Search Documents

By G. Sachs, G. Espey

SIMPLE methods can be used for the determination of the residual stresses in thin-walled tubing if the stresses consist of high tensile stresses at the one surface and high compressive stresses at the other surface Such a stress distribution is approximated in sunk tubing and in deep-drawn shells It is possible to cut sections from such articles in such a manner that a major part of the residual stress is relieved by a bending of the part that is separated from the adjacent metal The circumferential stress is evaluated from the change in diameter D, occurring on splitting a length of tubing (Fig Ib),1-5 or from deflection resulting from the cutting out of a circumferential tongue (Fig Ia) G The bending moment M released by such a flexure is [ ] The release of this bending moment corresponds to the release of stresses, which, in a thin section, vary linearly from one surface to the other, and have the following value in a particular fiber a certain distance (zx from the surface [ ] where C is the section modulus and d is the thickness of the section, the ratio AI C being d 2 for a rectangular section* The maximum stress values at the surfaces are [ ] For most purposes the simpler equations [ ] will be satisfactory, where Dm is the average of the mean diameters of the tubing

Jan 1, 1941

By S. L. Crouch

This paper describes a numerical procedure for the computation of the displacements and stresses induced by the mining of a tabular ore deposit in faulted ground. The numerical procedure is based on the displacement discontinuity method, which can be regarded as an application of Salamon's 'face element principle' to cases in which the reef plane is faulted into several sections, or even folded in an arbitrary way. An element of a fault is modelled in the same manner as an element of the reef, except that a fault element is allowed to undergo permanent inelastic deformation (i.e., slip) if the stresses transmitted through the fault-filling material satisfy a Mohr-Coulomb yield condition. An iterative technique for the incorporation of a Mohr-Coulomb yield condition in the general displacement discontinuity method is explained. This technique is illustrated by means of a simple example involving the mining of a flat-lying reef intersected by a fault. The displacements and stresses at selected locations along the fault are examined as the reef is mined, element by element. A consideration of the energy changes reveals that the occurrence of slip along a fault leads to a sudden increase in the energy release rate due to mining as the excavation intersects the fault. The energy release rate then falls off abruptly to a value less than that which would occur in the absence of any slip, and gradually builds up to re-establish the conditions that would exist in unfaulted ground.

Jan 1, 1979

By R. E. Ricksecker, W. M. Baldwin, R. McC. Baker

INTRODUCTION THE development of residual stress in strip during rolling has not been systematically studied. A few scattered papers1-3 mention the existence of residual stresses in rolled strip or touch upon some of their consequences,4 but there is no report of experimental studies in the literature describing the effect of roll diameter, strip thickness, reduction per pass, metal or metal temper on the magnitude of residual stresses developed in strip. A knowledge of the effect of these factors is of utmost importance since the present trend in some mills to roll thicker castings brings the rolling operation directly into that set of conditions which, as will be brought out in the present paper, can develop residual stresses of a high order of magnitude. Fundamentally, residual stresses are developed when a metal is inhomogeneously unloaded from a plastic stress state. A quantitative treatment of the problem requires a reasonably complete understanding of both the plastic stress state existing in the metal during deformation and the elastic stress state that would exist in the metal if the metal deformed as a perfectly elastic body. Our knowledge of either state during rolling is so meager that we can make no more than certain limited predictions. The external stress state* operating between the roll and the metal consists of compressive stresses acting almost perpendicularly to the strip surface but vary [ ] ing in intensity both across the width of the strip and along the length of contact between the roll and the strip. An example of such a stress distribution is shown in Fig I. The nature of the internal stress state, produced by this distribution, is not known. Various investigators,5-7 however, have felt that a qualitative similarity must exist between the internal stress state so produced and that produced in a wide strip that is compressed between two flat-nosed punches. In the latter case the external stress state is represented by a uniformly distributed compressive stress acting perpendicularly over the face of the tool. The elastic internal stress state in this case is complex-the principal stresses showing

Jan 1, 1948

By Yi Luo, Jian Yang, Hua Jiang

Surface subsidence events induced by underground longwall coal-mining operations can cause various disturbances to surface structures, ranging from integrity and stability to functionality problems. Highway bridges, as a kind of special road construction that can only tolerate smaller movements and deformations than road pavements, are particularly susceptible to severe influence caused by subsidence-induced ground movements and deformations. However, based on accurate subsidence prediction and correct influence assessments, efficient and effective mitigation and remediation measures can be designed and implemented to ensure the continuous service of bridges, safety of travelers, and smooth mining operations. In this paper, based on the predicted final and dynamic surface movements and deformations, the techniques to assess subsidence influence on the integrity, stability and functionality of bridge structures (such as decks, beams and abutments) are presented. A number of mitigation measures to protect bridge structures are recommended, along with an actual application case.

By D. L. Buchanan, ed. sci.

The issue comprises 10 contributions on PGE mineralisation, of which 9 were presented at the symposium organised by the IAGOD Commission on Ore Deposits in Mafic and Ultramafic Rocks and the BRGM-CNRS University of Orleans research group. The editor's introduction and summary of the papers is presented together with the title page, contents list and cover photograph of a harzburgite ridge, dunite boundary and chromite quarry in the Shetland ophiolite on Unst

Apr 1, 1994

By P. Davis

With new mineral deposits found in areas of difficult terrain, and annual production capacity increasing in mines over the last decade, the aerial ropeway is proving to be a viable, economic method of transportation from mine to processing plant. Of the more conventional designs, a bicable ropeway is more suited to difficult country than the simpler monocable. The bicable, however, does have limitations in the difference in levels it can accommodate in one section at a given capacity. This is noticeable where hilly terrain and high capacity imposes a limit on the length of each section. Increasing the number of sections for a relatively short conveying distance tends, in the case of conventional bicable, to unbalance the normally favorable economics of the ropeway. In addition to analyzing hauling rope stresses, other areas have to be considered when looking at high capacity ropeways. Bucket capacity, speed, and the wheel load on track ropes are examples. These and other factors led British Ropeway Engineering Co., of Sevenoaks, Kent, UK, to produce the twin-track system. Using twin track ropes, larger capacity buckets, and, if the height differential warrants, the installation of twin hauling ropes, BRECO produced a ropeway design for areas of hilly terrain and at higher capacities than had been considered suitable for aerial ropeways. Designs have been produced for systems handling 1.5 kt/h (1,650 stph), and the potential exists for expansion to above 2 kt/h (2,200 stph). The arrangement of ropes provides high stability of the cars and is especially suited to areas where high winds occur during normal operation. This development allows the aerial ropeway to be applied economically in difficult areas and at the increasingly high capacities demanded by engineers. Ropeway Transports Limestone to Sudan Cement Plant Maspio Cement Corp. of Atbara, Sudan, will soon use an aerial ropeway to deliver its entire limestone requirement 20 km (12 miles) from quarry to plant. The Atbara plant is located north of Khartoum, near the east bank of the Nile River. The quarry is west of the river, in hills rising from flat desert country. The original transport system was a 24-km (15-mile) railway from the quarry to the west bank and a monocable ropeway that crossed the Nile and continued to the fac¬tory, a distance of about 2.5 km (1.5 miles). This original ropeway had a capacity of 60 t/h (66 stph). With the extension of cement-making capacity in the late 1970s, 2.5 kt/d (2,755 stpd) of limestone was required and a new mono-

Jan 3, 1984

Small scale' table concentration tests have many critics. Many metallurgists consider that such tests are of problematical value because of the difficulties involved in conducting and interpreting them.Many kinds of small-scale ore dressing tests are difficult to conduct, and there is, perhaps, good reason for thinking that table concentration tests are amongst the most difficuIt.Interpretation of results from small-scale tests is the responsibility of the metallurgists and engineers in charge, and it is often held that small-scale table concentration tests are particularly difficmlt to interpret.TESTING FOR TABLE CONCENTRATIONOn analysis it appears that the difficulties encountered in conducting small-scale table concentration tests are of three fairly distinct kinds. Firstly, there are difficulties due inherently to the smallscale nature of the operations; for example the smaller width of all mineral bands on the table and the less complete separation due to the shorter length of travel between the feed and discharge points.Secondly, there are the effects of batch operation owing to the fact that the mineral particles behave differently during the initial period when the sample is just beginning to spread over the table, the middle period when feed and discharge are even and continuous, and the final stage, when the last of the sample has been added and the table is beginning to empty itself.

Jan 1, 1954

By Sir John Cadman

IN THE changed circumstances which now confront the world, an international open-door policy is the only way to keep pace with the world's demand for oil. You may rest assured that as far as the British Empire is concerned, American capital for the develop-ment of oil resources is welcome, and little obstruction will be found in the way to permit the use of foreign capital in the group of countries which constitute the British Empire. In the war days we worked in close cooperation and harmony, but in disbandment of the Petroleum War Service Committee, when the war ended, I feel that it left its task unfinished. In the wake of war there appeared a ghost of war-time conditions in the form of belief that Great Britain was straining to corner the petroleum resources of the world. I am certain that if the war-service committee had continued its work in the period of reconstruction the real story would be known and this sinister ghost would have long since vanished before the truth.

Jan 2, 1922

By Aug. J. Jr. Bowie

(Read at the Wilkes-Barre Meeting, May, 1877.) Brief Outline of the General Topography of the Gold Regions of California. THE topographical features of California, as demonstrated by the explorations of the State Geological Survey, are found to be exceedingly simple. Three equidistant parallel lines can be used in conveying a general idea of the physical geography of Central California. A straight or " main axial line," whose course would be north 31° west, passing through the culminating peaks of the Sierra for a distance of five hundred miles, can be assumed as the eastern boundary of the State. A second parallel drawn fifty-five miles west of the " main axial line" will skirt the western base of the Sierra Nevada, along the edge of the foot-hills. A third parallel run equidistant from the second will represent "as nearly as possible the western base of the Coast Ranges." These parallel lines divide the State into three belts, namely, the Sierra, the Great Valley of California, and the Coast Ranges. " This arrangement of the physical features holds good for a length of four hundred miles in the direction of the main axial line, comprising almost the whole of the agricultural and the greater part of the mining districts."* The section of the country which is of immediate interest to the miner is the western slope of the Sierras. These mountains, rising in a short distance from the Sacramento plains to elevations of over seven thousand feet, with occasional peaks ten and twelve thousand feet high, are cut by numerous deep and precipitous gorges or capons, through which drains the immense watershed of the Sierra, supplying the main rivers of the State and ultimately emptying into the Pacific Ocean. Between these capons, ridges or divides are formed, on top of * See vol. i, p. 5, Geological Survey of California. J. D. Whitney, State Geologist.

Jan 1, 1878

Dynamic shocks, which occur in mine hoisting systems have been measured by various investigators over the past 30 years. In 1966 the most intensive analytical investigations were being planned in Bochum, Germany, where equipment then was being constructed to measure the power generated in any particular dynamic shock. Between 1953 and 1956, in Broken Hill, N.S.W., accelerations of the shaft conveyances were measured and analysed. The "effective mass" of the conveyances at the time of the shock was then and still is considered as indeterminate and not easily measured. It is believed that probable peak forces can be determined by the product of the static mass and the accelerations. The subsequent problem of the elimination of the dynamic shocks becomes one of possibly increasing the frequency and thus reducing the amplitude, after identifying and evaluating the shock generators. In addition, judicious use of the clearance between the shaft conveyance and the guide, as a zone in which to absorb vibrations, is a factor which has been overlooked in earlier investigations on This topic.

Jan 1, 1971

By Schneider CL

The calculation of the liberation spectrum in the product from continuous milling operations is a problem of considerable importance, and it is difficult to solve because the population balance equation must be integrated in two-dimensional space. Complete solutions require a very detailed knowledge of the complex interactions between the fracture patterns and the mineralogical ore texture when brittle particles are subject to impact fracture. Most of the liberation models that have been developed to date apply only to batch comminution processes and under these conditions the liberation problem can be studied in isolation. When the comminution is continuous and forms a unit operation in a flowsheet that includes classification and separation operations, the situation is very different, and then the liberation of the minerals must be described when single particles of known mineralogical composition are fractured. Important industrial examples are conventional milling circuits closed by hydrocyclone and regrind mills in flotation plants. This paper presents an efficient computational algorithm for the calculation of the liberation spectrum produced by continuous milling operations. The algorithm relies heavily on the detailed internal structure of the Andrews-Mika diagram. The modifications that are required to make this diagram apply to practical ore minerals, and the internal structure of this diagram can be established using single-particle fracture on mono-size, mono-grade material but suitable liberation models are essential to interpret the data in terms of the cross transfer coefficients required for the population balance procedure. Models proposed by Leroux (1992) and King (1990) are compared to experimental data.

Jan 1, 1993

By M. E. Tyrrell, Alan H. Goode

The application of a simple, two-dimensional computer technique for evaluating rock burst potential in cut-and-fill stopes was investigated. The principal purpose of the study was to compare the effectiveness of high-modulus fill and destressing as aids in the control of rock bursts. Two conclusions that are probably of general applicability are drawn. First, high-modulus fill is ineffective as a means of increasing the mine stiffness and acts to control rock bursts only if it supports enough load to reduce substantially the stresses on the unmined vein material. Second, destressing is most effective if it is performed when the vein material is near the point of failure.

Jan 1, 1975

Longwall mining in Australia is approaching maturity. Longwall production from 'state of the art' Australian longwall mines now rivals similar US based longwall operations. Regrettably however, Australian gate road development rates in general fall short of the required development to longwall production ratios that are required to sustain annual longwall production capabilities. By contrast, most US based longwall mines achieve the required development to longwall production ratios to sustain their longwalls. This is despite many having to drive three heading longwall panel gate headings to meet regulatory requirements.

Jan 1, 1998

By J. P. Kerr, W. H. Cordell

Conditions in the oil and gas industry in Indiana were about the same in 1935 as in 1934. This is especially true of the old Trenton area and the Harrison County area where production was steady and almost no exploration and development took place. The past year has seen an increase in drilling activity and a decrease in oil and gas output in southwestern Indiana. In the state, 224 wells were completed in 1935, of which 48 were oil wells, 61 gas wells, and 115 dry holes. A few of these were old gas wells deepened to oil horizons. Twenty-six wells started during 1935 were not completed by Dec. 31. Approximately one-half the wells drilled were within proven areas. A relatively large number of wildcats, especially in Daviess, Pike and Gibson Counties, were in search of new gas supplies to supplant the diminishing resources in those counties. The decreased production of gas was due largely to the fact that existing supplies declined more rapidly than new fields could be brought on. The Alford field, in Pike County, which produced the bulk of the supply in 1934, was called on to do likewise in 1935, but was unable to respond sufficiently to keep up the yearly production for southwestern Indiana. During the last half of the year, the Oaktown field, Knox County, was connected with one of the principal pipe lines of the state, which helped to keep gas production above an unusual low. The decline in oil production was due almost entirely to proration during the first eight months of the year. The proration affected Daviess, Pike, Gibson, Sullivan and Vigo counties, which produce about three-fourths of the total for the state. After proration was lifted, the wells never quite reached the conditions existing before proration. The average daily production per well in Indiana is less than two barrels. The outstanding development in Indiana in 1935 was the drilling in the Oaktown field immediately before and after the laying of the 6-in. pipe line to the field. Almost without exception the wells came in with an open flow of two to four million cubic feet. At the end of the year, 26 wells were connected to the pipe line. Development of this field will

Jan 1, 1936

By J. P. Kerr, W. H. Cordell

Conditions in the oil and gas industry in Indiana were about the same in 1935 as in 1934. This is especially true of the old Trenton area and the Harrison County area where production was steady and almost no exploration and development took place. The past year has seen an increase in drilling activity and a decrease in oil and gas output in southwestern Indiana. In the state, 224 wells were completed in 1935, of which 48 were oil wells, 61 gas wells, and 115 dry holes. A few of these were old gas wells deepened to oil horizons. Twenty-six wells started during 1935 were not completed by Dec. 31. Approximately one-half the wells drilled were within proven areas. A relatively large number of wildcats, especially in Daviess, Pike and Gibson Counties, were in search of new gas supplies to supplant the diminishing resources in those counties. The decreased production of gas was due largely to the fact that existing supplies declined more rapidly than new fields could be brought on. The Alford field, in Pike County, which produced the bulk of the supply in 1934, was called on to do likewise in 1935, but was unable to respond sufficiently to keep up the yearly production for southwestern Indiana. During the last half of the year, the Oaktown field, Knox County, was connected with one of the principal pipe lines of the state, which helped to keep gas production above an unusual low. The decline in oil production was due almost entirely to proration during the first eight months of the year. The proration affected Daviess, Pike, Gibson, Sullivan and Vigo counties, which produce about three-fourths of the total for the state. After proration was lifted, the wells never quite reached the conditions existing before proration. The average daily production per well in Indiana is less than two barrels. The outstanding development in Indiana in 1935 was the drilling in the Oaktown field immediately before and after the laying of the 6-in. pipe line to the field. Almost without exception the wells came in with an open flow of two to four million cubic feet. At the end of the year, 26 wells were connected to the pipe line. Development of this field will

Jan 1, 1936

The Nelson province was chosen as the prime area for rhenium sampling, based on its mineral associations. Sample preparation involved benefication by grinding and flotation. A modification of published procedures for rhenium analysis was developed and the results compared with those obtained for molybdenum on the same samples using atomic absorption spectroscopy. The results of the analysis for both metals is discussed and the relationships between rhenium and the molybdenum mineralisation of this region is commented on. A metallogenic province is defined for molybdenum and rhenium and the tectonic setting for this is discussed. Some consideration has been given to rhenium possibilities in Fiordland and the Coromandel Range.

Jan 1, 1980

By Gennaro G. Marino

During the preliminary design stages of the Illinois Division of Natural Resources(DNR) building, it was discovered that an old coal mine was present some 70 m (220 ft) beneath the building site. The new DNR building to be constructed is 36 m (120 ft)wide and 134 m (440 ft) long. It has three stories above grade and abasement level. The building is oriented north-south and has east and west ponds next to it (Fig. 1). The building is located on the State Fairgrounds in Springfield, IL. Given the history of surface subsidence of these underground coal mines in the Springfield area, there was concern about the potential for future subsidence at the building site. Mine subsidence events in the area have resulted in more than 0.9 m (3 ft) of settlement and have caused significant structural damage.

Jan 1, 2000

By A. W. de Villiers

This paper explores the behaviour of methane in the goaf during longwall mining, together with some methods for the control of methane emissions into the goaf, the working face, and the ventilation system. Experimental work done at Twistdraai Colliery, Sasol Coal, is referred to, as well as the gas-drainage system being practised at West Cliff Colliery in New South Wales, Australia. Gas drainage is discussed briefly, and certain suggestions are made in regard to coal mining in South Africa.

Jan 1, 1989

By A. Eilers

NO one who has visited our Western mining districts, and studied the economical part of the beneficiation of the ores occurring all over that vast extent of country, can underrate the high importance of the above subject. By far the larger number of the districts which contain smelting ores, i. e., argentiferous and auriferous lead, or copper ores, are situated in the Great Basin, that great plateau between the Rocky Mountains on the east, and the Sierra Nevada on the west, almost the whole of which is comprised at present in the boundaries of Nevada, Utah, and part of Arizona. This region is essentially a barren country. The extreme dryness of the atmosphere permits but a scanty vegetation in the plains; and even in the detached mountain-chains running through it-generally from N. to S., or from N. W. to S. E.-there are no trees found except dwarfed pines and mahogany, at the head of sheltered ravines, and a few cottonwoods and willows, which fringe the insignificant streams, before the water sinks in the arid plains. Nearly all the mountain-chains in this region are rich in silver ores. That class of these ores which is adapted to amalgamation, and rich in silver, has been worked with profit for more than ten years. But before the advent of the transcontinental railways, mining was restricted to these ores alone, and the consumption f fuel could be met with the scanty supply of forest trees in the immediate vicinity of the mining districts. Since, however, the Union and Central Pacific Railroads have brought the Great Basin nearer to the commercial centres of the East and the Pacific coast, thus reducing the expenses of freight and labor materially, other silver deposits, containing poorer ores in greater abundance, have been rapidly taken

By G. L. Oldright, T. B. Brighton, C. M. Dice

The base bullion from the lead blast furnace contains varying amounts of the impurities left in the smelter feed by the concentrator, regardless of the method of smelter operation. These impurities may be held in part in mechanical suspension rather than being present as true alloys. However, usually there is little free space in the crucible in which to separate these drosses before the bullion is taken from the lead well. When such a dross is melted in a laboratory crucible and allowed to cool, the products obtained are lead bullion, speiss, and matte in well separated layers. Typical analyses of layers are: Analyses. Per Cent Element Bullion Speiss Matte Pb.............................................. 92.0 41.2 38.3 Cu.............................................. 2.4 36.3 40.6 As............................................... 4.0 16.5 4.3 Sb............................................... 0.7 0.2 0.4 S................................................ 0.6 1.9 13.1 Fe............................................... 0.0 0.0 0.0 Totals......................................... 99.7 96.1 96.7 The absence of iron in these products drossed from the blast-furnace bullion proves that the impurities for the greater part are not simply finely divided blast-furnace speiss or matte that has been dissolved or dispersed in the lead, but are held in solution by the liquid metal and rise to its surface as infusible compounds when the temperature of the bath is lowered. In general, the drosses made locally are metal sulphides and arsenides and not oxidized compounds. The large content of metallic lead also does not seem to be retained because of oxidized compounds

Jan 1, 1937