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By Paul E. Nilles

For every single BOF heat, the steelmaker must control the refining operation in order to satisfy at turndown the following conditions : - to reach the correct steel analysis (C, S, P, ...) in the shortest time possible, i.e. without reblow; - to maintain the temperature of the metal in a narrow range; - to produce the optimum steel weight. It is obvious that during refining limited time and scarce information are available and only very few corrective actions can be taken. For this reason, it is of the greatest importance to facilitate the control of the BOF process by taking adequate measures before and during charging of the converter. These are : - the availability of accurate and reliable equipments for the classical measurements, 5.e. weights, temperatures, flow-rates, analyses, etc... - the operation of an optimal charge calculation model which takes into account all information concerning the preceeding heats and the charged materials. '

Jan 1, 1972

OPEN-HEARTH refractories are not merely an accessory to the furnace. They themselves ore the furnace, to all intents and purposes. The steel work of the main structure is merely a frame which helps to support the refractories; and the regenerators, a necessary part of the furnace system, consist almost entirely of refractories with very little supporting structure. Not only do refractories constitute the essential part of the furnace, but they also carry the liquid steel all the way to the point where it begins to solidify. On leaving the furnace the liquid passes through a refractory runner into a refractory-lined ladle, then through a refractory nozzle closed by a refractory stopper on the end of a refractory- protected rod. The liquid is sometimes sent through an additional refractory-lined tun-dish, a supplementary ladle, or a refractory runner for bottom pouring, until it finally enters the iron mold in which it solidifies. Even in the mold, refractory materials are sometimes used to provide a non-conducting "hot top." These materials, from ladle to hot top inclusive, are often referred to as the "pouring-pit refractories." CAUSES OF FAILURE Compared with the equipment used in most industrial processes the open-hearth furnace has a relatively short life. The most important quality of an open-hearth refractory, therefore, is its rate of failure. The discussion here of the individual refractory materials will therefore keep uppermost the question "Why, how, and where does it fail?" The principal causes of failure of open-hearth refractories are, in their order of importance: 1. Reaction with iron oxides. 2. Reaction with slag. 3. Flow and failure under load. 4. Melting. 5. Spallimg. 6. Mechanical breakage. Reaction with Iron Oxides and Slag. This is by far the most important cause of failure. Liquid iron oxide comes very near to being the

Jan 1, 1944

By T. K. Perkins, W. W. Krech

Jan 1, 1969

By C. K. Leith, W. J. NEAD

(Glen Summit Meeting, June, 1911.) . ONE Of the most significant developments in the iron industry in recent years has been the discovery and opening of enormous reserves of low-grade ore in eastern and northeastern Cuba. The two principal fields are the Mayari and the Moa, situated on Nipe bay, in the Province of Oriente. A less well-known district of the same type is that of Baracoa, at the east of the island, and another is in Camaguey province in central Cuba. In the comprehensive estimates of the iron-ore reserves of the world, published during the summer of 1910 by the International Geological Congress in Sweden,' these Cuban deposits are estimated at about 2,000,000,000 tons. Certain it is that the reserve is a large one. The Spanish-American Iron Co., the Juragua Iron Co. (Bethlehem Steel Co.), the U. S. Steel Corporation, and others have been active in this exploration.. The Spanish-American Iron Co. has established a port for the handling of these ores at Felton, has built a railway 16 miles to the ore-fields, and has opened up deposits for steam-shovel mining. Its expenditures have reached an aggregate of about $6,000,000 in preparation for the handling of these ores. Shipment of the ore to Sparrow's Point, Md., has begun and may be expected to rise to a considerable amount in the near future. The ore reaches this point at a cost per unit of iron considerably lower than Lake Superior ores, and the presence of a low percentage of nickel gives a desirable steel. It is not the purpose of this article to consider these ores from a commercial stand-point, but rather to discuss their-origin. If our conclusions are correct, they throw light on the character of the deposits which should have some commercial significance. 1 The Iron Ore Resources of the World, an inquiry made upon the initiative of the Executive Committee of the Eleventh International Geological Congress, Stockholm, vol. ii., p. 795 (1910).

Mar 1, 1911

THE primary interest in the subject of this chapter lies in the fact that various heats of steel made to the same chemical specification do not always have the same properties. The properties considered here, of course, are those inherent in the ingot immediately after solidification and not qualities imparted by variations in subsequent mechanical or thermal treatment. The expression "made to the same chemical specification" is used because some of the variations in properties are due to variations in chemical analysis within the specified ranges of those elements commonly specified and determined. Other variations in properties are due to variations in those constituents of steel (elements or compounds) that are not ordinarily included among the elements specified, thus not a part of the specified "composition." The term "constitution" is used to include not only the specified composition but also the nature and distribution of every element or compound contained in the steel entering the ingot mold ; also included are items such as aluminum oxides and nitrides, presence of soluble gases, and dispersion of nonmetallic particles. When it is considered that the constitution of steel is determined by the addition or absorption into the bath of all such constituents from whatever source, it follows that constitution is of necessity the final result of steelmaking practice. It is the agency through which steelmaking practice operates to control the properties of the steel. The term steelmaking practice is here used in the broad sense, meaning the control of all the materials entering the steel and of the conditions under which the process is carried out. Steelmaking practice, thus defined, establishes the chemical system within which the reactions between components must proceed in obedience to the laws of chemistry. Thus the chemical constitution of the steel is established and, through constitution, the properties of the metal are established. In the preceding chapters it has been shown how the constitu-

Jan 1, 1964

By A. F. Crawley

The density and viscosity of 1iquid thallium have been measured by absolute methods to temperatures of about 200° and 150°C, respectively, above the melting point. These new data reported, especially density data, do not closely confirm previous work. Density p, in g per cu Cm, is shown to vary linearly with temperaluve t, in °C, according to the equation p = 11.658 - 1.439 X l0-3t. The viscosity data obey the well-known Andrade equation nv1/3 = A exp C/vT , the constants A and C for thallium having values of 2.19 x A and 79.648, respectively. This paper reports some new data for the density and viscosity .of liquid thallium. Measurements of these fundamental physical properties were undertaken as part of a continuing research program at the Mines Branch, Department of Energy, Mines and Resources, Ottawa. Canada. A literature search has revealed that data are so scarce that there could not be a consensus on the true values of the density and viscosity of liquid thallium. To be more specific, there exists only one set of viscosity data' and only two acceptable sets of density data,273 one of which is limited in scope.3 In Liquid Metals Handbook,3 another density study is reported but indications of impurities in the thallium render the results suspect. In this situation, further careful experimentation was required to realize the true density and viscosity of thallium. EXPERIMENTAL METHODS Density. Densities were determined using a graphite pycnometer. The technique and its accuracy have been discussed in earlier papers.4'5 It is considered that experimental data can be obtained which are accurate within +0.05 pct, all sources of random and systematic errors having been evaluated. Density results for thallium were identical whether measured under an atmosphere of argon or a vacuum of 5 x 10-6 torr and, for the most part, the argon atmosphere was used. Viscosity. Viscosity measurements were made in an oscillational viscosimeter by an absolute method—the liquid metal being held in a closed graphite cylinder. Design and operation of the apparatus, constructed in this laboratory, have previously been discussed.6 For thallium, runs were made under a vacuum of about 2 x 10-6 torr. To evaluate viscosity coefficients from the various experimental parameters, the mathematical analysis of Roscoe7 was used. Measurements of the necessary parameters and the accuracy of these measurements have also been discussed.6 The cylinder dimensions were corrected for the anisotropic expansion of graphite, as discussed for density measurements.4,5 It is well-known that thallium oxidizes rapidly and hence a newly machined surface quickly tarnishes in air. The oxide film, however. is nonadherent and is easily removed by rubbing or by solution in water. Hence, immediately before use, both density and viscosity charges were immersed in water, wiped dry, and quickly transferred to the apparatus which was then rapidly evacuated. Specimens removed after determinations were only slightly tarnished and there was no other evidence that tarnishing affected the results. For example, the sharpness of the specimen edges from the containing vessels indicated complete filling by the liquid metal. Thallium of 99.999 pct purity was used in this investigation. Because of its high toxicity care was exercised in handling this material. For example, the melting procedure to prepare machinable ingots was carried out in an open, well-ventilated area, while protective gloves were always worn when handling the solid metal. RESULTS AND DISCUSSION Density. Measurements were made over a tempera-ture range of about 200°C above the melting point. The results are listed in Table I and plotted in Fig. 1. From the graph it is evident that the relation between density and temperature is linear. Such a relation has been observed before in this program for other metals and alloys475 and elsewhere by other workers. A least-squares analysis of experimental data gives the equation: pT1 = 11.658 - 1.439 x 10-3t where p = density in g per cu cm and t = temperature in "C. In Fig. 1, together with the present results, the data of Schneider and Heymer2 in the corresponding temperature range have also been plotted. Evidently, the two sets of data do not agree well, the results of Schneider and Heymer being about 0.6 pct higher. Viscosity. Viscosity data were obtained from the melting point, 303.5°C, up to 457.5"C. The data are listed in Table I and in Fig. 2 the plot of these results demonstrates a smooth curvilinear relation between

Jan 1, 1969

The Sub-committee on Coal Mining, since its appointment, has been collecting data about subsidences in coal mines in this country, and thinks that almost all of the available data about occurrences of this sort in bituminous mines has been collected. Similar data is being compiled for the anthracite regions, which it is hoped will be ready for the 1927 meeting. As most of the bituminous seams are nearly level, the records obtained give the problem in its simplest form, without complications due to the pitch of the seam. Copies of the questionnaire, Appendix A, were mailed to all of the coal operators' associations, to most of the large operating companies and to many engineers, with the request that any data on the subject be returned to the committee, or that advice of any subsidences known be given: the replies to most of the questionnaires were general, although some specific cases were given. Many of the companies were unable to reply to all questions, as they lacked the necessary data, but in nearly every case where accuratc data was available, it was cheerfully furnished, and any additional information requested was secured. All specific cases of subsidence were followed up by correspondence, and in several cases by personal inspection. Figs. 1 to 31 were made from the information furnished. Table 1 gives measurements of elevations taken in one case at intervals from October, 1913, to May, 1918. With one exception, where the evidence cannot be released on account of a lawsuit, it is believed that the cases submitted with this report include practically all that have happened in bituminous coal mining in this country of which actual measurements were secured. Some of these have been published by Young and Stoek,l and some have been secured from other publications. In collecting these data, the subcommittee had the Engineering Societies Library extend its bibliography to date; this list is given in Appendix B. To assist in the study of the problem, all of the subsidence literature in English was examined for cases in which spccific measurements were given, and the essential data for each case are shown in Appendix C.

Jan 1, 1927

By Charles Will Wright

THOSE that attended the seventeenth International Geological Congress held in Russia last summer had an excellent opportunity to gather data and to form impressions on the progress made in the industrialization of the country, particularly with regard to the mineral industries. Several trips to places of interest were arranged, supplementary to the technical sessions held in Moscow, the one to the Ural region being that which I selected as being most likely to be of interest. The accomplishments of the last decade in opening up new mines and building new metallurgical plants in the Soviet Union have been outstanding. This could only be accomplished by a central government ready to employ the best technical talent, which was

Jan 1, 1937

By T. S. West

Completion and production data presented for three wells in the Oakville area of Live Oak County, Texas, which were completed near the gas-oil or water-oil contact, indicate that coning may not be as prevalent a cause of failure in such cases as is commonly assumed. Failure in the cases discussed is indicated to be due instead to: (I) erosion of the formation, (2) flowing out of mud filter cake, or (3) failure of the cement. An open-hole gravel-pack type of completion procedure is proposed for preventing failures of this kind by preventing movement of all solid material in the space in which completion is made. Various combinations of layers of gravel, sand, and cement are utilized for this purpose. Experimental results and theoretical discussion as to the applicability of gravel pack completion are included. Introduction This paper is primarily a study of the reasons for failure of oil-well completions near the gas-oil or oil-water contact, and suggests a procedure for increasing the efficiency of this type of completion. The value of improvement in completion effectiveness near the gas or water zone is not confined, however, to wells of relatively thin oil columns. Thick oil columns become thin as depletion progresses. It would seem to follow that the minimum distance from the gas or water zone at which completion can be made in a new well indicates the limit to which depletion may be carried in a well having an oil column of any initial magnitude. Only four ways can be postulated in which high gas-oil or water-oil ratio can initially occur if the zone exposed for production is within the oil column: 1. Failure of the cementing material. 2. Vertical coning. 3. Failure along the boundary between the cement and the wall of the well. 4. Failure of the formation comprising the wall of the well. Cementing materials such as portland cement and plastics have reached a high stage of development. Failures of this type are probably due almost always to extraneous causes such as mud contamination rather than to faulty cementing material. Vertical coning can and obviously does occur. However, the usual occurrence of thin impermeable streaks in sand sections and the success with which open-hole drill-stem tests can be made near the gas-oil contact suggest that over-all effective vertical permeability, and in turn vertical coning, is less prevalent than frequently is assumed. Much has been written on failure by flowing out of the mud filter cake between cementing material and the formation. A filter cake is always present if, prior to cementing, mud has come in contact with a permeable formation at pressures exceeding the pressure head of the fluid it contains. Mechanical methods are in use for removing filter cake during the cementing operation? which undoubtedly are of

Jan 1, 1947

By T. S. West

Completion and production data presented for three wells in the Oakville area of Live Oak County, Texas, which were completed near the gas-oil or water-oil contact, indicate that coning may not be as prevalent a cause of failure in such cases as is commonly assumed. Failure in the cases discussed is indicated to be due instead to: (I) erosion of the formation, (2) flowing out of mud filter cake, or (3) failure of the cement. An open-hole gravel-pack type of completion procedure is proposed for preventing failures of this kind by preventing movement of all solid material in the space in which completion is made. Various combinations of layers of gravel, sand, and cement are utilized for this purpose. Experimental results and theoretical discussion as to the applicability of gravel pack completion are included. Introduction This paper is primarily a study of the reasons for failure of oil-well completions near the gas-oil or oil-water contact, and suggests a procedure for increasing the efficiency of this type of completion. The value of improvement in completion effectiveness near the gas or water zone is not confined, however, to wells of relatively thin oil columns. Thick oil columns become thin as depletion progresses. It would seem to follow that the minimum distance from the gas or water zone at which completion can be made in a new well indicates the limit to which depletion may be carried in a well having an oil column of any initial magnitude. Only four ways can be postulated in which high gas-oil or water-oil ratio can initially occur if the zone exposed for production is within the oil column: 1. Failure of the cementing material. 2. Vertical coning. 3. Failure along the boundary between the cement and the wall of the well. 4. Failure of the formation comprising the wall of the well. Cementing materials such as portland cement and plastics have reached a high stage of development. Failures of this type are probably due almost always to extraneous causes such as mud contamination rather than to faulty cementing material. Vertical coning can and obviously does occur. However, the usual occurrence of thin impermeable streaks in sand sections and the success with which open-hole drill-stem tests can be made near the gas-oil contact suggest that over-all effective vertical permeability, and in turn vertical coning, is less prevalent than frequently is assumed. Much has been written on failure by flowing out of the mud filter cake between cementing material and the formation. A filter cake is always present if, prior to cementing, mud has come in contact with a permeable formation at pressures exceeding the pressure head of the fluid it contains. Mechanical methods are in use for removing filter cake during the cementing operation? which undoubtedly are of

Jan 1, 1947

By L. W. Saperstein, Y. J. Wang

The development of computer programs to solve complex ventilation networks has reached a point of refinement where these programs become a necessary tool of the ventilating engineer. Such a program is presented. This program has an increased efficiency over its predecessors; it also includes the important facility of fixed quantity branches. This is in addition to the earlier capabilities of free-splitting, internal or external fans, and natural ventilation pressures. The program is written in Fortran IV with double-precision arithmetic and is listed here. Sample problems with input and output are also given. The recent, and presumably continuing, official interest in mine safety is bound to result in more stringent control requirements for ventilation. Anticipating this requirement, the Dept. of Mining, The Pennsylvania State University, has developed a computer program for the solution of complex mine ventilation networks. It is the opinion of this department that the program has sufficient merit to warrant its use in normal industrial operating conditions. Although the undergraduate mining engineering students of this department are routinely trained to use the program, it was felt that this training did not present a fast enough means of dissemination; consequently, this paper was written. The conception of the program is not new;1; however, the present version incorporates features that changes it from a scientific endeavor to a useful operating tool. These features include those of earlier programs, such as free-splitting, external or internal fans, and natural ventilation processes plus the important ability of handling fixed quantity branches, and of increased efficiency giving reduced cost. The facility for fixed quantities will be discussed in more detail. The solution of any network depends upon satisfying Kirchchoff's laws. These state that the sum of flow at any junction is zero, and that the sum of the pressure drop in branches totals the pressure drop in the mesh constituted by those branches, that is that the pressure drop around any mesh is zero. The terminology is derived from Synge," and is, in fact, that used by Topologists. A branch is any airway of uniform characteristics; a junction is where two or more airways meet (the minimum number of two airways is useful for describing the point where a low resistance airway changes into a high resistance one due to some physical constriction); a mesh is a path, along some branches, that returns on to itself, but does not need to traverse the same branch twice in order to do so; and a tree describes all those branches in a network which, while connected through all the junctions, do not form any meshes. Obviously the branches-in-tree are open-ended and can be shown to be one less than the number of junction (J-1). The branches-out-of-tree, also called basic branches, are equal to the number of basic meshes and are M = N — J + 1, where M is the number of meshes and N is the number of branches. The major difference between this network and an electrical one is that the law attributed to Atkinson for pressure drop is utilized rather than Ohm's law. Atkinson stated that the pressure drop (potential) is equal to a resistance factor multiplied by the quantity squared. This is written H = RlQlQ where H is the head loss. Q? is written in this factored fashion so that H will always have the same sign as Q. A negative sign is used to indicate that flow in a branch is opposite to that of its containing mesh. A mesh takes the direction of its basic branch. Utilizing Atkinson's law in Kirchchoff's second law and bearing in mind that the first law must remain satisfied, the program will determine all quantities, or head losses as they are related, for the branches of the network. The program uses a Geuss-Seidel form of in-teration, starting from an arbitrary Q and using a correction factor of the type first suggested by Professor Hardy Cross' that will handle the nonlinear equation of Atkinson's law. A fuller description of the interative process is included in Wang and Hartman.' Iteration continues until the correction factor is less than or equal to a preset error (E) or until a maximum number of iterations (MAXIT) have been reached. Utilizing an E of 50 cfm, sample problems have had rapid solutions. Rapidity of solution is also ensured by the method of selecting meshes and basic branches. This is done by the computer, which chooses the highest resistance branches, fixed quantity branches, and those containing fans, as basic branches. Natural ventilation pressures are handled as fans of constant pressure and may be assigned to any branch. The computer will generate a fan characteristic by polynominal fitting if a few operating points from the desired fan are input. A fan may be placed in any branch of the network, except those with fixed quantities. The strength of the present program over its earlier versions is its ability to handle fixed quantity branches. This means that certain branches can have their quantity determined, or preset, by the ventilating engineer. Operating under this constraint, the program will analyze the network and output the pressure change necessary to achieve this desired quantity. A call for positive head loss would require an auxiliary fan; negative head loss would require a regulator. This represents a powerful tool for the ventilating engineer who must insure that certain quantities of air pass across the operating faces or through working stopes. McPherson6 suggested that a ventilation program would be useful for determining in advance which branches were receiving inadequate air, and that subsequent calculations would then indicate the necessary corrections. The present program makes these corrections. Thus the mine manager can know immediately the consequences of changes to his system;

Jan 1, 1971

By D. W. White

The kinetics of isothermal transformation of ß-to-u uranium have been studied over a broad temperature range in alloys containing from 0.3 to 4.0 atomic pct Cr. Two modes of transformation are indicated by the existence of two C-curves in the TTT diagram. The upper temperature mode is regarded as a nucleation and growth mechanism, whose rate is controlled by diffusion of chromium in the ß phase matrix. The lower temperature mode is martensitic in nature. The M, temperature increases with decreasing chromium content, suggesting that the two transformation processes become synonymous in unalloyed uranium. URANIUM metal undergoes two allotropic transformations in the solid state. The a phase, orthorhombic in crystal structure,' is stable from room temperature up to about 665°C. The ß phase, characterized by a complex tetragonal structure,' prevails from 665" to about 770°C. The y phase is body-centered-cubic3 and is the stable modification from 770°C up to the melting point (about 1130"). In uranium of reasonable purity, neither of the two high temperature phases can be retained by quenching. However, the addition of certain alloying elements to uranium makes it possible to retain either the y-uranium phase or the ß-uranium phase at room temperature. Chromium alloyed in small amounts with uranium will permit retention of the ß-uranium phase in a metastable state at room temperature upon quenching from a ß-phase temperature.' From available information' on the equilibrium phase diagram for the U-Cr alloy system (Fig. I), it is to be expected that, however sluggish in its rate, the ß phase in such alloys should decompose eutectoidally to a phase and elemental chromium. It was the aim of this investigation to measure the rate and study the nature of this decomposition as a function of temperature and of chromium content. The investigation was reported in classified literature about five years ago and has recently been declassified for publication. In the meantime, there have appeared the papers of Holden,5 Mott and Haines,".' and Butcher and Rowe8 ealing with the metallography and the crystallography of the ß-to-a transformation in U-Cr alloys. These investigators have confirmed several of the phenomenological observations that will be described in the present paper and have examined in considerable detail certain aspects of the transformation and its mechanism. Although all of these investigations have concerned themselves experimentally with U-Cr alloys for the most part, an important consequence has been a clearer understanding of the nature of the ß-to-a transformation in uranium metal itself. Experimental Procedure This investigation dealt with a series of uranium alloys varying in chromium content from 0.3 to 4.0 atomic pct (0.066 to 0.90 weight pct). On five of the alloys, rates of isothermal transformation from the ß to the a phase were measured over a wide temperature range, leading to the development of TTT (time-temperature-transformation) diagrams. Transformation rates were measured over certain narrow temperature ranges on additional alloys. The alloys were prepared by vacuum melting and casting, using zircon or magnesia crucibles and graphite molds. Electrolytic chromium was used as the alloying addition, and the uranium was Mallin-ckrodt biscuit metal that had been vacuum remelted and cropped to remove many of the nonmetallic impurities that had floated to the top of the ingot. The ingots, 3/4 or 1 in. diam, were reduced in size by swaging. Alloys containing less than about 2 atomic pct Cr were swaged at 250° to 275°C, with initial and intermediate anneals at 550°C after every 75 pct reduction in area. Alloys with higher amounts of chromium were swaged at 550" to 600°C, although at the smaller sizes some of them were reduced by the procedure used on the more dilute alloys. Before use as test specimens, the swaged rods were annealed at 700" to 720°C for several hours, followed by slow furnace-cooling. The purpose of the anneal was to achieve the maximum amount of solution of the available chromium into the ß phase, as well as to remove extensive preferred orientation. The isothermal transformation rates were measured dilatometrically, using a quenching dilatometer and an experimental technique similar to those employed by Davenport and Bain in their original work on the transformation kinetics of austenite in

Jan 1, 1956

By R. A. Wagstaff

SINCE the time of the early Egyptians, the use of copper has been a boon to the life of most of the civilized world. Its use has been varied; in many connections, the art by which it attained its greatest usefulness has been lost. In this paper an endeavor will be made to take into consideration some of the many changes that have occurred during the last 40 years of copper-smelting operations. During that period the copper blast furnace has been almost forced out of existence by new methods of ore concentration-first, gravity concentration, and then flotation. These new methods of concentration introduced many new factors into the metallurgy of copper. The product was wet, it was fine and it was high grade. To overcome all these factors many changes have been necessary throughout the smelting agenda. New equipment has been necessary for transportation, unloading, sampling, bedding and moisturing in all smelting plants, especially the custom smelter. During the early days of "flotation," little was known about filtering or the use of an alkaline circuit; often the concentrate going to the smelter contained 20 to 25 per cent moisture. It is easy to imagine the difficulty arising with a product of this nature when it had to be shoveled by hand labor. To meet these conditions, mechanical unloading and sampling devices were soon developed. In many instances such good progress was made that actual costs for handling this unfavorable product were lower than those formerly incurred on the old product. Today most sampling of copper ores and concentrates is being done by mechanical sampling, pipe or augur sampling, or shovel sampling. Where concentrates are uniform in metal content, a great many of the plants now use pipe or augur sampling. For spotty ores, the old shovel sample with cone and quartering during the final stages is still in use. Where big tonnages are handled, mechanical sampling of concentrates is being done, with satisfactory results. To curtail slow and tedious cutting and mixing procedure, mechanical mixing boxes, splitters and cutters are used to cut down labor costs. MILLING As crude ores become scarcer, the use of milling operations increases. The few crude ores that are still smelted are used as fluxing types. To use these ores finer grinding has been found advantageous. This has made for better bedding and fluxing conditions, which in turn makes for faster smelting, lower fuel consumption and better metal recovery. The degree of fineness is more or less determined by the nature of the product. Most plants have set a standard of through ¾ -in. mesh screen for roaster- reverberatory smelting and through ¾ in. mesh screen for converter fluxes. For some refractory ores; even finer grinding has been found to be advantageous for good reverberatory smelting.

Jan 1, 1944

By C. T. Holland

This discussion is concerned with those com-J- paratively infrequent bumps that eject material from the failed mass with enough energy to wreck heavy machinery and seriously injure or kill people. In such cases there is a loud report, and the pressure waves set up in the mine atmosphere wreck ventilation controls several hundred feet from the site of the failure. Vibrations are induced in the earth's crust which may be detected several miles from the point of origin, and explosive gases may be released in large quantities." Usually a dense suspension of dust is produced from the failed mass, together with dust placed in suspension by the resulting air blast. These rock bursts or bumps have also been called mountain shots, bounces, pillar bursts, and crumps. Such occurrences, when extensive, are serious catastrophes, and may force abandonment of the mine.' CAUSES OF ROCK BURSTS Rock bursts in coal mines have occurred in sev-eral places under diverse geological conditions, mining methods, and/or practices. A study of many such occurrences indicates that they depend on the following conditions: 1) cover thickness of 500 ft or more, 2) cover composed of strong members and having a strong member lying close to or on the coal bed, and 3) a floor that does not readily heave. The minimum thickness of cover under which coal mine rock bursts occur is based on observation. Under unusual circumstances involving very strong roof members and/or mining systems, and/or practices especially likely to induce bursts, a burst conceivably could occur under less roof. Under special circumstances rock bursts have occurred in marble quarries almost at the surface.' Furthermore, under very heavy cover it is likely that controlling roof members need not be as strong and as close to the coal bed to cause bumps. Just what constitutes a strong roof or roof member is open to question. Obviously the strength of a roof member is determined by its thickness, the distance between bedding planes across which little or no bond exists, the spacing and development of joints, and the inherent strength of the rock material. Strata sections showing roofs under which rock bursts in coal mines have developed are illustrated in Fig. 2. In several instances the strength of rocks composing the roof of mines developing bumps has been tested. The tests (Table I) show that these rocks develop considerable strength in compression, bending, and shear and that in some cases the strengths are very high. No quantitative data are available concerning joints in roof members over coal beds where rock bursts have occurred, but the author has examined many mines subject to bursts and has received the impression that joints in the shales immediately over the coal beds are always present and well developed. In the main sandstone or conglomerate members themselves, however, where observed, he has yet to see a fracture system indicating well developed joints. Undoubtedly joints are present, but the evidence indicates that they are few, poorly developed, and widely spaced. In a mine subject to bumps, moreover, actual measurements of roof spans up to 225 ft between supports under a cover of about 800 ft have been made before roof failure occurred. Such spans signify strong roof. In coal beds subject to rock bursts, the bottom rock is usually a sandy shale. A few tests (Table I) have been made on the floor rock of coal beds. Observations in mines indicate that they are usually weaker than roof rocks and that under load they show more plastic effects. Observation in ground subject to bursts invariably indicates a relatively strong floor highly resistant to heaving, although some heaving may occur. Other factors listed as favorable to rock bursts are: 1) mountainous surface; 2) steeply dipping beds; 3) proximity of faults, folds, and other similar geologic structures. Many bursts have occurred in mines under mountainous country, although many bursts in mines under a surface with little relief indicate that thickness of cover, not relief, is the essential factor. In steeply dipping beds, many bursts occur in mines that are essentially flat, and rock bursts have been recorded in beds dipping as much as 35o Most rock bursts in the U. S. occur in beds that dip less than 10 pct. It is also true that most U. S. coal is produced from beds dipping less than 10 pct. Geologically, faults are regarded as providing stress relief, but in the vicinity of faults, as well as sharp folds, it would seem that residual stresses could be present. The fact that rock bursts occur in areas remote from faults and sharp folds suggests that their presence is not necessary for this phenomenon to take place. There have been many bursts close to faults and folds, and it may be assumed that occasionally such structures accentuate their occurrence3 The conditions and circumstances under which they occur, coupled with the effects produced, leave In the Crowsnest Pass coalfield, British Columbia, a rock burst is estimated to have released 1.8 million cu ft of methane.

Jan 1, 1959

By Walter E. Duncan

The ores treated at the concentrating plant of the Mahoning Mining Co. at Rosiclare, Ill., come largely from the blanket replacement deposits of the northeastern part of Hardin County, Illinois, and consist of complex mixtures of galena, sphalerite and fluorspar in a gangue of quartz, limestone and sandstone. The several minerals are so intimately inter-grown that they are not liberated at the sizes usually treated by gravity concentration in the usual fluorspar plant. For this reason, an all-flotation method of concentration was developed in cooperation with the station of the U. S. Bureau of Mines at Rolla, Mo.1 This flotation separation made possible the commercial production of four coyentrates: (I) lead, (2) zinc, (3) acid-grade fluorspar and (4) metallurgical-grade Auorspar.2-3 Although fluorspar had been floated in Canada in 19214 and a plant at Rosiclare had been floating fluorspar since March 1929, fluorspar flotation was given considerable impetus by the Mahoning developments, since some features of the separation were quickly adopted by other fluorspar companies. The Bureau of Alines5 reports that in the 10 years preceding 1938 only 50,552 tons of fluorspar flotation concentrates were produced in the United States. The rise from this almost nominal figure to 153,750 tons (largely acid grade) in one year (1944)6 is indicative of the activity in fluorspar flotation occasioned by the war. The industry thus proved to be in a position to expand and keep up reasonably well with the requirements imposed upon it by such developments as occurred in high octane aviation gasoline alkylation, in the use of Freon as a refrigerant and as carrier in the Aerosol "bug bomb," and in the atomic bomb project as well as in the expansion of other activities requiring hydrofluoric acid; for example, the aluminum industry. Despite the fact that the greater portion of acid-grade fluorspar produced in the last few years went directly into war uses, the future of the acid-grade field still appears bright. As a result of the activity in fluorine chemistry during the war, it seems likely that in the relatively near future almost every phase of human endeavor will find some fluorine compound involved. The other three concentrates produced deserve some attention in these introductory remarks. The lead concentrates first produced contained both zinc and fluorspar but these did not interfere with their marketing. As will be pointed out later, the quality has steadily improved until today it is a relatively high-grade product. Although some zinc smelters accept concentrates containing limited quantities of fluorspar, it is a very objectionable impurity. Since flotation methods fail in the complete removal of the fluorspar, chemical methods were developed for

Jan 1, 1948

By Walter E. Duncan

The ores treated at the concentrating plant of the Mahoning Mining Co. at Rosiclare, Ill., come largely from the blanket replacement deposits of the northeastern part of Hardin County, Illinois, and consist of complex mixtures of galena, sphalerite and fluorspar in a gangue of quartz, limestone and sandstone. The several minerals are so intimately inter-grown that they are not liberated at the sizes usually treated by gravity concentration in the usual fluorspar plant. For this reason, an all-flotation method of concentration was developed in cooperation with the station of the U. S. Bureau of Mines at Rolla, Mo.1 This flotation separation made possible the commercial production of four coyentrates: (I) lead, (2) zinc, (3) acid-grade fluorspar and (4) metallurgical-grade Auorspar.2-3 Although fluorspar had been floated in Canada in 19214 and a plant at Rosiclare had been floating fluorspar since March 1929, fluorspar flotation was given considerable impetus by the Mahoning developments, since some features of the separation were quickly adopted by other fluorspar companies. The Bureau of Alines5 reports that in the 10 years preceding 1938 only 50,552 tons of fluorspar flotation concentrates were produced in the United States. The rise from this almost nominal figure to 153,750 tons (largely acid grade) in one year (1944)6 is indicative of the activity in fluorspar flotation occasioned by the war. The industry thus proved to be in a position to expand and keep up reasonably well with the requirements imposed upon it by such developments as occurred in high octane aviation gasoline alkylation, in the use of Freon as a refrigerant and as carrier in the Aerosol "bug bomb," and in the atomic bomb project as well as in the expansion of other activities requiring hydrofluoric acid; for example, the aluminum industry. Despite the fact that the greater portion of acid-grade fluorspar produced in the last few years went directly into war uses, the future of the acid-grade field still appears bright. As a result of the activity in fluorine chemistry during the war, it seems likely that in the relatively near future almost every phase of human endeavor will find some fluorine compound involved. The other three concentrates produced deserve some attention in these introductory remarks. The lead concentrates first produced contained both zinc and fluorspar but these did not interfere with their marketing. As will be pointed out later, the quality has steadily improved until today it is a relatively high-grade product. Although some zinc smelters accept concentrates containing limited quantities of fluorspar, it is a very objectionable impurity. Since flotation methods fail in the complete removal of the fluorspar, chemical methods were developed for

Jan 1, 1948

By R. W. Heckel

The conzpaction of metal powders is analyzed through density-pressure curves as a three-stage process — die filling, individual particle motion, gross compact deformatim. The densification occurring during each of these stages is evaluated quantitatively. The amount of densification in the first and second stages is primarily a function of particle geometry. The densification taking place in the third stage is dependent mainly upon the material. AT the present time the densification of powders during compaction is usually described by terms such as "compactibility," "compressibility," and "compression ratio." Schwarzkopfl has proposedthat compactibility be defined as the minimum pressure needed to produce a given green strength, while compressibility be used to indicate the extent towhichthe density of a powder is increased by a given pressure. Compression ratio is generally defined as the ratio of the compact density obtained at a given pressure to the apparent density of the loose powder. 13alshina found that the pressure imposed on a compact affects the relative volume of the compact according to the following relation: hP= - LV + C [ll where: P is the applied pressure, V is the relative volume of the compact, Ratio of the specific volume of the compact to that of the material without porosity. Lisa constant described as the modulus of pressing and is determined by the slope of a plot of h P vs V, and C is a constant which is determined by the intercept of a plot of InP vs V. Several drawbacks of the Balshin analysis may be noted from Fig. 1, which is a plot of pressure (loga-

Jan 1, 1962

By AIME AIME

AN unusually interesting meeting devoted to the discussion of the ways and means of improving coal mining practice, through the larger use of machinery underground, was held in the Auditorium of the Engineering Societies Building on March 11. The meeting was organized by the Materials Handling Division of the A. S. M. E. and held under the auspices of the Metropolitan Section of that Society and the National Coal Association. The New York Section of the A. I. M. E., which had been invited to participate, found itself unable to do so formally because of a conflicting date for its March meeting but informally did its part to aasure the success of the meeting. As a result of the discussion at and preceding the meeting, the National Coal Association, through Walter Barnum, chairman of its research committee, has asked the A. S. M. E. and A. I. M. E. to join the Association in a study of the present problems of the bituminous coal industry. Messrs. Harry L. Gandy, Calvin W. Rice and H. Foster Bain have been selected to act as a committee which shall develop plans for a joint program.

Jan 1, 1926

By E. L. Jr. Spain

THE deposits described in this paper occur over much of Wayne County and in the southeast portion of Hardin County, Tennessee, and in the northeast and northwest portions of Mississippi and Alabama respec-tively. The presence of tripoli in this region has been known for some time and descriptions of various occurrences in Tennessee have been made by Jewell1 and Miser2, while Hilgard3, Lowe4 and Logan5 have treated the deposits that occur in the adjacent portions of Alabama and Mississippi, but there has not been a general survey of the entire field summarizing completely the geology of the deposits with respect to their origin and stratigraphic relationships. During 1934, while engaged in surveys of mineral resources through this region for the Tennessee Valley Authority, the writer collected data with this in mind, and has assembled them in this report. He is indebted to H. S. Rankin and N. A. Rose, of the Tennessee Valley Authority Geology Division, for field assistance.

Jan 1, 1936

By J. M. Roberts, N. Brown

The stress-strain behavior of zinc single crystals was measured over a strain range of 10-6 to 10-2. The phenomenon of macroyielding was observed in detail and plastic strains were detected at almost zero-stress. Closed hysteresis loops were observed during loading and unloading in the strain region of about 10-5. From the hysteresis a frictional stress on the dislocation of about 6 psi was obtained. A preliminary analysis indicates that impurities are primarily responsible for the friction. Nonelastic Strains as much as 10 -4 were recovered depending on the amount of prior deformation. Part of the recovered strain occurs instantaneously upon unloading and the remainder occurs at zero stress. The time dependence of the recovered strain was measured. THIS investigation is concerned with the details of plastic deformation preceding the ordinary yield point as measured with the usual strain sensitivity of about 10-4. The approach leads to internal friction observations in the hitherto neglected frequency range below 10-1 cycles per sec. It is believed that if the phenomenon of macroscopic yielding is to be understood, then the stress-strain curve in the neighborhood of the macroyield point should be greatly magnified. It may then be possible to determine whether macroscopic yielding is a unique event or whether it is a process which begins gradually at a lower stress. In the case of low-carbon steel a unique event obviously occurs at the macroscopic yield point as indicated by a drop in the load, but copper appears to exhibit a gradual transition from the elastic to the plastic state. In zinc the yield point is rather abrupt although the data indicates that some plastic deformation precedes large scale yielding.' One of the purposes of this investigation is to determine whether there is an abrupt transition from the preyield microstrain region to the region of macroscopic deformation. Such a rapid transition would support the concept that there is a critical stress for yielding. The concept that yielding is a unique event associated with such phenomenon as activating a Frank-Read source, freeing the dislocation from solute atoms, dislocations cutting through dislocations, or dislocations moving freely by one another, has been expounded widely on theoretical grounds. It is hoped that highly sensitive measurements of strain in the neighborhood of the macroscopic yield point will shed some light on the event known as the "Yield Point". EXPERIMENTAL METHOD 1) Specimens—High-purity zinc was cast into spherical graphite moulds in air and grown into spherical single crystals by the Bridgman method under a positive pressure of Argon gas. Spectro-graphic analysis of cleaved sections from four crystals showed a purity of 99.994 pet Zn. The specimens were acid machined with an 1/8 in. gage section in a form similar to those used by Parker and co-workers.2 Bausch type grips were fastened to the specimen by Epon VI adhesive. The specimens were oriented so that only [1120] (0001) slip occurred. Fig. 1 shows two of the specimens in the grips. Prior to each test, the gage section of the specimen was given a concentrated HNO3 chemical polish followed by alcohol rinsing and air blast drying. 2) Test Method- The shear tests were performed on an Instron testing machine and the experimental set-up was made very "hard". Strain could be measured to a sensitivity of 10 -6 by means of a capacitance gage extensometer. The design and calibration of this type of extensometer to measure microstrain, as applied to pure shear and tensile tests of metals, will be the subject of a separate paper—therefore, only a brief account will be presented here. The method essentially consists of attaching a

Jan 1, 1961