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By R. M. Asimow

The magnetization curves for specimezs containing superparmagnetic particles are considered. It is shown that the curves may differ from a Langezlin function because of particle anisotropy, particle interactions , and the presence of a size distribution of particles. The various causes of particle anisotropy are considered, and magnetization curves for specimens with cubic and uniaxial anisotropy are presented. The magnetization curves depend on the In the particle-size below 100A it is quite difficult to obtain quantitative size and shape information on precipitate particles. All of the available techniques have their limitations; however, quantitative applications of superparmagnetism have not been developed as fully as possible due to a lack of analysis of the complete magnetization curve. With such an analysis it appears possible to obtain from a single magnetization curve of a specimen containing randomly oriented SPM (superparamagnetic) particles a quantitative volume distribution and a description of the particle shape.* sign of the anisotropy energy and in the case of a negative uniaxial anisotropy (prolate spheroids) the resulting curves may differ very considerbly from a Langevin function. A graphical technique is developed whereby it is possible to separate out the effects of the size distribution, the particle interaction, and the particle anisotropy. Thus it is possible to obtain quantitative values for both the particle shape and the size distribution. Langevin function2 I/Is = ctnh(HVIs/k T)-k T/HVIS [ 1 ] where I, is the saturation magnetization, V the particle volume, H the applied field, T the particle temperature, k the Boltzmann constant, and I the magnetization in the direction of the applied field. Such behavior is rarely if ever observed in actual systems. One explanation for this is that the SPM particles do possess a significant anisotropy and thus the magnetic energy associated with the particle depends on the direction of magnetization in a more complicated way than for the isotropic particle of Eq. [I]. In general the magnetic energy E of an isolated SPM particle embedded in a nonmagnetic matrix can be expressed as a sum of several contributions: E = Eh + Ed+Es+Ec [2] where Eh is the external field energy, Ed the energy resulting from the particle demagnetizing factor, E, the magnetostriction energy, and E, the crystalline anisotropy energy. In each term we consider only the part dependent on the orientation of the magnetization vector and the particle axes as the shape of the magnetization curve will be determined by these contributions. Following the same procedure used in deriving the Langevin function,

Jan 1, 1965

By C. T. Cox

The title of this short paper necessarily implies that friction articles comprise a distinct and unique field and are different from the other metal-powder articles, such as bearings, electrical contacts, and magnets. However, this distinction is rather hard to define in that it is really one of degree and not Of kind. It would appear that the main distinction is that friction are are articles of rather large pressing area. In other words, they are articles in which the area Of the mold in which the metal powder is pressed is relatively large. Other articles made from meta1 powders are generally of rather small area, usually a few square inches, while in friction articles the area ranges up to several hundred square inches. The satisfactory production of meta1-powder friction articles involves many production problems and a large number Of these are accentuated by the large area' Since it is impossible in the short space of this Paper to describe adequately all the problems involved, I have thought it best to merely mention some Of them and to place particular emphasis upon a problem that is common to all metal-powder articles, although it is of greater importance in the making of friction articles. This problem has to do with the effect On the properties of a friction article of small variations in the composition. However, before discussing the problems, it is probably appropriate that some mention be made of the limitations on the use of friction articles. Most engineers are familiar with the general field that can be characterized as constituted by clutch facings and brake linings, and undoubtedly have heard many stories of how metal-powder friction articles have had a service life 10 times as long as nonmetallic friction materials, and of instances where metal-powder friction articles have operated satisfactorily where no other material could be used. These instances should not be regarded as criteria for the assumption that metal-powder friction articles are capable of universal use in the friction field and will always outperform other materials. On the contrary, metal-powder friction articles are unsuitable for numerous applications, either on a performance or on a cost basis. Metal-powder friction articles will not replace wooden block brakes for wagon wheels nor cast-iron brake shoes for railway car wheels, to mention just two obvious examples. Metallic friction articles cannot be used where they must act as heat insulatorsl for they have a relatively high thermal conductivity as compared with asbestos. This is a detriment in some uses, as in certain airplane brakes having hydraulic actuators provided with rubber seals. The metallic friction material readily transfers the heat developed at the braking surface back through the material to the rubber seal and destroys it. Within its limited field, metal-powder friction material has proved satisfactory, but many problems are involved in the Selection of the proper material to use in an application and in the commercial pro-

Jan 1, 1945

By Thomas Adair

Moderator-Thomas Adair is now a tunnel consultant with Perini Corp., Spring Lake, N.J. He has had 40 years experience in tunnel and shaft-sinking work in both soft and hard rock, as well as subaqueous rock. He has used moles in various locations and has traveled around the world studying the problems. SOME BRIEF COMMENTS ON "MOLES" by Thomas Adair We of the Perini Corp. have been, over the past 15 years, in the forefront of the battle to develop the mechanized miner. We have contributed much to pioneer, develop, and promote the use of the mining machine. Our money and talent have not been spared in this effort. However, we are sorry to say that as of the present time (1968), at least from the economic stand- point, this effort has not been very rewarding. But, I must say to those who are presently involved in the work of building mining machines, do not be discouraged. There is money in it. We of Perini Corp. know because we put it in there. It has been estimated that during the next 15 years, some $20 billion will be spent on underground excavation; more than 13 thousand miles of sub- surface tunnels will be excavated throughout the nation. An aggressive, properly structured research and development effort would produce, within the next five or ten years, a better excavation technology and improved boring system capable of reducing present costs drastically, with a resultant great saving. The time for this effort is now, but where the enabling money for this effort will come from, I have no idea. Machine builders should be encouraged to design and develop a shield- type boring machine capable of continuous mining through varying types of ground or rock by incorporating the possibility of making minor modifications such as change of bit type, power package, etc. Such a machine could

Jan 1, 1970

By J. P. Nichols

Modern vibrating screening dates from about 1910 at which time the forerunner of the present day two bearing and four bearing circular motion inclined vibrating screens were first introduced. These simple machines consisted of a screen box holding some kind of a screening surface to which was attached an off-center shaft or a shaft with an off-center weight which was rotated. The rotation of these shafts caused a shivering motion to the screen box and produced the first vibrating screen. In the 1920's and early 30's, the box designs were improved and the mechanisms designs were also improved and by 1940, vibrating screens were an important part of most process plants. In the early days when the screen sizes were dictated by how much could be shoveled onto the screen box and by the force that a particular mechanism could produce, not much thought was given to the proper sizing of the particular units. As mechanism and body design improved the ability to predict vibrating screen capacity at various openings became more important. In the late 1930's, a set of empirical capacities came to be used. with few modifications, these capacities are still in use today, both by those companies that use a formula involving only the amount of fine material in a feed, and by those companies using a formula in which the total feed to a particular screen is used. In either method of calculation, the empirical values are based on these ideal conditions: (1) The material being fed to the screen contains 25% oversize. (2) The feed to the screen contains 40% half size material. (3) The material has a bulk density of 1.6 T/Cu.M. (100 lbs/cu.ft.). (4) The screening surface has an open area of 50%. (5) The material is dry, free flowing and relatively cubical. (6) The maximum screening efficiency required is between 90 and 95%. It is obvious that these conditions do not occur in natural or crushed size distributions. Therefore, modifications must be made to these empirical values to allow for the calculation of a vibrating screen for a particular set of conditions. Before we consider these various modifications, let us look at what happens to material as it is acted on by a vibrating screen so that we can better understand why the modifications are nec-

Jan 1, 1982

By C. A. Mitke

(Butte Meeting, August, 1913.) 1. Character of Gases which Caused Helmets to Get Out of Order. DURING September, -1911, the fire area in the Lowell mine continually increased and gases resulting from the fire came through the upcast shaft. These gases contained such a large percentage of sulphur dioxide that the men were unable to go up and down on cages, and, within a comparatively short time, repairs in the shaft were found to be necessary. Since the fire was in sulphide ores and extended into certain timbered sections, the gases contained varying amounts of SO2 CO2, and perhaps, at times, CO. The temperature in the shaft was generally about 97°, and the relative humidity from 97 to 99.5 per cent. The corrosive action of the fumes became apparent when the cables had to be changed more often than usual, the heads of lag screws .in the guides of the shaft disappeared, and the cages needed frequent repairs. It also became necessary to repair two compartments of the shaft by putting in 150 ft. of new guides between the 600 and 800 levels and lag screws in nearly all the old guides from the surface to the 800 level. 2. Ordinary Methods of Testing Helmets which were Unsatisfactory. These conditions required all work to be done by men wearing oxygen helmets. The Draeger type was tried, and was used until all repairs were completed. At first the helmets were. tested for air circulation and air tightness and the injector was tested by water gauge according to the methods recommended by the Draeger Oxygen Apparatus Co. Six arrangements, covering .these different tests, are illustrated in the catalogue and circulars of the company.

Jan 7, 1913

By R. M. Brick, Arthur Phillips, A. J. Smith

A previous publication1§ has described the effect of quenching stresses on the lattice parameter values of high-purity aluminum-copper alloys particularly with reference to the solution and precipitation of CuAl². A similar study has been made of the aluminum-rich aluminum-magnesium alloys. Attention has been directed in the present investigation to the magnitude of the quenching stresses as affected by the specimen size and shape, the number of solute atoms and the quenching rate. The effect of cooling stresses in causing plastic defomation or cracking has been considered in relation to the physical properties of the alloy On reheating alloys in the two-phase field, the time required for precipitation to occur has been observed in connection with the degrec of supersaturation, the rate of diffusion of the solute atoms as a function of the comparative atomic radii, degree of strain, temperature of reheating and grain size. A few qualitative comparisons on the relative effect of these factors have been drawn between the aluminum-copper alloys and the aluminum-magnesium alloys. Strain in Solid-solution Alloys A 10 per cent magnesium alloy ill the form of chill-cast bars was furnished by the Aluminum Company of America through the courtesy of L. W. Kempf. Additional alloys were prepared using alllminum (99.95 per cent Al) and high-grade magnesium. The alloys listed in Table 1 were melted in an Acheson graphite crucible under a flux of fused MgCl², CaC12, NaCI. Chill-cast rods were sealed under vacuum in Pyrex glass, homogenized several days at 450' C., air-cooled and machined to rods of from 1/8 to ¾-in. dia. Metal powders taken from these rods with a fine-toothed saw were again sealed under vacuum in

Jan 1, 1935

By W. T. Allan

Raw bituminous coal has been in general use as a blast-furnace fuel in Scotland for the last century, and although its use has now been largely abandoned and it has been replaced by coke in the majority of the few furnaces which are at present in blast in this country, coal-smelted pig iron is not yet a thing of the past; it is still being produced and marketed in competition with the more cheaply smelted product of the coke-fired furnace. Various factors have influenced this change in practice; the once plentiful deposits of coal of a suitable nature for the blast furnace are now not so easily obtainable; native blackband and clayband ironstones which are easily smelted in the coal-fired blast furnace, although still far from being exhausted, are not available except at a cost that is somewhat higher than that of imported ores, making them unattractive to the ironmaster that is compelled by circumstances to smelt his iron at the lowest possible cost. Within the last 15 years overproduction of synthetic nitrogen has led to progressive reductions in the price of sulphate of ammonia, the recovery of which together with the other by-products before that time materially assisted in reducing the working costs of the coal-fired furnace. Now the sale of the by-products recovered yields a diminished profit. When the cost of the product is the only consideration the small, s1ow-smelting, coal-fired blast furnace cannot compare with its large, modern, coke-fired competitor. Other considerations do not by any means all support the same side of the argument. In the smelting of pig iron to be used in the manufacture of steel where the quality of the final product depends so largely upon the control of the conversion process and so much less upon the physical quality of the pig iron used, the physical properties of the pig iron do not exert any appreciable influence upon the quality of the steel produced, therefore the methods employed in the smelting of the pig iron matter but little so long as the requisite chemical composition is reached. On the other hand, in ironfounding where the simple melting of the pig iron, which is the only treatment it receives before being cast into its final form, does little or nothing to modify its original charac-

Jan 1, 1937

By R. Maddin, N. Ujiiye

ALTHOUGH the cold-rolled texture for body-centered-cubic metals and alloys is well known (see, e.g., Barrett'), the pole figure representing the texture may be interpreted in two ways. It may be regarded as consisting of several ideal preferred orientations with an associated spread (a view which is shared among several investigators2), or it may be regarded as consisting of two sets of continuous preferred orientation also with an associated spread."." Recently, Chen and Maddin7 noted a stable (001) [loo] end orientation for molybdenum single crystals rolled at low rates of reduction provided the initial rolling. orientation" was close to the cube ori-

Jan 1, 1957

By Lancaster Jones

The gravity magnitudes obtained by means of observations with the Eötvös balance in the field are necessarily resultant or total effects due to all abnormalities of mass distribution, including even the effects due to the ellipticity and rotational motion of the whole earth. Since the object of the survey is to isolate the effects which arise solely from some particular subterranean feature, and to deduce therefrom the configuration and extent of this feature, the first step is to eliminate from the observed effects all those due to "disturbing" (i. e., unwanted) features, whether above or below the surface of the ground. The disturbing features have different characteristics, according to their situation relative to the center of the balance and to the horizontal plane through the foot of the balance, or station point; this diversity was recognized by Eotvos, who divided the total effects into so-called Normal, Terrain, Topographical, Cartographical and Subterranean effects. This classification has been adhered to by most subsequent investigators, but the writer prefers to employ the term "three-dimensional," which really indicates the essential character of the class of effect known as "Subterranean," at any rate from the standpoint of the computer of effects. Before disturbing effects can be eliminated, the features must be measured up or surveyed, whether by topographical, mining, or boring methods, and then the effects of each feature calculated and subtracted from the total observed effects. After this the problem of interpreting the residual effects will itself necessitate the computation of the assumed feature, or even a series of trial features. The task of computing gravity effects is therefore of great importance. In the early work, by Eötvös himself, the computation practically ceased when the terrain and topographical effects had been calculated, but later surveys have demanded an ever-increasing extension in the technique of computation. Certainly in surveys designed to locate minerals, particularly ores, the calculations have to be extended far beyond those of Eötvös, while his methods of computing both terrain

Jan 1, 1929

By J. Versluys

A well can flow exclusively through the casing or exclusively through a tubing but can also flow partly through a casing and at the top part through a tubing. The main principles of the flowing of wells under these conditions were explained in the author's former paper.' Practically all factors that influence the regular flow are dealt with therein. The question of irregular flow, however, will be discussed briefly here. As a rule, an irregular flow must be avoided, as it may be assumed that the efficiency is thereby very small, while on many fields it is injurious to the sand of the oil-bearing layer. Periodical flowing often occurs with rising mixtures of gas and liquid. The phenomenon can be explained if it is accepted that two conditions are possible in the mixture; namely, the foam condition and the mist condition. If there is no stabilizer in the liquid, the foam condition can exist only when the liquid forms a greater portion of the volume than the gas. The mist condition, on the other hand, can exist only when the liquid occupies a smaller part of the volume than the gas. The foam condition occurs when there are gas bubbles in the liquid mass, while in the mist condition drops of liquid are disseminated in a gas-filled space. For sake of simplicity, it has been assumed that the mist condition prevails when 50 per cent. or more of the volume is occupied by gas, while with less than 50 per cent. gas the foam condition will arise. For distilled water and for oils which do not tend to form stable foams this is probably approximately true. If this does not hold good, however, two cases are possible: (1) The fields of the two conditions overlap or (2) they do not meet. If the fields of the conditions overlap there is an intermediate field where either of the two conditions can exist, depending on the history of the mixture. Suppose the foam condition prevails first and the gas

Jan 1, 1931

By Franz R. Dykstra, R. F. Tatnall

A ferroalloy is defined as: "An alloy of iron with some element other than carbon used as a vehicle for introducing such an element into the manufacture of steel. The element may alloy with the steel by solution or, as the carbide, -neutralize the harmful impurities, by combining with them and separating from the steel as flux or slag before solidification."a The most commonly used ferroalloys are: ferromanganese, ferrochrome, ferrosilicon, ferrovanadium, ferromolybdenum, ferronickel, ferrotungsten, ferrocolumbium, and ferrophosphorus. Concern here is with the sources and markets of the major metallic alloying elements. The discussion is further restricted to those - ferroalloy ores, the principal use of which is in the production of steel. Phosphorus, silicon, and tungsten, for example, are ferroalloys of some economic significance, but other uses dwarf their alloying applications. Thus, this discussion will deal with the ores of managanese, chromium, nickel, molybdenum, vanadium, and columbium. As shown in Table 14.1B.1 ferroalloys serve to- facilitate processing and impart to the finished steel such characteristics as tensile strength, ductility, low-temperature impact, hardenability, high-temperature strength, corrosion resistance, toughness, and abrasion resistance. In the steel-making process, ferroalloys may be added in the charge, in the molten bath near the end of the finishing period, in the ladle, or in the molds. Timing of the addition depends on the effect of the addition on the temperature of the molten metal, the formation and elimination of reaction products, and the protection of subsequent additions from oxidation. MANGANESE General Approximately 95% of the manganese ore sold is consumed by the steel industry, either as ferromanganese or as manganese metal. Manganese is the universal alloy, without which good steel cannot be made. It serves as a scavenger, removing phosphorus, sulfur and, to a degree, oxygen from the melt. As an alloying material it makes steel hard, tough, and resistant to wear. Approximately 6 kg of manganese is required for every ton of common steel produced by United States steelmaking practice. The remaining 5 % of the manganese ore consumed consists of special or so-called "chemical" ores, including high-grade pyrolusite ores, electrochemically reactive "battery ores," and a number of special varieties, as well as those otherwise regarded as "metallurgical ores."

Jan 1, 1976

By W. F. Dietrich

This paper deals with the methods of mining the high-grade clays of California. The fact that the majority of the clay pits in the state are operated on a scale that is small by comparison with most metal mines causes a diversity of methods and gives rise to problems of selection of the method best suited to given conditions. Two or three operators in California produce approximately 500 tons per day of a single kind of clay from a single pit. About five varieties of clay are mined on a scale of 200 to 400 tons per day; not over 15 varieties are mined on a scale of 50 to 200 tons per day; and more than 50 varieties are mined at the rate of less than 50 tons per day. It is the aim of this paper to delimit, as far as the data at hand permit, the conditions and scale of operations that favor the selection of each dominant method of mining that is actually being applied at California properties. Details of the occurrence and utilization of the clays of California have been given in a recent bulletin1 and will not be considered here. Geographical and Geological Features of California Clay Deposits The greater part of the high-grade clays consumed by clay-working plants in California is mined from one of three producing areas in the state: (1) Lincoln, Placer County, on the eastern edge of the Sacramento valley, 30 miles northeast of Sacramento; (2) Ione, Amador County, in the foothills of the Sierra Nevada, 38 miles northeast of Stockton, and 12 miles west of Jackson, one of the important towns of the famous Mother Lode gold-mining district; and (3) Alberhill, Riverside County, 90 miles southeast of Los Angeles. Other districts of minor importance are near Cardiff and Carlsbad, San Diego County, and El Toro and San Juan Capistrano, Orange County. In addition, there are a number of isolated properties in various parts of the state.

Jan 1, 1928

By F. J. Mehringer, C. W. MacGregor

VARIOUS investigations have been carried out to determine the effects of cold-rolling on the common physical properties as represented by the yield strength, tensile strength, percentage of elongation and ordinary reduction of area. Very little information is available in the literature with reference to the effects of cold-rolling on the true stress-strain properties. Since the ordinary physical properties base both the stresses and the strains on the original dimensions of the test piece, which are greatly changed during the test, they are essentially empirical values and do not represent physically either true stresses or true strains. Consequently, they do not give an accurate picture of the effects of different conditions, both mechanical and metallurgical, on the strength and ductility of the material. It is not, however, the purpose of this paper to review the various advantages accruing from the use of true stress and true strain values, since these have been shown elsewhere,1-12 but to utilize them in representing the various effects considered. The true stress S and true strain (e = q') values mentioned above for the tension test are defined by1 [ ] where P, A, Ao are the axial load, the instantaneous area and the original area of cross section, respectively. From simultaneous readings of the axial load and the dimension or dimensions determining the instantaneous area of cross section, the true stress-strain curve is constructed by using the relations given in Eq. I. It is then the object of this paper to discuss the general effects of cold-rolling on the true stress and strain values for a low-carbon steel together with the effects of age-hardening and directionality on these properties. PRELIMINARY INVESTIGATIONS The material considered throughout the paper is a low-carbon steel of the following chemical analysis: C, 019 per cent; S, 0. 118; P, 0.092; Mn, 0.85; Si, 0.01. The stock was received in bars, 7 by 3/4 in., and was first annealed for one hour at 1650°F. followed by a furnace cool. Photomicrographs of this material showed considerable directionality even in the annealed condition. In view of the possible effects of the nonhomogeneity and directionality in this material, it was considered important to investigate their influence on the true stress-strain diagrams. In addition, the effect of strain-aging in this steel was also made the subject of a preliminary study. Elect of Aging on True Stress-strain Properties Since a certain time element would elapse between the cold-rolling operation and the final tension tests, it was determined to investigate the aging character-

Jan 1, 1945

By David B. Scott

When mining operations were first instituted in the mines of the Miami Copper Co., at Miami, Ariz., the relatively hard character of the ground in the western section of the property made it seem advisable to use a wide shrinkage stope and pillar system. The system as finally evolved was applied to the mining of 2,300,000 tons of ore by the use of stopes and pillars each 50 ft. in width. Development, mining and extraction of this reserve has been continuously in progress since 1910, and the final stages of extraction are now reached. A complete survey of all phases of this system can therefore be made. Modification in working methods was obviously necessary, and the system to be described is believed to be typical of the best features. Development The preliminary work had three main objectives: The opening of a haulage level, the construction of a drawing-off level, and the driving of sublevels for use in stoping. In addition to these, some extra sublevel drifting was necessary to determine exactly the boundaries of the orebody, the general outline having been determined by churn drilling. This development was based on the requirements of stopes 50 ft. wide, with pillars 50 ft. wide between each stope. The length of these units varied from 200 to 500 ft.. Haulage Level The tramming level was 50 ft. below the floor of the stopes, and the tramming lines were run parallel with the long axis of the stopes. These lines were also beneath the middle of the stopes and pillars. Each line therefore served one stope or one pillar, this arrangement making it possible to load along an entire stope without switching or uncoupling. This advantage is apparent principally during the process of stoping when rapid drawing of excess broken ore is desirable. Furthermore, the arrangement of the drawing-off level chutes at 25-ft. intervals, as shown

Jan 1, 1917

By Ilmar Stöckel, Gösta Harlin, Agne Rustan

INTRODUCTION This chapter is a continuation of the studies by Rustan and Stockel (1979, 1980) on techniques for automating ventilation in Swedish mines and construction works. The studies have been financed by the Swedish Board of Technical Development. As a result of the studies it has been recommended that a good solution to diesel exhaust emission would be automatic, step by step control of the fans near the working place. Diesel vehicles are the major polluters underground in the mines. Therefore, we have suggested that diesel vehicles regulate the fans The goal of the continued study has been to find a way for active diesel vehicles to start and stop gallery fans at both intake and return air. In this paper different methods for activating fans are discussed. The best methods are chosen and tested in the mine. In this study we have found that change of temperature is an inexpensive and effective way to start and stop crosscut fans in sublevel caving and radio signals seem to be an attractive system for starting and stopping gallery fans . This work has been done in close collaboration between LKAB in Kiruna and the University of Luleå, Divisions of Electronics and of Mining and Rock Excavation. An advisory group for the project has been established with ventilation experts from the mines, representatives of the local mine workers' unions, and authorities from the local offices of Governmental Inspection of the Workers Safety. VENTILATION SYSTEM STUDIED In the project the ventilation system at LKAB in Kiruna was studied. The mining method used is sublevel caving with 9-13 m slice height. The air above ground is heated in winter by hot water and the main fans push the air down to a main distribution level along the 4000 m long and about 100 m wide ore body. From the distribution level, air is taken through shafts down to the sublevels, where it is pushed through the levels by local gallery fans on both the intake and return sides, Fig. 1.

Jan 1, 1981

By J. P. Van Kleunen

9.3-1. Introduction. The demands of industry for handling materials at higher rates and at reduced costs have had a very significant effect on belt conveyor technology. Although the general appearance of the belt conveyor today is essentially the same as it has been for the past several decades, the similarity ends there. Each component comprising the conveyor system has been continuously improved through design and materials technology to enable present conveyor systems to operate at ever-increasing rates and reliability. For example, twenty years ago the strongest commercially available, fabric-reinforced conveyor belting had a tension rating of 50 lb per ply-in. Currently, fabric-reinforced belts are available with ratings of 350 lb per ply-in. and steel cable reinforced belting is available with tension ratings of 3000 lb per in. of belt width (3). These technological advances have therefore enabled the belt conveyor to not only attain acceptance as a preferred method for in-plant movement of bulk materials, but also to be used for long distance transportation of bulk materials, particularly in areas of adverse terrain. The information contained in this chapter is intended to assist the reader to make basic decisions regarding the use and application of a conveyor system. The design of an overland conveyor transportation system or an in-plant process conveyor is accordingly beyond the scope of this article. Many comprehensive technical works covering the design of a belt conveyor are currently available from the manufacturers of materials handling equipment (6, 7, 9, 11). The design handbook published by the Conveyor Equipment Manufacturers Association is particularly recommended (2). 9.3-2. Conveyor Capacities. One of the most important factors in determining the proper size of a conveyor system is the rate at which material must be handled. Although tables and charts are available to the conveyor designer to assist him in his selection of conveyor components, only the

Jan 1, 1968

By Robert K. Warner

When a new mine is opened, and often when an operating mine must adapt itself to physical or economic changes, a mining system must be selected in complete detail. In the past the plan chosen was usually the product of the local staff alone, however limited the training and experience of that staff might be, which often resulted in the introduction of methods that were familiar to the staff, but not so well suited to the conditions as others unknown to the local men. A new management, noting the difficulties with the existing layout, might make modifications or complete changes, so that many mines in their history have seen a whole series of mining systems, each somewhat laboriously grafted on to its predecessor. This should not be interpreted as a condemnation of the older staffs for sticking to the tried systems, such as open square-sets in the early days at the Homestake, because they knew it would work after a fashion, nor does the statement apply to the technically trained, and usually broadly experienced staffs of most present-day properties. The older miners did not have the variety of tools and methods, nor the present freedom of transfer of information as to what the other man is doing, and so did the best they could under the circumstances. Finally, the higher grade of the ores made the choice less vital. The ever-increasing need to mine low-grade orebodies, with a fixed or even lower price for the metal produced, has caused an increasing need for low-cost mining. In most new mines this has simplified the problem of selection by eliminating from consideration all of the high-cost systems, but it has also complicated the choice by the necessity for refinement in detail and a close adjustment of the plan selected to all the conditions at the property. In these low-cost problems any textbook division of mining systems as applied to "beds, veins or masses" avails little as a guide. It should be realized at the outset that to be successful under modern competitive conditions a system of mining must be worked out with elaborate detail, with careful time scheduling and control of the various elemental operations, and that after it is introduced it must be run with a large amount of technical direction.

Jan 1, 1934

By G. Sherburne Rogers

Introduction. ONE of the features of oil-field work that puzzles operator, chemist and geologist alike, is variation in the gravity of the petroleum produced, on neighboring leases or even from adjoining wells. Few fields in the United States yield oil that is of uniform gravity throughout; in some, fields the different grades are produced from different sands, in a few from different formations, and in many from different areas in the same sand. In a few cases, perhaps, a common assumption-that the heavier oil is derived from the lighter through the escape of the more volatile constituents-is valid, but many cases can not be explained in this way. Although in the California fields the specific gravity of the oil generally decreases with depth, there are numerous exceptions to this rule; and, as in many other regions the light oil is found nearest the surface, it is evident that evaporation underground is generally an unimportant factor. It is generally recognized that the great differences between petroleum from widely separated fields are due largely to differences in age and degree of metamorphism and to variation in the composition of the original organic matter; but in the writer's opinion some of these broader differences, as well as most of the minor variations in the character of the oil from any one field, are clue to the local action of natural reagents such as sulphur or oxygen. This is particularly likely to be true if the oil has migrated from one formation to another, as in the California fields; and in some areas it appears that variation in sulphur content may even afford a rough index of the extent or distance of the migration. It is the purpose of this paper to call attention to the chemical action of sulphur and oxygen on petroleum, to show that the gravity of the oil from any one field is intimately related to its sulphur content, and to discuss the possi-

Jan 7, 1917

By Paul Tyler

FULLY a decade ago, demand for ground mica began to exceed supplies of scrap mica from manufacturing operations and of waste block from feldspar and sheet mica mining in the United States, with the result that in recent years the market has absorbed larger and larger quantities of mica recovered as a by-product from clay washing,1 as a joint product with kyanite,2 and by grinding schists. So far, only schists that contain a large percentage of mica have been utilized for making ground mica, but already there has been a good deal of wishful thinking with regard to recovering mica as an aid to the prospective working of low-grade gold ores and ores of certain base metals. With wet-ground mica selling at $60 to $100 a ton and even dry-ground mica worth over $20 a ton, many ores that could not be considered as otherwise workable under present conditions will show commercial possibilities if they can be made to yield even a relatively small percentage of salable mica. An interesting paper might be written on the coming role of industrial minerals as joint products of metal mines, It is largely a matter of mar-kets. Many years ago I watched the mess left behind the gold dredges in the mountains of Colorado and thought of the Denver sand and gravel operators who prided themselves upon their canniness in providing devices for catching gold merely as an incident to their regular business of selling what we miners classed as "tailings." Nowadays almost every milling or mining operation near settled communities finds use for at least part of its waste for road material or concrete aggregate and several eastern iron mines have gone into the crushed-stone business. Promoters now mention fertilizer "filler" as potentially salable at all the way from $1 to $10 a ton, or whatever is needed to cover costs of mining and treating the "ore" and leave the metal values as "clear profit." In emulating the pork packers in their efforts to utilize "everything but the squeal,"

Jan 1, 1938

By Ralph E. Grim

THE technology of clay minerals is defined, for the purpose of this review, as- the application of fundamental data regarding clay minerals, and techniques of handling them, to the various industries, arts, and professions concerned with clay materials. The aim of the paper is to narrate recent developments in clay mineral technology. This review does not claim to be complete, and perhaps gives undue emphasis to matters that have been worked on in the author's laboratory or with which he has some other connection. In the United States in recent years, particularly since the end of World War 11, interest in clay mineralogy has increased greatly. Many laboratories in many different fields have embarked on studies of clay minerals but unfortunately much of this work has not been published. CERAMICS In the field of ceramics, in recent years, a great deal of interest has developed in clay mineralogy. Papers too numerous to be reviewed here have been published portraying the clay mineral composition of substantially all the important types of ceramic clays in all countries. There has been a growing tendency to attempt to solve processing problems on the basis of clay mineral data rather than chemical analytical data. Likewise, there is an in- creasing tendency to control the characteristics of raw materials on the basis of clay mineral composition rather than chemical composition. In the United States in the last few years something like 50 differential thermal analyzers have been set up, and many are for the sole purpose of controlling raw material and processing. The ceramic industry is currently increasing its attention to the influence of exchangeable ions and soluble salts on physical properties. Ion concentration in clay suspensions has long been a matter of interest, but now it is also of interest in clays in the plastic state because of its recognized importance in the plastic, shrinkage, and bonding properties of clays. Students of clay have long recognized that an understanding of the plastic properties of clays is based on an understanding of the character of the water in clay-water systems, the nature of the binding force between individual clay mineral particles, and the factors that control the character of the water and the nature of the bonding force. In the last few years, some extremely important contributions have greatly increased the understanding of the nature of water adsorbed on the clay mineral surfaces. In this connection the work

Jan 1, 1952