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By Hans Lundberg

By electrical prospecting, orebodies that do not otherwise manifest themselves at the surface may be located. Conditions favorable to success with the methods are: Favorable geological conditions, such a proportion of minerals of good electrical conductivity in the orebody as will render the latter materially a better conductor than the enclosing rock, situation of the orebody within the range of influence of the electrical currents used and in proportion to this range a sufficient area of horizontal cross section of the orebody. The result is to permit of spotting drill holes accurately and to save the expense of drilling barren ground. THE art of prospecting, like other branches of mining, has developed rapidly during the last ten years, mainly because of the advancement of mining geology, but also because of the development of "geophysical methods," which are based on the different physical characters of minerals and rocks, e. g., specific gravity, elasticity, and magnetic and electric properties. These methods have proved of great value, especially in countries where the rock is covered by soil and direct geologic investigation is out of the question. In prospecting for orebodies, the methods based on studying differences in electrical conductivity have proved most successful; for which reason, the methods of electrical prospecting have been subject to the most energetic and systematic work, especially in Sweden. This paper gives a brief description of the methods of electrical prospecting now in use, especially the new electromagnetic methods, which have not been described before. The great differences in the electrical properties, especially in conductivity, between ore minerals and rock minerals are fundamental to all methods of electrical prospecting, for which reason, the electrical conductivity of ore minerals and rock minerals has been carefully studied in connection with and previous to the development of the various methods of prospecting with electricity. Ore minerals with a metallic luster, such as chalcopyrite, iron pyrite, galena, specular iron, magnetite, etc., also graphite and a number of cows, have considerably higher conductivity than the surrounding rock and soil (see Table 1). The figures of the table denote the specific resistance W, expressed in ohms for a cube with an edge of 1 centimeter.

Jan 7, 1925

By H. G. Moulton

THE INCREASING scale of mining operations over the past decade, particularly in connection with the exploitation of large bodies of comparatively low-grade copper ores, has made necessary the study of the behavior of rock under failure. When extractions of as high as 40,000 tons a day are reached in steam-shovel operations and as high as 20,000 tons per day in underground mining operations, it is evident that excavations soon become of such size that the behavior of the rock will often be dependent on fundamental principles applicable to more or less homogeneous materials under stress, rather than on weathering or local planes of weakness. In the ordinary rock excavations encountered in civil-engineering practice, such as excavations for subways, highways, railroads, etc., rock faces are not carried to depths sufficient to develop any pressures, or consequently any failures, except those due to loose masses resulting from local planes of weakness. When, however, orebodies whose tonnage is measured by hundreds of thousands are to be extracted by steam-shovel operations in open pits, it is necessary to determine if possible in advance the slopes that the sides of the pits will assume, for these slopes influence the shape of the excavations and thereby the amount of ore that may be extracted by the open-pit method. When large orebodies are mined underground at depths of 300 to 500 ft. (91 to 152 m.) by caving methods, the surface subsiding as the ore is withdrawn, it is necessary to determine in advance the outermost limits of fracture in the subsiding surface, for on the delineation of these limits depends the location of surface improvements, mills, smelters, etc. and also the location of development work, such as hoisting shafts, main haulage levels, and all other underground openings that must remain undisturbed during the period of ore extraction. Heretofore, in civil-engineering practice, it has been assumed that earth and rock behave differently in failure. For the calculation of earth

Jan 2, 1920

By A. R. Troiano, E. A. Steigerwald, F. W. Schaller

The kinetics of crack propagation in a hydrogenated high-strength steel at subzero temperatures indicated that cracking progressed in a discontinuous fashion. The delayed failure process thus involves a series of crack initiations rather than the continuous growth of a single crack. The incubation time required for the initiation of delayed failure was controlled by the diffusion of hydrogen. The activation energy for the process was 9120 cal per g-alom. As the test temperature was lowered the incubation time constituted a greater percentage of the total tinze to fracture, and al -50°F the incubation and fracture times were essentially coincident resulting in instantaneous, catastroplzic fracture. A unique feature of hydrogen embrittlement is the delayed failure process in which the material fails under the action of a sustained load even though it is capable of supporting a higher load for a finite period of time.')' Delayed failure of steel and titanium is characterized by an incubation time, preceding the initiation of a crack in a highly localized region, and the subsequent growth of the crack to ultimate failure.3-5 The kinetics of crack growth in hydro-genated high-strength steels have been studied through the use of resistance measurements and have an important bearing on the mechanism of delayed failure. Delayed failure is believed to be merely a facet of hydrogen embrittlement in which sufficient time is allowed during a test for hydrogen diffusion. The current theories employed to explain hydrogen em-brittlement can be grouped into two types. one6-8 explains the embrittlement on the basis of the pressure exerted by molecular hdrogen in lattice voids or defects while the other9-10 attributes the embrittlement to the influence of hydrogen in the lattice. The mechanism used to explain the nature of the crack kinetics in delayed failure is based on the stress-induced diffusion of hydrogen to the area of maximum triaxiality.3 When the hydrogen concentration in this region reaches a critical value, a crack is nucleated. This initial crack propagates instantaneously until stopped by the higher fracture stress of the adjacent material of lower hydrogen content. The continuation of cracking must then await the further diffusion of hydrogen to the new region of triaxiality near the base of the crack where another initiation will occur. From this mechanism it follows that crack propagation is nothing more or less than a series of initiations with limited fracture. The purpose of this investigation was to examine the kinetics of crack growth in an effort to determine whether or not the process was discontinuous. Studies of crack propagation were conducted at low temperatures to retard the diffusion of hydrogen which is presumed to be the rate controlling process in delayed failure. MATERIALS AND PROCEDURE Specimen Preparation—A commercial heat of air-craft quality SAE-AISI 4340 steel, designated as Heat G, was furnished by the Republic Steel Co. in the form of %-in. hot-rolled bars. The material had the following chemical analysis: Composition of 4340 Steel—G Heat C Mn Si Ni Cr Mo 0,395pct 0.82pct 0.29pct 1.76pct 0.85pct 0.25pct Notched tensile specimens with less than a 0.001 in. radius, Fig. 1, were used throughout the investigation. The specimens were heat treated to a 230,000 psi strength level according to the following sequence: a) Normalize bar stock at 1650°F for 1 hr, b) Stress relieve at 1200°F for 4 hr and furnace cool,

Jan 1, 1960

By J. E. Steiner, J. M. Hodge, M. A. Orehoski

Ingots of four steels (1045, 1080, Ni-Mo-V, and Ni-Cr-Mo-V) were cast at pressures varying from about 1 to 760 mm of mercury, so as to obtain a range of hydrogen contents in each steel. The susceptibility of these steels to flaking was evaluated by cooling hot-rolled blooms at a range of cooling rates, varying from water quenching to slag cooling, and studying the occurrence of flaking as a function of cooling rate. The steels exhibited differences in susceptibility to flaking, and a tlzreshold value for hydrogen content for each steel was found, below which the susceptibility was very low and above which the susceptibility increased markedly with increasing hydrogen content. Mechanical property evaluations, metallogvaplzic exantinations, and X-my diffraction determinations o,t retained austenite were made on samples from the blooms. A mechanism of flaking which is consistent with the observed behaviors, the effects of hvdrogen content, and the differences in susceptibility among the steels investigated is postulated, based on the results of mechanical property evaluations and metallographic and X-ray diffraction studies. ThE important role of hydrogen as a factor in the occurrence of "flakes" or "hair-line cracks" in steel has now been established by many investigations. These have included investigations by steel producers and forging manufacturers, to whom the prevention of flaking is a very real and serious problem, and many research studies aimed primarily at establishing the mechanism of this behavior Several investigators3 have reported that steels cast at reduced pressures (absolute pressures of about 1 mm) not only are low in hydrogen content but are essentially insensitive to the formation of flakes. These investigations have shown that a general relationship exists between hydrogen content and susceptibility to flaking. The difficulty of obtaining suitable samples of steels of a given composition with the desired range of hydrogen contents, particularly in the relatively large sections in which flaking most commonly occurs, has been the principal obstacle to quantitative evaluations of these relationships. Steels with intermediate hydrogen contents between 1 ppm, and the 4ppm or higher of air-cast steels are generally not available in commercially produced steels. Laboratory procedures, in which the hydrogen is introduced into solid steel samples by heating in a hydrogen atmosphere under pressure, generally involve a limitation in the size of the sample which can be treated, and thus are not representative of the behaviors in large sections. The availability of a facility at the South Chicago Works of U.S. Steel, in which several ingots could be cast from a single heat of steel at total air pressures ranging from 0.25 to 760 mm of Hg, has made it possible to overcome this obstacle and to obtain ingots of a given steel covering the intermediate range of hydrogen contents desired. These ingots, furthermore, are of a size suitable for the production of product with section sizes large enough to be representative of the products in which flaking most commonly occurs in commercial production. In these experiments, this facility was used to study the relationships between hydrogen content and the susceptibility to flaking of four steels, two plain carbon steels at 0.45 and 0.80 pct C and two low-carbon alloy steels representing a medium and a rather high hardenability level. These flaking studies were supplemented by evaluations of mechanical properties and by metallographic studies on samples from the blooms, in order to obtain pertinent information on the factors other than hydrogen content which influence the susceptibilities of these steels to flaking. Based on the results of these tests, a mechanism for the initiation and propagation of the flaking cracks, which is consistent with the observed behaviors, is postulated. MATERIALS AND EXPERIMENTAL WORK Steelmaking and Conversion. To provide material for the investigation, five 29- by 35-in., hot-topped, big-end-up ingots were cast from each of four 80-ton, basic electric-furnace heats of four different steels (a 1045 steel, a 1080 steel, a Ni-Mo-V steel, and a Ni-Cr-Mo-V steel). A double-slag practice was used on all steels and the two plain carbon steels were Si-A1 deoxidized with an addition of 2 lb of A1 per ton, while the Ni-Mo-V and Ni-Cr-Mo-V steels were deoxidized only with silicon and

Jan 1, 1964

By W. M. Gray

The determination of the state of stress existing at a point in any solid body requires the determination of the six components of the stress tensor relative to a convenient set of axes. One general method of doing this in rock is to make strain or deformation measurements associated with local relief of stress in a number of boreholes penetrating a limited volume in the vicinity of the point at which the stress is to be determined. The stress is assumed to be constant throughout this volume. Leeman1 has described a number of the instruments that have been developed for making deformation or strain measurements in boreholes. Panek2 has described the application of statistical methods to the determination of the average components of ground stress from sets of measurements made in boreholes by means of deformation meters of the type developed by the U.S. Bureau of Mines. In this paper attention is given initially to the strain cell developed for use on the flattened ends of boreholes by the Council for Scientific and Industrial Research (CSIR) , South Africa. The equations required for evaluating the average components of ground stress from measurements made by means of the CSIR strain cell are derived. These equations are similar in form to those applying to measurements made by the borehole deformation meter developed by the U.S. Bureau of Mines. The results of an investigation of the properties of the equations are described. These results are important in the practical use of both the instruments mentioned above and any instrument based on similar principles.

Jan 1, 1968

IN the early period of steelmaking, ingot structure and segregation were of no practical importance. Crucible melting required very small ingots that gave little segregation, and a small inserted hot top prevented pipe. As larger ingots were poured from bessemer converters and open-hearth furnaces, segrega- [ ] tion, piping, and gas evolution became increasingly important. The techniques of making semikilled and rimmed ingots were developed with little knowledge of the actual mechanism of the process. The first studies of solidification were made by the Brearleysl and Gathmann,2 who used stearine to show the effects of shrinkage and mold shape. Fig 11-1 is a picture of a series of stearine ingots at various stages of solidification. These studies showed that the liquid solidifies at a nearly uniform rate from the sides and bottom of the mold and demonstrated the formation of

Jan 1, 1951

By B. S. Norris, Charles R. Austin

The stresses which initiate deformation processes in metals are fundamentally important in the study of the mechanical properties of metals. A point of inflection in the load-elongation curves obtained for single crystals' has been rather too readily interpreted as a true yield point, and the critical resolved shearing stress on the plane of slip taken as a material constant. Even early work showed that the stress at this point varies with rate of loading, but it has not been generally appreciated that creep tests under static loads alone are suited for determining the existence or nonexistence of a yield point.* It has now been shown by Miller that single crystals of zinc3 when loaded statically begin to yield at loads too small to measure; as a result there is no case now known, apart from that cited in the present paper, in which a true critical stress for yielding has been demonstrated for single crystals of metals. The case of iron has especial interest: the existence of an upper and lower yield point and of an elongation at the yield point in ordinary iron and steel marks this substance as unusual, though the effects have been found to a very minor degree in other metals and alloys. $ Most alloys do not show such marked phenomena when appreciable yielding begins, and accordingly modern practice is to speak of the yield strength of such materials, a stress read from the load-elongation curve after elongation has begun, rather than yield point. The special behavior of iron suggests that it is more likely that single crystals of iron should have a true yield point than other metals. The study of the mechanical properties of metals and alloys requires a determination of the crystallographic mechanism of deformation, wlletller deformation proceeds by slip, twinning, or cleavage, or a combination of these, and a determination of the stresses that induce these modes of deformation. With this information, a study of the rates of work-

Jan 1, 1938

By B. S. Norris, Charles R. Austin

The stresses which initiate deformation processes in metals are fundamentally important in the study of the mechanical properties of metals. A point of inflection in the load-elongation curves obtained for single crystals' has been rather too readily interpreted as a true yield point, and the critical resolved shearing stress on the plane of slip taken as a material constant. Even early work showed that the stress at this point varies with rate of loading, but it has not been generally appreciated that creep tests under static loads alone are suited for determining the existence or nonexistence of a yield point.* It has now been shown by Miller that single crystals of zinc3 when loaded statically begin to yield at loads too small to measure; as a result there is no case now known, apart from that cited in the present paper, in which a true critical stress for yielding has been demonstrated for single crystals of metals. The case of iron has especial interest: the existence of an upper and lower yield point and of an elongation at the yield point in ordinary iron and steel marks this substance as unusual, though the effects have been found to a very minor degree in other metals and alloys. $ Most alloys do not show such marked phenomena when appreciable yielding begins, and accordingly modern practice is to speak of the yield strength of such materials, a stress read from the load-elongation curve after elongation has begun, rather than yield point. The special behavior of iron suggests that it is more likely that single crystals of iron should have a true yield point than other metals. The study of the mechanical properties of metals and alloys requires a determination of the crystallographic mechanism of deformation, wlletller deformation proceeds by slip, twinning, or cleavage, or a combination of these, and a determination of the stresses that induce these modes of deformation. With this information, a study of the rates of work-

Jan 1, 1938

By L. E. Mannion

Sodium carbonate (soda ash) is one of two principal commercial alkalis. Its principal competitor is sodium hydroxide. The use of sodium carbonate is recorded in ancient Egypt, where naturally occurring brines and solid salts provided impure soda for early glassmaking. Until the 19th century, soda ash (as well as potash) was recovered mainly by leaching wood or other plant ashes. In 18th-century Europe, for example, leaching seaweed ash with hot water produced a brown laundry lye. One of the better grades of this material was a Spanish product, barilla, which analyzed 24 to 30% Na2CO3 (Hou, 1942). The modern chemical industry was born in 1691 with the LeBlanc process for making sodium carbonate from salt, sulfuric acid, and lime. English industry used this process extensively in the 17th and 18th centuries. The next major advance was in 1863, when Ernst Solvay devised the ammonia-soda, or Solvay process. The first of many Solvay plants was built in 1874. These supplanted the LeBlanc method and dominated worldwide soda ash production until 1974, when mined sodium carbonate became predominant. Although considerably less important until recently, natural sodium carbonate deposits historically have supported small soda ash operations throughout the world. Shortages during World War II stimulated production of "natural" soda ash from such deposits, particularly at Searles Lake, CA and Lake Magadi, Kenya. More spectacularly, increased production from the vast trona deposits in Wyoming has virtually supplanted the Solvay process in the US. Principal producers of natural soda ash as well as the character of the source deposits are listed in Table 1. [ ]

Jan 1, 1983

By F. L. Bosqui

INTRODUCTION The history of the development of gold metallurgy in South Africa is divisible into two periods: That preceding the introduction of the cyanide process on a commercial scale in 1890; and the 24 years intervening between that important event and the present time. The period between the discovery of the banket reefs of the Witwatersrand and the year 1890 was one of phenomenally rapid progress in mining development, but of no special interest to the metallurgist. There were no strikingly original or distinctly local advances in the treatment of gold ores. Californian practice in stamp milling and amalgamation prevailed, in mills ranging in equipment between 5 and 50 stamps, operating within a wide range of efficiency, and under the trying conditions usually en¬countered in a new and isolated field. The somewhat incomplete records of gold output of that period show that in December, 1887, there were 20 producing companies in the Witwatersrand district, of which 10 had mills, the largest being of 20 stamps. The only official record of returns for May, 1887, was that of the Wemmer mine, whose modest achievement with a 5-stamp, mill was 100 tons crushed, producing 887 oz. 3 dwt. of gold. This is interesting in view of the .present-day output of this field, which in 1913 reached 8,430,998 oz. The rapid increase of production during this first period (May, 1887, to January, 1891) is shown by the following summary for the year 1890:1 Total tons crushed 702,828 Number of stamps in operation 1,046 Average number of tons crushed per stamp per day 2.36 Yield of gold, ounces 494,817 Yield per ton, pennyweights 13.36 The stamp duty ranged between 1 ½ and 4 tons per day, according to weight of stamp, fineness of screen, and operating skill available. The prevailing weight of stamp was about 900 lb., and the screen, 900 meshes to the square inch.

Jan 5, 1915

By R. A. L. Black, J. E. Jennings

The problems of slope stability in open cast mines are examined. A criterion, the instantaneous stripping ratio, is suggested for use in the design of pit slopes and as an index of control at all stages of the exploitation of the orebody. This criterion may also be related to safety and to the maximizing of profits. Two approaches to safe design of slopes, one from the point of view of soil mechanics and the other from the point of view of rock mechanics, are described and critically compared. The effect on slope stability of the regional tectonic stress field is discussed. Explanation is given of the application of the Terzaghi effective stress concept to problems in both soil and rock environments, including possible effects when borehole deformation techniques are used to measure stresses in rock in situ. A company embarking on open cast mining is faced with two basic questions: 1) will the venture be profitable and 2) can it be carried out with safety? The two questions are obviously interrelated because both depend upon the slope angles adopted for the pit. The cost of open cast mining depends largely upon the stripping ratio, defined as the volume of overburden that must be removed to the volume of ore recovered. The steeper the slope angles, the more favorable the stripping ratio, but the stability of the slopes, and therefore the safety of men and materials in the pit, require that the angles be made relatively flat. Consequently, the design depends upon a compromise: the slopes must be steep enough to result in economical mining and flat enough to ensure safety. Today there is a world trend towards deeper mining by open cast methods. This is mainly due to the higher cost of underground mining and the lower cost of open excavation resulting from the introduction of large modern earth and rock-moving machinery. Deeper open cast mining has led to a very great increase in the volumes of wasted overburden, and much thought is being given to the considerable economic benefits which would result if pit slopes could be made steeper by even one or two degrees. The result has been an increasing interest in research into slope stability problems in the expectation that the application of scientific principles will provide solutions leading both to economies and to more predictable operation of the mines. In at least four places, the U.S., Australia, Western Germany and Southern Africa, comprehensive investigations are at present in progress, and it is the object of this paper to review some of the more important aspects of these programs. RELATION BETWEEN ECONOMY OF OPERATION AND SLOPE ANGLES The main object of any industrial enterprise in a free economy is to make a profit. In mining, where profits must be made from a wasting capital asset, a further definition of the profit motive is imposed, namely that the economic aim should be to maximize the total possible profit. But since profits deferred for a number of years are not as valuable as profits that are immediately available, it is usual to discount deferred profits at some rate of interest which reflects their current or present value in the hands of the investor. Thus, in mining the logical aim can be defined more closely still: to maximize the present value of the total future profits. In commercial terms the present value represents the market value of the operation as a going concern. Many factors enter into the forecast of current and future profits. They include the volume of production, the price of the salable product and the cost of production. Current profits can be estimated with reasonable accuracy by the operating engineers; but it is the task of economists and management to assess future trends in the mineral markets and in the economy as a whole, and together with the engineers, they can then estimate the future cost and profitability of the mining operations. In open cast mining, the rate of ore production once decided on remains a virtually constant factor unless a major change in the capital structure of the mine is made. But one factor over which the operator has a considerable measure of control is the ratio of the volume of ore mined to the volume of waste over-

Jan 1, 1963

By D. L. Ritter, N. J. Grant, B. C. Giessen

Forty-six alloys covering the complete concentration range of the Nb-Rh system were examined by metallographic and X-ray methods; solubility limits of terminal ad intermediate phases and transformation and solidus temperatures were determined. There are nine intermediate phases; two eutectic, five peritectic, two eutectoid, and three peritectnid reactions were encountered. The experimental methods and the constitution diagram are described in Part I. Part 11 deals with the crys -tallography and relation of the intermediate phases. The Nb-Rh system was selected for study for three reasons: first, it was hoped that the anticipated similarity of the Nb-Rh phase diagram to the Ta-Rh1 and Ta-Ir2 diagrams treated earlier (see also Ref. 3) and to the Nb-1r4 diagram treated simultaneously would allow a crystallographic and comparative evaluation of the intermediate phases in these related systems; second, it was likely that the previous experimental methods could be carried over without significant change; and third, it was expected that the interesting mechanical properties of the a1 phase of the Ta-Rh and Ta-Ir systems would also be encountered in similar phases of the new systems, and that these phases could be investigated more closely. The phase diagram had not been treated fully in the literature; only brief surveys of some intermediate phases were found.5-7 It was attempted to cover the details of the phase boundaries, Part I, as well as to present the crystallography of the intermediate phases, Part 11. EXPERIMENTAL METHODS Specimen Preparation and Treatment. The following high-purity starting materials were used. 1) Niobium powder, 99.8 pct pure, mesh size -60 +200, from Wah Chang Corp., Albany, Ore. The analysis furnished by the supplier showed the following major impurities: Ta, <500 ppm; Zr, <500 ppm; 0, 300 ppm; Fe, 280 ppm; Ti, <I50 ppm; W, Si, <100 ppm; C, N, 30 ppm; all other impurities, <30 ppm. 2) Rhodium powder, ground sponge, 99.9+ pct pure, mesh size -80, from J. Bishop Co., Malvern,

Jan 1, 1964

By Arthur Taggart

THE major portion of the work described in this paper was performed by R. W. Young,+ a graduate student in the department of Mining and Metallurgy, Sheffield Scientific School, Yale University, working under a cooperative agreement between the Hardinge Conical Mill Co., the Sheffield Scientific School, and himself. Since this cooperative scheme is at present in effect in the case of a considerable number of other students in the department and since it is the hope of the school that the privilege thus extended may be utilized even more freely in the future by mining and manufacturing companies, it may not be amiss at this point to give a summary of the general plan. Briefly it is as follows: A graduate student, whose undergraduate work in this or other universities shows promise of ability to handle research work, is chosen by conference between the company and instructor involved. The aim of the company in the agreement then entered into is to obtain the solution of one or more of the technical problems with which it may be confronted, or, at the end of 1 or 2 years, to obtain as an employee a man especially trained in its work. As. a means to accomplish one or both of these ends, the company furnishes the machine, apparatus, or material to be tested and pays the student during his graduate work a small salary, usually just sufficient to cover his living expenses, tuition and fees. The aim of the student is special training along a line in which he is particularly interested, the attainment of his advanced degree, and the chance to show to his future employer ability to handle such problems as may be presented to him. In return for the financial aid which he receives he agrees to devote at least half of his working time to the special problem submitted by his company. The other half is devoted to study of the collateral subjects required by the department for the granting of the degree which the student seeks. The student further agrees to enter the employ of the company in question at a wage not greater than that paid in like positions to recent graduates not specially trained and to remain with his employer at such wage for at least 1 year. If the student is to obtain a degree, the special work forming the basis of his investigation must be such as will involve real research and not mere routine manipulation. The subject is chosen by conference between the three parties to the agreement. The work is carried on under the direct supervision of the instructor involved. The school furnishes the general laboratory and library equipment essential to the pursuit of any extended investigation, In

Jan 4, 1917

By W. H. Herrnstein, J. B. Clark, E. C. Utley, A. J. McEvily

The ratio of the endurance limit (10&apos; cycles) to tensile strength of age-hardened aluminum alloys is approximately 0.3, whereas the ratio for annealed alloys is about 0.5. The lower value for the age-hardened alloys has been associated with the instability of coherent precipitate during cyclic loading, but it has not been definitely established whether this instability is due to overaging or reversion during cyclic loading. The results of the present investigatzon support the reversion viewpoint. In this work specimem of 2024-T4 aluminum alloy were aged for 16 hr at 150°C after cycling for 10 pct of the life at 25.000 psi. These specimens were then tested to failure and exhibzted a marked increase in fatigue life. It is proposed that during the early stages of fatigue in this alloy dislocations cut through the coherent precipitate and bring about the reversion of the precipitate. Subsequent aging at 150ºC induces reprecipitation in the precipitate-free zones so that the weakened regions are strengthened and the fatigue life is extended. It Is recognized that the fatigue strengths of precipitation hardened aluminum alloys are unusually low relative to their tensile strength.&apos;-= This feature is illustrated in Fig. 1 where it can be seen that age-hardened alloys have lower fatigue ratios (the ratio of the fatigue strength to the tensile strength) than those in the annealed or cold worked state. Further, as shown in Fig. 2, the more an alloy is dependent upon precipitation hardening for its total strength, the lower is the ratio of the fatigue strength to the tensile strength. This state of affairs has been associated with an instability of the metastable metallurgical structure of precipitation hardened aluminum alloys during cyclic loading. Evidence2 in support of this view is that the fatigue ratio increases in these alloys as the test temperature is lowered, thereby indicating that thermo-mechanical instability, rather than some other factor such as a non-uniform distribution of precipitate, is the factor responsible for the low fatigue ratio at room temperature. Two mutually exclusive proposals have been ad- vanced to account for this instability. Hanstock has proposed that overaging takes place during cyclic loading, and in support of this view, Broom et a1.2 have indicated that an overaging process might be promoted by the large numbers of vacancies which are created during cyclic loading. The creation of vacancies by radiation4 has been shown to lead to rapid overaging. Hanstockl obtained visual evidence of overaging in an aluminum alloy after cyclic loading, but in this instance it has been pointed ou? that because of the high frequency used (60,000 cpm) the observed effect may have been due to normal high temperature precipitation around energy dissipating cracks. Efforts to discern visual evidence of overaging in this alloy at lower test frequencies were not successful.3 The alternative postulate3 is that reversion takes place during cyclic loading and leads to localized soft spots at which fatigue cracks are readily initiated. Evidence for this process has recently been provided by Polmear and Bainbridge5 who demonstrated metallographically that regions depleted of precipitate were created during cyclic loading of an aluminum alloy. Inasmuch as precipitate particles bordering the depleted region had not grown in size, it was concluded that the solute atoms which had constituted the missing particles had gone back into solution. No mechanism for the reversion process was presented. The present study was undertaken to investigate further the conditions leading to instability during cyclic loading, and to determine whether reversion or overaging had taken place as a result of cyclic loading. BACKGROUND AND TEST PROCEDURE In order to differentiate between the processes of reversion and overaging, rest periods at an elevated temperature, which ordinarily would insure additional precipitation, were used in this investigation. It was expected that after a period of cyclic loading an elevated temperature rest period would result in a decrease in the remaining life of the specimen if overaging were occurring during cyclic loading, whereas in the case of reversion, reprecipitation would occur and the fatigue life would be extended. Such an expectation is based on the assumption that the crack-nucleation phase is a significant portion of the total fatigue life, and that such a treatment is of influence in the crack-nucleation stage and is relatively unimportant thereafter.

Jan 1, 1963

By M. R. Pickus

THE study of the plastic deformation and recrystallization of metals has been the subject of many investigations. In regard to the simple deformational processes, such as tension and compression, the early knowledge gained from studies of polycrystalline material has been supplemented by many significant researches on the behavior of single crystals. Unfortunately, this has not been true for more complicated deformational processes. As far back as 1927, G. I. Taylor1 wrote: It is impossible in the present state of knowledge to do more than give a possible reason why (face-centered cubic) crystals set themselves with a (110) direction in the plane of rolling, and at right angles to the direction of rolling. The explanation of why the orientation of the crystal axes round the transverse direction is what it is, must be left till the distortion of metals, and particularly single crystals of metals in the process of rolling, has been studied in greater detail. That this gap in the systematic study of deformation and recrystalliza-tion has not yet been filled was indicated by C. H. Samans,2 who wrote in 1934 that "only four investigations upon cold-rolled single crystals of any of the face-centered cubic metals have been reported in the literature." Of these four studies, only those of S. Tanaka3 and T. Sakao,4 both of whom worked with aluminum crystals, had quantitative significance. The other two, carried out by F. Wever5 and W. G. Burgers,6 were of a. qualitative nature. It is our hope that the present investigation may contribute some-thing to the knowledge necessary for a rationalization of the origin of rolling textures in terms of the known behavior of single crystals, and may add pertinent information concerning the recrystallization characteristics of deformed single crystals.

Jan 1, 1938

By T. S. Spicer

The relationship of coal characteristics to the principal types of firing equipment has been known to the coal combustion engineer, but is not as familiar a subject for purchasing agents, salesmen, consumers, and executives of coal-producing and consuming companies. This general survey of characteristics determined by standard laboratory tests, of major types of combustion techniques, and of the relationships between the two is directed toward the latter audience. It will also serve as a review for those actively engaged in the combustion of coal. Although the relationship of coal characteristics to the principal types of firing equipment is well known to the experienced coal combustion engineer, apparently there is need for a summary article on this subject. The author has received numerous requests for such a paper from purchasing agents, coal salesmen, coal customers and executives of coal-producing and consuming companies. Consequently, the scope of this paper will be directed to this audience, with the hope that it may serve also as a review to others actively engaged in the combustion of coal. The magnitude of this subject is so great that only a brief general treatise is possible. The author realizes that because there are so many special cases and exceptions to the generalities which follow, he is in jeopardy of contradicting himself. It is the hope, however, that the many references cited will prove valuable to those who wish to study the details excluded by necessity, due to space and time limitations. Hence, the characteristics of coals as determined by standard laboratory tests will be discussed; the major types of combustion techniques reviewed; and then the characteristics and firing will be related. CHARACTERISTICS OF UNITED STATES COALS The coals of the United States range from lignite to anthracite and each has its own general characteristics. The extensive coal fields of the U. S. are shown in Fig. 1 and the estimated reserve according to rank for each state is illustrated in Fig. 2. Coals may be classified according to rank as shown by Table I from the ASTM Standards on Coal and Coke, D-338-38.1 The basis of this classification is ac- cording to fixed carbon and heating value (Btu per pound) calculated to a mineral-matter-free basis. The high-rank coals are classified according to fixed carbon on the dry basis; and the low-rank coals according to Btu on the moist basis. Agglomerating and slacking (weathering) indices are used to differentiate between certain adjacent groups. While rank is not itself a characteristic it does signify certain characteristics that accompany a class of fuel. Anthracite, for example, immediately implies a hard, free-burning, smokeless coal of low volatile matter, usually having an ash of high fusibility. Coals may also be classified according to grade as described by ASTM Designation D-398-37.1 This quality classification is determined by size, calorific value, ash, ash-softening temperature, and sulfur. This type of classification is not used as extensively by the industry as the rank classification. Fig. 3 shows the heat value of different ranks compared to proximate analyses. Coals may also be classified by sizes, as shown in Tables IIA and IIB, and sizes can be on both top and bottom limits. If this is done, then the coal is called double screened; otherwise, either top or bottom sizes can be specified as a limit. Bituminous coal sizing varies from field to field and depends upon the market demand. The common sizes and their main uses are outlined in Table IIA. Anthracite is usually available in many sizes at the colliery, and Table IIB summarizes standard sizes and names. Although rank, grade, and size designations help identify and describe a coal in question, there still remain other characteristics such as indicated by moisture, free swelling index, grindability tests, etc. A bituminous coal information chart Table III) suggested for use in studying the available coals in a region, lists origin and chemical and physical characteristics. Even this more comprehensive list does not completely spell out all the characteristics of a heterogenous material like coal. For example,

Jan 1, 1961

By Kenelm C. Appleyard

In introducing to an American audience a description of the work done in dry coal separation in England and in Europe generally, it is perhaps desirable to give a short history of the development outside the United States of the particular processes with which the author is connected, and perhaps to stress a little the differences in the nature of the conditions to be faced. England actually presents one set of problems and the Continent of Europe another, since the character of the coals to be treated is entirely dissimilar, and the attitude of the coal industries towards coal preparation is also dissimilar. England for generations has been working by hand good seams of clean coal of the highest possible quality and has not felt any pressing need to clean its coal. Most Continental countries, however, especially in Central and Western Europe, have been working friable and often very dirty coals for so long that a washery is accepted as a part of the normal equipment of a colliery, with the result that the art of wet washing has reached a high state of perfection, particularly in Belgium and Germany. The advent of machine mining has intensified the problems to be faced in all countries, and in England has been coupled with the working out of the best seams in the older coal fields, thus bringing about the necessity of working thinner and dirtier seams with resultant difficulties as regards marketing the products, while Poland, with clean and well prepared coal, has in recent years been attacking established British markets in Scandinavia. In recent years, therefore, interest in coal preparation has been steadily gaining ground in England, although it has not yet reached Continental dimensions. Broadly speaking, the differences in preparation problems between England and the Continent boil themselves down to one of size. In England, for example, with the exception of the Kent coal field, the proportion of coal of a size less than ? in. to the coal less than 2 in. is very much less than on the Continent, and since the principal difficulties in dry cleaning lie in the fines it is easier to produce good figures on

Jan 1, 1931

Jan 1, 1969

By Robert E. Palmer

The Hawkesworth detachable drill steel shank and bit were invented by A. L. Hawkesworth, while he was a mechanical foreman for the Anaconda Copper Mining Co., at Butte, Mont. Mr. Hawkesworth died on June 16, 1925, at the time that his invention was practically a proved success. The first application for patents was made by him in November, 1918, and the bit is now being manufactured under patents issued in 1922 and 1923. The credit for its development in the early stages belongs to A. L. Hawkesworth, Roy S. Alley, Harry A. Gallwey, E. J. Bowman and various officials of the Anaconda Copper Mining Co. Later improvements, manufacturing problems and the direct usage in the mines were originated and perfected by the mechanical department under C. D. Woodward, E. R. Borcherdt, head of the Rock Drill Equipment Department, Robert E. Kelly of the Mechanical Department, and various operating department heads of the Anaconda Copper Mining Co. The author wishes to acknowledge the assistance of these officials in the preparation of this paper. Comparison of Costs Using Regular Drill Steel and Detachable Drill Steel In 1922 production was satisfactory and sufficient enough to warrant a complete installation in an operating mine. The study and tests were made at the Badger State mine, the production of which averaged 1200 tons of ore per day. E. R. Borcherdt, head of the rock drill equipment department, was in direct charge of the trials, installation, operating problems and records during the entire .period, arid still continues in that position. This mine is a typical Butte mine, operated through a standard four-compartment shaft, served by a double drum hoist and an auxiliary hoist. The texture of the ground and ore has all the variations from soft to very hard granite and sulfide ore with production from levels between the

Jan 1, 1930

Jan 5, 1976