Search Documents

By B. Trentini

In the spectacular development of pure oxygen steel-making, the process using the vertical lance converter LD, is at the present time the most widely employed. Proper control of slag composition during the steel-making process appears to be essential in achieving satisfactory blowing from both the metallic yield and metallurgical points of view. The paper illustrates the primary importance of the presence of a large quantity of metal droplets in the slag during the process. In the case of both phosphorus and hematite pig iron, it can be deduced from the phase diagrams and confirmed by experimentation that nonhomogeneous slags are one of the causes of slag overflowing during the blow. The problem is however a complex one and further physicochemical studies appear necessary. Finally, the new continuous steelmakingprocess developed by IRSID is described. PEOPLE who knew Henri Marion Howe have said that he took great pleasure in speculating on the future of metallurgical processes. It is therefore not inappropriate to devote, in his memory, some description and discussion to processes unknown to the world of his time, in particular oxygen steelmaking and continuous steelmaking. The first industrial application to steelmaking of tonnage oxygen produced by air liquefaction was made in Germany just before the war and consisted in enriching the air blown through the bottom of a basic Begsemer converter in order to melt a higher proportion of scrap and to produce steels with lower nitrogen content than is achieved with conventional practice. While this process was being developed after the war, mostly in Western Europe, steelmakers were becoming increasingly familiar with the technique of blowing pure oxygen from the top, first by means of consumable steel pipes, with or without refractory shielding, and later by water-cooled lances, designed for the purpose and affording longer life. The field was then open for the wide use of pure oxygen in steelmaking, either in existing processes such as open-hearth or electric furnace, or in new processes. These new processes can be broadly classified according to the category of furnace employed. In the case of the vertical converter taken as the first category, bottom-blowing of pure oxygen causes extremely rapid wear of the refractory tuyeres, and although various expedients have been tried to overcome this drawback (such as mixing oxygen with CO2 or H2O or using high pressure oxygen), they have had to be abandoned. The solution for vertical converters has been found in top-blowing with a vertical water-cooled lance; this is known as the LD process or basic oxygen converter process.

Jan 1, 1969

By K. J. Brondyke, P. D. Hess

Lack of correlation between densities of aluminum alloy samples solidified under reduced pressure (vacuum gas test) and hydrogen content of the metal is explained on the basis of inclusions serving as nuclei for hydrogen bubble formation. As a result of these findings, the vacuum gas test is suggested as a practical tool to indicate metal cleanliness and the potential effects of hydrogen. Visual obseroation of the sample during solidification under vacuum provides more useful information than that obtained either from density meas -urements or sectioning of the solidified sample. A rapid, practical method of detecting and measuring gas in molten-aluminum alloys has been sought for many years. The development of the vacuum gas test appeared to solve this problem. However, the vacuum gas test is subject to certain limitations, and the results must be interpreted mindful of these limitations, as described herein. Since the only gas which is appreciably soluble in aluminum is hydrogen, the terms gas and hydrogen will be used interchangeably in this paper. In the early days of the aluminum industry, when techniques were not as refined as they are today, it was customary to pour small "pancakes" of alumi- num on a metal plate. These were allowed to solidify under atmospheric pressure. Excessive gas in the metal was evidenced by the appearance of small bubbles on the surface of the "pancake".' It is obvious that such a method would only show very high gas levels far above any which could be tolerated by today's standards of quality required for most applications. Various attempts were made to develop methods which would be more sensitive. Among these were measurements of density of aluminum alloys solidified under controlled conditions, radiography of cast slabs, and examination of fractures. The method which showed the greatest promise and appeared most practical was the solidification of a sample of the molten aluminum alloy under vacuum. The samples so solidified are evaluated either by observation for bubble emission during solidification, by sectioning the solidified sample and examining for porosity, or by determining the density of the solidified sample. This test is known internationally as the Straube-Pfeiffer test or the reduced-pressure solidification test, but in America it is commonly referred to as the vacuum gas test2-' and will be so designated in this paper. The determination of density appeared an attractive and convenient means of providing a numerical rating for the samples. Attempts were made in some instances to correlate densities to hydrogen contents. Unfortunately, the visible loss of gas during solidification of samples with high gas contents precluded a correlation of vacuum gas test densities with the observed gas evolution. This led to Alcoa's use of two different pressures; 50 mm of

Jan 1, 1964

By Louis Raymond, John E. Dorn

The object of this investigation was to analyze the recovery that arises when the stress on a specimen undertaking creep is reduced. For this purpose annealed specimens of high-purity aluminum were precrept under a stress of 1000 bsi to a strain of 0.08 following which the stress was reduced for various periods of time to 10, 250, 500, or 700 psi. When the original stress was reapplied the subsequent creep curve lay above that for the unre-covered state and below that for the original annealed state. Analyses on the kinetics of this recovery as a function of the temperature gave a stress-sensitive activation energy that decreased as the reduced stress was increased from a value of 64,000 cal per mole at 10 psi to 37,000 cal per mole at 750 psi. Recovery was also detected and measured during creep under the reduced stress. Following a short initial period, the creep rate under the reduced stress increased monotonically until it reached the secondary-creep rate for the reduced stress. The temperature dependence of this phenomenon was also shown to be correlatable in terms of the previously deduced activation energy for recovery. The activation energies for creep of most pure metals at high temperatures have been shown to agree well with those for self-diffusion.'j2 Since the true secondary stage of creep is usually due to the steady-state balance between the rate of strain hardening and the rate of recovery, it is generally thought that the activation energy for recovery of the creep-induced substructure equals that for creep itself. A shoft time ago, however, Ludemann, Shepard, and Dorn~ found that the activation energy for recovery of the creep-induced substructure in high-purity aluminum under zero stress was almost twice that for self-diffusion, namely about 65,000 cal per mole; obviously recovery under reduced stresses differs in some significant way from the recovery that accompanies the secondary stage of creep. The major purpose of this investigation is to study the effect of stress on the re- covery of the creep-induced substructure in order to provide a better understanding of the recovery mechanism itself. EXPERIMENTAL TECHNIQUE High purity aluminum, containing 0.004 pct Cu, 0.002 pct Fe, and 0.001 pct Si, used in this investigation, was in the form of 0.100-in.-thick sheet which has been cold-rolled to the H-18 temper. Creep specimens were milled from the sheet with their tensile axes in the rolling direction. All specimens were then heated at 686°K for 1 hr followed by air cooling in order to produce an annealed structure which exhibited a uniform equiaxed grain size of about 4 grains per mm. Tests were run in creep machines fitted with Andrade-Chalmers type of lever arms so contoured as to maintain the stress constant to within 0.05 pct of the reported values. Constant temperatures to *O.l°K were obtained by complete immersion of each specimen in a temperature-controlled and agitated bath of molten KN02-KNOs mixture. Where changes in temperature were involved, the change was effected in less than 2 min by manually replacing one bath by another controlled at the second temperature. Displacements over the gage section were sensed by linear differential transformers, the output of which was autographically recorded. The calculated strain measurements were sensitive to 5x EXPERIMENTAL PROCEDURE The following analyses are based on extensions of the previously announced effect of the temperature on the creep strain,2 namely for a = constant, where e = the total true tensile creep strain for a given applied true tensile stress, t = the duration of the test, R = the gas constant, T = the absolute temperature, Q, = the activation energy per mole for creep which is independent of the stress, / = a function of 8, = and of the stress, and a = the stress. The validity of this correlation for high-purity aluminum is demonstrated in Fig. 1 for temperatures in the near vicinity of 600°K; the activation energy for creep, Q,, which is approximately that for self-diffusion, is insensitive to the applied stress

Jan 1, 1964

By A. W. Ross, William Marsh Baldwin, T. S. Howald

The related subjects of preferred orientation, directionality in physical properties, and earing tendencies of wrought metal strip have attracted the attention of metallurgists to such an extent that in the past 20 years hundreds of researches have been published on this one general problem. The anisotropy of tensile strength and elongation have been exhaustively studied in their relationship to the occurrence of ears in cups drawn from strip'-~O.~g and, to a lesser extent: yield strength7."-l7 and stress-strain curves'5 have been investigated. Despite the tremendous fund of knowledge thus accrued, no simple quantitative correlation of directionality and earing tendencies has yet been found. In a sense, this is not surprising. The formation of ears in a drawn cup clearly is a special phase of the general study of metal flow; in particular (as will be brought out in the course of this paper), ears are due to anistropy in the rates of deformation of the metal in the radial, circumferential, and "thickness" directions of the original blank. It would be difficult to effect a correlation between caring tendency and a property that may be completely independent of the flow of metal, or at best related to metal flow in an exceedingly complex fashion. Yet, it is this correlation that has been attempted; tensile strength and elongation are attributes of metal rupture. a phenomenon that has quite admirably been shown to be distinct from the phenomenon of metal flow,21 while yield strength and stress-strain

Jan 1, 1946

By William Marsh Baldwin, T. S. Howald, A. W. Ross

The related subjects of preferred orientation, directionality in physical properties, and earing tendencies of wrought metal strip have attracted the attention of metallurgists to such an extent that in the past 20 years hundreds of researches have been published on this one general problem. The anisotropy of tensile strength and elongation have been exhaustively studied in their relationship to the occurrence of ears in cups drawn from strip'-~O.~g and, to a lesser extent: yield strength7."-l7 and stress-strain curves'5 have been investigated. Despite the tremendous fund of knowledge thus accrued, no simple quantitative correlation of directionality and earing tendencies has yet been found. In a sense, this is not surprising. The formation of ears in a drawn cup clearly is a special phase of the general study of metal flow; in particular (as will be brought out in the course of this paper), ears are due to anistropy in the rates of deformation of the metal in the radial, circumferential, and "thickness" directions of the original blank. It would be difficult to effect a correlation between caring tendency and a property that may be completely independent of the flow of metal, or at best related to metal flow in an exceedingly complex fashion. Yet, it is this correlation that has been attempted; tensile strength and elongation are attributes of metal rupture. a phenomenon that has quite admirably been shown to be distinct from the phenomenon of metal flow,21 while yield strength and stress-strain

Jan 1, 1946

By Alexander Field

INTRODUCTION THE Bureau of Mines is investigating the problem of slag viscosity, its variation with the temperature and with the composition of the slag, and its effect upon the distribution of the sulphur between molten iron and slag, as introductory to a series of contributions to the theory of the metallurgical processes. The method of measurement, viscosity, apparatus, furnace and other accessories mentioned in this paper have been described fully in a Bureau of Mines report.1 THE LITERATURE ON SLAG VISCOSITY The viscosity of blast-furnace slag had not been measured previous to the investigation described in this report. A number of investigators have determined the "fusibility," or softening temperature, of slags by means of the cone method or, other deformation method, but these methods supply only limited information regarding the temperature-viscosity relations.-of the slag in question. Any deformation method that may be employed indicates only the temperature at which the slag attains a more or less definite viscosity, the magnitude of the value obtained depending on the method used. For details of the various methods used by different investigators, see, the Bureau of Mines paper already referred to. An isolated measurement by Doelter on a single mixture at 1,300° C. represents the highest temperature reached in the various viscosity investigations previous to those described in this report, in which results have been referred to absolute units. Arbitrary deformation tests have of course been made at much higher temperatures.

Jan 2, 1917

By J. M. McKenzie

p-n junctions to detect and measure the energy of single quanta of electromagnetic radiation are described. Useful energy range is from 1 kev to several Meu. Achieved energy resolution varies from 30 pct at 6 keu to 0.12 pct at 2 Mev. Parameters affecting the perfornzance of the present detectors and desired of a new material are discussed. DURING the last 6 years semiconductor detectors have been used extensively to detect and to measure the energy of charged particles. These detectors are made from reverse-biased p-n junctions. Electron-hole pairs are created in the depletion region of the junction, Fig. 1. The carriers are separated by the electric field and give rise to a pulse of current in the external circuit. This current pulse is proportional to the number of carriers and hence to the energy deposited in the depletion region by the ionizing event. More recently the discovery of the lithium drift process, first in silicon' and then in germanium,2 has extended the use of semiconductor detectors to the detection and the energy measurement of single quanta of electromagnetic radiation. These detectors now have a useful measurement range extending from the soft X-ray region, about 6 kev, to the hard y ray region of several Mev. Surface-contoured avalanche diodes can be used to extend this range down to 1 kev. There is however a desire for other materials suited to higher operating temperatures, and particularly for those materials with high y ray stopping power. The most important advantage of the semiconductor detector over gaseous and scintillation detectors is the average energy, E, required to form an electron-hole pair. Fig. 2 shows the quantum efficiency for germanium as a function of photon energy.3 At the band-gap energy, 0.7 ev, an electron-hole pair is generated by the absorption of the photon and the quantum efficiency is unity. The quantum efficiency remains constant at unity between 0.7 and 3 ev. It then increases as additional electron-hole pairs are formed by secondary ionization of the initial photoelectron. The rate of increase is about 1 electron-hole pair per 3 ev (actually 2.9 ev for germanium and 3.6 ev for silicon). This figure is constant irrespective of the particle type (electron, proton, a particle, heavy ion) and energy. In an ionizing event an incident particle of energy E will create N = E/e ion pairs. The statistical fluctuation in this number is proportional to &. The fractional energy resolution is therefore proportional

Jan 1, 1968

By John V. Beall

On the banks of Huzzah Creek there is a roadhouse where a group of Ozark folks were whiling away a Sunday afternoon last spring. "How about some of that 'Who Broke the Lock Off the Hen House Door,' " suggested Spinny. The old man obligingly picked up the fiddle and began the sprightly tune. His long, seamed face had ruddy cheeks and a grey stubble jaw. A thick fedora was pushed back off his scraggly hair and he wore a heavy jacket. It was 73 degrees fetchin up for 75 on that May afternoon, so naturally he sweated. The Ozark is fiddling country. The natives, to whom a half dollar looks as big as a manhole cover, put great store by fiddling, along with the other fine things of life such as fishing and horse raising. On the wooded hills, 1200 to 1700 ft above sea level, there are numerous tumbling streams with plump fish, and in clearings along the roller coaster roads are long-legged, frisky looking horses. People in the Ozarks have a reputation for self-reliance. However, they are cheery and friendly to strangers. Trespassers are very seldom shot at-except if they do something wrong or by accident.

Jan 7, 1963

By James P. Graham

In this paper the authors present the background information to preheating and its development and describe the facilities available at the British Carbonization Research Association. The results obtained at BCRA including those collected during commissioning of the new plant at BCRA are summarized and reference is made to the research work planned for the next stage. The enlarged test-plant facilities at the British Carbonization Research Association embrace both 10-t (4.2 m high) and 17-t (6.5 m high) test ovens and two types of preheater, the preheated coal being charged by either gravity or pipeline. During the commissioning of the new equipment, an extensive programme on preheating was initiated and the paper includes the results obtained so far. These cover tests on wet and preheated coals and commercial blends, the use of Rosin- and Cerchar-type preheaters and charging by both gravity and pipeline systems to the 10-t and 17-t ovens. Accordingly, for the first time a direct comparison is possible of both the performances of the plants and the qualities of the respective products. The paper also outlines the findings from a study of the carryover of solids during the charging of preheated coal and of the treatment of those solids.

Jan 1, 1977

By John Norton

IN recent years, the damping capacity of metals has come to be recognized as an important index of certain types of structural change. In a number of instances, this property has proved to be particularly sensitive, but insufficient work has been done to permit a general inter-pretation. There is considerable question at the present time as to just what factors are responsible for the internal dissipation of energy when a metal is carried through a cycle of stress, and these factors must be ascertained if the value of the damping method as a metallurgical tool is to be determined. Since internal stresses are among the chief causes of dissipation of internal energy, or damping capacity, it was thought that a study of the changes in damping during the recovery and recrystalliza-tion of a cold-worked metal might throw some light upon the subject, particularly if the damping changes were correlated with other properties that are better understood. Probably more work has been done on the recrystallization phenomena of alpha brass than on any other metal, so this was chosen as the material for the present investigation. Damping measurements on brass have been made by Förster and Köster.1 They showed that the annealing of a brass that had been cold-drawn to 50 per cent reduction produced a rapid fall in the damping, a flat minimum occurring at approximately the temperature of recrystal-lization. The damping remained at a low value until grain growth was well under way and then it increased rapidly with increasing grain size. Köster and Rosenthal2 continued the work in greater detail. They pointed out that the damping decrease does not correspond to the hard-ness drop but occurs at a lower temperature, suggesting that the relief or redistribution of internal stresses has a large effect while the actual recrystallization effect is small. They also show the increase in damping at the higher annealing temperatures. Their curves are reproduced in Fig. 1.

Jan 1, 1940

By Thomas S. Nye

Mineral exploration in the United States relies heavily on theoretical geologic concepts and indirect methods such as geophysics and geochemical prospecting, as there are few exposed areas of mineralization which have not already been explored. In Mexico, ore grade samples can be cut at the surface on vein, replacement, and disseminated types of deposits in many areas. The problem is not in finding a mineralized area but in deciding which mineralized area can be explored and developed at the least risk and cost, with the greatest profit potential within the framework of Mexican mineral economics and that nation's government policies. Socio-economic Posture Mexico, prior to World War II, had suffered from more than one hundred years of intermittent wars and exploitation by internal and foreign elements. Consequently, the basic facilities which today's society takes for granted were scarce or non-existent in most of the country. Travel was largely a matter of negotiating poor dirt roads, riding horseback or walking. Relatively few people were literate and medical facilities were luxuries for the wealthy. Mexico's leaders were, however, determined to improve the lot of their people, within a system of private enterprise and personal freedom. Long-range programs initiated at about the time of World War II to provide infrastructure-education, health and welfare, transportation, power, water, communication-are now established fully or in part for most of the country and are being continually expanded.

Jan 12, 1972

By C. W. Gibbs, E. K. Parks

In 1929 the Standard Oil Company of California commenced the development of a device for obtaining temperatures and pressures in flowing and shut-in wells and of suitable running equipment for such a recorder. Although simple in principle, the recorder has required much experimental work in its development. The various problems have now been solved to such an extent that it is believed that the apparatus affords a sturdy and reliable means for obtaining information regarding depth pressures,—apparatus that may be turned over to a well gang for routine operation. As an example of the rough usage the device will withstand a recent incident may be cited. Owing to failure of the lowering line at the conclusion of a run a recorder was dropped some 6300 ft. through 2 1/2-in. tubing filled with gassy oil. The device was fished out undamaged and with the pressure record intact, although the instrument had been subjected to a pressure greater than 2300 lb. per sq. in. for some 24 hr. after impact at bottom. Description of Recorder The instrument is of the continuous recording loaded spring type (Fig. I). Temperature is not recorded continuously but is obtained by maximum recording thermometers in an auxiliary thermometer well. The entire instrument assembly, from bottom of the recorder to top of the socket, is 6 1/2 ft. long and weighs less than 25 lb. The maximum outside diameter of the recorder shell is 1 1/4in., and all attachments need be no larger. This permits lowering the device inside 2-in. tubing. The operating principle is simple. The well pressure acts upon a piston A resisted by the extension of spring B. The spring deflection is recorded by a stylus C upon paper within the recording drum D. Springs.—To improve accuracy at lower maximum well pressures five interchangeable spring assemblies are used. These have maximum pressure ranges of from 250 to 5000 lb. per sq. in. Piston diameter is the same in all cases, and each spring is designed for a deflection of about 5 in. for maximum pressure loading. A complete spring assembly there-

Jan 1, 1934

By John J. Croston

The year 1935 witnessed one of the world's oldest industries—gold mining—attain the stature of a billion dollar business. Preliminary estimates indicate that somewhat over 30,000,000 oz. of gold was produced, the largest output ever recorded and exceeding the previous year by more than 11 per cent. Of this huge total the Witwatersrand field produced about 10,800,000 oz., compared with 10,480,000 oz. in 1934. Russia was apparently the stellar performer, and from incomplete data it appears that between five and five and a half million ounces were produced by the Soviets compared with 4,200,000 last year and 2,814,000 in 1933. The United States nosed Canada out of third place with a production of 3,546,000 oz. against 2,916,000 in 1934, while Canada increased her total from 2,965,000 to 3,291,000 oz. Similarly, gains of lesser magnitude were made in Australia, the Gold Coast and other countries. As a result of great activity in developing outlying areas on the Rand, and the great number of new companies building mills in Canada, Australia, the Gold Coast and the United States, the years 1936 and 1937 should see new high records, as these new producers will more than offset any decline in the older properties. The whole world has become "gold conscious" during the past three years. It has been the subject of innumerable articles by economists and others, but, unfortunately, because of their lack of actual mining knowledge, they have treated the production of gold as a static affair, ignoring geological and technical factors. It is hardly necessary to draw attention to the fact that the world's gold-mining industry was slowly but steadily shrinking in importance, owing to the gradual depletion of known deposits that were profitable to work at costs existing prior to 1929. The International Geological Congress at Pretoria and the League of Nations Committee drew attention to the estimates of the mining experts of the various governments predicting a steady falling off in world production. On the Rand there

Jan 1, 1937

By B. Wilhelmi, W. H. Somerton

Simultaneous measurement of pore and elastic properties of socks under a wide range of triaxial stress conditions may be made with equipment and methods developed in this paper. Tests were run on three outcrop sandstones at several confining pressures and axial stresses up to approximately 80 percent of failure stress. The greater reduction in porosities and permeabilities occurred in the hydrostatic loading portion of the stress cycle, but substantial reductions in both properties did occur upon application of deviator (triaxial) stress. Triaxial elastic moduli were calculated from strain gauge measurements. Both Young's moduli and shear moduli were found to increase with increasing confining pressure. Poisson's ratios increased with axial stress but showed no consistent change with confining pressure. Only very general relations were observed between pore and elastic properties. The lesser decrease in porosity and permeability at higher stress values is related to increase in rigidity of rocks at higher stresses. INTRODUCTION Many investigators have studied the effects of hydrostatic stress on the properties and behavior of rocks. A few have studied the effects of triaxial stress fields on individual physical properties of rocks. To our knowledge no one has measured simultaneously pore and elastic properties of rocks under a wide range of triaxial stress conditions. This is the purpose of this work. Rocks exist in the subsurface under what Jaegerl refers to as "polyaxial" stress conditions (all principal stresses unequal). When two of the three principal stresses are equal, this is referred to as triaxial loading. The triaxial method of loading is most commonly used in modern testing work because experimental difficulties in measuring physical properties of rocks are greatly reduced over polyaxial testing. Although triaxial loading may not reproduce subsurface conditions precisely, subsurface stress conditions are never known precisely anyway. Triaxial testing would seem to be more realistic than testing under hydrostatic loading (all principal stresses equal) for application of results to subsurface problems. The objectives of this work were threefold: (1) to develop methods of measuring simultaneously pore and elastic properties of rocks under triaxial stress conditions, (2) to determine whether changes in these properties are of sufficient magnitude to be considered in subsurface calculations and (3) to attempt to relate changes in pore properties and elastic properties since they will have been measured at the same time under identical loading conditions. REVIEW OF EARLIER WORK PORE PROPERTIES Several investigators have studied the effects of stress on the physical properties of rocks. Fatt and Davis2 showed the reduction of permeability of rock with hydrostatic loading. McLatchie et al.3 and Knutson and Bohor4 related permeability reduction to compessibility of reservoir rock, again under hydrostatic loading. Wble,5 and later Redmond,6 evaluated the effects of applied radial pressure on conductivity, porosity and permeability of sandstones. In this latter work, no axial stress was applied. Dobrynin7 reviewed much of the previous work done . on the effects of overburden pressure on physical properties of rocks. He concluded that changes in physical properties are controlled to a large extent by pore compressibility of the rock. Several sets of curves developed from empirical relations are presented. These curves permit estimation of change of properties with net overburden pressure, knowing the pore compressibility and porosity of the rock. Net overburden pressure is defined as (Pe - 0.85 Pi ) where Pe is the

By Henry F. Hebley

In preparing this paper it has been the aim of the writer to keep the problems of both producers and consumers in mind. Until now, no attempt has been made to familiarize each group with the other's practice and limitations. This paper is an effort to acquaint the readers with some of the factors pertaining to the problem and cost of mining and preparing steam coal, and also to the economics of producing steam with such coal. In recent years all lines of endeavor have turned to intensive mechanization in order to lower the unit cost of production. The average fuel consumption in steam electric generating stations has dropped in 20 years from 4.0 lb. to 1.4 lb. per kilowatt-hour; while the modern power station can generate 1 kw-hr. on a fraction under 1 lb., or 13,000 B.t.u. coal. Also, the amount produced per man has in that same period risen from 3.8 to 8.2 tons, owing to the use of modernized equipment below ground for coal cutting, drilling, shooting, loading, hauling and hoisting. Unfortunately, the rapid speed of 5 tons per minute of operation at which the coal is loaded mechanically precludes any appreciable removal of impurities at the coal face, so that the raw coal is hoisted containing a markedly higher percentage of impurities than the hand-loaded coal, which was subjected to the scrutiny of the miner during loading. Also, during the past 20 years, certain seams of coal lying close to the surface have been made economically available by the improved design of electrically operated shovels and draglines for the removal of overburden running as high as 56 ft. This strip coal frequently contains so much ash in the raw state (Table 1) that it would have no sales value. Therefore, coal preparation must be adopted to beneficiate the raw product. Some seams in the United States have a decreasing ash content with decreasing size, owing, in all probability, to the fact that the coal is friable while the impurities are hard, causing a concentration of the low-ash material in the fine sizes. Illinois No. 6 coal being rather hard, naturally the reverse is true.

Jan 1, 1938

By Max Mason

IN 1923 a Western mining company was experimenting with the device of an inventor designed to locate buried ores by radio. Because the progress was slow and the results were confusing, the company began to doubt the usefulness of the method and invited me to review the whole question of the application of physics to ore detection. I was fortunate in securing the cooperation of several physicists who had worked with me during the war on the problem of submarine detection. This group has been increased and has been studying the problem of physical exploration for ores since that time. It was evident that the problem is a big one, with many angles of approach. Its general features may be set down, in rough outline, as follows: The soils, rocks and ores hidden beneath the surface differ, one from another in many respects. These differences may be made to furnish a clew for the physicists working from the surface. To bring these differences into action the physicist creates some kind of an effect, which penetrates into the ground and is distorted and, reflected when it meets boundaries between different sorts of underground structure. In other words, he sends a message down, and the rocks and ore send back signals in, reply. In picturing this process, we should not regard the ground as dense and impenetrable. The kind of messages used pass through the earth about as readily as a sound wave travels the air. If, then, the fundamental procedure is to shout down questions in the hope that an orebody will hear and answer back to us, it is clear that a large part of the expert's study must relate to the kind of questions best suited to the temperament and intelligence of orebodies. It will be easier for the ore to, reply to some of our questions than to others, and it is for us to find the right questions. In certain cases, we are-spared the necessity of using a messenger, because nature has already provided one. For example, we already have a terrestrial magnetic field which auto-matically and continually conveys messages from underneath. We also have available the earth's gravitational field which furnishes us

Jan 1, 1927

By Henry F. Hebley

In preparing this paper it has been the aim of the writer to keep the problems of both producers and consumers in mind. Until now, no attempt has been made to familiarize each group with the other's practice and limitations. This paper is an effort to acquaint the readers with some of the factors pertaining to the problem and cost of mining and preparing steam coal, and also to the economics of producing steam with such coal. In recent years all lines of endeavor have turned to intensive mechanization in order to lower the unit cost of production. The average fuel consumption in steam electric generating stations has dropped in 20 years from 4.0 lb. to 1.4 lb. per kilowatt-hour; while the modern power station can generate 1 kw-hr. on a fraction under 1 lb., or 13,000 B.t.u. coal. Also, the amount produced per man has in that same period risen from 3.8 to 8.2 tons, owing to the use of modernized equipment below ground for coal cutting, drilling, shooting, loading, hauling and hoisting. Unfortunately, the rapid speed of 5 tons per minute of operation at which the coal is loaded mechanically precludes any appreciable removal of impurities at the coal face, so that the raw coal is hoisted containing a markedly higher percentage of impurities than the hand-loaded coal, which was subjected to the scrutiny of the miner during loading. Also, during the past 20 years, certain seams of coal lying close to the surface have been made economically available by the improved design of electrically operated shovels and draglines for the removal of overburden running as high as 56 ft. This strip coal frequently contains so much ash in the raw state (Table 1) that it would have no sales value. Therefore, coal preparation must be adopted to beneficiate the raw product. Some seams in the United States have a decreasing ash content with decreasing size, owing, in all probability, to the fact that the coal is friable while the impurities are hard, causing a concentration of the low-ash material in the fine sizes. Illinois No. 6 coal being rather hard, naturally the reverse is true.

Jan 1, 1938

By Fred C. Bond

MANY grindability tests have been made in the Allis-Chalmers laboratory since the tabulated results were last published.1 The lists of standard ball-mill and standard rod-mill grindability tests are brought up to date in this paper, and considerable new material is added. This includes a tabulation of open-circuit grinding tests, with impact and compression-crushing tests. The standard ball-mill grindability tests (Table I) were made in a standard laboratory ball mill, 12 by 12 in. inside, running at 70 rpm, with a charge of 285 iron balls ranging from 1 1/2 to 3/4 in. in diameter and weighing 20,125 grams. Seven hundred cubic centimeters of minus 6-mesh stage-crushed dry feed was used, and the circulating load was maintained constant at 250 pct by adjusting the number of mill revolutions for each grinding period. Tests were made at all mesh sizes from 28 to 200, and the grindability is the number of net grams of screen undersize produced per revolution. The table includes 479 tests. It has been calculated that the ball mill does 52.3 joules of useful work on the ore per revolution2 with 93 joules input to the mill. The standard rod-mill grindability tests (Table 2) were made in a laboratory tilting rod mill, 12 in. in diameter by 24 in. long inside, with a wave-type lining, running at 46 rpm. The grinding charge consisted of six 1 1/4-in. diameter and two 1 3/4-in. diameter steel rods, all 21 in. long and weighing 33,380 grams. The mill was rotated level for eight revolutions, then tilted up 5° for one revolution, down 5° for one revolution, and returned to level for eight revolutions. It was discharged by tilting downward at 45° for 30 revolutions. Feed consisted of 1250 cc of minus 1/2-in. stone and the circulating load was maintained constant at 100 pct by adjusting the number of mill revolutions for each grinding period. Tests were made at all mesh sizes from 3 to 65, and the rod-mill grindability is the number of net grams of screen undersize produced per revolution. The table includes 105 tests. The impact and compression-crushing tests (Table 3) are given in a table that is an extension of a previous publication3 in which the method of testing was described in detail. Two equal hammers weighing about 30 lb each were arranged to strike simultaneous blows on opposite sides of the test specimen. Broken pieces of rock passing a 3-in. square and retained on a 2-in. square were set up with the smallest dimension between the hammers, and this distance was measured. The height of the hammers was increased slightly before each blow until the specimen broke, and the foot-pounds per inch of thickness was calculated. Ten pieces

Jan 1, 1947

By Leonard Klein

Reduction of oxygen-containing copper has always heretofore been brought about with wood poles. This paper reveals the first successful, economical, and Practical substitute for poles: a gaseous reductant, of which the production and plant use are detailed herein. THE art of fire refining of copper, consisting of melting, oxidation, slag removal, and finally reduction with wood poles, has been practiced for many centuries. An authentic record, discussed in detail in De Re Metallica,* mentions that as early as 1200 A.D. workers in this field of metallurgy were already acquainted with and practiced the basic principles of copper purification. Undoubtedly, the art was well developed marly centuries before the first written records began to appear. Notwithstanding the many advantages gained by application of mechanical con. trivances and by the tremendous increase in size of operations over the centuries, the reduction phase of the process has persisted essentially the same to the present time except for a very recent breakthrough. Numerous articles have been published and many patents have been issued on the subject of substitutes for wood poling in the past half century. They have dealt with a variety of gaseous, solid, and liquid reducing agents. But to the knowledge of the writer, no procedure has ever been prosecuted to a complete success on a large operating plant scale with the single exception of gaseous reduction of oxygen-containing copper revealed in detail herein. A natural gas-air reformer with ample capacity for

Jan 1, 1962

By Carlos G. Valenzuela

The value generally accepted for stacking-fault energy, of copper has been approximately 40 ergs per sq cm based on Fullman's2 value for the coherent twin-boundary energy and the assumption that is twice the twin boundary energy However, Thornton and coworkers8 determined that the lower limit of for copper is approximately 60 ergs per sq cm, based on measurements of dislocation-node radii. They suggested that the assumption of = 2t is invalid. It is the purpose of this note to present results which indicate that the values of obtained by measurement of twin-grain boundary intersections and the values obtained by measurement of dislocation-node radii are actually compatible. The most reliable values for of the a brasses, based on electron-microscope observation of dislocation nodes, are probably those values reported by Smallman and Green6 who applied the Siems correction (1961) to data obtained by Howie and Swann.3 These values shown in Fig. 1 give an extrapolated value of approximately 70 ergs per sq cm for pure copper. In the present work, Fullman's method for determining the stacking-fault energy of copper was extended to the a brasses. High-purity copper (99.999 pet) and high-purity zinc (99.999 pet) were mixed in proportioned amounts and melted in sealed and evacuated quartz tubes. The alloys were homogenized for a week at 750°C and chemically analyzed by means of X-ray fluorescence. These alloys, along with a specimen of pure copper, were rolled to 98 pet reduction and a thickness of 0.009 in., resealed, and annealed for 40 hr at 715°C. Values for the ratio of twin-boundary energy to the grain-boundary energy, it gb, were obtained from measurements of dihedral angles formed at the intersections of twin boundaries and grain boundaries by using Fullman's2 mechanical analogy of surface tensions acting at the intersection of an annealing twin and a grain boundary. The angles between the twin traces and the grain boundaries were measured for a large number of twin-grain boundary intersections at a magnification of X500 using a rotating mechanical stage on a Reichert metallograph. The rotary stage has a calibrated angle scale with vernier so that measurements can be made to 0.1 deg. The mean twin-grain boundary energy and standard deviation were calculated for copper and each of the brasses by the use of an IBM 7072 computer. It was found that the mean value of gb stabilized after approximately 100 twin-angle measurements. This was determined by plotting the mean against the number of angles measured. Since the measured angles deviate from true dihedral angles, a correction factor for grain orientation, discussed below, was applied. The stacking-fault energy was then calculated from these values and the values of grain-boundary energy derived by Taylor.7 The data obtained are tabulated in Table I. Values for stacking-fault energy are plotted in Fig. 1. The value of gb for the specimen of 1.03 pet Zn is close to the value obtained by Fullman2 for OFHC (99.98 pet) copper, 0.045. It is believed that the purity of the copper affects gb significantly. The 99.999 pet purity Cu used in this investigation yielded a value of yt/ygb, 0.76, which is much higher than that obtained by Fullman. Additional evidence suggesting that the purity of

Jan 1, 1965