I S D C S T R I d L AND ENGINEERISG CHE;1.fISTRY
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Greases that are not pure enough to be made directly into soap are subjected to some kind of aqueous aaponification, usually with a small amount of sulfonic acid saponifier, which gives glycerol solution and crude fatty acids. These can be made white and pure by distillation in vacuo with smerheated steam. Consumption, etc.
%Xause of the recovery of glycerol as a by-product, soap is now sold much cheaper than would have been possible
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by old methods, and because of its superior qualities both for household and toilet purposes it gives greater satisfaction in use than ever before. The consumption of soap has thus grown to be enormous, more than anyone can conceive. People once experiencing the many advantages derived from its use cannot Dossiblv do without it. There is no more accurate measure of {he enlightenment of a race than a gage of the amount of soap used by it. The use of soap is bound t o continue as civilization advances,
The Portland Cement Industry’ By Richard K. Meade 10 WEST CHASE ST., BALTIMORE, MD.
HE American Portland cement industry and the AMERICAN CHEMICAL SOCIETYjust missed being twinsthe first plant for the manufacture of this important building material being the Coplay Cement Company, established in 1875, by David Saylor, at Coplay, Pa. This concern is still an active producer, but has, of course, grown to many times its original size. The site of this works is in the famous Lehigh cement district, which produces about one-third the cement made in the United States. Other works were established about the same time in other parts of the country. Most of these failed. They were all, including Saylor’s plant, quite small, manufacturing only a few thousand barrels of cement a year by primitive methods of European origin. Today the production of cement in the United States averages about half a million barrels per day. The advances in the art of cement-making during the intervening fifty years have therefore been most notable. While the quality of the product has been steadily improving, the greatest advance in the industry has been largely mechanical and along the line of efficient quantity production. At the same time, the chemist has been an important factor in this development. With the introduction of large units and the handling and proportioning of such immense quantities of raw material, many chemical problems were encountered and solved, while the constant demand for uniform material of high quality requires that the industry now employ a large number of well-trained and experienced chemists. Many of the cement-makers of the last fifty years have themselves been chemists. This is notably true in Europe; while in this country the destinies of some of our large cement works have been in the hands of chemists-at least so far as the management of the plant is concerned.
T
Beginning of the Industry
The invention of Portland cement is generally credited to one Joseph Aspdin, a bricklayer of Leeds, England, who took out a patent in 1824 on “an improvement in the modes of producing artificial stone,” the specifications of which describe essentially the production of Portland cement. To his product he gave this latter name because when hardened it resembled stone from the famous quarries of Portland, England. The establishment of the American industry occurred chronologically about midway in the present life of the industry as a whole. The methods employed a t the first works in this country did not differ materially from those employed in Europe a t that time, or indeed, for that matter, 1
Received June 4, 1926.
from the early process employed by Aspdin. Naturally, the materials were somewhat different from those used i n Europe, but the steps in the process and the machinery employed were essentially the same. By Saylor’s time the value of chemical control of the process had been recognized, and all the early successful American mills had 8, chemist and a laboratory where the raw materials were properly proportioned and the product was subjected to a few simple tests. Saylor selected as his chemist John W. Eckert, a graduate of Lehigh University, and his scientific knowledge undoubtedly had much to do with the placing of the product from the Coplay works on a sound footing with architects and engineers. Theory of Cement Manufacture
Portland cement is made by combining a calcareous material, such as limestone, marl, or chalk containing lime, with an argillaceous one, such as clay or shale containing silica and alumina. These raw materials are intimately mixed by finely grinding the two together and this fine powder is then burned until it just begins to fuse or vitrify. The resulting powder, called “clinker,” after cooling is mixed with about 2 per cent of gypsum and ground so fine that a t least 78 per cent of it will pass a test sieve having 200 meshes to the inch. If the cement is to be satisfactory, the raw materials must be of proper composition a t the beginning and the proportioning must be carefully done. So far as chemical composition is concerned, it is doubtful if the intervening years between 1876 and 1926 have seen much change in the ideas as to standards set. It has generally been recognized that cements high in lime, provided they are sound, are stronger and more regular in setting properties than those low in lime. In order to manufacture a sound cement from materials high in lime, however, it is necessary to grind the raw materials very finely. The more efficient machinery now used for pulverizing allows much finer grinding than was possible in 1876, and consequently the tendency of late years has been to produce Portland cement higher in lime, and so better, than was done fifty years ago. The strength of the concrete made from cement is largely influenced by the fineness of the cement. Owing to the improved machinery, cements are ground much finer now than they were in 1876, with the result that they are much stronger. The present output of any cement mill is much more uniform than it was in 1876, on account of improved methods of handling, storing, and blending the raw materials, the clinker, and the cement itself. In 1876 the theory of the composition of Portland cement
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wm decidedly nebulous. Vicat, Collet-Descotils, Berthier, and Fremy had prior to this advanced the theory that cement was composed of silicates and aluminates of lime, but their studies were limited and unconvincing and these scientists disagreed widely among themselves. Today, as a result of the painstaking research work of LeChatelier in France a n d our own chemists, Newberry, Richardson, Day, Shepherd, Bates, and Rankin, we are fairly certain that the essential constituents of Portland cement are the 3CaO. SiOz, 3Ca0.Al2O3, and 2Ca0.SiZO3, and that the setting and hardening are due to the hydrolysis of these compounds, forming colloidal bodies which act as a mineral glue. Relative to the formation of clinker, the writer established the relation which exists between the fineness of the raw material, the time in the kiln, and the temperature of burning and expressed this in the form of a mathematical equation, as follows: D X T X F = C in which D
T F C
= = = =
time temperature fineness of the raw materials a constant-namely, clinker
If we increase any one of the three variables D, T , and F , one or both of the other two will decrease. Thus, if we grind the materials finer, the temperature and time in the kiln necessary to form clinker, one or both, may be less.
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with the kiln top in which the drying was done. Sometimes the gases from beehive coke ovens were employed, the coke being used in the kilns. The dried slurry was then burned in small intermittent “bottle” kilns, so-called because of their shape (Figure l), somewhat as lime is still burned in the older plants, by spreading a layer of coke and then one of dried slurry, and so on until the kiln was charged. The resulting clinker was somewhat softer than the present-day product and was ground between millstones and bolted similar to methods employed in old-time flour mills. The cement was generally shipped in barrels and the packing was done by ordinary barrel packers. Saylor employed a soft argillaceous limestone from which to make cement, attaining the proper composition by mixing the various layers of rock found in his quarry. This material, being massive, was first crushed in small jaw crushers, then reduced still finer by “pot crackers,” and finally ground dry by means of millstones. The material was then mixed with water and a little cement to keep it from falling to a powder on drying, dried, and burned in upright kilns, The cement mills of 1876 were usually located convenient to water power, just as was the practice with flour mills of that day. A few mills were driven by steam engines and line shafting. Cement Manufacture Today
The industry today bears but little resemblance to that of fifty years ago. Where the manufacturer then talked of a Manufacture of Cement in 1876 few barrels of cement he now speaks of thousands, and where The process of manufacture employed in 1876 varied each mill ground and each kiln burned 40 or 50 barrels of somewhat a t different works according to the materials cement per day, it now produces a thousand or two. The employed. In Europe, cement was made almost universally old water-power mill and the intermittent kiln are now in from soft chalks or marls and clay. These materials were ruins and covered with moss, or else entirely torn away and as found in nature, often in the form of a fine powder, and replaced by other equipment. Two processes are employed in the modern cement init was only necessary to break up the lumps and thoroughly incorporate the two materials by trituration with water dustry just as they were in 1876-the wet process and the in a wash mill. The proportioning was done by weighing dry process. These differ in the method of grinding the the two materials in barrows or carts as dumped into the raw materials and of controlling the composition. A modern cement mill wiil produce from 2000 wash mill. The chemical comto 6000, or even more, barrels of position was controlled by measc e m e n t per day. This requires uring the volume of carbon dioxide large units for crushing, grinding, liberated on treatment of a weighed and burning, but essentially the sample of material taken from the process is the same as fifty years ago. wash mill, with acid in an appaHard, massive materials, such as ratus called a calcimeter, the carlimestone, cement rock, shale, and bonate of lime being calculated from clay, are now generally employed. the volume of gas so found. M a r l i s but little used in this The clay a n d c h a l k w e r e country today, alkali waste a t one thoroughly incorporated and any or two plants, chalk not at all. lumps broken up in the wash mill, Electric or steam shovels load so that the material was discharged the rock in the quarry and the from the latter in the form of a thin crushing of these hard materials slip or “slurry” containing from 40 is u s u a l l y done in two stages. to 50 per cent water and practically Mammoth jaw, gyratory, or rollno heavy grit. When the chalk or jaw crushers capable of crushing any marl contained l u m p s of h a r d rock passing through the dipper of material, shell fragments, etc., the the steam shovel used for loading in wash mills could not reduce these the quarry are employed to crush sufficiently fine and in such cases to pieces 8 or 10 inches and under, the thin slurry was ground to the while swing hammer mills or small r e q u i r e d fineness by millstones. g y r a t o r y crushers reduce these The slurry was then spread in a pieces still smaller. thin layer on the floor of an esThe pulverizing is done in either pecially constructed oven and dried. one or two stages. If one stage is Sometimes the waste gases from the e m p l o y e d , it is usually done in kilns were used for this. The Figure 1--Old B o t t l e Kiln Employed for Burning C e m e n t F i f t y Years Ago compartment tube mills. A few of Johnson kiln was invented in 1872, Such a kiln would produce about 200 barrels of the older plants, however, employ and this had a long flue connected cement in one week.
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Griffin or Fuller mills to grind the raw material. Where driven by means of electric motors, which are directly the grinding is done in two stages, Bradley-Hercules mills connected to the latter through speed reducers where necesor Kominuters and, a t a few of the older mills, Griffin mills, sary, and flexible couplings. Fuller mills, or ball mills are used to reduce to 20-mesh The cooling of such a mass of red-hot clinker as is produced product and tube mills for the fine grinding. A two-stage by a modern kiln presents quite a problem. This is now tube mill 7 by 26 feet will grind about 1500 barrels of raw generally effected by means of rotary coolers through which material or cement per day, while a Hercules mill and a air is drawn, the cooling of the clinker serving to preheat 7 by 26-foot tube mill will grind about 2400 barrels of either the air for combustion. Some mills allow their clinker to material in this time. cool in piles in the air, handling it by means of cranes and If the dry process is employed, the materials are always grab buckets. dried in rotary driers before being ground. In the wet The clinker is ground by mills similar to those now employed process water is added as the material goes into the pulver- for grinding the raw materials. From 2 to 3 per cent of izing mill. gypsum is always added before grinding, in order to regulate In the dry process the correct chemical composition is the setting time of the cement. The handling of the prodobtained by mixing the materials in proper proportions uct at all stages of the process, from the quarry to the cars, is automatic. Bucket before they are introelevators, belt, pan and duced into the grinddrag conveyors, and for ing mills. Sometimes, fine materials s c r e w notably in the case of conveyors are all excement rock, the mixtensively used. A reing is d o n e a t t h e cent interesting develcrusher. More generopment in the handling a l l y , h o w e v e r , the of cement, powdered materials are crushed coal, and dry ground separately, s t o r e d i n r a w m a t e r i a l is by separate bins, and then means of an ingenious drawn out and proporworm pump and a pipe t i o n e d automatically line ( F u l l e r- K i n y o n by some form of weighsystem). ing device, such as a poidometer, just before The ground cement is being sent to the grindstored in huge stock ing mill. At a few of h o u s e s , consisting of the newer mills the fully g r o u p s of reenforced ground raw material is c o n c r e t e silos, each s t o r e d in large silos. from 25 to 35 feet in Here it is analyzed and diameter and from 50 the contents of various to 75 feet high and Figure %Modern Rotary Kiln A kiln of this type 9 feet in diameter by 160 feet long will produce about 1000 barrels silos are mixed as deholding from 5000 to of cement daily. sired to give a more 7000 barrels. Such a regular composition. stock house frequently In the wet process the slurry is usually stored in tanks has a storage capacity of a quarter of a million barrels. provided with agitators. The contents of these tanks are The cement is packed by the Bates system in bags which are analyzed and mixed, as may be indicated by this analysis, tied with a wire tie, before the cement is placed in them, in larger basins also provided with agitators and generally the filling being done by means of a tube which enters the bags through a flap valve sewed in the bottom of the bag. located under the kilns. In the case of either dry materials or slurry, the burning The filling and weighing are automatic. The packages of is done in rotary kilns (Figure 2). These are now being cement are usually dropped on a belt conveyor as fast as made very large-9 to 11 feet in diamet,er and from 150 filled and so conveyed to the door of the car, the stacking in to 250 feet long. I n the case of slurry, the drying is done the car being done by manual labor. A good operator in the upper part of the kiln. The kiln itself is now heated can pack with one machine 6000 bags per day. Today, the process is under constant chemical control by pulverized coal, except when natural gas or oil are cheaper. This utilization of the former fuel in the cement industry con- a t all stages. The quarry and clay pits are usually thoroughly stituted the first successfullarge-scale application of pulverized prospected, the drillings from the blast holes are also often coal. The rotary kiln is an English invention, but was first saved and analyzed. The composition of the dried ground applied successfully to cement-burning in America by Ameri- material or of the slurry is checked before burning, often can cement chemists-H. J. Seaman and S. B. Newberry, a t two points-an acid and alkali determination of the carbonate of lime being universally employed for this purpose the one adapting it to dry and the other to wet materials. A kiln 9 x 150 feet will burn 1000 barrels per day, while in America. The burning is usually inspected by the chemist one 10 x 200 feet will produce 1700 barrels per day, by and all the product is thoroughly tested before being shippedthe dry process. I n the wet process, a kiln 11 X 250 feet the methods of test employed and the specifications under will produce 1500 barrels, or the output of about 30 kilns such which cement is sold being entirely the product of the last fifty years. as were used in 1876. The United States manufactures more than half the The waste gases from the kiln are now utilized for power generation by passing them through water-tube boilers cement produced in the world, practically all of the domestic and economizers. With properly designed apparatus it is product being used in this country. Its production is usual to generate all the power necessary to operate the mill more than four times that of either the British Empire or from the waste gases. All machinery is now generally of Germany. Last year this amounted to about 160,000,-
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000 barrels and was valued a t more than $250,000,000. It is natural, therefore, that the contribution of America to the technology of cement, made entirely during the last fifty years, should be towards economic quantity production, and incident to this notably the invention of the dry process,
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the successful application of the rotary kiln, the use of pulverized fuel for heating the kiln, the development of large units for crushing and pulverizing, the utilization of the waste heat from the kiln for power generation, and the automatic sacking of cement.
The Steel Age-1876
to 1926’
By John A. Mathews CRUCIBLE STEEL COMPANY OF AMERICA, NEWYORK, N. Y.
HE writer’s recollection of the “Centenilial” centers around some toy ducks, swans, and fishes that swam about in a tub of water obedient to a small permanent bar magnet. Then there was a popgun, which probably accounts for my militaristic tendencies. Such war-breeding toys should not be given children! We should have a Constitutional Amendment forbidding them and my fond but thoughtless aunt-herself a n educator-should have known better than to bring me a gun-pop or otherwise. It is well nigh impossible for the children of today to comprehend the amazing developments of the past half-century. They take for granted the telephone, electric light, and radio; the trolley-car, automobile, and airplane; yet probably the youngest member of the AMERICAN CHEMICAL SOCIETY has lived through a period in which the production of iron and steel has exceeded that of all previous centuries. The history of iron, however, goes back to remote antiquity, or possibly to twice the age of the Christian era. When steel replaced wrought iron quite generally as a metal of construction, a great advance occurred, and this dates approximately from the year 1876, and the period since may quite appropriately be called the Steel Age. That was the last year in which the iron railroad rail exceeded the production of the steel rail.
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Steel-Making Prior to 1876
Steel and steel-melting processes were not new. The venerable crucible process is nearly two hundred years old; it could never be the basis of a “tonnage” industry, but as a “quality” method it has not yet been surpassed. The Bessemer and the Siemens-Martin processes came along in the late sixties and these gave the real tonnage impetus and challenged the position of wrought iron. There was strong prejudice to be overcome and no doubt much of it justified by difficulties encountered in the operation of radically new methods. It must be remembered that routine chemical analyses were not customary when these methods began and chance selection of ores was the controlling influence in most cases and meant the success or failure of local enterprises. And they were local enterprises too, for the great transportation systems were lacking and the small plant serving a local district flourished in many states and a t a still earlier date was sprinkled over the colonies. In Pennsylvania alone there were about 275 furnaces as late as 1876, and since that their number has declined but the capacity of the individual unit has steadily increased. The blast furnaces a t that time used anthracite, raw bituminous, coke, and charcoal as fuels; over half of them used anthracite, while coke furnaces were even then in excess of charcoal furnaces. All steel made prior to 1876 was “acid;” that is, the crucibles or furnace linings were of siliceous material. Such furnaces are primarily melting and not refining furnaces. To make good steel in them requires good raw materials and these are 1
Received June 8, 192G.
not so abundant as we might desire, while vast quantities of ores too high in phosphorus for acid steel were useless. Just a t this time the “basic,’ process was being developed, by means of which not only Bessemer but also open-hearth steel and pig iron could be dephosphorized and mountains of ores became available. The use of basic linings of magnesite and dolomite and strongly basic lime slags accomplished this and gave to the steel industry its strongest stimulus toward quantity production. The basic process created the Steel Age. With this began the day of big things-big furnaces, big mills, big companies later becoming big corporations, big buildings, big ships, and big guns. In 1876 iron was on the decline, and all steel was of acid manufacture, but although experiments were in progress the basic process had not been announced or patented. Barbed wire and wire nails were new inventions; experiments with ship plates of steel had been made, but no large vessels entirely of steel had been built; steel for bridges was just being introduced, iron being entirely used in the great Girard Avenue Bridge in Philadelphia of 1874, while the Eads Bridge a t St. Louis used some steel; the “skyscraper” was unknown. The blast furnace of that day produced between 50 and 75 tons per day. The United States had produced pig iron a t the rate of 2 million tons a year somewhat prior to 1876 and nearly one-half of it was made in Pennsylvania, the old furnaces in the eastern part adhering to anthracite, while the Pittsburgh district was developing coke fuel. Soft Bessemer steel was substituted for wrought iron for tin-plating, and the new Edgar Thompson Steel Company showed a t the centennial exposition a 62-pound rail 120 feet long, a record length a t the time. Chemical control methods in plants were almost unknown and the metallurgist as we know him today was not in evidence. Empirical methods prevailed, but that does not mean that the steel was not good. These pioneers were steel-makers and would not have recognized themselves if called “metallurgists.” Practice was far in advance of theory. The microscope, the pyrometers, scientific heat treatment, hardness testing, and the underlying chemistry of processes had yet to receive recognition in the industry. Development since 1876
The years between 1876 and 1926 have been years of development and growth rather than years of invention or discovery of fundamentally new processes. The basic process is the great exception, and the introduction of electric furnaces about 1900 really represents the development of electrical generating methods and the reduction in the cost of wholesale power; they are either basic or acid in character and, while permitting of certain reactions that cannot be carried out in the older processes, their metallurgy is not very differentfrom that of the open hearth except for the use of the reducing slag. Steel was melted in the electric arc long before it was a commercially feasible thing to do. This period
