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By Chester O. Ensign

Many publications to date have advocated under- seas mining operations, optimistically overlooking the paucity of information on mineral distribution and the ocean environments in which minerals occur. Such articles (smattered with opinion, as is this article) are herein tempered by my more conservative views on the economics of mining under the seas. For purposes of this paper, underseas mining refers only to the deeper surficial deposits of the continental shelf and the deep sea floor, i.e., the deposits of phosphorite and manganese nodules.

Jan 9, 1966

President Howe : It is not so clear to me that the facts which Dr. Waldo brings forward really argue that the nature of the combination between copper and aluminum differs from that of the combination between copper and zinc or copper and tin. As regards electric conductivity, I suppose that the fact, which he thinks points to a special intimate kind of union between aluminum and copper, is that the line in his Fig. 1 is neither straight nor uniformly curved, but that its curvature varies rapidly, not to say abruptly. But we find just such variation in like curves for the copper-zinc and copper-tin alloys. Thus, a slight addition of zinc or tin to copper causes a change in color wholly out of proportion to the quantity added; and, as we add zinc or tin to copper, the tenacity rises very greatly, only to fall off abruptly with further additions of either of these metals. Dr. Waldo : My curve related only to electrical conductivity. The President : If irregularity in one physical property argues

Jan 1, 1895

By Charles H. Jones

Jan 1, 1905

By Webster, Wm. Reuben

THE greatly enlarged demand for small sizes of seamless copper tube which has recently occurred, due particularly to the rapid growth of the electric household-refrigerator industry, has emphasized the superiority of phosphorized to tough pitch copper for the purpose of producing this commodity. In the manufacture of this material exceedingly heavy reductions by cold drawing are employed, customary practice involving as much as 90 per cent. reduction of cross-sectional area in four runs without intermediate annealing. Although this superiority has long been recognized by tube makers, no quantitative expression of it has heretofore been published. It is believed that the data herewith presented mill serve this purpose. Recent investigators are not in agreement as to the relative mechanical properties of copper containing small amounts of oxygen as compared with copper containing sufficient oxygen to produce that condition known as tough pitch. Hanson, Marryat and Ford1 found that "oxygen has a relatively small effect on the properties of copper." Johnson, on the contrary, states "it cannot be denied that it (tough pitch copper) is inferior to deoxidized copper . . . where severe mechanical manipulation is concerned." These authorities in the reports of their investigations, as might be expected from their conclusions, do not present data of a character requisite to a conclusive determination of the question.

Jan 1, 1927

By A. C. Fieldner

THE total annual energy production from coal, petroleum, natural gas and water power has been increasing at a fairly constant rate during the thirty years ending in 1930. But since 1913 the demand for the competitors of coal has increased at a rate faster than that for coal. During the last twenty years, the curve of coal production has had a generally horizontal trend; in fact, the 1930 production of coal was six per cent less than that of 1913. Economists attribute this loss of demand to greater efficiency in coal utilization and to displacement of coal by oil and natural gas. These two factors are about equally responsible, and it is evident that research has been intimately concerned with both. About sixty per cent of the bituminous coal mined in the United States in 1929 was used for generating steam, either in stationary or locomotive boilers. A decade ago seventy per cent or more was used for this purpose. This change is due largely to tremendous advances in fuel economy.

Jan 1, 1933

By W. M. Myers

Certain minerals possess inherent color and other properties that make them suitable for the pigmentation of paints, mortar, plaster, concrete, face brick, and other materials. Their production is one of the most ancient of mineral industries and their use by primitive man is well known. These natural pigments have some economic factors in their favor, particularly wide geographic distribution, low cost of production, ease of preparation, chemical stability, and permanence in use so that they continue to form the basis of a small but useful industry. When used in paints such pigments act as a filler and supply body and opacity in addition to color. Natural mineral pigments are prepared for the market by the comparatively simple operations of washing, grinding, blending, and calcining. Any one, or all of these processes may be applied to a single pigment. The development of synthetic pigments and the use of by- product materials have introduced competition with the products of nature and are having a growing influence on the economic position of the mined minerals.

Jan 1, 1949

By Thomas T., Read

THE education of adolescents to perform the duties and assume the responsibilities of maturity has been a characteristic of human society since the dawn of history. In the beginning the members of the immediate family performed this function, and in modern life they still have an important part in it. Possibly religion was the first field in which education began to be functional; young people were sent for instruction to a teacher who had a broader and deeper knowledge of the subject than was possessed by the family. It does not seem necessary for our purpose to attempt to determine how, when, or where instruction in the practical arts first' began to become functional, and the brief outline which follows must suffice. The discovery and utilization of mineral substances to improve and maintain the conditions of human living is a practical art, which must have had an almost accidental origin and have been developed by empirical experiments. We do not know, nor would it be useful to try to fancy, how men first learned that they could make use .of mineral substances to their benefit, but how- ever that knowledge was initially gained it was certainly trans mitted through instruction in the family. At first such activities must have been merely a .minor part of the making of a-living, but in time those who excelled found it better to devote them-

Jan 1, 1941

By Leon W. Dupuy

Many articles have been written describing peculiar and particular types of drilling. Little correlation has been made between the character of ground to be drilled and sampled and the type of drilling most desirable for procuring satisfactory samples. In development work, the engineer and metallurgist often desire the recovery of a sample in as physically natural a condition as possible, particularly when the sample must provide material for process tests as well as chemical and physical analyses. This paper describes the results of experimentation in drilling unconsolidated materials carrying titanium minerals in the Magnet Cove area, Ark. The drilling was most difficult in that the ground varied much in consistency, and it was vitally necessary to recover a physically natural sample. Ordinary churn drilling recovered a sample that could be analyzed chemically, but the sample was not in its natural state. The problem was successfully solved by utilizing and further developing methods used in the oil and clay industries.

Jan 1, 1949

By O. D. Sherby

In 1938, Kanter' revealed that the steady-state creep rate of low-carbon iron alloys could be correlated by an activation energy expression, where the activation energy for creep, Qc, was found equal to about 90.0 kcal per mole for most of the alloys investigated. He suggested that creep at high temperatures might be controlled by some sort of solid self-diffusion process since the value of Qc was about equal to the known value for self-diffusion, Qd. Correlations were not further attempted along these lines until many years later, when new evidence2-8 was presented suggesting that Qc = Qd for many metals. This equality now appears to be established for ten metals (Al, Pb, Ni, Mg, Cd, In, a Fe, y Fe, Cu, and Au). This experimental fact prompted several investigators to postulate various mechanisms of dislocation motion which would yield an activation energy for creep equal to that for self-diffusion.7-9 Possibly the most accepted theory is that based on dislocation climb7 where a dislocation is envisioned to surmount a barrier by an atom-vacancy exchange process, thereby "climbing" from one slip plane to another. Such a model would suggest that the steady-state creep rate, i, should be directly proportional to the rate of self-diffusion, D, for a given creep stress. In order to more clearly reveal the relationship between creep and diffusion, and to eventually determine the correct model, it would be desirable to obtain data showing correlations between i and D, rather than with a comparison of the temperature coefficients, Q. It has been known for some time that the self-diffusivity of iron atoms is greatly decreased when body-centered-cubic (a) iron transforms to face-centered-cubic (y) iron. This has been ascribed to the more close-packed structure of y iron. The diffusivity ratio at the transition temperature is Da/Dy =350. Correlations of creep data for a and y iron5 reveal that the creep rates under a given stress at the transition temperature differ by about the same ratio (ea/ey 2 200). It would be difficult to reconcile these results on any other basis than that the diffusivity of atoms probably controls creep of iron in some very direct way. No other published data on other allotropic metals appear currently available for further checking such a possible correlation between i and D. Thallium transforms from a hexagonal close-packed (a) structure to a body-centered-cubic (ß) structure at 230°C (503°K) and the self-diffusivities of the two structures have been determined by shirn.10 His results are plotted in Fig. 1 where it will be noted that Dß/Da = 25 at the transition temperature. It would appear desirable, therefore, to determine the creep rates of polycrystalline a and ß thallium at the transition temperature, as well as determine

Jan 1, 1959

By C. E. McWhorter

IN underground mining recent trends toward mining large tonnages of low-grade ore have created, among other things, a need for cheaper and more flexible ore transport. A relatively new development has been the adaptation of shaker conveyors to meet this need. Although widely used in coal mining, only in the last few years have shaker conveyors been used in underground metal mining. The equipment consists of a driving engine, either electric or air powered, upon which is mounted a drive trough supported in ball-bearing frames. The trough line, or conveying medium, is made up of a number of sections, each section connected to another, usually with bolts. The length of each trough section is controlled by the length that can best be handled underground, but is usually from 9 to 13 ft over-all. The length of a complete conveyor line is determined by the character and weight of material to be handled as well as by the size of the ore body. Trough lines vary in lengths from 100 to 300 ft and the trough has a cross-section area of 127 sq in., and is 22 in. wide by 6 ½ in. deep.

Jan 1, 1948

By D. Turnbull, J. H. Hollomon, J. C. Fisher

Application of the concepts of nu-cleation and growth to the analysis of experimental transformation data has led to valuable descriptions of phase transformations, an outstanding example being the transformation austenite —* pearlite which has been examined with particular care by Mehl and co-workers.&apos;-5 In addition to the pearlite transformation, the proeutectoid fer-rite and proeutectoid carbide transformations are known to proceed by nucleation and growth. Martensite, on the contrary, until recently was thought to form by a mechanism involving neither nucleation nor growth; however, extension of standard nucleation theory6 suggests that martensite, bain-ite, and the other products of austenite decomposition all grow from nuclei in the parent phase. The theory that martensite forms by nucleation and growth is strongly supported by recent experimental work of Kurdjumov and Maksimova.7 The concepts of nucleatioli and growth have been fruitful also in providing a sound basis for quantitative theoretical treatments of the kinetics of phase transformations. For example, Volmer and Weber8 and Becker and Döring9 developed the theory of nucleation from fundamental considerations to a point where excellent agreement was obtained with the results of experiments on the condensation of supercooled vapors. As a result of their analysis, the kinetics of vapor-liquid transformations now can be predicted. It seems probable that application of the theories of nucleation and growth to a quantitative study of austenite decomposition similarly will clarify the nature of the individual transfor: mations involved, and will enable the calculation of austenite transformation kinetics. In the present paper, the theories of nucleation and growth are applied to the austenite ? martensite transformation in steels. The analysis begins with a discussion of nucleation in single component systems. Martensite appears to be coherent with the parent austenite, hence the nucleation theory is modified to include the effects of elastic distortion. Nucleation in the two component iron-carbon system then is discussed, for most steels are primarily alloys of these two elements. Finally, M. temperatures and martensite transformation curves are calculated for each of several alloy steels of varying carbon and chromium content, and are compared with those determined experimentally by Lyman and Troiano10 and Harris and Cohen.11 Nucleation Theory NUCLEATION IN SINGLE COMPONENT SYSTEMS6,12-14 The work required for reversible formation of a region of phase within the parent a phase is expressed conveniently as the sum of two terms: W1 = Aa, the product of the area of the interface and the interfacial free energy, and W2 = VAf, the product of the volume of the region and the free energy increase per unit volume associated with the transformation. The total work is therefore W = Aa + VAf. When a is more stable than ß, Af is positive and W increases without limit as the volume increases. The transformation a ?ß does not occur. It is nevertheless true that small regions of phase ß enjoy temporary existence here and there in the a. The equilibrium number of ß regions of given size is proportional to exp(— W/kT) per unit volume of a, assuring that larger (ß regions occur with diminishing probability. When a is less stable than ß, Af is negative and W passes through a maximum as V increases. Assuming for simplicity that regions of ß are spherical, as is true when the interfacial tension is isotropic and there are no elastic strains, W = 4r2a + (4/3)*r3Af The maximum value of W is W* = 16iro3/3Af2 [1] for regions with radius r* = -2o/Af. [2] For single component condensed systems it has been shown14 that the steady rate of nucleation of 0 per unit volume of untransformed a is nearly proportional to exp[- (W* + Q)/kT] where Q is the activation energy for the unit processes of adding or removing one atom from an embryo or nucleus. If To is the temperature at which a and ß are in equilibrium, the rate of nucleation is a maximum at a temperature 0 < T < To where (W* + Q)/kT is a minimum. P regions smaller than critical size are called embryos; they tend to grow smaller and disappear, only exceptionally growing larger. Regions equal to or larger than critical size are called nuclei. A critical size nucleus may grow indefinitely large or may shrink back to a, either process decreasing the free energy of the region.

Jan 1, 1950

By Y. Nakada, U. F. Kocks, B. Chalrners

THE orientation dependence of work hardening has previously been studied over the entire range, i.e., including special orientations of high symmetry, in aluminum1-3 and silver.* The differences between various orientations are substantial, and the trend is the same in all fcc crystals. However, there are quantitative differences in behavior between aluminum and silver at room temperature, particularly in the (100) orientation. While many experiments on gold have been reported,5&apos;9 none included the special orientations. We therefore undertook tension tests on gold crystals of the axial orientations (100),(110), (Ill), (211), and, as a representative of single slip, one whose Schmid factor was 0.5 (hereafter referred to as m = 0.5). Single crystals of dimensions 1/4 by .1/4 by 6 in. were grown from the melt1&apos; at a rate of 4 in. per hr, using gold of 99.99 pct purity obtained from Handy and Harman. A growth rate of 1/8 in. per hr, or a purity of 99.999 pct,ll produced no difference in results. The crystals were annealed at 1000°C in air for 24 hr and furnace-cooled down to room temperature, after which they were electro-polished in a solution of potassium cyanide (40 g), potassium ferrocyanide (10 g), soda (20 g), and enough distilled water to make 1 liter of solution, at a current density of 0.02 amp per sq mm. After 2 or 3 hr, a very smooth surface was obtained by this method. Nine m = 0.5, two (loo), one (110), three (Ill), and one (211; crystals were tested at room temperature in a floor-model Instron machine at a tensile strain rate of 0.5 pct per min. The accuracy of the stress measurement was k10 g per sq mm up to 500 g per sq mm, k2 pct for higher stresses. The strain measurement was accurate to t2 pct. The scatter of stress at a given strain among the crystals of the same orientation was small, *5 pct being the largest. The representative stress-strain curves for various orientations are shown in Fig. 1. Table I summarizes the work-hardening parameters as used by seeger.12 Results of other investigators are also included in this table for comparison. There are no previous data for the corner orientations. Values for m = 0.5 crystals agree fairly well with those of Berner. Tm is defined as the stress at which the stress-strain curve begins to deviate from linearity of Stage 11. However, in practice this is a very difficult value to estimate because each investigator has a different idea of linearity. Therefore, the comparison with the values of other investigators may not be valid. In the present experiment, (100) crystals had the highest 111, followed by (111) crystals. The work-hardening rate in Stage I1 was highest for the (111) crystal followed by the (100) crystals. Our value for 0x1 of m = 0.5 orientation agrees very well with those of other investigators. 1) Single-Slip orientation (m = 0.5). These crystals were oriented so that the primary-slip vector was contained in one side face. The dimension perpendicular to this side should then not change if single slip indeed takes place. Within the accuracy of measurement, this dimension did not change during the deformation. Since the accuracy is k0.2 pct, the amount of secondary slip is less than 0.7 pct of the slip on the primary-slip system at 30 pct tensile strain. This is in conformity with the results obtained by Kocks" for aluminum crystals. The tensile axis moved toward (211) during the deformation. Slip bands, Fig. 2(a), were very fine and closely spaced. Some deformation bands were observed. There were no clear-cut cross-slip traces such as the ones observed on aluminum m = 0.5 crystals. 2) (111) Crystals. The orientation of the tensile axis was stable during the deformation. From this observation, one can deduce that at least three slip systems must have operated, and probably all six because the remaining three all have cross-slip relation to one of the first three.&apos; It was very difficult to observe the slip markings. Consequently, we could not confirm by this method that six systems were operative during the deformation. At high strains (above 50 pct shear strain), this orientation had the highest stress-strain curve. At 80

Jan 1, 1964

By Clyde E. Williams, V. N. Krivobok, C. H. Herty

THE extreme effect of the depression on the steel industry is well illustrated by the fact that the amount of iron ore shipped from the Lake Superior district was the lowest in 47 years. Something over 3 1/2 million tons of ore was shipped in 1932, compared with over 65 million tons in 1929. It is not surprising then that practically no advancement in iron ore beneficiation has been made. Improved research and development work, however, was continued at the Michigan College of Mines in the survey of the lean iron ores of Michigan with reference to the possibility of their concentration; at the University of Minnesota in its large-scale jigging studies of Lake :Superior ores; and at Battelle Memorial Institute in the development of improved jigging of iron ores. The successful operation of the new Hadsel mill at a gold property in California gave such low grinding costs on a quartz ore as to give much encouragement in the iron ore industry for a cheapening of the cost of grinding lean ores for concentration.

Jan 1, 1933

By Michael J. Bailey, Peter M. Douglass

INTRODUCTION Spoil pile slope failures can have costly consequences. In- stability in the form of a single major event or as a recurring problem can &apos;mean lost production, lost resources and damaged mining equipment. In extreme but not uncomnon cases, a major spoils slide can force the closure and abandonment of a pit. Slope stability is affected by mine operating practices as we1 l as geologic conditions and material parameters. Mine operators can enhance spoil pile stability through constructive changes in their operations. Attention to the causes of in- stability can lead to development of operating practices tailored to site specific problems. Action aimed at limiting future instability is frequently more cost effective than continually "coping" with unstable spoils. The effect of mine operations on material properties is often overlooked because the "data" are not easily quantified nor input directly into stability analysis equations. We have found, however, that miners&apos; experience with their own operation, as well as data pooled from similar operations, yields relation- ships which can be utilized to solve stability problems. The repetitive nature of area type surface coal mines with successive spoil pile rows further enables the development of useful site specific relationships. Stability problems can be mitigated by applying these relationships.

Jan 1, 1983

By Samuel S. Wyer

THE following description of methods for conducting gas-producer tests is probably the first attempt to give the subject an analytical, thorough and comprehensive treatment. In some cases where tests have been made, the methods have been so unsystematic and ambiguous that it has been impossible to secure comparable results. To eliminate this difficulty, the following provisional code of gas-producer tests-which has some resemblance to the code of boiler-trials of the American Society of Mechanical Engineers-has been developed. The primary object in testing a gas-producer is to determine whether the producer is working satisfactorily or, what is the same. thing, to see if the efficiency is as high as it should be with the type of producer in question, and also to find out if the composition of the resulting gas is adapted to the work it has to do. In order that the test shall be of any value, it must be thorough and comprehensive, and must be conducted with skill and care. When so conducted, the test will reveal the economy of the producer; and, by making suitable changes, the efficiency will often be increased very much. As a result of the tests made by Jenkins, 1 the efficiency was raised from 56.2 to 71.2 per cent. This shows the large saving that may frequently be made in the fuel-consumption by studying the results of a careful test.. The log of the test, given in Fig. 1, shows that, just as soon as the temperature became regular, the percentage of CO, decreased and that of CO increased.

Mar 1, 1905

By J. D. Hanawalt

Significant strides were made in the year 1948 leading to further recognition of the place of magnesium as a common commercial metal, rather than as just a premium aircraft material. One of the factors contributing to this recognition was the price stability and, in many cases, price reduction of magnesium products in 1948. In contrast to most other metals, manufacturing advances in magnesium outweighed the effects of increased labor and other costs. At the present time, many magnesium extrusions, die castings, and permanent mold castings can be purchased as cheaply as their aluminum counterparts in these forums, though competitive prices for sheet still await the inauguration of a modern tandem rolling mill for magnesium, such as has already been demonstrated.

Jan 1, 1949

By W. G. SWART

THE best estimate on reserves of iron ore in the Lake Superior district is that made, in 1920, by Mr. R. C. Allen, amounting to 2,947,225,000 tons of assured and probable ore. This includes direct- shipping or so-called merchantable ores, and those capable of beneficiation by demonstrated processes. De- ducting from this the 287,000,000 tons shipped since 1920, leaves a present reserve of approximately 2,500,- 000,000 tons, or; about 50 years&apos; supply. The assured ore in this estimate is given as 1,560,500,000 tons, which checks Mr. Lake&apos;s estimate of 1,528,948,000 tons, or about 30 years&apos; supply. This is not a long time in the life of the steel industry, and it can be readily appreciated that the matter is important enough to war- rant the attention it is beginning to receive. The first question that engages our attention is, What is merchantable ore? In 1902 the average of all Mesabi shipments was 56.07 per cent iron and 4.35 per cent silica. Twenty-five years later it had dropped to 51.99 per cent iron, with silica up to 7.92 per cent. It has remained around these figures for&apos; ten or twelve years and, except for a probable rise in silica, can stay there for an indefinite period. Most of these figures I am giving cover the Mesabi Range. Including the other ranges does not change the figures greatly, and the Mesabi Range commands the situation, since it produces about 65 per cent of the total annual tonnage and, according to Mr. Allen, contains 81 per cent of the assured reserves, 50 per cent of the probable reserves, and 66 per cent of both the assured and the probable reserves.

Jan 1, 1926

By M. L. Fuller

IN connection with an investigation in this laboratory on the high-zinc side of the copper-zinc system, it was observed that well developed segre-gate structures of the Widmanstätten type were formed when a secondary phase precipitated from the solid solution of copper in zinc. This paper presents an analysis of the crystallographic relationship between the segregate and the solid solution matrix. The data to be presented are an interesting addition to the literature on segregate structures in that the plane of segregation is one of the less densely populated planes. In agreement with the generalization of C. H. Mathewson and D. W. Smith1 the plane of segregation in the matrix con-tains the direction of closest atomic packing of the lattice. Furthermore, the matrix and the segregate are both hexagonal close-packed, which has not been reported hitherto in the literature.2 The increasing com-mercial importance of zinc alloys containing copper makes this funda-mental study of value to the metallography of zinc alloys.

Jan 1, 1933

By C. Laird, C. E. Feltner

An investigation into the effect of a material&apos;s slip character on its high strain fatigue properties has been carried out using copper and Cu-7.5 wt pct A1 as representative wavy and planar slip mode materials, respectively. In copper, the constant term and exponent in the Coffin-Manson equation, ?EpNf1/2 = const, are unaffected by the temperature of testing or the history of the metal. On the other hand, in Cu-7.5 wl pcl Al, while the exponent is invariant, the constant is increased with respect to copper and increased further with decrease in temperature. The life in Cu-7.5 wt pct A1 is double that of copper at room temperature and about four times at 78°K. Fractoflaphic studies indicate that these diffevences in life are associated with the early stages of cracking. In copper, severe surface rumpling provides crack nuclei at pain boundaries independent of&apos; testing temperature or the history of the metal. In Cu-7.5 wt pct Al, the planar slip mode of deformation prevents grain boundary folding; crack nucleation is therefore mainly transgranular and the increase in life with respect to copper is associated with a prolonged linking-up stage of such transgranulay cracks. At the lower temperature the increased difficulty of cross slip inhibits multiplication of trans-granular cracks and retards the linking-up process, giving a further enhaancement in life. It is expected that such behavior will be found general in materials of wavy and planar slip mode, respectively. STAGE II crack propagation in high strain fatigue takes place by a repetitive process of crack tip blunting in the tension part of a fatigue cycle followed by resharpening of the crack in the compression part.1-3 This mechanism has come to be called the "plastic relaxation process".3 At very high strains (lives to failure less than 103 cycles), most of the life of a specimen is spent in crack propagation by the plastic relaxation process.4,5 Since the differences in the cyclic strain hardening behavior of metals and alloys are comparatively small in this strain range,6,7 the amount of blunting at a crack tip depends primarily on the applied strain amplitude. The rate of crack propagation in this life range is therefore nearly constant with respect to material and temperature of testing. In the longer life portion of the high strain fatigue range (l03 to 103 cycles to failure), a considerable fraction of the lives is spent in crack initiation and Stage I growth. Grain boundaries have frequently4,5,8 been found to be the sites for this growth which is also associated with a surface folding process.4&apos;5 Such folding behavior may also be general in any material having a grain structure and capable of plastic deformation. It has therefore been suggested475 that the universality of the Coff in-Manson law,9&apos;10 constant,* where ?Ep is the plastic strain range and Nf the number of cycles to failure, is reflected in the approximate invariance of both the crack initiation and propagation behavior. It happens that, in most investigations of the phenomena associated with failure,4,5,8 materials with a wavy slip mode have been used as vehicles for the studies, or else "normally" planar slip mode materials have been tested under conditions giving rise to wavy glide deformation, e.g., stainless steels cycled at high temperature.&apos;&apos; The purpose of the present investigation was to determine whether or not different cracking phenomena would occur when the slip mode of a material is planar and if the associated life to failure would be different than that of a wavy slip

Jan 1, 1968

By S. A. Falconer

D. A. Dahlstrom—Mr. Falconer has done an admirable job of proving the adaptability of the cyclone to the beneficiation of a very difficult size range in the preparation of coal. The addition of the cyclone to other coarser size methods makes it economically feasible for the coal operator to rigorously control his marketed products at a high and uniform quality level down to the 48 and 100-mesh size. Furthermore, it should be pointed out that by utilizing the cyclone as a deslimer or classifier the —3 200-mesh fraction, usually containing large percentages of undesirable material, can also be quickly and cheaply removed from the clean coal. Advantages of such a step are several: (1) Reduction of ash content, especially where clays and slimes are serious. (2) lower moisture content of the final coal. (3) easier mechanical and thermal de-watering of the fine coal due to higher cake and bed permeabilities. The author has indicated that adjustable control means should be installed on the cyclone operating on a heavy-media slurry. This also holds true for the cyclone acting as classifier, deslimer or preliminary dewatering agent and is worthy of special emphasis. Such controls, while not necessarily automatic, must be simple, rapidly adjustable, and require a minimum of attention. Three methods available to the operator are (1) throttling valve on the feed line, (2) back pressure valve on the overflow, and (3) adjustable diameter underflow nozzles. The first two, while fulfilling the specifications, suffer the disadvantage of restricting capacity if severe throttling is necessary. The third method has little effect on capacity and easily maintains an underflow of correct moisture content. Several designs are possible, but two find the widest application. The first was developed by Robert Piros of The Truax-Traer Coal Co. and uses a simple casting containing two holders for underflow nozzles which can be rotated about an axis parallel to the cyclone centerline. These holders retain the underflow nozzle flush with the conical section walls. When a change in nozzle diameter is required, the new size is placed in the spare holder and rotated into place. A second design utilizes a soft rubber cylindrical tube which is compressed or released from three sides, causing the inner diameter of the tube to decrease or increase. This is achieved by using a machine-threaded,

Jan 1, 1951