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By Guy D. Bruno

Through the remainder of this century, world consumption of fluorine per ton of primary aluminum produced will continue to be substantially reduced. Growth of the primary industry will offset some of the unit consumption, but demand for new fluorine sources will decline sharply. Continued application of dry fume scrubbing system will be the most significant factor in reducing demand.

Jan 1, 1979

Jan 1, 1916

By G. T. Lineberry

Power requirements for a piece of mobile mining equipment are largely dependent on the set of conditions in which they must operate. These conditions are isolated and key parameters are identified. The effect of operating conditions on power determination is investigated. A simulation technique is developed to predict ranges of power demands for off-highway haul units as an archetype, permitting the analysis of changeable operating conditions. This program uses given data, conditions, and probabilities and ranges to solve for individual components of power, which can then be summed. By adopting such a technique, a systematic and rational determination of power is made possible. The usefulness of this basic approach in the determination of power requirements for other mobile mining equipment is emphasized.

Jan 1, 1983

By T. Vasilos, J. T. Smith

THE mechanism of pressure sintering, or hot pressing, for ceramic materials, has been investigated by several researchers.1-8 Plastic flow has been suggested as the rate-determining mech-anism1,2 while grain boundary sliding3,4 and fragmentation processess have been found controlling in other studies. Vasilos and Spriggs5,6 have reported that pressure sintering occurs by a diffusion-controlled mechanism. For the pressure sintering of metals, investigations with lead7 and with tin6 have not identified the operative mechanism during consolidation of these powders. This note reports the results of a pressure sintering study initiated to determine the mechanism controlling the densification of spherical copper powder. Temperatures of 300°, 400°, 500°, and 600°C at 2500, 5000, 7500, and 10,000 psi pressures were investigated. The copper powder for this study was obtained from Metals Disintegrating Co., Elizabeth, N.J. The minimum purity was reported to be 99.9 pct. The powder size was -325 mesh and a lineal analysis showed the average size to be less than 1 p. An alumina die body and punches were employed. Graphite spacers were placed between the copper powder and the punches before pressing. It was expected that the graphite would form carbon monoxide with any entrapped air and form a reducing atmosphere within the die cavity. This condition was generally realized during pressing although a minor amount of oxidation occurred at 500" and 600°C. The oxide particles were located randomly in the pressed samples and were not considered to influence the densification process. Calibration tests showed the temperature of the copper pellet to be about 20°C less than the die wall temperature, probably resulting from heat losses through the punches. This difference was compensated during the experimental pressing operations. The hot pressing equipment employed for this work has been described by Spriggs et a1.9 and was calibrated with a Baldwin-Lima-Hamilton load cell. Travel of the punches was monitored with a dial indicator showing increments of travel to 0.0005 in. Relative density was calculated at selected time intervals for a known copper weight, punch travel, and die diameter. The accuracy of this calculation was *1 pct. Average grain size after hot pressing was obtained by lineal analysis. Typical densification curves are presented in Fig. 1 and Fig. 2 where relative density is plotted vs log time as a function of applied pressure for the 300" and 600°C pressure sintering temperatures, respectively. The curves for 400" and 500°C were similar to those at 300°C and consequently are not shown. The curves at 300°C as well as 400" and 500°C do not show an end-point or limiting density for a particular applied pressure. At 600°C, a density in excess of 95 pct of theoretical has been reached such that further densification is extremely slow for the 5000, 7500, and 10,000 psi pressures. It is suggested that further densification at these pressure levels may be retarded or prevented by discontinuous grain growth, by entrapped gases, and by other microstructural limitations as described by Cob1e.10 The curve for 2500 psi hot pressing pressure is a straight line over the time interval although a slight change in slope may be occurring at the last time intervals. The plastic flow models,1,2 derived for hot pressing, predict the existence of an end-point (or limiting) density dependent on the yield point of the material at the temperature of interest. The yield stress of copper at a 0.005 strain level has been

Jan 1, 1965

By E. E. Bauer

Technical data describing the critical points for selection of the proper hammer and of the boom and power pack for mounting on mobile gyratory crusher installations are presented. Charts describing typical rocks with breakability indexes for hammer selection are included. Comparative data of representative available hammers along with criteria for evaluating hammer selection are also presented. Factors affecting the selection of the boom and the power pack, as well as optional features for ease of operation and improved safety are described.

Jan 1, 1986

By U. K. Custred

To the layman, the term "strip mining" usually applies to the appearance of mined-over land after an operation is completed, not to the technique. This attitude, however, is becoming pass6 in the central Florida pebble phosphate field as eight mining companies in the area pursue a mutual program of land reclamation. The Florida phosphate industry is fortunate in this respect because it occupies an area favorable to reclamation. The terrain is flat; overburden is sand and clay which will support vegetation fairly readily; a high ground water table naturally converts mine pits into lakes. Too, this is water which readily supports marine life, not the acidic water so frequently found in the coal industry.

Jan 4, 1963

By Wilbur Stout

IN Ohio, the annual output of coke made from native coals has averaged not more than 70,000 tons, or about enough to run a 200-ton blast furnace. Raw coal locally mined from the Sharon, or No. 1, bed was used for iron smelting in Mahoning furnace at Lowellville, Mahoning Co., as early as 1846. This practice was continued in the Youngstown district until the coal became scarce and the Connellsville coke more popular. At present, the Sharon bed contributes a part of the fuel for the production of ferrosilicon iron at Jackson, Jackson Co. About one-third native coal and two-thirds soft coal are used. In this state, coke, on a commercial basis, was first made in Jefferson County probably about 1861 or 1862. The coals used were the Steubenville Shaft, or Lower Freeport, and the Strip Vein or Middle Kittanning. The practice, however, was discontinued before 1880 because of the competition of superior foreign cokes. Beehive ovens, later built at Leetonia, Columbiana Co., were operated for only a few years; the coal used at this place is the Lower Kittanning or No. 5. In a desultory way, slack from the Pittsburgh coal has been coked at a few places in eastern Ohio, and attempts, either for experimental or for commercial purposes, have been made in other parts of the State. Small quantities of coke were made from the Upper. Freeport coal at Salineville, Columbiana Co., and near Nelsonville, Hocking Co.; the results were poor. Tests were made of the Middle Kittanning coal near Zanesville, Muskingum Co., at Moxahala Furnace, Perry Co., and at Washington Furnace, Lawrence Co.; the cokes were all high in sulfur and ash. Attempts were made to coke the Clarion coal at Vinton Furnace, Vinton Co.; a small battery of molding ovens and a pile of high-sulfur coke yet remain to tell the story. The Pittsburgh coal was coked on a commercial scale at Utley and at Lathrop, Athens Co.; but the operations were not successful and were soon abandoned.

Jan 9, 1919

By Gunnar Thaning, Goran Mathisson

The iron ores mined by LKAB in the north of Sweden have excellent beneficiation properties. This gives LKAB a favorable position as regards the production of low silica pellets for direct reduction. LKAB has concentrated on developing and marketing grades of pellets for the Midrex-Purofer-HyL process group, i. e., such direct reduction processes carried out in a shaft furnace or a static bed using reformed natural gas as a reducing agent. The paper deals with properties and quality demands of iron ore pellets for such processes. Matters such as the effect of the residual magnetite in the fired pellets on the degree of metallization, the amount and composition of the slag phase in the pellets, the mechanism of the disintegration during reduction, the state of swelling of the pellets during the conditions prevailing in these processes, the importance of the porosity, the improvement of the reducibility and lowering of the sticking tendency of the pellets by small additions of suitable additives, and the influence of the pellet size are discussed. A special test procedure for direct reduction pellets has been elaborated by LKAB. Thus, three metallurgical properties are routinely determined separately, namely reducibility, reduction strength, and sticking. The test methods are described. Finally the present and future LKAB pellets for direct reduction are presented with respect to chemical analyses and metallurgical properties.

Jan 1, 1980

By Joe O. Ledbetter

INTRODUCTION Health physics as a profession really got a significant start during the Manhattan Project of World War 11. The Health Physics Society has recently published its 25th anniversary issue of the journal (June 1980). There was concern over radiation exposures during and after uranium production, especially about radium and its daughter products [Jackson 19401 and, as evidenced by the frequency of articles in the literature, there still is. The reason for this concern was expressed by Harley as "Workers engaged in the mining and pro- cessing of radium-bearing materials are exposed to dusts of the parent, to radon, and to the radon daughter products. In- haled radioactive particulates may be retained in the lung or redistributed to other organs of the body. Relatively minute de- posits of radioactive substances, particularly alpha emitters, have been clearly shown to be the etiological factor in a variety of injuries to industrial and re- search workers. " [Harley 1953] Emphasis in measurements has been placed on radium in water and radon in air, since these are the principal mobilized phases; however, it should be kept in mind that radium-containing particles do become suspended in air as aerosols and radon absorbs in liquids. Much of the uranium mining and production is being carried out aboveground. The principal difference between underground and surface (pit or leach) mining of uranium is the reversal in the relative importance of roles for the types of radiation dose. For aboveground the major radiation exposure is external gamma ray, whereas for underground it is internal alpha; for aboveground, the whole body penetrating is of greater importance than the lung alpha dose. AS a result of the politics involved and the law- suits for any and all diseases as being occupationally- caused, today , more than ever before, the successful performance of the activities connected with uranium production--before-, during-, and after-the-fact-- must include the provision of first class radiation protection. Such protection can be achieved by good measurements, thorough risk evaluations, and adequate controls. Meeting the ALARA (As Low As Reasonably Achievable) philosophy necessarily entails the determination of what is reasonable exposure. The necessary and sufficient elements of radiation safety under the ALARA dictum require a hard look at the dose versus effects data. There are times when the health physicist needs to make decisions of judgement rather than compliance with a well-defined regulation value. In order to facilitate such decisions, the real world must be separated from opinions that are merely artifacts of statistical variation and from the unprovable "what ifs" that are slanted to question the morality of any non-Luddite. UNITS VOCABULARY FOR DOSIMETRY There have been many radiation quantifying and dosimetric units introduced in the past. Fortunately, most of them did not catch on enough to become required knowledge for reading the health physics literature. The unit definitions necessary for our purposes here are the following: -curie (Ci)--unit of radioactivity equal to 3.7 x 10 10 disintegrations per second Webster&apos;s 19711 or the quantity of radionuclide that undergoes 3.7 x 10 nuclear transformations per second. Environmental levels of radioactivity are usually measured in picocuries (10-l2 Ci) per cubic meter for air and in picocuries per liter (pCi/~) for water and sometimes for air. .roentgen (R)--exposure dose of x or gamma rays that gives 1 esu of charge (either sign) to 1 cc of dry air @ STP. The roentgen is equivalent to an energy absorption of 86.7 ergs/g of air [Gloyna and Ledbetter 19691. .rad--radiation absorbed dose of 100 ergs per gram of absorber. The SI unit for absorbed radiation dose is the Gray; 1 Gy = 100 rads. orem--radiation absorbed dose of 1 rad times the quality factor (QF) for that radiation. The QF is 1 for x rays, gamma rays, beta rays, and posi- trons. For heavy ionizing particulate radiation, QF is a function of the amount of energy trans- ferred per unit length of travel, i.e. , the linear energy transfer (LET); the values of QF:LET in keV/um are as follows: 1:<3.5; 1-2:3.5-7; 2-5:7-23; 5-10:23-53; and 10-20:53-175 [Morgan and Turner 19 671 . For radiobiology, relative biological effectiveness (RBE) is recommended for use instead of the quality factor above that is for radiation protection: the RBE is the ratio of the dose of 200 kVp x rays to the dose of radia- tion in question (both in rads) to cause the same

Jan 1, 1980

By W. C. Weslow

AN extended program devoted to the development of a matrix for holding diamonds of a size and. kind not heretofore generally used is being carried on by the Carboloy Company, and this paper describes the part of the development that affects mining and its allied industries. Labora-tory and field work so far has indicated the following: 1. Tungsten carbide and cobalt form the most desirable known matrix material for the holding of diamonds for drilling work. 2. Industrial bort diamonds in sizes and of a class not generally heretofore acceptable and therefore less expensive can be successfully held in this cemented carbide matrix. 3. In exploratory drilling, the combination of bort diamonds, impreg-nated throughout a matrix of tungsten carbide and cobalt, when fabri-cated onto drilling crowns, is an indicated economic substitute for drilling crowns in which the diamonds are set by hand, mechanically or by casting. 4. This impregnated type of drilling crown or bit has definite possi-bilites of revolutionizing the drilling of blast holes, particularly in the harder formations. This will be brought about by the development of high-speed light-weight rotary equipment using an impregnated diamond bit to replace the percussion drill now in general use. (The development of this rotary equipment is well past the laboratory stage at this time.) 5. That the use of a rotary bit is a preventive measure in the fight against silicosis. The development of this product was started by G. F. Taylor at the Research Laboratories of the General Electric Co. It was early recog-nized that it had possibilities in the drilling field and the present product is the result of considerable experimental work with other powdered metals as well as with tungsten carbide and cobalt.

Jan 1, 1940

Although the Suggestions to Institute Authors, as revised and amplified over the years to meet changing conditions and experience, have had as their primary objective the guidance of the author who is preparing a paper for record in the TRANSACTIONS, there are in this current version many excellent suggestions for the preparation of any material for publication by the Institute In this connection it should be emphasized that in a sense, and to a degree determined by the editors, the Institute has in its journals "a place for everything," especially a place for the article of practical nature that is of immediate but not necessarily permanent interest Such articles may be referred by the Institute Technical Publications Committee to the editors or submitted directly to them , [Papers (TECHNICAL PUBLICATIONS and TECHNICAL NOTES) authorized for the TRANSACTIONS are, with the discussion, gathered together at the end of the calendar year and with a table of contents and index, bound, according to Branch classification, as volumes of the TRANSACTIONS

Jan 1, 1952

By S. Shapiro, G. Krauss

The strutural and cr~stallo~aphic features of the plates of austenite produced by the martensite to aus-tenite or reverse martensitic tramformation have been determined in an Fe-33 wt pct Ni alloy. Micro-focus X-ray techniques and single-surface trace analysis 072 bulk samples yielded two distinct habit planes, (0.174, 0.309, 0.~35)~ and (0.375, 0.545, 0.749jM. The former plane uas the one predorninantly observed and its existence was verified by transn~ission electron microscopy. The orientation relation-ship between the reversed austenite and the parent martensite was approximately the same as the Nishiyamna and other relationships reported for the direct tramformation. Replica and thin-joil obser-vations show that both high densities of tangled dis-locations and occasional twins constitute the fine structure of the reversed austenite. Application of the phenomenological theory to a variant of the predominant habit plane defines an irrational plane and direction for the second shear in accordance with the comnplexity of the fine structure. The shear accompanying the reverse martensitic transformation is at least 0.51, the maximnum value of- the tangent oJ the tilt angle measured on surface replicas. A mechanism relating the fine transformation twins in martensite to the nucleation of reversed austenite of the predominant habit is proposed. The reversal of Fe-Ni martensite takes place both at the edges of martensite plates and in a piecewise fashion within them.&apos; The shear-type nature of the reverse transformation is verified by the surface relief which accompanies both edge-type reversal2 and the fragmentation of plates of martensite&apos; as a result of rapid heating above the A, (austenite start temperature). The orientation relationship between the edge-type reversal product and the parent martensite, as determined by transmission electron microscopy, is reported to be within 4 deg of either the Kurdyumov-Sachs or Nishiyama relationships,&apos; but there is no work at present in the literature relating to the crystallography of the platelike reversed austenite. The fine structure of reversed austenite after heating to 50°C above the Af is reported4 to be composed primarily of tangled and jogged dislocations in concentrations up to 10" per sq cm. A replica investigation of partially reversed Fe-Ni martensites5 corroborates the increase in dislocation density following reversal and presents indications of other possible modes of fine structure. This paper reports on an investigation performed to examine in detail the morphology and crystallography of the plates of reversed austenite and the shear which accompanies their formation in a matrix of Fe-Ni martensite. EXPERIMENTAL PROCEDURE Discs of a high-purity Fe-32.9 wt pct Ni single crystal served as the starting material. The single crystal had been produced in the course of an earlier investigation6 and the carbon content was determined at the time to be 0.006 wt pct. The M,, and the A,, were respectively -120" and 300°C. Partial transformation to martensite was performed at -125°C and reversal of some of the martensite was accomplished by heating in the temperature range 340" to 355°C. Most samples were heated to the reversal temperature by immersion&apos; in a salt bath for 2 min. For surface-relief studies some polished and etched Samples were heated in a tube furnace for ten min in a hydrogen atmosphere maintained over the samples throughout the heating and cooling cycles. Samples were prepared for metallographic examination by electropolishing and etching with an HC1-HNOs-H20 et~hant.~ On one of the surface-relief samples two sets of fiducial scratches were placed on the etched sample by drawing it over a slurry of 0.06 p alumina on a "microclothJ&apos;. The orientations of individual plates of martensite were determined by X-ray analysis. A Rigaku-Denki microbeam X-ray generator in conjunction with a Micro-Laue camera with facility for precision location of the sample in front of the beam was employed for this purpose. The collimator size was 30 p and the specimen to film distance was 5 mm. The Laue photograms were enlarged to an equivalent 3-cm specimen to film distance for analysis. The orientation of each of the plates of martensite was compared to that of the parent austenite and the relationship be -tween the two phases was, in all cases, within a few degrees of those predicted for the direct transformation. The orientation relationship between one of the larger plates of reversed austenite and its parent martensite was determined in a similar manner. The habit plane of the islands of reversed austenite in the X-rayed plates of martensite was determined by a single-surface trace analysis. Each reversal island had with the parent phase one comparatively straight boundary which was presumed to represent the habit plane trace. The pole locus technique7 was applied to traces from six different plates of martensite to determine the indices of the habit plane. A 40-cm stereographic net was employed for this analysis The morphology and fine structure of the reversed austenite were studied by electron microscopy of pre-shadowed direct carbon replicas,5 and the macroscopic shear was evaluated by a two-stage replica technique similar to that employed in electron fractog-

Jan 1, 1968

By Ralph Wilcox

THE diamond drilling of certain characters of unstable rock forma-tion, as, for example, the copper-bearing schists of the Miami district in Arizona, is rendered most difficult by what is known as " caving" of the sides of the drill holes. As this caving is very greatly increased by the action of flowing water, it occurred to me, after experiencing a great deal of difficulty with caving in diamond-drill holes which I was drilling for the Miami Copper Co., that if I could substitute air for water, much of the caving-with resultant difficulties, such as decreased speed of sinking and increased consumption. of diamonds-would be overcome. After some experimenting, I found that it was perfectly practicable to substitute air for the water; forcing the air down the hollow rotating rods in the same manner as is done with water, the air passing out around the bit, which is thus cooled, and ascending on the outside of the rods to the collar of the hole, carrying the borings in just as satisfactory a manner as had been done by the water, but without the accompanying destruction or caving of the sides of the drill holes such as had been so generally experienced with the water. When water was encountered in the drilling this water was forced up to the collar just as it would have been had water been used in the .drilling, but with the correspondingly decreased flow there was relatively less washing or caving of the sides of the drill holes. The only change necessary in the arrangement of the drill is that a cross instead of a tee is used at the collar of the hole. A tightly woven jute bag is attached to one arm of the cross, for collecting and filtering the sample; and when drilling in dry ground a jet of water is attached to the opposite arm of the cross, to collect the dust and wash down the sample into the bag. The rods rotate through a stuffing box attached to the upper opening of the cross. The distention of the jute bag by the issuing air indicates the operating conditions as sufficiently as did the flow of water when using water in the drill hole.

Jan 10, 1913

By Felix Wunsch

WHILE the effect of the cold-junction temperature has been known by many, its consideration has been ignored in a number of installations, resulting at tunes in a very considerable error. In fact, the magnitude of this error may amount to over 100° in some cases. While hand-operated correcting devices for portable checking pyrometers may be entirely satisfactory, it is, of course, desirable to have such apparatus en¬ Millivoltmeter Thermocouple Platinum Wire Mercury FIG. 1.-EARLY `METHOD OF AUTOMATICALLY COMPENSATING FOR COLD-JUNCTION TEMPERATURE CHANGES. tirely automatic, when applied to curve-drawing or printing pyrometers, otherwise there is no assurance that the record is correct. Numerous methods for automatically compensating for cold-junction temperature changes of thermocouples have been proposed and used in connection with millivoltmeters. One of the earliest proposed was that shown in Fig. 1. A bare resistance wire was immersed in a column of mercury located near the cold junction of the thermocouple. An increase in temperature near the cold junction resulted in a rise of the mercury column, which short-circuited more of the resistance wire causing an increase in the potential difference across the millivoltmeter, which compensated for the decreased electromotive force of the thermocouple.

Jan 9, 1919

By Robert J. Brison

On the basis of experience accumulated during the completion of some 150 gold/silver process development projects, general guidelines are presented for developing the most cost effective process for a specific project. Steps involved in process development for lode ore deposits generally include a review of pertinent background information on the ore deposit, sample procurement and preparation, sample characterization, study of concentration possibilities, investigation of leaching and metal recovery methods, economic evaluation of alternative processes, optimization of the selected process, a pilot plant program if warranted, and finally, process design and feasibility studies. Each of these steps is discussed, with emphasis on the relation between technology and economics.

Jan 1, 1984

By E. C. Herkenhoff

THIS subject may be controversial. Personal preferences influence the final selection of cyclones, and side issues such as costs, floor areas, head room, and ease of replacing worn parts all enter the picture, but the following comments and data should apply to most cyclone selection problems. Broadly, the uses for cyclones in wet classification may be divided into three fields: 1) Open circuit operation, for two products, in which feed rate and sizing vary and the products vary. For example, feed may be divided into a sand product and a slime product. 2) Open circuit operation, for two products, in which feed varies, one product to have constant sizing. This calls for adjustment in either the apex or the vortex aperture. 3) Closed circuit operation, the finished product to have constant sizing. Most classification jobs fall in this category.

Jan 8, 1957

By S. A. Falconer

Much attention and publicity has been given, during recent years, to grinding, classification, flotation, and thickening. The various technical papers, and symposiums held to discuss these important phases of milling, have contributed to a better understanding of the fundamental principles and operating variables involved. Another important part of milling— to the flotation operator—is a treatment step to which frequently too little attention is given—"conditioning," or the treatment the ground mineral pulp receives before it enters the flotation machines. "Conditioning" is a hackneyed and frequently misused term, commonly employed to describe the pretreatment of surfaces of minerals in ore pulps or mill products prior to froth flotation. In general, such pretreatment is for the purpose of changing the flotation characteristics of these mineral sur- faces to enable them to respond in some desired predetermined manner when subjected to flotation. Taggartl states that the function of conditioning is "either to insure selective collector coating of one mineral species while another species is not; or to take such steps as will compensate for departure therefrom." As 0. C. Ralston has stated? ... we are still faced with the fact that some mineral particles are water-avid, others air-avid, and that by properly modifying them they may be enhanced or diminished in desirable or undesirable avidity. Coatings on minerals must still be assumed to fall into three classes: (1) a coating of immiscible oil, (2) a layer of adsorbed substance, (3) a chemically produced coating. It is submitted that the process of preparing mineral surfaces for subsequent flotation treatment should take into consideration physical as well as chemical means for altering the normal flotation response of the mineral surfaces. A more descriptive word than "conditioning" is needed to designate broadly these procedures. The minerals in many ores cannot be made to respond in a normal manner to usual methods of "conditioning" with selectivity modifying reagents, until they have been cleansed, or interfering slimes and soluble salts have been removed from the ore. Therefore, it appears important to include under the general subject of "conditioning" a discussion of the purposes, methods used, and some of the advantages of these pretreatment steps. This is dealt with under the subject heading " Initial Treatment of Mineral Surfaces and Ore Pulps." Under this broader interpretation, the methods employed for treating mineral surfaces to alter their flotation characteristics may be divided into three general classes: 1. Physical methods.

Jan 1, 1950

By Max Mason

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

Jan 1, 1927

By Shosei Serata, Bruce Gardner

A system of three new field instruments has been developed to measure, in situ, the three basic classes of geomechanical parameters: material properties, stress state, and creep deformation. The significance of this development is that it represents a successful adaptation of recent computer technology to underground rock mechanics work, opening up new possibilities in underground mining methods. The system was developed to meet the application requirements of the stress control method of mining, a method which is based on the actual geomechanical conditions of the underground, rather than upon conventional linear-elastic, idealizations of ground conditions. These instruments enable in situ measurement not only of elastic, but also post-elastic, yielding, and failure conditions of geological materials, establishing the stress control method on a truly scientific foundation. In order to evaluate the present status of this field instrumentation system, case examples of underground mine openings designed with the stress control method are reviewed and analyzed, in terms of the effectiveness of the three instruments for informing and guiding the site-specific application of stress control design.

Jan 1, 1984

By A. L. Bailey, B. A. Landry

All who are even generally aware of the tremendous rate of increase in coal washing operations must realize the growing importance of the float-and-sink test. I believe it is conservative to estimate that, in the past decade, the dollar volume of float-and-sink testing has increased tenfold. It is a simple matter of economy, then, to examine the factors that determine the cost of adequate float-and-sink testing. When the Coal Preparation Section of the Bureau of Mines entered upon a greatly expanded program of such work in connection with the synthetic liquid fuels investigations, it seemed advisable to examine these factors experimentally. The principal consideration that differentiates float-and-sink test sampling from general purpose sampling, is that the original particle size must be preserved. Therefore, the total cost of the test will be directly affected by any standard that might be proposed to limit sample bulk reduction at any given particle size. For this reason, the relationship of sample size to variability of results was the first factor to be studied experimentally. Of course, the matter is rendered complex by the circumstance that the float-and-sink test, not a simple analytical measurement but a process test, comprehends a number of more-or-less independent items of fundamental data; and as shown in the report, the&apos; variability of the samples differs with respect to these different items. This condition and the wide variety of situations in which float-and-sink test data are used, in combination with other factors, to study complex process operations, indicate the difficulty of setting up fixed standards for float-and-sink sampling and testing. At this stage at least, it is the intent rather to obtain experimental data on the principal Factors involved so that the reader may arrive more intelligently at a procedure adapted to his problem. The authors of this paper have presented experimental data showing the relationship between size of sample and particle size for different variability tolerances with respect to percentage of sink. In further studies, data are being collected to appraise also the variability of the samples with respect to float-ash content and size consist. The scope of this work will be broadened to cover particle sizes up to 4 in., and a third series of tests has yielded similar data for a much cleaner type of raw coal. Thus, the further studies will make available a fairly comprehensive meas- ure of variability with respect to size consist, percentage of sink, percentage of middlings, and percentage of ash in the float, for three coals ranging from 3.87 to 17.68 pct in refuse content (heavy sink material) and from 4.18 to 17.52 pct in middlings. Introduction At present there are no published standards for float-and-sink test sampling. During the rapid expansion of float-and-sink test work, varying procedures have been based on adaptations of the ASTM standards for sampling coal for analyses. For this reason, a special study of gross sample reduction has been undertaken to determine the limits for this step in the operation where no reduction in particle size is to be made before testing. Float-and-sink tests are made whenever a thorough study of coal characteristics is desired. The tests may be made on samples from coal-cleaning units such as jigs or tables, or coal samples may be tested which are taken from a loading boom, railroad car, or the coal seam itself. The resultant gross sample may be large and pose a problem of sample reduction. The question is, then, how much can the sample be reduced and still fall within preassigned limits of accuracy of the original gross sample of coal? Coal from channel samples may be crushed to liberate impurities and then separated into various gravity fractions from which washability curves are drawn; from these curves, it is possible to determine the cleaning characteristics of the coal. However, coal samples from coal-cleaning units cannot be

Jan 1, 1950