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By J. McD. Porter

In many of the old placer-mining districts are still to be found large tracts of gold-bearing gravel not suitable to be worked with a dredge, because the bed is too shallow or the gulch too narrow. Frequently there is not enough grade to handle the gravel successfully by ground-sluicing or a bedrock flume, or it contains too many boulders to be worked succeeefully with the ordinary hydraulic pipe or tube elevator. In southwestern Oregon, two practical placer-miners named Ruble, after working for years trying to make money out of placer-ground coutaining many large boulders, invented and patented a hydraulic elevator of an entirely new type, and one that has been found to work very successfully in flat ground and in gravel containing many large boulders. It is a very simple contrivance. A few years ago I acquired the property near Pierce City, Idaho, known as the American placer-mine. Various attempts had been made to work this ground. A bed-rock flume had been installed by one company, an Evans elevator by another, and still other methods were tried on a smaller scale. All were

Jan 1, 1910

By G. H. Bruce, C. E. Williams

The trend toward deeper drilling, together with the attcndant increase in power requirements for circulation of the drilling fluid, has emphasized the need for a critical examination of the factors affecting the removal of bit cuttings from the hole by the drilling fluid. The ability of drilling fluids to lift cuttings is called their carrying capacity. A series of laboratory and field experiments has been conducted to determine the minimrim annular velocity necessary to remove cuttings, and to investigate the effects of properties of drilling fluids on their carrying capacities. Consideration of the results of these experiments led to the following conclusions: 1. Turbulent flow in the well annulus is most desirable from the standpoint of cutting removal. 2. Low viscosity and low gel are advantageous in removing cuttings. 3. Increase in mud weight is effective in increasing carrying capacity. 4. The carrying capacity is higher when the pipe is rotated than when it is not. 5. If turbulent flow can be maintained, an annular velocity slightly higher than the slip velocity of the largest cuttings to be transported should keep the bore hole clean. This implies velocities of 100 to 125 ft per minute rather than the presently used 175 to 225 ft per minute. INTRODUCTION Power Savings by Reduction of Annular Velocities A large portion of the power expended in drilling operations is consumed in circulating the drilling fluid. An important factor in establishing the rate of mud circulation is the minimum velocity in the annulus necessary to remove bit cuttings. Empirically, it has been found that average annular mud velocities of about 200 ft per minute will remove cuttings. It was not definitely known, however, whether annular velocities of about 200 ft per minute were just above the minimum necessary to remove cuttings, or whether such velocities could be materially reduced without sacrifice of the ability of the mud to remove cuttings. It is apparent that if annular velocities could be reduced without impairment of cutting removal, a considerable saving in power requirements would result. Need for Research on Carrying Capacity The ability of a drilling fluid to transport cuttings is called its carrying capacity. Although it has been recognized that the carrying capacity of a mud is affected by mud properties such as viscosity and density1,2,3,4 there have been various views in the industry as to the effects of these mud properties on carrying capacity. The economic importance of the problem of carrying capacity and the scarcity of information on the subject indicated that research on the problem was needed. THE FACTORS AFFECTING CARRYING CAPACITY Qualitative Determination of Factors The mechanism of cutting transport is closely related to that involved in the separation of material by settling processes. A considerable amount of research has been done on settling problems, and discussions of sedimentation theory can be found in standard texts.5,6 Consideration of the information available from these sources, together with consideration of the mechanism of cutting transport, leads to the conclusion that the factors affecting carrying capacity are the dimensions of the system, the physical properties of the cuttings. and the physical properties of the drilling fluid. system Dimensions and Their Effect The dimensions of the fluid circulating system of importance to carrying capacity are the bore hole size, drill pipe size, pump capacity, and pump speed. These dimensions determine the annular velocity of the drilling fluid. Physical Properties and Their Effects The physical properties involved in the interaction between mud and cuttings are the density and shape of the cuttings and the density, viscosity and gel strength of the drilling fluid. The effect of the density factor on carrying capacity is fairly obvious; high density difference between cuttings and fluid results in a low buoyant force and therefore decreases carrying capacity. The effect of cutting shape is less obvious. Although

Jan 1, 1951

By C. E. Williams, G. H. Bruce

The trend toward deeper drilling, together with the attcndant increase in power requirements for circulation of the drilling fluid, has emphasized the need for a critical examination of the factors affecting the removal of bit cuttings from the hole by the drilling fluid. The ability of drilling fluids to lift cuttings is called their carrying capacity. A series of laboratory and field experiments has been conducted to determine the minimrim annular velocity necessary to remove cuttings, and to investigate the effects of properties of drilling fluids on their carrying capacities. Consideration of the results of these experiments led to the following conclusions: 1. Turbulent flow in the well annulus is most desirable from the standpoint of cutting removal. 2. Low viscosity and low gel are advantageous in removing cuttings. 3. Increase in mud weight is effective in increasing carrying capacity. 4. The carrying capacity is higher when the pipe is rotated than when it is not. 5. If turbulent flow can be maintained, an annular velocity slightly higher than the slip velocity of the largest cuttings to be transported should keep the bore hole clean. This implies velocities of 100 to 125 ft per minute rather than the presently used 175 to 225 ft per minute. INTRODUCTION Power Savings by Reduction of Annular Velocities A large portion of the power expended in drilling operations is consumed in circulating the drilling fluid. An important factor in establishing the rate of mud circulation is the minimum velocity in the annulus necessary to remove bit cuttings. Empirically, it has been found that average annular mud velocities of about 200 ft per minute will remove cuttings. It was not definitely known, however, whether annular velocities of about 200 ft per minute were just above the minimum necessary to remove cuttings, or whether such velocities could be materially reduced without sacrifice of the ability of the mud to remove cuttings. It is apparent that if annular velocities could be reduced without impairment of cutting removal, a considerable saving in power requirements would result. Need for Research on Carrying Capacity The ability of a drilling fluid to transport cuttings is called its carrying capacity. Although it has been recognized that the carrying capacity of a mud is affected by mud properties such as viscosity and density1,2,3,4 there have been various views in the industry as to the effects of these mud properties on carrying capacity. The economic importance of the problem of carrying capacity and the scarcity of information on the subject indicated that research on the problem was needed. THE FACTORS AFFECTING CARRYING CAPACITY Qualitative Determination of Factors The mechanism of cutting transport is closely related to that involved in the separation of material by settling processes. A considerable amount of research has been done on settling problems, and discussions of sedimentation theory can be found in standard texts.5,6 Consideration of the information available from these sources, together with consideration of the mechanism of cutting transport, leads to the conclusion that the factors affecting carrying capacity are the dimensions of the system, the physical properties of the cuttings. and the physical properties of the drilling fluid. system Dimensions and Their Effect The dimensions of the fluid circulating system of importance to carrying capacity are the bore hole size, drill pipe size, pump capacity, and pump speed. These dimensions determine the annular velocity of the drilling fluid. Physical Properties and Their Effects The physical properties involved in the interaction between mud and cuttings are the density and shape of the cuttings and the density, viscosity and gel strength of the drilling fluid. The effect of the density factor on carrying capacity is fairly obvious; high density difference between cuttings and fluid results in a low buoyant force and therefore decreases carrying capacity. The effect of cutting shape is less obvious. Although

Jan 1, 1951

By L. K. Smith, E. M. de Kock, J. van der Walt

A unique and systematic approach for analysing alternative methods of ventilating and cooling large hot mines is presented. The important factors that have a bearing on ventilation and cooling requirements and practices, such as air flow through the mine, geographical distribution of heat loads, micro ventilation considerations etc., are dealt with. Analysis of these leads to the definitive ventilation and cooling strategies, air and water process design, detail specifications and design of associated plant and equipment.

Jan 1, 1982

By Edward Steidle

THAT veterans are crowding the colleges is no longer news; 78 per cent of the 1916-47 enrollment in mineral industries curricula in the United States were veterans, but the rapid comeback from an estimated 1262 total mineral industries students in 1944-45 to 11,422 in 1946-47 is almost astonishing. The figure, which includes 1008 graduate students, is a substantial increase over the previous top record of 9619 in 1938-39. A small part of the increase is caused by the larger number of women entering the field, of whom there were c 9 in 1916-47. Petroleum leads the curricula with 34.5 % of the enrollment, metallurgy is second with 28%, and mining is third with 18%. Table 1. shows all curricula offered and those accredited by ECPD. Using the Mississippi River as a dividing line, 31 colleges in the East and 27 in the West offer curricula in the mineral industries.

Jan 1, 1948

By W. H. McFarland

The mechanical properties have been determined for a large number of alloy-free martensitic steels with carbon contents ranging from 0.08 to 0.20 pct and with manganese contents of about 0.4 to 0.5 pet. These steels were tested 1) as water-quenched, 2) after quenching, temper rolling, and tinning, and 3) after tempering treatments which involved temperatures from 400o to 1300oF and times from 1 min to 8 hr. The majority of these tests represent steel from commercial-size coils, i.e., strip 32 in. wide, coil weights up to 20,000 16, and steel thicknesses from 0.0055 to 0.024 in. As a result of these treatments, it has been shown that as-quenched low-carbon alloy-free steels can be produced with tensile strengths ranging from 140,000 to 220,000 psi and tensile elongations from 3.0 to 4.0 pet in 2 in. The tensile strength of the as-quenched martensites can be represented by the equation, tensile strength (ksi) = 119 + 560 (wt pet C). The response to tempering of these steels is related to previous work by Muir, Averbach, and Cohen and by Grange and Baughman. Strain aging of low-carbon martensite has also been investigated. If low-carbon steels are defined as those steels with a maximum carbon content of 0.2 pet, it is found that the literature on low-carbon, alloy-free martensites contains little data on the mechanical properties of these steels. However, the following facts concerning low-carbon alloy-free martensites seem firmly established:'-' 1) The major factors in controlling the strength of the martensite appear to be a) fine structure, b) the internal strain resulting from the transformation, and, particularly, c) the amount of carbon in solid solution. 2) In low-carbon steels, the martensite is auto-tempered and is in the form of needles with only minor amounts of internal twinning, whereas the martensite in high-carbon steels forms as plates which are internally twinned on a fine scale. 3) Care must be taken in comparing the results of work that has been done on low-carbon steels with varying amounts of alloying elements to data on plain carbon steels. As has been noted by Irvine, Pickering, and Garstone,6 alloying elements generally lower the martensite start temperature and, thereby, decrease the amount of auto tempering obtained during the quench. This makes it difficult to

Jan 1, 1965

By John J. Egan

THE present list of problems relating to the physical chemistry of steelmaking has been prepared by the Committee on the Physical Chemistry of Steelmaking, from answers to a questionnaire Submitted to a number of metallurgists engaged in both industrial and educational work throughout the United States. The purpose of the project is to make available to research laboratories a list of problems, all reduced to their simplest terms, the solution of which would aid in creating a better understanding of the steelmaking process. It is not intended to restrict the problems to practical steelmaking. The list also includes the study of the properties, and their correlation, as well as the physical and chemical reactions, of all Substances that occur or that may be in any way associated with steelmaking operations, Such as metallic substances, refractories, nonmetallic inclusions, and the constituents of slags. Many of the problems can be carried out in university or other research laboratories. Others may be most successfully attacked by cooperation of the research men with the operating personnel. It is the Committee's earnest wish that this cooperation be fostered. It is requested that investigators who are working on any of the problems listed and who anticipate future publication of their results, notify the Secretary of the Committee that such investigation is in progress. Suggested additions to the present list are also requested. The Committee is undertaking to act as a clearing house for information regarding the topics in this field that are being actually studied. Interested persons are invited to correspond with the Secretary. I. Data involved in the state of equilibrium for the various systems (laboratory work, almost entirely). A. SPECIFIC HEATS, HEATS OF FORMATION, ENTROPIES AND FREE ENERGIES OF VARIOUS PURE ELEMENTS OR COMPOUNDS; ALSO CERTAIN TYPICAL SLAGS AND REFRACTORIES. I . Determination of specific heats and entropies of oxides, sulphides, nitrides, etc. over a wide temperature range. 2. Determination of free energies of oxides, sulphides, nitrides, etc. over a wide temperature range. 3. Determination of the heats of formation of the oxides, sulphides, nitrides, etc. 4. Determination of the thermodynamic properties of the more important mineralogical constituents of the basic open-hearth slags such as calcium silicates, calcium phosphates, calcium ferrites, manganese silicates, FeO and Fe2O3. 5. Determination of the specific heats of open-hearth slags, including liquid silicates, if possible.

Jan 1, 1941

H. Van F. Furman, Denver, Colo. (communication to the Secretary): There are some statements in Dr. Carpenter's interesting paper which appear to require explanation, if not modification.

Jan 1, 1901

By Charles H. White

Discussion of the paper of A. L. Sweetser, Tress., xxxviii., 236. CHARLES H. WHITE, Harvard University, Cambridge, Mass. (communication to the Secretary*) :-Those interested in leaching-processes gladly welcome contributions on either laboratory-tests, such as are reported by Mr. Sweetser, or mill-tests made on larger quantities of ore; and especially valuable are such reports, even with negative results, if the methods adopted are the outgrowth of an intimate knowledge of the conditions to be met. It seems very desirable, therefore, that as complete details as possible be given in reporting on such tests, particularly with respect to the character of the ore under examination. The questions of prime importance in the sampling of ore and in the making up of charges for laboratory-tests are those respecting its grade and uniformity. In Mr. Sweetser's paper the first of these questions is answered definitely, but the answer to the second, although apparent on inspection of the results, might be more strongly emphasized with advantage, since it is only on account of the extreme uniformity of the ore that the satisfactory results obtained could have been expected. It seems advisable to call attention to the fact that for average ores, and more particularly for uneven, or 11 spotted ores, the quantities used by Mr. Sweetser are not usually regarded as sufficient to insure satisfactory results. Let us examine the method somewhat in detail. The ore was crushed to pass a 5-mesh screen, and a sample of 45 lb. was taken out for assay and tests. The diameter of the largest grain of this ore, according to Richards,1 was 2.67 mm.-assuming here, as in the following cases, that the wire of the screen was of the largest size used for the purpose, thereby giving any possible advantage in this respect in favor of the method. The table in Richards's book, p. 852, shows that 45 lb. is a sufficient quantity for a fair sample with uniform ores, but not sufficient

Jan 7, 1908

By P. Crowther, G. J. Lamprecht

The solubilities of silver, zinc, and cerium in liquid sodium, in the temperature ranges 100 to 270°C, 190° to 550°C, and 120" to 460°C, respectively, have been determined. From the solubility data the heat the entropy the partial molal enthalpy of mixing the excess entropy and the partial molal free energy of solution for the systems Nu-Ag and Na-Zn have been calculated. For the system Na-Ce the observed negative is discussed in terms of the solubility of the oxide Ce2O3. In an earlier publication the results obtained in the study of the solubility of tin' in liquid sodium are presented, as well as the detailed analytical procedures used. 1) REAGENTS Spectroscopically pure metals as supplied by Johnson Matthey and Co, were used to produce the following tracers: 253-day Ag110, 245-day zn65, and 325-day ce141. The tracers were prepared by irradiation in a thermal neutron flux of 4 x 10 13 neutrons cm-2 sek-1. To obtain a uniform amount of the required specific activity, needed for each solubility experiment, the radioactive metal was diluted with the corresponding inactive metal, by melting them together in an inert atmosphere. The liquid sodium used contained 11 ±2 ppm of O,1 determined by the vacuum distillation method.' The oxygen was assumed to be present as the oxide NaD. 2) THE SYSTEMS: SODIUM-SILVER AND SODIUM-ZINC Plots were made of the log of the mole fraction of silver, Fig. 1, and of zinc, Fig. 2, dissolved in the liquid sodium vs reciprocal absolute temperature. The equations for the solubilities, based on the least-squares fit to each plot, are: where Xi is the mole fraction metal dissolved in sodium, T is the absolute temperature, and s is the standard deviation in the value of log Xi. The heats and the entropies lution were calculated from the solubility data by In neither of the two cases was any intermetallic compound formed between sodium and the solute metal as was the case for tin.' Thus, for the silver and zinc systems the pure metal was taken as the reference phase. Since the solids in equilibrium with the liquid sodium were the pure metals, one can calculate the partial molal enthalpy of mixing and

Jan 1, 1969

By Robert H. Richards

If one holds up a prism, or wedge of glass, with narrow angle, say l° to 2O, and compares the transmitted image with the image seen above or below the prism, the former will be found to be thrown to one side by an amount varying with the angle of the wedge. Speaking of the two rays as the direct ray and the bent ray, we may say, that when the bisecting plane of the prism is at right angles to the line of sight, the angle between the direct ray and the bent ray will be constant for any given prism. If now we place a prism or wedge of glass in such a position that it half-covers the objective of a telescope, we shall obtain on looking through it two images of every object seen—one image by the direct ray, which comes through the unaovered half of the objective, the other which comes through the prism, and is the image by the bent ray. The angle of divergence of these two raps will be constant and unalterable, whether the telescope is directed to a near object, with its eye-piece at increased distance from its objective, or upon a ' distant object, with eye-piece nearer to the objective. That is to say, if the " throw " or apparent dislocation of the image is one foot in one hundred feet it will be two feet in two hundred, ten feet in a thousand, and so on. The usual form of stadia-telescope has at the focal point of the objective two spider-lines, placed at a definite distance apart and intended, let us say, to represent a throw of one foot in one hundred feet. But as the distance between lines remains the same, while the distance from the objective to the webs diflers with every variation in the distance of observed objects, it follows that the angle between the lines of sight which these two spider-lines define cannot be con stant, but must vary with every increase or decrease of distance be tween the instrument and the object viewed. If in Fig. 1 we represent three positions of the spider-lines by W1, W2, W3, and three objects corresponding to those positions by 01, O2, 0, at near, medium and distant positions, we see at

Jan 1, 1892

By George Burgess

I. INTRODUCTION THE suggestion has often been made that it would be highly desirable, at least for certain grades of steel, to be able to control more certainly, by pyrometric measurement or otherwise, the temperatures of the operation of the open-hearth and other furnaces used in the manufacture of steel and iron. That the properties of the ingot and finally of the finished steel product are intimately related to the final temperatures attained by-the metal inn the furnace and to the temperature of casting, has been recognized by metallurgists for a long time, and this question has been very thoroughly treated, especially by Prof. Henry M. Howe, and by A. W. and H. Brearley.1 It is the object of this paper to demonstrate that in so war as casting temperatures of furnaces, steel ingots, and similar operations involving the temperatures of streams of iron and steel are concerned, well-known pyrometric methods s may be easily applied-if certain recently determined corrections are made and precautions taken-with a relatively high degree of accuracy. Greater but not insurmountable difficulties will be encountered in. the case of open-hearth furnace temperatures, while for" those of the converter type a ready solution does not seem practicable. It appears that certain essential data have always been lacking in reporting observations such as those of Le Chatelier in 1892. Thus the correction to be applied for the characteristic radiation-or emissivity¬has hitherto not been adequately taken into account nor the limitations of the several possible pyrometric methods clearly recognized.

Jan 2, 1917

By James S. Foster, Paul G. Shewmon, Frank V. Nolfi

Analytical expressions are developed for the kinetics of dissolution or growth of a spheroidized, solute rich stoichiometric Precipitate in the surrounding matrix. There are two limiting cases; in one the rate of dissolution or growth is limited by long range solute diffusion through the matrix and in the other by the transfer of atoms across the mrdrix-precipitate interface. In the former case local interfacial equilibrium exists while in the latter it does not and the rate of dissolution or growth is controlled by an interfacial reaction. The analysis treats both limiting cases as well as mixed control in a single development, where it is found that the thermodynamic state of the interface is completely specified by a single parameter, o, defined by where K is the reaction rate constant, D is the matrix solute diffusivity, and R, is the precipitate radiz~s. If K is infinite then a is zero and local equilibrium prevails; if K deviates infinitesimally from zero, then a is very near unity and an interfacial reaction is rate controlling. Mixed control occurs for intermediate values of o. From the analytical results, numbers are computed which are useful in determining the duration of interfacial reaction or mixed control; following this time period, long range diffusion is rate controlling. THE rate controlling process or processes governing phase boundary migration has been the subject of much speculation and investigation. Traditionally, the most widely assumed boundary condition in quantitative treatments of this problem has been that of local interfacial equilibrium. This condition implies that long range diffusion of one or more elements controls the migration and is referred to as "diffusion controlled migration" (herein DCM). In contrast to the above view is the proposition that local interfacial equilibrium does not exist and that transport of atoms across the interface is rate controlling. Consequently, this mechanism is referred to as "interface controlled migration" (herein ICM). In processes of the latter type, the activity, a, of one or more elements is discontinuous at the phase bound- ary and the flux, J, across the boundary of a given element is some function of its activity discontinuity, a. One of the most comprehensive contributions to a mathematical description of phase boundary migration is due to am.' His analyses are applicable to precipitation in binary systems in which a) the precipitates are spherical* solute rich compounds of constant

Jan 1, 1970

By H. O. Pickard

The Hoover and Mason Phosphate Co. made extensive tests with a rig manufactured by the Paris Manufacturing CO. as shown in Fig I. It is powered by a 20-hp Wisconsin air-cooled gasoline engine, through a single reduction gear and flexible coupling. The machine operates a 4-in. auger with a detachable cutting head, as shown in Fig I. The auger length is 3 ft 4 in. and the cutting head averages 7 in. The unit has a drilling capacity of 100 ft and can drill an average prospect hole in less than 15 min. The weight of the motor is used for the thrust feed for driving the auger and head down, aided by the spiral shape of the auger. The rate of downward motion—i.e., the feed—is regulated by a handwheel. The string of tools is withdrawn from the hole by a gear train controlled by a hand-operated clutch. In fairly dry strata, not of the consistency of mud, the action of the auger

Jan 1, 1948

By H. O. Pickard

The Hoover and Mason Phosphate Co. made extensive tests with a rig manufactured by the Paris Manufacturing CO. as shown in Fig I. It is powered by a 20-hp Wisconsin air-cooled gasoline engine, through a single reduction gear and flexible coupling. The machine operates a 4-in. auger with a detachable cutting head, as shown in Fig I. The auger length is 3 ft 4 in. and the cutting head averages 7 in. The unit has a drilling capacity of 100 ft and can drill an average prospect hole in less than 15 min. The weight of the motor is used for the thrust feed for driving the auger and head down, aided by the spiral shape of the auger. The rate of downward motion—i.e., the feed—is regulated by a handwheel. The string of tools is withdrawn from the hole by a gear train controlled by a hand-operated clutch. In fairly dry strata, not of the consistency of mud, the action of the auger

Jan 1, 1948

By O. Bergmann, R. E. Lueders, R. R. Ellefson, H. M. Brennecke, D. S. Davies

A new hydrometallurgical process has been developed to recover copper from sulfide ores. Copper is leached in a staged reactor system utilizing nitric and sulfuric acids at 105OC. Iron is removed from the pregnant liquor as a jarosite, and cathode copper is electrowon directly from the purified pregnant liquor. The spent electrolyte is recycled. Nitrogen oxides evolved from the leach are reconverted to nitric acid and are also recycled. Sulfur is rejected as So, jarosite, and gypsum. The process is highly versatile and can recover precious metals, molybdenum, and zinc when these elements are present. Continuous, integrated, semi-pilot plant operations using chalcopyrite ores demonstrated 99% copper leaching and production of cathode grade copper. Economic evaluation shows that the process is competitive with pyrometallurgical and other hydrometallurgical processes.

Jan 1, 1982

By Shozo Saito, P. A. Beck

Mettrllographic and X-ray diffraction study of Cb-Co alloys in the Composition range of 7 to 33 nt. pct Cb, after annealing at 1175 °', showed that near 25 al. pct Cb on MgNi,-lype hexagonal Laves Phaseexists in a narrow composition range, and that an MgCl- type cubic Laves Phase occurs between approximately 27 and 32.6 ut. pd Cb. Lattice parameter and density measures indicated that, in both phases. the deviations from proper Loves sloichimetry result from the substitution of cobalt atoms for some 0f the columbium atoms. Tlle same phases occurant 1000'C, together with an additional phase of unknown structure, which appears between the hexagonal Laves phase and the cobalt-bose terminal solid solutions KOSTER and Schmid' identified a phase corresponding to the composition VCo,, and more recently the crystal structure of this phase has been determined.' In the Ta-Co system Korchynsky and Fountain recently found two intermediate phases at the composition Taco,, one of them metastable. In contrast to the V-Co and the Ta-Co systems, in the Cb-Co system no intermediate phase has been found4 at the composition CbCo,. The present investigation was undertaken in order to reexamine the question of the existence of such a phase. EXPERIMENTAL PROCEDURE Twelve alloys were prepared by arc-melting in a water-cooled copper crucible under helium atmosphere. Electrolytic cobalt and 99.9 pct pure colum-bium powder have been used as starting materials. It was found that melting losses can be reduced by compressing the colunlbium powder in the form of thin pellets before melting. For the alloys used the melting losses were not higher than 1 pct. The intended compositions of all alloys and the chemical analyses of three of them are given in Table I. Specimens from all alloys were annealed in evac- uated fused silica tubes at 1175°C for 3 days and quenched in cold water. A second set of specimens of most alloys was annealed at 1000°C for 7 days and then quenched in cold water. The annealed and quenched specimens were examined metallographically, using the following etchant: 60 pct glycerine +20 pct H,NO, + 10 pct HF + 10 pct water. Powder specimens for X-ray diffraction were prepared by crushing annealed solid specimens in a mortar. Alloys containing 27.3, 28, 29.7, and 32.6 at. pct Cb annealed at either 1175" or 1000°C were very brittle and it was found unnecessary to reanneal the powders. However, alloys containing 24.8 at. pct Cb, or less, especially those annealed at 1000°C, were much less brittle and re-annealing was required to remove the strains present in the crushed powders. In each case reannealing was done at the same temperature at which the corresponding solid specimens were annealed and it, too, was followed by quenching in cold water. In many instances X-ray diffraction patterns were also taken of the polished and etched solid specimens and compared with the corresponding X-ray diffraction patterns obtained with powders. The X-ray diffraction patterns were taken with an asymmetrical focusing camera, using CrK radiation. For precision lattice parameter measurements some X-ray diffraction patterns were taken with a symmetrical focusing camera, again using CrK radiation. EXPERIMENTAL RESULTS A microscopic examination of the alloys annealed at 1175°C revealed that the alloy containing 25.5 at. pct Cb was composed of a single phase, but that the 24.8 at. pct Cb alloy did contain a small amount of a second phase, identified by means of X-ray diffraction as having a fcc structure, undoubtedly the terminal solid solution based on cobalt. Apart from the few very weak lines corresponding to this minor phase, the X-ray diffraction patterns of these alloys could be well interpreted in terms of a MgNi,-type hexagonal Laves phase structure. The indexing of the X-ray diffraction pattern, Table 11, yas based on the lattice parameter values a, = 4.740A and c,

Jan 1, 1961

By J Price, M. R. Geer, H. F. Yancey

COAL mine operators recognize coal as an abrasive material, because the wear of drilling, cutting, and conveying equipment is reflected as a cost item for replacement of parts. Similarly, industrial consumers of coal experience abrasive wear on all coal-handling equipment. Operators of pulverized fuel plants are doubtless most keenly aware of the abrasiveness of coal, because under the high contact pressures developed between coal and metal in pulverizers, abrasive wear is increased many fold. Moreover, experience in operating pulverized fuel plants has demonstrated that some coals are much more abrasive than others. Hardgrove' stated that maintenance costs entailed by the wear of grinding elements is often a more important variable than the cost of the power required to pulverize different coals. Craig2 also reports that one coal may cause pulverizer parts to wear several times faster than another. It is apparent, therefore, that those concerned with pulverizing coal could profitably employ a method for estimating the abrasiveness of different coals, just as they utilize standard tests for thermal value, grindability, and ash-fusion temperature to assist in selecting the most suitable and economical coal to use in a particular plant. The objective of this investigation was to develop a test procedure that would be suitable for general use in estimating the abrasiveness of coals. However, few, if any, of the standard tests now used for evaluating the properties of coal are the product of a single investigation or the result of a single investigator's efforts. Rather, in each case, a testing procedure was devised by one investigator, used by others on a wider variety of coals, and finally refined completely as the result of the joint efforts of a number of interested people. Thus, the test procedure for estimating abrasiveness developed in the course of this work may not be refined sufficiently in its present form for general use, but it may serve as the starting point from which an acceptable test procedure can be developed. The method has been used thus far on only about a dozen coals, and there has been no opportunity to attempt a correlation between experimental results and actual plant experience. Only wider use of the procedure by other investigators and correlation with plant experience can determine to what extent the method will have to be modified to render it suitable for general application. Test Method Although the literature contains no record of an attempt to devise a method for estimating the abrasiveness of coal that could be used industrially, several investigators have tested properties of coal that are closely related to its abrasiveness. The abrasiveness of a material generally is considered to be related to its hardness, and hardness tests for coal have been employed by Heywood,' O'Neill," and Mathes. Also, the resistance of coal to abrasion, a property that presumably is related to the abrasiveness of coal, was measured by Heywooda and by Simek, Pulkrabek, and Coufalik.2 11 these investigators tested only individual pieces of coal. Since coal is a heterogeneous material having components of varying properties, tests of this type can yield results having little more than academic interest. Only a test method that utilizes a representative sample of coal can give results that are useful industrially. The abrasion tests used for various other materials have been considered for adaptation to testing the abrasiveness of coal. The tests used for metals,7-9 paving and flooring,'" and rubber," cannot be used because coal is not sufficiently abrasive.~ The present experimental work was begun before World War II and was conducted by three research fellows"'" working under a joint agreement between the University of Washington and the Bureau of Mines. After a great deal of preliminary work with a variety of apparatus and materials, a test procedure was developed which consisted of rotating a test disk 2Yz in. diam in a steel mortar containing the coal sample. The shaft carrying the test disk at the lower end and a 100-lb load on the upper end was free to move vertically. The bed of coal in the mortar was kept fluid by low-pressure air admitted through a port near the bottom of the mortar. Measurable wear on an Armco iron disk could be obtained in this test procedure, but, despite extensive efforts to eliminate them, several major disadvantages remained in this test method. First, with most coals the amount of wear on the iron disk did not exceed a few milligrams. Second, a single type of disk was not applicable for all coals. A smooth iron disk gave satisfactory results with both bituminous and sub-bituminous coals, but hardly any wear with anthracite or coke. A disk having studs or projections gave more satisfactory abrasion losses with anthracite and coke and presented no operating difficulties with free-burning bituminous and sub-bituminous coals. It could not, however, be used with caking coals because these coals formed a

Jan 1, 1952

By V. F. Swanson

A petrographic study was made of the type and sources of mineral contamination occurring in Florida phosphate rock products. Emphasis was placed on contaminants in the screened rock (+1 mm), since this portion of the product undergoes no physical beneficiation except for scrubbing to remove slimes. Since iron and aluminum contents of the finished product affect the salability, special emphasis was placed on identifying types and sources of these contaminants and relating chemical composition to visual characteristics. Wavellite derived from the overburden was the major aluminum contaminant with some aluminum being included as secondary clay balls. Iron occurred as phosphates in the overburden and as colloidal oxides included in the phosphate pebbles. Chert and limestone contamination derived from the Hawthorne formation underlying the phosphate matrix.

Jan 1, 1972

By R. T. Hukki, P. Voutilainen

This paper describes a new apparatus for continuous wet fine-screening. Its preferred size range seems to be from 0.1 to 1 mm. The supercritical trommel screen is a short cylindrical trommel of wedge-bar type construction operated at a speed greater than the calculated theoretical critical speed and at a speed lower than the speed at which particles introduced into it will centrifuge. The paper describes results obtained with the prototype supercritical trommel screen in pilot plant scale. The results point to a high capacity and simultaneously to a high sharpness of screening. Finally, an analysis is presented of the forces acting in screening on a supercritical trommel screen. In the era of high speed, high capacity processing of raw materials the conventional slowly rotating trommel screen is often considered a relic from the times passed. A typical trommel screen is the cylindrical trommel rotated about a horizontal or slanting axis at a relatively low speed. Its screening characteristics are well known. Trommel screens of various types of construction, methods of operation, performances and other characteristics have been described in detail by Taggart.1 The theoretical critical speed of a trommel screen is defined by the same well known equation as that applied for grinding mills: where ncritical = the numerical value of the theoretical critical speed in rpm, D 1 = the inside diameter of the trommel in feet, and D2 = the inside diameter of the trommel in meters. ncritical corresponds also to the centrifuging speed provided that the coefficient of friction f between the trommel surface and the outer layer of the charge is = 1.0. In a general case: From Eq. 2 it is seen that in all cases where f < 1.0 the centrifuging speed of the trommel is greater than the theoretical critical speed. The supercritical trommel screen concerns screening operations within that speed range which is between the theoretical critical speed defined by Eq. 1 and the centrifuging speed defined by Eq. 2, under conditions such that the coefficient of friction f<1.0. It is reported by Taggartl that the optimum speed of a conventional cylindrical trommel screen 36 in. in diam was experimentally found to be about 16 rpm. From Eq. 1, the critical speed of this trommel is 44.2 tpm. The indicated optimum speed corresponds to (16/44.2) x 100% = 36.2% of the theoretical critical speed. The optimum speed range based on information available seems to vary from 33% up to 45% of the theoretical critical value. The trommel screen operated at a supercritical speed: operates at a speed greater than the calculated theoretical critical speed; operates at a speed lower than the speed at which the charge introduced into it will centrifuge; operates within the supercritical speed range in such a way that the coarse fraction of the charge must slide in respect to the inside surface of the trommel; the outer layer of the said fraction next to the screen tends to proceed in the same direction as any selected point on the trommel surface, but now at a lower speed, and indeed at a subcritical speed; allows to a certain degree adjustment of the maximum determining particle size x of the fine product simply by a variation of the speed of the trommel within the supercritical speed range. With increasing trommel speed, finer and finer material only will get the opportunity to find its way into the fine product while the screen opening remains constant. In conventional practice, the low speed trommel is generally used for sizing of coarse and medium coarse material, but seldom for fine screening. The characteristic feature of the product passed through the conventional trommel is that the determining size x of the biggest particle is barely smaller than the nominal size of screen opening. The supercritical trommel screen, on the other hand, is best suited for sizing of relatively fine material. Furthermore, the characteristic determining size x of the biggest particle in the fine product can be substantially smaller than the nominal width of the screen opening or slot. In the trommel screen best suited for the applications

Jan 1, 1965