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By E. A. G. Colls

IN all branches of the chemical industry, corrosion plays a very costly part unless it is suitably com-batted, and as a result it is probably correct that chemical and design engineers are more corrosion conscious in the field of chemical industry than in others. Most metals occur in nature in combination with other elements. The refined or reduced state to which man converts them for his use, by removing the combining elements, leaves them in an unstable condition. Therefore in most of the media to which the metals are exposed they are constantly combining with the constituents of their environment, or in other words they are continually being corroded. Similarly, nonmetallic materials are corroded by undergoing chemical change. The rate at which corrosion takes place varies widely from metal to metal and medium to medium. In practically all cases the corrosion of metals in solutions (electrolytes) is electrolytic in nature and the rate of corrosion is dependent on many factors such as temperature, pressure, internal stresses, galvanic action, metal-ion concentration, and so on. In the chemical industry substances must be handled which are particularly corrosive to materials of construction. At the chemical plants of The Consolidated Mining and Smelting Co. of Canada, Ltd. (otherwise known as Cominco), situated at Trail, B. C., Canada, the following are some of the materials that have to be handled: Gases. Sulphur dioxide, sulphur trioxide, carbon dioxide, carbon monoxide, oxygen, hydrogen fluoride, ammonia, hydrogen sulphide, and oxides of nitrogen. Liquids. Solutions of ammonium sulphate, ammonium sulphite, ammonium nitrate, caustic soda and potash, sulphuric acid, nitric acid, hydrofluo-silicic acid, hydrofluoric acid, phosphoric acid, aqua ammonia, and formic acid. Solids. Gypsum (containing phosphoric acid), ammonium sulphate, ammonium nitrate, phosphate rock, caustic soda, potash, and phosphate fertilizers.

Jan 1, 1951

By Jacob Masliyah, Zhenghe Xu, Lujie Yan

"Understanding adsorption mechanism of polymeric organic process modifierssuch as carboxymethyl cellulose (CMC) on talc hasbeen a major challenge due to anisotropic nature of talc basal planes and edge surfaces. The main objective of this study is to investigate the adsorption of CMC on the basal planes and edge surfaces of talc.Smooth basal plane and edge surfaces of talc were prepared successfully by simple cleavage and sophisticated ultramicrotome cutting method, respectively. The prepared surfaces were characterized by atomic force microscope (AFM) imaging to be sufficiently smooth for colloidal probe force measurements using AFM. Anisotropic surface charge characteristics were determined,with the basal planes to carry a permanent negative surface charge and edge surfaces featuring a pH-dependent charge characteristic. The adsorption of CMC on talc basal plane and edge surfaces at pH 9 in KClaqueous solutions of various ionic strengths wasinvestigated by in situ AFM imaging technique. Themorphology of adsorbed CMC on talc basal planes and edge surfaces was found to be significantly different, due to different binding mechanisms involved. Interaction of CMC with the talc basal plane was found to bedominated by hydrophobic interactions while its binding with the talc edge surface was mainly through chemical complexation and hydrogen bond. The amount of CMC adsorbed on both talc basal planes and edge surfaces increased with increasing ionic strengthof solutions. The methodology developed in our study opens the door to probe polymer adsorption on anisotropic phyllosilicate surfaces, which can help us better understand the mechanism of polymer adsorption on specific mineral faces."

Jan 1, 2014

By C. N. Garman

Homestake-New Mexico Partners operate a 750-tpd carbonate leach uranium concentrate mill near Grants, N.M. The highly mineralized water available as process water leaves much to be desired. The 628 ppm as CaCO 3 makes the use of raw water very troublesome in pipes and on filter cloths. However, the residual sodium carbonate in the final filter cake going to tails makes an ideal softening agent. To take advantage of this fact, all makeup water used in the mill is first used as tailing slurry dilution water and comes to the mill from the tailings pond. The 5-acre tailings pond serves as a thickener and 100 to 150 gpm of nearly clear solution is decanted to a pump to be returned to the mill. Since this tailings water has small quantities of uranium in the solution an ion exchange scavenger unit was installed to remove as much uranium as possible. The ion exchange raffinate is then used as final filter wash ahead of the tailings slurrying step. In spite of the large settling area this return water is not clean enough for ion exchange feed. The solids present are very fine and composed of approximately 15 pct (by weight) burnable carbonaceous material common to the sandstone uranium ores in the area, 40 pct SiOz plus 45 pct CaC03. Laboratory work showed that this material responds very well to flotation. Before deciding to use flotation, various clarifying systems such as pressure leaf filters, sand filters, and continuous vacuum pre-coat filters, were considered. Each of these could have solved the problem but with much more operating labor, more reagents and greater installation costs than the flotation step. About 100 to 150 gpm of fouled water is fed to two 66-in. Fagergren cells, in series. Reagents used at the beginning were Arquad 2HT75 and Arquad C50, at the rate of about 1% lb per 8-hr shift, or about 0.0053 lb each per ton of ore. This did not completely remove the solids but does an acceptable job. Approximately 75 pct of the slimes are a size that can be caught on a 41-Whatman Paper are removed. Removal of these slimes also allows much better settling of the coarse nonfloatable material. Advantage is also taken of this fact in a small settling tank ahead of precipitation. Removal of this amount of the slimes makes the ion t:xchange feasible. PREGNANT SOLUTION CIRCUIT The carbonate? leach-caustic precipitation method of uranium concertration does not provide for any process purification step ahead of precipitation. Therefore, any fine solids getting into the pregnant solution through the filter cloth show up in the final concentrate. This, of course, lowers the grade, and, at times, the slimy nature of these very fine solids rendered final filtration of the concentrate difficult if not impossible At Homestake-New Mexico Partners a 75-ft thickener was available for gravity clarification of 100 to 120 gpm of this pregnant solution. However this did not sufficiently remove the slimes. Laboratory investigation of the whole range of flocculants that were suggested by literature, salesmen, and friends failed to turn up anything of consequence. A continuous vacuum pre-coat filter would do the job and was investigated. The capital cost and the operating labor and materials made this a last chance choice. Following work done in the metallurgical laboratory on the tailings return water, it was found that some changes in the reagent strengths and combinations made a very definite decrease in the solids in the pregnant solution. Concentrate grade improved about 5 pct anti the final product after drying had an appreciably greater bulk density. Compared to a cost of about 2.2e per ton for pre-coat filter opelation for cleaning just one circuit, flotation costs less than 1.0 per ton of ore for cleaning two circuits. While a pre-coat filter would do a more thorough job, the flotation does all that is required for either circuit. Gravity causes the froth produced to run back into the leach circuit. This does not appear to result in a build-up of objectionable slime. No extra manpower is required; the operators in the separate areas can observe the operation of the cells and mix the small quantities of reagents as needed. Normally the 66-in. Fagergren cell requires 15 hp per cell, but this very dilute slurry needs only 10 hp for both cells. Originally, a combination of the two Arquads mentioned previously served as frothers and promoters. As further testing

Jan 1, 1962

Commonwealth of Pennsylvania, Department of Internal Affairs, Topographic and Geologic Survey, Harrisburg, Pa George H. Ashley, State Geologist All available printed Bulletins may be obtained through the Commonwealth of Pennsylvania, Division of Documents. Where a price has been set on the publication, checks should be made out to the Commonwealth of Pennsylvania. A Syllabus of Pennsylvania Geology and Mineral Resources has recently been published by the Survey as Bulletin G1, and consists of a general survey of the state An appendix of this bulletin also gives a complete bibliography of Survey publications It will be sent upon request. The State Geological Survey has gone through several phases and reorganizations, publications of three of them being numerous and important A fire, in 1927, destroyed supplies of many of the papers of the present Survey. Available bulletins of the present Survey are: Bulletin M6: Bituminous coal fields of Pennsylvania, in 4 parts available as follows: pt 1, General description of coal, 50 cents; 3, Bituminous coal resources, 25 cents, 4, Analyses of bituminous coals, 25 cents Bulletin M10, Fire clays of Pennsylvania; Mll, Molding sands of Pennsylvania; M12, Anthracite culm and silt (1928); M13, Feldspar in Pennsylvania; M14, Magnetite deposits of French Creek (1931); County Report C1, Adams County, pt 1, Geology and geography (in press), County Report C2, Geology and mineral resources of Greene County (in press); Topographic and Geologic Atlas A5, New Castle Quadrangle (1929), $1; Topographic and Geologic Atlas A27, Pittsburgh Quadrangle (1929), $1; Topographic and Geologic Atlas A168, Lancaster Quadrangle (1930), $1. The present Survey has also issued a number of short mimeo¬graphed bulletins any of which will be sent upon request Briefly they are: No. 15, Mineral resources of Pennsylvania; 20, Iron ores; 28, Magnesite; 40, White clay deposits, Monroe County; 45, White clay deposits, central Pennsylvania; 47, Manganese, Eastern Pennsylvania, 48, Pyrite from bituminous coal mines; 59, Bog

Jan 1, 1933

It has long been recognised that applications of the Net Present Value (NPV) investment decision making methodology can have serious deficiencies in situations where investment can be delayed and, once made, various options allow increases or decreases in the level of output. NPV valuation can undervalue the project if it does not incorporate future flexibilities or ""options"". It is important to realise that a proper valuation of a project (ie, valuation of its future cash flows) must incorporate an analysis of optimal future decisions involved in managing the project. Current valuation cannot be divorced from a consideration of future decision making. There is now a considerable amount of literature, mainly academic, identifying and exploring ways of remedying these deficiencies in the application of NPV. While the necessity of period by period analysis is sometimes acknowledged, little if any practical illustrative model building has been published to date, aside from algorithms using continuous time stochastic processes which deny access to the uninitiated.

Jan 1, 1994

By Ernest J. Conway

This report presents engineering drawings for six material handling devices for underground coal mines. The devices were designed under a U.S. Bureau of Mines program to reduce injuries from material handling during mine and equipment maintenance. The six devices are (1) scoop-mounted 1411: boom, (2) swing-arm boom, (3) heavy-component lift-transport, (4) mine mud cart, (5) container-workstation vehicle, and (6) timber car. Each device is described briefly, and recommendations are made concerning the design of new devices.

Jan 1, 1989

By Zhenglong Li

A process has been developed to recover titanium from a blast-furnace slag which contains about 20-25% Ti02 and 12% Fe. In this process. "hot" slag from the blast furnace is directed to a separate furnace where it is reheated with additives to form two simple slag phases: one is titanium enriched anosovite (Ti3O5) and the other is a titanium lean non-crystal glass phase. The modified slag is then processed by conventional beneficiation techniques to produce a marketable titanium concentrate and a usable slag material. This paper focus on separating anosovite from glass by electrostatic separation and froth flotation.

Jan 1, 1996

By Charles White Merrill

Silver consumption in the arts and industries of the United States during 1930 and 1931 has remained remarkably near the high level established in 1929. Undoubtedly the sharp drop in the price of silver has been an important factor in supporting consumption, but silver's peculiar properties and uses probably have been an even more compelling reason for its sustained utilization. In its most important use - sterling silverware - it seemingly has most serious competition, but well established tradition protects the demand for sterling ware and the law forbids the term "sterling" to be applied to any material not containing at least 92.5 per cent silver. The photographic industry is dependent upon properties of certain silver salts possessed by no other material. Consequently silver is indispensable to all photography, including the huge motion picture industry. Other uses for silver could be listed which, because of special features, likewise have tended to maintain the consumption of silver in the arts and industries of the United States. The figures which this report makes available for the first time are the detailed silver consumption figures for the arts and industries of the United States for 1930 and 1931. These figures have been tabulated with the previously published(3) figures for 1928 and 1929 thus presenting a 4-year statistical record of silver consumption. All quantities are given in troy ounces, 1,000 fine.

Jan 1, 1932

By Danuta Szyszka

This paper presents results of tests performed to determine minimum concentration of a surfactant used at which coalescence of air bubbles during flotation has low probability to occur. The measurements of the critical coalescence concentration, also known as CCC, were carried out in a device consisting of glass cell into which air was pumped by peristaltic pump through capillaries. The flotation foam was recorded with a high resolution digital camera. Basing on the video records, average diameters of the air bubbles were measured and the values obtained were subsequently used to determine the CCC values. The author of paper determined the CCC values of surfactants tested using the linear regression method, and subsequently analyzed the results obtained. To define initially the capability of a tested surfactant to flotation, efficiency of multiparticle model flotation and flotation of individual size fractions were determined in a flotation apparatus for laboratory use in the presence of only foam making agent at CCC value pre-determined during the tests previously carried out. The tests of coalescence phenomenon were carried out with use of selected flotation frothing agents.

Jan 1, 2014

By Joe Holmes, Peter Langlois

"Falconbridge’s Raglan Concentrator, located at the northern limit of Quebec’s Nunavik Region, has been in operation since December 1997. Originally designed to process 800,000 tonnes per year of high grade nickel ore, plant capacity is currently approaching 1,000,000 tonnes per year. Optimization of the ABC grinding circuit has proven to be the most challenging component of this capacity increase. Concurrent flotation circuit modifications have allowed concentrate grades to increase from 16 to 18 percent nickel, while maintaining recoveries. Concentrate drying problems encountered during the first 15 months of operation have been addressed through equipment upgrades. The challenges associated with surface deposition of filtered tailings in an arctic environment are now better understood, and detailed design of the progressive reclamation cover is underway.GRINDINGCircuit OverviewOre from open pit and underground mining operations is introduced to the underground ore handling system via surface and underground truck dumps. Two underground bins with a combined capacity of 4000 tonnes provide roughly a day of live capacity for ore storage. Ore from the two bins is conveyed to a 150 tonne surge bin immediately ahead of the grinding circuit in the concentrator.The Raglan grinding circuit has a conventional ABC configuration (Figure 1) with a design capacity of 100 mtph (800,000 tonnes per year). The 24’ AG mill is powered by a 3000 hp motor with variable speed drive. AG discharge is sized on a 8’x16’ single deck vibrating screen, with screen oversize recirculating to a 5 %’ short head cone crusher (400 hp) before returning to the AG mill. Screen undersize is combined with ball mill discharge to feed up to 5 15” Krebs hydrocyclones. The ball mill is a 14’x 21’ overflow mill driven by a 3000 hp motor at 73% critical speed. Target Pgo for the grinding circuit product is 65 microns"

Jan 1, 2001

By Thomas J. Witzig

This Bureau of Mines report is a background study of the International Tin Agreement. Attempts at stabilizing the tin market prior to the agreement are detailed, as well as the conditions and negotiations that set up the agreement. Details of the five consecutive 5-year agreements beginning in 1956 are presented, with emphasis on membership and the agreements' primary tools: the buffer stock and export controls, Attention is focused throughout on the United States activities during the period, especially with regard to its strategic stockpile, and its involvement with the agreement culminating in its membership, for the first time, in the fifth agreement beginning in 1976. Considerations leading to the U.S. decision to join are detailed, and U.S. activities in the negotiations for the sixth agreement are presented. The status and outlook for the agreement are discussed, and evaluations of the effectiveness of the agreement and its components are reviewed.

Jan 1, 1981

By J. Oliver, J. Cleason

"With maintenance costs rising and an increasing demand for higher production, the use of sealed spherical roller bearings can reduce maintenance costs while providing increased production uptime. The sealed spherical bearing has increased bearing life by slowing the ingress of contamination. This paper will describe how contamination and bearing wear is reduced by reviewing case histories from coal and metal mines that improved their production by decreasing downtime using sealed spherical roller bearings. INTRODUCTION The spherical roller bearing (SRB) is a robust rolling element bearing that can accommodate high radial loads, low to moderate axial loads, and misalignment with no loss in carrying capacity. (i.e. Figure 1) Because of these characteristics, it is a favorite in mining applications and many other heavy industry applications. Primary applications are the various pulleys on conveyors. Coal and hard rock mines have hundreds of miles of conveyor lines and countless head, tail, drive, and idler pulleys. Maintaining the bearings on these pulleys and replacing bearings that have failed can be a huge expense to a mine in components, labor and downtime. Ideally, the bearings are replaced when the pulley is changed out according to the maintenance cycle, about every 4 years. Reality, however, causes the bearings to be changed out every year, or sooner. These premature bearing replacements can cause production shut downs for as long as 8 hours. Conveyor pulleys have been targeted at many mines as the single biggest maintenance pain point.The primary reason for replacing conveyor bearings is internal wear from fine, solid particle and water ingress through the bearing housing seals. (i.e. Figures 2 & 3) Traditionally, the bearing is mounted in a split pillow block housing (SAF, FSAF, SDAF or SNL are typical industry styles) with only labyrinth seals (LER/LOR) for protection against the ingress of contaminants. The bearings are lubricated with grease. A common way to extend the MTBR is to purge the bearing system with large quantities of grease to flush out the contaminants. If the bearing, and thus the housing seals are not frequently purged with grease, fine solid contaminants enter the housing and bearing through the labyrinth cavities."

Jan 1, 2015

The first part (lH of this work dealt with the process of recrystallization of single crystals of lead after deformation by creep, as revealed by macroscopical examination. It was shown that when recrystallization commenced, a crystal, termed the primary crystal, started to grow at the edge of the specimen and extended into the body of the specimen along the slip planes. At some stage during the growth of this crystal, other crystals appeared at the boundary of this first crystal and fragments of the parent crystal. From thispoint, recrystallization was accelerated with relatively rapid necking down of the specimen until fracture occurred.All those crystals formed after the primary crystal were given the term secondary crystals. In the present paper is given a detailed account of the orientations of the primary and secondary crystals.EXPERIMENTAL METHODThe size of the test pieces and the manner of loading were given in the previous paper (1). X-ray back reflection photographs were taken of the individual primary and secondary crystals and from them were determined the orientations. The path of the X-ray beam was perpendicular to the surface of the creep specimen.In view of the large number of photographs needed, gold...

Jan 1, 1940

By Roger L. Amelunxen

El presente texto describe el modelo dinámico de aplicación denominado Aminpro-Flot, el cual simula el proceso de flotación de minerales basado en las cinéticas de los minerales principales que componen la mena procesada. El El modelo incluye recuperación por arrastre mecánico, mecanismos para simular el grado de apuramiento, provee recuperaciones y leyes de concentrado de una sección de flotación. En este sentido, el modelo es robusto y fácil de usar ya que el usuario debe tener un buen entendimiento de la manera de extraer las cinéticas de la zona de colección de una prueba de flotación en el laboratorio. Por ello, se da un ejemplo para que los lectores interesados puedan construir su propio modelo, de forma que este es usado para el diseño y optimización de plantas de flotación, eliminando las pruebas de pilotaje.

Sep 12, 2005

By H. F. Porter

MUCH has been written relative to the errors involved in the use of a galvanometer for measuring thermocouple electromotive forces. In general, it may be said that accuracy with a galvanometer is secured only at the sacrifice of durability, unless manual adjustment is made in the operation of the instrument to overcome the errors of resistance. and resistance changes. The pyrovolter and the potentiometer both require manual adjustment for every reading, readings being taken on a "null" method. To the end that some of these balances may be eliminated and only an occasional balance be made as a check reading, the "continuously deflecting pyrovolter" was developed. Essentially, the operation of the continuously deflecting pyrovolter is to determine the resistance of the thermocouple circuit, though its value is not noted or indicated, then throwing in series with the thermocouple sufficient resistance to bring the sum up to some standard value for which the indications of the galvanometer will be correct. This result may, however, be accomplished in a somewhat simpler manner, for which general method patents are now in the course of application. If we devise a galvanometer circuit so that by means of a simple adjustment the resistance of the entire circuit will be rendered equal to some constant predetermined value, we may rely on the galvanometer to give correct e.m.f. indications (assuming that the errors of temperature resistance coefficient and cold junction have been properly allowed for), and will indicate temperature continuously where the e.m.f. measured is developed by a thermocouple.

Jan 9, 1919

By John Campbell, E. S. Baker, G. W. Jones

"INTRODUCTION In previous reports 5,6./ results were given showing the amount of natural ventilation that takes place in manholes (capacities, 74.1 to 308 cubic feet) when the number of ventilation openings in the manhole cover ranged from no openings to a maximum of 4g.The tests warranted the general conclusion that the ventilation or air changes taking place in, a manhole increase as the area of openings in the cover of the manhole is increased, and are proportional (with the exception of a few erratic tests) to the area of the openings in the cover. The area of the openings was the chief factor that affected ventilation.The results did not show any marked change in rate of ventilation due to increased capacity or shape of manhole, when the results were expressed in terms of air changes per day versus area of ventilation openings in square inches per 100 cubic feet of manhole space.It was observed during these investigations that in certain tests that showed erratic results (that is, did not agree with the general average for a given set of test conditions) the wind velocity during the test period was also abnormal. In view of these findings it was decided to conduct a series of tests in which the wind velocity across the openings in the manhole cover could be controlled accurately to determine the effect of wind velocity on ventilation rate."

Aug 1, 1938

By K. Hanna

Early identification of adverse geologic conditions and high stress concentrations during the high-speed extraction of coal using modern mechanized long wall systems is a major challenge facing the mining industry. Often, unexpected geologic anomalies that affect rock mass quality are encountered more rapidly, leaving the mine operator with insufficient time or information to deal with the changing ground conditions. The RockVision3DTM seismic tomographic system, developed by NSA Engineering, Inc., offers substantial benefits over conventional geologic/stress-detection methods and has been used successfully in coal mines worldwide. Tomographic images, produced economically and in near-real time, are easy to interpret, allowing mine operators to deal with potential hazards on a day-to-day basis. This paper focuses on the application of RockVision3DTM technology for delineating hazards caused by stress and geologic anomalies. Case studies for two bump-prone coal mines will be discussed. For example, (1) in a German deep (>1,130 m) mine, the drilling-yield method was used to verify the effectiveness of this technology in detecting stress anomalies ahead of longwalling; (2) in a Polish mine (-500 m deep), two longwall panels 4 km apart were monitored to assess structural and stress-related factors contributing to differences in mining conditions and magnitude of structural failures.

Jan 1, 1999

By Frank L. Nason

RECENT explorations with a diamond-drill, originated and conducted by Mr. J. A. Van Mater, Superintendent of the Lehigh Zinc and Iron Company, have revealed some very important geological facts, which, it is believed, will be of special practical interest to mining engineers. During these explorations the writer was frequently called in consultation, and hence the facts here recorded are almost entirely the results of personal observation. The franklinite-deposit upon which the explorations were conducted has a long continuous outcrop. Figs. 1, 2 and 3 give a map and sections. Beginning at the extreme southern point,

Jan 1, 1895

By R. W. Stahl, H. E. Sanford, J. B. Benson

"As movement or transportation of coal is second only in importance to actual mining, and as the latter is wholly dependent on the former, the efficiency of the haulage system often determines the efficiency of the entire plant. Safe or accident-free transportation is essential, also, because no attempt is made to divorce safety and efficiency, it being realized that they are inseparable.Most of the Ruhr mines were opened decades ago, and many features that were considered up-to-date then are now obsolete. Progress in developing haulage systems has been slow, chiefly because it would be very costly to change many to accomodate more modern equipment. These systems are being altered or modernized slowly, as capital permits. The only revolutionary changes that have been made in mine haulage are the use of larger locomo¬tives and cars, in the movement of shuttle cars, and in the adoption of skip hoisting. Most Ruhr shafts, however, will not accomodate large cars, the secondary roadways are too narrow for large locomotives, and the coal is too soft to permit skip hoisting because degradation would be too great. Therefore, notable advances have been made only at newer plants, where allowances have been made for modern equipment.The shafts are deep (average 2,300 feet) and of comparatively small diameter. The small bore was designed to reduce costs of sinking and lining. Generally, the shafts are lined throughout with masonry; however, most of the buntons and guides are wooden.The hoisting engines arc installed in masonry structures, and where more than one hoist is used they are placed on opposite sides of the shaft to eliminate as much noise as possible (fig. 1). This arrangement also prevents an engineer from acting on any signals except those transmitted to him. A few hoisting engines are mounted in the headframes (fig. 2). The hoisting engines are equipped with overwind, overspeed, and auxiliary braking devices, which are tested frequently and kept operative at all times. The signal code is displayed in view of the engineer, and a light or dial indicator informs him of the cage's position in the shaft. Many hoists are equipped with re¬cording devices, which show on a continuous chart the speed of hoisting as well as any delays throughout the 24-hour period.A Koepe system of winding is in general use because of the depth of shafts (fig. 3). With this system, a single rope passes over a single-groove, large-diameter sheave attached to the motive power, and the ends of the rope, after passing over the head sheaves, are attached to the cages. A flat tail rope suspended in the shaft and connected to the bottom of the cages serves to balance the system. Both steam and electric engines are used to activate the hoisting system, end the engines are capable of moving at least a 50-percent overload.The ropes are necessarily of large diameter (2-1/2 inches and greater), and flexibility decreases as rope diameter increases. To overcome the unwieldiness .of large-diameter ropes as shafts become deeper, a four-rope system is being tried at one mine (fig.4). In this system the load is equalized between four ropes which permits much smaller ropes to be used. All hoist ropes are inspected daily and discarded after 2 years service unless special permission for longer service is granted by the Mine Inspectorate, and then only after thorough visual and electromagnetic inspection."

Jan 1, 1950