands being removed before hot rolling commences. For the first pass or two through the hot mill, only a light pinch is applied to ensure adhesion between the plates and the ingot, and therefore the rolling procedure is much the same as with unclad material. After hot rolling, and at the required stages in cold rolling, the metal is annealed to remove work hardening and restore ductility. Annealing technique varies with the composition, form, and condition of the metal, but in general consists of heating to a temperature within the range 345-400°C and soaking for a specified time. Batch-type air furnaces heated by gas or electricity are usual for annealing flat slab and sheet; continuous furnaces are often used for coils. Cold rolling. The oldest method of

cold rolling, and one which still has its uses for certain types of sheet, consists in passing the sheets between the rolls of a 2-high mill, and returning them over the top roll. Each sheet is given a number of passes, the reduction in gauge being obtained by screwing down the top roll. This method gives only a small reduction at each pass but confers a smooth finish to the sheet, and with special attention to the rolls results in a highly polished product. Very thin sheets are often rolled in packs, two or more being passed through the rolls together, thus sharing the "play" in the roll bearings which would be appreciable for a single thickness and would introduce difficulties. Sheet produced by this method has only one bright surface. For the production of large batches, flat sheet is ordinarily rolled in coils,

ALUMINUM

usually as it comes from the hot mill, and annealed in coil form. In cold rolling it is passed between the rolls of the mill into a coiling machine which applies tension to the metal, tending to pull it through the mill, on the ingoing side of which a braking device provides "drag tension." This tension during rolling enables heavier reductions to be made by eliminating frictional interference. In modem practice the old 2-high mill is replaced by a 4-high on which the work rolls which actually touch the sheet are relatively small and are supported and prevented from bending by "back-up" rolls of very much larger diameter. The area of contact between the rolls and the sheet is thus reduced, and the pressure upon the sheet correspondingly increased, making possible even bigger reductions in each pass, and the resulting sheets are of uniform thickness to within close limits. The latest type of plant has two or more 4-high mills in line or "in tandem." With this arrangement the sheet leaving the rolls of one stand passes directly into those of the next, under tension all the time, and is coiled up after emerging from the last mill in the train. A great deal of sheet material is sold in coils, particularly in widths of two feet or less. Wider .sheet is usually sold in flat pieces; if produced in coil form it must be flattened and cut to length. Finishing. The last fabrication process for flat or coiled sheet is "finishing" -stretching flat and cutting to exact size-and this must be done before artificial aging. A stretching machine has wide jaws to grip the ends of the sheet and stretch it until all ripples and uneveness are removed. The jaw-marked ends of the sheet are then cut off and the sheet sheared to exact size on a guillotine shear. Certain types of material are not stretched ( for example, very long coils) and a sufficient degree of flatness is attained by means of roller levellers. It may not be possible effec-

17

tively to stretch work-hardened material of fully hard temper, and in this case it may be flattened by roller levellers. Additional finishing processes are required for corrugated sheet and circles. Flat sheets are corrugated in a brake press or a rolling machine, and circles are either blanked out from flat strips in a blanking press or cut on a circle cutter. Process scrap. Scrap is produced at various points in the production process: in the form of swarf from the machining of the ingot, and side and end trimmings at intermediate stages and at the final shearing operation. All this is normally reabsorbed in the furnace charges, the thinner sheet trimmings being compressed into bales for ease of handling and to avoid excessive loss by oxidation when charged into the furnace. Foil rolling: Foil is rolled in much the same way as coiled sheet, the main essentials being that the mills must be extremely accurate to enable the very thin material to be rolled without breaking. Pack rolling is often employed, and special attention is paid to sudace finish. Here again modem mills are of the 4-high type, running at high speed. Foil is not normally produced in anything except commercial purity aluminum, the harder alloys being unsuitable for this method of working and their higher mechanical properties not being required. EXTRUSION

Extrusion is the forcing of material through an orifice ( or "die") from which it emerges in the desired crosssectional shape-like toothpaste from a tube. This is the principal method of fabricating aluminum and aluminum alloy rod, bar, channels, tubes, and the almost unlimited variety of sections used for structural, architectural, and other purposes. A horizontal press is generally used,

18

MA!I.UFACTIJRING PROCESSES IN CANADA

which in its simplest form comprises a cylindrical container of great thickness and strength, at one end of which is provision for holding a die. At the other end is a ram actuated by air-hydraulic pressure, by means of \Jvhich the cylinder of metal, or ingot, is forced to flow through the die aperture. Extrusion

capable of extruding shapes which fall within a circle of about 15 inches diameter. Each press is generally provided with several different sizes of container to meet varying requirements of size and type of section to be produced. The total weight which can be extruded in one piece depends on the

F1c.. 3. Extruding aluminum in a 3,500-ton press.

presses vary considerably in size, design, and details of operation. Hydraulic pressures of 3,500 pounds and 4,500 pounds per square inch are common, but may be more or less than this. The rating of a press is the total force that can be applied by the ram, and this obviously is a function of the hydraulic pressure available and the size of the ram. Presses rated at 5,000 tons are

length of the stroke and the power of the ram, and pieces weighing up to 1,000 pounds or more are available from modem equipment. It should be noted that factors other than the capacity of the press limit the length of an extruded section. These include equipment for straightening and heat treatment, and difficulties of handling in the works and on despatch to customers.

ALUMINUM

Extrusion is a hot-working process and breaks down the cast structure of the metal. In hot rolling, metal is squeezed out in the direction of rolling only, whereas in extrusion the "flow lines" within the container follow curved paths. When the metal is subjected to the pressure of the ram, it has to find a way out through the aperture of the die, and is thoroughly worked in the process. When it has passed through the die, the original crystalline structure has been broken up and a definite directional grain has been developed. Thus intricate and thin sections are more difficult to extrude than heavier and simpler shapes. To ensure that the necessary force is available, a container of suitable size is chosen so that the ram can impart the required unit pressure upon the ingot. The speed of extrusion is affected by the shape and size of the section, and the composition and temperature of the metal. In the case of many alloys, the fastest speed occurs towards the lower end of the temperature range, but several metallurgical factors have to be considered, and usually the optimum temperature is between 400 and 500°C. Average speed covering a wide range of section shapes varies from the maximum which can be handled in the case of pure aluminum ( which may be as high as 200 feet per minute) down to only 2 or 3 feet per minute for the strongest alloys. During extrusion the temperature of the container is kept constant by electric heating elements, thermostatically controlled. The ingot, after preheating in a gas or electrically heated air furnace, is pushed into the container, at one end of which is the die. A steel pad is inserted behind the ingot, and the ram then forces the metal through the die. A certain amount of metal is normally left in the container after extrusion, and this "butt end" is withdrawn with the pad and the die from the body of the press. The butt end is severed from the

19

extrusion and the die is returned to the container for the next ingot. When a tube or hollow shape is extruded, a hollow ingot may be used, and a mandrel is positioned in the die opening so that the metal flows through the annular space between die and mandrel. Some presses are equipped to pierce solid billets. An alternative method of extruding hollow shapes is now employed for certain alloys, obviating the use of the usual long mandrel. The solid ingot is extruded through ports of a special dieholder into a mixing chamber in front of the die orifice. The metal flows round a stub mandrel which projects into the die orifice and is an integral part of the dieholder. The extrusion pressure causes the separate streams of metal to weld so that the shape which emerges is a complete hollow section. This is known as the "port-hole" method of extrusion. Heat treatment. Both non-heat-treatable and heat-treatable alloys are extruded. For heat treatment of extrusions, air furnaces are generally used, and these may be horizontal or vertical, the latter including both pit and tower furnaces. Horizontal furnaces for solution heat treatment of extrusions are usually heated by gas or electricity, and are provided with quench tanks and suitable charging and quenching mechanism. The quench tanks are generally sunk into the floor in front of the charging end of the furnace. The extrusions are loaded on a carriage, which is power-driven into the furnace and after heat treatment is rapidly withdrawn and lowered into the quench tank. The tower or vertical furnace, as it is usually called, may be heated by electricity, gas, or oil. The heating chamber is cylindrical, and is built above ground, with a pit beneath as deep as the furnace is high. The quench tank is mobile, being mounted on a wheeled carriage which straddles the pit and runs on rails on either side. The extrusions are

20

MANUF ACTUBING PROCESSES IN CANADA

suspended from a spider, which is by stretching on a hydraulic stretcher. lowered to the carriage beside the There is frequently a good deal of twist, quench tank, and the carriage is then necessitating "detwisting." Light sechauled under the furnace and the load tions are stretched on a machine, but hoisted up into the heating chamber. twist and any remaining bow are reIn due course the quench tank is run moved by hand. Heavier sections are under the furnace and the load lowered detwisted mechanically, and there are into it. In this way a very rapid and facilities for this on the big stretching uniform quench is obtained. The car- machines, one "head" ( essentially a riage is then hauled to one side and clamp which grips the extrusion) being the load lifted out of the quench tank. rotated in the opposite direction to the Vertical furnaces are finding in- twist while the other remains fixed. creasing favour for large production, Straightening is also accomplished by especially for tubes and hollow sections means of "Hexipresses," mechanically or in which distortion is particularly to be hydraulically operated. avoided. They are very costly to install, requiring deep excavations for the pit DRAWING and a great deal of structural work for Drawbenches are used for the prothe furnace, but two or more furnaces may be erected alongside one another duction of thin-walled tube, for reguwith a much less than proportionate in- lating the shape of certain sections, and crease in cost of excavation and with for obtaining close dimensional accuvery little additional expenditure for racy on machining stock of simple loading and unloading equipment and shape, such as rounds, squares, and hexagons. A drawbench has a fixed diefor haulage. Precipitation ·treatment is carried out holder and a gripper head mounted on in horizontal air furnaces similar in type a carriage. This carriage is arranged to to the solution heat treatment furnaces. run on a track over an endless squareOperating temperatures, however, are section chain, which is driven by an of course lower, and no quench tank electric motor so that the top run moves or special rapid-quenching mechanism away from the die. The carriage has a hook or "dog" which is engaged with for the carriage is required. A simplified form of heat treatment the chain when the section has been is sometimes applied to extrusions in gripped, and the latter is then pulled certain alloys. The temperature at through the die. When the section has which the metal leaves the die is suffi- completely passed through, the hook is ciently near to the appropriate tem- disengaged, and the carriage is returned perature for heat treatment, and as soon to the die by means of an endless wire as each length leaves the die, it is rope driven by a separate motor in the quenched in cold water. This is known opposite direction to the chain. as "quenching at the die," and with suitTube is produced by drawing down able sections the properties obtained hollow round sections of comparatively are not inferior to those conferred by thick wall, which as extruded are known solution heat treatment. as tube blooms. These are always of Finishing. Certain finishing processes larger outside diameter than the resultare necessary for extruded products, ing tube. One end of the bloom is,hamwhether heat treated or otherwise. All mered, swaged, or rolled to a point, and extrusions require straightening. Heavy this is pushed through the opening of sections may be run through a roller the drawing die. A rod with a cylindristraightener which removes the worst cal steel bulb is thrust into the open of the distortion, and this is followed end of the tube right into the die, and

ALUMINUM

the jaws of the drawbench carriage are then gripped on to the swaged end and the tube is drawn through the die. Heavy lubricating oil is used in drawing, the tube being smeared liberally inside and out, and in addition flood lubrication by force pump is sometimes provided. The amount of reduction in dimensions-outside diameter, inside diameter, and wall thickness-depends on the material and final size required. Many different sizes of finished tube ( and also several tempers of non-heattreatable alloy) may be produced from one size of bloom, and the drawing programme is planned accordingly. If the required reduction exceeds a certain amount, one or more stages of annealing may be necessary. Before annealing or heat treatment, the lubricant must be removed, and this is done by washing in a degreasing medium. Annealing furnaces are generally similar to aging furnaces, but must of course be capable of operation at higher temperaturesup to about 430°C. Tubes of suitable composition may be heat treated after drawing. PRODUCTION OF ROLLED BAR AND WIRE

Although extrusion is also a common method of producing rod and bar, these products are usually rolled. "As cast" cylindrical or square-section ingots may be used, but certain strong alloys are often first extruded. As with the production of sheet, the first step is hot rolling, for which the stock is preheated in the same way. The bar mill is usually of the 3-high type. These rolls are set fairly close together, and the surface of each roll has a series of circumferential grooves, diminishing in size and changing in shape from one end of the roll to the other. If the middle roll turns clockwise, the top and bottom rolls tum anti-clockwise. The stock is thrust between the grooves of the bottom and middle rolls, and drawn through to the other side of the mill,

21

where it is gripped in tongs by the operator, who thrusts it into another pair of grooves between the top and middle rolls, which draw it back to the side from which it started. Each successive pass is through a smaller pair of grooves, so that the stock is progressively reduced in thickness. The shape of the stock may also be changed at each pass, though not necessarily progressively. In modem installations, the successive reductions are accomplished in continuous mills. The first few passes are made in a manner similar to that described above, except that no hand labour is required. After the bar stock is reduced far enough, it proceeds to "looping mills." In these mills it is progressively reduced by each succeeding stand. The movement of the stock through the rolls and from one stand to the next is provided by the rolls, and the "loops" or changes of direction are brought about by an ingenious arrangement of guides. Rolled bar is used principally as stock for forging and for machining, in which the extra hot working is advantageous. Wire stock is taken several stages further than bar, until it is rolled down to about " inches in diameter, when it is coiled preparatory to cold drawing, or, if necessary, annealing. The coil is then put on a wire-drawing machine, in which it is cold drawn through one or more dies and recoiled. If further reduction is required, the wire is annealed and redrawn until the desired gauge is reached. FORGING

Hot forging is the method of fabrication by which the metal is heated until it becomes plastic and is then hammered or pressed into the required shape. In forging aluminum alloys, the hot-working temperatures are relatively low and critical, the upper limit being fixed by the hot shortness of the alloy

22

MANUFACTIJRING PROCESSES IN CANAD.A

and the lower limit by the workability of the metal. Too high a temperature results in crumbling, while if forged too cold the metal becomes difficult to deform and liable to grain growth as a result of critical amounts of cold work. Since aluminum is forged below red heat there is no visible indication of temperature. Strict furnace control is essential and automatic pyrometric controlling and recording instruments are a necessary feature of the forging shop. In most cases "as cast" metal cannot be forged directly into an intricate die because the resulting product would not be worked sufficiently to ensure a uniform fine-grained structure which would confer optimum mechanical properties. Thus forging is usually preceded by any of the hot-working processes: rolling, extrusion, or kneading. The last is laborious and is therefore used to produce large-size forging stock only; rolled or extruded forging stock is more economical in the smaller sizes. Gas-fired muffle furnaces are often employed for preheating, and electrically heated furnaces, with forced air circulation, are also widely used. Whichever type is employed, the furnace must be designed so that the temperature throughout the whole chamber is uniform and controllable. The forging temperature, which is critical, varies according to the alloy, the limits for extruded or rolled stock being 440-475°C. The essential components of a forging hammer are the anvil on which is placed the metal to be shaped, and the "tup" which strikes it. The blow is always vertical to take advantage of the weight of the tup, which may be as little as 100 pounds or as much as 30 tons. The tup is always lifted by mechanical means, but the term "power hammer" is only applied when the fall of the tup is controlled mechanically to regulate the force of the blow, the

power usually being provided by steam or compressed air. With "gravityoperated" hammers, the tup falls on the work, and the force of the blow is controlled by varying the height from which it is released. Three methods of forging are practised: hand, drop, and press. In hand forging the work is turned and moved and the blows of the hammer regulated to produce the required shape. Swages, fullers, and other hand tools are sometimes interposed between the hammer and the work, but in general the article is shaped by manipulation only. Accurate or intricate forgings cannot be produced in this way, and generous machining allowances are necessary. Nevertheless, hand forging is very useful where the quantities required do not warrant the cost of forging dies. It is also adopted for rough-shaping stock for forming under a drop hammer, the hand-forged stock being described as a "dummy" or a blank. In drop forging the method of shaping the work is fundamentally the same as in hand forging, but the dummy is placed between dies bearing the impression of the component, which are attached to the tup and anvil of the hammer. An intricate shape may require more than one stage of forging, and this can be accomplished at a single preheating of the stock by arranging rough ("blocker") and finishing impressions side by side in the one die, or by using two separate sets of die blocks and treating the two stages as independent forging processes. In the latter case it is usually necessary to reheat the partly formed stock before forging in the second set of dies. For certain types of work, forging rolls are employed for preforming the stock prior to die forging. The rolls are made with cavities of the desired shape and make one revolution before reversing. The preheated stock is inserted into the rolls, which on revolving squeeze the metal into shape.

ALUMINUl\I

FIG. 4. Forging aluminum.

23

24

MANUFACTURING PROCESSES IN CANADA

Whereas in drop and hand forging the work is deformed by sudden impact, in press forging the action is that of squeezing the metal into the desired shape. Furthermore, the forging action of the press may be developed in more than one direction-from the side as well as from above and below-and this enables undercuts to be produced. As with drop forging, pressing may be carried out in several stages according to the complexity of the finished product, and the dies must be so designed as to achieve the optimum movement of metal at each stage. Severe forming may result in damage to the stock and excessive wear of the dies. On the other hand, many stages of forging may be uneconomical. A compromise is therefore necessary. Forging presses are operated hydraulically or mechanically. Small presses are often of the mechanical type while large presses, capable of exerting a pressure ranging from 1,000 to 30,000 tons, are usually hydraulically operated. The majority of forgings are used in the manufacture of stressed components for which a strong alloy is required. Alloys most commonly forged therefore are heat-treatable, heat treatment following the forging operation. Normal practice is followed, care being taken to control the temperature within very close limits. Design of forgings. In designing an article for production by forging it is necessary to bear in mind the limitations imposed by the forging process. It is obvious that the original volume of metal of the stock or the blank must be greater than that of the finished forging to ensure that the die impression is completely filled. The excess metal squeezed out between the die faces (known as "flash") is subsequently trimmed off. During the forging operation the metal flows from the shallow to the deeper areas of the die cavity, and it is desirable that this flow should be smooth and gradual in order

to prevent the building up of excessive pressures within the die which may even rupture thin webs in the forging. Mechanical properties in a forging depend markedly on the direction of grain flow, inferior properties being obtained across the grain. It is clearly desirable, therefore, that the direction of flow should be so arranged as to resist working stresses most effectively. For large-scale repetitive work the forging which needs little machining will often be justified, though if the shape lends itself to automatic machine work rough forging followed by heavy machining may be a cheaper method of production. The maximum size of an article which can be produced by forging depends as much on the nature of the article as on the equipment available. Hand forgings are not subject to any very definite size limitation, but difficulties in manipulation-especially if the piece is bulky or awkward in shape-make it necessary to restrict the size. Drop forgings ranging from a fraction of a pound to over 600 pounds in weight may be produced. Maximum weights and dimensions of press forgings are more difficult to define, depending essentially on the equipment and the nature of the product. CASTING

Casting is the simplest process for manufacturing aluminum components. The metal is melted and poured into moulds of the required shape, and is not subjected to working or forming. These moulds may be of sand ( sand casting) or machined from iron and steel. Of the latter, two distinct types are in common use : the "permanent mould," into which the metal flows by gravity ( called gravity diecasting in the United Kingdom) and the "die," into which the metal is forced under pressure ( called pressure diecasting in the United Kingdom) .

ALUMINUM

Melting and pouring. Alloying may be undertaken at the foundry as described earlier, or ingot of the required composition bought ready-made. Where size of production justifies melting a large weight of alloy at a time, reverberatory furnaces may be used. For pouring large castings, metal may be taken direct to the mould or die. In the case of small castings, metal is transferred to small oil- or gas-fired "baleout" holding furnaces of some 200 to 400 pound capacity for use as needed. Where only small output of metal in any particular alloy is required, melting may be accomplished in tilting furnaces of 500 to 1,000 pounds' capacity. Melting pouring temperatures are carefully controlled to give the optimum conditions for the production of sound castings. A good general rule for pouring temperatures is that they should be as low as possible, but high enough to avoid misruns. The molten metal may be "degassed" as discussed in the earlier section on Remelting and Pouring, and then dross is skimmed from the surface. Sand castings. Sand moulds are used in the production of large castings or of others of which the quantity required is insufficient to justify the cost of machining a die. Moreover, in certain cases castings may be too intricate to produce by diecasting. The pattern is the model of the casting required, around which sand is rammed in the preparation of the mould. In arriving at its dimensions suitable allowance is made for contraction of the metal after solidification. The material from which the pattern is made depends upon the number of castings to be produced. For small quantities, patterns are usually made of wood; for large quantities, or where production is likely to be extended over a long period of time, metal patterns are often used, since they resist more satisfactorily the abrasive action of the sand and are not subject to deterioration on

25

storage or by contact with the moisture in the sand. For large-scale production with moulding machines, metal match plates and multiple patterns are generally employed. Moulding sands are essentially natural sands, and are used in the condition as dug from the quarry. Core sands consist of silica sand to which an artificial binder has been added to give the desired strength. Linseed oil, molasses, and Bentonite clay are among the substances used for this purpose. Small sand moulds are hand rammed, and larger moulds may be rammed mechanically by pneumatic jolt- or squeeze-moulding machines. Cores are rammed in special boxes made of wood or metal and then baked in gas- or cokefired conveyor ovens, to remove moisture and enable them to be handled without damage. In the case of small simple types of core, manufacture can be largely mechanized by the use of core-blowing machines and metal dies. Moulds may be used in the "green," "skin dried," or dry condition. "Green" moulds are used as rammed, while in the case of "skin dried" moulds, moisture is driven from the surface of the mould only, by heating with a gas torch. Dry sand moulds are used only for small castings such as test bars and require to be dried in an oven prior to use. The design and placing of the "runner" are matters of the utmost importance, since turbulence and splashing during pouring must be minimized, and at the same time the mould must be fed as quickly and as uniformly as possible, and air pockets prevented. Massive parts of the casting should not, in general, be fed through thin sections, in which solidification will take place more rapidly and perhaps restrict flow. "Risers" are cavities made in the mould to provide reservoirs of hot metal. They are usually placed over thick sections, particularly those remote from the runner, so as to feed adjacent sections and prevent the formation of shrinkage

26

MANUFACTURING PROCESSES IN CANADA

cavities. It is sometimes necessary to provide "vents" in the mould to allow steam and gases to escape, and thus obtain sharp definition. Metal "chills" are often placed in the surface of sand moulds to hasten solidification and cooling of massive portions of the casting. The rate of cooling influences mechanical properties considerably, a slow rate giving rise to coarse crystal formation which is a source of weakness. Permanent mould casting. Though other non-ferrous metals are cast in permanent moulds, the process is particularly associated with aluminum alloys. The iron and steel moulds vary greatly in size and character, some comprising twenty or more separate pieces which when assembled not only form a mould of the required shape, but permit the casting to be extracted quickly and satisfy the numerous other conditions upon which depend the rapid production of sound castings. Casting procedure is simple. The mould is situated close to a holding furnace, from which the metal is taken in a ladle of appropriate size. For large castings, two or more pourers may be required. Before casting is started the mould is heated with gas jets, but even so it is necessary to fill the mould several times with molten metal before stable working conditions are reached and satisfactory castings can be produced. The principal advantage of permanent mould casting is the high rate of production. Permanent moulds are fairly costly, since they have to be machined from iron and steel castings, and several weeks may elapse between the placing of the order and first deliveries. Thereafter the cost per casting is much less, so that the total quantity required determines the economic case. However, other advantages are associated with permanent mould castings. Closer dimensional accuracy and smoother finish are assured, so that machining allowances may be reduced

to about half those required for sand castings, and in some cases machining can be eliminated altogether. Not only is there saving in machining time, but the reduction in weight of metal purchased may be appreciable on a large order. Iron moulds cool the metal much more quickly than sand-hence the term "chill moulds"-and a finer grain structure results, with higher mechanical properties. Permanent mould casting is necessarily less flexible than sand casting, complexity of shape greatly increasing cost of dies and introducing difficulties in production. The choice of alloy is more critical: desirable foundry characteristics include fluidity in the molten state, low shrinkage on solidification, fair strength at temperatures just below the solidification range, and small contraction in cooling. A permanent mould should be designed so that the metal solidifies progressively towards the heavier sections, and these sections must be fed with hot metal to replace that drawn from them on solidification of adjacent parts of the casting. Alloys that have high shrinkage on solidification need generous feeding with heavy risers. Sluggish alloys will not flow satisfactorily into very thin sections, and "cold shuts" may be formed by solidification of one or more streams of metal before the mould is completely filled. This may be avoided by pouring at a higher temperature, but only at the risk of excessive oxidation of the molten metal and the formation of coarse grain in the thicker sections of the casting. Coating the mould with a solution containing, usually, whiting and a binding agent contributes to good finish and sharp definition of corners, assists the metal to fl.ow in the mould, and facilitates withdrawal of the casting. Portions of the mould in which air might be trapped must be vented, special vent plugs being provided. To vent large surfaces fine grooves may be cut in the face of the mould, and small

ALUMINUM

gaps between cores fulfil the same function. The mould coating also acts as a heat insulator and reduces the rate of chilling of the molten metal. By varying the thickness of the coating, the relative rates of solidification in various parts of the mould can be adjusted, in much the same way as chills are used in sand moulds. On cooling, the metal tends to contract on to the cores and projections in the mould, and this may cause cracking of the casting ( especially in a hot-short alloy) or leave internal stresses which may eventually result in distortion or even fracture. To minimize trouble from this source, steel cores are withdrawn as soon as the metal in the runners and risers is set, and the casting is removed from the die as soon as it is sufficiently strong. To prevent contraction flaws it may be necessary in some cases to use sand cores, particularly where extremely intricate or deeply recessed coring is required. Diecasting. The highest rate of casting production is given by diecasting, in which the molten metal is injected into the mould cavity under pressure. The most satisfactory type of diecasting machine for aluminum is the "cold chamber" type, in which molten metal is poured from a hand ladle into the chamber and is then forced, in a pasty condition, into the closed die by means of a pneumatically driven plunger. After solidification, the die is opened and the casting ejected mechanically. For very large quantities of castings the heavy initial outlay in dies is often well repaid, especially since excellent surface finish is obtainable, and machining is only required where precise dimensional accuracy is demanded.

27

Only alloys with the very best foundry characteristics can be diecast, and owing to the rapid chilling the metal receives on entering the die, castings are apt to be underfed and therefore porous towards the centre. For these reasons highly stressed articles are seldom diecast. Finishing. Castings, after rough inspection, are fettled, that is, extraneous metal such as runners and risers is trimmed off, generally by means of a band saw. Heat treatment, where applicable, is conducted in air furnaces .. Final inspection may include examination for cracks, X-ray examination, or pressure testing.

In all the above processing operations, many improvements are being made in both the equipment and operating practice and these bring about important contributions to the aluminum industry. In the reduction plants today. larger and more efficient pots and longer potlines are being introduced, with consequent savings in the amount of electricity required per pound of metal and in carbon electrodes. In the fabricating processes, many mechanical improvements are being developed and put into effect in the various mills on a continuous basis. All of these factors have helped to make aluminum available more cheaply and, generally speaking, the price trend in the industry has been downward. With all these factors contributing to the ever increasing range of applications, there is every indication that consumption in practically all countries of the world will continue to increase steadily and that processing facilities in the industry will keep pace with the demand.

Beef BY G. MOORE AND T. HERCUS CANADA PACKERS LIMITED-ST. BONIFACE

is the processing and merchandising branch of the Canadian livestock industry. Leader among food processing industries, it had an annual production valued at over $809 million in 1955. The 153 commercial processing plants which reported official statistics employed 23,655 persons who received over $83 million in wages and salaries. In terms of value of factory shipments, meatpacking ranked fifth among Canadian manufacturing industries. Prior to the development of the meatpacking industry, slaughtering was a local enterprise. Even today, local and farm slaughter accounts for a significant part of the total meat supply. In 1956, it was estimated that about 25 per cent of the cattle and 30 per cent of the hogs were slaughtered outside of regular meatpacking establishments. As Canada's population has increased, however, meatpacking plants have grown up at the outskirts of the major cities. Toronto became the leading meatpacking centre of the Dominion. The Toronto-Hamilton area accounts for the major part of the province's inspected1 MEATPACKING

lGovemment inspection: all packers engaging in export or interprovincial trade must operate under the aegis of veterinary inspectors appointed by the federal Department of Agriculture. These inspectors examine all animals before slaughter and at various stages of processing, to detect disease or other unwholesome conditions. They are also responsible for inspecting the meatpacking plants to see that they conform with a rigid sanitary code. Meat products from inspected plants may be used with confidence because they are free from disease and are prepared under clean and sanitary conditions.

slaughter with ten fully inspected meatpacking establishments. Meatpacking is also an important industry in the Greater Winnipeg area. From a very small beginning before the turn of the century, increasing numbers of livestock were processed each year, until in 1913 the largest stockyards in the Commonwealth were opened in St. Boniface. By 1925 meatpacking had become the largest manufacturing industry in Manitoba and has maintained that position ever since. In 1955, slaughtering and meatpacking led Manitoba's manufacturing industries in terms of the selling value of factory shipments which amounted to $99,000,000. Except for two large plants, a number of small and medium-sized establishments characterDISTRIBUTION OF FULL-TIME INSPECTED MEATPACKING ESTABLISHMENTS AND PERCENTAGE OF SLAUGHTER BY PROVINCES

(1956-7) 0

No. of Percentage plants of slaughter+ Prince Edward Island Nova Scotia New Brunswick Quebec Ontario Manitoba Saskatchewan Alberta+ British Columbia North West Territories

1

.40

2 10 19 7 7

1.23 13.98 34.04 19.39 4.07 20.24 6.65

10

5 1 62

0 Derived from the Report of the Veterinary Director General, Department of Agriculture, Canada, March 31, 1957. t Cattle only.

BEEF

ize the Montreal area; four plants in the city itself, and six plants elsewhere in the province. These are responsible for 14 per cent of the total inspected slaughter for all of Canada. Calgary and Edmonton account for the Alberta output. All the inspected plants in British Columbia are located in the Vancouver area. The principal meatpacking companies with plants throughout Canada are: Canada Packers Limited with head office in Toronto and twelve plants under inspection from Charlottetown to Vancouver; Swift Canadian Company Limited with head office in Toronto and six plants under inspection across the Dominion; and Bums and Company Limited with head office in Calgary and seven plants under inspection. Livestock Production The eastern agricultural region of Canada-the St. Lawrence plains, the Ottawa Valley, and peninsular Ontario -supplies the beef cattle for the meatpacking plants of Toronto and Montreal which account for about 53 per cent of the total inspected slaughter of all Canada. In the West, the southern zone of the prairies provides the grazing land for beef cattle. Located near the producing area are the sizable meatpacking plants of Calgary and Edmonton which derive the benefit of low transportation costs. At the eastern end of this prairie agricultural region is the city of Winnipeg with its several large meatpacking plants. The cattle processed in Vancouver are produced in the mountainous district of southern British Columbia and in Alberta. As one would expect, peak marketing of livestock occurs in October and November when stock is brought in off pasture and decisions are made as to whether they will be fed throughout the winter or sent to market. At this time, cattle deliveries are about a third higher than the yearly average; at their lowest point, deliveries are about 20

29

per cent below the year's average. Compared to this seasonally variable supply, the demand for meat by consumers is much more stable. This is not to say that changes in the weather, special holidays, ·racial and religious customs, and other factors do not influence meat purchases to a considerable degree. But by and large the weekly sum set aside for meat by consumers in their food budgets tends to be fairly constant. ·1t is evident that the job of fitting a variable meat supply into a stable pattern of demand throughout the year is no simple task. It involves fluctuations in price and extensive cold-storage programmes. Purchase of Livestock When a Canadian livestock producer has beef cattle ready for market he has several alternative channels through which he can offer them for sale. He may ship his cattle by truck or rail to a public livestock market and make arrangements with a commission agent to offer the cattle for sale; or he may sell direct to a trucker or a shipper, or to a buyer from one of the meat packers who is stationed right in the producing area. On the other hand, he may decide to deliver his cattle directly to a meatpacking plant. When livestock is shipped to a public market, it is received by employees of the stockyard company. The animals are driven to pens of a commission firm and released to the charge of the commission agent who then offers them for sale. Commission firms employ expert livestock salesmen whose responsibility it is to get the highest possible price for all cattle shipped to them. Buyers from meatpacking firms, after determining their sales requirements, inspect the day's offerings and bid on each lot according to their estimate of what the cattle will grade and yield as to quantity of dressed beef. When deciding on his bid, the buyer works from dressed beef costs back to live prices. If a com-

30

MANUFACTURING PROCESSES IN CANADA

mission agent thinks that the bid is too low, he will offer his livestock to a second packer, and so on until he is satisfied that he has the best bid. Immediately after purchase, the stock is driven to a scale and weighed for payment. At this point the responsibility of the commission agent ends and the stock becomes the property of the buyer. The packer then moves the cattle from the stockyards to his own pens and holds them until he is ready to slaughter. Many livestock producers and shippers prefer to sell their stock direct to the meatpacking plants. The principle advantage of this method to the producer is the fact that he saves the cost of yardage which he must pay at the public stockyards and the commission which he must pay to the commission agent for selling his livestock. When he ships direct to the packing plant, the producer receives the going price for the grade of livestock which he has shipped. Beef Dressing Operations Operations required for the processing of beef logically begin on the upper floor of a multi-storey plant thus allowing the use of gravity chutes to carry by-products to lower floors for further processing. Finished products are shipped from docks located on the main floor. In recent years, mechanical conveyors have partially replaced gravity chutes since they combine flexibility with economy. Further, construction of one-storey plants is being favoured over those of four or five storeys since a more direct and even flow is achieved. The operations which convert cattle to !Jeef are immobilizing, sticking, hide removal, evisceration, government inspection, and chilling. The most modem method of slaughtering cattle is known as the "Can Pak System"-a system developed by Canada Packers Limited. This system eliminates much of the hard work of

the old method. It provides mechanical devices to make the work easier and permits the butchers to work in an upright position. Following is a description of the Can Pak System with a brief reference to the old. In preparation for slaughtering, cattle are held in resting pens, where possible, for twenty-four hours, without food but with an abundance of water. For slaughtering, cattle are driven into a large box, formerly known as a knocking box, which is raised above the level of the floor to permit a mechanically controlled false floor to open after the animals have been immobilized, discharging them onto the open floor. The operator stands on a raised platform above the stunning box and delivers a blow to the centre of the animal's forehead with a captive bolt gun. The unconscious animals are then shackled and hoisted to an over-head rail suspended from the ceiling. This rail usually carries a power-driven chain which moves over the entire area of the dressing floor, conveying the carcass to and from the various operators' work areas. The carcass is hung by the hind leg on "travellers" built of a special type of metal which has been designed for maximum strength thus eliminating any danger in transporting exceptionally heavy carcasses. Carcasses are conveyed first to a bleeding bay where an operator inserts a knife, inclined upwards, through the front wall of the jugular vein. This method of sticking ( Trafer method) produces a free flow of blood which improves the finished appearance of the carcass. The Kosher method is used when required for the Jewish trade. Under special rules laid down by the Jewish people, the animal's throat is cut by a knife which has been blessed by a Rabbi. The Kosher committee not only does the slaughtering but also stamps the beef cuts with a special mark to indicate that they are Kosher. After the animal is fully bled, the

BEEF

head is skinned and severed, and head and carcass are tagged to identify them for government inspection. Should an inspector discover some form of disease in the glands of the head, he will be able to identify the corresponding carcass by the tag. Following the removal of the head, the free hind foot is skinned and cut off at the first joint, and the carcass is "changed-over" on the rail so that the other hind foot may be removed. The front feet are also removed at this stage. The hide is opened down the middle of the belly and is then cleared from the flesh on the sides of the carcass usually by mechanical dehiders. The hide is then removed from the rump, and the aitch bone or pelvis bone is cut through. Retail buyers judge the age of the animal by the appearance of the pelvis bone. The hide is pulled from the side to the back by a mechanical hide puller operated by compressed air cylinders. This revolutionary innovation in modem beef-dressing operations is called the Can Pak Hide Puller and was invented by Canada Packers Limited. This method allows the hide to be pulled away evenly, leaving a smooth surface on the carcass. Sawing of the brisket or breastbone is performed by an electric power saw. The saw is provided with a guard to hold back and to prevent puncturing of the large stomach when the brisket is cut. Next, the hide is eased off the back with a knife and allowed to drop. It is then graded, weighed, and delivered by gravity chute to the hide curing department. The earlier method was more arduous, hazardous, fatiguing, and costly, requiring the hung carcasses to be lowered manually from the moving rail and placed in beds. Hides were removed by knife by the worker from a stooped position. The carcasses then had to be hoisted back onto the moving rail.

31

After removal of the hide, an operator splits the remainder of the belly, and the viscera are removed. The pluck, consisting of the lungs, heart, and liver, is next removed and all these internal organs are dropped onto a moving table. The speed of this table is synchronized with the rate at which the cattle are moving along the conveyor chain. It is therefore possible to determine from which carcass the internal organs have been removed. Government inspectors thoroughly examine the glands and viscera for any trace of disease or contamination. Again, at any sign of disease, they are able to identify all parts of the carcass. The internal organs which pass inspection are conveyed by gravity chute to the offal department for processing, while any found not completely free from disease are condemned and shipped to the inedible rendering department. After evisceration, the carcass is split down the backbone into two equal parts, known as "sides," by means of a power saw or a large cleaver depending on the type of cattle. At the next work station, the operator partially cuts the fin bones along the back. This operation, called scribing, improves the appearance of the side and prevents the meat from shrinking away from the bone. Kidney suet, fat, and kidneys are removed next. Portions of the side are trimmed and the shoulder is lifted in a pumping motion in order to remove any surplus blood that may have accumulated in this natural pocket. The sides of the beef then enter a large metal cabinet which contains a number of high pressure water sprays, mechanically directed up and down the sides. The pressure of the directed sprays insures thorough washing. The sides pass from the cabinet and are conveyed over a scale on the rail where the weight is recorded along with the sex of the animal and the grade of

FIG. 1. Cattle being driven to the killing floor.

FIG.

FIG.

3. The Can Pak Hide Puller.

5. Boning beef on a conveyor.

FIG.

FIG.

2. Beef dressing floor.

4. Sides of beef in the cooler.

FIG.

6. Loading beef into cars.

BEEF

the dressed beef. After weighing and grading, the sides are wrapped in a special cloth called a shroud. These shrouds are washed daily and are applied when warm. They have a twofold purpose. They not only bleach out and remove any blood stains but also improve the conformation by giving the fat a smooth surface. These cloths are pulled tight around the sides and held fast by small stainless steel pins. After shrouding, the dressed sides of beef are conveyed to the cooler for chilling. The quicker the carcass is dressed and placed in the cooler, the less opportunity there is for the development of bacteria. The fundamentals of preserving fresh meat involve sanitation, low temperature, and the rapid transfer of the warm carcass to the cooler. The faster the carcass can be brought down to a temperature of 40°, the better are the possibilities of increasing the keeping time. Coolers are kept clean and sanitary and have a good circulation of air to remove the heat from the carcasses as quickly as possible. The coolers are refrigerated by means of ammonia coils. This system permits control of humidity and reduces the tendency of meat to become dry and turn dark. It is also found to be good practice to "kill" into coolers that are prepared for receiving hot carcasses only. If chilled carcasses were hanging in the same cooler, the fluctuations in temperature caused by the hot carcasses coming in would be detrimental and reduce their keeping time. Before any further processing can take place, it is considered good practice to keep carcasses in the cooler for at least 24 hours. Modern methods of fast chilling require this length of time to remove the internal body heat from the carcass. The internal temperature must be kept at 42° or less. Grading Beef After the carcasses have been chilled, the shroud cloths are removed. Every

33

carcass is then marked with the "Government Approved Establishment" stamp. Each packing plant has its own number on this stamp. This stamp protects the consumer by indicating that the meat has been slaughtered under the rigid rules and regulations of federal government inspection. The government grader examines every chilled carcass and selects those which belong to the three top brands, Red, Blue, and Standard. Thus, throughout the process, each carcass has been graded three times, first mentally by the buyer in the stockyards, next by the packer's grader who weighs and grades the hot carcass in the beefdressing department, and finally by the government and packer's graders after the carcasses have been chilled in the cooler. It is essential that the final grading of the carcass be within certain specifications laid down by the government, and the consumer is thus further protected by the government grader's stamp, which is placed on all beef and cuts falling in the three top brands of beef. After the carcasses have been graded, they are moved on for further processing according to the grade. Some carcasses, for instance, are cut into the various wholesale cuts for shipment to retailers. These wholesale cuts permit the retailer to purchase the type of cut he can sell in the numbers he requires. Thus beef processing in many ways represents the manufacturing assembly line in reverse. It could be contrasted with the automobile industry, which starts with parts and ends with completed cars. Beef processing starts with livestock, and ends with fresh beef, other meat products, and by-products. Beef By-products The modern era of the meatpacking industry began sixty years ago with the establishment of large-scale plants able to handle all livestock offered and

BY PRODUCTS CASINGS

I

......":6~'~=

GLANDS

FIG. 7. F1ow process chart: principal operations (multi-storey construction).

BEEF

CUTTING

35

BEEF MECHANICAL

CONVEYOR CHAIN

7

HOISTING ~ A_ __ STOCK

BLEEDING AREA

CHANGEOVER

Gov'T INSPECTOR

HOLDING------~

PENS

!LEG REMOVAL AREAS FRONT & HIND LEGS

MARSHALL! NG AREA

(HEAD)

r---,

~c~o rT~~; r--,

REMOVAL OF HIDE

REMOVAL OF HIDEI

FROM UNDER PORTION

n

Rn.fo~;;;;1GI F~~, I

HIDE PULLER

l'..ret11

AITCH BONE

IHIDE

FP.OM

WfA5ANO

MECHANICAL

I cuyeR

BAOSKET'-.._/ L_J

I

PUSHER-SAWING.__._____;

I

I

BACKING

REMOVAL, GRADING & WEIGHING

OF HIDE

E.VISCERATING TABI.E

( 80movin~ table)

HAN'ol~o~~:::~==:::!:~

SPLITTIINGII ~

LOIN

SAWING

_;:::::::t~===~

5CRl8LJIN'-G~-::"::.._~-;-~";._';_';,._=_;

REMOVAL OF GOV'T KIONEV FAT =MEF===;INSPEC~ WASHING BEEF WEIGHING & \ GRADING ~ •

=>

::=====::::::: _J

L

ICOOC,R

SHROUDING

CONVEVEOTO

Fie. 8. Beef dressing floor layout, Can Pak System.

to · distribute meat products on a national scale. At that time the main emphasis was placed on the primary products, and by-products were developed haphazardly. There grew up around the large packing plants a number of small firms which bought the unfinished by-products and pro-

cessed them into salable products. For example, refineries took the lard, soap factories bought the tallow, fertilizer plants carted off the tankage and blood for the manufacture of mixed fertilizer. Gradually the production of these byproducts was taken over by the meatpacking 6nns, and more fully integrated

36

:MANUFACTURING PROCESSES IN CANADA

processes were developed. The application of chemistry in recent years has made improvements and development of new by-products possible. Hides. Hides were the first useful byproduct of the meatpacking industry. They are also the most valuable, and represent about 10 per cent of the dressed carcass weight. In order to preserve them until they are required by the tanner for making leather, they are piled into large rectangular packs interlayered with salt. After 30 days they may be shipped safely but should not be kept over 60°F for more than a few weeks, or some spoilage may occur. More recently some packers have cured hides in saturated brine. This process takes only 14 hours. The saving in time is partially offset by higher cost for equipment. Hides are sold by the pound, and graded as steers, cows, and bulls. Branded hides ( branded by the rancher, with a hot iron for identification) are discounted, since part of the leather is damaged. Hides with knife cuts are called No. 2 and are also discounted. Hides from small packers, which generally have not had a good reputation for quality, sell at a lower price than those from large packers. Country hides, taken off by farmers and other small killers, sell at a very low price as they are usually badly damaged and poorly cured. The buyer is represented by a broker who examines the hides as they are removed from the pack and bundled for shipment. Rendered fat. In dressing beef, considerable fat is recovered from the abdominal cavity. On very fat cattle, some fat may be trimmed off the exterior. These edible fats are rendered by various methods. The best grades of fat, when rendered at about 145°F, produce oleo stock. This delicately flavoured product is in demand by fish fryers. It may be chilled to let the

harder portions grain out, and then pressed in cloth bags, to separate the softer oleo oil from the hard oleo stearine. The oleo oil is an important ingredient in the very best fancy biscuits. The stearine is used in some shortenings. Other edible fats and bones are rendered in steam pressure tanks or dry rendering cookers at temperatures of 230° or higher, producing edible tallow used mostly in shortening. Inedible tallow is produced from visceral materials, carcasses, or parts condemned by the government inspectors, and any animals dead on arrival. They are crushed, and rendered in large agitated steam-jacketed kettles, at a temperature of 240° or higher destroying any diseased organisms. The cooked material is put into a press which squeezes out the inedible tallow and leaves, as a residue, the tankage. Inedible tallow is used largely in soap and animal feeds. The tankage, sometimes called meat scraps, is used as animal feed. Casings. Parts of the intestines are manufactured into casings used in the manufacture of sausage. The process consists of separating the long runners from the membrane and fat which hold them in place, then in specialized machines removing the contents and the mucous lining. They are graded according to diameter and quality, and put up in bundles of standard length. Salt is used for preservation. A large percentage of beef casings are exported. In recent years, artificial casings have cut heavily into the market for beef casings, with the result that many packers do not save casings at all. Glands. Pharmaceutical by-products of the meatpacking industry are vitally related to the physical and mental welfare of people everywhere. Their production is a comparatively recent development and has come about as a direct result of scientific research car-

BEEF

ried on by medical centres and by the large meatpackers. Research has proven that glands ( especially ductless glands) serve an important function in the human body. Similar glands found in animals have been found to have great value in medical preparations. Some of the most important of these are: pituitary used during surgery to prevent shock; thyroid used for thyroid deficiencies; pancreas used for the preparation of insulin; and parathyroid used in the treatment of paralysis. One of the most recent developments is the recovery of gall for the production of cortisone. The sawing of glands must be carried out quickly since deterioration occurs rapidly when the animal dies. Dry ice is used as a fast-freezing method minimizing decomposition and the growth of bacteria. Blood. Roughly 7 per cent of the dres¥'d carcass weight is recovered as blood. Part of this, collected in a sanitary manner, is used for blood sausage and other sausage products. The bulk of it, however, is dried for use as animal feed. The drier is a steam-jacketed kettle having an agitator. Some packers produce a specially dried blood which is used in the manufacture of plywood glue. The drying process in this case consists of atomizing the liquid blood and drying it as it falls through a current of warm air. Bones, hoofs, and horns. Some bones from beef-boning operations are made by a steam-pressure rendering process into steamed bone meal which is used as a source of phosphate for fertilizer. A highly purified but otherwise similar product is edible bone flour used for its calcium content as a diet supplement. Shin bones are cooked, cleaned, and dried for use by button manufacturers. Hoofs and horns are generally dried and ground for use as a slow-acting fertilizer.

37

Shipping Refrigeration has made it possible for meatpackers to distribute fresh meats to all domestic markets. The most common method of shipping beef is by refrigerated railway car. An important part of the packer's daily operations is the production of ice in sufficient quantities to refrigerate these cars. It may well be that mechanical refrigeration, which permits more uniform control of temperature, will soon replace this cumbersome method. Considerable success has been experienced in mechanically refrigerating motor transports, which have come into common use within the last few years. Location of Plants In order to minimize transportation costs and because of the perishable nature of meat products, processing plants have always been located at the edge of the great population centres. In the United States, an opposite trend has developed. The use of refrigerated cars has enabled the industry to overcome the handicap of geographical location. As only 50 to 60 per cent of a steer is beef, transportation costs are actually reduced when the meatpacking plant is located near the grazing and fattening areas. From the first concentration of slaughtering and meatpacking at Cincinatti, the industry has been migrating west to the agricultural interior. It is significant that the five leading United States meatpacking centres, Chicago, Kansas City, Omaha, St. Louis, and St. Paul, are all within the western grazing area. There are several other factors in addition to the proximity of the plant to the market, or the source of supply, which may influence the final decision on location. Transportation facilities must be adequate to ensure a regular supply of livestock and packaging materials. Refrigerator cars must be available in sufficient quantity to handle

38

MANUFAcruRING PROCESSES IN CANADA

the daily shipping requirements. Trucking has grown in importance, not only for deliveries of livestock but also for shipments of canned meats and other products; indeed, the increased use of refrigerated trucks and transports for long-distance hauling of fresh meat products is one of the most significant recent developments in this field. The

adequacy of these facilities is therefore a serious consideration. Other matters governing location of plants are the availability of a large labour force, cold storage plants of sufficient capacity to accommodate the plant's storage programme from one season to the next, and adequate supplies of water, electricity, and fuel.

Brewing* BY R. R. SERVICE o'JCEEFE BREWING COMPANY LIMITED

SINCE the brewing industry in Canada is closely controlled by government regulations, it is relatively easy to obtain accurate information about almost all phases of plant operations from published statistics. In the period from 1917 to 1956, production of beer, ale, stout, and porter increased almost eightfoldfrom approximately 27 million to 215 million gallons. During this time, the gross value of products increased steadily until the industry was ranked thirty-fourth when compared with other leading industries in Canada. This listing, moreover, is somewhat artificial since it is based on selling value of factory shipments, excluding duties and taxes which form a major part of the cost to consumers of malt beverages. If these levies were taken into account, the brewing industry would rise to approximately thirteenth position in the Canadian economy. Growth in production brought with it a corresponding increase in use of the principal ingredients of beer-malt and hops. As much as 20 per cent of the total amount of malt used by the industry in the late twenties was imported. Both plant research workers and business leaders realized that this could be a potential weakness. As a result new types of barley suitable for malting were developed and tested. 0 The author is indebted to T. G. Ferguson for permission to use certain photographs and drawings in this paper, and to H. L. Bayley of O'Keefe Brewing Company Limited for reading and checking the manuscript.

Farmers were encouraged to grow these grades of barley by the payment of special premiums, with the result that only 26,040 pounds of barley malt were imported into Canada in the seven years from 1950 to 1956 inclusive. Up to the present time, however, it has not been possible to increase similarly the domestic production of hops. Hops require special growing conditions of moderate temperature and high humidity which are found in Canada only in certain areas of British Columbia. This fact, combined with the need to use several varieties of hops to obtain a fine blended flavour in beer, has meant that about half of all hops used have been imported from Europe or the United States. Exports and imports of the finished product do not represent a major part of total sales. In 1956 imports equalled only about one-tenth of one per cent of Canadian production and exports about rn per cent. It is interesting to note, however, that even though exports represented such a small proportion of total sales, their value was 162 per cent greater than that of hops imported. In the past thirty years, the number of employees in the brewing industry has doubled while production increased almost fivefold in a slightly smaller number of plants-ample evidence of major improvements in productivity. Total salaries and wages also increased about six and one-half times during this period.

40

MANUFACTURING PROCESSES IN CANADA

History of Brewing Archaeologists have established beyond doubt that a form of barley beer was brewed in large earthen vessels ahnost six thousand years ago. Beer was mentioned in the Egyptian Book of the Dead which is stated to be about five thousand years old, and according to the extract of the Mirror of Chinese History, beer was known to the Chinese in the twenty-third century B.C. Herodotus attributed the invention of brewing to Iris and reported that early Egyptians drank a liquor fermented from barley which they called Zythos. Earliest exact evidence of a brewhouse dates back to about 2000 B.C. Excavations made at Thebes in 1919-20 by the Metropolitan Museum of Art unearthed a small model brewery from the tomb of Meket-R,e. As might be expected, earthen vessels with wooden paddles for stirring formed the major pieces of equipment. Two significant developments took place during the early history of brewing. Up to the seventh century, brewing was a process which could be carried on only during the winter months. The keeping qualities of the product were poor, too, so that beer could not be stored for use during warm weather when it was most needed. By the seventh century, however, a different type of brew called '1ager" had been developed, and it was found that this could be brewed in spring and held in cool mountain caves for summer consumption. The ninth century saw a second major change-the addition of hops to beer. This addition improved the keeping qualities of a brew and enhanced the aroma of the finished product. From this time on there was little change in brewing until about 1876, when Louis Pasteur proved that yeast caused beer to ferment. Before his time, many brewers believed that the difference between good and bad brews was

in the type of spirits which looked over the process. After he had pointed the way, however, the laboratory began to replace the spooks, and today the brewing industry makes valuable use of techniques and practices which have been developed through research. The development of bottling as a practical procedure gives us a good example of the value of Pasteur's work. Beer was first bottled experimentally in 1561, but it was not until the acceptance of the pasteurization process that beer could be bottled on a large scale with definite assurance that it would retain its flavour and sparkle for even a few short months before consumption. And so the stage was set for the brewing industry to expand and keep pace with the industrial growth started by the Industrial Revolution. The superstitions and myths which shrouded the early history of the industry were about to be dispelled by the onslaught of a small army of agronomists, bacteriologists, physiologists, doctors of medicine and hygiene, chemists, and engineers.

Types of Beer There are many types of beer with different characteristics and flavour, body and colour. For our purposes, we shall consider only three types, ale, lager, and stout, since they represent the main classifications of beers now sold in Canada. Although the origin of the word "beer" is doubtful, it is thought in some quarters to be derived from the Latin word bibere ( to drink). The word beer is also a generic term which can mean ale or lager depending on local custom. For example, at the present time in Quebec and in the central part of Ontario a customer ordering "beer" would probably be served ale, whereas in the United States he would be served lager. Ale is made from barley malt, usually without adjuncts, and has a pronounced hop aroma and flavour. Fermentation

41

BREWING

CHART I SUMMARY OF THE BREWING PROCESS

Malt received and stored at brewery

I I

Malt husks cracked in mill Weifhed Malt mixed with water and heated (mashed to release enzymes)

I

.

\Vort separated from grain (in tauter tub)

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Wort boiled with hops (spent grain sold for cattle feed)

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\Vort separated from hops (in hop jack)

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Wort to hot wort tank (hops used for farmland improvement)

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Wort cooled by city water and brine (heated city water used in process)

I

\Vort to fermenters where beer and carbon dioxide are produced (aged in glass lined tanks for 2 to 3 months; surplus yeast dried for human and animal use; carbon dioxide collected and stored and later returned to beer)

I

Filtered and carbonated

I

Cold storage 10 to 14 days

I I

Filtered and carbonated

I

Keg-racking tanks

I I Warehouse I Kegs

Licensed authorities

I I Bottles I Warehouse I Licensed authorities I Bottling tanks

Home consumers

is carried out with a top fermentation yeast which is primarily responsible for its distinctive character. Lager is brewed from barley malt usually with the addition of adjuncts which help produce a lighter-bodied product. Fermentation is carried out with a bottom fermentation yeast at lower temperatures than ale with a resultant change in flavour. Stout is a top fermentation beer, similar to ale, but heavier and darker.

It has a strong malt flavour and a sweet taste, and is produced with a caramelled or highly roasted malt. Principal Ingredients Malt, hops, and water are the main ingredients of beer, although small quantities of other cereal grains may be added if desired. These latter additions are grouped into a general classification called "adjuncts." Malt. The production of malt from

42

MANUFACTURING PROCESSES IN CANADA

.barley is .. complete industrial process In the malting process, the kernels .separate from brewing. Indeed, few of barley, which have been stored after Canadian or American breweries have harvesting at least one to two months, are steeped in water until the grain their own malting plants. Barley is the most suitable grain for holds approximately 45 per cent moisbrewing purposes. It is one of the ture, and allowed to grow under ideal hardiest of known cereals, and is easily conditions of temperature and humidity malted for use in brewing. The solubles in either a large rotating drum or on extracted from barley malt are of a more a specially designed malting floor. This desirable character and their extraction growth shows as small rootlets extendmore complete than those of other ing from a white tip near the embryo grains. In addition, barley malt is easily of the kernel and a shoot or acrospire handled in the brewing process and growing along the seed under the husk. produces sufficient surplus enzymes for When this acrospire becomes threeconversion of the starch in all adjuncts quarters the length of the kernel all used. growth is stopped by kilning the malt Quality control in brewing actually in two stages. The moisture content is begins in the selection of the type of reduced in the first stage to a level barley chosen for malting. In Canada, between 8 and 14 per cent of the dry the recognized standard is Ontario malt weight, and in the second to beAgricultural College No. 21 and no tween 3¾ and 4 per cent. The malt is barley is accepted by the maltster un- then ready for cleaning, storing, blendless it consists of 90 per cent O.A.C. 21 ing, and shipping. Hops. The hops used in a brewery or a barley with equivalent malting characteristics. High standards are are really dried clusters of blossoms maintained by the payment of premium from the female hop plant. They give rates for malting barley and through beer its characteristic mildly bitter control of the seed sown. The result flavour and pleasant aroma. After dryhas been the development of a new ing, hops are compressed slightly and variety, "Montcalm," which is actually wrapped in burlap for storage in resuperior in many respects to the recog- frigerated rooms held at a temperature nized standard and is now widely used of 32°F with a relative humidity of less ' than 75 per cent. Air currents are in Canada. The purpose of malting is to develop avoided in these rooms, all cooling the enzymes in the kernels of grain. being accomplished by fin coils susBarley kernels are composed primarily pended from walls or ceilings. Hop of starch and high molecular weight bales are set up on wooden battens so proteins, which, as such, are indigestible that convection currents can carry cool to a young plant, but which are con- air all round each bale. Under these verted by enzymes set free in the ker- conditions, hops can be stored for 18 nels of grain when growth is started. to 30 months without deterioration, but The maltster, therefore, allows the grain after that time, their value for brewing to germinate and halts further growth purposes declines. Water. Beer contains about 90 per in his kilns after the enzymes are thoroughly distributed through the body cent water, and approximately ten to of the kernel. They are then in a posi- fifteen barrels of water are used for tion to convert starch to sugars and cleaning, cooling, and steam generation dextrins, and high molecular wei,:?;ht for each barrel of beer produced. Thus insoluble proteins to low molecular a good deal of attention has been paid weig;ht soluble ones, when the malt is to the characteristics and chemical analysis of water. Originally, differences masned in the brewing process.

BREWING

in water compositions helped to account for variations in the flavour of brews turned out in such famous brewing centres as Burton-on-Trent, Dublin, and Munich. It is now realized that no one water is suitable for all types of beer. Presentday brewers, therefore, are prepared to convert city tap water found in most major brewing centres to water with characteristics favourable to the production of any specific type of brew. This may involve reducing, increasing, or changing the type of water hardness, removing certain substances such as phenols which might impart objectionable flavours to beer even though they are unnoticed in drinking water, or changing the concentration of the metallic or hydrogen ions. All this, of course, cannot be done without incurring costs, and it follows therefore that water should be selected which lends itself most readily to the type of beer produced. Adjuncts. The use of adjuncts in a brew yields three results: ( 1) a paler colour, ( 2) a greater stability especially in bottled ale or beer, and ( 3) less satiating effect. Materials normally used as adjuncts are com, rice, wheat, barley, and soya beans, to mention a few. These products are used in a multitude of forms varying from grits, meal, and flakes to syrup-for example, corn syrup. Brewing Operations in the brewhouse are designed to process and extract brewing materials and to produce hot wort boiled with hops for subsequent cooling to the proper temperature for fermentation. Figure 1 outlines in pictorial form the sequence of events in the brewing cycle. Incoming whole mait ( the product of the malt plant) is received by truck or freight car at a brewery and immediately placed in storage in large bins. When required for brewing, it is with-

43

drawn from the bottom of these storage bins and conveyed through a weighing device-either scale hopper or automatic weigh scale-to a revolving cylindrical screen called a cleaning reel which is located above the malt mill and usually connected directly to it. Clean malt then drops into the malt mill where it passes through three sets of rollers which have been adjusted to split the husk surrounding each malt kernel without unduly crushing or breaking the grain body. This is done so that water will be able to reach the malt kernels directly without having to soak through the protecting husk. In the malt mill, the hard steely ends are separated from the ground malt and by-passed to a scale hopper where they are combined with cereals, that is, adjuncts, for further processing. The ground malt is diverted directly to a scale hopper for accurate batch weighing before the mashing operation. Mashing produces complex organic chemical changes in the malt. Briefly, it is aimed at making the dry ground malt soluble. Water at a temperature of 115 to 120° F and ground malt are introduced simultaneously through a fore masher into the mash mixer so that the malt is thoroughly wet. The mixture of malt and water is then heated for various periods of time at suitable temperatures so that the enzymes have an opportunity to convert the starches and proteins to usable, soluble forms . The resulting solution is called "wort." The above description applies to an all-malt brew, but malt and adjunct brews are handled in almost the same manner. Cereals and malt are boiled in the cereal hopper and then pumped over to the mash mixer for mashing with malt in a similar manner to allmalt brews. Various amounts of adjunct are used by different brewers. Ii:,. Canada, 20 to 30 per cent adjuncts may be used in lager brews; the percentage of adjunct is much higher in the United States.

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6. Elevation of an open hearth: (a) metal; ( b) slag; ( c) burner; ( d) slag pocket; ( e) air uptake or waste gas downtake; ( f) regenerative chambers; ( g) hearth; ( h) roof; ( i) air port.

IRON AND STEEL

(a)

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Fie. 7. Furnace roofs : (a) suspended arch roof; ( b) compressed arch roof.

hot gases are preheating the other set. At given intervals, usually every 15 to 20 minutes, the air How is reversed: the cold air blast is changed from the spent checkers to the freshly heated checker chamber and the spent checkers absorb heat from the exit gases. The reversing control on the air blast may be manual or semi-automatic. The life of the open hearth furnace is primarily dictated by the life of its refractories. These are subject to reaction with iron oxide and with the slag, and to softening or melting under the high temperatures of the hearth. They are also subject to spalling or mechanical breakage resulting from carelessness during charging. The first acid open hearth furnaces were lined throughout with silica bricks. These are inexpensive and are capable of withstanding the high temperatures

129

involved. The first basic open hearth furnaces were also built of silica brick with grain magnesite rammed on top, since suitable basic bricks were not available. When basic bricks made of magnesite were finally introduced, they were still unsatisfactory as they had poor thermal resistance and low physical strength. However, in recent years a satisfactory basic brick has been designed, made of chrome ore and magnesite. Although the hearths of many furnaces are now being lined with a basic brick, silica brick is still employed to a large extent for walls and roofs. Its desirability for roofs is based primarily on its combination of light weight and high compressive strength. However, the design of the suspended arch roof has enhanced the possibility of employing the weaker basic brick in roof construction. Other refractories such as dolomite and chrome ore are used for specific applications. Dolomite is popular as a repair material for the sides and banks of the furnace, and chrome ore, because of its chemical neutrality, is used to separate courses of silica and magnesia bricks; it has the disadvantage, however, that it is readily attacked by iron oxide. Over a period of time the lining of the open hearth furnace develops cracks and holes, which are filled between heats when the furnace is empty, usually by throwing shovelsful of sand or dolomite evenly over the sudace of the hearth or walls where the cracks or holes have occurred. In modem plants a machine has been designed which will mechanically spray the filler material on the furnace lining. This machine has been found to be especially useful in repairing the hardto-reach back wall. Fuels. Up to the early 1900's producer gas was almost exclusively employed as an open hearth fuel, both in Europe and in North America. Its popu-

130

MANUFACTURING PROCESSES IN CANADA

larity probably stemmed from the fact that it could be produced easily and economically from coal. Later, as the by-product coke came into prominence, coke ·oven gas and coal tar became popular fuels. At present, coke oven gas and coal tar are still widely used, but have been supplanted to some extent by fuel oil. Fuel oil and tar are flexible in use and have a luminous flame which radiates heat more readily than any of the other fuels mentioned. Pulverized coal, which gives a concentrated, highly luminous flame, has been tried, but was found to require excessive air for combustion; moreover, the ash particles formed are carried to the regenerators where they are deposited, increasing the corrosion of the brickwork and contributing to the rapid filling of the slag pockets. Operation. The purpose of the open hearth is to produce a steel of specific composition from a charge of scrap iron, pig iron, sinter, limestone, and hot metal. This is accomplished by the complete fusion of all the ingredients except the hot metal and the formation of a suitable slag that will remove undesirable elements such as phosphorus, sulphur, silicon, manganese, and carbon. Once these elements have been removed the heat is tapped, and made up to the final composition by ladle additions. The charges are usually classified according to the percentage of hot metal employed in combination with scrap iron, pig iron, sinter, and limestone. The most widely used is known as the 50--50 charge in which equal amounts of scrap iron and hot metal are employed. In the stock yard the raw materials, scrap iron, pig iron, ore or sinter, and limestone are weighed and placed in "charging boxes" and transferred to the charging floor of the open hearth by means of "buggies." There they are picked up by a mechanical device called a "charging machine," pushed through the furnace door, and

dumped onto the hearth. Light scrap is charged first, limestone second, and the heavy scrap with ore and/ or sinter last. Placing the light scrap on the bottom protects the hearth from damage by the heavier scrap; the limestone is also prevented from sticking to the bottom of the furnace and retarding the initial rate of slag formation. The hot metal is added after the rest of the charge has partially melted and slightly oxidized. The melting period is considered to begin when the scrap iron has been charged into the furnace and to end when the bath is completely molten. During the melting period the elements iron, manganese, silicon, etc., are oxidized. After the addition of the hot metal its silicon and phosphorus are oxidized, and enough heat is liberated to help bring the entire contents of the furnace to a state of complete fusion. The oxides, which have a lower specific gravity than molten iron, rise to the surface; at the same time limestone ( CaCO3 ), which has been calcined by the hot metal to CaO, combines with them to form stable compounds. This combination of oxides is called a slag. The first elements to be oxidized are silicon and manganese which enter the slag as MnO and SiO 2 • If sufficient lime has been added the phosphorus will be oxidized to P 2 O 5 and will combine in the slag as calcic phosphate. As the temperature of the hearth and limestone rises the calcination of the limestone becomes vigorous, resulting in what is known as a "lime boil." During the lime boil the bubbles of CO2 rising to the surface serve the purpose of agitating the bath acting as an oxidizing agent for the metal and speeding up the transfer of heat. The fluxing action in the furnace may be assisted by the addition of fluorspar ( CaF2 ) , which tends to make the slag more fluid. The slag produced in the open hearth performs one of the most important

IRON AND STEEL

functions in steelmaking. The ability of the slag to form various stable complexes with the oxides of the impurities and to hold them in solution, preventing them from reverting to the metal, may be considered as the basis of open hearth refining. At the end of the melting period it is desirable to obtain a carbon content of the bath of approximately .5 per cent above the specified carbon for the steel as this permits a more efficient "shaping up" in the refining period. The refining period, which may be called "working the heat" or "shaping the steel" includes the final removal of phosphorus and sulphur to the required levels and the reduction of carbon to a level which will permit proper finishing of the heat. The slag is brought to the proper condition for the finishing period and the required temperature for tapping is attained. During this period various tests must be run to determine the composition and viscosity of the slag, and the composition of the bath, so that the melter can make any additions that may be required. The final removal of sulphur and phosphorus is obtained by proper adjustment of the slag composition to a relatively high degree of basicity. Carbon is removed by the addition of iron ore, sinter, or mill scale which reacts with the carbon forming CO. As the CO boils violently to the surface it flushes out the non-metallic particles such as silica and iron oxide, bringing the steel to a state where its temperature can readily be raised to the temperature suitable for tapping. The progress of the boil is always kept under full control; samples of metal are drawn periodically to check the rate of "carbon drop," that is, the rate at which the carbon is being oxidized from the metal. The refining period blends into the finishing period, which is considered to begin when the action of the last addition of ore subsides, and to end when

131

the ingots have been teemed. Depending on the particular plant's practice, at the end of the refining period the bath may be "blocked," in order to slow down or to stop the carbon drop so that final adjustments may be made. Blocking is accomplished by the addition of a deoxidizer such as spiegeleisen, ferro-manganese, or silico-manganese which will reduce the oxygen content of the molten metal below that established by the carbon-oxygen equilibrium after the boil. After blocking, the bath will remain dormant from 20 to 30 minutes depending on the amount of material added. However, after the silicon or manganese has been fully oxidized the bath may "open up," that is, the carbon-oxygen reaction start again. The degree of deoxidation employed will depend on the type of ingot structure desired : killed, semi-killed, or rimmed. These terms refer to a series of ingot structures that can be obtained by controlling the amount of gas evolution during solidification. This is accomplished by the addition of a suitable deoxidizer, such as aluminum or silicon, which is made to the ladle or the mould or both. When the bath has finally been shaped and blocked the heat is tapped. For best tapping conditions the temperature of the bath should be at least 72°F (40°C) above the freezing point of the alloy. The tap hole may be opened with a hammer and crowbar, oxygen lancing being used if necessary. In recent years what is known as a "shaped charge" has been developed. The shaped charge consists of a small charge of explosive in a specially designed container which effectively causes the blast to be directed in a specific direction. This method provides a good, clean, fast tap and is considered to be much safer as the charge can be detonated from a distance. Additions, based on the final analysis of the bath, of such elements as car-

132

MANUFAC'l1JRING PROCESSES IN CANADA

hon, manganese, and chromium required to make up the final composition are made to the ladle as the heat is being tapped. The ladle is then transferred to the pouring deck where the hot metal is teemed into the ingots. ELECTRIC REFINING

The principle of heating by electricity was discovered in 1800, but it was not until 1879 that Siemens first employed the electric arc as a source of heat in steelmaking. Two of the first men to design practical furnaces were P. L. V. Heroult of France, who in 1888 employed the arc furnace in the manufacture of aluminum and calcium carbide, and Stassano of Italy, who designed an electric furnace to refine liquid pig iron. The first electric furnace to be used in North America was installed in 1905 at Sault Ste. Marie, Ontario, and was closely followed by one at the Halcomb Steel Company, Syracuse, New York. There are two major types of arc furnace, the direct arc and the indirect arc. The direct arc which has proven most successful in steelmaking is embodied in the Heroult type furnace ( Fig. BA). The essential feature of the direct arc furnace is that the carbon electrodes arc with the metal, the bath being heated by radiation and contact with the arc. In the indirect arc furnace, illustrated by the Stassano furnace ( Fig. BB), the arc is passed between two electrodes, the bath being heated entirely by radiation. The Heroult type of furnace used extensively in North America consists of a circular hearth into which are fed three electrodes from the roof. Because of facilities of transformation and transmission, alternating current is employed. Low voltage and high current are required. All of the power supplied to the furnace is not available for heatting because of electrical phenomena and the variation in the power factor which is the ratio of the total power

(c;)

Fm. 8A. Direct arc type furnace ( Heroult type) : (a) electrodes; ( b) metal bath; ( c) hearth. Fm. 8B. Indirect arc type furnace ( Stassano type): (a) electrodes; ( b) metal bath; ( c) hearth.

that could be delivered to the electrodes to the actual power that is delivered at any one instant. apparent watts power f ac tor= actual volts X amps The closer the power factor can be kept to unity by various adjustments in the operation of the electric furnace, the more efficient is the furnace. Electric refining processes, like the open hearth processes, are of two types, basic and acid. The principles of refining are similar to the open hearth, the only differences being in design and operation of the furnace. Differences in operation. Electric furnaces employ an all-solid charge rather than a solid-liquid charge. The open hearth, which is an oxidizing process, can eliminate the elements silicon and carbon readily, whereas in the electric furnace, which does not provide as strong an oxidizing atmosphere, it is difficult to remove large quantities of these elements without excessive ore additions.

IRON AND STEEL

In the open hearth the heat is mainly obtained by radiation from a flame produced by the oxidation of a particular fuel such as oil or gas. In the direct arc electric furnace all the heat is produced by an arc centred between the electrodes and the bath. The electric furnace may be either charged at the side or the top. If it is top-charged the roof is constructed so as to permit it to swing to one side, the material being dropped into the furnace from a specially designed bucket which has a false bottom. In the side-charged furnace charging is accomplished in the same manner as in the open hearth. Advantages. (a) Higher temperatures can be produced as the electric arc provides almost unlimited possibilities for the generation of heat. ( b) The electric furnace is especially adaptable to making alloy steel as alloy additions can be made directly to the bath. The result is a steel of a more uniform composition as bath additions have sufficient time for thorough mixing and melting. ( c) The regulation of heat is more precise than in the open hearth, and thermal efficiency is much higher enabling steel to be made in much shorter times, the limiting factor being the time required for completion of furnace reactions. Disadvantages. (a) Electrical power at present is more expensive than the various open hearth fuels. ( b) The size of the electric furnace is limited because the heating of the bath is dependent on the ability of the metal to conduct the heat to the other parts of the furnace. Thus the electric furnace definitely has an application in the production of alloy steels; however, it appears that, at least for some time, it will not compete successfully with the open hearth furnace. TEEMING

Following the refining in the open hearth and the tapping of the heat, the hot metal is teemed or poured from the

133

ladle into iron moulds and permitted to solidify; the resultant casting is called an "ingot." After the ingot has completely solidified it is transferred to the "stripper" where the mould is stripped from the ingot. From the stripper the ingot is transferred to the bloom mill where it is preheated in a soaking pit furnace until a uniform temperature has been established throughout. This uniformity of temperature is vital to the successful rolling of the preheated ingot in the bloom mill where slabs, blooms, and billets are made. Ladl,e construction. The ladle is usually of circular cross-section, tapering inwards from top to bottom, the taper being provided to facilitate the removal of "skull" which occasionally forms on the sides and bottom of the ladle. The ladle shell is of steel sheet and is lined with a fireclay brick. Fireclay brick expands at high temperatures providing tight joints which prevent seepage of the hot metal between the bricks thereby reducing damage to the lining. Pouring is accomplished through a fireclay nozzle located on the bottom of the ladle. Pouring. The rate of flow of the molten stream, and the rate of rise of the molten steel in the mould, are the most important factors in teeming when effect on ingot sudace is considered. The optimum rate is governed by many factors such as grade of steel, size and design of moulds, temperature and fluidity of molten steel, and ferrostatic head, that is, height of metal in the ladle. At present three general methods of teeming are employed: (a) top pouring; ( b) basket pouring; and ( c) bottom pouring. Top pouring ( Fig. 9a) is a relatively inexpensive method, a fact which probably accounts for its popularity, as approximately 85 per cent of all steel made today is top poured. The use of pouring baskets ( Fig. 9b), pouring boxes, or tun dishes allows

134

MANUFACTURING PROCESSES IN CANADA

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Fm. 9. Pouring methods: (a) top pouring; ( b) basket pouring; ( c) bottom pouring.

more than one ingot to be poured from an intermediate pouring vessel. The metal is usually poured through a large nozzle into a basket and from the basket through two or more smaller nozzles into the moulds. By this method a constant ferrostatic head may be obtained affording a steady rate of flow which contributes to better surface formation and provides a greater opportunity for the separation of non-metallic inclusions from the solidifying ingot. The bottom pouring assembly as illustrated by Figure 9c consists of a pouring funnel, fountain, runner, and ingot mould. By pouring into the fountain or "downgate" the metal is made to enter the mould through the bottom. In this way the rate of flow of the metal will be reasonably constant, and the metal will rise steadily in the mould with very little agitation as the main force of the stream is absorbed in the downgate and runner. Another advantage in this method is that anywhere from two to eight moulds may be poured simultaneously by a suitable arrangement of runners from the downgate. The number of moulds employed may also serve as a variable in establishing the rate of flow of the metal into the individual

moulds. This method is usually employed where a very good surface is desired. Formation of pipe. As the liquid metal cools and solidification proceeds, three major contractions in volume occur, the first during cooling in the molten state, the second during solidification, and the third during cooling in the solid state. The :first two represent about a 5 per cent decrease in volume and result in the formation of a pipe because of the simultaneous solidification and contraction of the metal. Segregation. During solidification the majority of the atoms of the various elements are trapped in place, but some are pushed out in front of the advancing solid liquid interface. The result is that the last metal to solidify, that at the centre of the ingot, contains increased concentrations of various elements. Carbon, phosphorus, and sulphur will segregate in this manner, but manganese and silicon appear to be relatively unaffected. This phenomenon, which is present in all ingots, occasionally occurs to such a degree as to make the metal unsuitable for further processing.

135

IRON AND STEEL

Solidification and ingot structure. As previously indicated, there are three main types of ingot structure ( Fig. 10 ) , killed, semi-killed, and rimmed, which depend primarily upon their degree of deoxidation, that is the degree to which the evolution of gases from the liquid metal has been suppressed by means of a deoxidizer such as aluminum or siliconL In a killed steel all the gas evolution is suppressed by the presence of deoxidizing elements. Practically all the shrinkage as described above is confined to a large top cavity, the steel below the cavity being of sound structure. In a killed steel, chemical segregation is at a minimum. The amount of pipe in the main body may be reduced by the use of hot tops. The hot tops principally provide a reservoir of hot metal for the main body of the ingot to draw from during solidification. The hot tops greatly increase the yield from

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killed ingots, as they increase the amount of usable metal which is free from pipe. Gas evolution from a semi-killed ingot is usually not enough to cause any marked change in the process of crystallization, and semi-killed ingots are structurally similar to killed ingots. The gas evolution, however, does compensate for shrinkage and reduces the amount of pipe by forming a series of blow holes in the top of the ingot. Evolution may be increased materially through the use of less deoxidizer, resulting in rimmed steel. This structure is identified by a series of blow holes which are formed relativelv close to the ingot wall. During the formation of these blow holes the steel between the ingot surface and the blow holes is left relatively free of impurities such as carbon, manganese silicon, or slag inclusions. Ingot moulds. An ingot mould must

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136

MANUFAcruRING PROCESSES IN CANADA

be designed so that it will produce a sound ingot relatively free from shrinkage cavities, free from surface defects, and with the harmful segregation phenomena reduced to a minimum. These factors, of course, cannot be completely controlled, but may be influenced to some degree by the contour and shape of the mould. Stripper. After the hot metal has been teemed into the moulds and has solidified, the ingot is transferred to the stripper ( Fig. 11) where the mould is removed. The ingot is then transferred to the soaking pits in the bloom mill where it is preheated preparatory to being rolled. Soaking pits. Soaking pits are usually

of the recuperative type. The air and fuel are injected into the heating chamber through a shaft in the centre of the furnace. The spent gases are removed through ducts at the sides of the furnace and passed through the recuperator. The recuperative principle involves the continuous transfer of heat from the hot gases to the cold incoming air. This is accomplished by passing both the hot and cold gases through adjoining chambers ( separated by a single wall) simultaneously. In the soaking pits the ingots are usually heated to about 23~2500°F ( 1260°1371 °C); it is very important to subsequent rolling that the ingot be at a uniform temperature.

Fie. 11. Stripper.

moN AND STEEL

Steel Finishing METALLURGICAL PRINCIPLES

From the bloom mill on, the ingot is subjected to many physical treatments, such as hot rolling, cold rolling, and annealing. The science behind these operations is what is known as "physical metallurgy." Mechanical deformation. If a metal after being subjected to the stress of tension or compression returns to its original shape, it is said to have undergone an elastic deformation. When a metal, however, has been subjected to a stress and does not return to its original shape it is said to have undergone plastic deformation. The ability of steel to deform plastically is the property which permits its reduction by rolling. When a metal is deformed plastically it is said to have undergone mechanical deformation. Rolling. Rolling consists of deforming a piece of steel by passing it between two rolls ( Fig. 12), one set vertically above the other. A reduction in the thickness is effected by having the roll gap ( that is, the distance between the rolls ) smaller than the thickness of the steel. The rolls are power driven, and are made to rotate in such a direction

( bl

'\

Fie. 12. Effect of rolling on internal structure: (a) rolls; ( b) equiaxed structure; ( c) cold-worked structure ( note flattening and lengthening of grains).

137

as to draw the metal through as it is being reduced. In this way the metal is subjected to a compressive force and a forward rolling force simultaneously. This results in a marked elongation in the rolling direction and some increase in width. Assuming no increase in width or "lateral spread" the amount of "elongation," that is, the increase in length in the rolling direction, will be proportional to the "draft," that is, the percentage reduction in thickness. The lateral spread, though relatively small, cannot be overlooked as it is a function of the draft and the cross-sectional shape of the piece entering the rolls. In practice metals may be rolled cold or hot (approximately 2400°F (1316°C)). Cold and hot rolling affect the structure of the steel in different ways and both have a particular application in steel finishing. Cold rolling. Mechanical deformation by rolling forcibly changes the shape of the crystals in the steel ( Fig. 12 )' and, as the metal is reduced in thickness, the originally equiaxed grains are flattened and elongated. Also, when metals are mechanically deformed, they become harder. This "work hardening" results from the increased ability of the metal, after having been mechanically deformed, to resist further deformation. The resistance to mechanical deformation increases as the material is further cold reduced, with the result that the physical properties of the metal are changed. With an increase in percentage reduction, the hardness, the elastic limit, and the ultimate tensile strength will increase, and the ductility of the metal will decrease. Thus, the maximum percentage of cold reduction that can be achieved on any given type of steel depends upon: (a) the rate at which the metal will work-harden ( some alloys will take a greater percentage reduction than others before reaching a particular hardness) and ( b) the ability of the mill to withstand the increased load re-

138

MANUFACTURING PROCESSES IN CANADA

quired to reduce the work-hardened material. Recrystallization. When a coldworked metal is heated to what is known as its recrystallization temperature ( approximately 900°F ( 482 °C) for steel), tiny equiaxed crystals will nucleate and, if heating is continued, will grow at the expense of the surrounding distorted structure until a completely equiaxed structure has been formed

(b)

(a)

mately equivalent to doubling the time at the original temperature. Such variations in control allow some degree of control of the resultant physical properties to be achieved. This principle is embodied in the annealing process described later. Hot rolling. In hot rolling the material must be at a temperature above its recrystallization temperature. Thus, although the structure is as deformed as

(c)

(d)

Fie. 13. Recrystallization and grain growth: (a) cold-worked material; ( b) recrystallization, formation of small crystals in the cold-worked matrix; ( c) completely recrystallized material; ( d) grain growth ( original grains ( c) have become larger).

( Fig. 13). Further grain growth may be achieved by heating for a longer time at temperatures above the recrystallization temperature. Thus, by recrystallization and grain growth, the strong, hard, elongated structure produced by cold rolling4 may be transformed to an equiaxed structure restoring, to some degree, the original properties of the material such as softness and ductility. The recrystallization temperature is influenced by the percentage of cold reduction and the composition of the metal; grain growth is influenced by the maximum temperature and the time at maximum temperature. A rise of about 10 degrees in temperature is approxi-

=

4Percentage reduction W 1 - W 2 /W 1 , where W 1 is the original thickness and W 2 the thickness after cold reduction.

it is after cold rolling, it immediately recrystallizes. The recrystallization and subsequent softening of the metal permits large percentage reductions without the hardening effect inherent in the cold-rolling process. In steelmaking, this facilitates the rolling of large ingots down to slabs and the rolling of slabs down to plate and sheet. Construction of rolling mills. The rolling mill consists of a pair of rolls strong enough not to bend or break under load, and a framework or housing which will maintain the position of the rolls, not allowing them to spring apart as the metal passes between them. The maximum percentage reduction that a rolling mill can attain is governed by the maximum width to which the roll gap can be set and by the load that the rolls and housing can withstand with-

139

IRON AND STEEL

out failure. The passage of a piece of steel through the rolls in one direction is known as a "pass," and the amount of reduction effected during one pass is termed a "draught." Mills may be divided into two classes: reversing mills and non-reversing or continuous mills. Reversing mills, in which the steel is passed through the same set of rolls back and forth until the total reduction is accomplished, are employed mainly during the early stages of rolling, such as in the bloom mill, where the weight of the piece being rolled is considerable and where the material, if hot rolled, can maintain its temperature for long periods of time. Non-reversing mills are employed for hot strip rolling and cold rolling. The steel is passed through only in one direction, the total reduction being accomplished by a series of mills in tandem. In small plants where the tonnage produced does not merit a continuous mill, reversing hot strip and cold mills are used. Rolling mills may be designed for rolling flat products such as sheet and strip or they may be designed for rolling complicated shapes, such as rounds, squares, rails, and I-beams. Those rolling flat products are of four standard types classified according to the num-

(a)

( b)

her of rolls, that is, 2-high, 3-high, 4-high, and 6-high ( Fig. 14). The 2-high mill consists of two work rolls through which the strip is passed. The 3-high mill is similar to the 2-high in that during one pass only two rolls are being used. In continuous operation the material is reduced by employing both the upper and lower sets of rolls alternately, the steel being raised or lowered to the desired level by an elevating mechanism which raises or lowers the roll table. The advantage of the 3-high mill is that the rolls do not need to be stopped and reversed for the return pass, but may continue rotating in the same direction, thus saving time and power. The 4-high mill is a 2-high mill with 2 "back-up" rolls, the work rolls usually being small. The smaller the roll, the less is the area of steel in contact with the roll face, and the less the force required to squeeze the metal and reduce its thickness. However, thin rolls will be unavoidably weak and heavy backup rolls must be employed to provide support in the vertical direction. In the 6-high mill where the work rolls again are very small, two back-up rolls are employed to provide support in both the vertical and horizontal directions. Because of the size of the

(c)

(d)

Fm. 14. Rolling mills: (a) 2-high mill; ( b) 3-high mill; ( c) 4-high mill; ( d) 6-high mill.

140

MANUFACTUBING PROCESSES IN CANADA

work rolls the 4-high and 6-high mills are used only for the reduction of relatively thin material, in the order of one inch or less. These mills are widely employed in continuous hot strip rolling and in continuous cold rolling. · All unbacked rolls, such as those employed in the 2-high and 3-high mills, tend to "spring" as a piece of steel passes through them. This occurs more at the centre than at the outer edges and results in the sheet steel being thicker at the centre than at the edges. As the rolls warm up, thermal expansion will compensate for some of the effect, but the rolls should nevertheless be provided .with a positive camber, that is to say, the rolls should be larger in diameter at the centre than at the ends to reduce the spring effect. The extra diameter is usually about .01 to .1 inches. In the 4-high and 6-high mills little or no spring occurs. However, to offset the effects of thermal expansion a slight negative camber must be employed. Mills used in rolling complicated shapes, by their very nature, can only be 2-high. To roll a rail or section from a bloom requires considerable care and planning as the steel must be reduced from a relatively short square bloom into a piece some 30 to 60 feet long of intricate cross-section. The rolling of a typical section will be briefly outlined later. A mill equipped with grooved rolls is rated according to size by the distance between the roll centres; for example: 12-inch mill, 14-inch mill, and so on. Plate and sheet mills, which employ smooth rolls, are described according to the barrel length of the rolls. THE BLOOM MILL

The modem blooming mill ( Fig. 15) gets its name from the ancient word "bloma," meaning mass or lump. In the early smelting furnaces such as the Catalan forge, the white-hot mass of sponge iron that was removed from the

furnace was hammered into the form of a small bar or bloom. Similarly today, the ingot, which is the first solid form of steel, is reduced to smaller rectangular cross-sections in a bloom mill. Thus, the bloom mill provides the first physical treatment that the ingot receives. The ingots, having been uniformly heated in the soaking pits to approximately 2400°F (1316°C), are reduced to blooms, billets, or slabs in a 2-high electrically driven reversing mill, which has two heavy, grooved rolls, one directly above the other. The top and bottom rolls are alike and are so mounted that the grooves in one exactly coincide with the grooves of the other. The grooves vary in width and depth according to the size of the ingot and the size of the semifinished product to be turned out. The ingot is passed back and forth between the rolls and gradually reduced to the desired size. An ingot 19 X 23 inches in cross-section can be rolled down to a bloom 6 inches square in about sixteen passes and in less than 2 minutes. Obviously, all the rolling cannot be done on only two sides of the ingot, as this would result in a flat product with very little control over the width. Thus, from time to time during rolling, the steel must be turned in order to roll a11 four sides. The devices employed are called manipulators and serve to tum the ingot as ·well as move it sideways so that it will enter the proper grooves in the rolls. Products. A blooming mill can produce either slabs, blooms, or billets. Many blooming mills roll only blooms which are later delivered to billet mills for conversion into billets. The width of the product that can be rolled on blooming mills is somewhat limited so that a third type of mill called a slabbing mill is sometimes provided. There are no strict definitions of slabs, blooms or billets, but in ~eneral they are of the following specifications: A slab is usually of rectangular cross-

IRON AND STEEL

141

Fm. 15. Bloom mill.

section varying from 2 to 6 inches in thickness and from 24 to 60 inches in width. Slabs are produced for rolling into plate or strip. A bloom may have a square or rectangular cross-section. The square crosssection may vary from 6 X 6 inches to 20 X 20 inches. The main difference between blooms and slabs is one of cross-sectional shape. Blooms form the intermediate product in the rolling of structural shapes such as I-beams and rails. Occasionally, when a very good surface is required on billet stock, an ingot will be rolled into blooms, conditioned, and then re-rolled into billets.

A billet is essentially a small bloom of square cross-section, never larger than 5 X 5 inches. Billets form the intermediate product in the manufacture of rod and wire and small structural shapes such as angles, tees, zees, etc. Shears. The blooms or slabs, after having been formed in the bloom mill, are trimmed while still hot, removing the "fish tail" from both ends. The cuts are taken far enough along the bloom to ensure that all unsound metal is removed. These ends, known as "crop ends," after being cut off fall down a chute into a bucket where they are

142

MANUFACTURING PROCESSES IN CANAVA

collected and sent back to the open hearth as scrap. Bloom shears are designed to cut blooms 10 X 10 inches in cross-section, requiring an operating pressure of about 700 tons. Heavy shears for cutting slabs may require up to 3,500 tons of pressure. Conditioning. Slabs, blooms, and billets, before being rolled into their respective final products, are inspected for surface defects and may be subject to conditioning. Conditioning consists of either chipping with a pneumatic chisel, scarfing with an oxyacetylene torch, or grinding with an abrasive wheel to remove surface defects such as small cracks and surface irregularities. MANUFACTURE OF SHEET AND STRIP

By definition, sheet or strip is a flatrolled product which is less than .2 inches in thickness. If it is greater than .2 inches the product is classed as plate. Sheet and strip are differentiated in that sheet consists of short lengths of strip, strip being the name given to the long, continuous form of the material. Sheets are usually stored in packs, whereas strip by its very nature must be stored in coils. A further classification of the sheet and strip is according to width. If the material is less than 18 inches in width it is known as "narrow" sheet or strip, and if it is greater than 18 inches in width it is known as "wide" sheet or strip. A majority of the steel produced today takes the form of sheet or strip to be used in the manufacture of automobiles, refrigerators, stoves, pots and tin cans. Sheet. The first sheet produced was not cut from lengths of strip, as is done today, but was rolled directly as sheet from "sheet bars." Sheet bars were preheated to a suitable temperature and then passed back and forth through a simple 2-high mill, usually hand-fed, until the required thickness was produced. In cases where extra thin sheets were required, the roller would pass the

sheets through the mill in packs in order to obtain the required thickness. The sheet processes were rather laborious as compared with the newer and more up-to-date strip-rolling methods, and as previously mentioned, sheet is now produced by simply cutting strip into shorter lengths. Strip. For the production of strip, slabs are preheated to approximately 2400°F ( 1315°C) in a continuous slab furnace, and passed through a scale breaker to remove the thick, crusty scale which is formed during heating. The scale breaker is a small rolling mill which only provides enough reduction in thickness to break, and thus remove, the heavy scale formed during heating. After scale breaking the slab is put through a roughing operation which reduces the thickness of the slab to approximately .75 inches. The roughing may be accomplished by a single 2-high reversing mill or, in larger and more modern plants, may be done continuously by a roughing train which consists of three or four 2-high mills in tandem. In a continuous mill the product of the roughing train is passed through a finishing train which usually consists of six 4-high mills in tandem ( Fig. 16). The steel entering the first stand at approximately .75 inches may be reduced to .05-.1 inches. It may enter the first stand at approximately 300 feet per minute and leave the sixth and final stand at speeds of up to 2,000 feet per minute, or approximately 30 miles per hour. If hot-rolled sheet is required the strip is cut into shorter lengths by a set of flying shears located at the exit side of the last stand. As previously mentioned in the section on mills, strip may be rolled on a reversing 4-high mill, coiler furnaces being required on both sides of the mill to keep the strip hot. The strip, after being rolled to its final "hot band" thickness, is run out on a roller table where it is cooled by water sprays and then coiled. The hot-

IRON AND STEEL

14'3

Fm. 16. Hot strip mill, showing six stands (mills) in tandem.

rolled strip, cut up into sheets or in strip form, may be sold directly as a hot-rolled product, but usually it is further processed by cold rolling and annealing to meet the more rigid specifications of gauge, finish, and physical properties required for end products such as tinplate, deep drawing steels, and so on. Continuous pickler. In preparation for cold rolling, the strip is pickled to remove all the scale formed during hot rolling. The continuous pickier, through which the strip is passed as a continuous sheet, consists of an uncoiler, a welder for joining coil ends, a looping pit to permit stoppages for welding without stopping the strip as it passes through the acid, pickle baths, a rinse bath, driers, a side trimmer, roller leveller, and coiler. The acid treatment is effected by passing the strip through

four separate acid tanks of differing concentrations of sulphuric acid which flows counter-current to the direction of the strip and is most effective at about 200°F . The acid concentrations usually increase from the entry end of the pickier. The acid may be from 6 to 10 per cent sulphuric acid by weight in number one tank, from 10 to 15 per cent in number two tank, from 15 to 20 per cent in number three tank, and from 20 to 25 per cent in number four tank. After the final acid tank the strip is rinsed and dried and then side trimmed and coiled. Side trimming, which consists of cutting off approximately one inch of material from both edges of the strip, is done to remove any defects produced during hot rolling and to trim up the sheet in preparation for cold rolling. Three layers of scale are formed on

144

MANUFACTURING PROCESSES IN CANADA

steel: a layer of FeaO4 on top, a layer of Fe2O3, and finally a layer of FeO next to the steel. Sulphuric acid is relatively inactive with respect to the two top layers of FeaO• and Fe2Os and their removal is effected mainly by the ability of the acid to reach and dissolve the FeO layer through cracks and pores. Cold rolling. Cold rolling is used for several reasons. In hot rolling, reduction to thickness of less than .03 inches is not possible because of the inability of the thin strip to maintain the high temperatures required. At the same time a better surface quality can be produced by cold rolling; then by controlling the subsequent heat treatment, the process of "annealing," the desired physical properties ( within the limits dictated by the composition of the steel) can be obtained, resulting in a more uniform product. There are several types of cold reduction mills in operation. They are classed with respect to the type of the mill ( 2-high, 4-high, etc.) and as to the type of operation, that is, reversing or continuous. A typical reversing cold mill consists of a single stand with a tension reel located on both sides. On the entry side of the mill, means are provided for uncoiling and feeding the coil through the mill to the tension reel on the exit side. After the first pass the tail end of the coil coming from the uncoiler is gripped by the second tension reel on the entry side of the mill. During each pass, the reel serving as the payoff unit is operated as a generator to provide a back tension, feeding the current produced into the driver reel motor. On the last pass the strip is released by the payoff reel and removed. A reversing mill is flexible, but cannot compete in tonnage with the tandem mill and consequently is restricted to plants where the tonnage is low or there is a wide diversity in the type of product. The continuous cold mill consists of an uncoiler, three, four, or five 4-high

mills in tandem, and a coiler. The strip is successively reduced by each mill in the chain, the last mill imparting the finish gauge to the material. Continuous mills have been operated at speeds of 1,000 feet per minute on a three-stand mill ( three mills in tandem), 3,000 feet per minute on a four-stand, and 6,000 feet per minute on a five-stand. In a five-stand, the five mills are each driving the material being rolled, usually at speeds synchronized to provide a tension in the strip between each unit. The total reduction may vary from 2.5 to 90 per cent producing strip of .065 to .008 inches in thickness. In cold rolling, greater pressures and greater driving forces are required to give a specific percentage reduction than are required in hot rolling. In any given pass the result of the compressive forces exerted by the rolls on the steel and the tensional forces along its length between the rolls must exceed the elastic limit of the steel to produce permanent deformation. The forces required are at a minimum during the first pass, but as rolling continues the force required increases progressively, as cold working greatly increases the elastic limit. The ultimate strength is also increased, but much more slowly, hence much of the cold reduction is performed on very hard steel having very little residual ductility. Heavy reductions at high speed on any of the various types of mills generates considerable heat and not only raises the temperature of the product, but also that of the rolls. The heat generated is dissipated by a system of flood lubrication in which water-soluble oil or a mixture of oils is directed in small streams or jets against the roll bodies and the surface of the steel. Steel for tinplate is usually reduced to approximately .008-.014 inches in thickness, and steel rolled for automobile bodies, office furniture, and household equipment is usually in the range of .025-.065 inches in thickness.

IRON AND STEEL

Annealing. After cold working the hard strip must be annealed to reproduce its original softness and ductility. During annealing the strip passes through three stages, heating, soaking, and cooling. In a typical annealing cycle the rate of heating, length of soaking, and rate of cooling will have a decided influence on the physical properties of the steel, and it is by control of these factors that ( within limits set by composition) any desired physical properties can be obtained. Present-day annealing furnaces are of two types, box annealing and continuous annealing. Of the two types, continuous annealing is a relatively new process, box annealing being an older and more widely used method. A box annealing furnace ( Fig. 17), depending on its size, may consist of from one to four stools placed on a refractory base. Strip is annealed in coil form and the coils are stacked on the stools. Steel covers are placed over the stools and are provided with a sand seal to make them relatively gas tight. They are also provided with a means of

145

introducing an inert gas. A large, portable, radiant tube-type furnace is lowered over the covers on to the refractory base. Gas is burned within the long tubes to provide the heat necessary for the operation of the furnace. All annealing is done in a slightly reducing "controlled atmosphere" to avoid oxidation which would impair the quality of the steel surface. Because of the large masses of steel involved, the time required for complete recrystallization and grain growth ranges from 70 to 100 hours. In continuous annealing the strip is uncoiled and passed through a specially designed furnace as a continuous strand, the time required for complete recrystallization being only in the order of seconds. The rapidity with which the material can be recrystallized is mainly due to the rapid heat transfer that can be effected by the use of a single strand. Because of the speed with which the strip is annealed, the rate of heating, length of soak, and rate of cooling become critical, and a much closer control must be exerted as compared

Fie. 17. Radiant tube annealing furnace, showing coils and base.

146

MANUFACTURING PROCESSES IN CANADA

with box annealing. In continuous annealing, as in box annealing, the strip is heated in a controlled abnosphere. The hardness which can be attained during the continuous annealing process is not as low as that which can be produced by box annealing. Consequently, although continuous annealing is finding wide application in the manufacturing of products such as tinplate, it is not likely to replace the box annealing process. Temper rolling. After annealing the steel is in a relatively soft condition, and to prevent an effect called "banding" from occurring when the manufacturer uses the material, it is "temper rolled" or "skin rolled." Banding is caused by the local yielding of various parts of the steel sheet during manufacturing processes, which will usually result in fracture. Temper rolling is a cold-rolling process in which the annealed material is reduced in thickness from ½ to 3 per cent. The slight cold working, besides preventing bandings, also imparts a slightly better finish to the steel. After temper rolling the steel sheet is

directed into various channels depending upon the intended product ( see Fig. 20). Strip is usually cut into sheet before being shipped to the manufacturer, although today many users of sheet are installing equipment to handle strip in the coil form in order to achieve less waste of material. MANUFACIURE OF STRUCTIJRAL SHAPES

The rolling of structural shapes follows the same general pattern as the rolling of strip. Of course, the roll design is different. Roll design. In roll design there are a few simple points that must be considered. First, the piece must be able to pass in and out of the grooves in the rolls. This means that certain passes can only be made with the piece in one position; for example, I-beams cannot be rolled as shown in Figure 18a, but must be rolled as shown in Figure 18b. For the same reason the flanges on a complicated structure such as the Ibeam must be tapered. Second, it is essential that an equal degree of mechanical work be given to all parts of the product so that the mechanical

TOP TOP

ROLL

ROLL

ROLL

80TTOM

BOTTOM

a.

b.

Fm. 18. Roll design.

ROLL

147

IRON AND STEEL

properties shall be uniform throughout. Third, it is impossible to have rolls in close contact as they will always spring apart when the metal is passed through. Finally, in rolling shapes that have light and heavy sections, such as a rail, the light sections cannot be fully formed until the heavy section is completely finished as the light thin section will cool rapidly and possibly crack while the heavy section is being finished. Figure 19 illustrates the various steps

BA.R -OF

METHODS

MILL

that must be employed in the rolling of various shapes. In the rolling operation the blooms must be heated to an even temperature throughout. Rolling may be accomplished on a 2-high or 3-high mill with two or more stands being employed to give the roughing and finishing passes. The sections are usually cut into lengths by a circular saw. Typical sections produced are angles, channels, tees, zees, I-beams, and rails.

ROLL PASSES METHODS

SHAPING

\111.RIOUS

SECTIONS FLA.T DIAMOND

OF

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SECTIONS

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(bl MOOERA.TELV SEVERE REOUC.TIOH. USED MOSTLY FOR MED . SP.RS

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Fie. 19. Shown above are a few of the passes required in the rolling of structural shapes.

~

._____:!_. \

RAILS

BEAMS

CHANNELS TEES ZEES ETC.

· CRUSHING PIGS

BARS

PIG CASTING

MACHINE

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HEARTH1 LIGHT SECTION MILLS

CRUSHltG IRON ORELSCREENING.ORE

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BY-PRODUCTS

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Frc. 20. Flow diagram of an integrated steel plant.

TINPLATE

DEEP DRAW

STEELS

IBON AND STEEL

Packaging and Loading The packaging, loading, and shipping of steel products is as truly a precision job as the manufacture of those products. Steel is produced to meet customers' specifications, and it is equally important to pack and load it not only for protection in transit, but also to suit the customers' conditions and unloading equipment. Plates and bars are usually loaded on open railroad cars in unsecured lifts, weighing a minimum of five tons. Structural shapes are generally shipped in lifts of a minimum of five tons, and are usually transported in open top cars. The standard net weight of cut-length sheets in a regular single-lift package is five tons. Some purchasers, however, are able to handle packages weighing up to ten tons which is more economical with respect to handling costs. Tinplate, which has a highly finished surface, must be carefully packed. The automatic feeding devices and highspeed can-making lines require that tinplate be free from buckles or frayed edges. Today, most steel is packed in multiple package containers, covered with waterproof paper and a corrugated fibre outer cover. Light gauge steel angles are employed to protect comers and edges from damage. Cold-rolled strip in coil form may be wrapped with paper or burlap, and must be securely tied. Coils are generally loaded in open cars or trucks. Freight-car loading rules governing steel products are issued by the Association of American Railroads. If trucks are used for shipping, some products may require less packaging and bracing than they would require if shipped by rail. This at times may be an important economic consideration. Inspection and Control Although steel is produced in very large tonnages, a great deal of care is taken to ensure its quality. As many as

149

170 tests may be made during the processing of the raw materials to the finished product. During the first stages of steelmaking, such as the blast furnace and the open hearth, tests are performed to ensure the correct composition of the metal and slag and also to ensure that the impurities are removed. At the blast furnace, both metal and slag samples are taken during the cast to determine the composition of the pig iron for the open hearth and to determine how well the slag has removed impurities. In the open hearth as many as 37 tests may be taken. As previously mentioned, the type of slag, that is, its composition, basicity, and viscosity, is very important in eliminating the undesirable elements, and consequently periodic slag tests are made to check these factors. Scrap employed in the open hearth will undoubtedly introduce various undesirable elements such as copper, tin, chromium, arsenic, and antimony. A knowledge of the extent to which these "residual elements" are present is very important, for they can affect the physical properties of the steel. Thus, soon after meltdown, before any additions are made, a sample of the steel is taken for analysis. Chemical analysis may be employed, but a method widely used by the steel industry today is spectrographic analysis. It is based upon the fact that the elements, when in the form of a vapour, each have a specific wavelength which when dispersed through a series of prisms will form a "spectrum" made up of lines representing the various elements in the vapour. Hence by means of a spectrum various elements can be recognized. In spectrographic analysis the steel sample in the form of a pin about ¼ inch in diameter is made one electrode of a spark gap, the other being carbon. When the sample is sparked the spectrum produced is dispersed by a series of prisms and photographed. From the position of the various spectral lines

150

MANUFACTUIUNG PBOCESSES IN CANADA

on the photograph, calibrated for wavelength and the relative intensity of the spectral lines as compared with a standard of known composition, the elements and their percentages can be determined with great accuracy. Carbon content tests are also taken throughout the heat, by means of carbometer. This test is based upon the fact that the magnetic permeability of a steel sample will vary with its carbon content. Thus by calibrating an instrument to measure permeability against known carbon contents, the carbon content of an unknown can readily be ascertained. The last steel samples in the open hearth are taken during the teeming of the ingots and are known as ladle analysis. This analysis, unless questioned, forms the basic composition by which the heat is identified throughout its life in the steel mill. The majority of the tests thus described mainly apply to control of composition in the blast furnace and the open hearth. After the ingot has been poured and rolled the majority of the remaining tests taken are to determine the physical properties of the steel. Micrographs are taken to determine its structure, tensile tests to establish its strength, Rockwell hardness tests to determine its hardness, Izod tests to determine its toughness, and many others, the results of which are used to determine the suitability of the steel for a particular product, and to serve as a control of quality throughout the various processes. After a piece of steel is polished, an outline of the crystal structure can be made to appear by "etching," that is, by immersing the sample in a suitable acid. The structure can then be examined under a metallurgical microscope, which differs from the standard type of microscope in that the image viewed through the eyepiece is produced by reflected light. The tensile test subjects a specially

machined specimen in the form of a rod to a tension force, the force required to break the specimen being taken as a measure of the strength of the steel. The Rockwell test measures the ability of the steel to resist deformation at a particular point. This resistance to deformation is measured by the depth to which an indentor can penetrate into the steel under a given load and is taken as an indication of the hardness of the material. The Izod or Charpy tests are used to determine the toughness of a piece of steel by measuring its ability to stand up under an impact force. A specially prepared specimen is rigidly clamped in a vice and subjected to the impact of a weighted pendulum. The loss in energy of the pendulum after hitting the specimen is the means by which the test is evaluated. This loss in energy is indicated by the lessening of the normal swing of the pendulum after the specimen has been fractured. Along with the tests for hardness, strength, and so on, steel products are subjected to a cupping test. The cupping test, commonly known as the Olsen or Ericksen test, consists of pushing a round ball, which is on the end of a ram, through a piece of steel that has been firmly clamped. The amount of stretching the metal will take, indicated by the depth to which the steel ball can be pushed before the metal fractures, is taken as a measure of the ductility of the steel. X-ray tests and ultrasonic tests have been designed to give an indication of the soundness of a piece of steel, that is, to determine the location and extent of any internal cracks or blow holes. In X-ray radiography a film is placed on the underside of the piece to be inspected and the X-rays are directed through the metal on to the film. Blow holes or cracks in the steel will appear as dark sections on the film. Similar work is being done with radioactive material, the radiation serving to pene-

IRON AND STEEL

trate the steel and expose the film. The use of a small radioactive specimen such as a "cobalt bomb" eliminates the need for the expensive X-ray equipment. In ultrasonic testing, defects are located by passing high-frequency sound waves throught the steel. When the sound waves hit a defect they will be reflected and the reflections picked up by a probe. The reflected waves are passed through an electronic circuit and are projected on the screen of a cathode ray oscilloscope ( similar to a small television set). A steel with no defects will be represented by a relatively straight line on the screen; a defect will be recorded as a marked deflection in the straight line on the screen. The position of the deflection on the screen is proportional to the depth of the defect in the steel. These are only a few of the more important tests employed to establish the physical properties of steel, that is, to check the quality of the material produced, and to establish the suitability of a given steel for a particular application. The role these metallurgical tests play in producing a satisfactory material for the various applications cannot be over-emphasized.

Classification of Steels Steels may be classified according to method of production, type of ingot structure, and composition. Methods of production ( open hearth, electric furnace, Bessemer) and type of ingot structure (killed, semi-killed, rimmed) have been discussed. Classification with respect to composition. Approximately twenty different elements ranging alphabetically from aluminum to zirconium are used today in various combinations and proportions in the manufacture of both plain carbon and alloy steels. Some elements are used because of the specific properties which they impart to steel when they alloy with it, that is, dissolve in the iron, or

151

when they combine with carbon, wholly or in part, to form compounds called carbides. Others are used because of their beneficial effects in ridding the steel of impurities or in rendering impurities harmless. A third group is used to counteract harmful oxides or gases in the steel. The elements of the latter group are merely fluxes or scavengers and do not remain in the steel to any great extent after the steel solidifies. Some elements may fall into more than one of the afore-mentioned groups. Most of the elements are introduced into the steel in the form of ferro-alloys ( alloys of iron) made especially for use as raw material in the manufacture of steel. Ferro-alloys are used because many of the pure metals are costly to obtain. Here the iron serves primarily as a vehicle for carrying the desired elements. All steel contains, in addition to iron, certain amounts of other elements such as carbon, manganese, phosphorus, sulphur, and silicon. Thus, the two principal grades of steel, carbon steel and alloy steel, are both alloys of iron with other elements, the proportion of these elements determining its classification. Carbon steel may be defined as a material in which there is no minimum content specmed for elements such as aluminum, boron, chromium, cobalt, columbium, molybdenum, nickel titanium, tungsten, vanadium, or zirconium, or any other element which may be added to obtain a particular alloying effect. The specified minimum for copper must not be less than .4 per cent and the maximum for the following elements must not be exceeded: manganese 1.65 per cent, copper .6 per cent, silicon .6 per cent. The properties of carbon steels, however, are not governed by their composition alone as these may be enhanced by rolling, drawing, forging, heat treating, and so on. Carbon steels may be classified as foJlows:

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MANUFACTURING PROCESSES IN CANADA

Classification Dead soft steel Soft steel Mild steel Medium steel Spring steel

Carbon content ( %) .1 maximum .2 ,, .15 - .25 .25 - .45 .85 -1.15

The steels listed above range in carbon content from .1 per cent to greater than 1 per cent. Iron which has more than 2 per cent is no longer classed as a steel, but becomes a cast iron.

Applications of various carbon steels. Dead soft steels are frequently used as a base for various coatings such as porcelain enamelling, tin plating, and galvanizing, because of the good surface properties obtainable. Because of their ductility they are also used for deep drawing grades. Steels of .15 to .25 per cent carbon are usually used in the manufacture of such products as bolts and nails where

TABLE II PRINCIPAL NON-FERROUS METALS USED BY STEEL INDUSTRY

Metal Aluminum Chromium

Reason for use

Typical applications

Removes gases and impurities; Seldom more than a trace aids surface hardness remains, except in nitrided steel Small amounts improve Tools; machinery parts; hardening qualities; more stainless and heat- and than 10% prevents rust acid-resisting steels

Cobalt

Holds cutting edge at high temperatures, improves electrical qualities

High-speed cutting tools, permanent magnet steel

Copper

Retards rust

Roofing and siding sheets, plates Sheet steel for roofing, auto gasoline tanks, etc. machinery parts

When mixed with tin, forms a rust-resisting coating for steel; small amounts alloyed with steel improve machinability Small amounts present in Manganese Small amounts remove gases all steels; 1 to 2% used from steel; 1 to 2% increases strength and toughness; 12% in rails; 12% or more for imparts great toughness and frogs and switches and dredge bucket teeth resistance to abrasion Tools; machinery parts; Molybdenum Increases strength, ductility, tubing for aircraft and resistance to shock fuselage Increases toughness, stiffness, Tools; machinery parts; Nickel strength, and ductility; in stainless steels; heat and large amounts resists heat acid-resisting steels and acid Forms corrosion-resisting Sanitary cans, kitchenware Tin coating on steel

Lead

Tungsten

Vanadium Zinc

Sources of supply U.S.A. and Canada Turkey, Union of South Africa, New Caledonia, Cuba, Greece, Russia, Philippines, Oceana Belgian Congo, Belgium, Canada, France, Mexico, Australia, N. Rhodesia U.S.A., Chile, Canada, Mexico U.S.A., Mexico, Canada, Australia, Peru India, Union of South Africa, Cuba, Gold Coast, Brazil, Russia U.S.A. Canada, Norway, New Caledonia

British Malaya, Netherlands, Belgium, United Kingdom, Bolivia Retains hardness and toughness High-speed cutting tools; India, Korean Republic, Bolivia, at high temperature magnets Portugal, Thailand, Brazil, China, British Malaya, U .S.A. Tools, springs, machinery U.S.A., Peru, S.W. Increases strength, ductility, and resiliency parts Africa, Rhodesia Forms corrosion-resisting Galvanized roofing and U.S.A., Canada, siding sheets, wire fence, coating on steel Mexico, West pails, etc. Germany

IBON AND STEEL

a certain degree of cold forming is required. Steels in this range may also be heat treated, whereas steels below .15 per cent carbon are not amenable to heat treatment. In the case where a tool or machine part is subjected to both shock and abrasion a mild steel may be casehardened. Case-hardening, which increases the carbon content of the outer layer of metal, provides a hard abrasive resistant surface while still maintaining the low-carbon, tough, ductile core. Steels of .2.5 to .45 per cent carbon are desirable because of their "hardenability," that is, response to quenching. From these steels may be made common hand tools such as pliers, open end wrenches, screw drivers, tin snips, etc. Carbon steels above .45 per cent carbon are chiefly used in parts for heavy machinery, such as crankshafts and collars, hand tools such as Stillson wrenches, hammers, hatchets, cutting tools and springs. Alloy steels. It was first thought that all that was necessary to produce an alloy steel was to add an alloying element to a heat of plain carbon steel. However, it was soon found that the manufacture of alloy steels requires more caution and detailed attention than does the manufacture of the simple carbon steels. An alloy steel is one in which the maximum of the range specified for the content of alloying elements exceeds one or more of the following limits: manganese 1.65 per cent; silicon .6 per cent; copper .6 per cent; or when a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized commercial field of alloy steels: aluminum, boron, chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium; or any other alloying element added to obtain a desired alloying effect. The development of alloy steels may

153

be attributed to the demands set forth by design engineers. In the era of automation, aircraft, and automobiles, steels were required to withstand the faster speeds and heavier loads. Steels which would resist abrasion, shock, fatigue, and corrosion both at room and high temperatures were urgently needed. To satisfy this demand metallurgical laboratories began experimenting and found that various elements when added in the proper proportions would give the desired properties. Today this search for new alloys continues and is evidenced by the production of such steels as titanium steels, vanadium steels, etc. A few of the more common alloy steels are listed in Table III. Two types of steels that will be discussed because of their importance are stainless steels and tool steels. Stainless steels. The formation of a light self-healing protective film of chromium-iron oxide is what makes stainless steel stainless. This film is resistant to many types of corrosive media such as water, air, food juices, some acids, and some alkalines. In the development of stainless steels consisting mainly of iron, carbon, and chromium, it was found that the addition of nickel greatly enhanced its anticorrosive properties and also made it relatively heat resistant, enabling its use at high temperatures. In a stainless or heat-resisting steel at least four of the following elements may be used: aluminum, carbon, cromium, columbium, copper, iron, manganese, molybdenum, nickel, nitrogen, phosphorus, selenium, silicon, sulphur, titanium, tungsten, vanadium, and zirconium. For example, molybdenum and tungsten increase high temperature properties; columbium and titanium improve corrosion resistance; aluminum and silicon retard a form of high temperature corrosion known as "scaling"; and phosphorus, selenium, and sulphur improve machinability. Tool steels. Tool steels may fall into

TABLE Ill How Representative types of steel ( carbon approx .. 4%)

SOME ELEMENTS AFFECT STEEL

Index of physical properties (compared with straight carbon steel) Breaking Relative strength elasticity Ductility Hardness

Straight carbon (C . 4%) 100 100 100 100 Medium manganese 145 155 138 ) 58 (Mn 1. 75%) 147 Straight chromium ( Cr . 95%) 157 177 63 :3 1/ 2% nickel (C .3, Ni 3 5%) 224 63 192 202 Carbon-vanadium 17~) 153 158 68 (C .5, V . 18%) Carbon-molybdenum 164 149 162 5:3 (C .2, Mo .68%) High silicon sheets (Si 4%) Electrical properties of prime importance Silicon-manganese 224 42 180 198 (Si 2, Mn . 75%) Chromium-Nickel 94 115 125 120 (Cr .6, Ni 1.25%) 225 Chromium-vanadium 229 52 202 (Cr . 95, V . 18%) 130 94 125 Chromium-molybdenum 135 (Cr . 95, Mo . 2%) Nickel-molybdenum 155 177 153 68 (Ni 1. 75, Mo . 35%) 151 158 Manganese-molybdenum 177 68 (Mn 1.3, Mn .3%) 6:3 :II ickel-chromium-molybdenu m 158 203 161 (Ni 1. 75, Cr . 65, Mo . 35%) High-speed steel (Tungsten 18, Cutting properties of prime importance Cr 4, V 1%) Magnetic properties of prime importance Cobalt magnet steels (Co 35%) 18-8 stainless (Cr 18, Ni 8%) 207 219 53 165 (cold worked)

Distinguishing characteristic

Typical uses

Railroad track bolts, automobile axles and brake levers Good strength and Logging and road and agricultural machinery. work-abilitv . Springs, shear blades, wood-cutting tools Rock drill and air hammer parts, crankshafts Toughness Resists impact Locomotive parts Resists heat

Boiler shells, high-pressure steam equipment

High electrical efficiency Springiness

Transformers, motors, generators

Surface easily hardened High strength and hardness Resists impact, fatigue, and heat Resists fatigue

Automobile ring gears, pinions, piston pins, transmissions Automobile gears, propeller shafts, connecting rods

Automobile and railroad car springs

Aircraft forgings and fuselages Railroad roller bearings, automobile transmission gears

Resists impact and Dredge buckets, rock crushers, turbine parts fatigue Resists twisting Diesel engine crankshafts Stays hard at high temperatures High magnetic strength Resists corrosion

High-speed metal-cutting tools Permanent magnets in electrical apparatus Surgical instruments, food machinery, kitchenware

IRON AND STEEL

two classes : carbon tool steels and alloy tool steels. A carbon tool steel may vary in carbon content from .60 to 1.4 per cent. The lower carbon ranges are used for hot forging dies, hammers, and chisels. Carbon contents in the middle of the range may be used for punches and threading dies. The high-carbon tool steels find use mainly in the production of drills, taps, and lathe tools. Tool steels with approximately .6 per cent carbon after proper heat treatment are characterized by great toughness and medium hardness. As the carbon content increases, toughness decreases and hardness increases. Alloy tool steels cover a wide range

155

of analysis. Alloying elements include manganese, chromium, vanadium, tungsten, nickel, and molybdenum. A special alloy tool steel has been designed for making intricate dies. It has a very low co-efficient of thermal expansion, and there is very little change in its dimensions during heat treatment due to the expansion and contraction of the metal. High-speed tool steels have been designed that will keep their cutting edge, although running red hot. These and many more tool steels have been, and are being designed to keep up with the ever quickening pace set by engineering designers.

Canada's National Magazines BY E. NYMARK MACLEAN-HUNTER PUBLISIUNG COMPANY LIMITED

A MAGAZINE is an instrument of communication. With the aid of ink and paper it carries messages in the form of articles, stories, editorials, advertising, pictures, drawings, and paintings. Before manufacturing begins, articles and stories are chosen for publication, editorial text and advertising copy are prepared, photographs are taken and paintings produced. These are combined by the magazine art department into a preliminary layout of the magazine. Photo-engraving and typesetting are the first steps in the manufacturing process. Photographs, drawings and paintings are sent to a photo-engraver, who produces their images on copper or zinc plates, known in the trade as "originals." There is one original plate for every picture or drawing that appears in the magazine. If the picture is to be reproduced in colour, there is an original for each colour. The photo-engraver makes a photographic negative of the original artwork. If it is a photograph or painting, he photographs it through a screen so that the reproduction will show the varying tones of grey or weights of colour. This is lmown as a halftone. If it is a line drawing, no screen is used and the finished engraving registers only black and white, with no intermediate tones. If the original artwork is to be reproduced in colour, the engraver photomechanically separates the copy into four basic colours-yellow, red, blue, and black. The image required for each colour is imposed on a screened nega-

tive and the screen is set at a different angle for each colour. The screen produces lines of dots on the negative, the number of dots to the lineal inch determining the degree of coarseness of the screen. When the engraving is to be printed on newsprint, a coarse screen (usually 65-line) is used. If finer screens were attempted, the ink particles, soaking into the porous newsprint, would run together, destroying the dot pattern. In printing on coated or enamelled paper, however, 120-line or finer screens can be used without "running together." The finer the screen, the more nearly the reproduction approaches the sharpness of the original artwork. In magazine colour printing it is general practice to use a 120-line screen on the red, blue, and black plates and a 133-line screen on the yellow plate. Use of the finer screen on the yellow plate helps to avoid a disturbing pattern that may appear when the same fineness of screen is used for all plates. The image is photographically transferred from the screened negative to a sensitized copper plate. Those areas of the plate which are not required for printing purposes are etched away with an iron oxide solution. Thus the area which is to print remains in relief; this area is in dot form, the image of those in the photographic negative. The printing of these dots in yellow, red, blue, and black, one set on top of the other or in combination with one another, allows reproduction of all shades of the spectrum. The work of the photo-engraver is inspected by printing an im-

CANADA'S NATIONAL MAGAZINES

pression of the original on a proof press. These impressions, or proofs, when printed in colour, are known as progressive proofs. The progressive proofs are sent to the printer along with the originals and are used as a colour guide in the pressroom. In the meantime, the editorial and advertising copy have been sent to the printer's composing room, where the typesetters translate it into "lead" type which is, in fact, an alloy of lead, antimony, and tin in varying proportions. A typical mixture is 84 per cent lead, 12 per cent antimony, and 4 per cent tin. Tin imparts flowing qualities to the lead and antimony gives it hardness. Copy received in the composing room may be routed through one of two typesetting methods : line casting or monotype. Headings are usually set by hand.

157

The line-casting process yields an entire line of type cast on the piece of lead, known as a slug. The slug is produced by an operator fingering a keyboard in much the same manner as a typist. When a key is depressed, a matrix is released from its storage magazine. In the side of the matrix is indented a numerical or alphabetical character which forms the mould in which the lead is to be cast. The matrices are collected mechanically to form the basis of the desired line, and then are transferred to the moulding mechanism. The hot lead mixture is poured into the mould and allowed to solidify. The slug, on which the required characters have been moulded, is ejected and trimmed to the specified width. The matrices are automatically returned to their original storage position to await further use. The slugs

Fm. 1. Une casting.

158

MANUFACTURING PROCESSES IN CAXADA

f' ..

'

i

+

'·

Fie:. 2. Monotype keyboarding.

are collected on a tray known as a galley. The monotype process yields a product wherein each character, alphabetical or numerical, is a separate piece of lead. An operator depresses a key representing the desired character on a typewriter-like keyboard and a hole is punched through a paper tape. This operation is called keyboarding. The tape is approximately 4}i inches wide and, when fully punched, resembles a narrow player piano roll. This paper roll is then placed in position in the casting machine, where it selects and positions matrices, allowing the required letters or numbers to be individually cast in metal. Selection is accomplished by applying compressed air to the roll as it unwinds. The location of the holes in the roll determines the course to be followed by the escaping

air, which causes each matrix to be positioned. Hot lead is poured into the matrix and the letter is formed, ejected, and collected on a galley. Galleys of editorial text, set by either the slug or monotype process of casting, are taken to the proof press where an impression of the type is made on a sheet of paper. This is known as the galley proof. The proof is examined for typographical errors and returned to the compositors who change the type to conform with the proof reader's corrections. A proof of the corrected type is pulled and sent to the editor who scans it for accuracy and, where necessary, makes other revisions. The type is corrected to conform with the changes and revised proofs are pulled. Each proof is then pasted in its correct location in a mock-up of the magazine. This mock-up is known as the dummy.

CANADA'S NATIONAL MAGAZINES

159

Frc. :3. Monotype casting.

Simultaneously, other compositors have been setting the advertising copy. A proof of the advertisement is sent to the advertiser or his agent for final approval. When this approval is received, the advertisements ( in type or plate form) and the editorial text ( in galley form) are brought together with the illustrations ( in engraving form) by the compositor to form a composite page. The model for individual page make-up is the previously prepared dummy. The assembled pages are again proofed and checked. Around the page is placed a steel frame known as a chase and the whole assembly is locked firmly together by wedges which are called quoins. Every element in the page is then checked for printing height, which should be .918 inches. The page can now be taken from the composing room to the electrotype foundry where

a printing plate is made. This plate is a duplicate of the page made up in the composing room and is curved to fit the cylinders on the printing press; it is formed as a nickel-faced copper shell backed up with lead. The first step in making a plate is to fabricate a plastic mould of the whole page. The page is cleaned thoroughly, pre-heated, and placed in a moulding press. A piece of plastic material, usually vinylite, is positioned over the page. Heat and pressure are applied to form the plastic mould. The mould is cleaned carefully with an alkali solution and pumice. It is next sprayed with a sensitizing solution and then with a solution of silver nitrate. The latter establishes a conducting surface necessary for nickel coating. The mould is then placed in a nickel-plating tank for about half an

160

MANUFACTURING PROCESSES IN CANADA

Fie. 4. Proofreading.

hour. Approximately .0015 inches of nickel is deposited on the mould. It is removed from the tank, washed with water and then placed in a copper fluoborate solution. At the end of about one hour in this solution .012 inches to .015 inches of copper is deposited on top of the nickel. On removal it is again washed with water and placed for four to five minutes in a tinning tank. Sufficient tin is deposited during this short interval to act as a bonding agent between the copper and the lead back-up metal. The metal unit, a thin shell of nickel backed with copper, is now stripped from the plastic mould. This shell is the surface of the printing plate; it is only necessary to back it up with lead which gives it both body and the required thickness for printing. One of the most modem processes

used for "backing-up" is centrifugal casting. The shells are positioned in a drum, the circumference of which matches that of the bearers on the printing cylinders. The drum is rotated at a speed of 780 r.p.m. Molten lead is poured on the back of the shell, centrifugal force holding the lead against the inside surface of the shell until solidification occurs. A complete circle of metal about " inches thick is formed. It is removed from the drum and sawn into page size yielding a curved printing plate. The plate is trimmed, bevelled shaved to exacting dimensions, and put through finishing operations to correct any remaining deficiencies. To relieve the light tones and accentuate the heavy tones in an illustration the plate must be processed to produce an uneven -printing sudace. This is accomplished by a mask which

CANADA'S NATIONAL MAGAZINES

161

Fie. 5. Page make-up.

is cut from laminated paper and placed over the image on the plate. The plate and mask are then run through a solidiSer which puts differential pressures on the plate, the differential depending on the manner in which the mask has been cut. The result is an extreme variation of .006 inches in height between the areas of the plate producing light and heavy tones. As plates are completed they are transported from the foundry to the pressroom. Plates used to print the magazine cover are delivered to multicolour sheet-fed printing presses. Plates used in printing the pages of the magazines are delivered to huge rotary magazine printing presses. The rotary magazine printing presses produce forty pages per impression cylinder revolution. Twenty of these pages are printed on one side of the

web of paper as it goes through the press and twenty on the reverse. Any or all of the forty pages may be printed in one, two, three, or four colours. There is also a fifth printing unit for each side of the paper, which can be used to obtain special printing effects not possible with the four regular printing units. Simultaneous multi-colour printing is made possible by an ingenious arrangement of plate cylinders. If all forty pages were to be printed in five colours, 200 printing plates in all would be made -40 printing in yellow, 40 in red, 40 in blue, 40 in black, and 40 in the fifth colour required. The plates are positioned on their appropriate cylinders, yellow plates on the yellow cylinder, blue plates on the blue cylinder, and so on. The cylinders are spiral-grooved, and plate hooks in-

162

MANUF ACTIJRING PROCESSES IN CANADA

serted in these grooves hold the plates securely in place. Accurate positioning of the plates on the cylinder is known as "getting register." If, for instance, the register of the red plate were out by the width of one dot in relation to the register of the blue plate, the illustration would appear fuzzy. The web of paper on the press travels around a large impression cylinder, against which the five smaller plate cylinders revolve. This is duplicated to print the reverse side of the web. Each plate cylinder in turn prints its image on the moving paper, so that in one revolution of the impression cylinder all colours are printed on all pages. The press has a top running speed of 1,200 feet of paper per minute, which produces 792,000 magazine pages per hour. It is a tribute to Canadian print-

ing craftsmen that, at this tremendous speed, excellent colour reproduction is obtained on many varied subjects, all printed at the same time. Since this piece of equipment folds as well as prints, the ink must be dried rapidly to prevent smudging. To perform this function large dryers are included on the press. Heat may be supplied by a gas flame, recirculating hot air, steam drum, or a combination of any or all of these. Drying is largely absorption of the oils and oxidation of the solvent. To expedite drying, the ink contains a volatile solvent having a flash point ( the point at which the solvent is released) of 415 to 615°F. The paper leaves the heaters and passes over water-cooled drums which harden the ink and reduce the temperature of the paper. The machine then folds the paper into page size. The final product

Fie:. 6. Magazine presses.

CANADA'S NATIONAL MAGAZINES

is known as a signature and may be composed of sections of four, eight, twelve, sixteen, or twenty pages depending upon the requirements of the magazine. The signatures are transported from the pressroom to the bindery. Meanwhile the covers are being printed. Plates are put on the press as described earlier. A heavier weight of paper is used and fed to the press in sheets rather than from a roll. Eight pages are printed at one time on one side of the sheet only. The press is run more slowly-5,000 sheets each houreliminating any extensive use of drying equipment. Ink for cover printing contains dryers which are primarily cobalt; some lead manganese may also be used. In the bindery, the sheets on which the covers have been printed are cut; the covers are folded and moved to the

163

binding machine ready for assembly with the signatures ( the inside pages). Two types of magazine binding are popular. One is known as saddle stitching, the other as side wire stitching. Saddle stitching requires successi~e pages of the magazine and finally the cover to be dropped over a saddle. Cover and pages are bound together by stitching wire driven through the back of the book. Side wire stitching requires the pages of the book to be laid flat; the last page of the book is placed in position first and all other pages, which are in signature form, are laid successively on top. Wire stitches are then driven through the side of the book and a cover is glued over the stitched pages. The magazines resulting from either of the stitching methods are trimmed to size ready for mailing to subscribers and

Fir.. 7. Saddle stitch binding.

164

MANUFACTURING PROCESSES IN CANADA

Fm. 8. Affixing address labels.

for sale on newsstands. Those to be mailed are sent through automatic mailing machines, which have been provide.cl with rolls of mailing labels bearing the subscriber's name and address. Each magazine, moving through the mailing machine, is stamped with an address label. The sequence of labels, which were printed earlier, is established in co-operation with the Post Office and relieves the postman of his sorting problem. The magazines are bundled, therefore, according to town and postal district or its equivalent, placed in appropriate mail bags, and delivered to the Post Office for distribution across the nation. Magazines that are to appear on newsstands are sent by truck and by rail to wholesale dealers who, in turn, distribute them to the local newsstands. The whole process is subject to

extremely rigid scheduling as it is important that magazines go on sale in Kelowna, B.C., or Kentville, N.S., on the same day on which they are available in metropolitan areas such as Montreal and Toronto. The magazine manufacturing industry is alive to new techniques that will improve quality and reduce costs. Already, the use of photographic film in place of lead type has moved beyond the experimental stage as has the electronic separation of colours for photoengravings. In the printing-plate field the search is for lighter materials that can be processed faster; magnesium and aluminum are both showing promise. Printing presses must run faster and faster to meet deadlines so that the needs of Canada's growing number of magazine readers may be served.

165

CANADA'S NATIONAL MAGAZINES

Articles Fiction

Ad Copy

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FIG. 9. Flow chart.

Petroleum BY G. A. PURDY IMPERIAL OIL LIMITED

THE KEY to Canada's progress has been the use of mechanical power. A hundred years ago when men and animals did most of the work, the return was small, whether the produce was food, tools, clothing, or building materials. Now, men have more leisure than ever before, but their ability to produce has been increased many times by powered machines. The energy for the machines comes from water power ( as electricity), coal, natural gas, and petroleum. Of these, petroleum is the greatest source of energy for power and heat in both Canada and the United States. In 1956 petroleum supplied 44 per cent of the energy consumed in the United States and 52 per cent of the energy consumed in Canada. Petroleum meets the requirements of modern industrial expansion better than any other energy source. Because petroleum is a liquid, it can easily be pumped wherever pipes can be laid-from oil field to refinery or from oil tank to engine. When burned, it provides heat without ash. A pound of petroleum provides as much heat as a pound and a third of coal, a pound and a half of alcohol, two and a half pounds of wood, or seven pounds of dynamite. Because of its high energy content, it is the only fuel suitable for aircraft. It permits ships to travel three times farther without refuelling than any other fuel except atomic energy. In diesel engines, it pulls bigger trains farther and faster at lower cost than steam locomotives. A farmer with hand tools would require thirty times as many hours to produce an

acre of wheat as would a farmer with petroleum-powered equipment. In Canada in 1957, petroleum supplied the power for half a million tractors, heated more than half of the four million dwellings, and provided power for over four and a half million of the country's motor vehicles. Almost three-quarters of Canada's railroad locomotives and practically all of its lake- and ocean-going ships obtained their power from petroleum. Approximately 90 per cent of petroleum is used for heat, light, and power. The remainder is the source of products without which the modern world would be impossible. In the form of lubricants, petroleum is essential to the operation of every machine regardless of the kind of fuel that powers it. Petroleum solvents have a place in products and operations ranging from paints to tire manufacture. Asphalts from petroleum are used in the construction of paved roads, airport runways, roofs, asphalt shingles, electrical insulations, and tires. Thousands of tons of waxes from petroleum are used annually in the food packaging industry for bread wrap, milk cartons, and the like. In one form or another petroleum is part of, or used in the manufacture of, almost everything we eat, use, and wear. Besides all this, petroleum is the raw material from which over half a million organic chemicals can be made, although only a few thousand are so made as yet. Hydrocarbons with new and different properties are made by tearing apart and rebuilding petroleum hydro-

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carbons. These synthesized hydrocarbons are the sources of the organic chemicals called petrochemicals from which thousands of modem commodities are made. Polyethylene "squeeze" bottles, plastic hose, synthetic tires, orion, nylon, rayon, dacron, terylene, and other synthetic fibres, household detergents, fertilizers, foam rubber, and latex-base paints are examples.

Development of the Petroleum Industry Although petroleum has been used as a burning oil, medicine, and waterproof cement since civilization began, its use was limited to the amount of oil or asphalt found at the surface of the earth. Some of the oil seepages and asphalt deposits such as those at Hit on the Euphrates River and at Baku on the Caspian Sea supported local oil industries of considerable size as long as six thousand years ago. The modem petroleum industry, however, began just a century ago. The incentive that led to its development was the need for an oil that would bum in lamps. Whales had been the chief source of such an oil, but as the middle of the nineteenth century approached the supply of whale oil decreased as the demand increased. By 1850 methods had been developed to distil a lamp oil from coal and during the next ten years "coal oil" became an important article of manufacture in Great Britain and the United States. A few men wondered if the scanty and uncertain supply of petroleum from seepages could be increased sufficiently to make petroleum an important source of lamp oil. The hunt for petroleum in Canada and the United States followed remarkably similar courses but the hunt began earlier, and in the earlier stages developed faster, in Canada. The Canadian story began in a swampy forest some twenty miles southeast of Samia, Ontario, where previous to 1850 oil had been seen on Black Creek ( a tributary of the Sydenham River) and patches of asphalt called

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"gum beds" had been discovered nearby. By 1852 Charles Nelson Tripp of Brantford had formed North America's first oil company to recover asphalt from the gum beds. He actually produced some asphalt in what was then a wilderness, but his company failed. In 1856 he sold his oil lands to a successful Hamilton business man, James Miller Williams. A year later Williams became the father of the North American petroleum industry by being the first to dig for petroleum, find it in ample commercial quantities, and distil from it a lamp oil which he sold for a dollar a gallon. J. M. Williams and Company continued as a successful oil company for over twenty years. Interest in the commercial development of petroleum in the United States began at about the same time as in Canada, but the first production of oil did not occur until 1859 when Edwin L. Drake drilled a 69-foot well into an oil seep on Oil Creek near Titusville, Pennsylvania. News of the Titusville discovery spread quickly and the United States petroleum industry literally sprang into being over night. As the search for oil spread over the United States, oil was found in great quantities and the petroleum industry expanded at a fantastic rate. The United States quickly became the world's leading oil nation, a distinction it continues to hold. The search for oil in Canada provided a sad contrast. Except for a small and short-lived field found in New Brunswick in 1875, the search for oil elsewhere in Canada was unsuccessful for over sixty years. Even with the discovery of oil in the Turner Valley near Calgary in 1934, Canadian petroleum supplied less than 10 per cent of the country's needs until 1948. Two years before, an Imperial Oil drilling rig had been located some sixteen miles southeast of Edmonton, to find oil-or drill the company's 134th dry hole in the

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Canadian West. On February 13, 1947, the drill released the first of the great Hood of oil which has made Canada an important oil nation. The Source of Petroleum Petroleum comes from sedimentary rock formations 10 million to 400 million years old. Its origin is a question for research and conjecture with the final answer still to be discovered. Indications are that petroleum was formed from organisms, mostly of microscopic size, which lived in immense numbers in the warm, shallow seas along the edges of the continents. When these organisms died their remains fell to the sea floor and were buried by sediments which, in time, became sedimentary rock. A commonly accepted theory holds that bacteria, which do not require oxygen to live, converted the fats of these buried remains into fatty acids which were then converted, by unknown means, into an asphalt-like material sometimes called kerogen. In the course of millions of years, kerogen was changed into petroleum by the heat and pressure generated as the sediments were consolidated into rock by the weight of later deposits. Oil is not usually found in the finegrained, relatively impervious shales and limestones, called source rocks, in which it was first entombed but rather in open sandstones and porous limestones called reservoir rocks that occur in the same general region as the source rocks. In all probability the oil was squeezed out of the sediments when these were compacted into rock, together with gas, created when the oil was formed, and large quantities of ancient sea water. The water, oil, and gas moved sideways and upward through the pores of sandstones and the cracks of limestones until they either escaped to the surface leaving behind only an asphaltic deposit, or were stopped by an impervious rock structure which forced them to accumulate in the

reservoir rocks. The dense rock stopping the upward movement is called the cap rock. As a mixture of gas, oil, and water accumulates under a cap rock, a vertical separation takes place because of the difference in weight in the three materials. Gas collects at the highest places and water at the lowest with oil in between. The gas, oil, and water fill the interstices of the reservoir rock. Oil does not exist in underground caverns or pools although the term oil pool is nearly always used to describe an oil accumulation. Prospecting Accumulations of oil are rarely marked by any surface indication. The finding of oil requires elaborate investigation, much deductive reasoning, and luck. The key men in the search are the petroleum geologists who make a threedimensional map of any region that has oil possibilities and mark on it the location and depth of rock traps that might contain oil. Their search takes place in areas composed of sedimentary rocks that have been formed by the consolidation of silt, sand, or lime deposited from seas that no longer exist. In an unexplored area, aerial photographs may be taken from which a generalized map can be drawn. In particular, the aerial photographs will show where rock strata are exposed and may reveal surface formations that hint at the structure of rock beds below. The exposed rock, however, is where the geologists must work. Mountains that have pushed up and exposed the edges of the rock strata buried underneath neighbouring plains are common hunting grounds for geological information. The geologists identify the exposed rock strata, measure the angles at which they dip and strike, trace rock faults, and, in general, learn from the exposed edges of the strata whatever they can to help them locate these strata under the plains below.

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On the plains the rock strata are largely buried under soil but here and there the rock may peak above the surface or be cut into by a river. Wherever the geologists can get at the rock strata they relate them with those observed on the edges of the plains

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Frequently, as in many parts of the Canadian prairies, the over-burden is so thick that examination of rock exposures and drill cores cannot provide sufficient information to plot the contours of the deeply buried strata. In such cases the geologists enlist the aid

FIG. 1. Reservoir rock. This drill core shows the porous nature of rock in which crude petroleum accumulates. ( Courtesy of Imperial Oil Limited. )

and attempt to draw a map showing the contours of the buried rock structures. Where nature has not sufficiently exposed the rock for study, the geologists will call for a core-drilling rig which will cut and remove from the earth a cylindrical cross-section of subterranean strata to a depth of a thousand feet or more.

of geophysicists who use physical forces to map subterranean structures. The most useful instrument for geophysical prospecting is the reflection seismograph. It records shock waves which are created by exploding dynamite and reflected from underground strata. The difference in time between the initial explosion and the arrival of

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MANUFACTURING PROCESSES IN CANADA

a reflected shock wave is a measure of the depth of the reflecting rock surface. By noting the time difference at a number of stations, the geophysicists can map the contour of an underlying rock strata. Other techniques employ the gravity meter which measures variations in the force of gravity caused by the type and location of subterranean rock formations , and the magnetometer which measures magnetic variations. Electric and radioactive logging methods are used to supplement geological information after a well is drilled. In electric logging the resistivity of rock strata at various depths is measured by an electrode that travels down a well. Variations in the resistivity indicate the type of rock encountered. Since the travelling electrode must touch the rock in the bore hole, electric logging can be carried out only in uncased wells. Radioactive logging may be carried out in cased wells since the gamma radiation on which the method depends readily penetrates steel pipe. The different amounts of gamma radiation emitted ( or reflected) by the different types of rock are measured by an ionization chamber ( similar to a Geiger counter) that is lowered down the well. In both radioactive and electric logging, a record is obtained which can be interpreted in terms of the types of rock encountered and the occurrence of water, gas, and oil. Despite the great amount of work, the use of the highest technological skill, and the expenditure of vast amounts of money, the chances of finding oil with the first well in a new area are slight. From 1947 to 1957, despite the great increase in geological information made available by Leduc, only one exploratory well in 75 discovered an oil field with a million or more barrels of oil. A commercial field is sometimes considered to be one with a reserve of two million barrels-enough

oil to supply Canada for less than three days. Drilling After the site of a potential well has been selected and a road built to the site, the drilling crew moves in with its equipment. The type of equipment will depend on whether the well is to be drilled by the cable tool or rotary method. Cable tools were originated many centuries ago in China where they were used to drill for salt and water. Prior to 1900, all oil wells were drilled by this system. Drillers around Petrolia used cable tools exclusively and developed such superior ones, particularly for working in difficult formations, that their equipment became internationally known as the Canadian rig. The rotary method, which is the most widely used today, was used first about 1900. It received much publicity when a rotarydrilled well brought in the Spindletop field at Beaumont, Texas, in 1901. This was the greatest oil field discovered up to that time; the discovery well gushed oil at a rate greater than the entire production of the rest of the United States. The two systems have certain features in common. Both require a derrick to support the drilling equipment and power to do the work of drilling. Both pulverize the rock being drilled-the cable tool by a pounding action, rotary tools by a cutting or grinding action. A cable tool rig is a two- to five-ton string of tools ending in a chisel-edged bit. The string of tools is lifted, turned, and dropped repeatedly. The bit chips and pulverizes the rock at the bottom of the hole. From time to time, the string of tools is run out of the hole and a bailer is run in to remove the sludge of rock particles and water that accumulates in the bore hole. The cable tool system in some cases has certain advantages over the rotary system. The equipment costs less, fewer men are needed to operate it, and it

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Fm. 2. A mobile drilling rig such as this can be lowered to large trucks and transported as a unit to another well site. Note the stand of drill pipe to the left of the derrick. ( Courtesy of Imperial Oil Limited. )

penetrates the hardest rock at an adequate rate. Cable tools are usually used for wells that are less than 2,000 feet in depth; the shallow wells typical of Ontario are commonly drilled with cable tools. A cable tool rig will make 20 to 150 feet of hole a day depending on the kind of rock being penetrated. A rotary rig which will make 100 to 300 feet of hole a day is generally preferred to the cable tool system for most rock formations because it drills much faster, penetrates to much greater depths, and is less costly than the cable

tool rig to drill deep holes. Wells in the Canadian West are almost invariably drilled by the rotary system. In rotary drilling a fish-tail or coneand-roller bit at the end of a hollow drill stem is rotated against the rock at the bottom of the bore hole. Drilling mud is continuously pumped down the drill stem and out through holes in the bit. The mud cools the bit and picks up the rock cuttings and carries them to the surface in the space between the drill and the bore hole. While in contact with the bore hole, the mud performs a

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MANUFACTURING PROCESSES IN CANADA

valuable service by plastering it and thus preventing caving and shutting off the flow of unwanted water or gas. If the bit encounters a stratum with a high gas pressure, the weight of mud in the drill stem and bore hole controls the pressure and prevents the well from "blowing." When a rotary bit becomes dull, the drilling stem, which may weigh as much as 100 tons, is pulled from the hole by means of a powered pulley system suspended from the top of the derrick. The drill stem is unscrewed in sections and stored within the derrick. When caving of the bore hole or ingress of water hampers drilling, the drill stem is pulled out and a string of casing is run to the bottom of the hole and cemented in place. Drilling is then continued with a bit that fits within the casing. If unfavourable formations are encountered at lower depths, more strings of casing are run into the hole, one nesting within another. In cable tool drilling half-a-dozen strings of casing may be required; fewer strings are needed in rotary drilling because of the plastering effect of the mud. When a bore hole enters a producing zone, a drill stem test may be run to learn if the production is worth the cost of running more casing. The drill stem is pulled from the hole and at the same time the hole is kept full of mud adjusted in weight so that it is heavy enough to keep the well from blowing. The bit is replaced with a valve that seals the end of the drill stem until it reaches the bottom of the well. Opening the valve permits oil to flow into the empty drill stem at a rate dependent on the pressure, porosity, and permeability of the oil-containing rock formation. If the oil rises to the surface, samples can be collected for examination. If, as frequently happens, the oil rises only part way, the valve at the bottom of the drill stem is closed and the oil in the drill stem is recovered when the drill stem is pulled up.

Sometimes it is necessary to encourage the flow of oil when tight formations are encountered. In the past, a charge of nitroglycerine was lowered into the well and detonated to fracture the rock. Much safer solid explosives are now used for the same purpose. If the surrounding formation is predominantly limestone, it may be opened up by pumping hydrochloric acid down the hole. The acid, which can be inhibited to protect the steel casing, dissolves channels in the limestone. Another process which has recently been introduced to open up sandstones is called hydraulic fracturing. A fluid with a viscosity high enough to hold coarse sand in suspension is pumped under very high pressure into the oilproducing formation. Fractures made by the high pressure are kept open by the grains of sand acting as props. Casing may be cemented in place above the producing area, or it may be run entirely through the oil-bearing stratum. In the second instance, holes must be made in the casing so that oil can get into the well. This is accomplished with a gun perforator. The gun is a cylindrical assembly which can be lowered by cable down the well and which fires a radial pattern of bullets as desired. The bullets go through casing and cement and into the formation. Cone-shaped charges have recently been used in place of bullets. The highvelocity, high-temperature jet formed when the charge is ignited bums a hole several inches into the rock formation. Production During the early days of the industry, the main consideration was to obtain as much oil as possible in the least possible time; about four barrels of oil were left in the ground, and usually lost forever, for every barrel that reached the surface. Since then much has been learned about the geological structure of oil fields and about the natural forces that cause the movement of oil. Special

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techniques developed by production engineers remove about half of the oil from the earth in general and up to 70 per cent of the potential in some fields. Laws based on the findings of production engineers regulate the spacing of oil wells and the rates at which the wells are allowed to produce oil. These conservation measures are extended by the use of secondary recovery methods whereby gas or water is pumped into oil-producing formations to force more oil to the producing wells. By such means, oil fields abandoned long ago have been brought into production again. Oil is forced through the void spaces of rock to a producing well and then up the well to the surface by pressure exerted on the oil by gas or water. In a new field the pressure is usually the same as the pressure that would be exerted by a column of water extending from the surface to the formation. At a depth of 5,000 feet, pressures of about 2,000 pounds per square inch are commonly encountered. In some wells, pressure is created by gas that has accumulated above the oil and under the cap rock. This gas-cap drive yields oil recoveries ranging from 25 to 50 per cent. In other cases the gas is dissolved in the oil and the driving force is known as dissolved-gas drive. The lower pressure in the well causes the gas in the formation to move to the well taking the oil with it. Since the gas tends to leave the oil behind, dissolved-gas drive is less effective in recovering oil than is gas-cap drive; its yield is about 10 to 30 per cent. Water drive is the most efficient means, and recoveries up to 70 per cent have sometimes been obtained. Salt water in vast quantities and under high pressure often surrounds oil traps. The pressure is such that the water is actually compressed. When a well provides a low pressure point in the formation, the water can expand one part in 2,500 for each drop in pressure of 100 pounds per square inch. In addition,

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the hydrostatic pressure of the water is available when the compressive force is utilized. By moving in behind the oil the water tends to lift the oil from the pores of the reservoir rock and to sweep it towards the wells. Oil is brought to the surface by tubing about two and a half inches in diameter hanging freely within the casing. At the surface and attached to the casing and the tubing is a group of valves, gauges, and pipes called a "Christmas tree" which controls the flow of oil and gas, records the pressures in the tubing and the casing, and permits access to the well for tests and servicing. Back in the days before the gas was saved, the mixture from the well flowed as a foaming stream into an open tank where the gas escaped to the atmosphere. Now, however, the line from the "Christmas tree" connects to a gas and oil separator which is essentially a vertical cylinder in which oil falls to the bottom while gas collects at the top. To make the separation more complete, screens and baffles are built into the separator and several separators may be used in series, each at a lower pressure than the preceding one. From the separator, the gas passes by pipeline to a processing plant where the gas is scrubbed with a chemical solution to remove hydrogen sulphide and carbon dioxide and is then separated by distillation or absorption processes into, usually, three parts: dry gas (methane and ethane) which is used as natural gas or is pumped underground to repressure oil-producing formations; liquefied petroleum gas (LPG) which consists of propane or butane or mixtures of these and is used as a fuel; and natural gasoline or casinghead gasoline which may be used as a highly volatile component of motor gasoline. When the driving force in an oil reservoir falls to the point where it will not lift the oil to the well head, some method of artificial lift such as a pump must be used. The pump is located at

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the bottom of the well on the end of the tubing with a sucker rod extending up the inside of the tubing to the surface. The sucker rod opens and closes valves in the pump so that, on a downstroke, oil that surrounds the pump flows into the pump, and, on the upstroke, oil is lifted up the tubing. A pumping unit or a pump jack located at the well head operates the sucker rod. Several wells are frequently pumped by means of one pumping unit with a pumping jack at each well. Oil wells usually have a definite life, although some of the first found in Ontario and Pennsylvania are still pumping a little oil each day. Generally the wells start with a flush period when the oil reaches the surface by the forces of nature. The flush period gives way to a settled period and then the well goes on the pump and becomes a stripper. In 1957 the estimated number of producing oil wells in the world ( not including areas controlled by the U.S.S.R.) was 614,568. Of these, 559,000 were in the United States and 11,600 in Canada. Oil production for the world ( including Russia) amounted to 17,530,000 barrels a day. The United States produced 7,160,000 barrels a day and Canada 494,800 barrels a day. Refining Petroleum refining is the separation of crude petroleum into portions or fractions and the subsequent treating or changing of these fractions as needed to make them into petroleum products. Most petroleum products including aliphatic solvents, kerosenes, fuel oils, lubricating oils, and waxes are fractions of crude petroleum treated to remove undesirable components. To some of these, non-petroleum materials may be added to enhance their usefulness. For example, soap is added to lubricating oils to make greases. Other products such as motor and aviation gasolines, aromatic solvents, and some asphalts

are totally or in part synthetic in the sense that they have compositions impossible to achieve by direct separation of fractions from crude petroleum. They result from chemical processes that change the molecular nature of selected portions of crude petroleum. Similar processes are used to make petrochemicals. A petroleum refinery is a group of manufacturing plants or units which varies in number with the variety of products produced. Most of these plants have a superficial similarity. A room lined with recording and control instruments, pumps of various kinds and sizes, distillation towers with attendant furnaces and heat exchangers, and a group of tanks are common parts of most refining plants. Each plant, however, has particular equipment such as reactors, regenerators, treating towers, and filters with which it carries out its specific function. While the processes are basically simple, the plants themselves are complex and their operation requires highly specialized knowledge. Each refinery uses the processes that can most economically manufacture the products needed for its market. While distillation, cracking, and treating are common to all refineries, these processes take such different forms that even the simplest refinery is unlike any other. Refineries become more complex and require more processes as the variety of products they manufacture increases. A refinery with half a dozen processes including distillation and cracking can produce gasolines, kerosene, and fuel oils. The manufacture of solvents requires two or three more processes; lubricating oil production the addition of at least five more; waxes another two or more. Asphalts, greases, coke, gear oils, liquefied petroleum gases, alkylate, and all the other kinds of products that can be made require half a hundred different processes. The processing units in a refinery are very costly. A crude petroleum dis-

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FIG. 3. Petroleum refinery. Crude petroleum is separated into fractions in the unit at the left; some of the fractions are processed into gasoline components ( cracked gasoline, polymer gasoline, light naphthas, butane) in the plants on the right. Units required for solvents, lubricating oils, waxes, greases, and asphalts are not shown. ( Courtesy of Imperial Oil Limited. )

tillation unit capable of handling 50,000 barrels of crude petroleum per day costs five million dollars or more. A treating plant which accomplishes only one step in the manufacture of a lubricating oil costs well over one million dollars. A complete refinery capable of producing gasoline, fuel oils, lubricating oils, greases, and asphalts costs twentyfive to a hundred million dollars depending on its size. In general, refinery construction costs fifteen hundred dollars or more per barrel of operating capacity. Since the market for petroleum products is highly competitive, processes are continually being modified and . replaced to make better products. For example, many costly catalytic reforming units are now being built for the sole purpose of improving the quality of gasoline. Petroleum refining begins with the distillation of crude petroleum into fractions. The nature of the fractions depends on the composition of the crude petroleum and on the type of finished products needed. Some crude petroleums do not have hydrocarbons that are

suitable for all needed products. For example, the fraction boiling in the kerosene range may be too aromatic for use as a kerosene. In this case the crude oil is distilled or run so that most of the kerosene fraction is included in a furnace fuel oil fraction and another crude oil must be obtained for the production of kerosene. A crude oil composed of suitable hydrocarbons, however, cannot produce all needed fractions at the same time. For example, the boiling range of stove oil overlaps that of kerosene; a crude oil that is run at one time for kerosene must be run at another time and in a different way for stove oil. Thus crude oils are separated into various proportions to produce fractions with different boiling ranges. The fractions may have the boiling ranges needed in finished products or fractions may be combined or blended to form the boiling range required. Fractions into which crude petroleums are commonly separated are given, with their boiling ranges, in Table I. The fractions down to and including

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:\IANUFACTURING PROCESSES IN CANADA

TABLE I CRUDE PETROLEUM FRACTI01'S

Fraction

Approximate . boiling range °F

Fuel gas

-259 to -44 -44

Propane Butane Light naphtha

30 to 300

Heavy naphtha

300 to 400

Kerosene 1

400 to 500

Stove oil

400 to 550

Light gas oil Heavy gas oil Vacuum gas oil

400 to 600 600 to 800 800 to 1100

Pitch

11 to 31

1100+

Uses Consists of methane, ethane and some propane; used as refinery fuel Liquefied petroleum gas Blended with motor gasoline to increase its volatility Component of motor gasoline; solvents; combined with heavy naphtha may be used as feed stock for catalytic reforming Catalytic reformer feed stock; solvents; blended with light gas oil to form jet fuels For wick type burners; available only from certain crude oils Same as kerosene but with a higher end point; blended with light gas oil to reduce its pour point Furnace fuel oil; diesel fuels Feed stock for catalytic cracking Feed stock for catalytic cracking; component in some fuels oils and diesel fuels; source of lubricating oil fractions Asphalts; heavy fuel oil when fluxed to proper viscosity with gas oils

1The kerosene, stove oil, and light gas oil fractions together are referred to as middle distillates.

heavy gas oil are separated from one another by distillation at atmospheric pressure. The portion not distilled consists of vacuum gas oils and pitch and is called reduced crude. Distillation under vacuum separates the vacuum gas oils from the pitch. By distillation under vacuum, vaporization takes place at temperatures that do not harm (crack) the petroleum components. If the reduced crude is of suitable composition, the vacuum gas oils may be separated into three lubrication oil fractions and a heavy gas oil. In general, none of the fractions or combinations of fractions as separated from crude petroleum are suitable for use as petroleum products. Each must be separately refined by treatments and processes which vary with the impurities in the fraction and the properties required in the finished product. The simplest treatment is the washing of a fraction with a caustic solution to remove sulphur compounds. The most complex is the series of treatmentssolvent treating, solvent dewaxing, clay treating or treatment with hydrogen,

and blending-required to produce lubricating oils. On rare occasions no treatment of any kind is required; some crude petroleums yield a light gas oil fraction that is suitable as furnace fuel oil or as a diesel fuel. The subdivision of crude petroleum into fractions and the subsequent processing of the fractions into products is shown in a simplified form in Figure 4. Many refineries produce more products and use more and different processes than indicated. The diagram illustrates both the complexity of a modem petroleum refinery and the impossibility of discussing all refining processes within the limitations of this chapter. The subsequent section on refining is restricted to a discussion of the manufacture of the most important petroleum product, motor gasoline. Manufacture of Gasoline For almost half a century gasoline has been the most important refinery product. During that time gasoline has changed from a simple fraction from crude petroleum to a blend of a num-

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t

TO PETROCHEMICALS

'

DISTILLATION

L

G AS Oil

EXTRACT

CRUDE WAX

✓ CRACKED

LIQUEF IED PETROLEUM

I DIESEL

MOTOR GASOLI NE

FUEL 01ts

FURNACE FUEL OILS

GAS

l

GRE~SES

I

LUBRICATING OILS

wlxes

I

AJH ALTS

HEAVY FU EL OILS

KEROSENE ANO STOVE OILS

Fie. 4. Flow through a refinery. This diagram shows only one of the many ways that crude petroleum may be subdivided into primary fractions and processed into products. Only the more important units have been shown. The volume of flow is approximately porportional to the diameter of the pipes in the diagram. ( Courtesy of Imperial Oil Limited. )

her of fractions most of which are manufactured by special processes. More research has been done on how to make and use gasoline than has been done on any other material. Consequently, methods of manufacturing have changed with the years as research has found better ways of making better gasolines. More equipment is used in the manu-

facture of gasoline, the equipment is more elaborate, and the processes more complex than for any other product. Among the processes used are thermal cracking, catalytic cracking, thermal reforming, catalytic reforming, polymerization, alkylation, coking, and the distillation of fractions directly from crude petroleum. Each of these processes may be carried out in a number

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MANUFACTURING PROCESSES IN CANADA

of ways differing in details of operation or in essential equipment or in both. For example, five catalytic cracking processes are now in common use. Since it is not uncommon for five or more other processes to be used in addition to catalytic cracking, the technical complexity of modern gasoline and of its manufacture is apparent. Before 1900 when kerosene was the chief product, gasoline was the portion of crude petroleum too volatile to be included in kerosene. The early refiners considered it a necessary evil because there was little use for it, and its disposal was dangerous. In time, uses were developed for gasoline. Varnish and paint makers used it as a solvent and

special lamps burned it to illuminate parks and streets. Some large buildings and factories made their own gas supply from gasoline. Naphtha launches, the sporty speed boats of the late nineteenth century, used gasoline as the fuel for their steam boilers. The supply of gasoline, however, was usually greater than the demand. One of the first major advertising campaigns carried out in the United States was for the purpose of selling surplus gasoline; in 1898 the American housewife was sold on the idea of using "cool, convenient and economical" gasoline stoves, and within a year gasoline was in short supply. Contributing to the gasoline shortage

FIG. 5. Atmospheric and vacuum distillation unit. The first step in the manufacture of motor gasoline is the separation of crude petroleum into fractions in this unit. ( Courtesy Imperial Oil Limited. )

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was a small and little-noted consumption in the internal combustion engines of the first automobiles. Within a few years the amazing growth in the number of automobiles changed what had been a problem product into a most valuable and very essential product. Gasoline and naphtha sales in Canada more than doubled in the period from 1906 to 1910 to reach 200,000 barrels a year. In the United States, production of gasoline and naphtha reached 11 million barrels in 1911, exceeding kerosene production for the first time. Although there were only 21,783 motor vehicles registered in Canada in 1911 the problem of satisfying their voracious appetites for gasoline was looming in the near future. When gasoline was unwanted, as much as possible of the lower boiling portion of crude oil was included in kerosene. Some of this lower boiling portion, amounting to 5 to 10 per cent of the crude oil, was too volatile to include in kerosene and was segregated as gasoline. As the demand for gasoline increased, more and more of the lighter kerosene components were included in gasoline up to the point where gasoline engines refused to digest them. The maximum suitable portion depended on the kind of crude oil and rarely exceeded 20 per cent of it in volume. To increase the supply of gasoline, more crude oil was run to the stills resulting in over-production of the heavier petroleum fractions, including kerosene. The problem of how to get more gasoline from less crude oil was solved in 1913 by the use of cracking. By this process fractions heavier than gasoline were converted into gasoline. The cracking process was the first of a number of processes developed during the past forty-five years to increase the volume or improve the quality of gasolines. These processes are discussed in the following paragraphs. Cracking. The term cracking means chemical decomposition by heat. Hea-

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vier oils are decomposed or cracked to lower boiling gases and gasoline. At the same time, higher boiling materials such as tars and coke are produced. The first cracking processes, which utilized only heat and pressure, are known as thermal cracking processes. Processes developed since the late 1930's utilize catalysts in addition to heat and pressure and are known as catalytic cracking processes. The first commercial cracking of petroleum for gasoline in 1913 was the most important technical development in the history of petroleum refining. Its importance rests not only on its ability to increase the supply of gasoline but on the fact that it successfully demonstrated that hydrocarbons as made by nature could be changed by practical means into other and more useful hydrocarbons. This provided the incentive to study ways and means of taking hydrocarbons apart and rebuilding them into new materials. As a result, new cracking processes were developed and other gasoline manufacturing processes such as reforming, polymerization, and alkylation came into being. Of current great importance are the synthetic fibers, plastics, rubbers, detergents, and other organic chemicals made by processes many of which have their roots in the cracking process. Petroleum hydrocarbons undergo cracking when subjected to temperatures over 650°F. The larger the hydrocarbon molecule, the higher the temperature, and the longer the time of heating, the greater wi11 be the amount of decomposition that takes place. Sufficiently high temperatures will convert oils entirely to gases and coke. Cracking conditions are controlled to produce as much as possible of the desired product, which is usually gasoline but which may be gases for petrochemicals or an oil of low viscosity for use as a fuel oil. The conditions that control cracking are temperature, length of time of heating, pressure, use of cata-

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MANUFACTURING PROCESSES IN CANADA

lysts, and the composition of the oil being cracked. Oil suitable for cracking, called cracking feed or cracking stock, may be almost any fraction obtained from crude petroleum. By far the greatest amount of cracking is carried out on gas oils-a term which is used to designate the portion of crude oil boiling between furnace fuel oil and pitch. Fractions containing pitch ( reduced crude) are also cracked, Cracking, as carried out to produce gasoline, breaks up large hydrocarbon molecules into hydrocarbon fragments of various sizes. The smallest fragments are hydrocarbon gases. Larger fragments are hydrocarbons that boil in the gasoline range. Some of the fragments join together to form molecules larger than those in the oil being cracked. The large fragments form heavy oils, tar, and coke. Consequently a series of hydrocarbons with a boiling range the same as for crude petroleum is created by cracking. The cracked material, however, is quite different from crude petroleum. It contains twice as much material boiling in the gasoline range but no fractions suitable for kerosene, lubricating oils, or wax, and little or no material suitable for asphalt. It does contain gas oils and residual oils suitable for light and heavy fuel oils and a much larger proportion of gases than is associated with crude petroleum as delivered to a refinery. From the chemical viewpoint too the products of cracking are very different from those obtained directly from crude petroleum. Cracked products contain paraffin, isoparaffin, naphthene, and aromatic hydrocarbons as does crude petroleum, but the proportions are different. In particular, cracked products contain large quantities of olefin hydrocarbons not found in crude petroleum. The proportion of isoparaffin and aromatic hydrocarbons in cracked material boiling in the gasoline range is higher than in gasoline fractions obtained

directly from crude petroleum. Since olefins, aromatics, and isoparaffins have high octane numbers, cracked gasolines have higher octane numbers than natural or straight-run gasolines. The high proportion of olefins and aromatics means that the portions boiling in the kerosene and lubricating oil ranges cannot be used as such. Olefins and aromatics cause a smoky flame from kerosenes and cause sludge in a lubricating oil. The gases formed by cracking are particularly important because of their chemical properties and their quantity. Only relatively small amounts of paraffinic gases are obtained from crude petroleum and these are chemically inactive. Cracking produces both paraffinic and olefinic gases, the latter being very active chemically. Olefinic gases are used in the refinery as the feed for polymerization plants in which high octane polymer gasoline is made. In some refineries the gases are used to make alkylate, a high octane component for aviation and motor gasolines. In particular, the cracked gases are the starting points for many petrochemicals. The first successful cracking operation to produce gasoline was developed by Dr. William H. Burton of the Standard Oil Company (Indiana) in 1913. Imperial Oil was the first company to obtain a licence to use the Burton process and built the first cracking units in Canada at its Samia refinery in 1914. The Burton process, known as pressure cracking, was a batch operation in which some 200 barrels of gas oil were heated to about 800°F in shell stills especially reinforced to operate at pressures as high as 95 pounds per square inch. After 24 hours in the still about one-half of the gas oil was converted to cracked gasoline which was then removed by distillation. While pressure cracking had successfully increased the gasoline supply, the search was continued for a better process which would produce cracked

PETROLEUM

gasoline at a faster rate and with less labour. During and after World War I a number of successful continuous cracking processes were developed. By these processes gas oil was continuously pumped through a unit that heated the gas oil to the required temperature, held it for the proper time under a suitable pressure, and then discharged the cracked material into distillation equipment. The tube and tank cracking process developed by the Standard Oil Company (New Jersey) is typical of the early continuous cracking processes. Gas oil was pumped through the cracking coil which consisted of several hundred feet of very strong pipe that lined the inner walls of a furnace. Here oil or gas burners raised the temperature of the gas oil to 800°F under a pressure of 350 pounds per square inch. The heated gas oil passed from the cracking coil into a large reaction chamber or soaker where the gas oil was held under the high temperature and pressure conditions long enough for the cracking reactions to be completed. The cracking reactions formed coke which in the course of days filled the soaker with a solid mass. When a soaker was filled with coke, the gas oil stream was switched to a second soaker and the first soaker was cleaned out by drilling operations similar to those used in drilling an oil well. The cracked material ( other than coke) left the operating soaker to enter an evaporator or tar separator, a tanklike vessel maintained under a much lower pressure than the soaker. Because of the lowered pressure all of the cracked material in the tar separator except the tar changed to vapour. The tar was pumped away for use as a special asphalt or as a heavy fuel oil. The vapour left the top of the tar separator to be distilled into cracked gases, cracked gasoline, and cracked gas oil. The last could be pumped back through the cracking coil to produce more cracked gasoline ( recycle opera-

181

tion) or could be used as an industrial fuel oil. Imperial Oil constructed the first tube and tank cracking units in Canada at its Calgary refinery in 1923. Tube and tank cracking units or similar thermal cracking units became part of almost every refinery in Canada and the United States. The original incentive to develop cracking processes was the need to increase the supply of gasoline. Since cracking could double the volume of gasoline from a barrel of crude oil, this purpose was realized. A second and equally important purpose was not recognized until well into the 1920's. This evolved from the ability of cracked gasoline to prevent knocking in gasoline engines. Knocking results when gasoline vapours are subjected to more severe thermal conditions than the chemical stability of the gasoline can withstand. Normal combustion of a mixture of gasoline vapour and air is characterized by a flame front that progresses uniformly and relatively slowly through the mixture. In the cylinder of an engine, normal combustion provides sufficient time for the pressure that develops to act on the piston and give it a powerful thrust. If, however, the mixture is preheated ( by compression or radiation) beyond a critical temperature, the flame passes through the mixture almost instantaneously, creating pressure waves that cause a knocking sound. The energy released by this explosive combustion is dissipated as heat instead of doing useful work on the piston. Thus, when knocking occurs the engine runs hotter and delivers less power. A typical automobile engine in 1915 had a compression ratio of 3.5 to 1 and developed about 25 horsepower. Neither straight-run gasoline nor cracked gasoline would cause knocking in such an engine. To meet the demand for more power from an engine of a given size,

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MANUFACTURING PROCESSES IN CANADA

automobile manufacturers increased the compression ratio of engines. The higher pressures subjected the mixture of gasoline vapour and air in the cylinders to more severe thermal conditions and knocking became a problem. Shortly after 1920 tetraethyl lead was discovered, and in a few years was widely used in "ethyl gasolines" to prevent knocking. During the 1920's it was also learned that cracked gasolines resisted knocking in the higher compression engines mote effectively than straight-run gasolines. By 1932 engines of the same size as 1915 engines but with 5 to 1 compression ratios were producing 80 horsepower without knocking because of the availability of tetraethyl lead and cracked gasolines. The demand for more powerful, higher-compression-ratio engines continued but the ability of tetraethyl lead to enhance the anti-knock property of existing gasolines was limited. The development of more powerful engines depended on the production of gasolines with better anti-knock characteristics. This problem became acute in the 1930's. One feature of the problem concerned the need to measure the antiknock characteristics of gasolines. This was solved in 1933 by the general use of a special single cylinder engine which accurately compared the antiknock characteristics of gasolines in terms of octane numbers. The octane numbers formed a scale ranging from 0 to 100, the higher the number the greater the anti-knock characteristics. Later ( 1939) a second test procedure was developed using the same test engine but under less severe operating conditions. Results from this test were also expressed in octane numbers. To distinguish the octane numbers obtained from the two test procedures, those obtained by the first method ( 1933) were called "motor octane numbers" ( indicative of gasoline performance at high engine speeds) and those by the second ( 1939) "research octane

numbers" ( performance at low engine speeds). Unless otherwise indicated, octane numbers are research octane numbers. With an accurate yardstick to measure octane numbers, refiners were able to learn the cracking conditionstemperature, cracking time, and pressure-that caused increases in the antiknock characteristics of cracked gasoline. In general, the refiners learned that higher cracking temperatures and lower pressures produced higher octane gasolines, but unfortunately more gas, tar, and coke were formed at the expense of the volume of cracked gasoline. To produce high octane gasolines, cracking coil temperatures were increased to 950°F and pressures dropped from 1,000 to 350 pounds per square inch. This was the operating limit of thermal cracking units. At temperatures over 9500F coke formed so rapidly in the cracking coil that the unit became inoperative after only a short time. Just before World War II, thermal cracking units were producing almost half the gasoline manufactured. The cracked gasoline had an octane number of about 70 as compared to 60 or less for straight-run. These were blended with light hydrocarbons to form a gasoline base stock with an octane number of about 65. The addition of ethyl fluid ( tetraethyl lead) increased the octane number to about 70 for the regular grade and 80 for the premium grade of gasoline. Since thermal cracking could not produce higher octane gasolines, something new was needed to break the octane barrier that threatened to stop the development of more powedul automobile engines. In 1936 a new kind of cracking process opened the way to higher octane gasolines. The new process was catalytic cracking. Catalytic cracking-or cat cracking, as it is commonly called-is basically the same as thermal cracking since heat is used. It differs however in its use of

PETROLEUM

a catalyst to direct the cracking reactions to produce more of the higher octane hydrocarbons. A catalyst is a substance that, by its mere presence, has an influence on a chemical reaction. It is not consumed in the reaction. The successful use of a catalyst to make higher octane gasolines removed the limitations on the design of more powerful automobile engines. World War II stopped automotive engine development but cat crackers were built to make 100-octane aviation gasoline. The race between the octane number of motor gasoline and the compression ratios of automobile engines resumed after the war and is still going on. Catalytic cracking has a number of advantages over thermal cracking. The gasoline produced has a higher octane number and greater chemical stability, and the effect of tetraethyl lead in further increasing the octane number (lead susceptibility) is enhanced. These effects are chiefly due to the lesser amounts of olefins and the greater amounts of aromatic and branch-chain hydrocarbons in catalytically cracked gasoline. Larger quantities of olefinic gases suitable for the manufacture of polymer gasoline and smaller quantities of the less useful methane, ethane, and ethylene are produced by catalytic cracking. Harmful sulphur compounds are less prevalent than in thermally cracked gasoline. Catalytic cracking produces less heavy residual oil or tar and more of the more useful gas oils than does thermal cracking. Finally, the process has considerable flexibility permitting the manufacture of both motor and aviation gasolines and a variation in the yield of gas oil to meet changes in the fuel oil market. The use of a catalyst is the important difference between catalytic and thermal cracking. Some chemical reactions are catalysed by a relatively small amount of catalytic material but the catalyst used in cracking is required in relatively large amounts, usually

183

several barrels for each barrel of gas oil being cracked. Consequently catalytic cracking units are characterized by large and elaborate facilities for handling the catalyst, involving reaction chambers, catalyst regenerators, conveyors, and separators. The catalyst is a solid substance, usually a synthetic compound of silica and alumina similar to clay. It is used in the form of pellets, beads, granules, or, most commonly now, as powder or spheres of microscopic size ( microspheres). In general, catalytic cracking processes operate by mixing vapourized gas oil with a catalyst. The ·catalyst does its part in directing the cracking reactions to produce more of the desired cracked materials and then becomes ineffective owing to the deposition of coke. Before further use, the catalyst is regenerated by burning the deposited coke under closely controlled conditions. The first catalytic cracking process was introduced by Eugene Houdry in 1936 with the backing of the Socony Mobil Oil Company and the Sun Oil Company. This was followed by the Suspensoid catalytic cracking process developed by Imperial Oil and placed in operation at its Sarnia refinery in 1940. During World War II this process was the source of hydrocarbon gases needed by a neighbouring synthetic rubber plant built by the Canadian government. These early processes have now been superseded by more efficient processes. The original catalytic cracking process developed by Houdry was a fixed bed or static catalyst process. The catalyst in the form of small lumps or pellets made up layers or beds in four or more drums called converters. Gas oil feed stock vapourized at about 840°F and under seven to fifteen pounds per square inch pressure passed through one of the converters where the cracking reactions took place. In about ten minutes, deposition of coke on the cata-

184

MANUFACTURING PROCESSES IN CANADA

lyst made it ineffective. By an automatically synchronized valve system, the feed stream was turned into a neighbouring converter while the catalyst in the first converter was regenerated by carefully burning the coke deposits with air. After about ten minutes, the catalyst was ready to go on stream again. Fixed-bed cracking yielded about 45 per cent of cracked gasoline with a research octane number of 88 to 95. Cracked gas oil and gases made up most of the remainder of the products. Suspensoid cracking developed from the thermal cracking process as carried out in tube and tank units. Small amounts of powdered catalyst were mixed with the feed stock and the mixture was pumped through a cracking coil furnace. Cracking temperatures of 1,025 to l,130°F and pressures of 200 to 500 pounds per square inch were used. Cracked materials were separated in the same fashion as in the tube and tank process except that the catalyst was separated from the tar by filtration. The Fluid catalytic cracking process introduced in 1941 in the United States by the Standard Oil Company (New Jersey) is now the most widely used process. It is characterized by the use of large quantities of a finely powdered catalyst. The catalyst particles are of such a size that when aerated or "fluffed up" with air or hydrocarbon vapour the catalyst behaves like a fluid and can be moved through pipes and controlled by valves. In this process, vapourized feed stock and fluidized catalyst flow tos gether into a reaction chamber where the temperature is about 950°F. The catalyst, still dispersed in the hydrocarbon vapours, forms beds in the reaction chamber where the cracking reactions take place. The cracked vapours rise from the catalyst beds and pass through cyclones located in the top of the reaction chamber. The cyclones are funnel-shaped vessels which give a whirling motion to the vapours. The heavier catalyst powder is thrown out

of the vapours by centrifugal force. The cracked vapours then enter fractional distillation towers where separation into light and heavy cracked gas oils, cracked gasoline, and cracked gases takes place. The catalyst, contaminated with coke in the reactor, is continuously withdrawn from the bottom of the reactor and lifted by means of a stream of air into a neighbouring regenerator where the coke is removed by controlled burning. The regenerated catalyst then flows to the fresh feed line where the heat in the catalyst is sufficient to vapourize the fresh feed before it reaches the reactor. The Fluid process yields about 50 per cent cracked gasoline with a research octane number of 95. Since the Fluid catalytic cracking process was introduced, other processes ( Orthoflow, Thermofor, Houdriflow, Houdresid, UOP), using a moving catalyst, have been developed. These produce essentially the same amount and kind of cracked products and differ primarily in the arrangements of the cracking and regenerating portions of the units, the type of catalyst, and the method of moving the catalyst. Thermal reforming. When the demand for higher octane gasolines developed during the early 1930's, attention was directed to ways and means of improving the octane number of gasolines obtained directly from crude petroleum. Straight-run gasolines frequently had very low octane numbers and any process that would improve them would aid in meeting the demand for more octane numbers. A process called thermal reforming was developed for this purpose and widely used in the 1930's and 1940's but to a much lesser extent than thermal cracking. The process is relatively little used today. Thermal reforming, like cracking, is a decomposition reaction due to heat. Cracking converts heavier oils into gasoline; reforming converts or reforms gasolines into higher octane

PETROLEUM

185

gasolines called reformates. The higher in World War II to produce a compoanti-knock quality is due primarily to nent for aviation gasolines known as the cracking of long-chain paraffins into hydrocodimer which consisted largely equivalent but higher-octane olefins. of iso-octane. Hydrocodimer has been The equipment for thermal reforming entirely supplanted by equivalent is essentially the same as for thermal lower-cost alkylate which is discussed cracking but higher temperatures are in the next section. used. The amount and quality is very Polymerization reactions are used for dependent on the temperature. In many purposes other than making gasogeneral, the higher the reforming tem- line. The reactions are controlled so perature the higher the octane number that they join together two, three, four, but the lower the yield of reformate. or other molecules. A product composed For example, a gasoline with an octane of two joined molecules is called a number of 35 when reformed at 960°F dimer, three joined together is a trimer, yields 92.4 per cent of 56-octane re- four a tetramer. Some polymerization formate. When reformed at l,028°F, it reactions join thousands of molecules yields 68.7 per cent of 83-octane refor- together forming semi-solids and solids. mate. By using catalysts as in the cata- For example, polyethylene from which lytic reforming processes discussed plastic "squeeze" bottles are made is the later, higher yields of much higher- result of joining thousands of ethylene octane gasolines can be obtained for a molecules into one giant molecule. Butyl rubber is a solid polymerization product given temperature. Polymerization. Cracking and thermal of isobutylene. The polymerization reforming processes created large reactions of concern to petroleum requantities of hydrocarbon gases. The finers are those that produce polymers demand for higher octane gasolines that boil in the gasoline range. Propyduring the 1930's increased the supply lene, butylene, and isobutylene are the of these gases until the gases themselves components in cracked gas used for became an economically feasible source this purpose. of more gasoline. By the polymerization During World War II polymerization process two gaseous molecules were processes using sulphuric acid and later combined into one liquid molecule; a phosphoric acid as catalysts were used motor fuel component known as poly- in the manufacture of high-octane commer gasoline or poly gasoline was thus ponents for aviation gasolines. Now only produced. the phosphoric acid process is used and The high research octane number of the polymer formed is added to motor this synthesized fuel made it a welcome gasolines. The first catalytic polymericomponent in motor gasolines. Polymer zation or "cat poly" plant using phosgasoline consists almost entirely of un- phoric acid as a catalyst was put in saturated or olefinic hydrocarbons. Con- operation in 1935. The first cat poly sequently it is unsuitable for inclusion plant in Canada was built after World in aviation gasolines because of its War II. The process is carried out as follows: relatively low motor octane number and its tendency to form gums during long cracked gases are passed through a periods of storage. Treatment of poly- purification unit where hydrogen sulmer gasoline with hydrogen at high phide, which would be converted to temperatures and pressures converts foul smelling mercaptans by the phosthe olefins into saturated hydrocarbons phoric acid catalyst, is removed. The which are chemically stable and have feed gas is then pumped through a high research and motor octane vessel containing the catalyst which is numbers. This treatment was used early in the form of pellets impregnated with

186

MANUFACTURING PROCESSES IN CANADA

phosphoric acid. The pressure in the vessel is about 1,000 pounds per square inch and the temperature is maintained at 400°F. Since the polymerization reaction gives off heat, water is circulated around the vessel to remove excess heat. The products of the polymerization reactions leave the vessel to enter a fractional distillation tower where polymer gasoline is separated from unreacted gases. About 90 per cent of polymer gasoline consists of unsaturated hydrocarbons. The motor octane number of the gasoline is about 82, the research octane number about 96. The addition of three millilitres of tetraethyl lead per U.S. gallon raises these octane numbers to 85 and 101 respectively. While the high octane numbers of polymer gasoline make it a valuable addition to motor gasoline, the volume of polymer compared to the volume of cracked gasoline is small. If the cracked gases from a cracking unit are polymerized, the gasoline yield of the unit is increased about 5 per cent. Canada's daily production of polymer gasoline in 1957 was 30,800 barrels. Alkylation. During the late 1930's a chemical reaction known as alkylation was developed to convert hydrocarbon gases into iso-octane. By this process the expensive hydrogenation in the manufacture of iso-octane from polymerized gases was eliminated and the yield of iso-octane from a given quantity of gases was doubled. Consequently the polymerization-hydrogenation process is no longer used. In the alkylation reaction isobutane, a paraffinic gas, is combined with olefinic gases to form isoparaffin hydrocarbons boiling in the gasoline range and consisting largely of iso-octane. The olefinic gases are produced by cracking operations; isobutane is a component of cracked gases and of gases from gas and oil fields or may be formed by the isomerization of normal butane. The product of the reaction is known as

aviation alkylate or simply as alkylate. Butylene olefins are most commonly combined with isobutane to make alkylate, but other olefins-ethylene, propylene, and pentylenes-are used. The product from the combination of ethylene and isobutane is known as neohexane. Because it has excellent chemical stability and high research and motor octane numbers, alkylate is a most important component in aviation gasolines. It is now also used as a component in some motor gasolines. Sulphuric acid and hydrogen fluoride are the catalysts used in commercial alkylation plants for the manufacture of fuel components. The first plants constructed early in World War II used sulphuric acid and these plants are still widely used. Liquefied isobutane and olefins are mixed and conducted to a reactor which contains sulphuric acid. By means of jets the isobutane-olefin mixture is injected into the acid where the alkylation reaction takes place. The reactor is maintained at a temperature of about 35°F by the evaporation of some of the liquid hydrocarbons within the reactor. The hydrocarbon-acid mixture is passed from the reactor into a settler where alkylate, the product resulting from the combination of isobutane with the olefins, is separated from the acid. The alkylation of isobutane with olefins using liquid hydrogen fluoride as the catalyst is similar to sulphuric acid alkylation. This catalyst more readily utilizes propylene and pentylenes, in addition to butylenes which are most readily affected by the sulphuric acid process. Refrigeration is not required in the hydrogen fluoride process and catalyst recovery is greater. A mixture of isobutane and olefins is dried by passage through a dessicant and then pumped as a liquid into the reactor where contact is made with the hydrogen fluoride. The reactor is maintained at a temperature of 75 to 105°F and

PETROLEUM

under a pressure of 100 to 160 pounds per square inch. From the reactor the catalyst and hydrocarbon material pass to a settler where hydrocarbons and catalyst are separated. The catalyst is recycled to the reactor. The alkylation product is treated to remove traces of catalyst and is then fractionally distilled as in the sulphuric acid process. Alkylate as made by both processes is composed of a mixture of isoparaffi.ns which have octane numbers that vary with the olefins from which they were made. Butylenes produce the highest octane numbers, propylene the lowest, and pentylenes are intermediate. All alkylates, however, have high octane numbers : 89 to 97 research octane numbers and 87 to 95 motor octane numbers. Alkylate is particularly valuable because of its high motor octane number which is only slightly less than the research octane number. Polymer gasoline, in contrast, has a spread of about fifteen octane numbers between the motor and research values. Gasoline components with high motor octane numbers have less tendency to cause knocking in engines operated at high speed. In 1957 Canada had a total daily alkylate capacity of 2,230 barrels. Catalytic reforming. Compression ratios of automobile engines increased after World War II from an average of 6.68 to 1 in 1946 to 9.47 to 1 in 1958. The highest compression ratio in 1946 was 7.25 to l; in 1958, 10.5 to 1 models were in use. The increase in compression ratio was made possible by increases in the octane numbers of gasolines. The research octane number of premium gasolines increased in Canada from an average of 84.5 in 1946 to 97.9 in January 1958. The extra octane numbers were produced chiefly by catalytic cracking. About 1950 it became apparent that catalytic cracking would not be able to provide as many octane numbers as would be needed by 1960, and a new type of refining process ,was therefore

187

required that would produce high octane gasolines in quantity. The needed process was found in catalytic reforming. Different versions of this process under such names as Powerforming, Catforming, Platforming, Ultraforming, and the like have been installed in most petroleum refineries. Like thermal reforming, catalytic reforming converts low-octane gasolines into higher-octane gasolines ( reformates). Where thermal reforming could produce reformates with research octane numbers of 65 to 80 depending on the yield, catalytic reforming produces reformates with octane numbers up to 100. Reforming does not increase the supply of gasolines. In the process of converting low-octane gasolines into higher-octane gasolines, a volume loss is incurred by the formation of gases. The higher octane numbers and yields of catalytic reforming over thermal reforming are due to chemical reactions caused by the catalyst. Chemical reactions in thermal reforming are limited to cracking-type reactions involving mostly the larger paraffin hydrocarbons in the naphtha feed. In catalytic reforming, several different types of reactions take place involving both paraffin and naphthene hydrocarbons. Most of these reactions release hydrogen, and consequently hydrogen gas is a by-product. The chief catalytic reforming reactions are dehydrogenation and isomerization. In dehydrogenation, hydrogen atoms are removed from loweroctane naphthene hydrocarbons to form high-octane aromatic hydrocarbons. For example, cyclohexane is changed into benzine and hydrogen gas. Isomerization refers to the rearrangement of carbon atoms in a hydrocarbon molecule. Isomerization of straight-chain hexane into a branched-chain isohexane causes an increase in octane number from 25 to 75 or more, depending on which of the several isohexanes is formed . Straight-chain paraffin hydro-

188

MANUFACI'URING PROCESSES IN CANADA

carbons may also be curled ( cyclized) into naphthenes and then dehydrogenated into aromatics. Thus a number of two-step reactions take place such as dehydrocyclization and dehydroisomerization. Cracking also takes place but the presence of hydrogen means that olefins are not produced. The various chemical reactions will have different degrees of signmcance depending on the composition of the naptha feed, the type of catalyst, and the operating conditions ( temperatures, pressure, time of contact with the catalyst, and concentration of the hydrogen gas). Catalytic reforming is particularly effective in removing sulphur compounds from a feed stock. As much as 11J'J'J: J> !J1J> i'JJJSi'J!JJ'.J.l.C'J'-!JJ!:.£ KNOllfR 5CR!IN

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vertical stack of highly polished, solid steel cylinders about twelve inches in diameter, each one resting on the one below. A roller at the bottom, 20 inches in diameter, drives the stack. The paper starts at the top, and winding around the cylinders passes back and forth to the bottom. It is subjected to increasing pressure as it moves downward and this pressure, combined with the friction incurred in passing through the stack, imparts a smooth surface. Finally the paper is wound, cut to the required size, rewound to allow for careful splicing of breaks which may have occurred, and wrapped for shipment. Some grades of paper may be watermaked or coated. The watermark may be obtained by pressing a rotating cylinder bearing a raised design against the damp paper. The design, where it comes in contact with the paper, thins it slightly imparting the mark. Paper may be coated either before or after it leaves the paper machine. In this operation, a film of lacquer, varnish, or some other material is applied to one or both sides of the paper to provide special surface properties such as opacity, printability, colour, or smoothness. A papermaking machine is a marvel of mechanical ingenuity. It is a factory in itself. A modern machine may be longer than a football field and capable of producing a continuous sheet of paper over twenty-five feet wide at a rate of more than two thousand feet a minute. Some machines make more than three hundred and fifty tons of paper a day. Paper may also be made on a cylinder machine. The general process is the

215

same as that already described. The main difference occurs in the form of the screen and the manner in which it receives the pulp. The screen on the Fourdrinier is essentially flat and beltlike. On the cylinder machine the screen is drum-shaped and revolves in a vat containing the pulp suspension. The paper is formed in separate layers as pulp, picked up by the screen revolving in the vat, and deposited on the underside of a felt belt that passes over the series of drums. The wet Javers laminate together on the felt formi~g the sheet, which is then passed through presses and dryers in much the same way as on the Fourdrinier machine. The number of layers will vary with the number of cylinders and vats employed, which in turn will be dependent upon the type of paper or paperboard required. Finishing. Newsprint is unwound, inspected, and cut to suit the needs of the customer, and rewound into rolls for shipment. Kraft paper for bags or wrapping may be treated to give it resistance to insects, water, grease, acid, or scuffing. Highly finished newsprint or fine paper may be passed through the rolls of a supercalender where further pressure is applied to improve surface qualities. Surface finishing of fine paper such as a linen finish or embossing may be obtained by passing the paper through patterned rollers. The finished paper is cut, sorted to remove faulty sheets, counted, trimmed, packaged, sealed, and labelled ready for delivery. The operations of the fine-paper finishing room are many and diverse. It is here that the ultimate in custom production is attained.

FIG. 9. Flow chart. (From Watershed to Watermark, Canadian Pulp and Paper Association, 1955.)

Rubber BY C. J. COON THE GOODYEAR TIRE&: RUBBER COMPANY OF CANADA, LIMITED

CANADA's thriving rubber industry is little more than one hundred years old, although rubber-that marvellous material with a bounce-has been known to the civilized world since the sixteenth century. In Canada today, the rubber industry employs about 25,000 people in 70 plants and manufactures a wide range of rubber goods suited to the demands of our technological world : footwear products, conveyor belting, industrial hose, motor vehicle tires. Tires and tubes alone account for more than 50 per cent of the $355 million worth of rubber goods sold each year. Behind the modem rubber factory with its complex machinery, research departments, and the like, lies a solid framework of achievement by European and American rubber pioneers who were endowed with courage, daring, and enterprise. It is a story of man's ingenuity-a story that continues to be written. Legend says that Christopher Columbus during his second voyage to the New World (1496) saw the natives of Haiti playing with a ball made from a strange bouncing material. The first authentic account of the white man's encounter with rubber describes Cortez and his men in Mexico watching Aztecs playing with a rubber ball about 1525. When Europeans began to colonize South America, they discovered the natives made a number of rubber products-shoes, hats, capes, bottles, jars, arrow quivers-by processing latex from "rubber" trees. The liquid latex was coated over fabric or clay molds and

the resulting product was dried over a smoking fire. By 1615 Spanish soldiers in Mexico were coating their capes with latex to protect themselves from the semi-tropical rain. Europe did not become aware of rubber, however, until the middle of the eighteenth century. The man responsible for bringing the new substance from the South American jungle to the European laboratory was Charles de Ia Condamine, a French scientist and adventurer. He was a member of a party of astronomers sent by the Paris Academy of Science to measure the arc of a meridian through the western part of South America. The astronomers finished their work in 1743 and de la Condamine decided to strike off on his own into the jungle. He travelled through the Amazon Valley collecting samples of rubber and learning from the natives how to process it. By the end of the century, Portugal had imported the first native-made rubber goods from the New World. About this time an Englishman, Dr. Joseph Priestly, named the new substance. He demonstrated how the material would "rub out" pencil marks, and the name "rubber" was born. Business men quickly saw the commercial value of a material that was pliable, waterproof, shock-resistant, and durable. However, a problem in processing remained unsolved: untreated latex coagulated readily and thereby was rendered unworkable. Experiments were undertaken to find a solvent for the material. Charles Mackintosh of Glas-

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gow discovered in 1823 that naptha was satisfactory for this purpose. He was able to establish a flourishing waterproof coat business, selling coats made of fabric covered with a rubber and naptha solution. Today "Mackintosh" has become a dictionary synonym for waterproof coat. Another rubber pioneer was Thomas Hancock, a successful London coach manufacturer. Hancock probably turned to rubber in search of a waterproofing material to protect stage coach passengers of the day. He patented and manufactured rubber gloves, shoes, soles, and garters, and in 1820, faced with the problem of utilizing scraps of materials left over from crude manufacturing methods, he discovered the principle of mastication, whereby scraps of rubber, when chewed up by a special mill, turned into a solid mass that could be moulded. Hancock later discovered the art of compounding when he experimentally added other substances to the rubber in his masticating mill. By 1835 European workers were manufacturing an impressive list of rubber goods including footwear, rainwear, air mattresses, life preservers, surgical goods, and fire hoses. The first rubber factory in the United States was established by the Roxbury India-Rubber Company in Boston in 1832. Canada's first rubber factory was begun in Montreal in 1854. One big stumbling block remained in the further development of the rubber industry: the stability of articles made from rubber was affected by changes in temperature. A rubber raincoat, for example, turned stiff in cold weather; and in the heat of summer, the rubber literally ran off the garment and emitted an offensive odour. Several people worked on the problem, notably Hancock in England and a hardware merchant, Charles Goodyear, in the United States. Goodyear was not a trained scientist, but for six years he experimented with numerous compounds,

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combining rubber with almost everything he could think of in his search for a stable product. He pursued his quest with unique single-mindedness, undeterred by the loss of his hardware business, the entreaties of his wife and friends, and a term in prison for indebtedness. He is said to have made his discovery by chance. One day in 1839 he accidentally threw a mixture of sulphur and rubber into the stove. When he recovered it, the material had turned into a black durable substance-vulcanized rubber. Some of the credit for this discovery goes to another American, Nathaniel Haywood, who sold Goodyear the patent for a similar process: when sulphur was mixed with rubber and exposed to the sun, the material gained a tough stable finish. In England, Hancock discovered the principle of vulcanization in 1844. Both he and Goodyear patented their processes about the same time. The introduction of the new process gave immediate stimulus to the rubber industry on both sides of the Atlantic. At last a method had been found to fix the rubber in a permanent shape, and to increase its elasticity and strength.

The Tire Industry By the middle of the nineteenth century, solid rubber tires began to appear on carriages as people discovered that rubber would reduce vibration and noise. In 1845, R. W. Thomson of England patented the world's first pneumatic tire. It was made of thicknesses of canvas cemented together and covered with leather. Thomson's discovery was not followed up, however, and it was not until 1888 that a BeHast veterinarian, J. B. Dunlop, conceived the idea of creating a cushion of air between the vehicle and a rubber tire. He established the Dunlop Tire Company which first manufactured pneumatic rubber tires for bicycles. Air-filled tires not only meant a smoother ride,

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MANUF ACTIJRING PROCESSES IN CANADA

but made higher speeds possible. The first automobile to be successfully fitted with pneumatic tires was driven in the Paris-Bordeaux trials of 1895. Pneumatic tires for trucks were not considered seriously as replacements for solid tires until World War I. As trucks became larger and heavier, solid tires placed a limitation on speed and were the cause of frequent breakdowns as a result of overheating. By the 1930's, pneumatics had found general acceptance. Solid tires continue to be used today where industrial applications require the transportation of heavy loads at low speeds. Dunlop taped his tires on the rim of the bicycle wheel, but this method was not suitable for larger vehicles. The "clincher" tire was introduced in 1890; the tire was stretched over the rim with a strong iron bar. Later the "bead" was introduced, with steel wire securing a straight-sided tire. It simplified mounting and removal since the tire rim was easily locked and unlocked on the wheel. The word "tire," the covering for the wheel, comes from "attire" meaning covering. But today's tire does much more than that. It absorbs shock and vibration from the road, provides traction for braking, permits the vehicle to operate at high speeds, and practically eliminates the noise of road contact. A tire is composed of two main parts, carcass and cover. The cover, which consists of the tread and sidewalls, has to be particlularly tough to withstand the shocks of the road and abrasion from the road and curbs. The carcass, or inner core of the tire, is built of several layers ( plies ) of rubberized fabric anchored to the rim of the wheel by rubber-coated wire beads. The carcass contains the air and is the foundation for the tread. In addition, the carcass of a passenger car tire contains two small rubber parts-the flipper strips which anchor the bead to the rest of the tire and distribute the internal flex-

ing to the sidewalls, and the chafing strips which protect the carcass from rim-cutting. A recent development in the industry is the tubeless tire. Tires without tubes are not new-some of the earliest pneumatic tires had no tubes, but they were not easy or economical to repair. Recent improvements in rubber compounding, tire-cord processing, and tire design have made possible a practical tubeless tire, and in 1956 all automobile manufacturers equipped their models with them. They are also available for trucks, airplanes, and farm and construction vehicles. The tubeless tire affords a high degree of protection from blowouts compared with the conventional tire with tube. Although it is not absolutely blowout-proof, the tubeless tire has eliminated most blowouts. For example, if a tube tire were bruised, damage to the carcass would result. Constant flexing of the tire would cause the damage to spread to the inside of the tire. When a crack appeared in the tire wall, it would pinch or chafe through the tube, causing a sudden blowout. A similar injury to a tubeless tire would cause only a slow leak. When a nail is picked up by a tubeless tire, no air escapes until the nail is removed. Since there is no separate tube, tubeless tires are thinner and therefore run cooler, are lighter in weight, and create less bounce. The tubeless tire is the outcome of intensive research on the part of tire engineers and represents several years of development. It is only one indication of the constant search and research for improvement that is going on in the laboratories of rubber manufacturers. New tread designs, better rubber compounds, improved fabrics are constantly being sought to keep pace with the increasing horsepower of new cars. The number of types of vehicles which move on rubber is increasing too. In addition to automobiles, vehicles depending on

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rubber tires include trucks, tractors, fann implements, buses, bicycles, airplanes, earthmovers, and industrial vehicles.

Sources of Raw Materials Rubber tires might just as well have been called "fabric" tires, or even "chemical" tires, because the rubber in the modem automobile tire accounts for just over half the weight of the tire; fabric-cotton, rayon, or nylonforms up to 20 per cent of the weight, and chemical compounds account for the remaining 30 per cent. Chemicals are essential for strengthening the rubber and aiding the vulcanizing process. Rubber. The chief source of natural rubber during the early period of its commercial development was South America. At the beginning of the twentieth century, with the market steadily increasing because of the advent of the automobile, Brazil controlled about 95 per cent of the world's supply. In 1876, however, an English coffee planter, Henry Wickham, who was later knighted for his efforts, had smuggled seeds of the Hevea Braziliensis out of the country. They were planted in Kew Gardens and since a moist, wann climate with an annual rainfall of 75 to 100 inches is required for growth, they were transplanted to Ceylon, Singapore, and Malaya, thus starting today's vast rubber plantations in the Far East. Plantations were developed not only by English companies but by Dutch and later by American firms; by 1920 South-East Asia was producing 90 per cent of the world's supply. The rubber plantation assured a more stable supply, at a more reasonable cost, than had been possible from the widely scattered native trees in Brazil. Latex, rubber in its natural form, is a colloid containing water ( 55 per cent) and rubber ( 44 per cent). Latex, although not the sap of the tree, is found inside the bark. About 300 trees a day

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can be tapped by one native plantation worker. He shaves off a thin layer of bark to form a sloping groove and the latex, a milky-white substance, trickles down the cut to be collected in small cups attached to the tree. He then takes his harvest to a central collection point; from there it goes to a factory for preliminary processing. Speed is essential in moving the liquid to the processing plant as latex partially coagulates and sours within a few hours of collection. At the plant, it is strained to remove foreign matter and diluted with water. Acid is added to speed the coagulation process. Coagulated latex, which looks like huge pieces of marshmallow, is rolled into thin sheets and moved to a smokehouse. In about ten days, the smoke has preserved it and turned it to a golden-brown colour. It is then baled for shipment to factories throughout the world. The future of natural rubber must be considered in the light of recent advances in the production of synthetic rubbers. The Japanese occupation of the Far East rubber plantations during World War II was a powerful stimulant to the synthetic rubber industry. The threat of failure of the Allied war effort through lack of rubber spurred scientists and engineers to develop synthetics that would satisfactorily replace the natural product. During the last year of the war, Canadian consumption of synthetic rubber soared to almost seven times that of natural rubber as the sources of natural rubber dried up. When the war-ravaged plantations were restored after the war, natural mbber consumption rose sharply and outstripped synthetic rubber, so that in 1950 two pounds of natural were being used for every pound of synthetic. Since then, however, the Canadian market has been almost evenly divided between the two types of rubber. The story of synthetic rubber begins in 1860 when an Englishman, Grenville Williams, discovered the principle of

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MANUFACTURING PROCESSES IN CANADA

making Isoprene. It and its close relatives are the basis of most synthetics. Sir William Tilden moved a step further and manufactured Isoprene from turpentine in 1884. The Germans were the first to manufacture products from synthetic rubber. Just prior to World War I, German scientists produced two synthetic rubber tires. A few were manufactured during the war, but were of such poor quality that the synthetic research programme was dropped when natural rubber again became available. In the United States, the first synthetic rubber was developed in 1931. That same year a new method of producing chemicals from oil and gas made possible the large-scale production of butadiene, a basic ingredient of synthetic rubber. When the supply of natural rubber was cut off during World War II, the Allies expanded the synthetic rubber industry and improved the product to the point where most rubber goods could be made from synthetic materials. Constant research is being carried out to improve synthetics. No single synthetic in widespread use is as good for all purposes as natural rubber, but some synthetics are better in certain respects. For example, one synthetic (Butyl) holds air up to ten times better than natural rubber and is used in making inner tubes; another has better resistance to oil and heat; and a third stands up better to extreme temperatures. Butadiene is a complex gas compound composed of hydrogen and carbon and is a product of the "cracking" of oil or the distilling of alcohol from ·grain. It reacts with styrene in a solution of soapy water to form a basic latex. Styrene, a hydrocarbon also, but of different molecular construction, is produced from coal. The latex is 'cooked" and an anti-oxidant is added as a preservative. Salt and sulphuric acid are added to the liquid causing it to coagulate. The curdled material is 4

dehydrated and the resulting particles are heated to remove all trace of moisture. The "roasted" particles are pressed into sheets and baled for use by the rubber products manufacturer. Canadian supplies of synthetic rubber come from the government-owned Polymer Corporation in Samia, the largest synthetic rubber plant in the British Commonwealth. Recent developments in the industry indicate that a synthetic tire that outlasts the life of the car may soon be produced. However, the cost of production may prevent its general acceptance. Synthetic rubber now in use has properties similar to natural rubber, but a different molecular structure. The laboratory production of a true synthetic rubber with the same molecular structure as the tree-produced material was first announced in 1955. Fabric. Fabric is essential in preserving the shape of the tire. A rubber tire without fabric would continue to expand when being inflated until it completely filled the fender well of the vehicle. Fabric accounts for about onefifth of the weight of a tire. Two Canadian tire companies, Goodyear and Firestone, have their own textile mills where the material is spun and woven into cord fabric ( for tire plies) and square woven fabric ( for smaller tire components). Cotton was the material originally used by tire-makers, but synthetic fibres developed in the past three decades have proved far superior. Cotton is still used in vehicle tires where speed is not important, for example in tractor tires. However, high speeds pose a major problem for tire engineers. Internal friction caused by rapid motion of the wheel generates heat and eventually weakens the fabric. This phenomenon is called "hysteresis." The use of rayon has helped to alleviate this problem. Since rayon is stronger pound for pound than cotton, less fabric and less rubber are required, and the resulting thinner

RUBBER

carcass allows heat to escape more readily. Rayon also stands up to bruising better than cotton. This synthetic fabric has longer fibres than cotton, is more uniform in quality, and its production cannot be seriously affected by the adverse weather conditions which affect cotton production. Rayon was first developed for use in truck tires where weight and heat are particularly hard on fabric and rubber. Its use has now been extended to the regularly priced passenger car tire. A newer and tougher synthetic fabric is becoming increasingly popular in premium car and truck tires. This is nylon, first used in North America in 1940 in wartime bomber tires where it proved effective in standing the tremendous strain of braking at high speeds under heavy loads. All airplanes are now equipped with nylon tires. Nylon is stronger than rayon and therefore yields a lighter tire. Moisture, which damages other fabrics, has little effect on nylon. Each strand of nylon is twice as strong as a steel strand of the same thickness. Compounds and solvents. About 30 per cent of the tire is composed of compounds and solvents. Rubber-compounding is an exacting science that plays a vital part in determining the wearing qualities of rubber used in tire manufacturing. Compounds are in no sense added to the rubber to "cheapen" the tire-as a rule compounds cost as much as, or more than, the same amount of rubber. A tire of the same design and weight as a modem tire but made entirely of pure rubber would have a tread no stronger than a rubber band and would last scarcely 50 miles even on the smoothest highway. The largest additive by weight is carbon black, the chief strengthener of rubber. Each passenger car tire contains four pounds of this substance. The tread and sidewall portion of the tire receive the largest amount because they are subjected to the most wear as a result of

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road and curb abrasions. Improved carbon blacks are constantly being developed to make sturdier tires. Another basic additive is sulphur, the ingredient which makes vulcanization possible. It is usually the last compound to be added because there is always danger of scorching and of prematurely curing the rubber. To get full benefit from vulcanization, a small quantity of two acids are added to activate the material during the process. Another group of compounds act as accelerators to speed up the vulcanization process and preserve the rubber from oxidation. Pigments may be added such as white for white sidewalls, anti-oxidents are added to help preserve the finished product, wax is added to give sheen, and softeners save the rubber from scorching and, by increasing its pliability, reduce the time required on the warm-up mill. To stretch out the supplies of natural and synthetic rubber, during World War II, a considerable amount of reclaimed rubber was added. Each tire also contains a small amount of steel in the form of steel wire beads. These serve to anchor the plies and clamp the body of the tire to the rim of the wheel. The wire is coated with bronze to prevent rusting and to aid adhesion with the rubber. Several strands encased in rubber make one bead. Thus the term "rubber" can be misleading when applied to vehicle tires. The tire industry d_!:lpends upon rubber but rubber alone will not make tires. The composition by weight of an average Canadian-made automobile tire is : natural and synthetic rubber, 54 per cent; carbon black, 20 per cent; other chemicals, 10 per cent; fabric, 14 per cent; steel wire, 2 per cent. The modem rubber industry draws upon the chemical, petro-chemical, and textile industries, and to a lesser extent upon the steel industry. This is true not only in tire making, but in the manufacture of other rubber products also.

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MANUFACTURING PROCESSES IN CANADA

The Manufacturing Process

Companies vary slightly in their manufacturing processes, but most processes are basic to the industry. In some cases two different methods of performing the same operations may be used by the same plant. The processes described here are for passenger car tires, which form the bulk of Canadian tire production. All pneumatic tires are made in a similar fashion. Rubber, the basic raw material, comes to the plant in two different forms. Natural or crude rubber comes from overseas plantations in large bales weighing up to 250 pounds. These bales are stored in a "warming room" at above-average temperatures to soften the rubber which may become hard and brittle if shipped in cold weather. When needed for production, the bales are put through a "pie-cutter," so called because the knives of the machine chop the bales into pie-shaped segments for easier handling. Synthetic rubber, most of which is made at Polymer in Samia, arrives in 60 pound rectangular chunks. These, much smaller in size than the bales of natural rubber, need no preparation before the compounding operation. Basically, the compounding operation consists of masticating the rubber to a dough and mixing in chemicals essential to further processing and to the qualities desired in the final product. The formula for a batch of rubber destined for the tread of a farm tractor tire, for example, is quite different from that for a batch intended for the tread of a passenger car tire. Essential additives include sulphur-necessary for the chemical reaction of vulcanization-and carbon black, the chief strengthening agent for rubber. Other elements determining the nature of the compound include anti-oxidents, waxes, oils, acids, and accelerators. The machine that accomplishes the delicate compounding operation is the Banbury Mixer, named after its in-

ventor F. C. Banbury, an American engineer. It is a huge machine that mixes up to 1,000 pounds of material at a time. The operations of the machine occupy three levels. At the top level, the raw materials are measured and fed into the mixing chamber. The actual mixing operation occurs at the middle level and the finished compound is extracted at the bottom level. At the top, or loading level, a set of scales measures each ingredient before it enters the machine; a conveyor belt moves the materials into the hopper door. Hinged at the bottom, the door is part of the loading platform while open. Closed, it seals the materials in the hopper and prevents the escape of fumes and heat given off during the mixing process. Some additives enter the mixing chamber through the loading door, others are injected automatically into the chamber after the door has closed. In the mixing chamber, a pneumatic ram descends to push the materials down against the mixing blades. Two rotors, of longitudinal spiral shape, revolve towards each other at different speeds, and thoroughly mix the batch in three or four minutes. They are cored for water circulation allowing for temperature control. Additional temperature control is obtained by water circulating inside the double walls of the mixing chamber. Compounding usually requires two trips through the Banbury Mixer. Sulphur, the curing agent, is added during the second trip because the heat generated by the mixing action of the giant rotors partially cures stock containing sulphur. The mixture leaves through the discharge door at the base of the chamber and falls on a rotary sheeter where it is shaped into a continuous strip 60 inches wide; then it is cooled in a water "bath." A conveyor moves the strip to a branding unit where it is marked for identification and to a soap dip unit where the stock is dusted with soapstone to prevent it from stick-

RUBBER

ing together. An inclined conveyor directs the strip up to the top level where it is cooled further, cut into sheets, and stacked. Before the invention of the Banbury Mixer in 1916, all the ingredients were mixed in open mills-two steel rollers turning towards each other. This system had many disadvantages. It took about 12 open mills to do the work of one Banbury; the chemicals and fumes made the millroom on unpleasant place to work; and the possibilities of human error in adding chemicals were considerable. The Banbury has removed the guesswork and the drudgery from this process. It requires fewer men and less floor space; it is cleaner, because the chemicals and rubber are completely enclosed; better control of temperature is obtained by water in the cores of the various parts of the mixing chamber; and the mixing procedure is safe for the operators. Open mills are used today only for warming up the productive stock prior to further processing. A careful check of each batch that goes through the Banbury is one of a long series of control checks made at each step of the manufacturing procedure. A "bad" batch mixed with other batches would ruin a large quantity of rubber. As soon as the rubber comes from the Banbury, a sample is sent to the testing laboratories where tests for specific gravity and elasticity are carried out. The productive stock, soapstoned to prevent adhesion and sheeted for easier handling, goes to the warm-up mills to be softened in preparation for the operations to follow. In the Banbury, a plasticator was added to enable the compound to be softened at a lower temperature, thus preventing overheating, which would leave lumps of partially cured rubber and render the batch unfit for further processing. The productive stock sheets are placed by hand between mill rollers which rotate to-

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wards each other. The stock rides in the hollow between the two rollers and is gradually pulled down until it coats one of the rollers. The millworker, stroking diagonally with a small knife, cuts the rubber sheet from the roller and places it on top of the two rollers. This procedure is repeated about a dozen times until the compound is sufficiently plastic. Then two stationary knives, a few inches apart, are set diagonally against the rubber to cut it away from the moving roller. From here it is moved away by overhead conveyors. At this point, the production procedure becomes more specialized. Some of the warmed-up stock goes to the calendering machine to impregnate fabric and some goes to various extruding machines for the manufacture of the tread and sidewall stock, for coating the steel wire beads, for the manufacture of tubes, or for the making of air-bags used in the final curing process of some tires. It was noted earlier that cotton, rayon, or nylon is essential to preserve the shape and strengthen the tire. On the calendering machine, the rubber and the fabric unite so that each thread of fabric is completely surrounded by a coating of rubber. But before the fabric is ready for this process, it must go through a preparatory operation. Fabric has a tendency to stretch under tension. Continual stretching or flexing of fabric causes what is known as fabric "growth." The tendency to grow, that is, the tendency of the fabric to stretch permanently, must be removed before it becomes part of the tire; otherwise the stretching of cords in a tire in service would cause endless trouble. A special process has been developed to remove this tendency. Each roll of cord fabric is unwound and passed through a splicer, which joins the ends to provide a continuous How of material; the fabric is then moved through a storage compensator, where

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MANUFACTURING PROCESSES IN CANADA

it is festooned, so that it may be kept taut during the operation. The fabric enters a liquid latex cement dip, takes three minutes to pass through a soaking area, and then enters a second dip of latex cement. Then it moves into a "blow-off' box where jets of air blow off the excess cement, in order to prevent "webbing" of the cement between the cords, and to allow the rubber during the calendering process to surround each cord completely. Between the second dip and the blow-off box, a set of rollers near the end of the operation exert the correct degree of tension on the fabric. Under tension the fabric is subjected to temperatures ranging up to 300°F. This operation "sets" the fabric so that it will not grow under the stress encountered in service. From the blow-off box, the fabric enters a two-storey tower where steam coils send the temperature soaring. Entering from the base of the tower the fabric rolls up and down over three "star" rollers. When viewed from the end, a star roller has the appearance of a multi-pointed star, because of a series of ridges around the circumference designed for minimum contact between the fabric and the roller and thus for minimum loss of the latex cement. Still wet from the cement dips, the fabric leaves the base of the tower and enters two drying harbours. Here air blowers dry the cement at about 300°F while the fabric is festooned on another series of star rollers. The fabric leaves the harbours in a completely dry state and is rolled on electronically controlled pull rollers which, as a result of their velocity of rotation, impart the required tension to the fabric. The amount of tension is governed by the type of cord fabric. From the pull rollers, the fabric is rewound, ready for the calenders. Sixty yards of fabric a minute can be processed through this unit. The calenders impregnate the fabric with rubber. Each calender consists of three hollow metal rollers placed one

above the other. The rubber stock enters between the top and middle rollers from overhead conveyors which in tum are fed from the rubber warmup mills. The fabric enters between the middle and bottom rollers. The hot rubber which winds around the middle roll is literally ground into the fabric by the action of the middle and bottom rollers which run at slightly different speeds. The temperature is controlled by water introduced into the hollow rollers. As the fabric turns on the bottom roller, it is coated on one side and its direction is reversed. It moves over a group of rollers designed to exert tension on the material, then enters a second calender where the other side is impregnated with rubber. The thickness of the rubber coating is measured on each calender by a Schuster Gauge which consists of an electromagnet and two rollers which ride on the calender roll. Any fluctuation in the thickness of the rubber coating is registered through an electric impulse which activates a dial. The rubber-coated fabric passes from the calenders to the cooling drums, a set of rollers set in vertical zig-zag positions and filled with cold water. The fabric threads between the rollers, then enters the wind-up where it is rolled into cloth liners. The stock is · identified by coloured threads introduced while the stock is still hot. The rubberized fabric moves to the bias cutter where, after being unrolled from the cloth liners, it is cut into sections by an automatic, motor-driven knife. These sections, or plies, are cut at an angle to the fabric cord. The tacky nature of the rubber allows them to be stuck end to end and rolled once more in cloth liners in preparation for tire building. Most passenger tires are made of four or six plies of calendered material. Larger tires-those for trucks and tractors, for example-are built of bands, each of which is composed of four plies. Plies are SC't so that the cord

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fabric in a given ply runs at right angles to that of adjacent plies. Flipper strips and chafer strips are made of square-woven calendered material. A Hipper is an extension of the circular bead and forms the bond between the bead and the plies. In service, · the Hipper distributes the Hexing action exerted on the rim over the whole tire. The calendered stock is cut on the bias and the ends spliced together by pressure from rollers. Chafer strips strengthen the bead and protect the plies from the cutting action of the rim. They are also cut on the bias from calendered stock. Depending on the size and type of tire, chafer strips are made of one, two, or three layers of rubberized fabric. The tread and sidewall stock is formed in an extruding machine. Since the rub-

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her used must t>e more plastic than that prepared for calendering, chemical softeners are often added. The compounds are forced through a hollow head which tapers towards a die leaving no possibility for air-holes to appear in the extruded product. The required force is applied by a screw, the only moving part of the extruder. As the materials are forced through the die, the tread stock and sidewalls are formed in a single operation. The rubber entering the extruder is at a high temperature. Additional heat is generated by the action of the machine. To minimize the possibility of premature curing, an extensive water-cooling system is provided in the form of a jacket built around the cylinder which encloses the screw. The shaped strip of tread and sidewall stock is automatically cut to

Frc . I. An extrusion machine. This rubber slab will become the tread and sidewalls. (Photograph by Gilbert A. Milne & Co. )

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MANUFACTURING PROCESSES IN CANADA

proper lengths, and cement is added to the ends in preparation for the tirebuilding operation. The tread and sidewall units are then placed on a large mobile rack resembling a book with metal leaves. The stock cools further in the "book" as it is carried to the tirebuilding department. In addition to the fabric and rubber, that is the carcass plies, and the tread and sidewall stock, there is the third main component-the bead which is made of rubber and bronzed steel wire. Wire enters the bead machine from reels, the number depending upon the size and type of tire. To maintain tautness, the wire is passed over three grooved wheels, one of which is stationary and the others free. These are heated to prepare the wire for adhesion with the rubber. The rubber coating is applied in an extruding machine. Several strands are formed into a circular band, fastened, and wrapped with woven cloth tape. The flipper strip of rubberized fabric is then pressed on and the beads are ready for the tire-builder. All the preliminary operations in the tire-making processes flow together in the tire-building department. The first tires were made with square-woven fabric, and the tire was built over a metal core, made of sections bolted together. The "green" tire and the core were placed in an engraved mold and cured. The engraving in the mold produced the tread design. After curing the core was broken and removed from the tire. The next development in curing was called the two-cure wrapped method. The tire was cured on a metal core, but the mold had no tread design and so produced a bald-headed tire. The tread was made separately: it was partially cured and the tread design molded on. Then it was cemented to the bald-headed tire. The whole tire had to be cured again. To keep the tread from running in the heat, it was necessary to plaster it with thick mud, and to bind it ,vith cross wrap to hold in the mud

and supply the necessary retaining pressure. Curing was done in horizontal heaters. The advent of cord fabric, in which the diameter of the cross fibres was reduced so that cord friction inside the tire would lessen damage to the longitudinal fibres, brought with it a new method of curing. The carcass was built on a core, then stripped from the core and an air-bag inserted. The carcass was cured in a smooth mold to produce a bald-headed tire. The air-bag was removed and a lighter one inserted, while the tread, which was not cured, was applied. The light air-bag was then replaced with the heavier one. Curing in an engraved mold finished the process. This method was used up until 1923 when the present single-cure method was developed. Today tires are built on a horizontal metal drum which is turned by an electric motor operated by a foot control. The materials for the tire are placed behind the tire builder on a stand which rotates automatically presenting the correct component at each stage in the operation. The tire builder first applies a coating of gum to the drum, and on it places two plies running across grain to each other. A second set of plies is added in a similar manner to the first. The beads with their attached flipper strips are added at each end of the drum. The flipper strips tie in the ends of the plies and are attached between the two sets of plies. Chafer strips are cut by hand and placed on top of the plies. The tread and sidewall section is rolled on after the ends of the plies have been turned down. Pressure from the operator's hands and from various wheels and rollers are used throughout the operation to "tack" each part in place. The drum of the machine is collapsed and the "green" tire removed. It is placed on a conveyor belt for storing prior to the vulcanization process. Green tires resemble small oil barrels with the ends knocked out. The

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227

Frc. 2. The assembly. (Photographs in Figs. 2 and 3 by Robert C. Ragsdale, A.R.P.s.)

bulge in the middle of the "barrel" will become the tread. The very important operation of vulcanizing is the next step. There are two methods currently in use. One method requires two basic pieces of equipment to perform the operations of shaping, curing, and molding the tire. The other method requires one piece of equipment to perform all three operations. The second method is superior for standardsize passenger car tires, but it is not economical as yet for the entire range of tires produced in a modem tire plant. The first phase of the longer operation imparts to the tire its basic shape. The green tire is placed on the table portion of a bagging machine. At the same time, an inflated rubber air-bag is drawn through a recess at the base of the platform. A ram falls pressing the two open ends of the drum-like tire

closer together. As the tire bulges out at the middle, the air-bag is automatically inserted. When the ram is released, the tire retains its "tire shape." But it is still soft and tacky and has no tread pattern. The air-bag inside makes it twice as heavy as its finished weight. The tire is cured and molded in the second piece of equipment, in a pot heater. The heater, about fifteen feet deep, is set vertically into the floor so that only about eighteen inches projects above the surface of the floor. The heavy lid is raised and a vertical ram rises from the bottom. The bald tires, which have been encased in metal molds, are placed on top of the ram which is lowered to accommodate each additional mold. The capacity of the heater is about twenty molds. When capacity is reached the heater lid is clamped in its down position and the

228

MANUFACTURING PROCESSES IN CANADA

FIG. 3. Green tires.

ram forced up against the pile of molds, exerting strong pressure on them. Steam is introduced into the heater for the cure. When the curing time is up, the steam is turned off and cold water sprayed into the heater. The molds are removed and opened, and the tire freed . The air-bag is removed from the tire by an extractor. The tire is placed on a conveyor for a trip to the final inspection deparhnent and the air-bag is returned ready to be used again. A newer development than the pot heater is the watch-case mold. After the airbag is inserted, the shaped tire is placed inside the heated mold and the two halves are closed much like the case of a watch. Steam is injected into the airbag. When the prescribed curing time is up, the "watch-case" opens automatically.

The second method now in use for making passenger car tires cures a tire in one-third of the time. The machine, called the "Bag-O-Matic," combines the curing, molding, and bagging operations. It resembles the watch-case mold, the chief difference being an inflatable, pliable, rubber bladder placed in the centre of the mold over which the green tire fits snugly when the mold is open. As the case top closes, the ends of the tire are squeezed together, the middle bulges out, and the bladder inflates to hold the tire wall tightly against the mold walls. Thus in 20 minutes ( for a passenger car tire), the green tire is changed from a barrel-shaped soft tire to a finished product complete with tread design. The Bag-O-Matic machine yields a larger production of tires with a smaller investment in molds.

BtmBER

229

Both the air-bags and the inflatable passing all tests, it is stored for shiprubber bladders may be manufactured ment to warehouses across Canada. in the tire plant. Air-bags are extruded from a tubing machine. The thick- Tubes The manufacture of tubes is much walled strip is cut into lengths, covered with soapstone, and stored for at least less complex than tire-making. Most 12 hours. Then the ends are cemented, tubes are made of butyl, a synthetic the valve inserted and the resulting air- rubber which, as was mentioned earlier, bag cured in a smooth-sided mold. The can hold air up to ten times longer than rubber bladder is made of thin strips natural rubber. Rubber from the wannof rubber. The strip is coiled around a up mills enters a tubing machine to be collapsible metal drum, one layer on extruded as a continuous strip of tubing top of of another. Removed from the on to a moving conveyor belt. Soapstone drum, the bladder is placed in a warm- is blown on the inside of the tube so that ing oven to speed the curing. Vulcaniz- the walls will not stick together. The ing takes place in a special mold. Both tubing is then cooled in a water tank air-bag and bladders must be replaced and dried. A branding unit prints the after a relatively short period in service. appropriate name and size on the tube, One problem inherent in vulcanizing marks the spots where it is to be cut is obtaining an even cure. Rubber is a into lengths, and cuts out the valve poor conductor of heat. It is possible hole. The valve is then fitted to the for the portion of the tire closest to the tube and the tubing cut into exact source of heat to be completely cured lengths. The ends of the tube are spliwhile the rubber farthest away from ced by an electric rubber welding the source of heat is just reaching the device which presses the ends together curing temperature. This difficulty has under pressure without causing an overbeen overcome by the introduction of lap. The tube is partially inflated and the air-bag ( which applies heat from cured in a watch-case mold which opens inside the tire) into the curing opera- automatically when the cure is comtion, and more recently by the adding pleted. The tube is tested in water to of different kinds of accelerators to the make sure no pin holes or other defects various compounds used in a tire; the mar the finished product. Each tube is cure of the part of the tire farthest deflated, folded, and boxed for shipfrom the source of heat is accelerated ment. relative to the cure of that closer to the Before tubeless tires became popular, heat source. Goodyear developed a lifeguard tube The cured tire passes by conveyor which was guaranteed against blowsystem to the final inspection depart- outs. Unlike conventional inner tubes, ment. Here small "whiskers" of rubber it consisted of two air chambers, one that are produced during the cure are inside the other. The outer chamber trimmed off. These are formed in pore was made of rubber and contained holes in the mold, which are provided about 40 per cent of the tire's inflated to release air trapped between the air. The inside chamber was made of rubber and the mold. The tires are cord fabric and contained the remaining coated with a black "paint" and then air. A two-way valve was used to inflate are required to pass a rigid series of the chambers and to maintain an equalinspections that weed out any mis- ized pressure between them. If a puncmolded or otherwise unsuitable tires. ture occurred, air would escape first The inside and outside are carefully in- from only the outer chamber and a safe spected and the tire is tested for stop could be made on the remaining balance. If the tire is successful in 60 per cent air pressure. Escape of air

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from the inner chamber did not occur too rapidly because of a narrow neck incorporated into the design of the valve. The most recent development in tire safety is the double air chamber tire, first introduced by Goodyear in 1956. This "Captive Air" tire is, literally, two tires in one. Should the outer air chamber be punctured, the inner "tire" of twoply nylon cord allows the motorist to drive for 100 miles or more before a repair is necessary. Further protection is afforded by two layers of steel wire imbedded in the inner shield which will deflect nails penetrating to the inner tire. Introduction of the new tire was seen as heralding the end of the passenger car's fifth tire, the spare. In fact, several station wagon models have been introduced with only four tires of this new type as their standard equipment. This new type of tire puts an end to dangerous roadside delays for changing tires, delays which are especially dangerous on expressways and heavily travelled superhighways.

Marketing Tire manufacturers have two markets

231

for their produd-original equipment and replacement. Servicing the original equipment market is a relatively simple matter. A tire company agrees to supply all, or a certain percentage of, an auto maker's annual requirements. The tires are shipped to warehouses situated near the automobile and truck plants. As required, they are fed directly to the assembly lines. Volume is based on the auto manufacturers' estimates of annual production. Rubber companies also supply as original equipment many other rubber parts, such as floor matting and radiator hose. The replacement tire market is serviced through thousands of retail outlets-service stations, garages, and tire stores. A considerable number are sold through department stores and auto accessory stores. The tire company's advertising is aimed primarily at this market because replacement tires usually are bought to satisfy an immediate need. The tire business is highly complex and exacting. Yet it must be flexible, ever ready to meet the challenges of new automobile design, performance, and public demand for longer milage and greater safety.

Textiles: Cotton BY J. R. DUNKERLEY* DOMINION TEXTILE OOMPANY LIMITED

CorroN is a vegetable seed fibre, consisting mainly of cellulose. The cotton hairs are attached to the seed and form a protective covering for it at maturity. The microscopical appearance of the fibre reveals a ribbon-like structure with irregular twists or folds known as convolutions which are found along the entire length of the fibre. The convolutions, which give it the tendency to cling, are responsible for its high commercial value. When a number of fibres are twisted together, a yarn that is relatively high in tensile strength results. The cotton plant belongs to the genus Gossypium, which belongs to the natural order Malvaceae. Many kinds of cotton are grown throughout the world, but in the main they may be resolved into three broad types. Type 1 is composed of long, fine, strong fibres of good lustre and from one to two inches in length. This type is the most valuable, the most difficult to produce, and the least abundant. It includes the Egyptian and Sea Islands growths derived from the botanical species Gossypium barbandese and Gossypium purpurascens. It is raised not only in Egypt and in the West Indies, but also in the southern United States including California. It is used when fine strong threads are required for closely woven fabrics such as broadcloth and fine hosieries. Type 2 is an intermediate cotton, coarser and 0 The account of finishing processes has been written by Mr. G. W. Smiley, Chief Chemist, Dominion Textile Converting Division.

shorter than type 1 with a staple length ranging from ¾ to 1%2 inches. The American Uplands growths belong to this group and are derived from the species Gossypium hartsum. This type is grown principally in North and South America. It is suitable for a wide range of textile products and constitutes the bulk of the commercial crop. Type 3 is the short coarse fibre group which is characterized by little or no lustre and ranges from % to one inch in staple length. It is composed mainly of the Indian and Asiatic growths, belonging to the species Gossypium herbaceum and Gossypium arboreum. The bulk of this type is produced in India and China; some is produced also in Turkey, southeast Europe, and southern Africa. A large quantity is used for home consumption; that remaining may be used for lower quality goods and for blending with wools in the manufacture of carpets, cotton blankets, and similar products which have thick lasting naps or piles. While the cotton plant generally grows well in warm climates, its commercial cultivation is somewhat limited. The portion of the earth lying between the equator and 34 ° latitude presents the most suitable conditions for the cultivation of cotton, in particular for the Sea Islands and American Uplands types. Suitable conditions imply plenty of sunshine for six to seven months each year with a mean yearly temperature of 68 to 86°F, 3 to 5 inches of rain each month during the stages of active growth, and a dry season to check the

233

TEXTILES: COTION

vegetable growth as the crop approaches maturity. In the United States, where yearly cotton production is controlled, 17,000,000 acres are cultivated by approximately 1,250,000 farmers. Hence the average acreage for each farm is relatively small when compared with that for other staple commodities. The over-all yield varies from 260 to 270 pounds per acre. The cotton plant flowers 80 to llO days after planting. The boll ( seed pods) opens or bursts 55 to 80 days after flowering occurs. The finer varieties of cotton take longer to mature and are therefore more apt to be attacked by insects, pests, and contamination. The mature fibre is picked as soon as possible after the boll opens thus minimizing deterioration by light and moisture. There are two methods of harvesting, manual and mechanical, the latter collecting trash as well as cotton. The mechanical method of picking has many difficulties which machinery manufacturers have sought to overcome. With economic factors in its favour, mechanized picking is gradually replacing hand methods. Ginning Cotton as picked from the field still contains seed and is known as seed cotton, containing only about a third of its total weight in cotton fibre. The process of segregation is known as ginning. In the United States it is commercial practice for a wagon containing about 1,500 pounds of seed cotton to be placed under a suction flue in the ginnery. The cotton is carried by a pneumatic system through a drying chamber; then it is moved to an extracting and cleaning unit, which removes the leaf and stalk gathered by the mechanical harvester. From here it is distributed to the feeders, where a further cleaning process takes place. It is then passed through the gin. There are two types of gins, the "saw" type which is used mainly for

intermediate and short-stapled cottons, or the "roller" type which is used mainly for the long-fibre growths. This latter type is slower in production by about 10 to 1, but eliminates damage to the fibres. The prinicipal element of the gin is a saw-toothed roller which is covered by a grid as in Figure 1. The grid permits only a portion of the teeth to pro-

Hopper feed box

Roll bo._

Fie. 1. Saw type gin.

trude into the seed cotton chamber. The protrusions pull the cotton away from the seeds in tufts; these in turn are blown off the teeth by an air blast and are carried by conduits to a collecting unit. The seed is retained by the grid and, when stripped of its fibres, falls to a bottom box, where it is transported from the gin. Ginned cotton, on reaching the collecting unit, is dropped into a large press box where it is tamped down. When sufficient weight is collected, the mass is compressed and banded to form a bale. Grading Variations in quality may occur from one bale to another as a result of the type of seed planted, type of soil available, and weather conditions prevailing. A standard grading system is therefore necessary to provide a common basis of evaluation for both the producer and the purchaser. The grad-

234

MANUFACTURING PROCESSES IN CANADA

ing system for American Uplands cotton is: ( 1 ) Middling fair ( 2) Strict good middling ( 3) Good middling ( 4) Strict middling ( 5) Middling ( 6) Strict low middling ( 7) Low middling ( 8) Strict good ordinary ( 9) Good ordinary

Middling indicates the basic grade, "strict" denotes the half grades, and all other categories are full grades. All grades above middling bring higher prices, while those below bring lower prices. The main considerations in grading cotton are length of fibre, colour, degree of foreign matter, and preparation and character. From representative samples drawn from the bale, the required information can be obtained either by the highly skilled judgment of dassers or by laboratory methods. If the latter are used, the important attributes can be measured and recorded by such instruments as the cotton fibre sorter, colorimeter, and the trash analyser, thereby minimizing error; fineness and degree of maturity may also be measured. Preparation of Yarn In the processing of cotton into yams, a manufacturer follows a procedure which will enable him to obtain the most satisfactory and economical results from the raw material at his disposal. His chief considerations are the type of cotton required, type of machinery at hand, and size of his plant. All plants are designed and laid out to process certain types of yams within specified limits and while it may be possible to produce beyond these limits such production is undertaken at an economic disadvantage. The sequence of operations in yam production is: blending and mixing the raw stock, extracting the impurities, disintegrating and fractionalizing the

cotton, forming the cotton into the nucleus of a thread, doubling and attenuating for evenness, and imparting twist to the fibres after the required degree of fineness has been achieved. In addition to the above there is a special process which is sometimes required called combing. This operation removes all fibres below a specified length, and yarns made by this method are used in fabrics where evenness, lustre, and strength are of prime importance. Blending and mixing. Shipments of bales are segregated by type, length and colour and laid down on the blending room Boor in groups known as "mixes." A mix may be comprised of between 12 and 32 bales. These bales are laid in close proximity to the various units of blending machines. It is usual practice to group the blending machines in blocks of four, each feeding to a common feed table for transportation to the next process. A blender ( Fig. 2) is a box-like machine with four main moving parts. A feed apron, which is located close to

Feed table

Spiked apron

FIG. 2. Blending machine.

the base of the machine, and which runs horizontally, carries the cotton forward from the rear reserve area towards the second prime mover, a spiked apron. This is a continuous canvas belt to which rows of spikes are attached and which is located in an almost vertical position. As the cotton comes in contact with the spikes, tufts of cotton are tom from the unopened layers of bales and transported upwards until they come in contact with the third prime mover,

TEXTILES: COTTON

known as a regulating roll. This roll consists of a spiked covered cylinder which is set at a distance from the spikes of the upright apron so that the regulating roll ( which runs counter to the direction of the upright apron) will pennit only lumps or tufts of a predetermined size to pass forward. The small opened tufts pass forward on the spikes of the upright apron, over the top of the driving shaft and downwards into contact with the fourth prime mover, the doffing roll. This roll, which is very similar to the regulating roll, is set close to the spiked apron and re~

235

through the operations of cleaning and opening it is in a light and fluffy condition. It still contains some impurities to be removed and it requires condensing in bulk for the next process. The machine employed for this function is known as the picker ( Fig. 3). A picker consists of one or two beating chambers of special design, incorporating a cage or condenser section, with a special calendering machine to compress the stock making it into a roll known as a "lap." Special precautions are taken to control cleanliness and regularity of density of the lap.

Supply from deaning unit

FIG. 3. Picking machine.

volves rapidly in the same direction, beating or stripping the small opened tufts of cotton down onto a chute leading to a feed table. From this brief description, it will be seen that it is possible to feed layers from various bales into one blender hopper, and with four such blenders feeding onto a common feed table, a fair blend of the original mix is obtained. From the blending room, the cotton is transported pneumatically to the opening and cleaning units. There are many different kinds of cleaning machines which are essentially rolls, beaters, grids, and mechanisms to produce air currents. These machines vary in design according to the experience of the various textile machinery manufacturers and also the required degree of extraction of impurities such as leaf, stalk and sand. Picking. After the cotton has passed

The picker is fed either by hopper feeder or by feed trunk, both of which have special control devices embodied in their design. The picker itself is comprised of a feed apron with a feed roll operated by means of a pedal. As the cotton passes between the feed roll and the pedal, it depresses the pedal and according to the amount of depression the feed roll is speeded up or retarded so as to maintain a constant weight of cotton passing forward to the beating chamber of the picker. In this chamber, beaters beat the stock against a series of grid bars and finally deposit it on two slowly revolving cages. From the cages, the stock is stripped off and fed to the calender section by two small rolls. The calender rolls exert pressure on the cotton reducing its thickness, roll it into a lap, and by means of a tripping mechanism measure it off in approximately 50-yard rolls.

236

MANUFAC11JllING PROCESSES IN CANADA

Carding. From the appearance of the lap, one does not get the impression that much progress has been made towards the making of yarn, but it must be remembered that the first operations are designed to clean, open, and unify the stock and deliver it in a uniform lap, which is of even density and capable of being unrolled at the next process-carding. The purposes of carding are to remove the residue trash remaining in the lap, to disintegrate the fibre masses so as to extract as much of the unworkable fibres as possible, and to prepare the

a similar functton to the picker grid bars, but since the tufts are small, the impurities are more accessible and the obstruction presented by the knife edge makes extraction easier. The saw teeth of the '1icker-in" bring the cotton fibres into contact with the cylinder. The cylinder is covered with a special type of fillet made of a cotton and wool foundation, with hardened steel pins or wires attached from the underside. The wires are bent so as to present a certain rake or angle to the path of the rotating "licker-in". As the cylinder's wires are rotating at a faster peripheral speed

a·~onn Dio9rarn of flat '

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mass· of processed fibres in a form suitable for the next process. The flat card (Fig. 4) consists of four prime movers: the "licker-in" ( 9'' diam.), the cylinder (50'' diam.), the doffer (24-27" diam.), and a series of flats. A lap is placed on a fluted wooden roll at the feed end of the machine and is slowly fed forward over a smooth feed plate until it contacts a small-diameter feed roll. The feed plate has a special nose rising slightly with the contour of the roll which assists feeding the fringe of the lap to the "licker-in." The latter is covered with special saw tooth wire; these teeth tear small tufts from the lap fringe and carry them downwards into the path of two knives. The knives have

than the "licker-in" teeth, the latter are readily stripped of the cotton and the cotton is spread out thinly on the ends of the cylinder wires. The cotton on the cylinder wires is subjected next to the prime function of the card, namely the disintegration of the fibre masses. This function is performed by a series of cast iron strips covered with wire fillet similar to that described for the cylinder; these assemblies are known as flats. The teeth of the flats oppose those of the cylinder. The flats move very slowly and for all purposes can be considered stationary. The small bundles of fibres loosely attached to the cylinder wires are "teased" or gently pulled by the slowly moving

TEXTll.ES: COTION

flat wires; any entanglements are pulled apart and any short loose fibres or knotted lumps are attached to the Hats. As the flats move slowly forward, they emerge from vital contact with the cylinder, and are stripped of impurities and pass over the machine ready for service again. The carded fibres, still attached to the cylinder wires, come into contact with a smaller cylinder called a doffer. The doffer is also covered with wire fillet and the teeth are so arranged as to present themselves in opposition to the wires of the cylinder. The doffer runs at

237

each hand, and pulled apart, will be straightened. This same operation can be performed by two pairs of rolls, the second pair revolving at twice the peripheral speed of the first, the ratio or draft being 2:1. li two slivers were passed together through this device the same size of sliver would emerge, but the variation would be averaged. The two operations described above are known as drafting and doubling, and are the basis of the drawing process. On a drawing frame ( Fig. 5) there are four or five pairs of drafting rolls and it is usual to place six or eight

Fie. 5. Drawing frame.

a slower speed than the cylinder and thus enables the wires to strip the carded fibres from it. The doffer in turn comes into contact with an oscillating stripping comb which deposits the fibres into a funnel, and thence they go to a coiling device which winds the ropelike processed cotton into a circular can. Drawing. The rope-like strand produced by the card is known as a "sliver" which is a thread in very coarse form. The fibres in a sliver are not parallel to any great extent. Finished thread requires twist for strength, and before twist can be imparted, the fibres must be parallel. Fibres of a mass of cotton, held firmly between finger and thumb of

cans containing slivers at the feed end of the machine. An appropriate degree of draft is arranged between the successive pairs of rolls; each pair in turn will run faster than the preceding pair. The product of this machine is a sliver evened and with parallel fibres. The amount of drafting and doubling which occurs on this machine varies with the quality and ultimate use of the finished product. Combing. Certain yams and fabrics are required to perform special functions. For example, in the manufacture of high-class knit wear, percale sheetings, and fine broadcloths, appearance and utility of the finished product de-

238

MANUFAcroRING PROCESSES IN CANADA

mand that little or no variation should occur in the yam. In order to ensure that only fibres of prime length remain, short fibres are extracted by means of the comber ( Fig. 6). Before the sliver can be presented to the comber, it is first made into a lap and in some cases the lap is re-processed so as to ensure an even lap, void of the irregular bulk of a sliver. This method of producing a uniform sheet is known as sliver and ribbon lapping. The comber has an intermittent action and functions as follows : the lap is placed on a pair of fluted rolls, which feed it over a smooth steel plate and then under a small steel feed roll. This feed roll is actuated by a ratchet motion and feeds only a specified amount of lap per cycle. As the feed roll passes this lap forward over the edge of the feed plate, a second plate, located at approximately 90° to the first, closes down on the bottom plate. These two plates are referred to as top and bottom nipper knives and trap or hold the lap sheet which is about to be processed. The whole of this mechanism is pivoted and is lowered into the path of a cylinder. The cylinder has teeth or combs which extend for approximately one-

third of its circumference. These teeth tug or comb out all fibres not held by the nipper knives, transporting them to a waste collector system. When the combing action is complete, the feed roll delivers the combed fringe forward to a previously combed lap sheet; the two fringes are attached and taken forward. Simultaneously the nipper knives close, the combed section is broken by detaching rolls, and a second comb called a "top comb" begins to operate. This comb retains the short fibres during detaching, and then moves from the sphere of action. The cradle lowers once more into the path of the cylinder and the second cycle of the operations begins. This whole complicated mechanical action occurs rapidly, ranging between 90 to 150 cycles per minute, and it is impossible for the untrained observer to detect the functions of the machine without assistance. There are various arrangements in the sequence of combing operations; some manufacturers insist that one drawing operation should precede combing, while others insist that combing should precede two drawing operations. The former arrangement is more widely adopted.

Fie. 6. Comber. One machine will consist of 6 or 8 combing heads. All the combed slivers ( 6-8} converge on a drafting unit at the end of the machine where they are coiled and placed in a can.

TEXTILES: COTTON

Roving frames. The sliver from the drawing or combing operation is too bulky for the spinning frames and therefore must be reduced in diameter. Reduction is achieved by "roving" ( Fig. 7). In this operation the sliver passes throught a drafting element which reduces the diameter of the yam, then through a flyer which imparts twist;

239

revolutions each minute of the bobbin so that its surface speed remains constant as the diameter of the package increases, preventing the roving from becoming stretched. The height of successive layers is decreased continually, yielding a cone-shaped package which will unwind easily when fed to the spinning frame.

Draftin9 element r-----, /',=, . '