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By David R. Mitchell, E. C. Carris

THE particular field of application of machines utilizing air currents as the primary separating medium is in the cleaning of fine sizes of bituminous coal. Approximately 18,000,000 tons of bituminous coal was cleaned by air machines in 1947, but such machines have not yet been applied in the cleaning of anthracite. This chapter is limited to a description of the processes in which the separation between coal and refuse depends mainly on a difference in specific gravity. Dry processes depending on differences in coefficient of friction, shape, or other property, are described in chapter 17. The possibility of using air for the separation of coal from refuse was recognized early by mining men and many attempts were made to develop commercial machines. Some of these early machines are described by Berrisford,1 Chapman and Mott,2 and Mitchell.3 Only two machines are extensively used today in the United States, the Stump air-flow jig and the American oscillating table. GENERAL CHARACTERISTICS OF AIR CLEANING MACHINES The principles of gravity concentration and the properties of air as a medium for separation were explained in chapter 9. It was pointed out that because of the low density of air a medium of sufficient density has to be built with the material itself. Hence there must be some device to impart to the bed the necessary mobility for proper classification. It was also noted that the compressibility of the air may cause "geysering" of the bed and disturbance of the hindered-settling classification if the correct balance of conditions is not maintained. Most devices use a vertical upward current of air through the bed of material. They differ by the method of imparting mobility to the bed and the method of removing the refuse. In general terms, the air machines can be divided into three types: 1. Pneumatic jigs where the air current is pulsated. 2. Pneumatic tables where the refuse is diverted from the direction of flow of the clean coal by a system of riffles fixed to the deck.

Jan 1, 1950

By B. M. Larsen

Attempting to review the fundamental aspects of segregation in steel ingots of all types in a paper of reasonable length, we encounter two difficulties: (I) the fact that a large number of different physical and chemical effects are involved, and (2) rather incomplete and confusing evidence on certain aspects of detail and mechanism in the freezing process in which the segregation effect is involved. The best solution seemed to be to link together most of the underlying factors into a simplified theoretical picture that appears to the writer to explain most of the observed data, in the hope that this will serve as a reasonably good target for discussion and criticism. Segregation effects, especially in steel ingots or castings, are often divided into " microscopic" and "macroscopic," depending on whether the variations in concentration of solutes or dissolved elements in the iron occur as: (I) a periodic variation over the small distances between the nuclei and the surfaces of the primary grains, or (2) as a larger scale effect involving concentration gradients over distances of the order of several inches, more or less. The reason for this somewhat artificial division is, of course, that it is only the macroscopic scale effect that has much practical importance. About the only effect of practical importance that results from microscopic segregation is the banded structure often left in rolled sections, and even this is relatively harmless in most cases. However, the causes of microscopic segregation also untlerly the larger scale effect, so we must first consider matters such as the formation and growth of crystal nuclei, selective freezing and diffusion, and others that are fundamental to all sepregation effects. Undercooling and Nuclei Formation It is probable that although the degree of undercooling is small in iron, as in metals in general, a certain amount of it takes place, and also that the number of crystal nuclei increases very rapidly with increased undercooling below the liquidus temperature. In practical terms this means that the nuclei number illcreases very rapidly with increased cooling or freezing rate, thus being dependent on the rate of heat flow out from the zone of crystallization. Temperature Gradients and Heat Dissipation during Freezing Each pound of steel evolves about 100 B.t.u. when freezing. In addition to this, the temperature gradient in the solidified portion (required to dissipate the heat as freezing progresses into the axis) necessitates a loss of heat required to cool the solid metal below its freezing range, which is equivalent to an amount of not so much less in magnitude. In a 5-ton ingot, the total would include about one million B.t.u. for freezing alone and about 0.4 to 0.5 million B.t.u. for the gradient, up to the end of the freezing period. Thus the rate of freezing depends primarily on the rate of heat dissipation. In the ordinary ingot shapes, the axial rate of growth of the solid

Jan 1, 1945

By D. H. Polonis, M. B. Kasen

AN unusual thermal etching phenomenon has been observed on the surface of a Cu-Si alloy. The observations were made during studies of vacancy condensation pit formation which were reported in previous papers.1,2 Figs. 1 and 2 are photomicrographs of the surface of a Cu-4.8 pct Si alloy after heating in vacuo (3 x X mm Hg) to 525°C and subsequently holding at that temperature for 16 hr in an impure (air-contaminated) argon atmosphere. Under these conditions preferential removal of silicon from the matrix by oxidation results in a surface which is entirely a phase overlying an a plus y structure. The light areas of Fig. 1 are regions in which very little thermal etching has occurred, while the majority of the surface has experienced severe etching. Similar regions in Fig. 2 are seen as plateaus above contours produced by net transfer of material from the specimen surface. Twin boundaries are also visible in Fig. 2. The difference in matrix mi-crostructure between Figs. l and 2 reflects the par- ticular orientation of low-index planes with respect to the surface of observation. Thermal etching contours of this type have been studied in detail by Hondros and Moore Both of the photomicrographs show that one or more dark spots are located approximately at the center of every protected area; where two spots are in close proximity, the protected areas have merged. The microstructures indicate that the anomalous resistance to thermal etching is related to the presence of these spots. Williams and Hayfield have shown that local regions of unusually high oxidation resistance can be caused by a surface monolayer of atoms with a work function higher than that of the base material. The result is an inhibition of the rate of electron removal from the base material and a decrease in the oxidation rate. The source of the protected layer may be either surface diffusion from contaminants on the specimen surface or pipe diffusion of solute atoms followed by migration across the surface. In the latter case the driving force is a difference in chemical potential resulting in a Gibbs adsorption phenomenon. In the present case, chemical polishing of the specimen surface precluded contaminants of a strictly surface nature. Consequently, diffusion of impurity atoms from within the lattice appears to be the most tenable explanation of the observed phenomena. The authors propose that the structures of Figs. 1 and 2 reflect the diffusion of impurity atoms along extended dislocations within the individual a phase grains prior to surface oxidation. The central spots within the protected regions are seen as sites of dislocation emergence which have become locally decorated with oxide in the manner discussed in Ref. 1. Williams and Hayfield observed protected regions adjacent to the grain boundaries of iron-contaminated copper which they attributed to the segregation of iron to the grain boundaries coupled with high dif-fusivity along the complex dislocation array at such boundaries. No evidence of such grain boundary protection was observed in the Cu-Si alloy; this

Jan 1, 1964

By B. H. Kear, B. J. Piearcey

The orientation and temperature dependence of the tensile and creep propevties oj Mav-M200 crystals halle been determined. Crystals oriented for single slip exhibit ,maximum ductility, minimum work hardening, and least creep resistance, whereas crystals in multiple slip orientations show nzinimu~n ductility, strongest work hardening, and greatest creep resistance. At 1400" and 1600°F there is a marked improzlenzent in creep strength for orientations approaching [001] and [111], indicating that interactions between dislocations gliding in intersecting octahedral slip systems play an important role in creep resistance. At 1800°F the creep strength is much less dependent on orientation, which is rationalized in terms of slip in cube planes as well as octahedral A frequent mode of failure in high-strength cast nickel-base superalloys is by intergranular fracture, particularly along those grain boundaries oriented transverse to the major stress axis. VerSnyder and ~uard' demonstrated that this problem could be overcome by eliminating transverse grain boundaries through unidirectional solidification. Piearcey and versnyder2 made use of this principle in the development of unidirectionally solidified gas turbine blades and vanes, where the growth direction of the columnar grain structure coincides with the axis of principal stress under operating conditions. The present investigation was undertaken to determine if further improvement in properties may be obtained by eliminating grain boundaries altogether, so as to take advantage of the well-known dependence of mechanical properties of single crystals upon the orientation. 1) EXPERIMENTAL PROCEDURE Single crystals of Mar-M200* were grown from the melt under vacuum by a modified Bridgman method. The melt was poured into a preheated alumina mold, and crystal growth was promoted from one end by appropriate gradient cooling. Tensile and creep specimens (2 in. diam by $ in. gage length) were prepared by a series of operations involving electrical discharge machining, precision grinding, and electropolishing. The orientations of the specimens were determined by the Laue X-ray back-reflection method. Tensile tests were carried out in aWiedemann machine with furnace attachment, using a strain rate planes. In all orientations imzpvouement in the strength charactevistics of the material can be induced by heat treatment. Creep ad stress rupture data for (001) oriented crystals are compared with similar data obtailted previously joy random polycvystalline material, and also columnar grained material having a prejevved (001) orientation. The single-crystal )material exhibits both longer rupture life and lower minimum creep rate at all temperatuves, and the rupture elongation is comparable with that in the columnar grained material. From these results it is concluded that single crystals should and useful application in gas-turbine blades and tanes. The optimum orientation for a blade is considered to be with its axis of principal stvess parallel to (001) ou (111). of 0.0001 sec-'. Load and extension were recorded directly on an X-Y recorder. The strain measuring device consisted of extension arms attached to the grips at one end and leading out of the furnace to an LVDT (linear variable differential transformer) at the other. Creep tests were performed using a standard constant load creep frame. 2) DISCUSSION OF RESULTS 2.1) Structure of Alloy. The structure and segregation in as-cast and heat-treated Mar-M200 has been described in detail else where.~ The main features are as follows: the as-cast material is heavily cored, due to pronounced dendritic segregation during solidification; the dendrites are rich in tungsten and cobalt whereas the interdendritic regions are rich in chromium, titanium, nickel, and carbon. The structure consists of -60 vol pct coherent precipitate of y', basically Ni3(A1,Ti), in a matrix of y (nickel-base solid solution), interspersed in the interdendritic regions with minor MC carbides and -y' eutectic. The y' particles, and y-y' eutectic, contain more titanium, aluminum, and nickel, and less tungsten, cobalt, and chromium than the y matrix. Heat treatment partially removes segregation, eliminates the eutectic, refines the y' dispersion in y, and gives additional partially coherent M23Cs carbide. An as-cast crystal, therefore, is composed primarily of two oriented phases (y + y'), whereas the normally heat-treated crystal consists of three oriented phases (y + y' + MZ3Cs). Typical electron transmission micrographs of the y + y' structure are shown in Fig. 1. Crystals grown in the (100) orientation develop a simple unidirectional dendritic structure, Fig. 2, since (100) happens to be the preferred direction of growth for dendrites in this material. Crystals grown in the {110) and (111) orientations, however, tend to promote equal growth, generally in separate colonies, in the two and three geometrically favored (100) growth directions, respectively. In other orientations of growth, a single (100) dendrite direction generally pre-

Jan 1, 1968

By W. R. Ingalls

The manufacture of zinc oxide directly from the ore is one of the most important contributions that America has made to the metallurgy of zinc. Heretofore, this has been done chiefly for the production of zinc and zinc-lead pigments, and the method has been known as the Wetherill process. While that term may properly be applied to the process for pigment manufacture, it must be recognized that the principles of the process are of far wider application; and that there is going to be wider application in the immediate future is more than an expectation. I have in mind the use of the process as a method of igneous concentration. Igneous concentration is broader in its scope than the Wetherill process, for it may be done in the blast smelting furnace, or in the re-verberatory, or by other means. Igneous concentration is a rather clumsy term, and I prefer to introduce the new generic expression of "zinc burning," which is convenient, readily understood, and precise, for in all cases the zinc oxide is reduced to metallic form, is volatilized and is then burned to zinc oxide, the latter happening, however, after the zinc has been separated from the residue of the ore. As previously indicated, zinc burning may be done either in blast or reverberatory smelting, the gangue of the ore being scorified and drawn off as slag, while other metallic minerals are reduced to matte or metal. Such processes have heretofore been practised on fairly large scales. Thus, F. L. Bartlett smelted zinc ores at Con City, Colo., in specially designed blast furnaces, wherein the smelting column was only about 18 in. high. Such a limitation was necessary in order to prevent zinky accretions in the shaft of the furnace, which in course of time would have interfered with its operation. In running the Bartlett furnaces it was easy to bar them off, indeed, to poke right down into the smelting zone, and keep things going freely. Some iron blast furnaces in Virginia and the spiegeleisen furnaces of the New Jersey Zinc Co. afford other examples of zinc burning in blast-furnace smelting, although in their cases the happening is incidental rather than a primary purpose. Just as zinc may be burned off in a blast furnace, so also may it be done in a reverberatory. Indeed, there is less trouble, in some respects, in a reverberatory, for therewith there is no shaft in which accretions may

Jan 1, 1918

By Paul Giesecke

SINCE most modem metallurgical plants are operated continuously and on a large scale, successful operation at maximum efficiency demands that an accurate knowledge of the performance at each stage of the process be available at all times. Quantitative analyses provide the most practical process guides, and it is essential to have analytical procedures that combine accuracy and speed. In continuous plant operations, large losses may occur if the time interval between the development of trouble at any stage and its recognition and correction is great. Many metallurgical plants are using rapid colorimetric and spectrochemical methods of analyses for control purposes. So-called "color coppers" may be cited as an example of the colorimetric methods, in contrast with the routine use of the ultraviolet spectrograph for the analysis of steels.42 By means of this more refined spectrochemical procedure, a complete quantitative analysis of the molten metal is obtained every few minutes. During the past two years the Physics Division and the Ore Dressing Laboratory of the American Cyanamid Company's Stamford Research Laboratories have collaborated in a study of the use of spectrochemical methods for the analysis of various metallurgical products. New methods have been developed, which have proved of practical value in plant operation. The following pages give a general review of the principles of spectrochemical methods and also the details of several specific analyses. PRINCIPLES OF SPECTROCHEMICAL ANALYSIS In general, it can be said that a visible light spectrochemical analysis can be performed for any ion or molecule that is naturally colored, or that can be made to react with another to produce a colored salt or complex. Whereas transmission measurements in the ultraviolet and infrared portions of the spectrum are most useful for the analysis of organic molecules, visible light measurements are of particular value for metal salts. Such elements as copper, manganese, cobalt, nickel, iron, molybdenum, vanadium, chromium, phosphorus, mercury, zinc, lead, and a great many others, can now be determined with a high degree of sensitivity, accuracy and dispatch. From the simplest of qualitative determinations, color analyses have been improved to such an extent that, at the present time, through the use of recording spectrophotometers, hundreds of accurate quantitative analyses can be performed by a single analyst during an 8-hr. day after the standardization curves have been established for the ions to be determined.

Jan 1, 1944

By E. H. Hamilton

WHEN starting a series of experiments on the use of powdered coal in lead blast furnaces to replace coke, I realized that in copper smelting the problem is simpler because the sulfur recovers the copper in the form of matte. In lead smelting there are greater difficulties because a reducing atmosphere must be maintained in the active, zone corresponding to each tuyere in order to get the best recovery of lead. Therefore, the feed of powdered coal must be quite regular, uniform and under control. The molten products issuing from the taphole are the resultant of the work of all the tuyeres and it can readily be con-ceived that one part of the furnace may be forming slag with a higher lead content than the slag formed in other parts of the furnace. At first, we used only one tuyere situated on the back of the furnace. This was for the purpose of getting all of our regulations under the regular operating conditions. We tried every known system of feed and found they were not dependable and our present system was finally worked out, and so far as we know, is the only working system that will give uniformly good saving in lead blast furnaces. We placed a Bristol self-recording thermometer on the feed floor. This gives a 24-hr. continuous record of the temperature of the gases leaving the furnace. We put a self-recording gage on the "15-lb." air used in the injector. A second recording Bristol gage was put on the low-pressure air (40 oz.). I realized that it was necessary that we should know the exact weight of coal going into each tuyere and that it should 'be under observation at all times. L. W. Kirk was assigned to the problem and developed the open sight feed and the distributor, so that we now have the coal being fed into each tuyere in sight of the men in charge. We have an apothecary's balance beside the furnace, and the operator takes the pan and inserts it under the stream of falling powdered coal for one minute, and places the pan on the scale, the other scale pan having weights indicating the desired amount to be fed to each tuyere per minute.

Jan 10, 1922

By John L. Schroder

The demands for increased productivity on the 1967 coal industry have generated new operating trends and fresh approaches to old methods, which have enabled the industry to keep pace with the expanding economy. Changes, while not radical in concept or design, have been plentiful and are marked by the refinement of the already tried, tested and proven. Perhaps not since World War II have there been demands on equipment manufacturers to design and deliver such diversified types of machines as those required by the industry in the past year. Equipment developments-following a plan which calls for higher productivity, lower maintenance costs and greater machine availability- have tended more toward increased horsepower and heavier, more rugged equipment. Electrical and mechanical components, designed in many instances with maximum reliability rather than initial costs as the main criterion, have contributed to the improvements in over-all performance. High-strength, specialty steels are finding use in a wide range of equipment applications. The horsepower capacity of electric motors being installed is more frequently being rated on a continuous basis rather than the former one hr or less and, as a result, fewer failures now occur because of overloading. These developments reflect the pyramiding cost of equipment down-time and represent definitive progress in reducing the magnitude of the problem.

Jan 2, 1968

By William Catron

BECAUSE the rich La Colorada orebody of the Cananea Consolidated Copper Co. does not outcrop at surface, after its discovery (by churn drill) and before mining was begun, a large amount of development work was done to learn the shape and extent of the ore and to provide for eco-nomic and effective mining. As these openings progressed, the actual shape of the orebody became known and with this knowledge came the realization that mining this rich and unusual deposit without loss of ore or danger to workmen presented several difficult problems. This paper will describe one of these problems; namely, the handling of an inverted cone-shaped core of barren rock, on the periphery of and below which the ore occurred. It was clear that as the ore was mined out from around and under this inverted cone of rock, weighing about 3,000,000 tons, it would hang over the workings, held suspended only by its own tensile strength and threatening to crash into the stopes below with disastrous results to men and mine. The method of mining developed during the years 1928, 1929 and 1930 anticipated and provided for the eventual collapse of this core of rock. In November 1936 the core settled clown gradually on the edges of the stopes, descending a total of about 50 ft. vertically. The men in the stopes had ample to warning and no lives were endangered. There were no air blasts in the mine. The core broke loose from its top support at the 500-ft. level along old fracture planes and evidently is crushed to the ninth level. Movement was of short duration; the following shift went to work in the stopes as usual. No ore was lost.

Jan 1, 1938

By Jerry Tien

Mine regulators are normally used for proper air distribution in underground mines. They are deliberately introduced resistance in the regulated airway, and by altering sizes, they can distribute specific air quantities to regulated splits and free splits (4, 5). The enactment of the Federal Coal Mine Health and Safety Act of 1969, the Federal Mine Safety and Health Amendments Act of 1977, and the regulations adopted by the Mining Enforcement and Safety Administration (now called the Mining Safety and Health ministration) prompted greater discussions of optimal mine regulator locations because of the Act's stringent ventilation requirements (2, 3). For example, by requiring the separation of the air used in the belt haulage entries from the intake and return airways, the regulations required the creation of a third type of airway---the neutral airway, as opposed to the intake and return airways, adding to the complexity of a mine's ventilation network. It is the intent of this report to show that panel regulators should be located in intake airways at the neck of a panel for a blowing fan system and in return airways at the neck of a panel for an exhausting fan system in order to achieve optimal air control. A computer simulation model is used to determine optimal mine regulator location.

Jan 1, 1983

By H. H. Bein

Most western industrial sands are feldspathic and contain feldspars in variahle amounts. A few deposits will show alumina contents of less than one per cent while others will contain over twelve per cent alumina. Some industries are not especially concerned with the amount of contained feldspar but are interested only in color and in size gradations. Other industries, however, are very much interested in alumina content and set up quite rigid specifications as to this content. Several western plants are beneficiating crude sands both to reduce the iron content and to control the feldspar content. At present, most of these plants are using flotation processes for both controls although a few plants do use magnetic separators for the reduction of iron content. Some work has also been done with electrostatic separators for the feldspar-quartz splits. The Sand Division of Del Monte Properties Company, Pebble Beach, California, has been operating a flotation plant for iron removal and the separation of quartz and feldspar since 1950. As mentioned before, control of alumina, especially in the quartz product, is very important. Some users require an alumina content of less than two per cent and others will demand a product of less than one per cent Al2,O3,. The standard Quinolate method for determining alumina is lengthy and time consuming. The HF —H2SO4 evaporation step is especially critical and, if forced, spattering is apt to occur with a resulting loss of sample. Standard procedure is to evaporate to dry ness overnight at a low temperature. Even with forcing under optimum conditions the procerlnre will take two or three hours to complete. A new method has been developed which allows an alumina determination to be made, in 10 or 15 minutes, on a sample of the quartz product as it is being produced. This pocedure, although simply an approximation, has been most helpful in showing whether or not the product being formed is meeting specifications. This procedure has also allowed a great reduction in samples formerly taken and analysed by the orthodox method. Whether a sample assays 1.75% A12O3, or 1.95% .41,0, is not so important as the fact that it is below the allowable maximum of 2.00%. Similar thinking would apply to products required to contain less than 1.00% A1,0,. The step by step procedures for the method are as follows: 1. Collect sample, drain or filter, and dry. 2. Split sample through standard Jones sample cutter to quarter or eighth sample, depending on size of original sample taken, then split down to about 5 grams through Sepor micro-splitter. 3. Screen through 50 mesh sieve (U.S. Series) and reject undersize. 4. Weigh out 2 grams and place in platinum crucible. 5. Etch with 3-5 mls 38.40% HF for 1 minute at room temp. 6. Decant and wash. 7. Stain for two minutes in same crucible with a 1% water solution of Nigrosene dye. 8. Decant and wash well. 9. Dry.

Jan 1, 1961

By Samuel Shallcross

THE principal function of the Bell limestone mine, of the American Lime & Stone Co., at Bellefonte, Pa., is to supply raw material to the company's modern rotary kiln plant at Bellefonte. Because mining costs are naturally higher than many open quarries with more favorably lying strata, it cannot compete, except to a limited extent, in the markets for road material and fluxing stone. In the broad sense, mining does have an advantage over the average open quarry when the end products are designed for and controlled by process and final inspection for the exacting demands of the industrial and chemical markets. Approximately 80 per cent of the output of the Bell mine is sold in the industrial and chemical markets. And as higher standards are set each year for construction and agricultural work, the remainder of the mine output goes to these two classes. Mining produces more fines than open quarries, and these fines are difficult to market; on the other hand, owing to absence of contaminating clay and impure rock, a greater percentage of the output of a mine is marketable. Because of the great production of fines, rotary kilns for lime burning are necessary when the stone must be mined. In 1921 the American Lime & Stone Co. operated 19 quarries and 72 lime shaft kilns spread over an area of 40 miles between Bellefonte and Altoona, Pa. At that time the line-production capacity of the 72 kilns amounted to approximately 700 tons per day. After 15 years the company operates three rotary kilns and six shaft kilns, with a combined output of approximately 500 tons of lime per day, concentrated in its single Bellefonte plant (Fig. 1). Its only stone-producing plants are now the limestone mine at Bellefonte and a construction-stone open quarry at Union Furnace, near Tyrone, Pennsylvania.

Jan 1, 1936

By Vasily P. Muravjev, Gennady I. Razgildeev

The theory of reliability is a powerful mathematical tool for determining optimum selection of components and application of electrical power to coal mines. In order to make this tool useful, statistical material on equipment life must be gathered and all failures carefully recorded. Statistical data can be applied to new apparatus design and can be used to determine optimum configuration of network and maintenance to reduce costs. Reference is made to underground power systems in the USSR. Technical progress in the last few years has occurred in the design and application of highly productive coal mining and transporting machinery. One of the most important problems facing mining engineers is to increase the availability of the machine to obtain higher productivity. However, machine failures and breakdowns of electrical power supply components cause serious delays in the coal-winning processes. In spite of the fact that electrical equipment and the power supply contribute only a small percentage of direct mine costs, electrical failures as well as power supply delays can result in severe indirect losses. It is necessary, therefore, to consider reliability and safety in the application of electrical equipment underground. To obtain the best results, it is necessary to investigate and evaluate the reliability of the electrical mining components (starters, breakers, motors, cables, etc.) and optimal methods for minimizing maintenance, the desired result being equipment which is efficient and safe. Electrical equipment reliability directly influences economics: the lower the reliability the more frequently failures occur, causing serious working delays and possibly huge economic losses. By the same token, while increasing the number of preventive maintenance calls per unit time might result in fewer failures, thus reducing delays, the cost of making more frequent maintenance inspections will increase; this is one aspect to be discussed in detail. Obviously, failures of identical types of electrical equipment (starters with the same current and voltage, etc.) are influenced variably by different working conditions, environments, quality of the apparatus, maintenance procedures (personnel, frequency, quality), load, and other factors. Hence, the lifetime of identical types of equipment will vary depending upon usage in terms of the foregoing factors. Thus for a given type of electrical component, these factors must be considered quantitatively; the interaction of all these factors are evaluated quantitatively by a statistical method using probability theory. Equipment reliability must be quantitatively determined from a study of equipment life, since no one laboratory test can reproduce all working conditions and environmental effects. Nevertheless, reliability theory applied to electrical mining equipment is a very powerful mathematical tool for selecting as well as evaluating certain parameters. It is necessary to select several reliability parameters so that one can obtain an expression for the total overall economic situation in terms of cost, taking into consideration damage caused by electrical equipment failure and cost of maintenance. To accomplish this result, such characteristics as apparatus lifetime, breakdown idle time, and losses (damages) can be determined quantitatively on a statistical basis. For identical electrical equipment working under similar conditions, the previously mentioned reliability factors are random variables and therefore can be characterized readily by a probability density function. Investigations carried out by the authors in the Kuznetsk Basin (Kuzbas) in West Siberia, USSR, show that the reliability factors of electrical mining equipment are well described by the exponential, normal, or Erlang's distribution in most cases. Mining electrical equipment life is well-described by the exponential law. The distribution of lifetime density is

Jan 1, 1971

By Francis Pyne

THE following notes are presented in an endeavour to point out the disadvantages attending the use of chrome brick in reverberatory furnaces used in the treatment of materials that are too valuable to allow any great amount of metal absorption by the brick. Several years ago one of the large Eastern copper refineries decided to utilize basic material in place of siliceous material in the walls of their reverberatory furnaces for the treatment of very foul blister copper, as the latter rapidly corroded the siliceous linings. It was also expected that there would be less slag formation, with a consequent decrease in the cost of treatment and a reduction in the metal losses. Magnesite brick were first used, but while the corrosive action of the foul material was greatly reduced, and the amount of. slag formed was very much less, the magnesite proved to be unsatisfactory in certain parts of the furnace, because of its tendency to crack and span badly when subjected to the alternate heating and cooling that takes place in a reverberatory refining furnace. This made many repairs necessary, and consequent frequent interruption in the operation of the furnace, which, together with the high price of the magnesite brick, ran up the cost of maintenance to an unreasonable amount. It was, therefore, decided to substitute chronic brick for magnesite brick in the parts of the furnace affected. The results, as far as the reverberatory furnace was concerned, were very satisfactory. The corrosion due to the action of the foul blister was small and the amount of slag formed was no greater than when using magnesite, and the tendency to crack and spill shown by the magnesite was eliminated. Gradually the use of chrome brick was extended to all furnaces; those treating blister copper as well as those melting cathodes, and the results were so satin-, factory that the siliceous roofs were replaced by roofs of chrome brick except in certain places where experience showed a more satisfactory performance on the part of the silica brick.

Jan 12, 1917

CHARLES CATLETT, Staunton, Va.-A great many important things have been said in an interesting way but the most startling, to me, is that for 25 years, the price has been in the neighborhood of $1.00, with a minimum of 86 cents and a maximum of about $1.25. It is evident that during all that time the price was inadequate. The amount paid to be divided between the land owner, the capitalist, and the laborer was too limited or too irregular to permit of a healthy condition; yet it is evident that the enormous industrial development of this country was fostered by this very cheap coal, probably the cheapest that has been provided in quantity in any country. I entered the coal business when the price was lowest and my interest and sympathy went out to the man who spent his days in the dirt and foul air of a mine and I was filled with schemes for helping. But at the end of the year, after exercising every economy and in blissful ignorance of proper depreciation and obsolescence, there was still only a profit of 1 cent per long ton for what I think is one of the best coals in the world, the best grade of New River coal. We are now paying a great deal more than we did a few years ago and probably will continue to pay more for some time; but any one who thinks we will not have low prices again is very young or very forgetful. Yet we must have larger profits if the industry is to be healthy, if the three parties to the production are to get adequate returns and be in shape to provide the improvements which will be needed to take the place of and supplement the man-power. This will come when the men are making so much money that the operator wants to replace the man by a machine, and when the operator is making so much money as to be in a shape to make the improvements. He will not put in machinery unless the machinery will save money. We have got to pay a higher prime cost for coal, but engineering skill will teach us how to handle it better and use it more economically, and the ultimate result ought to be of advantage to the public.

Jan 3, 1920

By Irving A. Palmer

During the past 15 years in this country there have been few additions to the literature of lead smelting. After the consolidation of the principal smelting companies at the beginning of this period it became the policy of the larger company not to permit the publication of details in regard to many of its metallurgical processes. This led to similar action on the part of some of its competitors. The result, of course, was a decided decrease in the number of papers written upon the practical side of the subject. Even upon the theoretical side the contributions have been few. It would seem that the industry as a whole has suffered from this general unwillingness to exchange information. While it is true that a given company is entitled to the reward that may come from its own development of a new process, it is also true that a still greater reward might be the result of a free exchange of ideas with other plants. This principle has been recognized for a long time in other metallurgical industries, notably those engaged in the smelting of iron and the manufacture of steel. It is pleasing to note that the leading lead-smelting company has very recently decided to modify its policy of secrecy, and to permit the publication of papers covering some details of its metallurgical methods. The statement has been made that there has been but little progress in lead smelting during the period just referred to. This impression is due in part, no doubt, to the scarcity of papers written on the subject. 'There has been, it is true, some discussion of the new sintering processes, but with little reference to detail, and to the effect that blast roasting has had upon the industry as a whole. In spite of the prevailing belief, it may be said that lead smelting, in common with other metallurgical industries, has made steady and substantial progress. It is the purpose of the present paper to discuss briefly some features of the industry as it is now conducted, with special reference to the blast-furnace practice in the larger silver-lead smelting plants of the United States and Mexico.

Jan 1, 1915

By Albert Stazicker

AT Climax the warehouse department operates as an independent unit similar to the mine and mill departments. It has the responsibility of receiving, checking, unloading, and storing all material and supplies delivered to the plant. In addition, the transportation of all supplies comes under the direction of the warehouse so that prompt delivery of supplies to all departments is one of its major functions. The transportation division operates heavy and light trucks, trailers, two large tractors, and two snowplows. In addition to delivering supplies it is also responsible for snow removal from the roads, hauling of sand and gravel for concrete and domestic coal to employees. and all miscellaneous work involving the use of tractors or trucks.

Jan 1, 1946

By Keith Leonard Sutherland, Ian William Wark

Mercaptobenzthiazole and its sodium salt are marketed under the trade names Flotagen and Flotagen S respectively, for use as collectors for cerussite and other minerals. The structural formulas for sodium rnercaptobenzthiazole and for sodium ethyl xanthate are: Chemically there is a resemblance between the two compounds, though the free acid (mercaptobenzthiazole itself) is much more stable than xanthic acid. Both are readily oxidized, e.g., by iodine to disulphides, and can be estimated by iodometric titration. Qualitatively they are similar as collectors in flotation, although there are quantitative differences between them that may be important in practice. It is deduced that the influence of the nitrogen atom is subordinated to that of the sulphur atoms, and that the dominant group of these compounds is the mercapto group —SH or —5Na. The general method of investigation has been based on contact tests. Two temperatures, 10" and 35" C., have been chosen, and with a standard concentration of 20 mg. per liter of mercaptobenzthiazole (i.e., of the free acid) the influence of alkali, cyanide and copper sulphate on contact at sulphide mineral surfaces has been studied. This standard concentration corresponds to about 19 mg. per liter potassium ethyl xanthate; it brings out the differences between the minerals better than a higher concentra-

Jan 1, 1939

By Ian William Wark, Keith Leonard Sutherland

Mercaptobenzthiazole and its sodium salt are marketed under the trade names Flotagen and Flotagen S respectively, for use as collectors for cerussite and other minerals. The structural formulas for sodium rnercaptobenzthiazole and for sodium ethyl xanthate are: Chemically there is a resemblance between the two compounds, though the free acid (mercaptobenzthiazole itself) is much more stable than xanthic acid. Both are readily oxidized, e.g., by iodine to disulphides, and can be estimated by iodometric titration. Qualitatively they are similar as collectors in flotation, although there are quantitative differences between them that may be important in practice. It is deduced that the influence of the nitrogen atom is subordinated to that of the sulphur atoms, and that the dominant group of these compounds is the mercapto group —SH or —5Na. The general method of investigation has been based on contact tests. Two temperatures, 10" and 35" C., have been chosen, and with a standard concentration of 20 mg. per liter of mercaptobenzthiazole (i.e., of the free acid) the influence of alkali, cyanide and copper sulphate on contact at sulphide mineral surfaces has been studied. This standard concentration corresponds to about 19 mg. per liter potassium ethyl xanthate; it brings out the differences between the minerals better than a higher concentra-

Jan 1, 1939

By B. C. Riblet

THE president of a large smelting and refining company once telegraphed me that they had acquired extensive mining interests in northern Peru and requested me to inspect their properties as it would be necessary to install a system of aerial tramways between their mines and treatment plant. The concentrator was about 50 mi. from the coast, reached by a fairly good motor road. From the concentrator an aerial tramway would he required, about 6 mi. long, to their first property, a gold and silver mine. The lower terminal of the tramway was at an elevation of 4000 ft. and the mine at an elevation of 9500 ft.

Jan 1, 1937