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By Todor P. Stefanov

The thermal draught within ventilation networks of underground mines depends to a great extent on the shafts depths and degree of change of ventilating air density. When the topology and space orientation of a ventilation network are constant, the dynamics of thermal draught is determined mainly by the variations of the heat- and mass-transfer processes in the openings. This conclusion follows from the well known basic theoretical notions about the thermal draught-aerostatics and thermodynamics [1]. Quantitative evaluation about the influence of heat- and mass-transfer processes on dynamics of thermal draught could be made through: direct mine measurements, special experiments and with the aid of mathematical models. The first two methods produce sufficiently accurative results, however it is very difficult to perform such studies, particularly when these processes are evaluated within a large scope and multifactor aspects. Mathematical models of thermal draught allow to overcome easily these difficulties. The degree of accuracy of results, obtained by this method, depends to a great extent on the degree of approximation achieved by the model to the real heat- and mass-transfer processes. In this paper, with the aid of Bulgarian developed method, algorithm and computer program V WT-4 - for complex evaluation of ventilation parameters in active mine ventilation networks [2], the authors investigate some changes in the thermal draught. Basically, the method is an iterating evaluation of an open set of equations, which represents relationships between the following basic parameters of a mine ventilation network: [ ]

Jan 1, 1980

By R. J. Mechin

IN the early part of 1934, the St. Joseph Lead Co. purchased from the Kadco Corporation three dust-removal units, two suitable for raise work, and the other for drifting operations. The equipment was installed at the Balmat mine, in St. Lawrence County, New York. The Kadco dust-control system can be briefly described as one in which hoods, through which the drill steel is drawn, control the dust at the drill hole, the dust is conveyed through rubber hose or pipe to a collector, where it is removed from the air stream, and the air is then available for recircula-tion in the working place. As during the last few years a number of studies had been completed for the purpose of determining whether or not the dust was effectively removed by the Kadco system, and as the dust counts taken in these tests apparently indicate that it was, the St. Joseph Lead Co. was only inter-ested in obtaining data to show the efficiency of drilling, expressed in terms of minutes per foot drilled, when -using Kadco equipment, in comparison with the former method of drilling dry in a raise and drilling wet in a drift. Comparative dust counts were taken at Balmat, however, by the Metropolitan Life Insurance Co. to show the difference in the dust content of the air in which the operators worked when drilling dry, wet, or with the Kadco equipment.

Jan 1, 1935

By E. Bane Kroeger

Plane failure in rock and soil slopes is usually caused by the intersection of a discontinuity plane with a slope face. Normally, these discontinuities are weaker than the surrounding intact rock and provide a surface along which movement can occur. The discontinuities are typically analyzed to determine the stability of a particular slope. One problem that arises when evaluating the stability of a planar feature is that the method for planar analysis is two-dimensional and has difficulty dealing with planes that are oblique to the slope face. Several researchers have stated in the past that planar failures are a special case of wedge failure. Wedge failures occur when two planar discontinuities intersect in an unfavorable manner. Sliding can occur along the intersection of the planes. Wedge failures are very common in rock slopes and can often be problematic. Wedge stability analysis methods are typically three-dimensional and can analyze planar features that are very oblique to the slope face. Wedge failure analysis can also be used to determine the stability of planar features with good success. One advantage to using wedge analysis over plane analysis is that a tension crack can be both non-vertical and oblique to the slope face in the wedge analysis. This allows the engineer to more closely match field conditions. It also negates the need for the engineer to have two separate software packages to analyze a single slope, saving both time and money.

Jan 1, 2002

By A. Anttila, S. Persson

The grinding mill is probably the most common unit operation in mineral processing. There is, however, much that can still be done in the way of optimization. This paper discusses the results of a well-controlled pilot-scale test in which the performance of a tumbling mill equipped with a conventional rubber lining and lifter bars was compared to a tumbling mill equipped with a smooth rubber lining of the magnetic type. The results indicate that the smooth lining is about 14% more effective with respect to energy consumption. By optimizing the size of the grinding media, the mill capacity can be increased in many grinding operations. In this specific case, grinding with a -20-mm ball charge required 26% less grinding energy than grinding with a -30-mm ball charge. The energy savings can, in most cases, be converted to an increase in capacity. The wear of the grinding media is difficult to assess over a short test period, but the results suggest that the wear is somewhat less when a smooth lining is used. A determination of the wear of the linings was not included in this study, but it is generally accepted that the use of magnetic linings reduces the lining costs dramatically. Computer simulation using the Millsoft code developed by Mishra et al. confirms and explains the increased effectiveness of comminution when a smooth lining and smaller grinding balls are used.

Jan 1, 2000

By Robert S. Setren, Jeffrey L. Ambs

The disposable diesel exhaust filter (DDEF) system developed by the U.S. Bureau of Mines and Industry cooperators for heavy-duty permissible, diesel-powered haulage vehicles, effectively reduces in-mine diesel particulate matter concentrations up to 95%. However, there are concerns about the hazards that exist when the filter is used in situations for which it was not designed. This work investigates the exhaust gas temperature limits to which the filter elements can be exposed without posing a safety or health hazard, such as 6re or off-gassing toxic compounds. A filter approved by the Mine Safety and Health administration and after-market filters were evaluated under varying engine exhaust conditions to determine if after-market filters pose an unacceptable hazard when used in a DDEF system. Filters were laboratory tested at engine exhaust temperatures ranging from 77°C to 290°C. Of the seven filter types tested, six appeared suitable for use on water scrubber-based cooling systems and two appeared suitable for use on dry heat exchanger type exhaust cooling systems with exhaust temperatures up to 150°C. Any filter elements used as exhaust filters on permissible diesel machines must be approved by MSHA for that application. Mine operators who wish to use an after-market filter element should request an MSHA field modification. MSHA will work with the mine and filter manufacturer to ensure its use in this exhaust system application does not pose a health or safety hazard.

Jan 1, 1995

By R. V. Ramani, S. Skankar

Available literature on the effect of re-entrainment on overall airborne dust concentration in mine airways or the fundamental mechanisms of coal dust re-entrainment in mine atmosphere is scant (Shankar and Ramani, 1991). Therefore, as part of the Respirable Dust Center's ongoing research, the following three-part study was undertaken: •a study of the re-entrainment phenomena of anthracite and bituminous coal dust particles in a wind tunnel under the influence of varying air velocities; •a study of the same in the Lake Lynn Laboratory Mine of the USBM with both air flow and walking by personnel causing re-entrainment; and •the mathematical modeling and computer simulation of the re-entrainment phenomenon. In this paper, results from the re-entrainment studies in the wind tunnel and the Lake Lynn Laboratory mine are presented. Comparing the results from the two studies, it was observed that increasing the air velocity increased the rate of re-entrainment (Shankar and Ramani, 1994a) and the rate of re-entrainment decreased with the time of exposure of the source dust to the flowing air. In addition, when the source dust was composed of particles of different sizes, the airborne dust concentrations due to re-entrainment were higher than when the source dust was composed of particles of the same size. The contribution of airborne dust concentration due to airflow was negligible compared to the contribution due to walking.

Jan 1, 1996

Corrosion is a chemical or electro-chemical attack on a metal by the surrounding medium, and it can be stated in general terms that a non-corrodible metal possesses that property either because there is no chemical action between it and the medium, or because the medium reacts quickly with the metal to produce a thin protective coating.When iron or steel is attacked by dilute mineral acids, for example, the products of the reaction are soluble and the formation of a protective film cannot take place; on the other hand, rusting produces a porous film which flakes away and offers little protection to the underlying metal. However, when chromium is alloyed with iron, its resistance to corrosion is improved because the films produced on such alloys become more adherent and tenacious as the proportion of chromium is increased. Chromium is thus an essestial constituent of the corrosion- and heat-resisting steels.During the 40 years which have elapsed since their initial development, these alloys have made an important place for themselves in in<lustry and commerce, and it is the object of this paper to 'describe typical examples of the many types which are available; also, to give some indication of their particular properties, and applications in the mining industry.NOMENCLATUREVery few of the alloys which are about to be described can strictly be considered stainless, and most are not steels in the sense that they can he hardened by quenching from...

Jan 1, 1951

By S. K. Kawatra, S. A. Moffat, K. A. DeLa’O, T. C. Eisele

It was observed that the efficiency of some autogenous grinding circuits was dependent on temperature, with the energy-efficiency of the grinding process decreasing in the winter months, accompanied by an increase in critical-size production. Several possible causes of this phenomenon were suggested, including: • Increased brittleness of the ore during blasting in the pit at low temperatures, leading to increased levels of internal cracking that would lead to rapid breakage to critical size in the mill; •Brittleness changes of the rock in the mill; and • Changes in the durability of the rock caused by either formation of ice on the surface, or freezing of water inside the pores and cracks of the rock. To determine which mechanisms were occurring, drop tests were carried out using frozen and unfrozen rock with varying degrees of porosity, both dry and water-saturated, and which had been blasted for mining in summer and in winter. These tests showed that there was no difference between the summer-blasted ore and the winter-blasted ore, and that durability changes in dry rock over the temperature range from 25ºC to -25ºC were negligible. However, water-saturated rock showed an increased resistance to breakage upon freezing, particularly when the rock was highly porous, or when a layer of ice formed on the surface. Seasonal changes in the durability of rock in grinding are therefore due to formation of ice in and around the rock.

Jan 1, 1995

By S. C. Lindsay, D. J. I. Evans

With each year that passes hydrometallurgical processes are being more widely used to recover base metals from ores and concentrates. Generally these processes involve liquid-solid separation of metal-bearing liquors from barren residues. This may be done by countercurrent decantation, thickening and filtration, or filtration or centrifuging only. Choice of method is governed by chemical and physical characteristics of the pulps; cost of labor, power, materials, and waste disposal; and even by the amount of capital available when building plans are under way. Since all these controlling factors change with time and location and with technological advances, the separation method must be re-evaluated when new plants or expansion programs are contemplated. At the Sherritt Gordon refinery in Fort Saskatchewan, Alberta, an ammonia pressure leaching process recovers nickel, copper, and cobalt from the nickel concentrate produced at Lynn Lake, Manitoba.' Pregnant liquors are separated from the barren leach residues in a thickener-filter liquid-solids circuit. The decision to use this type of separation was based on a summation of economic factors during the pilot plant and design stages. Although countercurrent decantation was not incorporated in the refinery flowsheet, the problems solved in thickening the leach residues and the experience gained in operating the commercial plant are pertinent to countercurrent decantation, particularly where it is applied to slow-settling leach slurries or slurries having a relatively high vapor pressure of a valuable, obnoxious, or poisonous vapor.

Jan 1, 1960

Provide mine safety personnel, MSHA inspectors, and original-equipment manufacturers with guidelines and a check list for inspecting rollover protection structures (ROPS) being used in mining operations. The Problem ROPS are provided on mobile surface mining equipment to protect operators from such safety hazards as machine rollovers, falling objects, and collisions. However, the protective capability of a ROPS can be greatly reduced if it is damaged. Certain kinds of damage, such as hair- line cracks, corrosion, and loosened bolts, may occur as a result of normal machine use but may not be recognized as unsafe by untrained personnel. Therefore, the Bureau of Mmes designed a manual which can be used by mine personnel when inspecting ROPS equipment. The Manual The manual was prepared to help acquaint mine safety personnel and MSHA inspectors with typical ROPS deficiencies and their causes. It provides a systematic means for inspecting ROPS so that the identified deficiencies and their causes can be corrected. It is suggested that an inspection of the ROPS be conducted after every 1,000 h of equipment operation, or sooner if the structure has been subjected to any unusual loads which could cause damage, such as a rollover, highwall caving, or collision. The manual also details common deficiencies in the structure and attachment hardware which may affect the service life. The checklist, when used as instructed in the manual, provides a means for systematically inspecting the structure to ensure maximum protective capability and conformance with applicable Federal regulations.

Jan 1, 1986

An image analysis system has been built which automatically digitizes camera input of rock fragments, analyses the digitised data to determine the sizes and shapes of the rock fragments, and outputs the analysed data to a printer in the form of a histogram or a scatter chart. The high speed of such a system allows for direct collection of data from material thrown into the air by blasting, material travelling on a conveyor belt, and material free-falling on to a stock-pile or into or out of a rock-crusher. Data on the blasted, un-crushed material provides information on changes in the lithology and structure of the rock face as it is quarried or mined: flatter fragments may represent approach to a brittle, unstable shear zone, or a change from sandstone to shale; so that the informa- tion reflects the effect on the sizes and shapes of the fragments by the blasting process and/or by the rock structure. The size and shape distributions of rock fragments produced during blasting and during processing may now be continuously monitored. Such detailed analysis of the results of fragmentation is labour-intensive and expensive when the size and shape distributions are obtained manually, but is cheap and efficient when using this image analysis system. Such a system will enable the results of blasting, quarrying, mining and crushing to be cheaply analysed and correlated with current and changing indus- trial practice so leading the way to increased productivity.

Jan 1, 1988

By G. R. Yourt

"Generally speaking the usual approach for controlling dust is three-fold:1. Suppress the formation of dust at the source.2. Confine dust that cannot be suppressed.3. Dilute and remove dust that cannot be confined.This discussion will be concentrated on the second approach, namely, confining and disposing of dusty air.Dust BehaviourBefore delving into actual design principles a brief discussion on behaviour of dust should be helpful. For prevention of silicosis only respirable dust, ranging in size from < 0.5 to 5u needs to be controlled. As particles of this size have insignificant mass and momentum they follow air movements very closely. Consequently if contaminated air around dust sources is confined within enclosures and leakages maintained, strongly indraft dust is automatically controlled and capture velocities are of no concern.Dust SourcesAt metal mining operations ore is prepared for wet concentration by crushing it to mostly <3"" in size. This usually involves a jaw crusher, one or two cone crushers, one or more screens and several conveyors. Dust is actually produced only by the crushing action but it is liberated also when numerous fine particles contained in the ore stream are dispersed by surges and vibration at the discharge of the crushers, screens and headpulleys of conveyors. Furthermore, dust is dis¬persed when the slime adhering to the underside of the return portion of belts becomes dry and is rendered airborne by vibration and by cleaning floors especially where the slime has dropped."

Jan 1, 1971

By E. P. Barrett

THE high-frequency laboratory induction furnace with a rotating liquid crucible enables research workers to conduct certain investigations heretofore very difficult or impossible to realize because vessels are not obtainable that are capable of resisting the physical conditions or the chemical actions to which they are subjected. Applications for patents covering commercial uses of centrifugal liquid crucibles were filed in the United States in 1919,1 in France in 1925, in the United States and Germany in 1926,2 and in France in 1927.3 In 1928, Schuette and Maier,4 of the Bureau of Mines, reported the construction of a whirling table beneath a high-frequency induction furnace. SHAPE AND SIZE OF CENTRIFUGAL LIQUID CRUCIBLES When a vessel containing a liquid is rotated, the inner surface of the liquid takes the shape f a paraboloid under the simultaneous action of centrifugal force and gravity. The internal dimensions of the paraboloid rotating liquid crucible are governed by the diameter of the container and its speed of rotation. Melted Wood&apos;s metal was poured into cylinders 2 ½ in. in diameter, which were rotated at 180, 300, and 468 r.p.m. When the metal was solid, a slurry of plaster of Paris was added, and rotation continued until the plaster had set. Fig. 1, a photograph of sections f the cylinders, shows the effect f speed f rotation of the containers upon the shape f the inner surface f the rotating liquid crucibles.

Jan 1, 1938

By Lacy JC

Human habitation of the Pacific Rim began when mankind began migrations out of its place of origin in the Rift Valley of Central Africa c. 4million years ago. This migration was erratic and largely controlled by advances and retreat of the various Ice Ages which, while limiting advances in areas of intense cold, at the same time aided migration thro-ugh the creation of land bridges as ocean levels declined during periods of glacial advance (Fig.l).Mankind began its trek to the Pacific from Africa across India then north into southern China and south into Indonesia (Fig.2). In part, these migrations stimulated early technological develop-ments to fulfill needs and adapt to environmental conditions; thus, these nomads developed stone and bone tools, animal skin clothing and the use of caves and other simple shelters. The earliest evid-ence of mankind&apos;s use of fire can be found at Zhou-koudaian near Beijing, c.400,000 BP.From China, the completion of the Pacific Rim&apos;s population can be attributed to the last Ice Age that dropped the ocean level by more than 300 feet and created land bridges about 40,000 BP allowing migration across the Bering Strait into Alaska and to Australia from Indonesia. The American migration reached Mexico about 30,000 BP, and by 6000 BP the occupancy of the Pacific Rim was complete when the first human settlers reached the southern tip of Chile.

Jan 1, 1990

PRESENTATION of the 1922 Washington Award to Capt. Robert W. Hunt, honorary member and twice president of the Institute, was made at the annual dinner of the Western Society of Engineers, in Chicago, on June 18, 1923, in the presence of 250 mem-bers and guests. W. L. Abbott, Chairman of the Award Commission, when delivering the presentation address, said The life of the Govern-ment of this country, as the lives of governments are usually measured, is short, barely 150 years, but meas-ured by what it has accom-plished, this country has reached a venerable age. The first 75 years of our country&apos;s existence were necessarily preparatory to the greater developments which came in the second, and that last half of our country&apos;s existence is ex-ceeded, by ten years, by the span of life of our honored guest. "Very little iron and steel were produced in this coun-try until after the birth of Robert W. Hunt. And it was not until after 1860, when as a boy of 21 he joined his fortunes with those of the Cambria Iron Works, that the iron and steel business of the country really took root. After a year or two with the Cambria Works, he left a promising position to go into the army, where he served for four years. After the close of the war he returned to the iron works and qualified himself as a metallurgical chemist.

Jan 7, 1923

By Elmer R. Kaiser

COMBUSTION of coal and transfer of heat from flames and gases to boiler surfaces continue to be of great interest to engineers here and abroad. Numerous investigations have been in progress to improve furnace and boiler performance and economy. The importance of better understanding of the processes and opportunities for improvement is apparent when it is remembered that heat from at least 500 million tons of coal a year the world over is being transferred to boiler water at efficiencies ranging mostly between 50 and 90 pct. Even slight gains in efficiency, economy, and labor saving become very significant when multiplied by the enormous quantity of fuel consumed. Also the competitive position of the large coal, oil, and gas industries in satisfying the fuel consumers is greatly affected by the achievements made through technical progress with each fuel. This paper is part of a continuing activity of Bituminous Coal Research, Inc., to extend the knowledge of coal utilization for steam generation and to seek promising directions for future research and development in cooperation with others. Particularly in the latter regard, numerous interviews were held during the last three years to seek the experience and advice of boiler and combustion- equipment manufacturers, electric-utility executives, and fuel engineers. A wealth of published information was also reviewed, which together with the interviews pointed to the advisability of further work on ash and sulphur control.

Jan 3, 1954

By Parsons A. E

The application of known pelletizing tech- nology was successful in the agglomeration of zinc concentrate into pellets of minus 6mm siz- ing using fine zinc calcine and sulphuric acid as binder. Subsequent roasting trials conducted in a 0.3 m diameter fluid bed reactor, showed that the pellets satisfactorily withstood hot physical abrasion during fluidization. Fines generation was low and the pellet calcine was hard, possessing excellent handling properties. Results of laboratory scale static pellet sinter- ing tests showed conclusively that the deterior- ation in sinter physical quality experienced with fine calcine was not apparent when the calcine was added to the mix in pellet form. Based on the results of small scale exper- imental work, a one tonne per hour pilot plant was constructed and operated. Several thousand tonne of pellets were produced-for fluid bed roasting in Badische Analin and Soda Fabrik (B.A.S.F.) turbulent layer (T.L.) roasters previously designed for roasting iron pyrite concentrate. Continuity of the T.L. fluid bed roasting operations was achieved when the waste heat boilers were replaced with atmospheric coolers and thus eliminated the problems of gas flow restrictions. Sinter plant trials were conducted over a period of two weeks with the addition of pellet calcine to the sinter feed. Results showed a marked improvement in sinter plant performance, and as a result of better bed permeability, increased sinter production was achieved, with- out significant deterioration in sinter quality.

Jan 1, 1974

By Russell C. Frith

Risk-based roadway roof support design is now a critical part of the Australian Coal Industry. Safe and efficient mining demands that roof support be tailored to the prevailing geotechnical conditions and coal mining legislation in New South Wales, Queensland, and Tasmania is clear in requiring that formalized roof support design be undertaken. The assumption of dead-load suspension of an otherwise unstable roof has been used in roadway roof support design for many years. However longevity does not necessarily translate into either a best or even reasonable practice in the current industry, particularly when pro-active strata management systems are now routinely used and reinforcing support design methods are available. The paper discusses why the assumption of dead-load suspension is fundamentally incorrect in almost all instances when pro-active or reinforcing roof support is applied and how it can easily result in misleading and potentially under-designed roof support systems under various circumstances. The commonly used design methodology of balancing the installed axial capacity of long tendons with the assumed ?weight? of a future roof fall is summarized, and several fundamental flaws are identified. The critical area of selecting the design Factor of Safety is also discussed in detail. Accepting that under certain circumstances the roof of a roadway will require it to be ?suspended?, suggestions are given for how a robust support system can be developed, designed and applied.

Jan 1, 2011

By Takahiko Okura, Satoshi Okano, Hiromichi Takebe

"Fine zinc concentrates tend to become sticky when roasted in a fluidized-bed reactor. The oxidation of high-purity ZnS powders and ZnS concentrates with different particle sizes were studied in terms of phase changes and particle morphologies. The sample materials were directly oxidized to ZnO in a roasting process performed over 700°C. Zinc oxide particles with diameters less than 0.5 ìðé formed at 700°C; the particle size increased by grain growth at 900°C. The coarse ZnS concentrate formed the oxysulfate ZnO2ZnS04 when roasted at 700°C; the sulfate transformed to ZnO at higher temperature.1. IntroductionRoasting is an important step in zinc extractive metallurgy because more than 80% of the world's zinc is produced from zinc sulfide concentrates using the roast-leach-electrowinning [1,2]. Currently, zinc concentrates with a finer particle size distribution are used to enhance recovery rate. However, the finer zinc concentrates tend to produce a sticky calcine in a fluidized-bed roaster [3].The factors that affect products in a fluidized-bed roaster include particle size, contaminant, O2 and SO2 partial pressures, and the feeding method of ore to the roaster. This study examined roasting behavior of high-purity ZnS powders and ZnS concentrates with different particle sizes. The phase changes and particle morphologies of the calcine samples producted from theZnS powders were studied."

Jan 1, 2012

By R. De Ruiter

"In times when mines are emphasizing cost reductions, a properly rebuilt shall conveyance can be more cost-effective than building a new unit. Awareness of the safety aspects of conveyance design along with proper maintenance playa large part in reducing operating costs. A knowledgeable operator can maintain a high level of safety and significantly lengthen the service life of a conveyance. Such an operator is also in a better position to determine when a major overhaul is necessary.After the decision has been made to rebuild, operators must decide who will do the overhaul. Whether the work is to be done in-house or contracted out, the goal is to achieve a conveyance recertified to ""as new"" condition. By dealing with conveyance rebuilds as an engineered product, operators can be certain they are getting a top quality product for their money.This paper deals with the engineering aspects of conveyance rebuilds. Actual examples of typical problems are discussed and corrective action outlined. Design considerations such as proper material selection, component fatigue due to cyclic loading, effects of stress concentrations and corrosion are all part of the initial design considerations that must carryover into the rebuild process. All too often equipment overhauls are done by people who are not experienced in conveyance design.As a manufacturer of mining equipment, Wabi has gained expertise over the past 70 years. By sharing this knowledge the company hopes to create a safer work environment and help to reduce operating costs."

Jan 1, 1994