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By D. A. Woodford

In a constant-load creep test, if the density of nlobile dislocations is assumed constant for strains exceeding that corvesponding to the minimum creep rate, it is shown that the creep rate may be approximated by the equation where E is the nominal strain, o0. is the initial stress, and a' the stress fov unit dislocation velocity. The constant C contains the mean density of mobile dislocations and n is a measure of the stress sensitivity of dislocation celocity. This equation is shoum to be applicable to published data on an alloy steel and on nickel. The degree of plastic instability and hence the creep ductility is dependent on the calue of n for these materials. When instability becomes gross and local macroscopic necking occurs, the assumptions are no longer valid. On the basis of this equation, and the strain-time relation derived from it, a method of predicting the creep behavior at different stresses is suggested. MOst analyses of creep data have been concerned with time-dependent transient creep or time-independ- ent secondary creep in constant-stress tests. The far more widely used constant-load test has been neglected in terms of a mechanistic approach. In general, since the strains involved are usually small, the same laws for transient creep may be applied to both types of tests. However, there is no steady-state creep in a constant-load test since the stress increases continuously. Any apparent steady state observed on a strain-time plot is either fortuitous or illusory, and is generally revealed as a continuously varying creep rate on a carefully constructed strain rate vs time plot.* Transient creep may be understood in terms of a simple differential equation representing the change in mobile dislocation density with time:' where p is the density of mobile dislocations. The first term on the right is related to first-order kinetics of dislocation multiDlication and the second to second-order kinetics of exhaustion. On the basis of this equation, several authors2-4 have found good agreement with experimental transient creep curves for a number of materials. When k1p = k2p2, a steady-state creep

Jan 1, 1968

By C. M. Fellman

THE over-all picture of safety in mining has been encouraging during the past few years, and in mining activities as a whole the trend in accident occurrence is downward. This is the more noteworthy when the type of labor used in mines during the war period is taken into consideration. The drafting of young mining employees into the armed services and the departure of others for work in other war industries took a heavy toll of young, husky, active men. Their places were taken in large part by older men who returned to the mines, or by inexperienced men with little if any knowledge of mining. Despite the lack of labor and especially of skilled labor, and the difficulty of obtaining new equipment as well as maintaining and replacing worn or broken equipment, and numerous other difficulties the mining industry not only reached and maintained maximum production but made the increase with little if any sacrifice of safety. In fact, in many instances better safety records were. established than in normal

Jan 1, 1946

By Henry F. Cooper, Lee Burford, John C. Thompson

In the past year or two, considerable effort has been expended to calculate the spherical wave propagation phenomena associated with explosions in a "hard rock" medium (Godfrey, 1969; McKay and Godfrey, 1969; Burford, et al, 1970). This effort was stimulated primarily by the recognition that early calculations predicted peak particle displacements which seriouly disagreed with field data. In most of the calculations mentioned above, rock was modeled as an inelastic continuum (see for example Isenberg, et al, 1970 for some recent results using "classical" elastic-plastic material property models). However, several investigators (Handin, et al, 1967; Cherry, et al, 1967) have shown that the simple classical yield surface models cannot simultaneously account for the observed brittle failures of intact materials under compression, extension and torsion. One approach to more correct modeling of dynamic rock behavior is to make the inelastic model more and more sophisticated. For ex- ample, recent experiments at the University of Utah (Swanson, 1969) have suggested possible modifications to the yield surface model that could better account for the ductile behavior of intact granite sam- ples under various states of stress. The approach followed in this paper proceeds in an entirely different direction. We want the physics which is built into our conception of rock to be as simple as possible while at the same time reproducing the most important features of rock's behavior. Therefore, we abandon the requirement that rock be treated strictly as a continuum. Instead we consider a "discontinuous" model in which one of the most significant characteristics of rock is treated..

Jan 1, 1971

By Orr Hamilton

VALUATION of a mine is an approximation of its true cash value which requires the application of fundamental principles of economics. Mines are valued from necessity, for the following reasons: (a) Transfers of titles. (b) Dissolutions of partnerships or corporations. (c) Mergers of mining companies. (d) Appraisals for the purpose of State and Federal taxation. (e) Establishment of the fact of worth as a basis of loans. (f) Determination of values as frequently required in litigation. (g) Listing of stock for sale by a reputable stock exchange. For the majority of purposes a valuation is required as at the present time, but for some purposes valuations as of bygone times may more nearly reflect the intrinsic worth of a mine because its subsequent history can never be, entirely ignored, but valuations made as at the present time are better indicators of cash values. Many mines with great intrinsic worth have been sold for small cash prices. The object of legitimate mine valuations is to deter-mine salable value, or that price in cash at which a transfer of the property from a willing seller to a willing buyer might be consummated, assuming that both vendor and vendee have knowledge of all pertinent data and that the owner, is not forced to sell at a sacri-fice-the definitions of fair market value precluding a forced sale.

Jan 11, 1923

By Colin C. Harris, Nathaniel Arbiter

The flotation operation can be analyzed in terms of three groups of variables. The first, largely independent of control by the operator, embraces the fixed physical and chemical properties of the ore minerals. The second includes all chemical and physical effects imposed on an ore after mining that influence its floatability. These can be either purposefully or accidentally applied. The third embodies the flotation-machine characteristics which realize the potential floatability of selected ore minerals in terms of grade and recovery levels. The machine effectiveness thus depends not only on its own contribution, but on the prior influence of all other variables on floatability. HISTORICAL DEVELOPMENT From the earliest days, flotation mills used many types of machines. Hoover 20 in 1914 mentioned as then important the Potter-Delprat tank for gas generation by acid, the DeBavay cones for skin flotation, the Elmore mixer and separation chamber for vacuum flotation, and his own modification of the Mineral Separation cell for the agitation froth process. Less important at the time were the MacQuisten tube and the Hyde cell. By 19274~ scores of machines had been developed and dozens had found their way into mills. From then on, however, under the scrutiny of competitive tests, many fell into disuse. Taggart in 19454~ classified processes broadly as skin flotation and froth flotation, dividing machines for the latter into the three categories: bubble column, pulp body, and combination.* Under 'bubble column' he listed all pneumatic, cascade, and subaeration cells; and under 'pulp body' those cells in which gas was generated by boiling, chemical action, and pressure reduction, as well as the agitation-froth type. At that writing skin flotation, the cascade machines, and all pulp body and combination machines were said to be extinct, leaving pneumatic and subaeration types dominant (u. S. practice). The process of elimination has continued to the present, with almost all pneumatic cells succumbing to the pressure of competition from subaeration machines. The only new machines to appear in recent years have been double-impeller types f and these have met with only limited acceptance.

Jan 1, 1962

By C. F. Willis

Many of the failures in vocational education are due to the fact that the educational methods were not designed to the capabilities, habits, and environments of those to be trained; rather they were based on the policy that education is education and lessons are lessons, whether for youngsters of fifteen or for men of forty. Vocational education among miners involves, first, a study of the men themselves, their habits, and the use of their leisure time; second, a study of the differences between the methods of teaching required for men and for children. Certain fundamental requirements of training methods for miners are reasonably universal and may be applied with success to any ordinary mining community. The rate of labor turnover is another consideration; it would be useless to design a four-year course for men who remain in one place only a few months. Length of Course The first consideration should be the length of the course. Few mining communities have a sufficiently stable population to make it possible successfully to carry on a course for over a year. While some men might complete a four-year course, the number is comparatively small compared with the number to whom a shorter course would be of service, and it is better to raise the standards of education even a little for a large number than to raise them to a high level for a few. It is perfectly possible to attain both objectives by arranging the courses in small units; all the units, when grouped together, should comprise a fairly complete course, yet any one unit should be complete in itself and of benefit to the workman. It should not take many of these units to make a miner or a timberman out of a mucker; but to do this the course should be short, because muckers seldom stay in one place long. By grouping a number of these units together it Would be possible for a miner to become a shift boss or a shift boss a foreman, and so on. As far as possible the units of the course should not be dependent on those preceding or following. The workman understands the completed job but he is not accustomed to carrying on several jobs at the same time and

Jan 1, 1920

By Gilbert Doan

AN extensive program of investigation is being carried out at Lehigh University in the study of arcs and arc welds of high-purity iron1, spon-sored by the Engineering Foundation. The part of that program reported in the present paper deals with welds made of high-purity iron in an argon atmosphere and for comparison with them welds made of the same iron in ordinary air. Welds of commercial steel also were made in argon and in air. The primary purpose of the study is to discover the basic physical constants of iron welds when not contaminated either by impurities in the iron or by the action of oxygen and nitrogen of the air during welding. Upon these constants can be founded such future studies as will determine what effects the various impurities and alloy elements present in steel have upon its welding characteristics, and what influence is exerted by the action of oxygen and nitrogen. The welding of steel involves such a multitude of variables, both of composition and of procedure, that development in the fabrication of this most important metal has necessarily been slow, wasteful, and in many instances discouraging. In the present investigation, the simplest possible condition has been selected; namely, iron practically free from contamination and a nonparticipating atmosphere, the inert gas argon. This simplification reduces the number of variables to a point where more rigid control of the system is possible. Although this study is significant for the contributions it makes to the science of steel fabrication, yet it is hoped that it will not be without value also in increasing knowledge of the nature and behavior of iron and steel in general. From the standpoint of open-hearth practice, and to

Jan 1, 1936

By George W. Healy, Ko Yamaguchi

In typical calorimetry the energy given off by a material under study is transferred to a water bath, whose temperature is sensed by a thermometer; for correct measurement the water bath must attain a uniform temperature to which the thermometer must respond. This introduces two sources of error, non-uniformity of the heat sink and a time lag until its temperature is registered. These errors may become important where a rapid process such as solidification of metals and alloys is being studied by means of Oelsen'sl quantitative thermal analysis. To overcome this difficulty, a calorimeter sink was conceived in which the water bath is replaced by a copper coil, which serves simultaneously as heat

Jan 1, 1967

By E. Teghtsoonian, K. G. Davis

Cobalt crystals of commercial purity have been tested in tension. Their resolved shear stress-shear strain curves are very similar in form to those for zinc, magnesium, and cadmium. There is an initial linear region for shear strains up to around 150 pct, the ratio of work hardening slope to shear modulus at room temperature being about 2 X x This is followed by an upturn, which is, PLASTIC deformation in metal single crystals with close-packed structures has been found strongly dependent on stacking-fault energy. The high stacking-fault energy hexagonal metals magnesium, zinc, and cadmium have been quite extensively tested, but up to now no data have been available for a comparable hexagonal metal with low stacking-fau1t energy' An however, smaller in magnitude for cobalt than for the other metals. Values for the critical resolved shear stress rise from 97 kg per sq cm at room temperature to approximately 170 kg per sq cm at -196 °C. The Cottrell-Stokes ratio is not constant either for variations in the strain rate or for temperature changes, its value decreasing with strain. investigation into the plastic deformation of cobalt, which has a very low stacking-fault energy, has therefore been undertaken. EXPERIMENTAL PROCEDURES Cobalt crystals in the form of rods 0.3 cm in diam were grown in an electron-beam floating-zone refiner at a rate of zone travel of 25 cm per hr. Details of the growing procedure are given in Ref. 1. The zoned cobalt rods had the following analysis:

Jan 1, 1963

By Christopher W. Schram, Allan B. Tanner, Frank E. Senftle, George R. Boynton, Philip W. Philbin

Abstract-A borehole sonde wing a 252Cf neutron source and a Ge(Li) gamma-ray detector was field tested in a coal bed in Belmont County, Ohio, to ascertain whether such a device could be useful as a coal-exploration tool. As the sonde was lowered into the borehole, successive spectra were accumulated over short time intervals. The intensities of the capture gamma rays from hydrogen and of decay gamma rays from aluminum were determined simultaneously in each spectrum. A log of the intensities versus depth shows the depth and thickness of the coal bed.

Jan 6, 1978

By P. A. Young

The historical background of on-strand cooling is given, together with a resume of recent practical developments. Laboratory test procedures are then considered in detail, for both productivity and quality parameters, with particular reference to the design of the Ravenscraig No 3 machine (Scotland). A heat transfer model is presented for a porous sinter with propagating cracks. The influence of cooling/sintering area ratio, sinter strength, granulometry, return fines, coke consumption and FeO levels are examined in relation to economics. A detailed comparison of capital and running costs for two different strands, designed for identical duties, but with off or on-strand cooling, is then given.

Jan 1, 1977

By Paul B. Barton

Unconventional mineral deposits are those that differ significantly from productive deposits in mineralogy, grade, or geologic setting. Thus, the initial representatives of each deposit type are, by definition, “unconventional” until they are exploited. The “unconventional” status changes to "conventional" because of economic shifts (e.g., bulk silver ores), because of technological innovations (e.g., froth flotation), or simply through the recognition of, and production from, novel mineral concentrations. Heretofore the discovery of new deposit types has been almost entirely accidental, but the long- established concept of the geochemical cycle provides a nearly untouched opportunity and challenge for the application of geochemistry in predicting novel, potentially economic, mineral concentrations.

Jan 1, 1983

By Karl Sundberg, Allen Nordstrom

Interesting results were recently obtained in geophysical prospecting at the Questa mine of the Molybdenum Corpn. of America in New Mexico. This paper describes that survey, which was carried out during October and November, 1927, by the Swedish American Prospecting Corpn. It is hoped that the paper will make it possible for the mining man to form an opinion of the applicability of geophysical prospecting under difficult conditions, showing, as it does, the results when prospecting for small small orebodies with comparatively poor conductivity, in a region of rough topography. Some principles underlying electromagnetic prospecting not known to be published previously will also be given in an elementary way, with special attention to the general structure of the electromagnetic field. Geological. Conditions at Questa The property is situated in the Taos range of the Rocky Mountains in northern New Mexico. About this region, L. C. Graton says:' The main range is made up of Pre-Cambrian granites, gneisses and schists but in the vicinity of Red River igneous rocks of later age are present almost to the exclusion of the older series. These younger rocks are divisible into two groups. The older of the two, probably Pre-Tertiary age, is represented by large intrusive masses of monzonite porphyry, usually containing considerable quartz. The more recent group comprises intrusive and probably effusive dark-colored andesites and coarse andesitic breccias, some of which contain fragments of the monzonite; there are also flows of rhyolite and beds of rhyolite breccia. The evidence regarding the relative age of the andesite and the rhyolite is not wholly satisfactory, but there is little doubt that the andesite is the older. The ore deposits, although occurring more commonly in the monzonite porphyry than in the rhyolite, nevertheless are believed to be genetically related to the rhyolite. They certainly cut the rhyolite or andesite in places, and hence fall in the late Tertiary. The molybdenite at the Questa mine occurs in veins in the alaskite granite porphyry belonging to the older part of the Pre-Tertiary eruptives. Overlying the granite porphyry is the granodiorite, capping the granite

Jan 1, 1929

By George A. Koenig

This new departure in assaying is the outcome of a long-felt desire to shorten the time required in muffle-assaying, as well as to do both crucible- and scarifi cation-work in one furnace. The first object in view was the gold-assay, which must always be a combination of the crucible- and muffle-work. The large lead buttons consume much time in their reduction by scorifying and cupelling. The Hoskins gasoline furnaces have been a great convenience, for years past, in that class of practice, where only one assay was required at a time. But even with them I found myself hampered, since the crucible-furnace only takes one crucible at a time, and my practice implies always duplicate assays. Another difficulty was to get the muffle up to the necessary heat and to maintain it at that heat. Whecever I had pumped myself into perspiration and out of breath, the question presented itself, " Is the muffle necessary to do this work properly ?" Hartmann and Plattner and all their blow-piping disciples have shown that very good results are obtainable by playing a direct flame upon the work-lead. Could this be done on the regular muffle-assay scale ? I placed a cupel upon a fire-brick, surrounded it with charcoal, and then played upon it with a Bunsen gas blow-pipe. The result was encouraging. With some care a 2.75-inch scorifier charged with 0.1 A. T. of a 100-ounce ore could be melted down and scorified without any apparent loss. I thought then of constructing a furnace with four blow-pipes in a row; but the combination of gas and charcoal seemed unpractical. Instead, I placed an F crucible, bottom up, in a Hoskins crucible-furnace. Upon this support I placed a charged scorifier. The rapidity with which a very refractory charge melted and scorified was simply amazing to me. Then a cupel was put in the place of the scorifier, the lid was moved sideways, and a blow-pipe was

Jan 1, 1899

By Cyril Smith

FOR several years an investigation has been in progress in the research laboratory of The American Brass Co. to determine the thermal and electrical conductivities of most copper alloys of commercial importance and several of scientific interest. This paper contains such data on the binary alloys of copper with silicon, aluminum, manganese and nickel, and on a large number of ternary or more complex alloys. Some inter-esting general relationships between the thermal and electrical conductivi-ties for all copper alloys at all temperatures are pointed out. The data for the copper-zinc, copper-phosphorus and copper-tin binary systems have already been published1,2 ? except for the electrical conductivity at 200° C., which is given in the appendix of this paper.

Jan 1, 1935

By Roderick K. Davey

Introduction in any business, it is essential that we select those alternatives which are not only technically feasible, but will be the most profitable to the business m terms of corporate objectives Some of the studies and activities requiring support of financial analysis to select the alternatives which most closely satisfy the management objectives and technical considerations are as follows 1 ) Cutoff grade determination. 2) Ore reserve estimation. 3) Production forecasts (long- and short-term) for an operating mine, development of a new mine, or expansion of an existing mine. 4) Evaluation of haulage alternatives. 5) Evaluation of equipment.

Jan 1, 1979

By Charles H. Behre

This paper deals with recent geologic studies in the slate belt of Northampton, Lehigh and Berks counties, Pennsylvania. The work was conducted under the auspices of the Pennsylvania Topographic and Geologic Survey. Three years have now been spent in detailed consideration of the economic geology of this region. In the field, particular attention was paid to the bearing of geology on quarry development and property valuation and the object of this paper is to summarize the results from that viewpoint. Excellent studies of a somewhat similar nature have already been carried out by Bowles,' but with the emphasis upon the details of quarrying and fabricating methods, rather than upon the geologic relations. The Northampton-Lehigh-BeRks District Location The region here discussed lies in east-central Pennsylvania and extends southwestward from Delaware River, on the New Jersey line, to the Schuylkill in north-central Berks County. It is an elongated belt occupying the northern sections of the three counties mentioned and lying along the southern edge of Blue Mountain. Its length is about 50 miles and its average width five or six, though in places it attains a maximum of 10 miles. There are no large cities in the region, but about 10 miles south are Reading, Allentown, Bethlehem and Easton. Railroads serving the slate belt are the Delaware, Lackawanna and Western, and the Pennsylvania along the Delaware River, the Lehigh Valley and Central of New Jersey along the Lehigh, and the Pennsylvania and Philadelphia and Reading on the Schuylkill. In addition, two railroads—the Philadelphia and Reading and the Lehigh and New England—cut obliquely through the slate region to reach the more isolated communities. Transportation facilities are thus excellent. The slate deposits of these three counties are conspicuously unified, both economically and geologically. In general type of marketable

Jan 1, 1928

By George B. Waterhouse

Jan 1, 1933

By A. R. Kinkel

THE Shasta copper-zinc district of northern California lies in the foothills of the Klamath Mountains at the northern end of the Sacramento Valley. It contains two main areas of base-metal ore deposits, the East Shasta and West Shasta districts shown in Fig. 1. The East Shasta includes the area from the Afterthought mine, near the settlement of Ingot on U. S. highway 299 East, to the Bully Hill mine, on the north side of the Pit River, 9 miles to the northwest. The West Shasta, a well-defined northeast-trending district about 8 miles long and 2 miles wide, west of the Sacramento River, Fig. 2, is the western part of the ore-bearing area formerly known as the Shasta copper belt. Referred to in the older writings as a copper arc, this belt was thought to form a crescent extending entirely around the head of the Sacramento Valley, the convex side to the north. Recent studies by the U. S. Geological Survey in cooperation with the California State Division of Mines show that there are two districts, one at each end of the so-called copper arc, which are distinct in geologic structure and ore occurrences, and that there is only sporadic and unconnected copper mineralization between them. Ore deposits of the two districts are similar in mineralogy, that is, they are largely massive pyritic ores containing copper and zinc with minor amounts of gold and silver, but the structure and structural control of ore deposition are different. The ores of the East Shasta district are replacements of steeply dipping shear zones in Triassic rhyolite and shale, whereas those of the West Shasta district are replacements of gently dipping rhyolite of Middle Devonian age and are essentially flat-lying. Thus there is marked lateral control of orebodies by shear zones in the East Shasta district and equally marked vertical control of orebodies by the stratigraphy in the West Shasta district. Geologic Setting The Paleozoic rocks of the West Shasta district range in age from Middle Devonian (?) to Missis-sippian. The oldest formation exposed is the Copley greenstone, probably Middle Devonian. It is composed of volcanic flows, volcanic breccias, and tuffs, all of mafic composition, but contains minor amounts of shale and rhyolitic tuff. Largely submarine in origin, it rests upon a base of older marine sediments, as shown diagrammatically in Fig. 3. The lower part of the formation is made up principally of flows, many of which are ellipsoidal, and the upper part contains most of the pyroclastic material. The formation is at least 3700 ft thick. The Balaklala rhyolite overlying the Copley greenstone is made up of many rhyolitic flows and beds

Jan 1, 1956