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By Frances Jane Cromwell, D. J. McAdam, G. W. Geil

In a series of papers, the authors and their associates have shown that the technical cohesion limit is affected by the same four factors that affect the flow stress, namely, the stress system, plastic deformation, temperature, and the strain rate.16-28 Moreover, each of these factors affects the technical cohesion limit in the same way that it affects the flow stress,t The influence of any one of these factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. As the term ilfracture stress' has come into use with the same significance as 'ctechnical cohesion limit," the authors are here using the shorter term with the understanding that it does not always refer to actual fracture. This paper presents the results of an investigation of the flow of notched and unnotched specimens betqrcen yield and fracture, A study has thus been made of the flow and fracture of metals as affected by the stress system, and of the ductility of metals as affected by the stress system throughout plastic deformation. Since two of the principal stresses were equal (S2 = S3), the stress systems can be represented in terms of the radial stress ratio, the ratio of the transverse radial stress s3 to the longitudinal stress S1.* The results of the experiments are represented by a series of their flow-stress curves for each Of the metals investigated, and these diagrams have been used for the development Of Other diagrams Of various types. Ludwik was the first to suggest that fracture occurs when the flow stress becomes equal to a technical cohesion limit. Although Ludwik was incorrect in his view that the technical cohesion limit depends only on the amount of plastic deformation and not On the stress system, he was 'Orrect in his view that the flow-stress curve for any stress system terminates at a point representing a technical cohesion limit. The authors have seen some recent references to assertions by other investigators that a point representing the fracture stress need not be on the flow-stress curve. The Ludwik principle, however, "auld Seem to be axiomatic, provided that the flow Stress and fracture stress are properly defined and that the fracture stress is properly determined. Disregard Of this principle has led to some untenable theories Of criteria for fracture. When a metal is very ductile, the conventional method of determining the ductility and fracture stress by dividing the breaking load by the sectional area after fracture, generally gives values that are much too high. With some metals and in some conditions, the fracture stress thus determined may be two or more times the

Jan 1, 1949

By W. J. Reagan

The problem of increasing output and decreasing percentage of rejections is a vital one in the manufacture of steel of any kind. The making of basic open-hearth steel for use in rolled steel wheels, tires for locomotive and car wheels, and forgings of various kinds, is a highly specialized industry. The increase in weight of railway rolling stock of all kinds, and the high speed that the public demands of transportation facilities, make it imperative that steel for use in this class of material shall be of the highest quality obtainable. During the past few years it has been the writer's good fortune to have opportunity to study the defects in basic open-hearth steel, and also the results obtained by various changes in open-hearth practice, on such defects. The opportunity for study and the details available are rarely found in the manufacture of steel of any kind. It seems reasonable to assume that many of the results determined here can be applied to the production of steel of other types with a decided improvement in quality, a decrease in the percentage of rejections and an increase in output. All of the material described is basic open-hearth steel with the following range of analysis: carbon, 0.50 to 0.85 per cent.; phosphorus and sulfur, 0.04 max.; silicon, 0.15 to 0.35; manganese, 0.50 to 0.75. All of this material is bottom-cast, therefore tapping and pouring temperatures are higher than in top-cast production. Ingots used in this type of work are of standard length with varying diameters. The ingot is known as duodecagonal, or twelve-sided. The standard body length is 88 in. and the hot top length, 14 in. Fig. 1 shows a typical ingot of this type. The diameter varies from 13 to 30 in. Ingots for special forgings, which cannot be made in molds of standard size, are made in molds of various sizes and designs. These ingots are sliced cold, into blocks of various lengths, depending upon the weight of the forging to be made. Fig. 2 shows the ingot after coming from the slicing lathe. Jusf sufficient metal remains between blocks to hold the ingot in one piece while it is being removed from the lathe; then steel wedges are inserted between the blocks and the blocks are broken apart. This affords abundant opportunity for inspection, as the interior of the

Jan 1, 1930

By B. Ball, D. W. Fuerstenau, P. C. Kapur

A two-phase distributed-parameter model of the flotation process has been extended to allow consideration of the important process parameter, concentrate grade. A simple expression is presented for the grade of concentrate in terms of the zeroth and first moments of the concentrate distribution. An example is given for a binary ore containing two pure minerals each having nondistributed rate constants. For extend-ing the model to the distributed rate constant case, a cubic polynomial zoas utilized to simulate the feed distribution. One particular example is considered and grade-recovery curves are generated to show the dependence of such curves on the initial feed distribution. Operating flotation plant engineers have traditionally evaluated plant performance in terms of the recovery of valuable mineral and the grade of the concentrate. In both operation and research, grade-recovery relationships have been used as a guide for selecting flotation conditions. Weissl illustrated the use of grade-recovery curves in plant operation and considered the grade-recovery relationship to be a metallurgical one. The extensive experimental work of Chi" using standard batch flotation tests on iron ores shows that, even with extensive statistical correlation of data, little insight can be gained into the basic fundamentals of these relations. Such relations must depend on the kinetic behavior of the various mineral species in the flotation circuit. In his flotation text book, Gaudin3 considered the relationship of recovery and of product grade to flotation kinetic indices, but he did not extend his calculations to yield grade-recovery relations. Although Gaudin used a simplistic model for his analysis, he did recognize that variations in flotation rates must result from variations in locking, surface heterogeneity, particle size and shape, among other things. In a recent paper,' we presented a model of the flotation process that could be readily analyzed with an analog computer. This model combines the concept of a distributed set of rate constants"" with that of the two-phase flotation model,8" resulting in a model more powerful and flexible than previous ones. The purpose of the present paper is to show how this model can be used to generate grade-recovery curves and to determine the dependence of such curves on the various kinetic parameters. In this paper, the model will be limited to the semi-batch case, but extension to the continuous case is a straightforward step.

Jan 1, 1971

By G. Ostberg

OXYGEN has frequently been considered responsible for phenomena in the metallurgy of cast iron which are not sufficiently explained by the presence of other elements. Oxygen and oxides have been regarded as critical factors, particularly for the solidification process, and specifically in the formation of graphite. However, the evidence for an influence of oxygen has mostly only been indirect or qualitative. Furthermore, quantitative data on the oxygen content of cast iron presented in the literature have often been less conclusive as being apparently determined with insufficient regard for the difficulties associated with the sampling and analysis. These problems, experimental and theoretical, have been studied in this investigation. An attempt is made to bring the views on the soluble amount of oxygen in cast iron on a level with the present understanding of the thermodynamics of these types of alloys. Although there are no experimental data on the complete multicomponent cast-iron alloys some conclusions have been drawn from investigations on simpler systems. The order of magnitude of the solubility of oxygen in cast iron is considered in the first part of the paper. The second part deals with the oxygen content actually present under practical conditions. First the possible sources of errors in sampling and analyzing methods are examined. Finally some observations on the oxygen and oxide content of malleable iron during the production process are made. THERMODYNAMICS OF OXYGEN SOLUBILITY When cast iron is saturated with oxygen the saturation phase is essentially carbon monoxide or silicon dioxide depending upon the composition of the iron, the temperature, and the rates of formation of the oxides.* The latter occurs accordiw to the O + C = CO, Kc0 - a COa J 20 + Si = SiO2, Activities are used here instead of weight pct concentrations, since activities are believed to show more sensitively the effects of the interaction of all the alloying elements. Calculations involving activities are, however, seriously hampered by lack of experimental data on the interactions between the components encountered in the multi component cast-iron system Fe-O-C-Si-Mn-P-S- and so on. In order to make an estimate of the oxygen solubility reason-

Jan 1, 1959

By Joseph Pogue

IN 1920, 531 million barrels of crude petroleum were consumed in the United States. As imposing as this figure is, the fact that the domestic consumption of crude petroleum has increased at an average rate of 10 per cent. a year for the past decade is more striking. Will this rate of increase in demand continue? If so, the year 1930 will call for 1260 million barrels of petroleum-a staggering volume. On the other hand, may we expect the demand for petroleum to grow as rapidly as it did when the automotive industry was having its most phenomenal expansion? If not, to what extent will the growth of oil requirements decrease? When and to what degree will the petroleum industry become affected by the economic law of diminishing returns? Obviously, this matter requires careful analysis, especially as both national and industrial planning must be predicated upon present estimates of the requirements of the future. The purpose of this paper, accordingly, is to project, as closely as present limitations of knowledge permit, the course of the demand for petroleum in the United States over the next ten years. At first, the problem of estimating the future of a demand as complex as that for petroleum might appear insoluble. Fortunately, however, there are several scientific methods of approaching the problem, centering around a study of rates of industrial growth, which lend considerable hope that the requirements of the immediate future in this field may be approximated with sufficient closeness to have practical value as a basis of action.

Jan 3, 1922

By C. D. Woodward

PRIOR to 1902, the tramming of ore from the stopes to the shafts, in the Butte mines, was done by man or animal power, but the demand for greater tonnage and the need for more improved methods of tramming the ore resulted in the installation of the compressed-air locomotive in a few mines. Some of the objections to animal haulage were thus eliminated, but this locomotive was not generally adopted, because of a number of limiting features. It was superseded by the electric trolley locomotive. The early types of trolley locomotives were not satisfactory from the operators' viewpoint, but. they had many economic advantages and after a number of years, in which improvements were constantly made in the structural details, they became dependable, so that the use of animals for main haulage in the mines has now been practically abandoned. There are now operating in the Butte mines of the Anaconda Copper Mining Co., 185 trolley-type locomotives, each of which has replaced five animals. It cost approximately $50 per month to keep an animal, hence the economies that resulted fully justified the expenditure of electrifying the haulage systems. The haulage conditions in this company's mines possess many advantageous features that are not always found in underground mine workings. The drifts and crosscuts are large, approximately 5 ft. (1.5 m.) wide by 7 ½ ft. (2.3 m.) high, and have curves of no less than 18 ft. (5.5 m.) radius; and the roadbeds of the drifts and crosscuts have a uniform grade of 0.5 per cent. toward the shaft, or in favor of the loaded trips. In all of the mines, except two, the track gage is 18 in. (45.7 cm.), and all tracks in the main haulageways are laid with 25-lb. (11.3 kg.) rails. The stations at the shaft are large, well-lighted, clean, and cool. The average temperature of ,the stations, however, is about 75° F. (24° C.), while the average temperature in some of the drifts and crosscuts is 92° F. (33.5° C.).

Jan 2, 1922

By L. A. Wilson, P. J. Root

The relative costs of heating a reservoir by steam injection and by combustion have been examined. The comparison was based on a model similar to that proposed by Chu.' The cost of boiler feed water, the price of fuel, pressure and plant capacity were parameters in determin-ing the costs of air compression and steam generation. The analyses compare the cost of heating to the same radius by the two methods. Results suggest that the two primary factors for comparison are the price of fuel and the amount of crude burned during underground combustion. The cost of fuel has a greater effect on the cost of heat from steam than it does on its cost by combustion. As a result, analyses indicate that when the price of fuel is low, steam may be unequivocally cheaper than air. The influence of heat loss is such, however, that as the heated radius increases combustion becomes relatively more competitive depending upon the amount of crude burned. This implies that steam may be cheaper for small stimulation jobs (huff and puff) but combustion may be more economically attractive for heating large areas (flooding). INTRODUCTION Use of thermal methods of recovery is an accepted fact today. After an induction period of several years, processes are being widely used that involve reservoir heating to augment recovery. Of the several techniques, steam injection and forward combustion appear to be destined to dominate the field. Although the objectives of both are the same, the basic differences between generating heat in situ and injecting heat after surface generation influence the cost in different ways. This study compares the cost of heating a reservoir either by steam injection or by forward combustion. There has been no consideration of recovery. Presumably, recovery from the swept region would be high in either case. The sole consideration was the cost of heating to the same radial distance by either process. PROCEDURE THE MODEL The basis for comparison was a mathematical model similar to that used by Chu' for combustion. The model simulates a radial heat wave in two-dimensional cylindricaI coordinates. It includes heat generation, conduction and convection within the reservoir and conduction in the bounding formations. Thus, heat losses from the formation are considered. Three significant modifications were made. 1. Equal logarithmic increments rather than equal increments were used for the mesh spacing in the r direction. By this technique large distances were simulated with relatively few mesh spaces. 2. A backward difference approximation to the convection term was used to avoid troublesome oscillations which result from a central difference approximation when the convection term is large. 3. The radial increments of the combustion zone motion were not necessarily uniquely related to the mesh configuration. The cumbersome step function introduced by the heat of vaporization of steam was circumvented by assuming the enthalpy of the steam to be a linear function of temperature between reservoir temperature and steam temperature. This is equivalent to assuming an average heat capacity numerically equal to the difference between the enthalpy of saturated steam and the enthalpy of water at reservoir temperature divided by the difference between the two temperatures. Heat losses obtained by this model are in essential agreement with those obtained by the analytical solution of Rubenshtein.' A detailed description of the model is presented in the Appendix. Using the model, the times required to heat to particular radial distances were obtained as a function of injection rate and other physical parameters. For the steam case, injected fluid was assumed to be saturated steam at pressures of either 500, 1,000 or 1,500 psia. The corresponding temperatures are 467, 544 and 596F, respectively. Thickness ranged from 10 to 50 ft and injection rate ranged from 100,000 to 1 million Ib/D. Reservoir and overburden temperatures at the injection well were assumed to be that of saturated steam at the injection pressure. The effect of maintaining the overburden temperature at the well at a different temperature (initial reservoir temperature) was examined with no significant change in behavior. The influence of wellbore heat losses for the steam case was determined in the following manner. The rates of heat loss as a function of time were estimated using an approach similar to that suggested by Ramey." he data were based on injection through 2%-in. tubing in 7-in. casing. Integration of these data over the entire iniection period yielded the total heat loss. Total heat losses were then corrected to their equivalents in steam (this number resulted from dividing the total heat loss by the latent heat). This was considered additional steam required to accomplish the reservoir heating and the total cost was increased accordingly.

Jan 1, 1967

From the historical account of the coal industry set forth in the preceding pages the reader will have learned that coal is extremely widely spread throughout the United States, and in most places it has been easily found, that it has been remarkably easy to develop, and, where the deposits were available to streams on which it could be transported to markets, it was opened almost as soon as the country was settled. Such were the mines along the James, Susquehanna, Monongahela, Ohio, Kentucky, Cumberland and Big Muddy Rivers. In other localities where such easy means of transport were not convenient, the early production was confined to local use, or to places to which it could be hauled by wagons, but everywhere small mines were established almost as soon as the country was settled, and these increased both in number and size as the available markets grew. These early mines were nearly always opened by local people, and the industry was so far-flung that its growth attracted little or no attention excepting when a labor disturbance or a breakdown in transportation occurred. Had it been concentrated in a few places as most metal industries were, or as the petroleum industry was for many years after it started, it is probable that much better records of its progress would have been kept. When the canal era began, in the eighteen twenties, coal was at first not considered as a valuable source of freight revenue, and much surprise was expressed that the receipts of the Schuylkill Canal were very largely from coal after the first few years, as was the case of the Union Canal though not to such an extent. Even the early railroads to the coal fields did not realize the extent to which the products of mines would figure in their revenues, and it was many years before railroads were built practically solely for prospective coal traffic; indeed this did not happen until some years after the Civil War. Map 12 shows the extent of the canal system in the United States in its relation to the coal fields at the time of its maximum development. It will be seen that only the coal areas in Pennsylvania, Ohio, and to a very small extent in Indiana were able to ship by canal at all, and that only a very small portion of such fields could do so. Looking backward, it is hard to understand the great hopes entertained of canals by their pro-

Jan 1, 1942

By P. J. Burkhardt, L. V. Gregor

The oxidation kinetics of single-crystal silicon has been investigated using extremely dry oxygen as the oxidant. Two techniques were used. The first involved a flow system with which incremental thickness measurements were made. This sytem provided an oxygen ambient at atmospheric pressure which had a moisture content of less than 0.1 ppm of water. The second technique involved measuring the change in volume of oxygen with time in a closed system. A temperature range of 900O to 1200 "C and a pressure range of 20 to 760 Tory were covered. Both techniques showed that a simple parabolic rate law holds only at the higher temperatures. At lower temperatures, the data up to 5000Å can be fitted well to a linear-parabolic equation. The two constants in this rate equation are examined in terms of a physical model. The parabolic portion of the low-temperature oxidatLon fits along the high-temperature curve of an Arrhenius plot. The parabolic rate constant for the flow-system technique can be expressed by k = 2 x 10-9 exp (L 31 kcalRT) sq cm per sec. The manostatic technique gave k = 1 x 10-exp (- 23 kcalRT) sq cm per sec. By extending the thickness range to over 104. a rate law of X = At seems to fit all of the data better than the linear-Pavabolic law. Here the exponent n increases from 0.518 at 1150 V to 0.637 at 900°C. PASSIVATION of silicon planar devices through thermal oxidation is of such great importance that considerable effort has been devoted to the study of the process.17 Much of this work involves hydrothermal oxidation, in which H2O is the oxidant: whereby H2 is produced. It has been proposed that the reaction proceeds by the formation of Si-OH groups and hydroxyl diffusion through the film to react with the silicon surface. Thus, the silicon oxide layer probably contains residual hydrogen in some form after oxidation in H2O and it has already been established that hydrogen has a marked effect on the electronic properties of oxide-passivated silicon surfaces. Silicon is oxidized by oxygen at elevated temperatures; but the rate of oxide formation is considerably lower than that for 0." By using dry O2 as the sole oxidant, the presence of residual hydrogen is presumably avoided. At present, the mechanism of thermal oxidation by dry O2 is a matter for conjecture, and the presence of small amounts of H2O was reported to have a marked effect on the rate of oxide formation10 (perhaps on the electronic properties of the surface, as well). Hence, this study of the kinetics of silicon oxide growth in 0, was undertaken: 1) to determine the oxidation rate at atmospheric pressure in a system designed to exclude rigorously all traces of H2O in the ambient 0,; 2) to obtain oxidation-rate data in situ in dry O2 by means of a continuous monitoring of the amount of 0, consumed during oxide growth. These objectives are complementary—the first assesses what effects (if any) are obtained by excluding H2O from the reaction, and the second expands this information while at the same time avoiding the uncertainty inherent in relying upon incremental measurements of oxide growth to furnish kinetic data. EXPERIMENTAL PROCEDURE The conventional silica open tube in a resistance-heated oxidation furnace is subject to sources of trace H2O, even after the input O2 is thoroughly dried and the outlet gas stream is passed through a trap to prevent

Jan 1, 1967

By Albert Sauveur

(Cleveland Meeting, October, 1912.) ALTHOUGH many metallurgists know that some pearlitic special steels can be made troostitic, martensitic, and even austenitic, without quenching, and, therefore, without exposing them to the dangers of the quenching-bath, the practical significance of such possibility does not seem to have received the attention it deserves. Let us recall briefly the mechanism of the transformation alluded to. In Fig. 1 (after Guillet) is shown the constitutional diagram of nickel-steel that; is, of alloys of iron, carbon, and nickel. Any steel the composition of which falls within the area LPO is pearlitic after slow cooling; any steel the composition of which is represented by a point within the area MLO is martensitic, and any steel within the area MNO is austenitic. Starting with pearlitic steel, then by increasing the carbon-content or the nickel-content, or both, the metal becomes martensitic and eventually austenitic; that is, its composition crosses first the boundary-line LO and then the line M0-and it remains martensitic or austenitic after slow (air) cooling.1 We have inn this way imparted to the metal without quenching it the properties of hardened carbon-steel. In other words, the steel is now self-hardening. Nickel cannot be introduced into solid steel, but by the well-known process of case-hardening it * Professor of Metallurgy and Metalllography in Harvard University. + Assistant in Metallurgy and Metallography in Harvard University. 1 The boundaries between the various zones are not, as a matter of fact, as sharp as indicated in the diagram, because pearlite is not transformed abruptly and in its entirety into martensite when a certain critical composition is attained, nor is martensite suddenly and completely converted into austenite. Greater refinement in the construction of the diagram would undoubtedly result in the introduction of troosto-pearlitic, troostitic, and troosto-martensitic zones between the pearlitic and martensitic areas and-of a martenso-austenitic zone between the martensitic and austenitic areas. Fur the purpose of this note, however, the existence of these transition-conditions may be ignored.

Nov 1, 1912

By M. Metzger, T. A. Read

The strengthening effects of hydroxide and synthetic plastic films in the creep of cadmium crystals were studied. The results were broadly consistent with the naive mechanical model. The dislocation-film reactions and the significance of the macroscopic stresses associated with certain films are discussed in the paper. ALTHOUGH a number of studies have been made of the strengthening of metal single crystals produced by surface films usually less than Ir in thickness, the mechanisms underlying this phenomenon are still not well established. Roscoe' first noted the critical shear stress and the stress-strain curve of cadmium-crystal wires to be raised markedly by the presence of oxide films. Subsequent investigators2-' have confirmed the effect for several metals and films including a number of plated poly-crystalline metal films. Harper and Cottrel1" with a thin film on zinc presumed to have formed as a result of etching and washing treatments) did not detect a strengthening at a rate of extension of 10 ' sec-' although at lo-' sec-' the film raised the flow stress by 7 pct at 0.0005 extension and by 22 pct at 0.01. The marked strengthening at moderate strains thus appeared to be the result of a dynamical effect dependent on the rate and amount of plastic flow. Other observations'. " are consistent with this view. The large effects of films on the tensile creep rate of single crystals were demonstrated when the observation of Andrade and Randall," that the creep rate of cadmium crystals increased on immersion in aaueous solutions of certain cadmium salts. was shown' * to hold only when a film was present initially and was explained by the attack of the solution on the film and the removal of its strengthening effect. Changes in the creep rate interpretable in terms of the removal or formation of various films have been observed by other investigators.3,8,10,31 Certain other experiments have been reported in which surface films or liquid environments have affected the plastic behavior of metals, but these are not within the scope of the present work which deals with the effect of solid films on single-crystal slip. Possible Mechanisms—The film does not significantly reduce the load on the crystal in the elastic range (the elastic moduli of film and crystal are not too greatly different and the area of the film is so small that its share of the load is negligible) so that the initial operation of internal Frank-Read sources is not affected. However, as Fisher" has pointed out, a source terminating on the crystal surface requires only half the critical stress for activation as an internal source of the same length and a relatively strong film (even a very thin one) would pin the free ends of the surface sources so that, if surface sources are responsible for plastic flow in a clean crystal. such a film would increase by roughly a factor of 2 the stress necessary for generation of dislocation loops at a given rate. The other general possibility is that the film resists the passage to the crystal surface of internally generated dislocations. If the film is adherent and if the specimen is to exhibit slip of the same general character as a film-free specimen, the film must deform or fail in shear at the active slip planes. The naive mechanical model, where shear-stress relaxation across the active slip plane in the metal transfers load to the film until it deforms and slip can

Jan 1, 1959

By L. D. Clark, S. S. Saluja

A physical law, governing the rupture of rock by confined explosive charge correspondent to current expressions for determining weight of charge to rupture rock burden, W, was developed in the form Q = cVw3 by two early investigators performing unique experiments with ice. The coefficient C, is found by trial blast. Recent physical tests conducted with rock, synthetic materials and ice to establish the validity of the theory on which it and other related formulae are based indicated: (a) that failure under hydrodynamic impact pressure is by tension rather than shear as was assumed; (b) that the fundamental law of mechanics, enabling the determination of Q = cvw3, modified to the form P = R x Sa x Wb is valid when low velocity explosives are used; (c) that rock breakage under the action of low velocity explosives is entirely due to explosion gas pressure, as was believed; (d) that under the action of high velocity explosive it is due to the joint effects of scabbing and gas pressure; and that further possible modification could make the above equation also applicable to these joint mechanisms. shape could be easily frozen and because large loads would not be required. They found: (a) that the not unfamiliar shearing equation for metals was applicable to ice where P = load in lb; S = periphery of pressure surface, in.; W = burden, in.; K = modulus of rupture by shear in lb per in.2; and (b) that "the form of cavity produced by the application of gradual pressure is similar to that obtained by blasting in rock under similar conditions of free face and pressure surface!" This similarity in crater shapes leads to the conclusion that rock would rupture by shear, as did ice, and its behavior under the force of a blast could be governed by such a relationship as P = S x W x K. Three important interrelated empirical expressions were derived and rock, charging and spacing coefficients C,, C, and e were established and substantiated by trial blasts. In checking the accuracy of the main assumptions, duplication of the ice tests, substituting rock, suggested that K is not constant and that P = K x W x S, though valid for ice, does not necessarily hold for homogeneous limestone.' Conclusions from this later work raised questions making continued investigation desirable because such conclusions do not destroy the practical value of the empirical equations or theory. Further study for the establishment of the relationship between load, burden and periphery of the pressure surface and possible application of these to the mechanism of rock blasting was undertaken by the authors of this paper. MECHANICAL TESTING - EXPERIMENTAL PROCEDURE Certain inconsistencies in the results of the aforementioned tests repeated on three types of limestone suggested these inconsistencies be attributed to rock inhomogeneity. It was also suspected that the loading speed, which could not be held uniform, may have contributed. The earlier work with both rock and ice

Jan 1, 1964

By A. C. Losekamp, J. B. Conway

Thermal-expansion data for, tungsten, rhenium, tantalum, .molybdenum, niobium, W-25 pct Re, Ta-10 pct W, ant1 Mo-50 pct Re are presented covering the range from room tempature to 2500°C. In these measureMents, made in a resistively heated tungsten tube furnace operating in a helium atmosphere, data for rod and sheet specimens were found to be identical; in addition, arc-cast and sintered tungsten were found to yield essentially identical results. Optical rneasurenlents of thermal expansion .made in any atmosphere other- than vacuum are subject to a refraction error which can be quite substantial. Specimens tested in helium appear shorter than when tested in racuum and hence a special correction factor must be applied to the helium data in order to obtain accurate results. WHILE it is true that linear thermal-expansion data for many of the refractory metals have been measured to very high temperatures, it is also true that except in a few instances the data from various investigators are not in good agreement. This is particularly evident in the case of tantalum and niobium although some tungsten data have been reported which differ by as much as 40 pct from the data of other investigators. Due to the sensitivity of both tantalum and niobium with respect to impurity absorption during exposure to high temperatures, it is probable that this single factor accounts for the majority of the discrepancies in the thermal-expansion data for these metals. However, this same factor can probably not be employed to explain the existing differences in the tungsten data. In all probability, these are due to errors in the measurement technique, to material composition variations, or to changes which take place in the material during the heating process (e.g., additional densifica-tion resulting from heating a sintered specimen above the original sintering temperature). In view of the discrepancies which exist in the linear expansion data reported for many of the refractory metals, the current study was initiated in an attempt to resolve such differences. Also, no high-temperature linear thermal-expansion data were found to be available for several refractory metals. Providing such data was another objective of the current investigation. MATERIALS In this study test specimens were employed in either rod or sheet form and in several instances both arc-cast and sintered material were employed. Material compositions are presented in Table I. Helium gas was fed to the furnace at a rate of about 0.5 SCFH and no special purification procedures were employed. However, the helium contained less than 50

Jan 1, 1967

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

DISCUSSION L. E. Djingheuzian (Canadian Dept. of Mines and Technical Surveys, Ottawa)—In their Summary the authors say: "Reconciling the grinding efficiency with good metallurgy is still a problem." In the discussion of the first paper8 in his reply to W. I. Garms, Mr. Myers states: "Our grinding process with smooth I-in. balls has reduced by nearly one half the metallic losses in the fine micron sizes of the tailing. This is simply because less of the fine micron sizes are produced. Since the + 65 mesh size is the same as formerly, a higher percentage of the intermediate sizes are developed. These sizes have the highest floatability, require the least reagents, and use less floating time. "These factors contribute so heavily to the overall economies that dropping our power grinding gain from 28 pct back to 19 pct is a small detail. However, we feel that this is only a momentary situation and that eventually the best features of the grinding and flotation processes can be brought together, which is as it should be." Italics are mine. The above statements, to me, appear to be the answer to the opening statement in the Summary. Denoting the costs at different power grinding gains as: Power Grinding Power Grinding Gain, 28 Pct Gala, 19 Pct Cost of grinding G G1 Cost of flotation F F1 Value of metallic losses T T1 where G1 > G2 F3 < F, and T1 < T, we have: G1+Fl+T1<G +F+T. Since the authors accept the idea that "grinding in flotation plants becomes part of the &apos;conditioning&apos; of the feed to flotation",4 i.e., that in flotation the ball mill is primarily a conditioning machine, it can be postulated that Tennessee Copper grinding at cost G1 is more efficient than grinding at lower cost G. This can be directly inferred from the Conclusion of the paper. Mr. Myers also emphasizes this at the end of his reply to Mr. Garms: "that grinding is for the purpose of preparing flotation feed and not grinding per se." This, to me, in the final analysis means that when the efficiency of grinding is weighted against the conditioning factor, the former becomes a function of efficient conditioning, hence, within the system in which proper conditioning is the dominant factor, the best grinding efficiency is provided by grinding which will contribute towards the optimum conditioning. This brings us again to the statement: "that if every grinding unit were considered as a conditioner for each following step, efficient grinding plants would become much easier to design."&apos; In other words, grinding equipment should be balanced against the flotation equipment and against chemical reactions taking place in the system. F. C. Bond (Allis-Chalmers Mfg. Co., Milwaukee)— The authors&apos; discussion of the probable ball motion in a slow speed high dilution mill is very interesting. When the 1-in. balls have worn down to about one fourth of their original weight they apparently first develop a flat surface; as wear progresses this flat face becomes concave, and other concave faces appear. It seems more probable that the first flat face may form at the softest part of the ball surface, and that each succeeding contact tends to force this flat face into sliding contact with a larger round ball; than that the flat faced ball tends to pair off with a particular round ball and to travel with it continuously. When the small worn ball has a flat face and is in sliding contact with a large round ball, the surrounding large balls will assume a more or less definite pattern, and slide against the worn ball, thus producing secondary concave faces. The primary concave face seems to be larger and better developed than the secondary faces. The ball charge can be divided into "concaves" which show at least one concave surface, "intermediates" which have developed flats or incipient concaves, and "rounds." Ball slippage is always present in a tumbling mill, and the mutual ball movement is necessarily a combination of rolling and sliding. The sliding motion is apparently concentrated upon the smaller worn balls which nest between the surrounding larger round balls. When each worn ball starts its upward path in the mill its primary flat or concave surface fits against a larger round ball, and the round ball slides upon it. The action may be something like that of the ball separator in a ball bearing, except that the worn sliding balls are always under considerable pressure. The material is ground under the combined influence of breakage 1—by impacts between falling balls and between falling and supported balls, 2—by being nipped between rolling balls, and 3—by being rubbed between the sliding balls. The rubbing action will be increased in the presence of worn balls with concave surfaces. The rubbing action probably produces a considerable portion of the finely ground slimes in the product. The worn balls commonly approach tetrahedrons in shape, and are very different from concavex, each of which has two equal opposed concave surfaces. Concavex were designed only to grind upon themselves, and not for use in combination with grinding balls. Their action in a grinding charge is very different from

Jan 1, 1952

GOD the Almighty has all things well ordered; in G particular, the effects and attributes of the seven planets whose reign and course (by the grace of God) determine for the most part not only our own life and death but also the growth and decay of vegetable and mineral life, so that the aforesaid planets generate and develop in a wondrous way the ores of gold and other metals in minerals, rocks, and earths. Specifically, the Sun develops the ores of gold, the Moon the ores of silver, Venus the ores of copper, Saturn the ores of lead, Jupiter the ores of tin and bismuth, Mars the ores of steel and iron, and so on. Since, however, no ore is made alone but each is made and wrought so that it is associated with other ores, it is necessary to know the art of separating the thus-made ores after they have become metals; as for instance, silver from lead and copper; gold from silver, and so on. [2]* If this is to be done usefully, you must be able to assay and must understand everything that is needed in connection therewith. It is obviously true and clear as light of day that some kinds of copper contain silver and some kinds of silver contain gold. In order that you may be able to separate them, so that each is obtained by itself and can be worked with profit and re ward you need first of all a true assay for the values of such metal. The assay, by revealing how great they are, whether the pure has been obtained separate from the worthless matter, and what the admixture is, advises you whether it would be worth the expense and the effort to start mining operations. Assaying also indicates how much silver there is in a centner of ore or how much copper and lead there are in

Jan 1, 1949

By George H. Gilman

THE campaign now being waged to improve the quality of the rock-drill bit is the natural outcome f the scientific development of the drilling machine during the past twenty years. In this development there has been a great increase of power output per unit of weight of machine. But the development of the rock drilling engine has been seriously hampered by the need of a drill bit that would withstand, without undue wear or breakage, the heavy rapid blows of the improved pneumatic hammer. This problem was difficult to solve because an increase in the weight or section of the drill-steel bar resulted in decreased cutting speed and higher operating costs of both the bit and its actuating engine. The solution, therefore, is to make the bit of steel that, for a given weight or section, will be more shock and wear resisting. In the attempt to meet these requirements, many of the drill-steel manufacturers alloyed the steel with vanadium, chromium, nickel, etc., on the assumption that such elements would improve the rock-drill bit but due to the sensitiveness of such steel to forging and heat treatment, higher cost, and lack f continuity of effort on the part of the steel manufacturer to perfect this product, but little progress has been made in the adoption of these steels and the so-called straight carbon steel is today recognized as the standard material for all rock-drill bits. The first step in improving drill-bit efficiency is the determination f the cause of breakage and wear. For this reason, in 1917, certain rock-drill manufacturers, in conjunction with some of the larger mining interests, conducted exhaustive tests in both the field and laboratory. It was then found that, in the main, the cause of drill-steel troubles is not attributable to the duty imposed upon it by the normal operation of the drilling engine, but to improper forging and heat treating of the bit and to the subjecting of the bit to improper use. The fact that it is possible to minimize the troubles attributable to improper heat treatment of the drill steel has been demonstrated and it is recommended that such knowledge be made available by teaching those interested in the production, use, and up-keep of drill bits the principles on which success in this direction may be achieved.

Jan 6, 1921

By Arthur C. Spencer

IN extension of a suggestion already made to account for certain features observed in the Juneau gold-belt in southeastern Alaska,&apos; it is the object of the present paper to indicate in detail certain conditions in which deformation of rocks under their own weight might lead to the production of fractures in which veins could be deposited. A direct, uniformly-distributed pressure of sufficient intensity applied to an elastic brittle mass offering strong resistance to deformation produces rupture. In a material of ideal properties the surfaces of rupture under such pressure would be shearing planes inclined at 45° to the line of force, unless there be preliminary deformation, in which case this angle would be greater than 45°. This general conclusion, resting upon ana¬lytical mechanics, is completely supported by the results obtained by Daubrée in experiments upon the deformation of wax and resin prisms under compression. Let us then first con¬sider one of Daubrée&apos;s diagrams. In the case illustrated in Fig. 1, four sets of fractures in two appproximately right-angled pairs (that is to say, in conjugate sets) were produced by end-wise compression of the square cross-sectioned prisms. These fractures cut the axis of compression at approximately equal angles, not varying greatly from 45°. The location of the four sets of fractures is obviously determined by the shape of the prism, since the material in each corner acts in a way as a buttress, permitting the bulging to take place most readily on the sides. By limiting the directions in which bulging may take place, results of a more simple nature could be obtained. Take, for instance, a square prism and place it between two fixed and

Nov 1, 1905

By L. Weyher, H. L. Lovell

This discussion is restricted to a very specific application of the cyclone - its use as a hydro-cyclone in the cleaning of fine coal. It is hoped that the development of the present data will assist in the further elucidation of existing qualitative models, and also in an enhanced application of the hydrocyclone and provide a base for further research. Discussed are the mechanisms of gravity separation in hydro-cyclones, test procedures, experimental observations, and industrial applications from these studies. Within the general area of unit operations, a considerable effort has been expended in theoretical and empirical research associated with cyclone operations. The motivation involves the industrial requirement for devices and techniques to manipulate small particles at low operating costs, a situation required in coal preparation. There are good reasons why the cyclone helps to satisfy this demand, because it combines operational simplicity (no moving parts) with versatility and high throughput capacity per unit area. The cyclone is one of the most widely applied tools in the process technologies. There are areas for potential cyclone application which have been only meagerly explored or not considered at all. This discussion is restricted to a very specific application of the cyclone - its use as a hydrocyclone in the cleaning of fine coal. It represents an initial presentation of a more comprehensive report. Coal preparation can appropriately claim the hydrocyclone since most of its predominant industrial uses have originated in this area and have spread into other applications, including the broad field of ore dressing, the petroleum industry, chemical processing, nuclear engineering and food technology. There is one operational principle common in all cyclones: A fluid is tangentially introduced into a cylindrical or conical container under pressure. A predominantly irrotational flow field1 is established within the cyclone (Fig. 1). The uniqueness of this flow is indicated by the variation in tangential velocity across the cyclone radius, which reaches a maximum a short distance from the center and decays toward the cyclone wall. In contrast, the tangential velocity in a centrifuge increases uniformly toward the wall. Usually two products are discharged from the cyclone. They differ in that one discharge consists predominantly of that portion of the feed fluid which moves along the wall axially away from the feed inlet, while the other consists predominantly of fluid spiralling along the central regions of the cyclone, in an axial direction opposite to that of the wall current. Fig. 2 indicates these discharge points schematically. The latter product may be termed the vortex-product, since it is discharged with the central vortex-current. In the case of conical cyclones, the former product may be referred to as the apex-product. Although the names "over- and underflow" are widely used, many cyclones are operated from extreme angular positions thus the proposed terms are less ambiguous. The cyclone feed fluid can be laden with solid particles or nonmiscible fluid drops. Such a feed component is discharged from the cyclone, after some residence time, into the one or the other product. Yet, the orifice through which a particle will leave the cyclone is dependent upon a number of factors. These factors, in a statistical sense, determine the path of the particle within the cyclone. Thus, different separation phenomena are possible and different process results attainable by the controllable variation of the particle path. It is then, to attain a fuller understanding of this particle path, to which this study is ultimately directed. It is anticipated that the detailed study of the data being developed will allow further elucidation of existing qualitative models. However, the development of a quantitative description of cyclone operation in terms of a mechanism is not currently feasible. The flow conditions in a cyclone are not fully understood even for a pure fluid, without the added complexity of the inclusion of multiple size-density particles. It is hoped that the development of the present data will also assist in an enhanced application of the hydro-cyclone and provide a base for further research. Some practical applications drawn from the data are suggested. Cyclone operations have been classified according

Jan 1, 1967

By Carl Swartz

FOR many years kettles used in the melting and refining of lead and other nonferrous metals and alloys have been made of cast iron. The logic of this probably lies in the fact that cast iron has been known as a material of construction for vessels of this type much longer than steel, and satisfactory fabrication from it has been more easily accomplished and better understood. As the capacity of lead refineries has increased, it has been only natural to increase the size of kettles. Today kettles of 150 to 250 tons are not uncommon. As the size of the kettles increased and better shapes were designed, the uniformity of material of construction became more important. Records kept over comparatively long periods of time have shown that the length of service of kettles has not been uniform. Many causes contribute to this and the importance of each has not yet been evaluated. Kettle design, kettle setting, method of firing and material of construction have been changed from time to time to obtain better service, but the variation in length of service is still great. A kettle may fail during the first few heats or may last through more than one thousand heats. The purpose of this article is not to present the conclusions of a finished piece of research on kettle manufacture and use, but to present a series of observations made over considerable time in the hope that others will publish data and that all may be correlated into a logical scheme which will result in better service and longer kettle life.

Jan 1, 1931

By B. A. Cheadle, K. P. Steward

Axial tensile, ring tensile, closed end burst, and free end burst tests were done at room tempe.vature and 300°C on three batches of Zircaloy-2 sheathing zuith different textures. Knoop hardness tests were also done on all batches. The mechanical properties of the tubes were largely dependent on the percentages of cold work, but were also markedly affected by the textures, particularly with respect to deformation behavio&apos;r. The deformation behavior observed confirmed Picklesimer&apos;s predictions, zuhereas Knoop hardness results could be correlated with texture and yield strength anisotropy after the ,method of Wheeler and Ireland. From the mechanical properties, and from efjectiue strain values deterrlzined at the fractures using a photoqid technique, it zuas concluded that tubing witlz a single preferred orientation of radial basal poles best combines strength and ductility for any given deqee of cold work. THE mechanical properties required in collapsible Zircaloy-2 fuel sheathing for water-cooled power reactors are strength to resist wrinkling deformation by coolant pressure and ductility to accommodate a small amount of deformation in service without rupturing. Zircaloy-2 tubing during fabrication develops pre- ferred orientations of the a Zr grains due to aniso-tropic deformation behavior, and these textures markedly affect mechanical properties. Picklesimer&apos; had predicted the deformation behavior of tubes with various textures, but the texture required to provide the optimum strength and ductility for a given degree of cold work has not been reported. To investigate this problem, tests at three transverse to axial stress ratios were done at room temperature and 300°C on three batches of Zircaloy-2 tubing covering a wide range of textures and percentages of residual cold work. Knoop hardness values were also measured to correlate with preferred orientation and yield strength anisotropy after the method of Wheeler and relland.&apos; 1) MATERIAL For this investigation, three batches of tube-reduced tubing were chosen from the Zircaloy-2 sheathing produced for the Douglas Point Reactor. Individual tubes were 191/2 in. long, 0.600 in. OD, and 0.0165 in. nominal wall thickness. The identities of the batches, together with their textures, are shown in Table I. The tubes had the normal Zircaloy-2 composition3 of 1.5 wt pct Sn, 0.3 wt pct Fe, Ni, Cr combined with the following oxygen concentrations: Batch VII 1140 to 1390 ppm 0 Batch VIII 1400 to 1750 ppm 0 Batch IX 880 to 1320 ppm 0

Jan 1, 1968