Search Documents

By John B. Hastings

The origin of the watery vapors of vulcanism has always been an object of interest and speculation to the seismologist, and as theories of the genetic origin of ore-deposits have of late years been pretty well narrowed down to the expiring forces of plutonic action, the same question has attracted mining engineers and geologists, as is well shown by the discussions of the subject in our Transactions. The important part taken by volcanic emanations in the origin of pegmatites and quartz-veins, described in my paper, Origin of Pegmatite,' and their latent power to concentrate into useful deposits such scattered gold as occurs in the Hartsel granite, make a discussion of their derivation but a natural third and final step. It is coilceded that enormous amounts of vapor accompany vulcanism, though perhaps we are apt to forget that steam has 1,700 times the volume of water, besides which the column seen over Vesuvius and other volcanoes is greatly mixed with air; the immensity of such volumes compared with solids and liquids is shown by the experiment of Gautier, who, by heating dessicated granite to 100' C., evolved from it gases 20 times, and steam 90 times, its own volume. Dana appraised the average amount of water left in ordinary rocks as 2.5 per cent. T. M. Read estimated that the Mississippi river carries to the sea annually 150,000,000 tons of rock material. If these Mississippi sediments, as deposited, contained 20 per cent. of water, it would be 600,000,000 cu. ft., or 4,500,000,000 American gallons, annually. Allowing the vapor suspended over a volcanic cone to be mixed with 80 per cent. of air, this amount of water converted into steam would replenish anew, every 9 min., a column 15,000 ft. high, 2,000 ft. in diameter at the base, and • 10,000 ft. at the top. Read's estimate is only half of the amount given in a more recent and probably correct one.2

Jan 1, 1909

By W. R. Hibbard, J. D. Nisbet

The high temperature properties of Fe-Cr-Co-Ni base alloys and the effects of hardening element additions on these properties are rationalized on the basis of general principles of alloying. DURING the past few years the base elements in high temperature austenitic alloys have gradually been changed from iron-rich materials to nickel-rich, then to cobalt-rich and more recently to various iron, cobalt, and nickel combinations, all with an approximately constant chromium content of 20 pct. Concurrently, the hardening additions of the incongruous* elements, have been shifted from small amounts of a single element to various ratios of molybdenum, tungsten, columbium, carbon, titanium, and aluminum with the percentages of these constituents continually increasing. It has been known that the typical soft high temperature alloy (such as Inconel) consisted of face-centered cubic austenite, but the effect of varying the composition of the base elements, iron, chromium, nickel, and cobalt, has not been broadly analyzed. Therefore, it was reasoned that the first major problem in the understanding of the properties or the further development of high temperature alloys was to study systematically the effect of composition upon the mechanical properties of face-centered cubic Fe-Ni-Co-Cr austenitic solid solutions. The matrix of the strong high temperature alloys (such as Inconel X) is usually also a face-centered cubic solid solution of iron, nickel, chromium, and cobalt but with additional phases which can be generally classified as intermetallic compounds and carbides. It is usually observed that combinations of the hardening elements, tungsten, molybdenum, columbium, tantalum, titanium, aluminum, carbon, and others have been used in these strong high temperature alloys. Thus, it was reasoned that a second major problem in studying these alloys was to understand the effect on mechanical properties of adding

Jan 1, 1954

By Duncan MacVichie

THE iron fields described here are located in the Iron Springs and Pinto Mining districts, Iron County, Utah. This region is in southwestern Utah, about 260 miles south from Salt Lake City, and is reached by the Los Angeles & Salt Lake railroad of the Union Pacific system. The iron fields lie at an elevation of 5500 to 7500 ft. above sea level, and are essentially desert in character. They are covered with a light growth of sage brush, piñon pine, and scattered cedar. Weather conditions are unusually favorable for all-year mining operations, the winters being mild with little or no snow; and the summers not excessively hot, the temperature rarely rising to 100° during the day, while the nights are invariably cool. The iron-ore bearing area extends from the Iron Springs district to the Iron Mountain mining district, being approximately 25 miles long in a northeast-southwest direction, and from 1 to 3 miles wide in a northwest-southeast direction. In the Iron Springs and Pinto mining districts, the ore occurs at various points around three sides of Granite Mountain and Iron Mountain. This is readily understood by reference to Figs. 1-4. These mountains are composed of andesite, which has been forced up through the surrounding sedimentary formation, in the form of laccoliths. An extensive report on the geology of these districts was made by Leith and Harder,1 who state: The three dominating geological features of the district are three large andesite laccoliths which constitute the Three Peaks, Granite Mountain, and Iron Mountain; lying in a northeast-southwest line across the area in question. Three unconformable sedimentary series, aggregating 4000 ft. in thickness, outcrop in successive rings around these laccoliths, dipping outward asymmetrically, very steeply at the contact, less steeply further away. Still farther from the laccoliths, lava-flows 2000 ft. thick rest in nearly horizontal attitudes on the tilted sedimentary rocks. These general relations are modified by faulting. All of the rock formations of the district are more or less covered on the middle and lower slopes by unconsolidated and partly consolidated erosion debris, both aqueous and subaerial, which spreads out on the lower ground to make the deserts.

Jan 7, 1925

By L. R. Jackson

It is convenient to have a consistent system of notation that will allow the representation of the entire range of complex stresses from hydrostatic compression to hydrostatic tension on plastic flow in a single diagram. Such a system is provided by making use of the fact that any complex stress system can be resolved into a hydrostatic tension or compression and a pure shear. Consider a stress system having the principal stresses This system can be resolved into a new system consisting of the three components and three pure shears. If Sm is positive, the net stress effect is hydrostatic tension; if it is negative, the effect is hydrostatic compression. In order to produce a systematic notation, a quantity that will be referred to as the "triaxial ratio" will be defined by the equation _ Sm Tr = Sm - Sm is given by Eq. I and Sl is the absolute magnitude of the largest principal stress without regard to sign. Table I lists the triaxial ratios for various common systems. Table i.—Triaxid Ratios for Various CommonSyslems Triaxial Ratio Stress System Tr Hydrostatic compression — SI - —St - -S³............................... -1 Torsion or shear -SI - S². S² = O..... O Simple tension SI. SI = SI = 0......... +0.33 Biaxial tension SI = S² S³ - 0......... +0.66 Hydrostatic tension +SI - +S³ = +S³. +1.00 Representation of Strains Strains will be plotted as "true" strains according to the system proposed by Ludwik.1

Jan 1, 1945

By W. Lawrence Austin

It has been suggested to me that some data, bearing on the treatment of silver ores in Southern Arizona, would be in accord with the objects of the present meeting. I have, therefore, made a few notes, gathered from practical experience at some of the best known works of that district. Presuming the general arrangement of a silver mill to be familiar to members, the subject having been repeatedly brought to the notice of the Institute, it is my aim in the following description of the modus operandi at the different mills to which I would invite your attention, to give simply such salient points of the apparatus as have a direct bearing upon results, together with the cost of materials, labor, etc. I have gone somewhat deeply into detail in my descriptions of machinery, thinking that possibly some of our members engaged in this branch of the profession might find something of interest among them. In an industry such as silver milling, where the various works are scattered over a vast extent of territory, and the conditions under which results are obtained are subject to the greatest variations, it is essential to go into rather minute details in describing plants, processes, etc., in order to afford a clear idea of the operations. Not only should results be given, but also the means by which such are attained. The milleralogical and chemical constituents of the ore, and its physical properties, throw a flood of light upon the success or failure of a process Figures representing totals I have subdivided as much as possible, so that the cost per ton for labor, castings, chemicals, etc., are apparent. Unless all these Factors are known, no accurate comparison can be drawn, since in this branch of metallurgy, more perhaps than in others, the weakness of any one link in the chain of operations demoralizes the remainder. That it costs $10 to mill in one

Jan 1, 1883

By M. N. Shetty, A. C. D. Chaklader

RECENTLY, it has been demonstrated that a considerable densification and interparticle bonding can be achieved if a pressure is applied to a powder compact while the material of the compact is undergoing either a decomposition reaction' or a polymorphic transformation.' The term "reactive hot pressing" has been coined to identify this process in which a phase change is combined with pressure to achieve interparticle bonding. This process is based on a principle which postulates that there is an enhanced reactivity and mobility of the molecular species at the phase-transformation temperature and this effect is utilized for interparticle bonding in powder compacts. This note summarizes the results obtained in an attempt to utilize this technique to produce ceramic-metal composites. In this case, a decomposition reaction of a compound (which after decomposition yielded an oxide) was used to achieve interparticle bonding in ceramic-metal composites. The reactive hot pressing was carried out in a Phillips induction heating unit, using either a graphite or a high-temperature steel die which functioned as both the susceptor and the hot-pressing component. The die was heated to the desired temperature in a helium atmosphere. All cermets produced by this technique were based on alumina as the ceramic phase. Different metal phases such as iron, copper, and chromium were used to study the effect of varying the metal phase on the properties of the composite. a Mono-hydrate (Boehmite) was mixed with different proportions of metal powders (-325 mesh) in dry condition in a mortar and pestle. No special precautions were taken for proper mixing. The mixtures were then compacted into a cylindrical form having an approximate dimension of 1 cm in diameter and 1 cm in height. For this compaction an ordinary

Jan 1, 1965

By Rodney P. Smith

The rate of motion of the boundary between a single-phase a-iron region and a two phase a-iron plus ?-iron, or a-iron plus cementite region has been measured on decarburization at several temperatures between 500" and 865°C. These data, together with data for the carbon content of a-iron at the boundary, yield the diffusivity of carbon in a-iron. The activation energy for carbon diffusion is 19.8 kcal per mole for the temperature range —50° to 150°C and increases to an average value of 23.0 kcaL per mole for the temperature range 727" to 865°C. AS part of an investigation of the diffusivity of carbon in iron using a steady-state method,' the diffusivity of carbon in a-iron was determined at the temperatures 802" and 851°C. The diffusion constant thus obtained was larger, by nearly a factor of two, than that predicted from the combined results of stanley2 and of Wert.3 It seemed desirable, therefore, to continue the investigation. Since the temperature range in which the steady-state method can be conveniently used is limited, we have chosen a decarburization method, based on the laws of diffusion in metal accompanied by a phase change.4,5 If the initial carbon content of the Fe-C alloy is such that two phases coexist at the decar-burizing temperature* and decarburization is car- ried out such that the surface is maintained at substantially zero wt pct. C, the carbon distribution after a time, t, will be as shown in Fig. 1. The boundary between the single-phase and two-phase regions moves from y = 0 to y = x in the time, t, where x is proportional4 to tl". If the initial carbon (content of the sample is Ci, and CB is

Jan 1, 1962

By C. A. Eligwe, F. W. DeVries, A. E. Torma

This study is an investigation on using hydrogen peroxide for tank-leaching of uranium with sulfuric acid. The optimum sulfuric acid concentration was found to be 0.03 mole 11 -'for a 25% pulp density suspension. The order of reaction with respect to sulfuric acid concentration was found to be ns0.75. The best results vith hydrogen peroxide were obtained at a 4.64 molar ratio of 6202 to U in the ore. The order of reaction was found to be zero with respect to hydrogen peroxide concentration. The theoretical maximum rate effect of Hz02 on uranium extraction was derived as Vm = 8.15 x mole &-'min-'. The highest rate experimentally attained was 8.09 x mole kL'min-'. It was found that the uranium extrac- tion was not affected by the pulp density up to the 50% used in this study. However, the final yieldswere significantly higher (over 90%) for leaches carried out in the presence of Hz02 than (less than 90%) for leaches carried out in the absence of H202. The reaction was found to follow a first order course with respect to substrate concentration (pulp density) regardless of the presence of H202. The effect of temperature was more explicit at moderate tempetatures (30 to 55 C) than at lower (10 C) or at higher (70 C) temperatures. At this latter temperature an almost complete extraction was realized even without H202. The apparent activation energies were found to be AEa = 2.68 kJ mole-' in the absence of H202, 0.5 kJ mole-'with Hz02 at 40 C to 70 C. and 4.72 kJ mole-' with Hz02 at 10 C to 40 C. All these activation energy values suggested that the uranium extraction process is diffusion controlled regardless of the presence of H202. Further, the change in activation energy in the presence of Hz02 indicates the possibility of change in the reaction mechanisms at lower and higher temperatures.

Jan 1, 1980

By Joseph Pogue

THE past year in the petroleum industry was one of overproduction, rising inventories, low prices, and meagre to vanishing profits. This outcome was the result of a long period of intensive and uncompensated effort on the part of both financial and industrial interests, to stimulate supply on the theory that the primary problem facing the petroleum industry was the development of an adequate reserve of raw material to protect a large and ever-growing investment. The stimulus was applied in various forms and through diverse channels: capital had, long flowed into the industry in excessive amounts under the attraction of large expected profits; the price level for crude petroleum had persistently been influenced -by speculative considerations, with the result that prices declined slowly in periods of flush production and were quick to advance in anticipation of statistical improvement, thus maintaining a superfluous degree of stimulus on wildcatting and on drilling; speculation in inventories had led to the unsound, or at least unusual, business practice of accumulating huge stocks of oil; and, above all, the industry had directed the potent force of technology to the expansion of supply and achieved radical results in accelerating oil discovery, speeding up the rate of oil extraction, and enlarging the recovery of gasoline and lubricating oils from the raw material. In short, the economic conditions of 1927 were exactly those to which the objectively driven enterprise of the petroleum industry had long been directed; and the undesirable financial consequences arising. therefrom reflected no lack of success in what had been set out to be achieved, but rather the failure to have established concurrently the necessary means of economic control to prevent the immediate conversion of reserves into current supply, and likewise the oversight in neglecting to apply the technological force to the enlargement and diversification of the market for petroleum products. Perhaps, when viewed in its longer perspective, 1927 will stand out as the turning point in the economic policy of the petroleum industry, when the technique of rationalizing production made its, initial claim for recognition.

Jan 1, 1928

By Wilhelm Flesch

THE object of development work in the field of gasification is to find a process by which all' fuels, regardless of their individual properties, can be gasified economically. This paper describes the development of the Winkler process. The economy of the gasification process depends not only on the degree of the gasification effect but also, to a decisive extent, on the costs of fuel, production, and installations. Fig 1 shows the relation between fuel costs and gasification efficiency for various types of fuels. Since the fuel cost in the gasification of coke amounts to two thirds of the price of gas, and the thermal unit in brown coal costs only one third of what it costs in coke, it is easily seen how profitably cheap fuels can be gasified, especially if these fuels require minimum preparation and gasification is done in the vicinity of the mines. These possibilities were a great advantage of the Winkler generators, which were installed 20 years ago in the central German brown-coal fields and, at that time, were without rival for the gasification of finely divided fuels. In the Winkler generator (Fig 2), crushed and ground solid fuels were, for the first time, successfully gasified with oxygen and steam on an industrial scale. Unlike the usual processes formerly employed on an industrial scale, this gasification, which proceeds continuously in the glowing, seething fuel bed, makes only extremely low demands on the fuel. The fuel no longer has to be in lumps and abrasion-resistant, but must be capable of reaction and must be fed into the generator in a grain size of 0 to 8 mm. Brown coal or bituminous coal, or their low-temperature cokes, can be gasified in the Winkler generator. Large plants using fuels are operating on an industrial scale in Europe and in Japan. Table 1 shows the results obtained by gasifying these, fuels in Winkler generators. The thermal efficiency of gasification, which is the relation between the calorific value obtained in the gas produced and that of the fuel consumed, gives no indication of the quantity of steam generated in gasification. The generation of steam in the waste-heat boiler of the Winkler generator adequately-covers the steam consumed in gasification. To obtain effective gasification in the Winkler process, combustible mate-

Jan 1, 1953

By O. A. Knight, Helmut Muller-Stock

The suppression of the austenite-martensite transformation that can be brought about by the addition of certain alloying elements, such as manganese or nickel, to plain carbon steel has been known for a long time, especially since Guillet's investigation at the beginning of this century. The extent to which the critical range is lowered depends upon the percentage and nature of the special element added. First the Arl point is lowered gradually, then at a certain percentage a sudden lowering to about 300" C. occurs. The addition of still larger percentages of the alloy may result in lowering the Ar, point to room temperature or below, in which case the steel remains austenitic at room temperature, especially after rapid cooling. The effect of alloying elements of this general type on the lowering of the transformation temperature is well illustrated by Sauveur(lJ$ in his Fig. 281a, reproduced here as Fig. 1. This type of curve is characteristic of both manganese and nickel though it requires about 21/2 times as much nickel as of manganese to produce the same result. The influence of nickel in retarding the transformation of austenite into the lower transition constituents is due to its lowering of the critical range of the steel, which is also well illustrated by Sauveur'l) (after Osmond) in his Fig. 284, reproduced here as Fig. 2. Scott('" presents a diagram illustrating the effect of manganese on the Ac3 and Ara points which is strikingly similar to the diagram above referred to in Fig. 2 concerning the effect of nickel. Lowering the critical range has the effect of increasing the viscosity, or, rigidity, of the alloy at the time when it is undergoing its transformation, which greatly slows down the transformation reaction velocity, and this, in turn, makes it easier to suppress, wholly or in part, the transformational changes. Reaction rates are normally much slower at low

Jan 1, 1934

By Eric Jette

IN thermodynamic studies of gas mixtures and liquid solutions, the respective problems have been greatly simplified by the use of two general limiting laws; Dalton's law of partial pressures and Raoult's law. It is generally recognized that these two laws have a common physical and chemical basis which may be stated as follows: The law may be expected to be strictly valid only for systems in which the different molecular species are so nearly the same in their physical and chemical properties that a molecule is unable to recognize whether its neighbor is one of its own kind or not. Positive and negative deviations from both laws are frequently encountered. The occurrence of negative deviations in both gases and liquids is ascribed to attractive forces which, in the more extreme cases, may be so large in magnitude and so highly specific in character as to lead to the formation of definite chemical compounds. Positive deviations in gases develop only at higher pressures where the intermolecular distances are so decreased that factors such as molecular size and shape, which ultimately become concerned with the repulsive forces, come into play. In liquid mixtures, positive deviations are generally considered as due to differences in the symmetrical (nonpolar) fields of force which surround the various molecular species and which are supposed to give rise to a tendency for each species to associate with its own kind and thus to "squeeze out" the other variety. Fundamentally this also involves the existence of repulsive forces between unlike molecules. If the fields of force are unsymmetrical (polar) a tendency towards compound formation results. Stated in more exact terms, strict adherence to the law means that the "activity" (or any adequate measure of this quantity) of a component in a mixture is a linear function of the molecular (or atomic)

Jan 1, 1934

By E. A. Koester

Kansas produced approximately 35,434,000 bbl. of oil in 1932 compared to 37,018,000 bbl. in 1931, a decrease of 1,584,000 bbl. or 4.2 per cent. These figures do not indicate the amount of oil that could have been made available from the state for the year. Many of the fields discovered during the year and some discovered in previous years were entirely shut in. Practically all flush production discovered within the last two years has been prorated in some manner or other. Probation Kansas production is under regulation as specified in House Bill 387, passed by the legislature in 1931, which became effective when published May 28, 1931. The principal features of the law are the prohibition of waste, including gas energy, the regulation and prevention of discrimination of purchasers, the marketing of oil ratably from wells in each field when the daily production is above 15 bbl. per well. This act gives the enforcing powers to the Public Service Commission. The Commission, having many other regulatory duties, appointed an Oil Advisory Committee, which, with the aid of the State Umpire, keeps records and makes recommendation for orders as to specific regulation of fields and conditions in each field. At the time the Commission was given authority to regulate production and marketing in flush fields, several of these had already been under voluntary proration and marketing restrictions by agreement of the operators. These gradually came under the control of the Commission by mutual consent. It is the policy of the Public Service Commission to follow the will of the operators so long as they do not have ideas or plans in conflict with the law. The cost of administration of this law is assessed against the operators according to the amount of oil taken from the fields in which ratable taking is necessary. There is a feeling that the whole state should share this expense, which is small, since it is beneficial to the older fields by assuring them 100 per cent market for their output by restricting the flush fields.

Jan 1, 1933

By R. F. Mehl, M. Gensamer

Creep investigators have made extensive studies to determine the interrelation of stress, temperature and the tensile creep rates of metals. It has been suggested that at small stresses the secondary or constant creep rates obey a simple viscous law. Building upon this suggestion, departure from pure viscosity as stress increases may be expressed mathematically as a consequence of reversibly altered viscosity or "flowability" in the same sense that temperature change reversibly alters viscosity. From the index to alteration of viscosity, a value for the energy of secondary creep may be derived having the magnitude of the free energy of vaporized metal. The suggestion is made that application of stress alters the energy of secondary creep. Strain energy is argued to be but a minor factor in the energetics of secondary creep. A deformation mechanism involving the large energy associated with secondary creep implies a sort of solid self-diffusion process. Evidence indicates that creep strain above the recrystallization temperature takes place by crystallographically directed self-diffusion at grain boundaries and points of crystal defects. A self-diffusion theory of secondary creep is proposed, embracing the principles of the Dushman-Langmuir theory of solid diffusion. An equation is suggested whereby the rate of tensile creep may be related directly to the physical and structural character of the solid metal. Basis of Investigation Much of the investigation that has been given to the creep characteristics of metals and alloys has been directed toward studying the dependence of creep rate upon stress. Great interest has centered upon the approximately uniform rate of flow that has been demonstrated for numerous metals and alloys. At temperatures above the strain-hardening ranges of materials, this uniform rate frequently is attained after a relatively short period of initial rapid flow, and the period during which it persists determines for most practical purposes the useful life of the

Jan 1, 1938

By Tracy Jarrett

IN making gold alloys possessing certain physical properties, such important factors as corrosion resistance, color, hardness and melting points must be considered. All of these requirements depend directly upon the composition. It is possible to obtain the same colored gold alloy by using different compositions, but in doing so one may bring in some undesirable property. Other investigations have been carried on in this field by F. E. Carter,1 E. M. Wise,2 and L. Sterner-Rainer.3 To make a complete study of the effect of composition upon these properties, a systematic investigation was carried on involving a range of copper content from 85 to 65 per cent. Elements such as zinc, silver and nickel were used to replace in part the copper content. The gold content in all the alloys remained constant. Only 10-karat gold alloys of those containing 41.6 per cent gold will be considered. All of the alloys were made in an induction furnace. Each alloy was cast in a 3 by ¼ by ¾ -in. ingot. The method of obtaining the melting points and making color determinations was described in a previous paper.4 The Rockwell B scale with the ball and 100-kg. weight was used for all hardness determinations. The submersion of test pieces in concentrated nitric acid is one of the standard corrosion tests used in the optical trade. A test piece in the 50 per cent cold-worked condition, ½ by 2 by 0.043 in., is blanked from a strip using a. die, and the weight, loss per square inch of surface is taken as a means of comparison. The time for this test is 2 ½ hr. of actual sub-mersion of the test piece in the acid. This standard test was applied to all of the 10-karat gold alloys discussed in this paper. The tensile tests were made upon strips of the dimensions shown in Fig. 1. The test pieces after blanking were annealed at 1300° F. for 20 min. and cooled in air. The "drop of the beam" method was used in determining the yield point, as there was a very marked "drop" when the yield point was reached.

Jan 1, 1939

By Joseph W. Roe

MaNY questions arising in the work of the mining engineer may be solved quickly and with suffcient accuracy by the methods of descriptive geometry; but, unfortunately, this subject is more often considered from a mathematical view-point than as an effective tool for solving practical problems. Some of the principles involved are merged into the ordinary operations of mechanical drawing, and are used unconsciously by the engineer in his every-day work. The rest are stowed away on the book-shelf with his forgotten or rarely-used college text-books. One reason for this condition of " innocuous desuctude " may lie in the uifortunate and often cumbersome notation which it has been found necessary to introduce. If some of these principles can be recalled to the engineer's attenti011 in terms of' every-day use they may prove of practical hearing. Recently, in talking with several mining engineers, I used some of the drawing-room methods of a machine-designer, to the evident surprise of those around me. These men were perfectly familiar with the methods, but their application to mining-work had not occurred to them. At their suggestion the present paper is offered, not in ally way as a treatise, but merely to suggest a certain point of view, in hope that it may lead others far more familiar with mining-problems to pursue the subject further. I. To Find the Strike. As the simplest and most fundamental problem, let it be required to find the strike of a vein when the location and elevation of three points on the outcrop are known. It mill be assumed for the present that the rein is a plane.

Jan 1, 1911

By Arthur Knapp

The ordinary well log is subjected to a great deal of criticism, much of which is well founded. Sometimes, though, the difficulty in interpreting the log is due to the fact that the geologist or engineer using the logs does not know the limitations of the drilling method used. The rotary drill, especially, has inherent limitations that make it difficult to secure definite information at all times. The identification of well-defined key beds is about all that can be expected from the rotary log. The formation in a drilled hole, as reported by the driller, has a direct relation to the speed with which the drill makes the hole or to the reaction of the various strata on the bit, called the "feel of the bit." When this is not thoroughly understood by the geologist or engineer endeavoring to interpret the log, the result is an erroneous correlation with other wells or a discarding of the log as worthless. General Terms Hard and Soft.—Hard and soft are relative terms. In the case of well logs, they are very misleading as they are used in connection with both resistance to abrasion and resistance to percussion. In technical rock classification, hardness is relative resistance to abrasion. The term brittleness is used in connection with resistance to blows. These terms are misleading to the geologist or engineer who is not familiar with both the cable-tool, or standard tool, method of drilling and the rotary method. In the case of the standard tools, the driller's report of the hardness of the formation is in terms of its resistance to blows. For instance, a cable-tool driller might be able to make from 30 to 50 ft. a tour in a brittle limestone, which he would call soft and at the same time he might call a relatively soft (from a purely mineralogical standpoint) gypsum hard, because it is somewhat elastic and is not readily broken by blows. The rotary driller would reverse the terms. The limestone is hard in that it resists the abrasive action of the bit, while the gypsum might be soft in that it is readily cut by the rotary bit. It is rare that wells drilled by the standard tools are correlated with those drilled by the rotary, but the technologist who has worked with well logs from one system might be misled when working with the other.

Jan 1, 1921

By Robert A. Stansbury

Keeping development ahead of retreat mining is a problem which occurs nearly everywhere longwall mining is used in the United States. As improved equipment technology has allowed the application of longwall mining to more difficult mining conditions, and with higher retreat rates, the problem has become more critical. Many factors determine development speed, including roof and floor conditions, mining heights, seam heights, and the number of entries. In an effort to maximize the rate of development and production from development sections, U. S. Steel's Gary District has used five entry, three entry, four entry and is planning two entry development panels at its different mines. With the introduction of various types of shield supports, it is now possible to utilize longwall mining in higher coal over 3 meters (10 feet), lower coal under one meter, in difficult roof conditions, and with soft floor. Improved shearers of 300 KW (400 HP) and more make cutting heights over 3 meters (10 feet) possible, and off pan shearers and improved Gleithobel plows make cutting less than 1 meter (40 inches) seam height possible. Longwall mining under these conditions puts an added strain on the ability to develop panels as fast as they are retreated. Poor roof conditions require a substantial amount of additional roof support to ensure that roof control in the head and tall entries will not hinder longwall retreat. The additional measures of longer bolts, resin bolts, point anchor resin bolts, roof mats, roof trusses, steel or wood cross bars, and roof grouting all place an additional burden on man power, installation time, and cost on the mining cycle. Additional roof bolting on development can cut the potential mining rate in half, and any roof falls cause significant delays to mining. Timbers and cribs can restrict ventilation and require more entries. Soft floor conditions can greatly impede development through tramming difficulties with shuttle cars and roof bolters, time required for cleaning and repairing roadways, and maintenance difficulties on equipment. High coal sometimes requires rib support to be Installed during the mining cycle, further cutting the mining rate. Mining low seams requires that roof or floor be mined in the head and tail entries as well as the track or tractor roadway entry to provide clearance of the longwall equipment. Mining this rock slows down the mining rate because of the extra material being mined and the extra wear and tear on equipment. To a large degree these conditions effecting development speed cannot be controlled.

Jan 1, 1981

By L. D. Jaffe, John H. Hollomon

Fox many steel parts it is desired to obtain the maximum toughness consistent with the strength required by the mechanical design. It is generally recognized that the greatest toughness at any given strength is found in steels having a tempered martensitic structure,1 and is virtually independent of the composition of the steel2 (except for carbon). The choice of the composition of a steel for the parts in question should be based, therefore, on hardenability considerations and on manufacturing facility and economy. In a recent paper3 the concept of hardenability was discussed and a somewhat new approach to the problem was suggested. The hardenability was defined in terms of the cooling conditions (speed of cooling) required to avoid the pearlite and the bainite reactions. Since all the alloying elements do not have the same effects on the two reactions, the bainitic and pearlitic hardenabilities must be considered separately. In order to design a steel for a given part, it is necessary to design a composition that has both sufficient pearlitic and sufficient bainitic hardenability. However, this requirement does not fix the combination of alloying elements to be used; an infinite number of steels would have the required hardenabilities. Other considerations limit the choice. For example, decreasing the carbon content increases the toughness at a given hardness, and for this reason low-carbon steels are often desired. Limitations or requirements of refining, casting, or forming practices often affect the level of some of the alloying elements. Price considerations enter. Frequently, however, it is very desirable to minimize the tendency toward quench-cracking while maintaining the necessary hardenability. This paper is concerned with suggesting a method for choosing compositions that will have the required hardenability together with minimum tendency toward quench-cracking. QUENCH-CRACKING Since only the case in which the entire part will transform to martensite in the particular quench employed is being considered, the analysis of the quench-cracking problem is somewhat simplified. Quench-cracking arises from the temperature gradients existing throughout the piece during cooling. Because of these temperature gradients, the contraction arising from the decreasing temperature and the expansion arising from the austenite-martensite reaction do not occur uniformly over the parts, and stresses are set up that tend to cause cracking. The temperature gradients can be reduced by decreasing the severity of quench. This, however, requires that the hardenability be correspondingly increased by increasing the carbon or alloy content. An

Jan 1, 1946

By George Watkin Evans

The need for mechanization in coal mining wherever it can be successfully introduced is evident when we take into account the fact that during recent years the coal-mine employee's wages have increased and his hours have been shortened. Coal is no longer King, and a brief study of statistics covering the production of coal, petroleum and natural gas and the development of water power will convince anyone that coal has had very powerful competitors during the past 10 years. Petroleum production in the United States between 1918 and 1936 increased from 100 per cent to 309 per cent. Water power increased from 100 per cent in 1918 to 270 per cent in 1936. Bituminous coal slipped from 100 per cent in 1918 to 75 per cent in 1936. The anthracite industry slipped from 100 per cent in 1918 to 50 per cent in 1932, but climbed to 55 per cent in 1936. In 1918, the State of Washington produced a little over four million tons of coal and the production of California oil, at that time, was a little less than one hundred million barrels per year. By 1929 the production of California oil had increased to a little over 292,000,000 bbl. or nearly 300 per cent as compared with 1918. By 1934 the production of coal in the state of Washington had dropped to about 1 1/3 millions of tons per year. Our neighbors in British Columbia had their coal production reduced from a little over 2 1/2 million tons in 1920 to less than 1 1/3 million in 1933. The North western Improvement Co., a subsidiary of the Northern Pacific Railroad Co., owns coal properties in various parts of Washington and Montana. The Northern Pacific is one of the very few railroads using any considerable quantity of coal in its operations. Practically all of the American railroads in the Pacific Northwest, except the Northern Pacific, are using cheap California fuel oil or electricity. This problem, of course, is not a new one in coal mining, and all of the progressive coal companies in the country have tried to meet competition from an overproduction of petroleum and an overproduction of natural gas as well as enlarged developments of hydroelectric plants.

Jan 1, 1938