Search Documents

By Martin J. Conway

DURING the past year, the intense interest shown by the metallurgical industry in the use of relatively pure oxygen has been evidenced by the number of papers dealing with its application and production. The reason for this interest is apparent when it is realized that, weight for weight, oxygen enters into the formation of steel equally with iron. In the manufacture of steel, approximately one ton of oxygen is required to produce one ton of ingots. Until the recent development of plants capable of producing oxygen at far lower costs than had ever previously been considered possible, the oxygen required for steel manufacture was used as it occurs in air, where it is associated with approximately four times its volume of nitrogen. Because of the diluent nitrogen more than 4 tons of total gaseous material per ton of steel must be handled rather than only approximately one ton required when pure oxygen is used. In addition, provision must be made to handle the large quantity of waste, gases resulting from the process. There are cases where the reduction in gas volume alone can justify the installation of an oxygen plant.

Jan 1, 1947

By D. M. Deason, R. M. Chhatre, G. Y. Onoda

INTRODUCTION The treatment of colloidal suspensions is a subject of increasing interest in mining and benefication (1). Colloidal suspensions are not readily operated upon by mechanical and physical methods useful with coarse suspensions, such as filtration, thickening, and flotation. This is because colloids are strongly affected by interfacial and interparticle forces that may be large compared with, and resistant to, external forces. The degree and type of interactions between colloids can be modified by small additions of reagents such as coagulants, flocculants, dispersants, and immiscible liquids. These alterations in turn change the properties of the suspension and provide possible opportunities for transforming suspensions to a more favorable condition for a given processing operation. Phosphate slimes are an example of a colloidal system of interest today. In the mining and beneficiation of phosphate rock in Florida, slimes are a waste product. The phosphate ore (called matrix in the industry) is slurrified hydraulically and pumped to a beneficiation plant, where the -150 mesh material is removed by cycloning from the coarser phosphate rock and silica. The resulting -150 mesh slurry, called phosphate slime, is pumped to large impoundments. The solid content of the slime entering the impoundment is around four weight percent, and over 80% of the solids is less than one micron in size. The immediate problems with phosphate slime relate to their disposal (2, 3). The disposal problem is associated with the very large volumes and the poor dewatering characteristics of the slimes. To have sufficient impoundment volume, large earthen dams are built around the mined areas. The volume above ground level approaches and

Jan 1, 1980

By W. Luyken

A NUMBER of articles have been published, notably those by R. S. Handy, R. T. Hancock and A. P. Watt in Engineering and Mining Journal, dealing with the calculations involved in ore dressing.. These publications demonstrate both, the importance of the subject and the lack of success in developing a generally recognized method for comparing enrichment effects. Considering that we may wish -to compare enrichment results on similar or dissimilar ores, that we may desire to make the comparison on the basis of either the absolute or the economical efficiency, and that the number of factors upon which the result depends is large, the question arises whether it is possible to set up a positive method for such calculations. In the following pages it is our aim to show that a sure, complete and successful way to overcome existing difficulties has been found. GRAPHICAL ANALYSIS OF ORE-DRESSING PROCESSES The following is from Truscott's Text Book of Ore Dressing (London, 1923) x = assay of ore treated (feed). y = assay value of the concentrate. z = assay value of the tailing. a = weight of feed. b = weight of concentrate. c = weight of tailing. C = fractional concentration = b/a= x-z/y-z (1) K = ratio of concentration = 1/C = a/b =y-z/x-z (2) R = fractional recovery = yb/xa = Cy/x. (3) 100R = percentage recovery. Copt = theoretically best concentration. 100 - Copt = waste in the feed.

Jan 1, 1929

By E. A. Trager, A. W. McCoy, H. R. Shidel

Sampling of the fluid from oil wells for percentages of oil, emulsified oil, and water during the last two years has brought out some interesting facts concerning oil-water emulsion. This result led to a laboratory investigation of emulsion, which substantiated the conclusions made from the field observations. The purpose of this paper is to present the information collected, the laboratory experiments, and our interpretation of the same. In order to define emulsified .oil exactly, give its synthesis and origin, and to show how and when it is formed in the wells, the work was necessarily divided into two separate lines—laboratory work and field observations. It is hoped that this study may lead to a discussion of such points so that the petroleum engineer, geologist, or technologist may be benefited by its practical bearing on oil-field management. Special credit is due Mr. Everett Carpenter, chief geologist of the Empire Gas & Fuel Co., for his assistance and cooperation in this work. Labobatory Investigations on Emulsified Oil Laboratory investigations were conducted in an attempt to learn the composition and some of the properties of emulsified oil, or B. S., as it is more commonly called, also to demonstrate, by laboratory methods, how B. 5. may be formed under conditions similar to those existing at the time a well is being pumped, and how it may be broken down. Literature bearing on this subject is widely scattered and very limited in scope. Bacon and Hamor define B. S., or bottom settlings, as "earthy matter, inert organic matter, or, in the case of Pennsylvanian petroleum, an emulsion of paraffin wax and water, which accompanies crude oil." In this discussion we will limit the term B. S. to that heavy, dark-brown emulsion, composed of a physical mixture of water, oil, and air with some included inert matter, either organic or inorganic. Possibly the first step in a description of this product should be a description of its physical properties, but since most operators are quite

Jan 1, 1921

By Luther Lennox

THE purpose of this article is not to compare one type of grinding machinery with another and to conclude from a series of tests that one particular machine is superior to all others. Neither is the reader asked to tire himself with the details of many tests to prove the statements herein made. The Chilean mill stands today almost, in outcast from the milling world. It ranks with the applicant for a job who has been given a trial along with others and condemned because he was not able to perform the definite task assigned as well as the others, and was forever eliminated. The judges did not tarry long enough to try this aspirant in a field of a slightly different nature. Even though it has been condemned, the writer contends that the published records will indicate that the trials were never shifted into the field of greatest efficiency for the Chilean mill. Those of us who cling to this outcast as a fine grinder in our milling operations do not wish, naturally, to be condemned along with the machine, and yet we feel that we are classed as behind the times, at least in this phase of our milling judgment. Hence there is considerable personal feeling in our efforts. During the last few years there have been published several papers on the relative merits of the various grinding machines. In two of these articles a comparison was made between Chilean mills and cylindrical grinders. In each case the Chilean mill came out second best from about all standpoints. The outstanding feature in these comparisons would seem to be the decided attempt to keep all conditions the same, so that each machine could be judged on its merit. As Mr. David Cole states, "We are inclined to regard a direct comparison of grinders arranged side by side, and making a product that affords as nearly as possible the same screen measure, as the Supreme Court in these grinding matters." The writer agrees that this is the very best method for true comparison between machines. The results in the two detailed tests should give the relative merits of the two grinders in doing the work assigned. And they probably do. The conclusion drawn in each case was adverse to the

Jan 9, 1919

By R. B. G. Yeo

The effects of alloy additions on the M, and A, temperatures of an Fe-22.5 pct Ni alloy have been determined. Increasing amounts of titanium, colum-bium, vanadium, and silicon raise and then lower M,while raising A, cmtinuously. Cobalt raises both M, and A,. Aluminum has little effect on Ms but raises A,. Chromium md nickel lower M, and A,. It is proposed that elements raise M, in accordance with their effect on the Ae3 temperature of iron until the lattice becomes stiffened against the shear transformation so that M, is then lowered. An anomaly, first pointed out by Zener,1 arises in steels when the addition of elements, such as molybdenum and tungsten, which raise the Ae3 temperature, also lower the M, temperature.2'3 During the development of a series of martensitic precipitation-hardening (maraging) steels, the effect of several elements on the transformation of austenite to martensite was studied. The results show that under suitable conditions several elements which raise Ae3 also raise the M, and A, temperatures. PREPARATION OF MATERIALS STUDIED A series of alloys was made in which cobalt, titanium, columbium, vanadium, silicon, aluminum, molybdenum, chromium, and nickel were added to an iron base containing 22.5 pct Ni. The compositions of the alloys prepared are given in Table I. The residual manganese contents of the heats were in the range of 0.030 to 0.35 pct, silicon 0.05 to 0.1 pct, carbon 0.0008 to 0.009 pct, and nitrogen from 0 to 0.004 uct. The allois were made as 50-lb induction heats starting with electro-iron and electro-nickel, melted in air to oxidize impurities. Additions of silico-manganese and ferro-silicon were made after which the power was turned off to allow the products of deoxidation to rise and be skimmed from the surface of the melt. The furnace chamber was pumped down to a pressure of 5 p and the charge was heated to 2900°F for the addition of other alloying elements. The heats were poured into five 10-lb ingots, making successive alloy additions to each. The ingots were soaked for 2 hr at 2300°F and hot-worked to 3/4-in.-diam bars. This stock was heated to 1500°F for 1

Jan 1, 1963

By George H. Ashley

It has been said that the Pittsburgh bed is the most valuable single mineral deposit yet known to man. The figures in Table 1 are presented in substantiation of that claim. Production and Value In order that the figures of Table 1 may have any weight, a statement must be made to show how they were arrived at. Because, to the writer's knowledge, no accurate separate figures ever have been kept of the production and value of the Pittsburgh coal bed, the states will be considered separately. Pennsylvania Accurate figures are obtainable for Pennsylvania for recent years because recent reports of the Pellnsylvania Department of Mines show the production from each mine and the bed worked at each mine. For recent years, therefore, it is only necessary to list the mines working in the Pittsburgh bed and add up their production. The value was obtained by treating each county separately, applying the average price for the county to the production of Pittsburgh coal in that county. Unfortunately for great accuracy, while production figures for individual mines are available for many years, the name of the bed being

Jan 1, 1938

By George H. Ashley

It has been said that the Pittsburgh bed is the most valuable single mineral deposit yet known to man. The figures in Table 1 are presented in substantiation of that claim. Production and Value In order that the figures of Table 1 may have any weight, a statement must be made to show how they were arrived at. Because, to the writer's knowledge, no accurate separate figures ever have been kept of the production and value of the Pittsburgh coal bed, the states will be considered separately. Pennsylvania Accurate figures are obtainable for Pennsylvania for recent years because recent reports of the Pellnsylvania Department of Mines show the production from each mine and the bed worked at each mine. For recent years, therefore, it is only necessary to list the mines working in the Pittsburgh bed and add up their production. The value was obtained by treating each county separately, applying the average price for the county to the production of Pittsburgh coal in that county. Unfortunately for great accuracy, while production figures for individual mines are available for many years, the name of the bed being

Jan 1, 1938

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

John Grifien (Pittsburgh)—I wish to congratulate the authors on this paper, which, I am sure, will promote a clearer conception of the various criteria which have been advanced as measures of coal-cleaning performance. Their clear descriptions of the more important criteria that have been advanced and explanations of their meaning and application have been sorely needed and, if widely promulgated and followed, should remove much of the confusion which, heretofore, has been evident. I suggest that much of this confusion has also arisen from lack of common agreement as to the exact meaning of the words and terms used in our discussions of this subject. I am sure I have been equally guilty in this respect and suggest it is time that we select a committee to study vocabulary as well as criteria, so that common understanding and agreement can be had. Thus, I suggest, that the title of this paper should have used the words "coal-cleaning performance" and not "coal-washery performance." My understanding is that "washery" refers to a complete plant and it has additional functions to that of coal-cleaning, such as control of size, moisture, etc. Also, I do not agree with the authors that the formulas given in their paper, the Fraser and Yancey formulas, are necessarily the only ones that can be called efficiency formulas. When a dictionary is consulted one realizes that the words "efficiency" and "efficient" have not precise meanings but only very general ones and must be further defined for each particular use, if they are to have any precise meaning. To my mind, the first of the Fraser and Yancey formulas given should never be used as expressing "efficiency" alone but only by the fuller phrase which truly expresses the kind of efficiency it states, which is "coal recovery efficiency." For complete clarity we then need only define "coal" for the particular circumstances under which the formula is used. This would recognize the fact, fully explained by the authors, that the limits in coal qualities imposed by the market have imposed a factor—and a variable factor—which has influenced any answer obtained by this formula. Such a procedure makes it entirely practical and logical to use the values of any of the qualities of coal—ash, sulphur, phosphorus, specific gravity—or a combination of them to define what is coal for that particular use of the formula. Further, it is clear to me that the criteria to be used must be dictated by the objective in view and the use for which the data are obtained. The authors clearly point out that the Fraser and Yancey coal-recovery efficiency formula is influenced by three factors, "one is determined by the coal, one is dictated by market or use conditions, and one is an inherent characteristic of the cleaning unit itself." The formula which uses the inverse of misplaced material as a measure of efficiency is also a coal recovery efficiency formula and is influenced in like manner by these three factors. As the authors point out, both are useless in obtaining data which enables a direct and valid comparison of the performance of a given cleaning unit on two coals where the other two factors vary or of the performance of two or more cleaning units of different types unless the values of the other two factors are identical. Much of the confusion in our discussions of and literature on coal cleaning has come from failure to understand clearly this fact. Many such comparisons have been made from which erroneous conclusions have been drawn. I am, therefore, particularly glad to see the authors' emphasis on 4?-1e criteria which indicate the "sharpness of separation. I feel that these are the essential criteria

Jan 1, 1952

By John G. Tate, George W. Nicolson, James L. Bruce

FOR more than 25 years modern mining has been carried on in the Island of Cyprus, Mediterranean Sea, by the Cyprus Mines Corp. of Los Angeles, Calif. The general features of these operations have been described.1 From 1935 to June 30, 1940, top slicing in the Mavrovouni mine produced in excess of 2,000,000 long tons. The rate for the last part of this period was approximately 50,000 tons per month. DESCRIPTION OF ORE BODIES The shape of the ore body now being top sliced in the Mavrovouni mine is an inclined irregular pyritic pipe or chimney of large dimensions, extending from unknown depths below the bottom level at elevation 250 ft below sea level, to the highest level at elevation 400 ft above sea level. The present surface above the ore body lies between 550 and 650 ft elevation. Undoubtedly the ore body extended to surface and was mined by the ancients by opencast and underground methods. The old pits were gradually filled up by erosion until now they show as slight depressions in the topography. The largest area of the ore body is at elevation 170 ft below sea level, where the horizontal section is almost elliptical, with a width of 600 ft and a length of 1000 ft. Below this elevation the shape of the ore body continues to be elliptical but with reduced dimensions. Above this elevation it rises flatly towards the south with a substantial depression in the upperside of the chimney and irregular ridges or wings rising on each side. It gradually grows smaller as it rises. The ore body is a pyritic replacement of andesitic extrusives which occur as flows and pillow lavas. With the exception of the upper portions of one or two small offshoots rising from the main ore body, all ore is completely surrounded by andesite. Most of the andesite lying above the ore body is covered by marl and clay sedimentaries of Miocene and later age. The Miocene is presumed to be older than the ore mineralization. That portion of the andesites which lies between the sedimentaries and the ore body has been broken by slumpage, and weathered, and iron-stained by the descending meteoric waters. It is a mass of crushed material that caves and follows downward readily as the top-slice stopes retreat. The main ore body is a heavy cupreous pyrites mass assaying on the average about 4.0 pct Cu; 48.0, S; and 42.0, Fe. In places the copper drops below 1.0 pct. On the borders of this heavy sulphide ore body lie disseminated cupreous pyrites ore deposits of large dimensions. Some portions of these appear to be closely related to the heavy sulphide ore, as the ratio of copper to pyrite is about the same. The greater part of the disseminated ore, most of which lies immediately to the east of the main ore body, contains less than 0.10 pct Cu and about 25.0 to 30.0 pct S. This probably can

Jan 1, 1947

By Wallace F. Lovejoy

The conservation of mineral resources as a public policy question has received a great deal of attention in the area of petroleum and practically no attention in other mineral areas, except, of course, soil and water. Some insights into mineral conservation problems and how these problems can be approached in the social decision-making process are significant. THE MEANINGS OF CONSERVATION Conservation means many things to many people .2, 11 Too often it is a label attached to a proposed program or policy to add respectability and to gain public acceptance. It is a term applied to specific resources in some contexts and to resources generally in other contexts. The oft-quoted comment of President William Howard Taft that conservation is something everybody is for, no matter what it means, succinctly illustrates the confusion over both the meaning of the concept and the policies required to implement a conservation program. This confusion goes quite deep and is more than a matter of semantics or emphasis. For example, the efficient exploitation of a mineral deposit which might be applauded as good conservation in terms of that mineral, might well result in destruction of or harm to the environment which might be viewed as bad conservation. Economics provides some tools to help solve this sort of problem, but there may be fundamental differences in value systems among groups in this society, so that ultimately society must collectively make a subjective political choice as to what is good or bad conservation policy.a An Economic Definition of Conservation The economic concepts of conservation have more relevance and are more easily applied to minerals than to many other natural resources. This does not mean that economics goes all the way in understanding mineral conservation, but at least it provides a framework for analysis which later can be altered to include noneconomic variables. Perhaps the greatest confusion in discussing mineral conservation arises in attempting to relate purely physical concepts with economic concepts. An economist is interested in maximizing or conserving values; he is not interested in maximum physical recovery or utilization. He wants to know the costs and benefits of using, or not using, resources. The economic theory of mineral-resource conservation can be labeled variously as the theory of exhaustion, the theory of resource exploitation, the theory of resource utilization, or simply as a special case of the broad theory of capital.4,28 Consideration of these labels illuminates the concerns of the econo-

Jan 1, 1976

By Herbert Clark Hoover, Lou Henry Hoover

MANY persons hold the opinion that the metal industries are fortuitous and that the occupation is one of sordid toil, and altogether a kind of business requiring not so much skill as labour. But as for myself, when I reflect carefully upon its special points one by one, it appears to be far otherwise. For a miner must have the greatest skill in his work, that he may know first of all what mountain or hill, what valley or plain, can be prospected most profitably, or what he should leave alone ; moreover, he must understand the veins, stringers1 and seams in the rocks2. Then he must be thoroughly familiar with the many and varied species of earths, juices3, gems, stones, marbles, rocks, metals, and compounds4. He must also have a

Jan 1, 1950

By J. M. Gaines

THE use of oxygen in electric furnaces is relatively old, and the practice has been employed by several steelmakers prior to the recent impetus given generally to the use of oxygen in steelmaking. This application has been described recently in several publications,1 and a number of patents relating to the application of oxygen in electric furnaces have been issued.2 An effort is made in this paper to assemble recent information relating to the use of oxygen in electric furnaces and to present this material from a practical viewpoint, to an extent consistent with the withholding of certain operating data which manufacturers consider to be confidential. The use of oxygen has been extended during the past months in a number of additional steel companies by incorporating oxygen practice into regular production and by much increased experimentation. Available records show that oxygen is used more or less regularly at present in 18 shops, of which six utilize the oxygen for production and the others for experimen¬tation. The number of furnaces per shop using oxygen varies from one to six. Many types of electric-furnace steel have been prepared with the assistance of pure oxygen, including low-carbon and medium-carbon killed steels, low-carbon rimming steel and low-carbon and medium-carbon stainless and alloy steels. Oxygen has been used in furnaces of all sizes up to 90 tons capacity for accelerating charge meltdown and for reduction of carbon.

Jan 1, 1947

By D. L. Murphy

As the world's demand for iron ore increases and available sources are depleted, increasing attention will be centered on deposits in the Quebec and Labrador portions of the Labrador Trough. Improvements in the beneficiation of low grade iron ore stimulate exploration for deposits amenable to concentration. This study is centered on the Mt. Wright-Lake Carheil area, lying between Wabush Lake and Mt. Reed in Quebec. Described in detail are the general lithology, structural and economic geology, and mineralogy of the iron-formation. The iron ore province of Quebec and Baffin Island extends from the southern shore of Baffin Island southeasterly through the Labrador Trough to Matonipi Lake, approximately 185 miles northwest of Seven Islands. (See Fig. 1.) Future geologic field studies will very likely extend the limits of the province to include the ferruginous and associated rocks of the Lake Mistassini area. At present, only the deposits near Knob Lake and Lake Jeannine (Mt. Reed) have been brought into production although in the near future several other properties including those at Wabush Lake will commence operations. Within the next decade or so, as the world's demand for iron ore increases and available sources are depleted, this region will undoubtedly become a major mining district. Initial reports of iron-rich rocks in Labrador date back to the investigations undertaken by A. P. Low near the turn of the century. During the ensuing years the country was prospected chiefly for precious and nonferrous base metals because of its inaccessibility and the low tenor of the iron ore. In 1945 an evaluation of the direct shipping ores near Knob Lake indicated that sufficient reserves were present to justify the enormous capital expenditure required to bring the deposits into production. Initial open-pit mining began in 1954 following the construction of a townsite, a 360-mile long railway to Seven Islands, and an elaborate loading dock. Recent improvements in the beneficiation of low-grade iron ore have stimulated widespread exploration for deposits amenable to concentration, particularly along the southwest extension of the Trough. The Mt. Wright-Lake Carheil area, bounded by longitudes 66O45' and 67 30' west and latitudes 52 30' and 52 45' north, is a nearly rectangular tract of slightly less than 500 sq miles. It is in Saguenay County, 174 miles north-northwest of Seven Islands (see Fig. 1). Except for the periods of the spring breakup and the fall freeze up, the area is readily accessible by air.

Jan 1, 1962

By Robert H. Richards

VERY little has been published recently on this subject in the mining journals or proceedings of societies. The attention of experts has been diverted perhaps by the demands for pan amalgamation of refractory ores. Yet free milling ores occur in many localities, and it may be interesting to have on record some data as to details of running a small test-mill, especially as details of results do not seem to be accessible to students and investigators. Küstel, in 1863, under battery amalgamation, dismisses the subject by stating that "amalgamation on copper-plated platforms, troughs, and other copper fixings" is " very imperfect, and mostly abandoned." J. Arthur Phillips says, in 1867, under placer mining : A well-amalgamated copper plate is considered as effective for

Jan 1, 1880

By Joseph Kuti

Longwall mining is the term used for the underground extraction of a wide and deep panel of coal. Such a panel may be blocked out by one or more entries on either side ("head" and "tail") of a longwall face. If all the entries are pre-driven, the panel extraction is termed longwall retreat mining. With one exception, all the longwall faces in the United States are of this type3 Prior to the general decline in the rates of production with Continuous Miners, the development of the multiple entries generally kept ahead of the longwall extraction rate. This is no longer the case: longwall extraction rates far exceed the rate of development. In addition to this problem, in newly established mines, the development of a haulage and bleeder system based on multiple entries results in a lead-time of three years or more before longwall mining can be applied. This is one reason why earlier projections and much of the optimism attached to longwall mining as a principal "savior" in the energy crisis should be viewed with some caution. The alternatives to retreat mining with multiple entries are: Modified retreat mining- where the tail-entry is being formed during the mining of-the panel ("2"-system). Some form of advance mining-where the head-entry or both head and tail entries are being formed as part of the longwall extraction process. These methods are well-known and well-established. Variants of them are being practiced in Canada, Central and South America, but not in the US. It is primarily the laws governing ventilation-conceived for room and pillar mining which prevent the rapid development of these techniques. Another aspect of longwall mining is that it requires a systematic and consistent approach in organization, roof control, ventilation and transport. It is for this reason that compliance with health and safety regulation is fairly well ensured if the longwall system has been well laid out and is subsequently well-run. Nevertheless, a management mentality raised in the great flexibility of the room and pillar system cannot always come to terms with the degree of forward planning and rigid discipline required to successful longwall mining. Research, development and other investments in the partial aspects of longwall mining are always of interest, but no massive trend to longwall can be expected realistically unless these major stumbling blocks in the basic law and basic approach are effectively removed.

Jan 1, 1980

By Henry J. Welge

Laboortory apparatus has been devised which permits study of the displacement of oil from cores by water and by gas. The cores used contained interstitial brine as well as oil. Experiments were run to determine the comparative effect of varying the properties of the fluids used. No great effect was noted on the maximum displacement achieved. This observation made it unnecessary in initial work to use fluids in their exact reservoir conditions. Consequently, the displacements were run at near-atmospheric pressure in Pyrex glass equipment, using stripped crude oils. Introduction and Theory The chief object of this work has been to determine the efficiency of gas and water as primary agents for displacing oil from reservoir rock under laboratory conditions in which capillary phenomena were predominant. To this end the maximum displacement of oil from cores has been ascertained. This maximum displacement may not be equal to the maximum displacement from a reservoir; but it will be a close approxirnation to it sometimes, and other times the laboratory information will be useful in reservoir engineering predictions. It is] believed that the laboratory experimental maximum represents the upper limit for the reservoir recovery. The experiments were carried out by obtaining cores of interest from the reservoir, and filling the pores with interstitial brine and oil with the restored state tech- nique.1 Then the oil was displaced from the core as described later, either by brine from below, or by gas from above. The former type of displacement suggests analogy to production by water drive, but not to water flooding, for reasons discussed below. The latter type of displacement is believed to simulate production by gas cap displacement. The displacements were performed by what may be termed the capillary-pressure method. The cores are placed in capillary contact with an oil-wetted membrane which has very small pores (about I micron in diameter). Pores of this size will transmit oil but Prevent the Passage of gas or water, unless the Pressures used are higher than the capillary Pressures employed in this work. Accordingly, use of the membrane makes it possible to apply a capillary pressure differential between the displacing phase and the oil in the core. AS in the displacement of brine toward that condition of oil and water distribution existing originally in the reservoir,' it may not always be desirable to reduce the oil saturation in this experiment to an absolute minimum. With reservoirs having small productive closure, it is preferable to evaluate and use a displacing pressure no higher than the capillary pressure, Ap, which will ultimately become available for displacement in the reservoir. This pressure may be calculated from a knowledge of the density of the oil-in-place, do, the density of the displacing phase, dl, and Ah, the vertical distance between the section of the

Jan 1, 1949

By P. R. Sheorey

I read this interesting paper on pillar strength in some detail because this is also my area of interest. It has long been the desire of mining rock mechanicians to predict pillar strength from laboratory compression tests. Considerable literature is available on compression strength of rocks and coal but many of these experiments were conducted not for pillar design but for rock behavior. I have a few comments on the author's approach to pillar design, especially equation (33). Two important factors, which the author seems to have excluded, can be added to the right side of equation (2): time-dependence of strength and the influence of mine environment on strength (moisture and weathering.) The author has taken considerable pains to analyze a large amount of testing data in [Table 1], yielding the various exponents ci of equation (2) (or the subsequent equations derived from it.) He has, however, not shown by means of a worked out example how these values of [Table 1] could be applied to a practical pillar design situation. It would have been interesting to compare predicted pillar size using equation (33) with an actual case. Alternatively, equation (33) could have been used to explain the failure of a pillar, if such a case history were available. Consider we have a large number of case histories of stable and collapsed pillars in a seam and we conduct a large number of tests in a laboratory press. The exponents [ci] can then be determined for actual pillars as well as for test specimens. Thus, equation (2) will read [ ] Since laboratory testing conditions (e.g., between steel platens) are different from the conditions on pillars, the exponents [ci] in

Jan 1, 1983

By P. Nyul, S. Caplan, M. F. Lamorte, T. Gonda

Therrnal resistance is measured on GaAs laser diodes in the temperature range 77" to 300°K. These data show that typically the thermal resistance increases fifteen times from 77 to 300°K. The increase is attributed to the decrease in thermal conductivity of Gds. Nornzalized thermal-resistance experimental and calculated from published thermal-conductivity data) values are compared and good agreement shown. In many practical applications, it is desirable to obtain high average power output from laser diodes. Average power output is determined in large measure by the external efficiency and thermal resistance of the diode.'-3 The average input power with which a laser diode may be pumped is dependent on the thermal resistance. Thermal resistance has been studied over the temperature range from 77" to 300°K which is usually of interest in practical applications. This correspondence presents data on thermal resistance for GaAs laser diodes and compares them to values calculated from thermal-conductivity data. Junction heating arises from three distinct components: 1) joule heating, 2) nonradiative recombinations, and 3) reabsorption of radiation. In high-threshold lasers, joule heating predominates.4 Typically, the nonradiative recombination is not negligible and contributes significantly to junction heating. The loss caused by reabsorption may be of the order of the joule-heating loss.' The fabrication and the geometry of laser diodes have been described in other publications.5 The data presented were obtained from diodes which were fabricated from the same region of a wafer to minimize differences. Fig. 1 shows four types of heat sinks employed in this study. In types 1 and 2, the laser cavities are alloyed; pressure contacts are employed in types 3 and 4, and indium is plated on the inside faces to improve the intimacy of contact between the diode and the heat sink. The thermal resistance R is defined by the following relationship: where AT is the junction-temperature rise above the heat-sink temperature for the diode power dissipation Pd. For measurement of thermal resistance, a direct current is passed through the junction, in the range from 1 to 50 pct of threshold. The diode is placed in the laser mode by superimposing a current pulse of low-duty cycle on the direct current.3 Junction-temperature rise is obtained from the time-resolved laser spectrum at the leading edge of the current pulse.' Typically, the laser line shift is 2.5A per OK. The resolution employed in these experiments is 0.5A; therefore, the accuracy in the temperature measurement is 0.2K. Typically, the temperature rise is 2" to 20°K. The power dissipation is the difference between the dc power input, and the radiation power exiting the diode. The measurement accuracy is less than 1

Jan 1, 1968

By Charles H. Grant

Some of the limiting factors relative to explosive crushing of rock and ways to overcome a few of these problems are presented. Relationships between borehole diameters, bench heights, and spacings, along with a review of the influence geometry has on energy as these are changed, are discussed. Efficiency in use of explosives and the decay of energy as it moves through rock and is absorbed and dissipated, is described, along with fragmentation as a function of spacings and energy zoning, etc. Communications are one of the major problems encountered. In an effort to provide a better understanding of the use of explosives, it is necessary to take a little different view of what explosives are, how to look at them as tools to fragment rock, and some of the problems encountered in doing so. First, take the explosive: although there are many factors involved, consider these as being reduced to only two — shock-strain imparted to the rock by the high early development of energy, and the gas effect which is a combination of heat, moles of gas formed, rate of formation of these gases which develop pressures, etc. First, consider shock energy by itself and assume there is no gas effect in the reaction. Fig. 1 illustrates a block or cube of rock, in the center of which is detonated an explosive charge which is 100% shock energy. Tensile slabbing would be seen on the surface and probably the cube of rock would generally hang together even though microcracks were formed. If the situation is reversed and an explosive whch has no shock energy and only gas effect (Fig. 2) is considered, the cube of rock would act as a pressure vessel and contain the pressure from the gas effect until it exceeded the rock-vessel strength; then the rock would break in a few large pieces. If these two kinds of energy are put together and the area of shock-strain around the explosive (Fig. 3) is considered, the two energies will be seen working together to furnish broken rock. The gas effect applies pressure to the microcracks formed from the shock energy to weaken the rock-pressure vessel and propagate these cracks to break the rock apart. It not only will be broken more finely, but will break apart at a lower pressure than the gaseffect case, since the shock energy has first weakened the rock vessel. Although tensile spalling from the shock-strain imparts momentum to the rock, the main source of displacement comes from the gas effect. The term "rock" is being used to mean any material to be blasted. These energies are absorbed by the rock in different ways. First, classify rock into two main categories: "elastic" and "plastic-acting." Elastic rock should be thought of as rock which can transmit a shock wave and is high in compressive strength, such as granite or quartzite. Since this elastic rock transmits a shock wave well, it makes good use of the shock energy from the explosive-forming cracks, etc., for the gas effect to work on. Plastic-acting rocks are rock masses which are relatively low in compressive strength and absorb shock energy at a much faster rate, thereby making poor use of the shock energy by not developing as extensive a cracked zone for the gas effect to work on. Rocks of this type are generally softer materials such as some limestones, sandstones, and porphyries. For the most part, the shockenergy part of the explosive reaction is wasted in plastic-acting rock, leaving most of the work to the gas effect. Since the ratio of gas effect to shock energy is different in different explosives, it is easy to understand why some explosives perform well in elastic rock and poorly in plastic-acting rock, and vice versa. Some of the most difficult blasting situations arise when mixtures of plastic-acting and elastic rock are encountered (Fig. 4). Fig. 4 shows an example of granite boulders cemented together with something like a decomposed quartz monzonite which is plastic-acting. The elastic granite boulders will transmit the shock-strain within itself, but when this shock tries to move through the monzonite to the next boulder, its intensity is absorbed by the monzonite and little shock-strain is placed on the adjoining boulder. In addition to this loss by absorbtion, shock reflection at the surface of the boulder will effect tensile spalling. The net effect is poor breakage of the boulders which do not have drillholes in them as they simply will be popped out with the muck. The same is true (Fig. 5) when layers and joints make

Jan 1, 1970