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By R. L. Manegold

This paper outlines the reasons for and the application of suspended magnets above belt conveyors for the purpose of removing tramp iron to protect equipment. The design of a magnet strong enough to extract iron through a distance of 24 in. is described along with the proper method of application in the field. Advantages of the suspended magnet in contrast to the conventional magnetic pulley are also discussed. IN RECENT years there has been a decided trend toward bringing ores and coal out of open-pit and underground mines by long, sloping single-stage belt conveyors. Because the high investment cost of haulage conveyors dictates maximum speed and full loading for economy, conveyor belts are running faster than ever before, with a greater burden on the belts. In addition, larger blocks of ore are being mined and conveyed. Rougher use of large mining equipment generates more tramp iron; mechanical loading rejects nothing. Therefore the extraction of tramp iron and other deleterious materials for the protection of haulage conveyors at transfer points, chutes, and idlers is becoming an increasingly difficult job. In our experience, the best method of protecting long haulage conveyor belts is to extract the tramp iron, at least the large tramp iron, ahead of the main haulage conveyor or series of conveyors. It is most practical to collect the tramp iron at the earliest source possible, usually directly after the primary car unloading dump or after the primary crushers, which are ordinarily not affected by tramp iron, see Fig. 1. The coal or ore from its primary source is fed by chutes or feeders onto a buffer or shock belt conveyor, a short, ruggedly built conveyor system that can be considered somewhat expendable. Its primary function is to bring the ore up to speed for transmission to the haulage conveyor. There is no assured method of protecting this conveyor from tramp iron damage at its feed end. Likewise, there is a possibility, although remote if the magnet applied to this belt is installed correctly, that the tramp iron extraction process will damage the shock belt, which is, however, short and comparatively inexpensive. Magnetic head pulleys with their maximum effective range of about 8 or 10 in. cannot be considered for large installations, even though they are desirable because of the continuous and automatic tramp iron removal feature. Further, the most dangerous form of tramp iron with respect to potential damage to a haulage conveyor is the long rod, roof bolt, or rail segment, which is not extracted satisfactorily because of the limited tangential contact of such an iron shape with the magnet. Magnetic head pulleys are also undesirable because the dribble or fines from the head pulley discharge at the same point as the tramp iron. Screens must be used to separate the fines from the magnetics, resulting in additional expense and loss of head room. Magnetic detectors have been used with success, but they only indicate the presence of iron, and the conveyor belt must be stopped for its manual removal. The stoppage of any conveyor means that all preceding equipment must be stopped or a cascade of material on the idle conveyor will result. Occasionally combinations of detectors and magnetic head pulleys are used. The detector precedes the magnetic head pulley and detects only large pieces of tramp iron, while the magnetic pulley subsequently takes out the smaller ferrous metals. Suspended magnets overcome the disadvantages of magnetic head pulleys, detectors or a combination of both. There are several magnetic extraction problems involved in applying a suspended magnet at this

Jan 1, 1953

By R. L. Manegold

This paper outlines the reasons for and the application of suspended magnets above belt conveyors for the purpose of removing tramp iron to protect equipment. The design of a magnet strong enough to extract iron through a distance of 24 in. is described along with the proper method of application in the field. Advantages of the suspended magnet in contrast to the conventional magnetic pulley are also discussed. IN RECENT years there has been a decided trend toward bringing ores and coal out of open-pit and underground mines by long, sloping single-stage belt conveyors. Because the high investment cost of haulage conveyors dictates maximum speed and full loading for economy, conveyor belts are running faster than ever before, with a greater burden on the belts. In addition, larger blocks of ore are being mined and conveyed. Rougher use of large mining equipment generates more tramp iron; mechanical loading rejects nothing. Therefore the extraction of tramp iron and other deleterious materials for the protection of haulage conveyors at transfer points, chutes, and idlers is becoming an increasingly difficult job. In our experience, the best method of protecting long haulage conveyor belts is to extract the tramp iron, at least the large tramp iron, ahead of the main haulage conveyor or series of conveyors. It is most practical to collect the tramp iron at the earliest source possible, usually directly after the primary car unloading dump or after the primary crushers, which are ordinarily not affected by tramp iron, see Fig. 1. The coal or ore from its primary source is fed by chutes or feeders onto a buffer or shock belt conveyor, a short, ruggedly built conveyor system that can be considered somewhat expendable. Its primary function is to bring the ore up to speed for transmission to the haulage conveyor. There is no assured method of protecting this conveyor from tramp iron damage at its feed end. Likewise, there is a possibility, although remote if the magnet applied to this belt is installed correctly, that the tramp iron extraction process will damage the shock belt, which is, however, short and comparatively inexpensive. Magnetic head pulleys with their maximum effective range of about 8 or 10 in. cannot be considered for large installations, even though they are desirable because of the continuous and automatic tramp iron removal feature. Further, the most dangerous form of tramp iron with respect to potential damage to a haulage conveyor is the long rod, roof bolt, or rail segment, which is not extracted satisfactorily because of the limited tangential contact of such an iron shape with the magnet. Magnetic head pulleys are also undesirable because the dribble or fines from the head pulley discharge at the same point as the tramp iron. Screens must be used to separate the fines from the magnetics, resulting in additional expense and loss of head room. Magnetic detectors have been used with success, but they only indicate the presence of iron, and the conveyor belt must be stopped for its manual removal. The stoppage of any conveyor means that all preceding equipment must be stopped or a cascade of material on the idle conveyor will result. Occasionally combinations of detectors and magnetic head pulleys are used. The detector precedes the magnetic head pulley and detects only large pieces of tramp iron, while the magnetic pulley subsequently takes out the smaller ferrous metals. Suspended magnets overcome the disadvantages of magnetic head pulleys, detectors or a combination of both. There are several magnetic extraction problems involved in applying a suspended magnet at this

Jan 1, 1953

By George A. Lamb

AMONG the main interesting developments in the coal market have been the changes that have taken place between the consumer groups. Important signs of these changes began to appear many years ago, but in a modest way, and were apparent only to the few fuel experts making broad statistical determinations. It is doubtful, however, that any of these experts appreciated the significance of their early findings, and perhaps none had the imagination to consider how extensive these changes might be eventually with respect to solid fuels sales and distribution. (Reference here will be principally to bituminous coal.) Railroad Fuel Major changes in coal use did become pronounced after World War II, and it did not take an expert to see what was taking place and how serious the impact was likely to be. First, was the case of the steam and diesel locomotives. The railroads had been considered the best coal customers; they were steady and large purchasers and usually paid a better price than most others. Railroad fuel provided the basic mine realization and it often was the source for operating cash during general market slumps. It was the outlet for 20 pct of the bituminous coal production, as much as 110 million tons in 1946.

Jan 2, 1957

By Lillian Erskine

WHILE brass and other copper alloys have long been listed as offering health hazards to their workers, it is questionable if the metals involved are alone responsible for the trades' records of morbidity. The entire science of foundry sanitation is the product of the past two decades; and the best standards now operative would have been regarded as little short of revolutionary prior to 1910. The special handicap to the conservation of the health of the brass founder's employees has been the fact that, unlike the iron founder, his business could be profitably carried on in almost any small and unsanitary quarters. As a result, writers on occupational disease have accepted brass chills or brass founders' ague as an inevitable feature of the trade; and respiratory disabilities, as well as phthisis and disturbances of the nervous system, are also included as prevalent among those employed. While there can be no question as to the basic accuracy of past investigations, there is every reason to doubt the necessity for an undue percentage of ill health among brass molders and casters who are safeguarded by scientific ventilating standards and by improving personal habits of sobriety. There is, however, need for a campaign of education as to the most approved practices and equipment whereby the employer may safeguard the health of his workers, and thereby reduce his labor turnover and increase his productive efficiency. Broadly speaking, copper, tin, and aluminum carry negligible health hazards. The toxic qualities of lead, however, are a menace; especially if scrap lead is recovered or bought for foundry processes. The rapid volatilization of zinc renders its fumes and flocculent condensation the chief problems in conserving the health of the brass worker. The frequent presence in the foundry air of traces of arsenic compounds, lead

Jan 2, 1919

By A. L. Bailey, B. A. Landry

W. W. ANDERSON and G. E. KELLER*—We want to compliment the authors on this very thorough paper. It gives information which the coal industry has needed for some time. We hope that the additional information which the authors are collecting will he available shortly. The mixing and riffling procedure that was followed for experimental purposes is obviously not practical in routine float-and-sink testing because of the particle size degradation which would result in handling the sample so many times. It is important to obtain our tloat-and-sink fractions with a minimum amount of handling of material. A statement is made in the paper (p. 80) that "the variable most likely to affect the size of sample required to meet a given preassigned accuracy would be the state or degree of mixing of the coal." We agree that this is a large factor, but do not believe it is the most important factor. Our own opinion is that the most important single factor governing the total gross weight of sample that must be collected is the percentage of the weight of material in the smallest fraction that results from the screening and float-and-\ink operations. In other words, size of sample is governed by the total number of fractionations that must he made, and the distribution of material within the fractions. We can imagine a coal with perfect mixing, but with such a small amount of material in some float-and-sink fraction in one of the coarse sizes that a much larger sample would have to be taken than would be the case with very poorly mixed material, but with a large percentage of coarse material more evenly distributed in all float-and-sink fractions. Our own observation of many float-and-sink tests that we have run in our own organization on many types of coal is that the size of sample that must be used on fine size float and sink is governed more by the requirements for weight of material to be used for analysis in the laboratory than by weight of material necessary to obtain accurate float and sink percentage of weight values. In other words, it is our opinion that very small samples can be used for float-and-sink fractionation in the fine sizes, but that accurate analysis of the fractions will depend on a larger weight of sample being pulverized for the laboratory than is necessary to establish the float-and-sink distribution with respect to weight. A. L. BAILEY and B. A. LANDRY (authors' reply)—The authors thank Messrs. Anderson and Keller for their comments based on long experience. It is agreed that the involved mixing and riming technique used may be disadvantageous from the standpoint of degradation. Fortunately, the paper does point out that the extended riming was unrewarding in causing further mixing. Two large unknowns remain, however: (1) how much of the mixing from the presumed highly unmixed state in the bed was achieved toward the random state during blasting, loading, transportation, screening, and further transportation to the point where the gross sample was taken, and (2) how much of the mixing took place during the preparation described preceding riming. As has been pointed out by one of the authors.6 the degree of mixing has a very large effect on the size of sample required and there are still too few experimental data to show at what stage of coal handling most of the mixing occurs. The discussion states that the weight of material in a screened fraction, or in a float-and-sink fraction, is more important than the mixing factor. We do not believe that these factors are comparable in this instance inasmuch as our purpose was to give minimum sampling requirements to achieve a preassigned accuracy in the percentages of float, middlings, or sink, and nothing more. The gross sample had already been screened and no further division by screening was made or contemplated; also, it was not intended that the middlings and sink fractions would necessarily be adequate for percentage ash or other determination. In other words, the sample obtained by the method outlined is not intended for washability studies but only for preparation plant control. Further experimental work has been done, since the paper was prepared, to investigate the effect of increasingly larger top and bottom sizes on the variability of float, etc., of a double-screened coal from Western Pennsylvania. Results will be published and eventually attention is to be given to the preparation of sampling specifications. E. H. M. BADGER*—I should like the authors to explain more fully the fundamental assumptions on which their Eq 4 is based. The equation is of the form s2 = p(l - p) which is the usual expression for the (standard deviation)2 when the chance of finding a particular kind of particle in the sample is proportional to the number fraetion, p. But instead of the number fraction, the authors have used the weight fraction, WF/W. The chance of finding a particular kind of particle in the sample can only be proportional to the weight fraction, if the average ?eig?ts of all kinds of particles, that is, float, midlings, or sink, are the same. Surely a much more justifiable assumption would be that the average volumes of the particles are the same, and, if this is so, Eq 4 would not be true. This may be demonstrated as follows: Let be the weight fraction of float, middlings, or sink, dl the density of this fraction, and d2 the density of the rest of the coal. Then assuming that the average volumes of the pieces in the three classes are the same, the number fraction, p, is given by ? P = d1/l-?/d2 + ?/d1 = ?d2/d1 + ?(d2-d1) The weight fraction, w, in terms of p is given by ? = pd1/(l-p)d2 + pd1 = pd1/d2 + p(d1-d2) _____ [61

Jan 1, 1950

By M. A. Mahtab

When characterizing orientations of rock joints in an engineering site with respect to mean values of the existing clusters or joint sets, a need may arise for a similarity test that allows grouping of observations from several adjacent sampling stations. Subjective judgment, though based on experience, may not produce realistic groupings in the data. A similarity test is developed in this paper for objective grouping of samples of joint orientations in engineering sites. The test is applied to the data from a large, geologically complex site of a potential open pit mine.

Jan 1, 1984

Seattle offered sunny, dry weather to about 2500 mining men who assembled September 10 to 14 for the 1961 American Mining Congress. The impact of snappy sessions on national mineral policy, state of the industry and foreign competition (to name only a few) was somewhat overshadowed by enthusiasm of conventioners for salmon fishing. This lordly fish, which mysteriously runs to its hatching place to spawn and die at this time of year, was not cooperating with the anglers in Puget Sound. However, this did not prevent consuming ample amounts of the deliciously prepared Quinault salmon at the "Potlatch" celebration.

Jan 10, 1961

By Roger E. Barthelemy

PRIMITIVE mining and metallurgy has today almost disappeared. Probably the only remaining tribal tin mining and smelting is practiced by the Laotian natives in one of the less known tin areas of the world. This district lies almost a thousand miles from the sea along the Mekong River, one of the longest rivers in the world, that marks the border between Siam and Laos, one of the five states forming French Indo-China. Less than twenty years ago it took more than two weeks' travel on elephant-back to reach the spot and today it still takes many days of travel, using all kinds of transportation from automobiles to native

Jan 1, 1938

By Otto F. Pfordte

In my paper on " The Refilling of Sulphides Obtaihed in the Lixiviation-Process with Hyposulphite Solutions " (Trans., xx., 37), I gave the outlines of a process for refining sulphides. In a subse-

Jan 1, 1893

TO THE BOARD OF DIRECTORS OF THE AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS Gentlemen: - I herewith present a report of some. of the more important activities of the Institute for the year of 1922. The outstanding feature of the year is the optimism felt by our members despite the continued depression in the mining industry. January 1, 1921, found many of our members out of employment or drifting into other industries to tide them over the depression, but almost universally the feeling has been that this was but a temporary condition and that sooner or later the necessary production of raw materials would enable these members to return to their former activities and renew their participation in Institute affairs. As the year passed conditions improved and, before it ended, many had found employment in their previous occupations. Bearing in mind that this depression has been very real, we have reason to be well satisfied with the work that the Institute has been able to do. The loss of members through inability to pay, dues has been large, and income has been correspondingly reduced, but it proved to be materially in excess of that anticipated early in the year, so that a substantial and unanticipated balance was carried forward toward the activities of 1923. PUBLICATIONS Following the example of other technical societies, and to conserve our resources, no Year Book was published in 1922. The lack of an up-to-date membership list for the use of our members was regrettable, but the saving of $5000 proved to be worth while. During the year, Volumes LXV, LXVI, and LXVII were printed and sent to members. These volumes were composed largely of the papers of 1920 and 1921, publication of which had been delayed partly through lack of funds and partly for the purpose of segregating into volumes those papers dealing with the same general subject. The segregation of papers had been suggested by a number of members who had advised that they were not primarily interested in all subjects

Jan 1, 1925

By J. L. Fitch, B. G. Hurd

The presence of gypsum in samples subjected to standard core analysis introduces serious errors in the measurement of water saturation and porosity. The magnitude of these errors, depending upon the type of analysis procedure used, has been evaluated experimentally and theoretically. Water-saturated pore volumes determined by vacuum distillation or retort procedures may be too high by as much as 48 per cent of the volume of gypsum present. The maximum error in this value determined by Dean-Stark extraction with toluene is 36 per cent of the gypsum volume. If pore space is measured by a Boyle's law type porosimeter the maximum erorr due to gypsum is 38 per cent of the original gypsum volume present. The conscientious core analyst may eliminate the errors caused by gypsum by either of two methods. He may apply suitable corrections for the water of crystallization removed from gypsum, or take special precautions to prevent dehydration of gypsum during core cleaning and alzalysis procedures. These alternatives are discussed and methods for obtaining reliable core analysis data are proposed. Gypsum (CaSO4 . 2H2O) occurs as a common mineral in many of the world's sedimentary basins. In addition to its presence as primary bedded evaporitic deposits, it is often found as secondary replacement zones and pore-fillings in host rocks. That it may cause false indications in porosity, both on neutron logs and in standard core analysis, has been generally recognized. False porosity interpretations from neutron logs result because the chemically bound water in gypsum attenuates neutrons as effectively as free water. Errors in core analysis result when gypsum is dehydrated prior to or during the analysis. Vacuum retort procedures used by many laboratories to determine fluid saturation and porosity effect a complete removal of water of crystallization from gypsum. The crystal water, distilled and collected with free water from the sample, is counted as water-sat11rated pore space. Dehydration of gypsum results in a decrease in volume occupied by calcium sulfate and a corresponding increase in pore volume. Thus, if gypsum is dehydrated by sample cleaning and drying procedures, subsequent porosity measurements with gas expansion or compression instruments will be high. The qualitative effect of gypsum on porosity determinations by retort procedures was discussed in a recent article by Bynum and Koepl3. They concluded that since false porosity was interpreted as being water saturated, determinations of oil content were not affected. Others in the industry, however, have pointed out that porosity values are often used with values of water saturation determined independently, e.g., from electric resistivity logs in making reserve estimates. Values of water saturation calculated from the formation resistivity using the Archie equation, S4= are actually low if values of are high due to gypsum. In this case, false porosity values due to gypsum could cause serious errors in calculations of oil-in-place. This investigation was made to determine quantitatively the effect of gypsum on porosity values determined by different core analysis procedures. EXPERIMENTAL PROCEDURES Dehydration of Gypsum The extent and rate of removal of water of crystallization from gypsum under conditions encountered in core analysis procedures were studied. Taken for the experiments were three types of relatively pure, naturally occurring gypsum, viz. selenite, satin spar and massive gypsum. Although all samples probably contained trace chemical impurities, each type lost the theoretical amount of water upon complete dehydration. An automatic recording thermobalance, similar to one described by Mauer2, was used to obtain dehydration rate data for samples heated in dry air. Water

By R. Hogg, D. W. Fuerstenau

Based on a simplified model for the motion of particulate materials in horizontal, rotating cylinders, approximate expressions have been derived relating the power consumption of a tumbling mill to its dimensions and speed of rotation and to the amount and nature of the charge. The basic assumptions underlying the model are that there is no slip between the charge and the mill shell, that the free surface of the charge remains essentially planar during rotation, and that there is no transfer of momentum from the material flowing down the free surface back to the mill shell. The relationships formulated from this model have been shown to be in excellent agreement with experimental results taken from the literature. While the requirements of the model are most clearly met at low speeds of rotation, the results appear to be valid even for speeds up to 70-80% of the critical speed. Poorer agreement between theory and experiment is found when the charge consists of relatively large particles (balls) and when the filling of the mill exceeds 50% of the available volume. Qualitative explanations of these deviations have been offered.

Jan 1, 1973

By W. W. Dudley

Inflow of ground water is an important engineering and safety consideration during construction of large openings underground. The initial step in predicting groundwater inflow involves hydraulic tests in exploratory drill holes. Zones within the area of interest are isolated in the drill hole by inflatable packers and are tested by measuring the water level responses to applied hydraulic stresses. These responses may then be translated into significant hydraulic characteristics of the tested rocks such as transmissivity, hydraulic conductivity, hydraulic potential, and storage coefficient by using a type-curve solution. Once the geometry and necessary hydraulic characteristics have been determined for the rock in the vicinity of the proposed opening, a model can be developed using certain assumptions that will lend itself to treatment with available mathematical methods. The mathematical method applied to the model considers conditions of partial penetration and nonsteady-state, leakyartesian, constant-drawdown discharge of ground water. A type-curve solution results in a curve that gives the variation of discharge (inflow) with time. This technique of predicting ground-water inflow has been used in planning construction of cylindrical chambers for use in underground nuclear experiments by the U.S. Atomic Energy Commission. These chambers have been constructed in low-permeability rocks at depths as much as 6000 ft and under hydraulic heads of thousands of feet.

Jan 1, 1973

By W. J. Heck

The need for a better understanding of the effect of fluid pressure on the strength of intact and jointed rock has long been recognized. The behavior of pore fluid pressure was first pointed out by Terzaghi 1 who suggested the application of the effective stress concept to rock and concrete. While the effective stress concept has been used for some time in the design of mass concrete dams, it only recently has been applied to rock. Robinson 2 and Handin et al.3 evaluated the effects of pore pressure on a variety of sedimentary rocks and demonstrated the validity of the concept. Work using pore fluids other than water has been done by Boozer, et al.4 who considered strain rate and temperature as additional variables. According to the effective stress theory, the effective stress, [a], is the difference between the total stress, [a], and the pore pressure, u, and is the controlling factor influencing frictional strength of rock, other parameters remaining constant. Assuming the Mohr-Coulomb failure criteria applies, the shear strength, T, is given by the equation [r=d+ (a-u)tan ¢](1) where [~F], the angle of internal friction, and c, the cohesion intercept of "no load" shear strength, are the effective stress parameters.* Robinson,2 Handin,3 and others have demonstrated that moderately porous sand-

Jan 1, 1972

By Charles Catlett

THE rapid development of the Portland-cement industry implies that the country is being very carefully searched for material suitable for its manufacture. Such material can be found at a great many places ; but deposits thoroughly satisfactory in chemical composition, and at the same time meeting all the other requirements connected with the economic production and profitable marketing of the product, are exceedingly few, if I may judge from the investigations which I have had to make in a number of States. The raw mixture which by its clinking and grinding forms Portland cement contains approximately 75 per cent. of carbonate of lime. This is found in nature as limestone or marl. The natural rock commonly carries either more than the required percentage of carbonate of lime (in which case it has to be reduced by suitable admixture of clayey ingredients) or less-in which case purer lime carbonate has to be added. The controlling ingredient, therefore, is carbonate of lime, or limestone of the right composition. Among the most serious difficulties is that of finding limestones low enough in magnesia to meet the exacting requirements of certain specifications. All engineers recognize that there is a limit beyond which it is not safe to let the magnesia go; but within that limit there is considerable difference of opinion. Until that difference is finally settled, no one would be willing to invest the large sum of money necessary for a Portland-cement plant, if it were not certain that the usual requirements in this particular could be satisfied. The usual limit in well-established specifications is 5 per cent. of magnesium oxide in the finished cement, but many specifications limit the amount to 3 per cent. These figures

Jan 9, 1907

By Jan M. Mutmansky

The primary purpose of this presentation is to analyze the strategies available to an operator using either stripping or stripping and subsequent punch mining on a given coal property. The initial concern is the formulation of a mathematical model, which allows an operator to determine and utilize the particular highwall height, which will maximize : (1) Total profit or (2) Profit per unit of operating time. The analysis centers on the relative costs and recoveries involved in a typical coal seam amenable to stripping, augering, and punch mining. The model defines the point to which the high-recovery stripping operation with increasing overburden removal and reclamation costs should proceed before the low-recovery augering and punch mining methods are employed so that the desired objective is achieved. Examples are presented, which exhibit the use of the model on typical operations. Present mining methods as practiced in the Eastern United States are examined in the light of the results. Recommendations for improving present strategies are made and the resulting economic ramifications are analyzed. Particular attention is given to the stripping ratios presently used and recommendations for improving present mining practice are presented. Implications of these recommendations to the design of strip mining equipment are discussed.

Jan 1, 1977

By Charles F. Johnson

A pulse technique is described for the measurement of bar velocity. A low frequency sine wave pulse is used which allows the wave-length to become much larger than the lateral dimensions of the test specimen. The low frequency pulse method has been tested and compared with the resonant frequency method and the results show that both methods give, on the average, equivalent velocities.

Jan 1, 1971

By R. Lagneborg

WhEN mechanical twins initiate cracking it has been proposed1 that the friction stress for dislocation motion, in the Cottrell criterion for brittle fracture2 should be replaced by the stress required to propagate a twin, ttp. TF is the fracture stress, d the grain diameter, ß a geometric constant, u shear modulus, and y the effective surface energy. Since TTp is likely to vary with grain size, it cannot be substituted by a constant in Eq. [I]. If an expression for the energy change caused by a twin in a stressed material could be obtained, it is in principle possible to compute the critical size of the twin, i.e., the size at which the system can decrease its energy spontaneously, as a function of applied stress, thus giving the stress required to just barely propagate the twin, i.e., TTP. Consider a circular twin disc with a radius r and having a lenticular cross section, Fig. 1. Twin dislocations3 of strength b exist in the twin boundary parallel to the twin plane, one loop on each atomic plane. Assume that the total numbers of loops, n, can be replaced by one circular loop of a multiple dislocation, nb with a radius r. The energy change of the system, AW, due to such a twin in an applied stress field can then be calculated: The first term is the total twin surface energy, the second the elastic energy due to the twin dislocations, and the third the energy released by the twin in the applied stress field. yt is the twin boundary energy, r, the radius of the dislocation core, and T the applied

Jan 1, 1968

By Chris Mills

The role of gravity separation in the mineral industry is briefly considered in perspective. The mineralogical and laboratory approaches to gravity process design are examined with emphasis on process technology selection. The equipment available for small scale and pilot test-work is discussed, particularly in regard to scale-up and the acquisition of reliable, accurate data. Transposition of performance data from pilot scale to plant scale is explained. The available types of full scale gravity separation equipment are discussed with emphasis on large high-capacity units. Plant layout and selection of ancillary equipment are considered.

Jan 1, 1978

By J. Lyndon Rosenblad

The strength of a jointed-rock mass is not well-understood. It is believed, however, that the behavior of a rock mass is governed by both the intact rock properties and the properties of the discontinuities. Rock research in the past has been concentrated on the determination of intact rock properties. Several studies are presently underway which should provide more insight into the properties of the discontinuities. Few research programs, however, have been undertaken with the intent of studying the composite rock mass behavior where either the intact rock strength or the properties of the discontinuities may control failure. There are three approaches available for studying the behavior of a rock mass, namely, field studies, mathematical models (finite element), and geomechanical models. A geomechanical model has been developed in this study where the strength and failure modes of a model rock mass are studied as a function of intact block geometry, joint orientation, joint properties, and confining pressure. The objective of this study is to gain some insight into the parameters that govern the behavior of a rock mass, which parameters are most important, and when these parameters control. This chapter describes only one phase of the study, the development of equipment for use with the rock-blocks model. The models being tested are approximately 22 x 22 x 6-in. The size varies slightly depending upon the joint orientation used. The equipment developed includes model material molds, reaction frames, loading apparatus, measuring and recording instrumentation, and other accessory equipment pertinent to the operation of a successful study. The usual problems in equipment development, such as uniformity of load application, loading capabilities, and reaction capacities are all

Jan 1, 1970