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By W. G. Jeffery, James F. McDivitt

THE FRAMEWORK Consider where you, the reader, would place the emphasis m your answer to the following questions on mineral supply. Do you think of the mineral resources of developing countries in terms of the contribution which they can make to world mineral supply or in terms of the contribution they can make to development of the country? Do you look upon developing countries as a source of minerals for world industry or as a potential enormous market for minerals? If you are from a developed country it would be surprising I£ you did not emphasize the first alternative in each case, but it is also possible that simply raising the questions will call for some mental adjustments, because usually we do not think in these terms. If you are among the two-thirds of the world's population which comes from developing countries, you might well emphasize the second alternative. And to a growing extent during the reaming decades of the 20th century this is where emphasis must be placed. Increasing amounts of the world's mineral production come from countries which are in the early stages of development. Mineral consumers of the world look to these regions for continuing supplies of material to help meet their ever-growing needs; the producing countries look to mineral exports as one means of stimulating and financing their economic development-this seems a happy and fortuitous relationship. But due to the complexities of world mineral supply, it is a relationship which is fraught with potential confusion and misunderstanding. That this is so is not surprising when one considers that many of the producing countries are new countries which are urgently trying to find the path along which they can move towards development; that the direction of the path is by no means clear because various theories of economic development, as a planned and deliberate process, are relatively recent in origin and none are well understood; and that the very concept of the less developed countries (LDC's) is a relatively new one. To further complicate the situation there has never been a clear under- standing of the full role which minerals play in economic development, either in the case of those countries which are already classed as developed, or in the case of countries which are in the process of development. Before embarking on an investigation of some aspects of the relationship between minerals and developing countries, it seems wise to establish broad terms of reference, which may not be totally valid but which will at least give an initial direction for a journey with no clearly definable goal. First it can be noted that the world has been divided somewhat arbitrarily into a group of countries that are termed developed or advanced and a group of countries which

Jan 1, 1976

By Richard P. Schoemaker

INTRODUCTION IN underground mining operations the effects of economic and mechanical factors on costs and profits can readily be appreciated and can perhaps be expressed in exact figures and percentages. Less apparent, but frequently more important, is the influence of physical stress. Stress causes failure of supports, collapse of openings, rockbursts, and other damage which directly affects the costs of maintenance, and also to a certain extent the accident rate. Stress can, however, if properly directed, be an aid to mining operations. The caving methods in metal mining and the long-wall method in coal mining are well-known examples. In large-scale mining operations it is almost impossible to neglect stress-control. A better understanding of the mechanism of rock pressure and the application of its principles to practical mining will inevitably lead to a reduction in operating costs. Many theories have been advanced to give the mining engineer a practical outline for stress-control but, although today most experts agree upon the principles of stress distribution around underground openings, there is still no generally accepted theory that explains all phenomena. The main reasons for this incomplete understanding of the problem are the lack of accurate knowledge of the physical properties of rocks under field conditions, and the great complexity of these conditions due to inhomogeneity of the rock, stratification, tectonic disturbances, and many other unknown factors. The research on the rock pressure problems has, however, yielded some valuable facts which, expressed in practical terms, and adapted to local conditions, may become a valuable aid for mining operations. The purpose of this paper is to give a review of the most important accomplishments of this research with respect to the stress phenomena around small underground openings, such as tunnels and shafts, so as to arrive at an outline of the problem as it stands today. Special emphasis is placed on a new theory by the German mining engineer, Rudolf Fenner, which has never before been published or discussed in English. THE PRESSURE DOME THEORY The formation of a dome-shaped space around underground openings is well known from field observations. When openings are made in rock under stress, the rock in the top of the openings will often fail, and caving will continue until the openings have assumed a dome-shaped form, after which equilibrium apparently is re-established. The oldest theory which attempted to explain the phenomenon is the "beam" theory, which postulates that the hanging wall consists of stratified measures that behave as independent beams with fixed ends and a uniformly distributed load. When failure of the beam occurs, inward shearing at the ends will cause the formation of a dome-shaped space. The pressure dome theory, which more or less evolved from the beam theory, merely

Jan 1, 1947

By O. N. Carlson, W. M. Paulson

A phase diagram is proposed for the Y-C system based on the vesults of thermal analyses, microscopic obsevvations, and X-ray diffraction studies. Three intermediate phases occur in the system: a congru-ently melting fcc phase with a wide range of homogeneity about the composition Y2C, an intermediate solid-solution region between 55 and 58 at. pct C, and a bct dicarbide melting congruently at 2415°C. All three compounds undergo a phase transformation at elezlated temperatures. A continuous serzes of solzd solutions exists between the fcc phase and the high-temperature form of YC2 with a maximum in the solidus at 2000°C and 30 at. pct C and a minimum at 1805°C and 54 at. pct C. THIS investigation of the Y-C system was undertaken as part of a nuclear materials development program. Yttrium-base alloys are of interest as possible containers for liquid metals, and carbides are currently receiving increased attention as high-temperature materials for advanced reactors and other applications. Previous work on this system was limited in scope, and the results were somewhat inconclusive and at times contradictory. Spedding et al.&apos; reported the existence of a triyttrium carbide having an fcc structure with a wide range of homogeneity and Dean et a1.2 reported the existence of a rhombohedra1 phase having the stoichiometry of Y2C. Bachella et a1.3 observed that the latter was the result of ordering of carbon atoms in the fcc solid solution. The ordering range was placed at 800" to 1000°C. Vickery et a1.4 reported a high-melting compound which they identified as yttrium dicarbide, and Spedding and coworkers1 determined the structure of this phase as bct with lattice parameters a = 3.66 and c = 6.17A. Samsonov et al.5 reported the melting point of YC2 as 2300" * 50°C. Recently Bowman et a1.6 found a transformation in the dicarbide from the tetragonal to an fcc form at 1320 20°C. Samsonov and coworkers7 reported a monocarbide of yttrium melting at 1950" * 20°C and also a sesqui-carbide melting at 1800" * 50°C. The existence of the latter has also been indicated by others,1&apos;8 but neither compound has been definitely established. The Y-C phase diagram shown in Fig. 1 was proposed by Chubb and Keller8 in 1964 based on the data available at that time. The tentative nature of this diagram together with the uncertain status of the compounds indicated that additional work on this system was needed. EXPERIMENTAL PROCEDURE Yttrium metal of 99.9 pct purity was prepared for use in this study by the reduction of YCl, with calcium to form a sponge product.9 The major impurities in this material were as follows: 100 ppm C, 150 pprn H, 20 ppm N, 300 to 1000 ppm O, <20 ppm Ca, <100 ppm Cr, <80 ppm Cu, 150 ppm Fe, <30 pprn Mg, <400 ppm Ta, and <100 ppm Ti. Alloys were prepared by arc melting yttrium sponge together with pieces of high-purity graphite rod in a purified argon atmosphere. Homogeneity was insured by repeated melting, inverting the ingot between melts.

Jan 1, 1969

By Michael P. Richardson

INTRODUCTION This paper is intended to be a summation of the state-of-the-art i n draw theory and draw- point spacing. Knowledge of this very important factor in the successful design and operation of a block caving mine is scarce and nonconclusive. It is hoped that the presentation of this paper will stimulate interest and discussion which will lead to a stronger understanding of these a1 1 important factors. Please note that block caving as used here- in refers to block, panel, and mass caving systems in general, not just to the specific system of block caving where discrete blocks of ore are prepared and caved as a unit. DRAW THEORY The knowledge of draw theory as related to the practice of block caving mines is, unfortunately, very limited. In recent years much work in draw theory has been done in respect to sublevel caving systems and an understanding of draw mechanics relating to sublevel caving seems to be emerging. This work is certainly helpful to those of us interested in block caving but the question of "what goes on up above" still hounds us since we are more interested in the region of draw which begins just above the area where sublevel caving interest ends. Herein is presented a brief summary of draw theory with an attempt to look at the factors which can help our understanding of the area of draw influence in block caving mines. Nature of Gravity Flow An understanding of the flow of granular material (rock, sand, grain, or prill as examples) is the first step toward understanding block caving draw. If we take a supported column of granular material and allow gravity flow through an aperture at the bottom of the column, an ellipsoidal shaped zone of disturbance of the in-place material will form and grow with extraction of material through the aperture. The volume of this zone of disturbance or loosening is about 15 times the volume of material extracted at any given time (Kvapil, 1980). Figure 1 shows the development over time of the zone of disturbance. The ellipsoid of disturbance represents a future ellipsoid of extraction which will equate to the volume of materia1 extracted by that future time. Extraction involves the movement of the particles located vertically over the drawhole directly downward while material outside this direct vertical volume moves radially inward and down toward the drawpoint as shown in Figure 2a. Figure 2b shows the result of this motion on originally horizontal strata within the ore column. Increased draw increases the eccentricity of the ellipsoidal volume or, in other words, the ratio of the height over the width of the disturbed area increases as ore is withdrawn from the column (Kvapil , 1980). This becomes important to block caving since eventually a vertical cylinder of draw will be approximated as this ratio increases without bounds. Figure 3 shows this result. The width of this draw cylinder is a critical dimension for the determination of draw point spacing in relationship to block caving mine design. McCormick (1968) for one, felt that within this cylinder of draw, mass flow would take place. This is the

Jan 1, 1981

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 W. A. Hustrulid, N. A. Ross

An analysis of the design of medium to hard rock tunneling machines is presented. The developed equations are used to compare performances and machine requirements using kerf and fixed pick cutters to bore a given rock. With the use of pick cutters, required thrusts can be greatly reduced and still achieve the same boring rate as with present day tooth or kerf cutters. It appears that the cutting coefficient, which for most boring machines is of the order of 0.1, should be increased to one or larger to facilitate rock removal by cutting rather than grinding. The depth of cut and the indexing distance should be greatly increased to make use of inherent rock weakness.

Jan 1, 1971

By M. Mathieu

The Rove tunnel is the means by which the canal from Marseilles to the Rhone Riverl penetrates the hills of Nerthe, lying between Mar- seilles harbor and Lake Berre, Fig. 1. The canal will communicate at sea level with both terminals. The original project planned a lock near the village of Marignane; but observations, pursued for more than three years, showed that the water surface gradient would average only 0.015

Jan 1, 1923

By M. Mathieu

The Rove tunnel is the means by which the canal from Marseilles to the Rhone Riverl penetrates the hills of Nerthe, lying between Mar- seilles harbor and Lake Berre, Fig. 1. The canal will communicate at sea level with both terminals. The original project planned a lock near the village of Marignane; but observations, pursued for more than three years, showed that the water surface gradient would average only 0.015

Jan 1, 1923

By R. J. Brison, O. F. Tangel

The development of a new method of mineral separation was sponsored by the International Salt Company, which requested Battelle Institute to investigate means for improving the quality and appearance of rock salt from the Company&apos;s Detroit mine. Although developed specifically for removing impurities from rock salt, the general method may be applicable to other separation problems. The principal impurities in rock salt from the Detroit mine are dolomite and anhydrite which represent 2 to 5 pct of the weight of the mined salt. In the size range from 114 to 112 in. (the range of primary interest in this project) the impurities are only partially liberated from the halite in normal production. Further size reduction to improve the liberation of impurities is not practicable in view of the market requirements for the coarse grades of rock salt. Laboratory separations in heavy liquids showed that, to improve the quality and appearance of the rock salt substantially, it would be necessary to remove not only free gangue particles but also a large proportion of the locked-in particles.

Jan 8, 1960

By E. C. Harder

IN view of the gradually decreasing known reserves of high-grade manganese ore and the rapidly increasing consumption of iron-manganese alloys in the steel industry, it is well to turn our attention to the development of low-grade manganiferous ore deposits and to the utilization of these ores in steel manufacture. The dependence of this country on imported manganese ore and ferromanganese has been forcibly brought to the attention of steel makers during the last few years by the cessation of manganese-ore imports from Russia, the restriction of manganese-ore imports from India and of ferromanganese imports from Europe. Should the importation of manganese ore from Brazil cease, the steel industry of this country would face a serious situation. The present practice of steel making requires ferromanganese in large quantities and ferro-manganese of the grade used at present can be produced only from high-grade manganese ores such as the United States appears to possess only in insignificant amounts. There are in the United States, however, large reserves of manganiferous iron ore which could probably be used extensively in the steel industry if certain changes in the practice of steel manufacture were made. Thus high-grade manganese ore could be conserved. Among the most important deposits of manganiferous iron ore in this country are those of the Cuyuna iron-ore district of Minnesota. It is probable that in case of restriction of foreign supplies, the users of manganese in the United States would have to rely to a large extent on the Cuyuna district to make up the shortage.

Jan 9, 1917

By G. H. Ruggles

POPULAR opinion, as it might be termed, has always been of the trend that a flotation reagent added to the ball mill during grinding would be more thoroughly mixed with the pulp and for that reason more effective in the production of low tailing. That there are other effects, inimical to good flotation, when using so-called chemical reagents, is brought out by the series of tests outlined in Table 2. It was defi-nitely proved that if either the T. T. mixture (20 per cent thiocarbanalid-80 per cent orthotoluidin) or po-tassium xanthate were added to the ball mill the result-ing flotation concentrate would be lower in copper and higher in insoluble than the concentrate produced by adding these same reagents without the ball mill cir-cuit. With the T. T. mixture four sets of tests were made. The screen analyses of the flotation feed show that there was very little difference in the original grind-ing. When the T. T. mixture was added to the head of the flotation machine the flotation concentrate had a little over 61 per cent solids -200 mesh. If the mix-ture was put into the ball mill the flotation concentrate had but 40.7 per cent of the solids -200 mesh for one set of tests, and 49.0 per cent for the other set. With the mixture at the head of flotation the total concen-trate was high in copper (34.715 and 36.525 per cent) and low in insoluble (13.20 and 11.61 per cent). The assay of the concentrate when the T. T. mixture was introduced into the ball mill was what might be termed low in copper (29.389 and 30.833 per cent). In one of these &apos;sets of tests (periods 8 to 11, third column) the insoluble was high, 16.81 per cent. The other run (peri-ods 12 to 15, fourth column) for some unknown reason shows a low insoluble, 12.72 per cent. With similar grinding the addition of potassium xan-thate to flotation produced a concentrate having 62.8 per cent -200 mesh, whereas with the potassium xanthate added to the ball mill the flotation concentrate was very coarse, only 36.4 per cent passing 200 mesh. The difference in the total assay of the concentrate is remarkable ; 35.847 per cent copper when the xanthate went to flotation and 30.44 per cent copper when the xanthate was added to the ball mill; insoluble, 10.94 per cent in the former instance, as 22.15 per cent in the latter.

Jan 8, 1927

By Jonathan S. Jackson, Bayne B. McMillan, W. Joseph Schlitt

Various dump leach models have been developed by Kennecott, and these are reviewed with an eye toward production forecasting. Some of the models have been bated on first principles, utilizing the chemistry and physics of dump leaching. While providing considerable insight into the leaching process, these have proved to be too cumbersome for use in estimating production. Other models have been based on a declining leach rate for a single block of waste. These permit good short-term projections of solution grades and production, but are inflexible with regard to changes in mining parameters because the trends are based only on historical data. Therefore, a simple and flexible computer model has been developed to aid in leach production forecasting and to provide a tool for assessing the impact of different mining plans on leaching. This program, LEACH, is based on annualized blocks of waste; input parameters are described and examples of its use are given.

Jan 1, 1980

. E. P. MATHEWSON, New York, N. Y.-I would like to call attention to the excellent plan for protecting the lining of the tanks from rough handling by the excavator. Many engineers, when considering mechanical excavators for lead-lined tanks, have been afraid that the machinery might get out&apos; of order and rip out the lining. This difficulty seems to have been entirely overcome in this installation, and those who have been responsible for its success deserve a great deal of credit. A. F. CASE,* Cleveland, Ohio. (written discussion t).-The application of the automatic unloader to the copper leaching process at Ajo was a very radical departure from the common use of this machine, inasmuch as the only previous use of this device has been in connection with the unloading of coal and ore from vessels on the Great Lakes. There are many phases in connection with the unloading of ore from lake vessels that are not presented in the extraction of ore tailings from leaching vats. For instance, in unloading from boats, it is necessary to provide means to reach under the hatches to parts of the cargo hold which do not lie directly under the hatches, and to work in inaccessible places that do not exist in a leaching vat. These necessities require complications that could be very easily dispensed with in this new application. On this account the unloader, is applied to the New Cornelia, plant, represents what is probably the simplest development of the machine that has ever been produced, and, manifestly, in its simplest form it could he expected to show results corresponding to its performances when installed with all of its complications. One of the requirements of vessel unloading is extreme vertical travel, when the bucket is required to reach the bottom of the, cargo hold, often 12 or 13 ft. below water-level, and discharge into a receptacle 30 ft. above-the water. This was materially simplified at Ajo for the reason that the vertical travel was never more than 20 ft. This condition immediately resulted in the possibility of shortening the walking beam which carries the bucket leg, and, in fact, in entirely reducing the size of all the working, parts of the trolley, walking beam, and bucket leg, as far as reaches were concerned.

Jan 11, 1918

THE CHAIRMAN (A. F. LUCAS, Washington, D. C.).-The activities of the Petroleum and Gas Committee for the half year have brought gratifying results, as exemplified by 14 technical papers, brim full of novel and attractive issues in which we are all keenly interested. I beg to extend my hearty thanks to all members and authors who have responded to my appeal, and to all those who have endeavored to meet the growing demand which has resulted in the augmented production of this commodity which is so essential for the Nation&apos;s welfare, comfort and safety. As you well know, within the last few years, petroleum and its products have been used for numerous and novel purposes, so that we have become accustomed to their use in thousands of activities, and pleasures as well, but we should also note that we have been wasting and misusing these wonderful products, apparently believing that their sources are inexhaustible.

Jan 1, 1918

By George H. Cook

At first sight this subject seems to belong to pure theoretical geology, but examination will soon show that it has important practical and economic interest to the mining engineer. The conclusion that all the northern portions of our country, as well as of the eastern continent, have, in the later periods of geological history, been covered with a thick bed of ice, is now accepted by geologists. This bed of ice, except in its greater magnitude, was like the modern glaciers of the Alps, and other mountains which extend above the line of perpetual snow. The marks it has left upon the surface show that it was comparatively thin on its southern edge, but that its thickness was much greater a little further north, and that it was several thousand feet thick at its kenviest parts. This variation of its surface would give it a descending slope towards the south, and cause the mass of ice, like a semifluid substance, to move in that direction,

Jan 1, 1879

By C. Richard Tinsley

INTRODUCTION The economic analysis (Chapter 3), the engineering studies (Chapter 10), the credit structure (and the consequential funding sources) - Chapter 11, and the overall feasibility structure for any venture are all directed to determining one major decision element: How much and how certain is the reward for taking these risks? Risk assessment is a surprisingly weak area of analysis and is usually addressed in a checklist fashion. It is much preferable to deal within a risk system so that the inevitable tradeoffs among risks are correctly made. DEFINITION The first step toward risk definition must be to ascertain all of the risks to which a project or a company is exposed; otherwise one will remain ignorant of the possibility of a financially crippling loss until it occurs. (Carter and Crockford, 1974). However, simply stating what "risk" is can lead to debate. For example, risk could be (adapted from Vaughan, 1982): -the chance of a loss - uncertainty of loss -possibility of loss - uncertainty -dispersion of actual from expected results - probability of an outcome different from the one expected - possibility of an occurrence of an undesirable contingency -a condition in which a possibility of a loss exists. For the minerals industry financier, the last definition is probably the most appropriate. However, from a mineral company&apos;s point of view the definition might well include the possibility of not achieving the expected financial return. RISK CLASSIFICATION Risk identification will be readily agreed as the all-important first step. There are five major "branches" of risk classification. These are: -Statistical -Modellers -Checklist -Project Financing -Insurance The Statistical set discovered probability theory and any risk discussion soon deteriorates into a mathematical jungle (Megill, 1977; Hartman, 1976; Reutlinger, 1970; and Pouliquen, 1970).Their use of terminology tells its own story: coin toss (binomial distribution), gamblers&apos; ruin, delphi (oracle) techniques, monte-carlo simulations, random walks, etcetera. These techniques inadequately represent the judgements necessary in an increasingly complicated and interrelated world. The risk Modellers have turned to the computer to handle these inter-relationships but soon find barriers because of "simultaneity". Certainly the computer has its uses to conduct various analyses (marketed as "sensitivity" analyses) but very often one finds that this involves changing one or two variables at a time, all other things being equal. Unfortunately, in a modern and complex world all other things do not remain equal. The statisticians will, no doubt, jump to their own defence by citing this

Jan 1, 1985

By H. B. Small

The Ottawa river, the northeastern boundary of the Province of Ontario, and the dividing line between the latter and the Province of Quebec, has long been famous for the rafts of timber floated over its waters from the depths of the forest, and other poets besides Moore, have immortalized its beauties in verse. But with the ad vent of the railway which now pierces the forest solitudes, the days of rafting were numbered ; and the boat song is now heard no more on "Ottawa&apos;s tide," or at such long intervals only, that, when heard, it seems an echo of the past. The lumber trade is fast leav ing Ottawa City, the old headquarters of the business; and such square timber as is now cut is gradually finding other outlets than shipment to Great Britain, and other channels of transportation than the Ottawa river. Skirting the northern shore of this great river runs a vast chain of hills, assuming at times the altitude of mountains. Their geological character marks them as remnants of the earliest land of this conti nent. Following the course of the St. Lawrence from the Gulf of that name to the confluence of the river with the Ottawa, the course of which latter they then pursue, the range has been styled " the Lau rentians." Rolling in long undulations, with rounded, rather than rugged or pointed summits, they leave a margin of 8 or 10 miles, dipping in a gentle slope to the water&apos;s edge, rich for agricultural use, and dotted here and there with farms and settlements. Beyond this margin bold hills stretch northerly to blue mountains, rich in iron, lead, plumbago, and other minerals. The Apatite District.—One of these minerals is apatite, or phos phate of lime, the use of which as a material for the manufacture of superphosphate as a fertilizer has become the basis of the industry bidding Fair to prove ere long one of the chief elements of Canadian trade. So rapid has been the growth of this new industry that if the lumber business were to disappear from this mineral district, its void would be filled by that which has sprung up in connection with phosphate.

Jan 1, 1893

By L. F. Coffin

Monotonic tension and controlled cyclic-strain tests have been conducted on an annealed steel at various strain rates and temperatures in the weep range. Evidence of a strain-induced precipitate reaction abozle 500°C was determined from pronounced cyclic-hardening effects, increase inflow stress, inter granular fracture, drastic decrease in low-cycle fatigue resistance, and loss in tensile fracture ductility, as well as through electron-microscopy examination. It was found that strain rate as well as temperature had a pronounced effect on these observations. A parameter of the form P = T(7.95 - log ip) was determined, which was directly related to the ductility, defined either as the true strain at fracture in the case of simple tension, or as 2N 1/2 ? E p in the case of cyclic plastic strain. A highly satisfactory comparison of the cyclic life as measured and as computed from the ductility predicted by this parameter was obtained for a range of temperatures from 400° to 650°C and for crosshead speeds of 0.002 to 0.2 in. per min. MANY metals subjected to sustained loading at elevated temperatures derive resistance to creep from solid-state reactions of various alloying constituents. These reactions can be many and varied, and occur as a consequence of time and temperature according to reaction-rate principles. Strong evidence exists that many of these reactions are influenced by plastic strain, the argument being put forth that dislocations act as sites for nucleation and growth for the new phase.&apos; Many examples can be cited where plastic strain during transformation influences the structure, and as a consequence affects the properties.2 The low-alloy steels serve as particularly good examples for investigating the effect which aging reactions have on resulting properties. Alloying elements such as carbon and nitrogen, and carbide formers such as manganese, chromium, molybdenum, and so forth, can, by the particular aging reaction which occurs, produce strengthening effects at various temperatures, and so endow strength to the alloy over a broad range of temperatures. These effects have been systematically studied by Glen both during creep3 and for constant strain-rate tension testing.4,5 The work of Glen is of considerable interest in connection with the present study, particularly in regard to the effect of various alloying additions on the true stress-strain curve and on fracture ductility at various elevated temperatures. He has shown that strain-age hardening occurred during plastic straining, which was quite specific both to the temperature of the test and to the alloying element involved. When strain-age hardening was noted at a particular temperature, a .minimum in reduction of area was also obtained. Provided the temperature for the minimum reduction of area exceeded 300°C, all minimum ductility fractures were found to be inter-crystalline in nature. For carbon steels containing molybdenum, two minima in reduction of area were noted, one occurring at 200° to 250°C, the precise temperature depending on the percentage of molyb-

Jan 1, 1964

By Ralph W. Bailey, William B. Price

During the past three or four years, the fabricators of silicon-bronze alloys have endeavored to induce users of phosphor bronze to use instead the silicon-bronze alloys, claiming that the silicon bronzes are superior to the phosphor bronzes for switches and springs, or where high fatigue resistance is desired. This paper gives the results of tests comparing several phosphor bronzes with a 3 per cent silicon bronze and a copper-nickel-tin alloy (Adnic), all processed by the Scovill Manufacturing Co. So far as the authors are aware, sheet-metal fatigue tests have not been made on any of the alloys included in this report, except on one phosphor bronze, material C, Table 1, which was tested by Townsend and Greenall1. Endurance Limit The majority of fatigue tests are designed to determine the endurance limit of a material. The number of repetitions of stress that will serve to establish an endurance limit varies with different materials. For ferrous materials, H. F. Moore2 has shown that stresses that do not cause failure up to 10,000,000 stress cycles will not cause failure up to 100,000,000 (and sometimes to 1,000,000,000) cycles. Thus an endurance limit for ferrous materials can be determined with a minimum of 10,000,000 stress cycles. For nonferrous materials, no such generalization holds. R. R. Moore3 has shown that for manganese bronze and elektron metal, 13,000,000 and 28,000,000 cycles, respectively, will serve to determine an endurance limit, while certain duralumin specimens gave no indications of having reached an endurance limit up to 400,000,000 stress cycles. J. B. Johnson6 showed that an endurance limit for duralumin was not found by tests running up to 500,000,000 cycles. H. F. Moore2

Jan 1, 1937

By J. F. Myers, F. M. Lewis

The purpose of the mill tests reported herein, was to determine the relative power efficiency of fast and slow rod mill speeds on the ores of the Tennessee Copper Co. The tests were carried out at the Isabella Mill of the Tennessee Copper Co. under normal operating conditions. Every effort was made to keep the ore supply and other conditions constant, but it will be noted that some slight variation did occur. The open circuit 6 by 9 rod mill, and ore, used in these tests have been previously described.&apos; Four motor drive pinions were available and the tests were performed in the following manner: each pinion was used to drive the mill for a period of one week. Constant sampling prevailed during the test run, and a composite sample for each speed test was made. Realizing that some slight liner wear took place during the four-week test-run, and that some slight variation of the ore may have taken place, a second and then a third series of four-week test-runs were made with the four different pinions. The screen analysis of each of the three-week run samples at the various speeds were composited and the results are shown in Table 2. The authors feel that the 22 weeks of operation consumed during these test-runs would represent fairly the effect of each mil1 speed. The data of line 37 show that within the error of sampling and plant operation, the tons of minus 65-mesh material generated per horsepower hour was the same at all four speeds. Obviously, rod and liner consumption could not be determined for each mill speed in so short a time. The rod load was maintained at a uniform level throughout the series of tests. The authors have operated rod mills at various speeds over the past several years, and it is their observation that rod consumption is directly proportional to the mill speed. Likewise, that the rod consumption per unit of work performed is a constant, providing that all other operating factors remain the same. It is a well known fact that the efficiency increases in a ball mill as the speed decreases. This is due to lateral segregation of the large and

Jan 1, 1950