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By H. M. Hobart

THIS paper deals principally with investigations undertaken by the Welding Research Sub-committee of the Welding Committee of the Emergency Fleet Corporation. The general object of the investigations has been to extend the use of welding in the construction of merchant ships and, specifically, to provide a definite basis for obtaining the best economy and efficiency in employing welding in place of riveting in the construction of the hulls of such ships. Composition of Ship-plate Steel The chemical composition of the steel employed in such hull construction varies with the thickness of the plates. Through the courtesy of Mr. H. Jasper Cox of Lloyd's Register of Shipping, the following information may be given concerning the kind of steel plate employed in American Shipyards in 1918 for the hull construction of merchant ships. Lloyd's requirements do not relate to the chemical composition. They require a tensile strength of 58,000 lb. per square inch (40.75 kg. per sq. mm.) for their lower limit and 72,000 lb. per square inch (50.59 kg. per sq. mm.) for their upper limit. For the information of the Committee, Lloyd's obtained from their surveyors at various works data of the carbon content, which is as follows:

Jan 2, 1919

THIS chapter and Chapter 19 deal with the heat quantities involved in open-hearth steelmaking, including the thermal efficiency of the furnace as a generator of high-temperature heat, the heat storage in the steel and slag produced and in the furnace walls, and the heats of the various chemical reactions involved in combustion, in the formation of slag, and the refining of steel. The fundamental laws to be considered are the first two laws of thermodynamics as applied to problems involving sensible and potential (or latent) heat only: 1. Heat input equals heat outflow plus storage. 2. Heat may be transferred only from a hotter body to a colder one. The first of these laws relates to the various heat quantities or the heat balance of the process. No one has as yet made an open-hearth heat balance that came out almost exactly balanced. The cause probably lies in the difficulties of accurate temperature and flow-rate measurements at the high temperatures involved and the inherent complexities in flow distribution and air leakage present in any real open-hearth furnace system. Some idea of the magnitude of the heat quantities involved can be obtained by a brief, crude outline of the heat balance of a 90-ton heat of steel. We will assume a 60 to 70 per cent hot- metal charge in a fairly fast working and only moderately efficient furnace, burning fuel oil, with a fuel consumption of around 4 million Btu per net ton of ingots produced. The time from start of charge to tap is 9 hr. During this period, the oil burned represents 360 million Btu and the sensible heat in the preheated air at the port ends is 117 million Btu, so that the total heat input at the ports is 477 million Btu. Heat stored in the steel and slag at the end of the heat, plus the various amounts absorbed by certain bath reactions, amounts to a total of 195 million Btu, but 120 million of this is supplied by the heat in the hot metal and by various heat-evolving reactions in the bath,

Jan 1, 1964

By John F. Elliott, John P. Hager

The standard free energies of formation of the lowest stable sulfides of chromium, molybdenum, and tungsten in equilibrium with the corresponding metal hazle been determined by reacting the sulfide and metal with H2(g)/H2S(g) mixtures. The reaction is A method for estimating the standard ~nolav entropies and standard entropies of formation at 298°K of the sul-fides of refractory metals is presented. The standard free energies of formation of the lowest sulfides of the metals in group VIa of the periodic table are probably best determined with the reaction* is known with greater accuracy than is that property for any other sulfur-bearing compound or solution which might serve as a reference phase to establish the chemical potential of sulfur for the essential re- However, there still remain significant problems to the use of Reaction [I] in studying these sulfides. First, the equilibrium gas ratios (Ph2S/PH2) are very small, and with the most stable sulfides in the series the ratios tend to be at the limit of the range for precise chemical analysis (10-4); and second, the reaction rate for the formation or reduction of these sulfides appears to be relatively slow. A primary reason for the latter problem is that the gas phase near the equilibrium concentration has very little capacity for transport of sulfur. It is to be noted that the thermo-dynamic properties obtained from the experimental results by Eq. [I] apply for 1 g-atom of sulfur in the metal-saturated compound even though the exact composition of the compound has not been determined. The work reported here is a study of the standard free energies of formation of the lowest sulfides of chromium, molybdenum, and tungsten, and of copper, by Reaction [I]. In planning the experimental program, it was decided that the technique that has been used previously3"' could be used with modification and that an improved analytical method was needed for determining H2S in the gas phase. THE EXPERIMENT The once-through flow of gas was selected in preference to recirculating the gas, a) because of the low sulfur capacity of the gas, b) because of the relatively slow rate of reaction and the danger of the

Jan 1, 1968

By H. H. Stoek

Mine models have three distinct uses: 1. As exhibits in expositions and museums. 2. As exhibits in law suits. 3. As illustrations in teaching mining engineering. All three uses are in a sense educational. The third, or distinctively teaching function, has not been extensively developed in America as it has been abroad, chiefly because of the cost of the models and the scarcity of model makers. In connection with expositions, such as the Columbian, the Louisiana Purchase, and the Panama-Pacific, a number of very good mine and metallurgical models were prepared with funds furnished by State commissions, by mining organizations or mining companies. At the close of these expositions, some of these models have been deposited in National or State museums or in educational institutions, but too many of them haw been lost, or have been stored away in some mining company's office or in the basement of some State building, where they have been lost sight of and have gradually fallen to pieces. A visitor to a German mining school is impressed by two facts: 1. The mining laboratories are in general inferior to those in America. 2. The mining museums are infinitely superior to ours, particularly in models exhibited. One may reply to this comparison by saying that a museum is necessarily a work of time. From the historical standpoint this is, of course, true, but it is not necessarily true in connection with a working museum intended to illustrate current practice. For instance, the oldest mining school in Germany, that at Freiberg, has much excellent historical material, but very little on modern practice, while Berlin, one of the youngest German mining schools, has a most extensive and valuable collection of modern appliances and models. This is true in spite of the fact that one of the best-known model shops is at Freiberg, from which many of the models to be seen in America have come. Because many of the models in American mining schools have come from

Jan 1, 1918

By C. L. Berrien

Many fires have occurred in the mines of Butte in recent years, and while all have been of a serious nature, simply because they were mine fires, six of them have been especially dangerous in respect to loss of life and property, and the expense of extinguishing or controlling them. It is not my intention to discuss the relative merits of methods used in fighting these different fires because the conditions under which they occurred varied in each case, and it was not always advisable to expend the large sum of money necessary to actually extinguish them if they could be bulk-headed off from the rest of the mine. It is needless to say that everything possible has been done to check all fires at the beginning, but without success in some cases; and it has then become necessary to bulkhead all connections to them, in which state several now exist. The mine fires of Butte, or fires in any mine, may be divided into two classes, namely: Those occurring in accessible workings, and those occurring in inaccessible workings; because these two conditions govern to the greatest extent the methods of fighting fires. Accessibility and inaccessibility in the case of mine fires concern not only new open workings and old closed workings, respectively, but also the condition of the ventilation in and about those places. When a fire is accessible at the start it should not be difficult to confine it to a small area and extinguish it in a relatively short time, but when it is impossible to actually reach a fire in old filled, abandoned workings, or there is no opening by which the gases may be conducted away from the fire zone, then the time consumed in changing those conditions permits the fire to increase to such an extent that it is a long, hard fight to overcome it. These different conditions have been met in Butte, and of the six fires of serious proportions the Steward mine fire and the High Ore-Modoc mine fire were in new accessible workings and were extinguished in a month or so. The Anaconda mine fire, the Leonard-Minnie Healy mine fire, the West Colusa mine fire, and the Mountain View mine fire, were all inaccessible. The Anaconda mine fie started about 25 years ago and though safely bulkheaded is still active. The Leonard-Minnie Healy

Jan 1, 1916

By M. J. Sinnott, J. C. Tobin

A technique for collecting and analyzing the small quantities of gases desorbed on heating metal powders has been developed. The gases collected from copper powders of various types of manufacture have been analyzed and found to contain H2O, CO2, and SO2. The quantities of gas evolved vary from 0.05 to 1.0 milliliter, under standard con-ditons of temperature and pressure, per gram of powder. The source of the gas has been traced to surface films on the powder. IN the powder-metal industry it is recognized that the presence of gases in the powders affects the processing and resulting properties of the sintered product. Several sources for these gases are possible; namely, chemical reactions with the sintering atmospheres, inclusion. of gases during compacting, dissolved gases in the metal powder, and sorbed gases on the metal-,powder surfaces.1, 2, 3 Since the quantities of the gases are relatively small, no direct attempt has been made to collect and analyze them nor to isolate their source. The work that has been done has been concerned with the dimensional stability of the product., its porosity, density, or mechanical and physical properties. Conclusions are drawn on the basis of studies of this type as to the probable effect of gases on these properties. 4, 5, 0 In the present investigation an attempt has been made to obtain quantitative data on the analysis and quantities of gases associated with copper powders manufactured in different ways. Apparatus was constructed to collect gases evolved from loosely packed powder samples on heating to various temperatures under a reduced pressure of helium. The powders were outgassed thoroughly in a vacuum prior to starting the collection operation in order to eliminate mechanically entrapped gases and to prevent the possible reaction of the powder with these gases. Experimental Procedures Materials—The major portion of the investigation was carried out on a single heat of water-atomized, oxygen-free, high-conductivity copper. A relatively coarse fraction of this powder, 20 to 100 mesh, was tested as a mixed powder and as various graded size fractions. The microstructure of this powder showed equiaxed grains and was clean and free from oxides and oxide eutectic. The particle size, as determined

Jan 1, 1959

By S. Epstein

THE new low-alloy high-strength steels are obviously here to stay. With 75 per cent higher yield strength and 50 per cent higher tensile strength than plain carbon structural steel, they permit 20 to 40 per cent weight savings and 10 per cent or more increase in pay load in the con-struction of railroad cars, buses, trucks, and a great variety of material-handling equipment. Their cost is low enough so that the extra cost of the new lighter construction over that with carbon steel offers an attrac-tive self-liquidating investment; in some instances new construction with these low-alloy steels may even be as cheap as with plain carbon steel. A considerable and rapidly growing demand for the low-alloy steels has already sprung up. The many steel compositions that have appeared on the market lately 18,27,28,29,30 to meet this demand would seem to indicate that no single composition is uniquely fitted for the purpose. However, no doubt some compositions are more suitable than others. The purpose of this study was, therefore, to compare the effects of the various alloying elements that might be used in the low-alloy steels in order to choose the metallurgically most logical composition, paying due regard, of course, to the economic aspects involved.

Jan 1, 1936

By C. O. Worden, E. K. Landgraf, C. A. Zapffe

Following the discovery of Parke and Ham that deoxidation control of cast molybdenum can be predicated upon simple fractographic examination, a special study of that metal was undertaken to investigate those patterns ascribed to forge-ability and nonforgeability. An elaborately developed system of cleavage patterns immediately rewarded the study; and they are reported here as a necessarily preliminary contribution calling attention to information which is both new in type and in origin. In general, the present observations confirm those of Parke and Ham, and Wood-side; but they also disclose a wealth of detail and correlated phenomena which greatly expand the earlier information. For example, the oxide pattern of nonforgeability is found to be complex, perhaps involving as many as three distinctive patterns, And the nature of the carbide seems to be at least twofold. In addition, transgranular facets are here shown for the first time. Elaborately complex, but in a characteristic manner, these facets depict distortion in original crystal growth which provides truly extraordinary patterns. No carbide and oxide forms display themselves transgranularly, except in profile as exceedingly thin superficial films at the grain boundaries. Crys-tallographic features are also rare—a condition undoubtedly resulting from the great substructural distortion; but occasionally registrations are found of cleavage on {00I}, and faulted areas believed to be Neumann-type deformation on I I121. Introduction Parbe and Ham,' and again Woodside,2 have reported that the forgeability of molybdenum cast by their Vacuum-electric-arc Process can be predicted with great dependability by a simple fractographic observation. They state that nonforgeability is the result of a grain boundary oxide which can be readily identified on the fracture facet at high magnification; and they convert the nonforgeable condition to a forgeable one by increasing the carbon content of the melt until the oxide structures subsequently observed in the fracto-graph become replaced by a second strongly marked pattern characteristic of carbide and coincidentally indicative of forgeability. Considerable importance immediately attaches to such observations: (I) because of their direct commercial application to one of metallurgy's inviting and relatively unexplored metals; (2) because of a general scientific curiosity regarding the nature of these characteristic markings; and (3) perhaps more important, because of

Jan 1, 1949

By Walter B. Lenhart

Introduction and Importance of the Industry Sand, as described in this chapter, is a crude product used for ballast on railroads and highways, and as the fine aggregate in concrete, mortar, plaster and in asphalt paving materials. The sand used in glass, as a molding sand, and as a source of silica is described in Chapter 43. Sand and gravel together constitute the mineral raw materials of largest volume produced from the earth. In 1958, as reported by the U.S. Bureau of Mines,21 680,080,000 tons of sand and gravel (including industrial sand) were produced in the United States. The nearest competitor was crushed rock of which 532,818,000 tons were produced. Coal, both bituminous and anthracite accounted for only 431,616,689 tons in the same year. In dollar value, sand and gravel were exceeded only by cement, crushed rock and fuels. Hence it is a major unit of the mineral-producing industry. As an example, one plant in California operates around the clock at an average rate of 1,500 tons per hour, and at peak intervals has shipped over 4,000 tons per hour, all by trucks. Nevertheless, it is controlled by one man through a panel of push buttons that control the crushing, screening, washing, grading, stock piling, and reclaiming of the products. Because sand and gravel are low-valued commodities, but are used in every construction undertaking in every city, village, farm, dam and highway, they are produced in almost every county in the United States and southern Canada, by thousands of individual operators, very few of whom operate in more than one community. Many operations, particularly those established to supply the needs of major dams that are under construction, or of major segments of new highways, are temporary in nature, and the equipment installed is more or less portable. Because of the bulky nature of sand and gravel, there is very little interstate movement, and almost no exports or imports, except a little movement back and forth across the border of the United States and Canada. First, the material needs definition. Definitions Sand and gravel have been defined as continuously graded unconsolidated materials that appear in the earth's surface as a result of the natural disintegration of rocks. Both normally appear together, but in a wide variety of sizes, types and range of size classification. The American Society for Testing Materials has tentatively revised its definition of "sand" as: granular material passing the 3/8-in. sieve and almost entirely passing the No. 4 (4760-micron) sieve and predominantly retained on the No. 200 (74-micron) sieve, and resulting from natural disintegration and abrasion of rock or processing of completely friable sandstone (ASTM Designation C 58-55T). The Society's tentative revision of its definition of "gravel" is: granular material predominantly retained on the No. 4 (4760-micron) sieve and resulting from natural disintegration and abrasion of rock or processing of weakly bound conglomerate (ASTM 125-55T). Sand and gravel deposits contain materials from the finest silt to the largest boulders. Chemical definition of the two materials is nearly impossible. Sand and gravel always are

Jan 1, 1960

By Dodge, C. E.

ONE of the first mining areas to be developed in Arizona was that in the district centering about Clifton and Morenci. Traces of metals were first noticed by Henry Clifton on an expedition in 1864. Definite copper outcroppings were also reported in the following year by General J. H. Carleton when he led his troops into the district on an Indian raid. Actual mining operations were started in the early seventies. and the first smelter was finished in 1873. Two adequately financed companies acquired most of the property, and both commenced production about 1882. These were the Arizona Copper Co.. owned by a group of Scotch investors, and the Detroit Copper Mining Co., afterwards purchased by the firm of Phelps, Dodge & Co. Later the Shannon Copper Co. acquired and operated a number of claims in the northern part of the district. These three companies all operated underground, mines independently for many years.

Jan 1, 1942

By F. Bonaccorso, G. Venturello, C. Antonione

A study of the effect of small amounts of interstitial impurities on recovery and re crystallization in high-purity iron (99.995 pct) has been undertaken. This paper gives results on the effect of carbon, introduced in small-dosed amounts @om 0.0005 to 0.0086 wt pct) by heating iron specimens of high purity m a static atmosphere of CO + ,. The materials prepared in this way, cold-worked 80 pct and subjected to a series of isochronal and isothermal annealings, were submitted to examinations by X-rays, micrographs, and hardness tests. It was observed that effect of carbon is remarkable in the sense of blocking recovery of mechanical properties up to the temperature at which re crystallization begins. On the contrary, carbon has a negligible effect on primary re crystallization temperature, when compared with the known effect of substitutional impurities. This is in agreement with the high mobility of interstitials. In effect, only a slight decrease, -20 pct, of the grain-boundary motion rate was noted, due to the interaction between the grain boundary and the carbon atoms. On the other hand, in the samples in which the carbon content is above the solubility limit at the temperature at which re crystallization occurs, a slight increase of nucleation frequency is noted due to the presence of precipitated carbides. ThE effect of purity on recovery and recrystalli-zation phenomena has been known for a long time; however, recently, new attention has been given to the problem since new methods for obtaining metals with extremely low impurity contents have become available. Most of this research work essentially concerns the effects of impurities which cause precipitates or give rise to substitutional solid solutions. The works of Bolling and winegard1 and Aust and utter' on lead, and Vandermeer and orddon' on aluminum, 01sen4 on nickel, and Abrahamson and Blakeney on iron should in particular be referred to. On the effect of this type of impurities a quantitative theory has been formulated by Detert and Lucke6 and has lately been discussed critically by Cahn7 and Gordon and vandermeer.' Interstitial solid solutions in iron have not as yet been studied. As the study of the effect of interstitials is of great interest both from a theoretical and practical standpoint, it was deemed useful to examine the effects of carbon, nitrogen, and boron on recovery and primary recrystallization of iron. There already is some work by Chaudron et al.,1-" on the effect of interstitials on iron; their work, however, mainly concerns secondary recrystallization. The present paper refers in particular to the effect of carbon. EXPERIMENTAL PART Preparation of Materials. The pure iron used for this research was obtained from FeCIS recrystal-lized and purified by extraction with isopropylic ether. From the ferric chloride purified in this manner, hydroxide was precipitated with a solution of very pure ammonia, and, by calcination in pure sintered alumina crucibles, oxide was obtained. Reduction of the oxide to iron sponge was performed in sintered alumina tubes with very pure hydrogen at 650°C; at the end of the operation temperature was increased to 900°C. Specimens for the experiments were obtained by sintering the sponge at 1480°C in pure Hz after a pre sinter ing treatment at 900° C. It is important to note that the treatment at 1480°C in Ha produces a further purification from more volatile elements such as zinc, cadmium, arsenic, lead, and tin. Details on the preparation and characteristics of this type of very pure iron are given in a previous work.'' Only the complete analysis performed by neutron-activation methodsz3 is given here, Table I. Some of the specimens prepared in this way were carburized in the 0 region with very low amounts of carbon by treating them at 700°C in a static atmosphere of Ha containing a definite amount of CO. The set-up used is described in Fig. 1. A gas-tight quartz tube containing the specimen to be carburized and an internal friction control specimen, after being evacuated, was filled with Hz

Jan 1, 1963

By D. J. McAdam

IN a recent survey of the literature, the author has found evidence incompatible with prevalent views regarding the technical cohesive strength and yield strength of metals. Some of the evidence regarding the technical cohesive strength was presented in a previous paper,21 and views were presented that are believed to be in better accord with the evidence. In that paper, it was shown that the technical cohesion limit (contrary to prevalent views) varies with the combination of principal stresses,† and that the influence of plastic deformation on the technical cohesive strength is not in accordance with prevalent views. In this paper, consideration will be given to both the technical cohesion limit and the yield stress as affected by the combination of principal stresses. Evidence will be presented that the variations of the yield stress and the technical cohesion limit with the combination of principal stresses are not in accordance with prevalent views. Consideration will also be given to ductility and work-hardening capacity, which depend on the initial difference between the technical cohesion limit and the yield stress. By the "technical cohesion limit" is meant the mean stress at actual or potential* fracture. An example of a technical cohesion limit is the "true" breaking stress of a tension-test specimen, the breaking load divided by the sectional area at fracture. The cohesion limit thus obtained for a ductile metal, however, has been greatly altered by the plastic deformation. It is important to consider the cohesion limit of the metal prior to this deformation, and the variation of the cohesive strength with plastic deformation. The relation between the cohesion limit and the corresponding flow stress† determines the ductility of a metal and the energy that it will absorb before fracture. In this paper, as in the previous paper,21 tensile stresses will be viewed as positive and compressive stresses as negative. The algebraically greatest principal stress will be designated S1, the least principal stress will be designated S3, and the intermediate principal stress will be designated S2. In the previous paper, attention was confined to stress combinations with two of the principal stresses equal (with the intermediate principal stress S2 equal either to S3 or S1). In this paper, consideration will also be given to the effect of stress combinations with all three principal stresses unequal. In the earlier sections of the paper (pp. 1 to 14), attention will be confined to stress combinations with

Jan 1, 1942

BASIC open-hearth slags have no obviously unique features when compared with slags from other metallurgical operations. Open-hearth slags form and exist at temperatures ranging from 2500 to 3100 F (1370 to 1700 C). In the course of an open-hearth heat, the liquid slag changes slowly and continuously in chemical analysis-the changes reflecting changes in temperature, changes in metal analysis, solution of charged materials, solution of feed additions, and solution of refractories. Through- out the process, the slag performs specific primary functions that are responsible for a large measure of the technical and economic importance of basic open-hearth steelmaking. It is intended in this chapter to present the chemical reactions by which the primary functions of basic open-hearth slags are carried out, to describe the physical and chemical principles governing the extent to which these reactions proceed and can be regulated, and finally to indicate the limitations imposed on other features of the process by the fulfillment of the primary functions. Basic open-hearth slags perform three primary functions. First and foremost, the slag provides a means of removing phosphorus from the liquid metal. The ability to remove phosphorus is largely responsible for the widespread use of the basic open- hearth process. Second, the slag serves as a controlling factor in transferring the oxygen required for the other oxidizing reactions. Third, the slag provides a means of eliminating some sulfur from the open-hearth bath. While the extent of sulfur removal is not comparable to that of phosphorus, the ability to remove some sulfur contributes much to the value of the process. The effectiveness with which the slag fulfills its functions varies with temperature and composition. Since operating temperatures are fixed largely by the specified nature of the product and the equipment, the speed and extent to which the functions of the slag are carried out depend largely on its composition. The necessity for regulating slag composition to accomplish the re-

Jan 1, 1951

By M. R. Geer, H. F. Yancey

WITH the exception of pneumatic processes and ii few special beneficiation methods of comparatively limited application, all mechanical coal-cleaning and mineral- dressing processes involve the admixture of solid particles with a liquid, generally water. Upon completion of the beneficiation process the solids must be reclaimed from the water. With coarse particles separation of solids from water is accomplished readily by the simple expedient of screening, but recovery of fine solids presents a much more difficult problem. Thickening and dewatering are practiced so generally, both within the mineral industry and else- where, that they have been the subject of study through the years and a number of processes for making the solid-liquid separation have been developed. Dorr-type thickeners have been standard equipment for many years, and more recently driers employing centrifugal force have gained in popularity. 1 A cyclone device employed to thicken the loess suspension is a novel feature of the loess heavy-medium coal-cleaning process developed by the Netherlands State Mines in the thirties. The cyclone thickener was first mentioned by Driessen2 in 1939 in a paper describing the loess process and has been the subject of two more recent reports by the same author.3 The cyclone does not differ greatly from cyclone dust collectors used in this country for years, except that it is operated wet rather than dry. Advantages of the cyclone over other thickening devices are its simplicity of construction, high capacity, and the fact that, having no moving parts, it is simple and inexpensive to operate. The Bureau of Mines became interested in the cyclone after one of the present authors observed it in operation in the Netherlands in 1945. The first experimental work with the cyclone conducted by the Bureau of Mines was an investigation of the unit functioning as a heavy-medium cleaner for fine coal-a use for the cyclone that was conceived long after it had been perfected as a thickener. The results of this investigation were published last year.4 The present investigation deals exclusively with operation of the cyclone as a thickener. OBJECT AND SCOPE OF INVESTIGATION Although the cyclone thickener has been dealt with in three reports by Driessen, its use as a thickener was not the principal subject of any of these reports and therefore neither the cyclone itself nor its operation was described completely. The design of the cyclone was described only in a very general way, only limited operating results were given, and virtually nothing was disclosed about the influence of the various possible operating variables. Moreover, the Netherlanders apparently had employed the cyclone exclusively for thickening loess and had not employed it on coal slurries. One English colliery has used a cyclone to thicken coal slurry,5 and as it appeared that

Jan 1, 1948

By H. D. Outmans

The paper presents a theoretical approach to the drilling problem based on rock mechanics and drilling fluid hydraulics at the bottom of the hole. The volume of the fractured rock around the vevtically penetrating bit tooth is expressed as a function of the tooth pressure, included tooth angle, drilling fluid pressure and formation characteristics on the assumption that fracturing is preceded by plastic flow. This assumption is verified by comparing the stress-strain state in the rock around the tooth to that in equivalent tri-axial compression tests described in the literature. An expression similar to the above is derived for the tooth penetration in the cuttings which have been retrained at the bottom. Combination of these two expressions leads to a relation between depth of tooth penetration in the virgin rock, the amount of cuttings retained and the other variables. By relating the cutting volume to the drilling rate, the hydraulic bit horsepower and the drilling fluid pressure, it is possible to arrive at formulas which express the drilling rate for viscous or turbulent flow at the cutting surface, for instant clearance, for retained cuttings, or for false tooth foundering as functions of such variables as the drilling fluid pressure, hydraulic horsepower at the bit, rotary speed and bit weight. Plotting the results as drilling curves and comparing them to published field and laboratory data justify the conclusion that the drilling model presented in this paper approximates the actual mechanism. The drilling curves serve to explain some characteristic features of the rotary drilling operation, and the equations may be used for numerical evaluation of the effect of changes in the magnitude of some of the variables on the drilling rate. INTRODUCTION Published laboratory data have established that consistent and relatively simple relations exist between the drilling rate and any one of the important variables. For instance, the drilling rate usually increases at an increasing rate with the bit weight. It increases at a decreasing rate with the rotary speed, decreases at a decreasing rate with increased drilling fluid pressure and plots as an S-shaped curve against the hydraulic horsepower at the bit. This relative simplicity seems difficult to understand considering that the drilling mechanism is a continuous process of generation and removal of innumerable individual cuttings, under different conditions for each. On the other hand, the drilling rate (although determined by this complicated process) only expresses the average rate at which cuttings are produced and cleared away. Ignorance of the drilling mechanism as far as individual cuttings are concerned, therefore, does not exclude the possibility of arriving at a concept of the drilling rate provided the mechanism is properly evaluated for the average cutting. It then may be concluded from the first sentence that this concept also should be rather simple in its final form, although not necessarily in its derivation. Two aspects of the drilling mechanism are difficult to evaluate — (1) the effect a penetrating drilling fluid has on the stresses around a bit tooth entering the formation and (2) the volume of rock fractured by a penetrating tooth which moves both vertically and horizontally. Thus, the scope of this paper has been limited to an evaluation of the drilling mechanism in formations which have a low permeability and are drilled with hard-formation bits. In the following sections, the drilling mechanism is analyzed in three steps. First, the effect of tooth pressure on the volume of fractured rock around the tooth is evaluated, assuming initially that the bottom of the hole is free of cuttings and, then, determining the effect of a layer of these cuttings. In the second section, the thickness of this layer is related to the drilling rate and the chip clearance time, and the latter to the hydraulic horsepower at the bit under conditions of laminar and viscous flow at the cutting surface. In the third section. the previous results are combined with the rotary speed into drilling equations which are then plotted and compared to experimental drilling curves. This section also contains some numerical examples of drilling rate computations. Some mathematical details are given in the appendixes. Finally, it should be mentioned that, although some drilling equations are already available, these equations (with the exception of one' which attempts to relate drilling rate to drilling fluid pressure) are all mathematical expressions for observed laboratory data; none considers the effect of delayed drill-cutting removal, an essential feature of the drilling mechanism.

By C. R. St. John, R. W. Lindsay, Charles R. Austin

Many of the factors influencing the creep behavior of ferrous alloys have been investigated and reported upon in the literature, including such variables as grain size, steelmaking practice, nature and stability of the microstructure, and the effect of alloying elements in steels. However, with respect to the latter, the microstructures involved are usually heterogeneous and as a result the effect of the addition is related to its effects on the various phases present in the microstructure. In the instances where this structure consists of ferrite and carbide, the behavior of the alloy addition will be related to its action in strengthening ferrite and in opposing temperature softening of ferrite as well as coalescence of carbide. The present paper is the third in a series comprising a comprehensive review of investigations on the properties of iron binary alloys.l,2 Its purpose is to describe the results of isolating one microstructural phase, namely ferrite, and studying its creep characteristics in both the unalloyed and alloyed conditions. This should aid in establishing to a large degree the importance of ferrite in the creep behavior of steels consisting of the previously mentioned ferrite-carbide aggregate. In view of the fact that the present investigation deals only with the effects of silicon, manganese, chromium, molybdenum, nickel, and cobalt, and to a certain extent with the effects of carbon, the review of previous literature will be confined to these elements. Practically no references were encountered dealing with the influence of these elements on the creep characteristics of the isolated phase. However, various contributions have dealt with the creep behavior of low-carbon steels alloyed with the elements under consideration. A particularly concise review in this respect is given by Bullens (Battelle)= and much of this material has been drawn upon. The definite improvement in creep resistance and high-temperature strength conferred by molybdenum is well known. Published suggestions by the A.S.M.E.4 permit of an increase of some 2000 to 5000 lb. per sq. in. in permissible design loads over a temperature range from 650" to IOOO °F. as a consequence of additions of 0.40 to 0.60 per cent of this element in carbon steels of the order of 0.25 to 0.35 per cent carbon content. Babcock and Wilcox Tube CO.5 has published data showing the pronounced increase in stress necessary to cause one per cent creep per 10,000 hr. when additions of 0.5 or I per cent molybdenum are made to a plain carbon steel. These data apply to temperatures over a range from 800° to1000°F. 4

Jan 1, 1945

By Hans Conrad, W. D. Robertson

FORMAL theories of yielding and flow have been developed to describe thermally activated plastic flow in metal crystals.'-" hey are all based on Becker's' original idea that thermal fluctuations aid the applied stress in overcoming internal barriers to flow and lead to the following relation. where j is the strain rate; C is a constant which includes a frequency factor, the entropy, the number of flow units, and the amount of strain associated with each successful fluctuation; E(T) is the activation energy associated with flow, and is a decreasing function of the applied stress, 7; k is Boltzmann's constant; and T is the temperature in OK. The various theories differ mainly in the model chosen and in the nature of the relationship between the applied stress and the activation energy. Beckerl and Orowan' suggest a relationship of the form E a(Ti — t)2, where .ri represents the stress required for flow without the aid of thermal fluctuations; Kauzmann,3 Cottrel1,5 and Seeger6,7 suggest E a(t — t) ; Fisher8 suggests E while Cottrell and Bilby4 suggest a more complex relationship between E and 7. Additional data are needed to test these various theories., esweciallv- in view of Dorn's9 ork. which indicates that the activation energy for creep is independent of the stress and strain. The present paper presents the stress-strain data derived from incremental loading of magnesium single crystals in tension and direct shear, in the temperature range of 78" to 364°K. Incremental loading was employed in order that the creep component of the strain could be determined. Stress-strain curves of aluminum10-13 and copper" single crvstals. derived from incremental loading tests, have been found to be in agreement with those obtained by the more conventional constant strain rate or loading rate tests. Two types of tests were conducted in the present investigation: 1) tests in which the temperature was maintained constant throughout the entire

Jan 1, 1958

By Frederick Laist

ABOUT six years ago the Anaconda Copper Mining Co. decided to investigate the possibility of extracting zinc from the ores of certain mines in the Butte district. These ores are of a complex character and contain so much iron and lead that the concentrate contains only 33 to 35 per cent. zinc. Investigations showed that while a high-grade concentrate could not be obtained by ordinary methods, such as tabling and magnetic treatment, a fair grade could be made by the Horwood process. In this method, the concentrate resulting from the flotation of all of the sulfides is given a light roast and this calcine is subjected to flotation in the presence of a large amount of sulfuric acid; the resulting concentrate contains most of the zinc and a residue contains most of the iron. The fact that the lead, copper, and silver are divided approximately equally between the zinc concentrate and the iron residue and the large consumption of acid, which ranged from 50 to 100 lb. (22 to 45 kg.) per ton of concentrates, were serious objections to this plan. The zinc recovery, moreover, was low, as a considerable percentage invariably accompanied the iron. While a profit might be made on the ores by the use of this process, it was thought that other and more promising methods might be devised. After carefully studying the field and doing some laboratory work on various processes that had been suggested, it was decided that the electrolysis of sulfate solutions was the most promising. We soon found, as have other investigators, that the only way to obtain a good zinc deposit is to have the electrolyte free from all metals more electro-negative than zinc, such as copper, cadmium, lead, arsenic, antimony, etc. Arsenic and antimony are particularly injurious, causing very poor current efficiency and small yield per horsepower when present in amounts so small as almost to defy detection-1 mg. or less per liter.

Jan 10, 1920

By William G. Kegel

Aside from having a usable product and good mining conditions, the greatest asset for a profitable coal mining organization is an effective mine maintenance program. The first step in acquiring this is the presence of good mechanics-men who have a desire to be mechanics and who want to know more about the design and control of the machines in their charge. The knowledge and ability to be found in a good mechanic is the result of ambition, curiosity, and determination. With these qualities as a start, the aspiring mechanic can launch his career if he begins learning all he can about mechanics, electricity, and hydraulics. The path is rough, but the goal is rewarding. Mining machinery probably absorbs as much or more abuse than any other heavy equipment in use today. And when one considers the conditions under which much of the repair work must be done, it can be seen that the mine operator needs the best of men and tools to perform the service. MOTORS AND POWER SUPPLY Mining machines, from their inception, have utilized the electric motor; and down through the years of mechanization, this power source has undergone many changes to better adapt it to the job. The first motors used were large, heavy-framed, open d-c motors (direct current), using a series or shunt winding. A motor having one or more field coils connected in series and themselves in series with the armature, is called a series motor (Fig. 1). The series motor had the advantage of quickly developing starting torque, and it was, and still is, the best motor for locomotive or shuttle car tramming service. The series motor, however, speeds up as the load is reduced and, if not properly controlled, can overspeed. The shunt motor, as its name implies, has one or more field coils in

Jan 1, 1973

By M. R. Goldick

THE Roan Antelope concentrator was originally designed with a nominal milling capacity of 6000 tons of copper ore per day but this was subsequently considerably exceeded. In broad outline the plant consisted of two No. 30 McCully gyratory crushers for coarse crushing, five 5 1/2-ft Standard Symons crushers in open circuit for secondary crushing, ten No. 98 Marcy ball mills arranged in five sections, each two-mill section with primary and secondary Dorr classifiers for two-stage grinding. One stage of flotation roughing was followed by two stages of cleaning, all in airlift type pneumatic flotation machines, with the final concentrates filtered on Oliver drum filters. Tailing was thickened in a 250-ft Dorr traction type thickener before pumping to the tailing dam. Concentrating operations commenced in June 1931, on the completion of the first two ball-milling sections and output was increased during the next few months as the remaining sections were finished. From the start, very few technical difficulties were experienced but a number of evolutionary changes have been made as a result of operating experience and the availability of improved equipment. These have resulted in plant and ore-flow alterations although the general scheme of ore treatment remains substantially as before. The main changes to date were the installation of a new crushing plant at Storke shaft, some 7000 ft west of the original Beatty shaft; the completion of a two-stage secondary crushing plant; an increase of 20 pct in ball-milling capacity; a change-over from pneumatic to a mechanical type of flotation machine for flotation roughing; the reduction of flotation cleaning from two stages to one stage. ORE TREATED Typically the ore treated consists of metamorphosed shales and sandstones with shales as the principal mineral-bearing rock carrying chalcocite, bornite and chalcopyrite as the main copper minerals. Chalcocite predominated in the original eastern end of the ore body but there is a pronounced trend to an increased proportion of the copper-iron sulphides as mining proceeds westward. Although the ore can be described as soft, this advantage is offset by the extremely fine dissemination of the copper minerals which calls for a high degree of comminution of the ore (90 pct minus-200 mesh Tyler standard) to give a reasonably satisfactory separation of mineral from gangue. Latterly, there has been a tendency for the ore to become harder as shown by a reduction in the ball-milling rate from a previous figure of over goo tons per ball-mill day to the present output of some 800 tons. Chalcopyrite is not so finely disseminated and has also proved more amenable to flotation than chalcocite. Nonsulphide minerals are mainly the so-called oxides such as malachite, cuprite and melaconite with some chrysocolla and

Jan 1, 1947