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By Herbert A. Stein, John B. Murdock

Perlite is a natural volcanic glass which expands into an insulation material upon the application of heat. This paper discusses the operating characteristics of eight different types of furnaces for the expansion of perlite. It also includes a section on the theory of perlite expansion which serves as the basis for the authors' analysis of the furnaces.

Jan 1, 1950

By Paul Merica

ONE of the most useful, and at the same time least commonly used, methods of thermal analysis for the determination of transformations in metals and alloys consists in the recording of the tune intervals required for successive increments of temperature change during heating or cooling, the temperature of the furnace containing the specimen being altered at a uniform rate. The curve obtained by plotting these time intervals as a function of the mean temperature of the specimen during the interval is called the inverse-rate curve. It is probably due to the fact that no simple and convenient method has apparently been available for the measurement of the successive time intervals that this method has not been so generally used as, for example, the differential method, for which several tykes of automatic or semi-automatic apparatus have been designed. Whenever this method has been used, the intervals have usually been measured with the use of a chronograph; its operation as practised at the Bureau of Standards' is as follows: The temperature of the specimen is measured by a thermocouple and a dial potentiometer. The operator sets the potentiometer at successive values of the electromotive force differing by equal increments, usually 0.02 millivolt, and records the exact instant on the chronograph, by pressing a contact key, at which the galvanometer coil passes through its null position. Two-second intervals are also recorded on the chronograph record, and the number of 'seconds elapsing between successive signals is afterward counted from the record and plotted as a function of the electromotive force or of the temperature. This is an admirable method and by it most minute thermal arrests may be detected, but it requires a good chronograph, which is generally difficult to obtain, and the time of one operator during the recording and, subsequently, to read the intervals from the record; the latter operation often takes from one to two hours.

Jan 7, 1919

By Charles Hawes

WHEN sulfur is encountered in objectionable amounts, it is regarded as the most trouble-some element for the mine operator to control. It exists in two conditions in iron ores, as sulfide in iron pyrites and as sulfate in gypsum and barite. The sulfate radical (SO,) may also be linked to one or more of the several other elements found in the iron ore compound. The only dependable method for the de-termination of sulfur, particularly when found in the insoluble residue, has been the so-called fusion method. This is a long and tedious process involving several hours for its completion. In looking for a more rapid method which would be .applicable to all iron ores, the writer investigated the work of M. Groger1 who in 1881 showed that by heating pyrite with iron out of contact with air, the pyrite is reduced to iron sulfide and from the latter all of the sulfur will be given off as hydrogen sulfide gas on treat-ment with hydrochloric acid. FeS2 + Fe = 2 FeS FeS + 2 HCl = FeC12 + H2S In 1891 F. P. Treadwell2 not only confirmed the results of M. Groger but also found that iron powder would reduce to sulfide the sulfate radical of any substance, including barite, if not found in excessive quantities. The writer found this to be true and developed a method, in cooperation with F. J. Baker, chief chemist, mining department, of the Cleveland-Cliffs Iron Co., Ishpeming, Mich., for the determination of sulfur in iron ores which is not only very rapid but also accurate. Pure iron ore powder, reduced by hydrogen, gave good results but was found to be very slow in reacting. A high silicon iron with a low sulfur content of 0.012 per cent was found to be. much more active than the pure iron and gave excellent results.

Jan 11, 1927

The following paragraph of appreciation of the Engineering Societies Employment Bureau is from the letter of a young engineer who found the Bureau of service. "I wish to sincerely thank you for the services rendered. They are of immense value to anyone located as I am, in a small town without the opportunities for keeping in touch with openings in manufacturing lines."

Jan 12, 1919

By Maurice Ewing

THE purpose of this paper is to present the results of the application of the earth-resistivity method of subsurface investigation to the problem of locating seams of anthracite coal beneath a mantle of soil and subsoil. Details are given of the successful use of this method in locating the outcrops of anthracite seams in actual prospecting. The presence of the outcrop of an anthracite seam is indicated at points where electrical resistivity tests showed relatively low readings. The reason for this is that in some localities the resistivity of anthracite was found to be about 0.0001 megohm-cm. compared to 1 to 200 megohm-cm. for shales and sandstones. For two reasons it is believed that the data sum-marized in this paper should be of particular interest. In the first place, most of the interpretations of the resistivity survey have been checked by subsequent drilling and some by the removal of the overburden and the exposing of the anthracite seams. It is infrequent that the oppor-tunity for checking results so thoroughly is given. In the second place, the fact that recent commentators1,2,3 on the application of geophysical methods to mining have concluded that direct prospecting for anthracite and other types of coal is not promising makes the good results obtained more significant. So far as the authors can learn, the only previous experiment with electrical methods in the Pennsylvania anthracite field was one made by Sherwin F. Kelly in 1922, when he used the self-potential method at Wilkes-Barre4. The profile he made does not show a very marked correlation with the geologic cross section. Kelly points out that stray currents from electric motors in the mines undoubtedly affected his results, but the experience of the present authors with stray currents from mining machinery suggests the possibility that the potentials measured by Kelly were due almost entirely to this effect.

Jan 1, 1936

By R. L. Vaughn, A. G. Moon

In 1972 a major renovation of the flotation and regrinding circuits was completed at Kennecott Copper Corporation's Chino Mines Division concentrator at Hurley, New Mexico. At that time a new lime distribution and control system was placed in operation. Lime is used to depress pyrite, and flotation at a high pH or alkalinity is required for optimum recovery of principal copper minerals, chalcopyrite and chalcocite with good rejection of the pyrite. Regrinding is also required to liberate chalcocite, much of which occurs as intimately associated chalcocite-pyrite middling grains. Accurate control of the lime addition is necessary to obtain both optimum metallurgy and minimum lime usage. At low pH levels, flotation cell control is difficult due to excess froth, but excessively high pH levels can go unnoticed because froth characteristics do not change from those experienced at the desired pH. With manual control of the lime addition, the desired pH can be exceeded for periods of up to two hours. Test Work Plant test work on a lime control system using conventional pH probes gave disappointing results with high electrode maintenance and poor control characteristics. For example, the rougher flotation cells are operated at a pH between 11.4 and 11.6 and the probes required cleaning at least once a day, and occasionally every shift. These high maintenance requirements were considered unreasonable for a plant-wide system using six or more control loops.

Jan 1, 1979

By D. Turnbull, J. H. Hollomon, J. C. Fisher

UNDERSTANDING of the diffusion problem has recently been furthered by the analysis of Birchenall and Mehl.1 They pursued the problem of the variation of the diffusion coefficient with composition for non-ideal solid solutions. Their analysis follows the tradition of Wagner,2 Jost,3 Dehlinger,4 and Darken,' who assumed the net flux of dif¬fusing material to be proportional to the gradient of a quantity related to free energy. The basic assumption in Birchenall and Mehl's formulation of the problem is that the net flux of diffusing material is proportional to a thermodynamic activity gradient. To estimate the applicability of the derived relations, they corrected the diffusion coefficients of carbon in austenite by utilizing Smith's' activity data for carbon, and the diffusion coefficients for zinc in copper with activity data computed from the vapor pressure measurements of Hargreaves.7 The corrected coefficients for carbon were virtually independent of carbon concentration. For the diffusion of zinc in copper a moderate variation of diffusion coefficient with concentration remained after the correction. The problem of diffusion can be formulated in another way than that used by Birchenall and Mehl. The method is that of chemical rate theory and has been used by Eyring and his coworkers8,9 as well as by Eyring and Zwolinski10 in a discussion to Birchenall and Mehl's paper. As yet the method has not been applied to substitutional solid solutions. On the basis of their assumptions, Eyring and Zwolinski derived a relation between the diffusion coefficient and activity that is identical with that of Dehlinger and Darken but which does not correct for the variation of the diffusion coefficient with concentration as well as does the relation derived by Birchenall and Mehl. It was thought that the theory of diffusion would be more complete if the inconsistency between the two analyses could be rationalized and if diffusion in substitutional alloys were analyzed on the basis of the concepts of the chemical rate theory. CHEMICAL RATE THEORY According to the theory of absolute reaction rates8 the reaction [A,+A2+ ... +.A;->X,+X2 +...+X; EqI] is viewed as taking place in two steps. First the reactants A1, A2, . . . A[i] combine to form an activated complex M with which they are in equilibrium; [A, + A2 + .. . + Ai = M. Eq 2] Second the activated complex decomposes to give the products X1, X2. . .. X[j]; [M->X1+X2+ ... +.X;. Eq3] It has been shown8 that the number of activated complexes decomposing per unit volume per unit time is given by the expression† [kT]

Jan 1, 1948

By G. C. Gambs

The electric utility industry is the largest customer of the coal industry and consumes nearly 50% of the present coal production in the United States. The byproduct of the burning of coal in utilities is ash in several forms including fly ash, bottom ash and bottom slag. At present, very little of the coal ash produced is being used and must be disposed of as waste. The coal industry should look upon this waste material as a valuable by-product which, if it can be sold for $2 to $4 per ton, will have the net effect of reducing the cost of coal to the utility by 1¢ to 2¢ per million Btu. There are many ways to use coal ash and thus benefit both the coal industry and the electric utility industry by reducing the cost of coal as burned. The solutions to the problems are obvious and all we have to do is apply them. The electric utility industry is the largest customer of the United States coal industry, consuming nearly 50% of present coal production. By 1980, the electric utilities are expected to burn over 500 million tpy of coal or 75% of total coal production. When coal is burned in electric utility plants, ash is produced in one of several forms. These include fly ash, bottom ash and bottom slag. At the present time, approximately 20 million tons of these ashes are produced and must be disposed of by the utilities at a cost of 50¢ to $2 per ton. In 15 years, more than double this quantity will be produced. Only a small quantity of this ash is put to any practical use. Much remains to be done about expanding uses for fly ash and bottom slag. It is well known that fly ash, when used to replace a portion of the cement in a concrete mix, will produce highest quality concrete. The Corps of Engineers and the Bureau of Reclamation have constructed dams and other concrete structures for years with fly ash as a partial replacement for cement. However, many construction firms do not use it. This can become an opportunity for the coal industry to reduce the cost of coal delivered to utilities. Any fly ash, or other ash or slag, which is sold by the utilities, reduces the cost of coal burned by the utility. As much as 1¢ to 2¢ per million Btu could be taken from the fuel cost for each ton of ash sold which otherwise must be disposed of at a cost.

Jan 1, 1967

By AIME AIME

PLANS are now well advanced for the joint meeting of the Institute and over a dozen other engineering societies in Chicago during the week beginning June 26: Engineers' Week at A Century of Progress. All engineers planning to visit the Fair will find it to their advantage to be present at this time so far as the Chicago attractions are concerned, and Eastern members will also have the advantage of special transportation arrangements on June 24 and 25. The tentative program is given at the bottom of the next page. Monday morning, June 26, will be reserved for registration of members and guests and the Woman's Auxiliary at the Stevens Hotel, where special rooms will be provided. A luncheon will also be served there, and in the afternoon, a technical session on nonmetallics. Instead of having the big family dinner that evening at the Stevens, as at first proposed, the local committee has planned to have it at the Fair Grounds, where special facilities have been arranged. A meeting of the Board of Directors and a few invited guests will precede the dinner. All members and guests are likely to be interested in visiting the Museum of Science and Industry, so that will be the sole event on the program for Tuesday morning, June 27. The big attraction there at present is the model coal mine, the first operative coal mine ever built for exhibit purposes. It is based on the Deutsches Museum mine at Munich, but goes far beyond that in realism, and takes the visitor on an extended tour underground. It shows him in half an hour more types of modern mining machinery and coal geology than he would be likely to see in a week's underground study in the coal fields. The Institute members will be the first group to go through this mine.

Jan 1, 1933

The co-operation of the members of the Institute is earnestly sought by the Committee on Nominations, recently appointed by the Board of Directors, in its work of formulating a ticket for officers and places falling vacant in the Board of Directors in February, 1916. The Committee must present the official ticket of nominations to the Board of Directors at its October meeting. Members are, therefore, urged to send promptly their nominations for officers and Directors in order that the Committee may have an opportunity to give them full consideration. The officers to be elected at the annual meeting in February, 1916, are: One officer, known as Director and President. Two officers, known as Director and Vice-President. Five officers, known as Director. The officers of the Institute whose terms expire are as follows: President, William L. Saunders (not eligible for re-election). Past President, Charles F. Rand. Vice-Presidents, Thomas H. Leggett, District 0; Fred W. Denton, District 4.

Jan 9, 1915

The co-operation of the. members of the Institute is earnestly sought by the Committee on Nominations, recently appointed by the Board of Directors, in its work of formulating a ticket for officers and places falling vacant in the Board of Directors in February, 1916. The Committee must present the official ticket of nominations to the Board of Directors at its October meeting. Members are, therefore, urged to send promptly their nominations for officers and Directors in order that the Committee may have an opportunity to give, them full consideration. The officers to be elected at the annual meeting in February, 1916, are: One officer, known as Director and President: Two officers, known as Director and Vice-President. Five officers, known as Director. The officers of the Institute whose terms expire are as follows: President, William L. Saunders (not eligible for re-election). Past President, Charles F. Rand. Vice-Presidents, Thomas H. Leggett, District 0; Fred W. Denton, District 4.

Jan 10, 1915

By John R. Riede

Most beneficiation plants utilize automatic controls to varying degrees-some have the bare minimum of controls, others qualify as semi-auto- mated operations; a very few are nearing what may be termed "fully-automated" status. But for those plants that produce a filter cake product, the lack of suitable instrumentation for measuring and con- trolling the moisture of the filter cake has been a major stumbling block to fully-automated operations. Today in many cases, this bottle-neck can be removed because various moisture measuring devices are now available to permit automation of the filtering stage. What are these devices? . . . Where can they be used? To answer these questions, two types of operating plants-one, semi-automated and the other, almost fully automated-can be examined. Both plants employ disc filters from which is produced a magnetic concentrate for pelletizing. (The control schemes and equipment depicted in this article are similar to those usable in drum filter plants.)

Jan 3, 1967

By A. N. Chirico

This paper reviews the three major distillation processes: multiple effect (LTV) evaporation, multi-stage flash distillation and vapor-compression forced circulation evaporation. Scale preventative measures are discussed for all saline water applications. Operational data is presented on the Freeport, Texas, demonstration plant, which is the first government facility to produce one million gallons per day of fresh water for a municipality. There has been much publicity concerning the water crisis that confronts many peoples today. There is little doubt that the arid regions - which include the Middle East, parts of Africa and the Caribbean — have suffered to no slight extent for the lack of this most precious commodity. But what about our own country? Government experts have extrapolated demands and flatly predict that by 1980 we will be faced with a shortage of 80 billion gal per day. The validity of this prediction has been disputed by others; however, it appears certain that there will always be a natural abundance in some areas, a shortage of supply in other areas. Distributing our total natural water resource equitably would be impossible. Transmission of water by means of aqueducts can be an expensive undertaking. The controversial Feather River Project in Calif. is an example. The estimated cost for this venture is a staggering three billion dollars. As our population continues to increase and our standard of living rises, agricultural and industrial requirements will be proportionate. What can be done to avoid a crisis? We can conserve and use our water for industrial and irrigation purposes more judiciously: we can attempt to eliminate pollution of our natural resources from sewage and industrial wastes; we can develop, while there is time, saline water conversion processes for the massive production of low cost fresh water. The scope of this paper will be limited to only the distillation type processes that are commercially feasible. The first step in making potable water is to find a source of raw material. An inexhaustible supply is provided by oceans in coastal regions, but the supply of water is more critical in the inland communities of our country. The source of raw material in these. regions is brackish well water and this must be utilized. There is a significant process difference when handling brackish water compared to seawater and this brings out an important fact: No single conversion method can be universally applied to solve all the water problems. Composition of the raw water and degree of distillate purity are factors which must be considered before a particular process is selected. Local conditions at the plant site, fuel costs, labor costs, disposal facilities, etc. are other equally important factors which must be evaluated. WATER CONVERSION PROCESSES Conversion processes commercially feasible today are: 1) multiple effect evaporation, 2) multiple flash distillation, 3) vapor compression distillation and 4) electrodialysis. The first three are distillation processes which take potable water out of the raw water, while the fourth is a membrane process which takes out the salt. In addition to the above there are a good number of other promising methods for production of potable water, many of them in the basic research stage. Freezing is another promising process with commercial potential. This process hinges upon the formation of ice crystals which are free of salt occulsions. Separation and washing of the crystals are problems that must be solved before this process can be considered commercially feasible. Freezing processes have several advantages mostly attributable to the low temperature of operation. This low temperature reduces the scaling and corrosion problems encountered in higher temperature operations. Several different freezing processes are being considered and will be tested in the pilot plant at Wrightsville Beach. One process is a flash freeze process, a second uses a secondary refrigerant such as butane for freezing, and a third process employs a secondary refrigerant particularly controlled to produce large ice crystals. Of the above processes, only the distillation processes are reliable when water of high purity is re-

Jan 1, 1963

By Charles Will Wright

The present struggle for economic and industrial supremacy by the Communist world is against the United States, its main target, and the other Free World nations. The basis of industrial power is minerals, so the Communist nations are building up mineral production within their borders, often regardless of costs, and are acquiring quantities of mineral products from Free World countries for future use. They are contracting for additional supplies and advancing funds for the development of these quantities. A number of the less developed mineral producing countries of the Free World are being infiltrated by Communists and Communistic influence. This situation is well known, but as yet little has been done to oppose these activities or to awaken the public to their seriousness. The Communist countries are still far behind the Free World Nations in production of many essential minerals. But, shortages are being made up from Free World nations in exchange for petroleum, manganese ore, chromite and other products. Restrictions on shipments of strategic materials to Communist countries have not been maintained.

Jan 1, 1964

By Andrew Corry

GEOPHYSICAL investigations based on radioactivity have been applied to the earth's crust for the purpose of discovering bodies rich in radioactive substances, or for the location of solutions with high emanation or radioactive-salt content, or for the detection of oil, which, in virtue of colloidal properties, has strong powers of radioactive absorption. RADIOACTIVE SUBSTANCES Radioactive substances are distributed in all rocks, waters, and gases in the earth's crust in small quantities. Granites and similar acidic rocks are richest in uranium and thorium, two chief radioactive substances; yet the quantities present in such rocks are of the order 10-12g., this concentration being expressed in grams per gram of the whole substance per cubic centimeter. In granites the uranium yields, according to Haddock, 3 X 10-12 g. of radium per gram of rock. In basalts the uranium yields 1.19 X 10-12 g. per gram per cubic centimeter. Of thorium the granites yield -2 X 10-5 g. per gram of rock; the basalts, 0.77 X 10-5 g. per gram. Certain series of alkalis of low atomic weight, like potassium and rubidium, show weak radioactivity; this property has no significance so far for geological research. The uranium is esti-mated indirectly from the electrical properties of one of its derivatives as a -gas (emanation) into which it is transformed. The thorium is expressed directly, though it is measured as a derivative, thorium emana-tion. There is a measure for the gaseous radium emanation, the curie, which is that quantity of radium emanation, or radon, which stands in equilibrium with 1 g. of radium. The concentration of the emanation is the Mache unit corresponding to 3.64 X 10-10 curie per liter. When gases become permeated by alpha, beta, and gamma rays, plus and minus ions are produced in them by the decomposition of neutral gas molecules, and under the influence of an electrical field these ions are given opposite motions. The measurement of the alpha rays and the bisection thicknesses of the beta and gamma rays is a means of analyzing unknown radioactive substances. These rays accompany the disintegration of radioactive substances and arise from "spontaneous internal changes

Jan 1, 1929

By A. F. Lucas

EACH day, the fact becomes more evident that the ever-growing demand for oil is farther outstripping production, regardless of the increase in output throughout the past twenty years. The development of known oil fields and the prospecting for new ones along present lines are not resulting, in, and cannot bring forth, supplies large enough adequately to meet the oil needs of the country. The usual methods of prospecting-for new supplies are insufficient to meet the exigencies of the situation which threatens, in the not distant future, to reach a critical stage. Were it not that within the last two years new and prolific oil fields have been discovered in northern Louisiana, central Texas, and California, this crisis would undoubtedly be now at our door. Stocks are being exhausted in spite of the rapid growth of imports. The time is therefore fast approaching when some radical departures must be made in the method of prospecting and developing old and new fields in order to increase our oil supplies. Methods and chances, that have seemed unwarranted will not only be given serious consideration, but, according to the results promised, will be put to the test. Meanwhile, however, nearly all the oil fields are responding to the stimulus of higher prices, whereby enormously growing capital is attracted to this important industry, both here and abroad; the increase in our petroleum production at the present time is due to this circumstance. Yet, although a most active search is being made for possible sources of additional supply, one section of our country is not yielding the results that, in my opinion, it is capable of producing: I allude to the coastal dome belt of Texas, Louisiana, and Mexico. The United States Geological Survey has estimated that three-fourths of a billion barrels are available in the ground in the Coastal Plain of the two states just mentioned. Numerous papers have been written on the subject of the salt domes of the Coastal Plain and more or less attractive theories have been advocated by leading geologists to account for their origin and the presence of the oil, sulfur, and salt associated in them. However, owing in part to the generally monotonously level country in which the coastal

Jan 9, 1920

By Warren A. Sinsheimer

ProbDly there has never been a year during which the petroleum industry expended so much effort as in 1929 in an attempt to rectify its ills. Eventually good will undoubtedly result, but as yet there have been no marked changes from the unhappy conditions familiar to all. Throughout the year remedies were sought that would cure the long-existing troubles of overproduction and waste. Proration of production and voluntary curtailment of output, for a short time considered the means for stability, not only failed but contributed to further waste and created a false sense of security. It encouraged a high rate of field development, weakened the economic structure by excessive development of newly discovered reserves and absorbed large sums of capital yielding meager or negative return. The manufacturing of gasoline by refiners without regard for market requirements furthered the unsatisfactory condition by falsely stimulating the demand for crude and placed on the market an oversupply of finished products, particularly gasoline. The marketing section of the industry has made progress by its adoption of the Code of Ethics as promulgated by the Federal Trade Commission and by the formation of an Export Association. The year 1929 opened not only with a current supply of oil exceeding demand but with an additional daily shut-in and potential supply variously estimated at from 3,000,000 to 5,000,000 bbl. This situation stimulated the industry, through the American Petroleum Institute, to attempt to work out an economically sound solution which would further conservation by bringing supply and demand into closer balance. Production Control After a thorough study of producing conditions, the committee of the American Petroleum Institute had for its recommendation that the production of crude oil in 1929 be held in check to an amount equal to that produced during the year 1928. The Federal Oil Conservation Board heard the appeal of the American Petroleum Institute and referred the matter to the Department of Justice. It was ruled that neither the Federal Oil Conservation Board nor the Department of Justice had the * Land and Oil Production Dept., Henry L. Doherty & Co.

Jan 1, 1930

By G. Derge, W. Peifer, J. H. Richards

INTRODUCTION A WIDE variety of metallurgical defects in steel have commonly been attributed to the presence of excessive amounts of hydrogen. These defects include flakes in rails and forgings, cracks in welds, and blisters in enameled ware. They have been related to hydrogen largely by circumstantial evidence because the proper sampling and analysis of steel for hydrogen has been known to be difficult and because no general agreement has existed with regard to the relative suitability and accuracy of available methods. The need for a direct approach to these problems has been widely recognized. This general situation has been well described in the publications of the British Committee on the Heterogeneity of Steel Ingots,1 and current approaches to the problem were reviewed in a recent symposium of the AIME.12 The plans described by the present authors at that meeting have now matured satisfactorily and will form the basis of this paper. The principle object of this paper will be to describe the methods of sampling and analysis which have been developed and to illustrate the usefulness and limitations of these methods by citing their application to a specific problem. The first problem selected for investigation was the behavior of hydrogen in rail steel. This was chosen because the occurrence of shatter cracks in rails has received a great deal of study over a long period of time. The defect can be controlled by the expensive procedure of slow cooling. However, it may be hoped that a better understanding of the factors influencing the hydrogen content of rails will lead to a more efficient control of this problem. Rails provide a good starting point for a more general study of hydrogen in steel because they provide a cross section large enough to develop cracks, yet small enough for convenient handling and sampling. Rails were also selected because they are made from plain carbon steel and it was felt that the initial work should not be complicated by the effects introduced by alloying elements. The considerations which determined the original planning of this study should be reviewed. The inherently complex nature of most hydrogen problems requires that a large amount of data must be collected for any particular case. This in turn means that any analytical procedure should be as rapid and simple as possible. The same objective of speed is indicated by the fact that it may finally become desirable to use hydrogen analysis in process control. It is also known that hydrogen is highly fugitive and that any procedure which facilitates early analysis of the sample without prolonged or irregular storage has distinct advantages. The most important previously reported methods of analysis may be classified into three general groups: (I) Vacuum fusion. (2) Vacuum extraction (without melting). (3) Total combustion.

Jan 1, 1948

By H. T. Clark, S. Feigenbaum

THE importance of measuring the temperature of molten steel in the open-hearth furnace has been recognized for many years. Poor temperature control may be costly to steelmaking operations and lead to a lowered quality of the steel. Low or excessive temperatures may shorten the life of the furnace, ladles and molds. Rates of reactions in the furnace and efficiencies of deoxidizers are known to change materially with a change in the temperature of the metal and slag. Ladle skulls and mold and stool stickers cause steel to be scrapped instead of being converted into useful products. Finally, the structure, segregation and surface condition of ingots are affected by the teeming temperature. Mill investigations of the effect of bath temperature upon steelmaking operations have been largely qualitative in character, based upon observations by practical melting men. The physical chemist has used the empirical information available and has reached reasonable and useful conclusions with respect to the various melting processes. The introduction of a reliable direct- reading pyrometer will permit accurate quantitative evaluation of the effects of temperature and should furnish a more rational basis for study of the thermo- chemistry of steelmaking. The problem is not merely one of making a small number of temperature measurements in the open-hearth furnace. This has been done by several methods to a degree of precision that was apparently satisfactory. Considerable effort by a number of investigators has been directed rather to the development of an open- hearth bath pyrometer that would be both accurate and practical for routine measurements. To be practical, the pyrometer should be inexpensive to operate; that is, the installation, operating and maintenance costs should be exceeded by the tangible benefits to the open-hearth operator. Temperatures from 2800° to 3100°F. are encountered in the open-hearth furnace. The surface of the molten metal is covered by several inches of slag, which prevents direct observation of the metal surface for optical or radiation measurements. Both slag and metal are highly reactive at these temperatures and will attack to a greater or lesser extent any material immersed in them. Adequate protection of thermocouples, which of necessity must be brought to the temperature of the bath, has generally resulted in a large, heavy assembly made up of .brittle materials, unsuited for handling on the open-hearth floor. The lie of the equipment was short and maintenance was an important consideration. EARLIER WORK Any one of a number of physical proper- ties of liquid steel could conceivably be used as a basis for temperature measurement. Efforts to the present time, however, have been confined largely to measuring either the thermal electromotive force generated between two dissimilar materials immersed in the steel or the intensity of radiation from the surface of the steel. These

Jan 1, 1946

By W. W. West

MACHINERY used for size reduction of materials may be divided into three classes-depending upon the manner in which the crushing force is applied. In the first class could be listed the primary crushing units, such as the jaw crusher and gyratory crusher-which crush to coarse sizes by applying pressure intermittently between converging surfaces. In the second class may be listed crushing units, such as the hammer mill, roller mill, and ball mill, which crush principally by grinding or attrition. In the third class is the impact mill which, as the name infers, crushes by impact. The second and third classes generally include machinery used as secondary units for intermediate or fine crushing and grinding. Theory of Crushing by Impact Throw a stone into the air and give it a severe blow while it is momentarily suspended, and it shatters into several pieces. The impact crusher uses this "batting" principle, but carries it one step further. As the material to be reduced enters the crushing chamber, it receives a severe free-air impact blow by hard-hitting beaters suspended from rotor discs. The shattered particles formed are then driven at high velocity against impact blocks, where a further reduction in particle size takes place. The rebounding particles from the impact blocks are again caught by the beaters, and the process repeated until the material is swept out of the open bottom of the crusher. Impact Crushing Versus Attrition Crushing Fig. 1 shows a Hammermill type of attrition crusher. This particular mill has central feed and is reversible. Because of the central feed, an impact section can be designed into it at the feed entrance for preliminary crushing, followed by the cage bar attrition area for final sizing. The material is caught and held in a crushing chamber enclosed by grate bars or perforated plate. It remains in this chamber until it is reduced to particle size small enough to pass through the openings between the bars or in the plate. In this manner the top particle size discharged from the mill is closely controlled. As the swinging hammers pass through the bed of material, the material is broken down by a scrubbing action between hammers and material, material and grate bars, and material against material. This attrition produces a rounded particle shape, accompanied by slivers and a comparatively high percentage of fines. The crusher is especially useful in industries where the material treated is not too abrasive, such as limestone, cement or coal plants. It can be readily understood that from the maintenance standpoint, it is not suitable for hard abrasive materials such as refractories and aluminum oxides. One common type of impactor is shown in Fig. 2. The bottom of this type crusher is entirely open and the passage of the material through the crushing chamber is almost instantaneous. Liberal clearances are maintained between the impact hammers and the anvil type breaker blocks. This eliminates practically all attrition. It is the elimination of attrition that makes the impactor particularly adaptable for reducing hard, abrasive materials. The impactor is also well suited for the reduction of wet or frozen materials, which clog an ordinary Hammermill. Particles broken by impact, when examined under the microscope, show a distinct tendency toward rough, cubical shape, with a minimum of fines. Another important factor in impact crushing is that crushing is accomplished along natural cleavage lines, thus freeing foreign ores or materials.

Jan 1, 1952