Search Documents

By Stanley D. Michaelson

THE selection of the proper size of grinding mill for a given installation has long been a subject of discussion by mill manufacturers, consulting engineers, and their clients. It would be presumptuous for the author to propose a simple cure-all. Instead this paper describes a method that has been used over a period of years to determine mill size with a reasonable degree of accuracy. Furthermore, this method claims no theoretical background, for ball milling, as practiced today, is still an art. The selection of the proper size and type of mill must, therefore, be made on an empirical basis. A ball mill, in order to grind, must deliver power through its grinding media to the material to be ground. Assuming that a mill is properly supplied with grinding media, ore pulp, and power, the amount of grinding done is closely proportional to the power expended. With this as a basic premise we can, for the moment, forget about type of mill (i.e., overflow, low-level mill, or other design) and base our calculation of mill size on the total power required to grind a ton of a particular ore from a given size of feed to a given size of product. When this is determined the type and size of mill, its speed, and the weight of the load of grinding media can be selected to absorb this amount of power. DEVELOPMENT OF TECHNIQUE Some years ago, W. L. Maxson, F. Cadena, and F. C. Bond, working in the Minerals Research Laboratory of Allis-Chalmers Co., Milwaukee, developed and described a laboratory technique for comparing grindability (or relative ease of grinding) of various ores at different mesh sizes of grind.1 Additional papers2 have described the work done since that time, and the most recent paper3 summarizes results for hundreds of tests on many ores and materials. The essentials of the testing method are: a I a by 12-in. laboratory mill operating at a constant speed of rotation, using a constant volume of ore, and a constant ball load having a relatively constant grinding surface. Tests are run at 250 per cent circulating load with the feed, circulating load and products screened on calibrated Tyler standard screens. Certain ores from operating mills, representing various mineralogical types, were selected for reference and designated "standard ores." In most cases, detailed studies of the grinding circuits were made when samples of mill feed were taken for grindability tests. Each analysis formed a basis for comparison of the grindability in the laboratory with actual power requirements for a particular grinding circuit. In addition, a critical study was made, to evaluate the differences in the various grinding circuits so that two or more field installations having different layouts (single-stage grinding, two-stage grinding, or others), and using mills of various diameters operating at various speeds with differing circulating loads, etc., could be compared. Large-scale tests by mill operators complemented by laboratory investiga-

Jan 1, 1945

S. Tandanand, Twin Cities Mining Research Center, U. S. Bureau of Mines As an addition to the fine reviews on drilling presented in the foregoing papers, we feel it would be appropriate to mention briefly some work in this area by the U. S. Bureau of Mines. The Bureau has had under way for several years at its Twin Cities Mining Research Center studies directed toward a better understanding of basic drilling mechanisms. The work includes drillability investigations with diamond rotary, and with percussive drilling systems, as well as fundamental studies of rock behavior under drill bit types of loading. Results of our work to date have contributed the following to the state of the art. MECHANISM OF ROCK FAILURE-Rock fragmentation through use of mechanical energy systems, including drilling systems, consists of two major components-machine and rock. The two components are related to each other by their functional behavior and their resultant motion which the components mutually influence. Forces in the systems are transmitted directly to the bit which in turn induces stresses in the rock. When the induced stresses exceed the strength of the rock, the rock fails resulting in penetration. Rock strength is a function of the forces applied to the rock. Stresses under a drill bit, regardless of bit configurations, are essentially compressive, resulting in a condition where the rock has the highest resistance to failure. The ratio of principal stresses induced under drill bits is an indication of the mode of failure in the rocks. Initially, compressive stresses under the drill bit cause rock to undergo inelastic deformation. The impression observed at the first stage of crater formation under the drill bit shows that rock is no longer elastic. Associated subsurface failure at this stage precedes total rupture which subsequently appears at the rock surface. Thus, explanation of crater formation, by applying theory of elasticity alone, is likely to be over-simplified. ENERGY VERSUS VOLUME OF ROCK REMOVED-Experimental results show that energy per unit volume of rock removed is constant for a particular rock and bit type. Rock offers a definite resistance to penetration, depending on the method of the energy application; this may be defined as the drilling strength of a rock. Energy consumption in a drilling system may be divided into two components: 1) Energy required to move the machine parts; and 2) energy consumption in breaking rock. Component 1 is dependent on the type of the machine. Component 2 is dependent on the strength properties of rock and the efficiency of the bit in rock cutting. The sum of the energy required in both components determines the total energy required in breaking rock. Our work in this area has included consideration of both diamond and percussive drilling systems. PENETRATION RATE-For a drilling rate expression to be useful in predicting field performance, it should include the operating characteristics of the drilling machine. Eq. 37, for example, is simply a statement of the fact that the drilling rate is determined by the power output of the machine (2pNT) and the power requirements to break the rock in the hole (AER). In order to predict the performance of a particular drill and the effect, for example, of the rotary speed, on the drilling rate, R, Eq. 37 must be modified to include the

Jan 1, 1967

By R. R. Nash, W. F. Sheely

Experiments were conducted on magnesium monocrystals in order to collect quantitative information on the mechanisms which limit the rate of basal slip. Using critical shear stress and creep data, activation energies for creep at low aid at high temperatures were derived. The activation energy at low temperatures is the same as that for jog formation and the activation energy at high temperatures agrees with that for climb. COTTRELL has suggested that at low temperatures, the expansion of dislocation loops under stresses near the yield strength is limited by the rate at____ which the expanding loops can cut the "forest" of dislocations passing through the glide planes.' On the basis of this mechanism, seeger2 has derived expressions for low-temperature creep and for the relation of flow stress of single crystals to temperature. In the work reported here, the authors have performed experiments designed to obtain quantitative data on the physical properties of the dislocation intersection mechanisms operating during basal slip in pure magnesium monocrystals. Above a critical temperature, dislocations thread-

Jan 1, 1961

By J. B. Reed, T. A. Read, H. Rosenthal

Although the season cracking of brass has been a subject of experimental investigation for more than thirty years, the mechanism that is responsible for this phenomenon is still obscure. While at- tempts to elucidate the stress-corrosion cracking of some alloys have been relatively successful, the principal accomplishments made in the studies of the season cracking of brass have consisted of improved techniques for the fabrication of articles of alpha brass, which reduce the danger of season-cracking failure in service. The primary purpose of the present paper is to collect the published experimental data which appear to be of importance to the development of an adequate theory of the mechanism of the season cracking of brass. Some of the possible mechanisms which have been proposed will also be discussed, together with some promising avenues of future attack on the problems. Several excellent survey papers on season cracking are available, including the recent ones by Croft and Sachs(1)2 and by Gibbs(2). The principal facts concerning season cracking, as presented in these papers, may be summarized as follows. The season cracking of alpha brass is a special type of stress-corrosion failure, which may occur in atmospheres containing ammonia, air, and water vapor. The stress causing failure may be either the

Jan 1, 1945

By R. T. Keyes, R. B. Clay, L. L. Udy, V. O. Cook, M. A. Cook

Based on compressibility and stress wave velocity in rock, initial explosive loading conditions, the thermochemistry of the explosive and reasonable description of the pressure-distance relations behind the shock front, the distribution of energy between the products of detonation and the burden are estimated as a function of time for various loading conditions. These include 'powder factor', loading density A (fraction of borehole occupied by explosive), and the explosive itself. Factors responsible for rock fragmentation are discussed in terms of: 1) 'release wave fracturing', 2) 'shear wave fracturing', and 3) 'release of loading fracturing' or 'rock bursting'. Release wave fracturing appears to occur only in the immediate vicinity of free faces, and shear wave fracturing only adjacent to the borehole under normal blasting conditions. Rock bursting is thus considered to be the most important means of rock fracturing in blasting. Means for maximizing it are considered. The most important factors to consider include maximum available energy A, explosive density p1, loading density A and 'powder factor'. Maximum efficiency is attained in general by maximizing the A . p1 product. This is achieved by using high density explosives at a loading density of unity (A = 1.0). Ways for achieving this condition are discussed. The bulk-handled aluminized slurry blasting agents have the desired properties for achieving optimum conditions for high blasting efficiency based on the theory outlined herein. Factors considered most important in the blasting of rock are: 1) The maximum available energy A, determined by the heat of explosion Q and the mechanical efficiency ?, a factor intimately associated with the mode of application (A = Q at highest gas concentrations). 2) The 'borehole pressure', pb, or the maximum pressure developed in the borehole after passage of the detonation wave and before the burden has had time to move or become compressed appreciably. (Owing to the short duration of the detonation wave at any particular point in the borehole, the fact that the explosive may not always fill the borehole completely and the further fact that the burden may not actually see the detonation pressure, the borehole pressure is considered more significant than the detonation pressure p2 as a performance factor in borehole blasting.) The borehole pressure is determined by the explosion or adiabatic pressure, p3 , and the loading density, A, or the fraction of the borehole filled by explosive. 3) The physical conditions important in the application of the explosive are: a) The 'powder factor,' (We/Wr), or the ratio of the wt of the explosive to that of the rock being blasted expressed as lb per ton or more generally in lb/cu yd. b) The bulk density, p1 ?. c) The 'burden' or 'line of least resistance,' the spacing between boreholes, the geometry of the borehole pattern and sequence of firing. d) The physical and chemical properties of the rock, most significant of which are possible heterogeneties, such as faulting, prefracture, and greater than micro-scale chemical heterogeneities. (This factor is not considered here but deserves a great deal of careful consideration.) All of these factors need to be carefully considered in the most economical engineering of a blast. Here is considered firstly an outline of the present status of dynamic rock mechanics, particularly as it pertains to blasting. The factors pertaining to the most efficient application of blasting agents are also considered, followed by a discussion of methods of application to achieve optimum explosives performance. ROCK MECHANICS Dynamic rock mechanics is currently a rapidly developing science contributing greatly to a better understanding and consequently the more effective application of explosives in blasting of rock.1-22 Basic to the development of the science of dynamic rock mechanics were the advances of Goransen23 and the Los Alamos and NOL groups24-28 concerning rock and stress wave phenomena and the transmission and reflection characteristics of stress waves at interfaces between different media. Basing considerations on this new knowledge as well as new experimental methods of study (ultra-high speed streak and framing cameras and electronic timers) the theory of fracture and failure of solids under impulsive loading by stress waves developed rapidly.14,16,27-29 Also the

Jan 1, 1967

"With a total value to date of well over $200,000,000.00 for its ore production, the Tintic mining district, which is about 100 miles southwest of Salt Lake City, ranks as one of the three main ore producing areas of Utah. In it are located the biggest silver mines of the country, silver having been the chief metal produced in the camp since its start. Tintic's silver production to date has a total value of over $ 100,000,000, approximately half of the value of the camp's ore production, the balance being roughly divided among lead, gold and copper.Discovery of the camp was made in the late sixties. Lack of transportation and ore reduction facilities delayed extensive development of the area for nearly a decade.In recent years Tintic's ore production has ranged from 350,000 to 400,000 tons annually. In 1 924 the camp produced one-eighth of the silver produced in the nation with an output of 7,729,700 ounces. Its lead production was 77,765,000 pounds and its gold production 26,285 ounces.The known mineralized area of the district is found in a broad syncline striking north and south. The west limb plunges sharply and extends for a distance on its dip of approximately one and a half miles to the trough. The east limb raises gently through a distance of about two miles to the east limit of known mineralization. This general structure is broken by local faulting throughout the district, the local structural conditions playing an important part in the ore deposition. The north end of the fold is obscured by a rhyolite flow and the south end stops against a monzonite stock."

Jan 1, 1925

In situ mining techniques have become prominent in recent years due to declining ore grades, rising costs, and increasing concern for miners' health and safety. Current practices depend heavily on the effective and uniform fragmentation of the ore zone of interest, which not only provides for proper media flow but also exposes additional surface areas to react with the processing system. Specifically, current applications have focused on blasting to a mined-out opening or, in the case of shallow de- posits, blasting to the surface void. In the former case, several obstacles are encountered, including proper initiation, uniform fragmentation, and a lack of swell space for the blast, which tend to produce less desirable results in the zone of' interest.

Jan 3, 1979

By R. D. Daniels, T. W. Wood

The tensile properties of columbium and Cb-H alloys containing up to 455 ppm H were studied as a function of temperature and strain rate. Hydrogen, introduced into columbium at elevated temperatures, using a thermal -equilibrium technique, embrittled columbium most severely at about —77°C. This elnbrittle ment occurred even at hydrogen concentrations of an order of 20 ppm. At higher temperatures, the hydrogen tolerance of columbium increased in relation to the increased solubility of hydrogen in tile metal. Below this temperature hydrogen tolerance, as determined by ductility and fracture stress, increased slightly. Strain rate had little effect on the tensile results for cross-head speeds over the range 0.002 to 2.0 in. per min. Strain aging during the tensile test appears to explain the ductility mininmum at —77°C. The apparent increase in hydrogen tolerance at lower temperatures is attributed to the low mobility of hyhogen. Experiments were performed in which samples were prestrained in tension at room temperature and tested to failure at —196°C. Results suggest that hydrogetz segregation to preformed crack nuclei can cause subsequent embrittlement even at temperatures where hydrogen mobility is too low to cause embrittlement in a normal tensile test. COLUMBIUM is an example of the class of bcc metals with ductile-brittle transition temperatures sensitive to the presence of interstitial atom contaminants. Hydrogen is one of these embrittling contaminants. The embrittling effect of hydrogen is less potent, perhaps, in columbium than in some of the other bcc refractory metals, but it is still a problem of both theoretical and practical interest. Unlike hydrogen in iron and steels, hydrogen in columbium is exothermically rather than endo-thermically occluded. The embrittlement process in exothermic systems has not been studied as extensively as that in endothermic systems, especially at hydrogen concentrations below the limit of solubility. The purpose of this investigation was to evaluate the embrittlement process in initially pure columbium as a function of hydrogen content, temperature, and strain rate. The Cb-H phase diagram, according to Albrecht et al.,1 is shown in Fig. 1. Columbium reacts exothermically with hydrogen producing a solid solution at concentrations of less than about 250 ppm (parts per million by weight) H at room temperature. At concentrations above the highly temperature-dependent solvus a second phase is formed. Like many similar hydrogen-metal systems,2 his system exhibits a miscibility gap with respect to hydrogen solution. Albrecht found the critical temperature of the miscibility gap to be about 140°C, the critical concentration to be 0.23 atom fraction hydrogen, and the critical pressure to be 0.01 mm Hg. Above 140°C there is a solid solution of increasing lattice constant extending across the phase diagram. Hydrogen concentrations of particular interest in this investigation were those below the limit of solubility in columbium. At hydrogen concentrations above the limit of solubility, columbium will contain the hydrogen-rich second phase and will be brittle under most testing conditions because the hydride generally precipitates as platelets with coincident matrix lattice strains.1'3 At hydrogen concentrations below the limit of solubility, the tensile behavior of columbium is expected to be more sensitive to the interrelationships between hydrogen concentration and mobility and the testing variables such as temperature and strain rate. Literature references to the hydrogen embrittlement of metals, especially ferrous alloys and titanium alloys, are too voluminous to mention. It is only recently, however, that detailed studies of the hydrogen embrittlement of columbium have been undertaken. Wilcox et a1.4 studied the strain rate and temperature dependences of the low-temperature deformation behavior of fine-grained are-melted columbium (1 ppm H) and the effect of hydrogen content (1,9, and 30 ppm H) on the mechanical behavior of columbium at a series of temperatures for a single strain rate. A strain-aging peak was ob-served at about -50°C which was attributed to the presence of hydrogen in the metal. Eustice and carlson5 studied the effect of hydrogen on the ductility of V-Cb alloys at a series of temperatures over the range -196° to 25°C. Pure columbium was embrittled by 20 ppm H which produced a ductility transition at approximately -70°C. Ingram et al.6 studied the effect of oxygen and hydrogen on the tensile properties of columbium and tantalum. A minimum in the notched-to-unnotched tensile ratio of hydrogenated columbium was obtained at about -75°C, but because of the relatively large hydrogen content employed (200 and 390 ppm) the ductility

Jan 1, 1965

By Eugene N. Cameron

Graphite is the hexagonal form of crystal-line carbon. It is found in nature locally as tabular crystals but occurs mostly as disseminated flakes, foliated, platy, or fibrous masses, or microcrystalline compact to earthy material. Graphite is characterized by its gray to black color, metallic luster, black streak, perfect basal cleavage, softness (H = 1-2) and unctuous feel. It is sectile and flexible and has a specific gravity of 2.1 to 2.3. It is an excellent conductor of heat and electricity and is inert to ordinary chemical reagents. It melts at a temperature of about 3500°C and vaporizes at a temperature of about 4500°C. In the presence of oxygen it oxidizes to CO2 in the temperature range 600° to 700°C, but it is stable at ordinary temperature and markedly resistant to chemical weathering. Although some natural graphite is nearly 100 pct pure carbon, most contains mechanical impurities of various kinds; quartz, biotite, muscovite, pyrite, iron oxides, and feldspars are the most common. Commercial graphite products have a wide range of graphite content, but the better grades contain 80 pct graphite or more. Both natural and manufactured (artificial) graphite are used in industry. Natural graphite products are divided into two broad categories based on grain size. Graphite composed of visible crystals is called "crystalline" graphite, whereas graphite so fine-grained that it is not visibly crystalline is termed "amorphous." The distinction is arbitrary, for all natural graphite is crystalline, and all gradations between the two commercial categories are known. Within the two categories the terminology used in industry is confusing and not entirely consistent. Crystalline graphite comes from two principal types of sources. The first consists of rocks containing disseminated flakes of graphite. This source yields the "flake graphite" of industry. The second comprises vein deposits of graphite, of which those in Ceylon are the most important and furnish the Ceylon graphite of industry. Amorphous graphite comes from any of a variety of sources, including some of those that yield crystalline graphite. Manufactured graphite is made by electric furnace processes, mostly from petroleum coke. Occurrence and Distribution of Graphite Deposits GENERAL Graphite is widely distributed in nature, occurring in igneous, sedimentary, and metamorphic rocks, and even in nickel-iron meteorites. Graphite deposits of economic interest, however, occur mostly in metamorphic terranes. Five principal geologic types of deposits are recognized: 1. Deposits consisting of flake graphite disseminated in metamorphosed siliceous sediments. 2. Deposits consisting of flake graphite disseminated in marbles. 3. Deposits formed by thermal or dynamothermal metamorphism of coal or other highly carbonaceous sediments. 4. Vein deposits of the Ceylon type. 5. Contact metasomatic or hydrothermal deposits in marble. DEPOSITS IN METAMORPHOSED SILICEOUS SEDIMENTS Deposits consisting of flake graphite disseminated in metamorphosed siliceous sedi-

Jan 1, 1960

By Kenneth S. Ritchie

The natural emulsion samples used in this study were shipped directly from twelve California oil fields, through the courtesy of the superintendents of the main producing companies in those fields. Representative parts of each sample were chosen for the slides. Preparation of the slides was generally made in less than two minutes, including time of exposure; in a few cases, about five minutes was required. The short time was intended to minirmize the changes in conditions. Whenever comparison was of value, standard conditions were established. Spreading by gravity was adopted instead of smearing. Cover glasses were not allowed to rest on the films. General Characteristics of Emulsions The main purpose of the general views (Figs. 1-16) is to illustrate the general characteristics of the dispersed droplets together with any other constituent or impurity that may be found in each emulsion. The magnification is given so that dimensions could be measured from the plates. The slides used for these views had spherical recesses; they gave the best light. Where crystals were intended to be shown in the picture a filter (green was the best') was usually used. Emulsions that showed a tendency to move by concentrated light were pictured without a condenser.

Jan 1, 1931

By C. C. Henning

IN any line of human activity logical handling requires an amount of attention to each phase that is in keeping with the importance of that phase. In the complex and rapidly changing field of modern ferrous metallurgy it is difficult to allot the proper degree of attention to the various subjects, and it is not surprising that one or more subjects of major importance should for a time be neglected. Bessemer steel is a good example of a neglected subject. It is largely taken for granted, inferior physical quality is assumed for it, and there is a lack of interest in its technical development and commercial application. Availability of supply is limited. In spite of this technical indifference, limited source and lack of commercial exploitation, bessemer steel con-stitutes a large volume of tonnage in daily use. There is a fairly prev-alent idea even among technical people that bessemer steel survives mostly because of low cost and by reason of a dwindling residue of applica-tions sufficiently common to permit of its use. The difference in cost between bessemer and open-hearth steel is governed largely by the relative cost of manufacture of pig iron and the market price of steel scrap. During the past four years there have been long periods of time during which the price of steel scrap was low enough so that open-hearth steel was considerably lower in manufacturing cost than bessemer. As to application, it may be pointed out that thousands of tons of this material in the form of bessemer screw steel are applied for moving parts in automotive and other equipment. Some forging work and considerable heat treating, particularly carburizing, is performed on this grade.

Jan 1, 1935

By J. T. Norton, A. L. Mowry

The monocarbides of the A subgroup elements in the fourth and fifth group of the periodic table in addition to being hard and refractory are of special interest in that they are isomorphous in crystalline structure. They are cubic with a sodium chloride type structure in which the metal atoms are essentially close packed in a face-centered cubic arrangement with the carbon atoms placed in the interstices between. Interstitial structures of this close packed type were first investigated systematically by Egg1 and he gave the rule for their formation, stating that the radius ratio of the nonmetal to the metal atom should not exceed the value of 0.59. The carbides of interest are those of titanium and zirconium of the fourth group and vanadium, columbium and tantalum of the fifth group. Table 1 shows the radius ratio using the Goldschmidt radii for 12 coordination for the metal atoms and the diamond radius for the carbon atom. It will be noted that while there is considerable variation in the size of the metal atom, in all cases the ratio is smaller than the limit of 0.59 placed by Hägg. It has been known for some time that these cubic carbides are soluble in one another, at least to some extent or, in other words, the metal atoms can be replaced, one by another without destroying the stability of the structure. Since the stability of these close packed interstitial substances appears to depend more upon geometry than upon the exact chemical nature of the atoms involved, it is of interest to examine the possibilities of replacement in these carbides in some detail. Hume-Rothery2 has pointed out the importance of the difference in size of solute and solvent atom as a factor in limiting the solubility in simple binary solid solutions. Largely on an empirical basis, he states that if the difference in size between solvent and solute atom is more than 14-15 pct of the solvent atom, the range of solubility is very restricted. The atom size was based on the distance of closest approach in the elements involved. While there is some question as to how one should calculate the size of the metal atom in the carbide structures, reference to Table 1 will show that zirconium is the largest and vanadium the smallest of the group and that the difference is about 15 pct. The Ti-Zr difference is about 9 pct and the others are smaller. Thus one would predict that if the size factor controls the solubility, all of the pairs except VC-ZrC would have wide or complete solubility whereas this latter pair is on the border line and might have restricted solubility. The purpose of the present investi- gation was to examine the solubility of the several pairs of carbides by heating them together until equilibrium was established and then examining the product by X rays. Previous Work Agte3 and his associates prepared various transition metal carbides and determined the melting points of binary mixtures. He concluded from the shapes of the melting point curves that there was extensive solubility in the case of the cubic carbides. Umanskii and his colleagues made an investigation of a number of pairs of the cubic carbides, using X rays and plotted lattice parameter vs. composition curves for the systems TaC-Tic, CbC-Tic, TaC-ZrC and CbC-ZrC. All pairs showed a continuous series of solid solutions. The first two pairs gave a linear relation while the latter two showed a negative deviation from Vegard's law. Kiefer and Nowotny, in a paper which became available after the present work was well advanced, investigated the binary pairs of the five cubic carbides by means of X rays. Relatively few points were obtained and results indicated that in some cases, at least, equilibrium was not reached at the temperatures used. The results indicated that solubility in the VC-ZrC system was not complete. All of the results of previous investigations indicated the desirability of a more detailed study. Materials The raw materials used were mono-carbides of titanium, zirconium, vanadium, columbium and tantalum and were the purest which could readily be obtained commercially. Spectrographic qualitative analysis showed that the CbC and TaC contained less than 1 pct

Jan 1, 1950

By E. H. Citron

CLEANING fine coal in jigs is not new in Europe, where the feldspar jig is being used almost exclusively for this purpose. A feldspar jig operates with an artificial bed made up generally of feldspar or other hard rock material. Dimensions and specific gravity of this material must be of suitable values for good bedding qualities. For good efficiency, the size should range between 1x2 in. and 2x2x½ in. thick. The disadvantage of an artificial bed is that it is not mobile and must be replaced every so often with new material to obtain good cleavage characteristics. A semi-mobile bed has been developed to retain only a part of the feldspar on the sieve screen— the other part is drawn off with the refuse material, from which it is reclaimed and returned to the jig feed. Recirculating this feldspar rock offers definite advantages. However, in time it will lose its original shape because of wear, and new bed material must be added to the jig feed. The latest feldspar jigs arc generally air-pulsated, Baum-type jigs, although more than 70 pct of the feldspar jigs operating in Continental Europe are still of the piston type. These jigs are very popular in Europe, but they do require a great deal of time and attention. New Theory to Eliminate Artificial Bedding: At the preparation plants of Pittsburg & Midway Coal Mining Co. it has always been the contention that a small piston-type jig could be developed to clean fine 1/4x0-in. coal down to 28 to 60 mesh efficiently by obtaining and admitting bedding material from the present plant refuse circuit to the jig feed. This eliminates use of artificial bedding materials. The jig should incorporate these essential adjustable features as follows: Adjustable Sieve Screen A screen that can be raised and lowered to increase or decrease washing compartment depth. The sieve screen also can be set on an incline level, or decline. Adjustable Plunger Eccentric Length of stroke can be adjusted to increase or decrease pulsion and suction. Variable Plunger Speed Variable speed reducer for decreasing and increasing the number of strokes per minute. Water Distribution Adjustable baffle plate separating the plunger and sieve compartment so the water can be distributed uniformly over the entire sieve screen area. Refuse Ejector Special unique rubber-type refuse ejector gate operated by air and electrically controlled (as a conventional jig). Automatic Control Conventional float that measures the specific gravity of the coal-water refuse medium in the jig is of the submerged type. The float is mounted on a vertical stem held in position by two parallel arms. A movable weight regulates the effective specific gravity of the float. The float stem can be raised and lowered, having a graduated scale to indicate the depth of bed for the setting of the float. Hutch Drawoff Hutch material is drawn from the cell compartment to the elevator compartment by gravity. The first one-cell experimental jig incorporating all these features was built in January 1955 by Ore

Jan 1, 1959

By R. E. Ogilvie, J. I. Goldstein

The a and y solubility limits in the Fe-Ni phase diagram have been redetermined at temperatures above 500°C. Both a diffusion-couple and a quench and anneal technique were used. The solubility limits were measured with an electron-probe micro-analyzer. The nickel concentration at the phase boundary is increased below 700°C and the a solid-solubility range is much larger than had been previously measured. The solubility limits are also extrapolated to 300°C. It is suggested that the solubility of nickel in a FeNi reaches a maximum in the temperature interval 400o to 500°C. THE equilibrium diagram has been of great use in the field of meteoritics, where the phase relations between kamacite (a) and taenite (?) in metallic meteorites can be described by means of the Fe-Ni diagram. The study of metallic meteorites by electron-probe microanalysis has cast some doubt on the accuracy of the presently available Fe-Ni diagrams.1, 2 Recent thermodynamic studies of the Fe-Ni system also suggest that the diagram may be in error.3 For these reasons the high-temperature (800o to 500°C) part of the diagram was redetermined. INTRODUCTION The currently accepted Fe-Ni diagram is that of Owen and Liu.4 Above 910°C, there is a region of complete solid solubility, ? (fee). Below 910°C, the a (bee) phase is stable in pure iron. The effect of increasing amounts of nickel is to stabilize the y phase. The phases that form when Fe-Ni alloys are heated or cooled bear little relation to the equilibrium diagram. If an alloy is cooled from the y state and held at a temperature within the a + y field, no evidence has been found for the occurrence of the y - a transformation.5 If the alloy is cooled to low enough temperatures the y phase breaks down into a supersaturated bee phase called a2. In fact, in alloys over 27 pet Ni the y phase is retained at room temperature.6 The a, phase has the same composition as the original y. The temperature at which a2 forms, the M, temperature, has been determined experimentally.' A state of equilibrium can be approached by cooling below M, to form a2 and then reheating the alloy into the two-phase region of the diagram. The y phase will then begin to precipitate out of the a2 phase and grow. The growth of the phase, however, is quite slow. Using the interdiffusion coefficients -Da of Goldstein et al.,8 it is estimated that it takes about 1 year to grow a 10-µ-wide region of ? at 700°C in a 5 pet Ni alloy. Owen and Liu4 used the technique just described to form the equilibrium phases. The phases present were determined by means of X-ray analysis. The accuracy of their diagram depends on the number of alloys available near the phase boundary at a given temperature. In this study two different techniques were used to determine the a/a + ? and ?/a + ? solubility limits. The inherent accuracy of both techniques was greatly improved over that used by previous investigators because the phase-boundary compositions were measured with an electron-probe microanalyzer. PROCEDURE The two methods used to determine the Fe-Ni diagram are the diffusion couple (D.C.) and the quench-and-anneal (Q.+A.) techniques. In the first method, diffusion couples whose diffusion path goes through a two-phase region of the phase diagram were used. A description of the technique used for making the diffusion couples has been described in a previous paper.' After the diffusion treatment a discontinuity in the resultant concentration vs distance profile was measured. The nickel concentrations in the a and ? phases at the interface of the discontinuity are the solubility limits of the a and ? phases in the phase diagram at the diffusion temperature. If the interface com-

Jan 1, 1965

By V. R. Garfias, C. O. Isakson

The production of petroleum in Mexico during 1930 was approximately 39,600,000 bbl., or 5,188,000 bbl. less than in 1929. The decline which has continued for the last eight years, will place Mexico in fifth or sixth rank as an oil-producing country. The production of the northern and southern fields near Tampico declined over 5,250,000 bbl., while that of the fields in the Isthmus of Tehuantepec moderately increased. The wildcat operations which have been conducted for some years near the international border along a 290-mile belt, extending roughly 170 miles northwest and 120 miles southeast from Laredo, Texas, have so far met with little encouragement, although the oil possibilities of the region warrant the belief that commercially productive fields will be discovered eventually. An interesting development during the year was the starting of construction of the oil pipe line from Palma Sola in the South Fields near sea level—over Sierra Madre at 8660 ft.—to Atzcapotzalco, a suburb of Mexico City at an elevation of 7350 ft. This line, about 146 miles long, has a diameter of 10 in. and an estimated daily capacity of 10,000 bbl., and with its terminal refinery at Mexico City will form a transporting and refining unit which should materially affect the distribution and marketing of refined products in the Republic. Development During the past year 148 wells were drilled, as compared with 214 in 1929 and 371 in 1928, the percentage of producers being 49 as against 47 in 1929. With the exception of one well in San Isidro, at the extreme southern end of the Golden Lane, the Jardln Paso Real area was the only sector of the old fields where new development could be considered as successful, all other producers brought in during the year being drilled in nearly exhausted pools to be operated as ('strippers." Northern Fields A total of 71 wells were drilled in the northern fields, of which 22 were producers; one well in Ebano was estimated at 5000 bbl. per day, while the general average of all producers was less than 300 bbl. Results

Jan 1, 1931

By M. Muskat R. D. Wyckoff

The phenomenon called "water-coning" is that, observed in many oil wells, in which bottom water gradually and frequently sudderlly displaces a part or all of the oil production when a certain rather critical production rate from the well is exceeded. To follow in detail the process of the formation of a water cone as it breaks through the oil zone and enters the well bore is a problem so complex as to make a theoretical analysis practically impossible. However, an analytical treatment of the flow system before the water has broken through and during the time that it lies statically beneath the oil zone with an elevated or "coned" surface can be carried through under certain approximations. To present an analysis which shows the essential characteristics of the coning mechanism is the purpose of the present discussion. Physical Basis of Theory and Meaning of Approximations As will always be true for flow systems where true water-coning is at all possible, the water will be supposed to lie beneath the oil zone because of its density contrast with respect to the oil. In fact, tinder the usual field conditions, when the pay horizon is reasonably homogeneous, the water most frequently enters the well through the lower zones, but even when it enters from intermediate zones it may, in the later life of the well, displace the bottom layers of oil, thus resulting in a system wherein the oil is effectively floating on the water.

Jan 1, 1935

By Dubois Eastman

BEHIND the contrasting liquid-fuel technologies of Germany and the United States lie the basic differences of scarcity and abundance. The chemists and engineers of each nation have developed processes that accommodate available raw materials. In the United States, processing is based on an abundant supply of petroleum, which is refined into a variety of fuels and lubricants. Germany has little indigenous petroleum but has a readily available supply of coal that can be converted into liquid fuels and lubricants. As a result, in Germany several basic processes have been developed for the conversion of coal into synthesis gas (carbon monoxide and hydrogen). In turn, this gas is processed into products. As a normal function of its researches into petroleum processing, the petroleum industry in the United States has made careful studies of various conversion and synthesis techniques. A number of oil companies are carrying out independent development programs with the aim of synthesizing hydro- carbon products that can be marketed at a price that will compete with the price of refined petroleum products. American oil companies hope to perfect synthesis processes that will directly benefit the consumer. A good example of progress in these terms is the synthesis plant at Brownsville, Texas, which is based on the conversion of natural gas to synthetic fuels and other valuable products. When this plant is operated at near capacity, it is expected that the products will be able to compete favorably for the consumer dollar. The complete gasification of coal is a technique well rooted in history. As a controlled process on a small scale, it goes back centuries. As a practical technique on a commercial scale, it dates back to 1839, when "producer gas" appeared in Germany for limited industrial use. By 1873, "water gas," or "city gas" as it is sometimes called, was being manufactured commercially in the United States for use in heaters and stoves. The water-gas process was the cornerstone for modern synthesis. To older methods that were concerned only with carbon and oxygen reactions, it added hydrogen by means of steam. Thus far the goal of conversion was to produce gas for heating, lighting, industrial use, and cooking. The long step forward to synthesis was made in 1927, when Germany started to make gasoline from coal by means of the revolutionary Bergius hydrogenation process. A year earIier, Franz Fischer and Hans Tropsch had announced their process, which finally reached the

Jan 1, 1953

By W. S. Pellini, F. N. Rhines

IN many of the otherwise well established alloy phase diagrams the solidus curves (temperatures at which liquid first appears upon melting) have not been located accurately, chiefly because the experimental techniques that have been most popular for determining solidus temperatures have been both cumbersome and subject to large errors. C. E. Homer and H. Plummer1 have described a sensitive and at the same time a very simple technique for locating the solidus curves in a number of alloys of tin. Their method consists simply in noting the temperature at which a specimen of the alloy ruptures under the influence of a light bending force. Although this method is not new, it has been little used for this purpose in the past; nevertheless, it appears so attractive in its possibilities of speed, simplicity, and precision that the investigations presently to be described were undertaken to verify its merits. The redetermination of the solidus and eutectic temperatures of the lead-antimony system was employed as a medium 0f experimentation. New values obtained in this way are believed to be sufficiently precise to warrant a revision of the currently accepted lead-antimony phase diagram (Fig. I). Determinations of the solidus of the lead-rich lead-antimony alloy series have been published by R. S. Dean2 and by E. E. Schumacher and F. C. Nix.3 Their points are represented in Fig. I. In their work the solidus was not located at antimony concentrations greater than 2 per cent; the curve was presumed to meet the eutectic horizontal at an antimony concentration of about 2.5 per cent. In the present studies the solidus has been traced to 3.5 per cent, where the eutectic horizontal is intersected (Table I and Fig. I). Within the range investigated by Dean and by Schumacher and Nix the agreement with their values is good. H. Seltz and B. De Witt,4 on the basis of activity measurements, have calculated that the intersection of the solidus and the eutectic reaction horizontal should lie at 3.86 per cent of antimony. The following determinations of the eutectic temperature have been reported: Roland-Gosselin,5 228°C.; Ewen,6 228°C.; J. E. Stead,7 247°C.; Campbell,8 228°C.; W. Gontermann,9 245° to 252°C.; R. Loebe,10 245°C.; E. Heyn and 0. Bauer,11 245°C.; H. Endo,12 250°C.; R. S. Dean,2 249° to 258°C.; E. Abel, 0. Redlich, and J. Adler,13 245°C.; W. Broniewski and L. Sliwowski,14 250° to 252°C.; H. Seltz and B. De Witt,4 250°C. A temperature of 249°C- appears to have been generally accepted in recent years; it is the value most frequently obtained by the method of cooling curves. Values below 249°C. have usually been obtained by inferior cooling-curve techniques; those above 250°C., by the method of heating

Jan 1, 1942

F. W. Gordon, Philadelphia, Pa.: There can be no objection to the use of cross-compound blowing-engines; and when they are condensing they are susceptible of great range of duty with slight loss in efficiency. By those who have use for the full heat of the waste gases, this type of engine is advantageous; but many furnaces are not so located. The pig-iron is their finished product, and the gases are to be employed only for furnace-use. In this case simple engines are preferable, being less expensive and having less parts to take care of. These reasons determined the introduction of the engines, a sketch of which is distributed at this session. There are three of these engines to furnish blast for two furnaces, for a make of abont 250 tons per day, using 75 per cent. anthracite and 85 per cent. magnetic ores; and they are expected to blow up to twenty pounds pressure per square inch. For blast-furnaces I prefer the single to the coupled engine, except

Jan 1, 1894

By R. L. Stephenson

IN plants casting electric-furnace ingots and converting them immediately into blooms, billets, slabs, bars or forgings, the criterion of quality performance is the soundness of the semifinished or finished product. When rejections are necessary, it is not always obvious whether the defects were caused by an unsound ingot or by improper treatment during the heating and forming operations. To evaluate the effects of the numerous factors involved, it is necessary to accumulate a large number of detailed observations and to analyze and interpret these data properly. Even after a thorough investigation has been conducted, it is impossible, in some cases, to isolate the cause of the defect and say that it is definitely the result of an unsound condition in the ingot or mistreatment of the ingot during further processing. Two factors that are extremely difficult to evaluate are the chemical composition of the steel and time from finish pour to charge in the soaking pits or "track time," and it is necessary to evaluate their combined effects before many other factors can be studied. Plain carbon, fine-grained steel in the range of 0.18 to 0.23 pct carbon, is very susceptible to cracking and the longer the elapsed time between the pouring of the ingots and stripping for charging into the soaking pits, the higher the billet rejections for cracks are found to be. Below 0.15 pct carbon and above 0.30 pct the track time

Jan 1, 1947