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By S. P. Marsh, M. E. Glicksman

"The effect of capillarity-driven diffusion on the recalescence of mushy zones is studied in pure materials. The solid-liquid mixture is formed by rapid partial solidification of an initially undercooled melt, and the ratio of the two phases is subsequently maintained constant by an externally imposed adiabatic constraint. A novel technique has been developed that permits tracking of the kinetics of the diffusion-controlled evolution process in situ using precision temperature measurements averaged on a length scale larger than that of the microstructure.The mean ""temperature of a mushy zone is slightly below the bulk equilibrium melting point, and is related to a characteristic length scale of the microstructure through an appropriate statistical average of the GibbsThomson equation. Theoretical considerations indicate that the diffusion controlled recalescence will progress as t- l / 3, where t is time. This behavior is experimentally verified for both succinonitrile (SCN) and ethylene carbonate (ETC), which have markedly different morphologies. The kinetic rate constant is observed to increase monotonically with increasing volume fraction of solid in the two-phase mixtures, although a firm theoretical foundation for this result has not been developed.INTRODUCTIONA dispersed multiphase system seeking equilibrium will generally contain variations in the local .free energy density. These density variations arise from such factors as variations in the bulk free energies of the phases and the distribution of interfacial energies. In this study, we examine the kinetics of diffusion-controlled recalescence in 1 solid-liquid mixture of a pure substance at its melting point. This type of two-phase system is particularly convenient to analyze because of the well-characterized physical properties of pure phases (crystals and their melts) and their interfacial energies, and the absence of any solutal effects."

Jan 1, 1986

By H. N. Kalia, J. B. Gresham

Several attempts have been made in the past 60 years to commercialize the vast oil shale deposits of the US. However, the industry has yet to become economically viable. To date, it has not been possible to produce oil from oil shales at a competitive price compared with oil produced by conventional methods. The development work, nevertheless, has been fruitful in furthering the art of thick bed mining and technology of in situ retorting. The in situ method has the potential of recovering oil from thick beds, and the resource recovery potential is much greater than that from underground mining and surface retorting. In situ methods require that the shales/marlstones be fragmented in place to induce adequate porosity and permeability to allow in situ heating of the fragmented shales. This can be accomplished by using explosives. However, it has been found that the existing blasting systems, though very efficient, have some drawbacks. The explosives become insensitive when shot in multiplevertical decks. They can also become insensitive when spaced horizontally at close proximity to other charges. Also, since the blasting is done in a very limited free face, the delay time that can be allowed between charges is also quite limited. Consequently, it is not always possible to routinely predict the performance of the blasting system. Furthermore, since it is not possible to undertake secondary blasting, it is imperative that the blast design function properly. Recent successful retorting by Occidental Petroleum Co. Of Retorts 7 and 8 suggests that some of these problems may have been overcome. This paper addresses some aspects of in situ retorting and problems that have impeded the development of a viable oil shale industry in the US.

Jan 1, 1986

Increase the safety of operators of front-end loaders by providing a means of monitoring the machine's stability. Approach Through a research contract, the Bureau of Mines developed a front-end loader stability indicator which provides the machine operator with a reliable, easily interpreted display assessing the stability of the machine. How It Works Statistics show that front-end loader accidents are the largest single category of machinery-related accidents in the surface mining industry. Many of the fatalities resulting from these accidents occur when front-end loaders rollover and either crush the operator who is trapped within the cab or strike the operator who is trying to jump to safety. Although rollover protective structures (ROPS) are required by law on front-end loaders to protect operators in the case of a rollover, these do not prevent the actual rollover from occurring. In fact, the operator has no way of evaluating the stability of the machine except by using personal judgment. The Bureau of Mines responded to this problem by developing a front-end loader stability indicator whose primary function is to Indicate to the operator when the machine is approaching an unstable situation which may trigger a rollover. The device bases Its interpretation on measurement of the normal loads on the machine's wheels. Strain gage instrumentation located on the machine is used to monitor the magnitude and change of forces acting normal to the front-end loader's wheels. These forces are direct indicators of the machine's center of gravity relative to its position on the ground. The strain gages are connected to electronic circuitry which amplifies and processes the signals. Stability or instability of the loader is relayed to the operator through a display of green, amber and red lights.

Jan 1, 1986

By J. J. Schwoebel

Resource Enterprises, Inc. (REI) is exploiting the coalbed gas resource by working in unison with active underground mining operations. At REI?s pilot project at the Soldier Canyon Mine, Carbon County, Utah, REI has drilled nearly 15,250 m of horizontal in- seam and slant boreholes during the initial two years of drilling activity. Produced gas has been sold to a natural gas transmission company on a continuous basis since mid 1983.

Jan 1, 1986

By C. M. Paiencia

The Bureau of Mines studied the potential availability of primary antimony (Sb) from demonstrated resources in 21 mines and deposits in market economy countries (MEC's). Twelve of these properties were evaluated as producers and nine as non- producers. The 21 studied properties contain 499,600 mt Sb as demonstrated resources, of which 304,000 mt is recoverable as antimony metal; another 973,500 mt Sb is contained in inferred resources. Recoverable antimony from demonstrated U.S. deposits is only 10,700 mt, just 3.5 pct of the MEC total. Domestic production of primary antimony from operating mines has averaged only 561 mt/yr over the 10-yr period 1975-84. This represents just over 5 pct of total U.S. consumption of primary antimony, which averaged 11,081 mt/yr during the same period. The United States will thus continue to rely on imported ores andlor concentrates, antimony oxides, and metal to satisfy domestic industrial requirements. At production costs up to $1.15/lb Sb, 110,000 mt of refined antimony is potentially available from 10 of the 21 studied properties. At $2/lb, 294,000 mt Sb is available, and at $3/lb, the total rises to 304,000 mt Sb available from all evaluated producers of refined antimony.

Jan 1, 1986

By J. E. Taylor

A detailed planning and design project has been undertaken at Callide Coalfields, as the first step towards implementing a fully integrated mine graphics system. The system, when fully installed, will support applications ranging from business graphics through to terrain modelling and computer-aided design. The conceptual design which will accomplish this is presented. The problems of retrospectively applying graphics standards to existing applications are discussed, and a practical solution outlined.

Jan 1, 1986

By L. A. Bertram, F. J. Zanner

"The goal of this paper is to present a tool to simulate transient melting of the electrode tip. This capability is needed to develop and test furnace control algorithms since experimental determination is difficult and expensive. Simulation incorporates parameters (including arc voltage, arc current, electrode gap and furnace pressure) from previous quasi steady experiments with 460 mm diameter Inconel 718 electrodes.Cathode heating rates (determined by classical as well as experimental arc models) are linked to these independent variables. After radiative loss adjustments to the heating, transient one dimensional melting is computed. IntroductionThe vacuum arc remelting (VAR) process attempts to improve the physical and chemical homogeneity of a static-cast electrode by remelting and solidification in a quasisteady manner. To achieve steadiness of furnace operation requires automatic controls based on inputs measuring physically relevant state variables of the process. Previous industrial scale VAR studies (1,2,3) involving stainless steels, superalloys, and other alloys have provided a basis on which control strategies of some generality can be proposed (4). Of these measurements, the data for Inconel 718 is the most complete, so discussion in this paper is restricted to this alloy.Studies of the In 718 alloy subjected to the VAR process have established that melt rate M (kg/hr) depends not only on the melt current 1m (kA) supplied to the furnace, but also on ambient gas pressure of CO, PCO (micron), and electrode gap ge (mm) as well (1):"

Jan 1, 1986

By Churchill J

A suite of software programs has been written to provide the field engineer or geologist with the capability to collect and store data directly into small, portable handheld computers. This allows the engineer and geologist to collect data in a more efficient manner as the data is collected in sequence and is verified at the time. Typical applications for this software include geological and geophysical logging, trucking surveys, mine surveying, condition monitoring, ventilation surveys and maintenance systems. The software allows the user to construct his own electronic notebook by structuring data input to the computer in a similar manner as is now done on pre-printed forms. The user can store all valid entry codes or numeric ranges in a dictionary and all data inputs made are validated against this dictionary. Once constructed the user may call the electronic data sheet into the unit and collect data which will be stored into the unit which has the memory capacity to record data for up to periods of 60 hours. The data can then be automatically transferred to mini/microcomputers for immediate analysis and report generation. The software may be used on a variety of handheld computers.However the generally rugged environments found in the mining industry limit the choices. In particular the authors have selected a unit weighing a little over one kilogram, which is rugged enough to fall off an underground survey vehicle, and survive when accidentally immersed in water,without losing data. This paper describes the software developments in detail. The project development work to produce this system has been funded by a grant from the Australian Mineral Industries Research Association and is supported by a number of large Australian mining companies.

Jan 1, 1986

By C. A. Holley

The generation of coal fines is a growing problem which has serious environmental and resource recovery Impact. Several methods of agglomeration are studied including the production of briquettes for the consumer market. Simplified process flow diagrams, "order of magnitude" plant capital cost and operating costs are presented.

Jan 1, 1986

It is a pleasure to submit to the National Critical Materials Council (Council) some of my thoughts concerning the important tasks which lie before you. It long has been my belief that America's economic health and national security may depend to a substantial degree on whether we have available to us an adequate supply of critical and strategic materials at reasonable cost. To the extent the Council can contribute to the identification and implementation of wise public policies which facilitate the achievement of that goal, we and our children should be grateful. Even before assuming office, President Reagan warned of the danger of undue dependence on imported materials essential to the Nation's defense and economic well-being. After his election, he appointed a transition task force on strategic and critical materials, and he later directed the Cabinet Council on Natural Resources and Environment to prepare .a National Materials and Minerals Program Plan and Report to Congress, which he forwarded to the Congress in April 1982. In 1984, my predecessor, Secretary Clark, established the National Strategic Materials and Minerals Program Advisory Committee, popularly known as the "Mott Committee" because of its distinguished chairman, retired Admiral William C. Mott.

Jan 1, 1986

By J. L. Fuller

Thousands of mine air samples are taken underground each year by MSHA inspection personnel in order to further assure that miners have a safe and healthy environment in which to work. While most air samples are taken with stain tubes, many samples are obtained in evacuated containers and returned to a laboratory for more accurate analysis on a gas chromatograph. In order to enhance the accuracy, reliability and repeatability of the samples taken with evacuated containers, improved procedures have been developed, which are described in this report, for filling two different types of evacuated sample containers using either mechanical or electrical pumps. In those instances, such as when sampling strata gases in drill holes, where mathematical calculations may be required for proper sampling, example calculations are provided. The use of a third type of evacuated container, which is generally restricted to non-specific sampling of the ambient mine atmosphere, is also described.

Jan 1, 1986

By P. R. Wotruba

The Fortitude gold-silver deposit is related to a "wallrock" copper porphyry system developed within Middle Pennsylvanian to Permian Antler Sequence rocks adjacent to a Middle-Tertiary altered granodiorite intrusive stock at Copper Canyon. Gold-silver ores of the Fortitude deposit occur with disseminated and massive sulfide replacement mineralization of skarn-like or calc-silicated limy horizons of the Antler Sequence contact meta-sedimentary rocks. A major, north-trending, steeply westward dipping normal fault was important as a conduit for hydrothermal fluids responsible for the metallization in the Fortitude area. Gold-silver mineralization is best developed near a marble front where retro-grade chloritization and destruction of prograde calc-silicate mineral phases is most prevalent. Fluid-inclusion studies performed on the Copper Canyon system indicate a wide variation in fluid chemistry during several hydrosilicate stages that ranged in temperature from 500°C to 220°C.

Jan 1, 1986

By A. Redfern, B. G. D. Smart

The ultimate objective of the development work presented in the paper is to devise an appropriate method for relating powered support specification to geological conditions and mining practice, thus enabling the longwall method of coalmining to be successfully implemented throughout the varied coalfields of the world. The paper begins with a review of various methods previously used to determine support rating, each method being analysed with regard to its source, the logic and theory which constitute the method, and subsequent recommendations. An alternative approach is then proposed, the Powered supports being considered to be one of three foundations, sharing load with coal ahead of the faceline which acts as another foundation, and the waste behind the supports which acts as the remaining foundation. The load/deflection characteristics of the coal and waste, which in turn are related to geological conditions and mining practice, are shown to affect the load transfer on to and hence the specification of the powered support. In particular the characteristic of the waste foundation is shown to be affected by the caving mechanism, an alternative form to that mechanism accepted for British conditions being proposed and designated "parting-plane-controlled" caving. A finite element solution for a beam on elastic foundations was used to translate the above concepts into numerical results, these results being compared with data from Indian and Chinese operating conditions. The Indian case study examines the effect of using a conventional chock type of support in a one-web back mode when mining towards a roof break generated ahead of the face, while the Chinese case study compares measured subsidence over a longwall with "blocky" roof conditions with the model results. The comparisons are encouraging, suggesting that the approach used is worthy of further development.

Jan 1, 1986

By D. R. Tweeton

A modified push-pull field test and a computer model of cation exchange were developed to aid in evaluating cation exchange parameters prior to in situ mining. Reliable determination of these parameters is essential when modeling restoration of groundwater quality. The field test involves a much larger volume and much less disturbance to the ore sample than is feasible with laboratory measurements. This test can be performed in two or three weeks. It is relatively inexpensive, requiring one injection- production well and two or more wells for collecting samples of leach solution. The use of the model in interpreting test results is illustrated with field data from an in situ uranium mine. Much of the research was performed by the University of Texas at Austin, and was partially funded by the Bureau of Mines.

Jan 1, 1986

By J. Flemming, R. O. Burt

"The Tanco pegmatite is located in the Bird River greenstone belt of southeastern Manitoba approximately 160 km northeast of Winnipeg (Figure 1). This pegmatite body was discovered in 1929 and subsequently attempts were made to exploit it for tin by Jack Nutt Mines Ltd. and later in the middle 1950's by Montgary Oil Ltd., who extensively developed but did not produce from, its lithium deposits. In 1966 systematic investigation of the pegmatite as a potential source of tantalum led to the founding of Tantalum Mining Corporation of Canada Ltd. (TANGO) in 1967 and production of tantalum concentrates from the Bernie Lake mine commenced in 1969. Tanco is currently jointly owned by Hudson Bay Mining and Smelting Co., Cabot Beryl co Inc. of Boston, and the Province of Manitoba. (Williams and others 1978, Burt 1979, Burt and others 1982), continued until the end of 1982, when, due to falling demand and prices, operations were suspended.During the 1970's Tanco had investigated the potential of the lithium orebody; carrying our research into both the concentration of the ore and into the production of lithium chemicals. However lithium chemicals were in an over-supply situation, due in part to the production from Chilean brine deposits (Buckley, 1983), and Tanco' s own plans were put into abeyance. The potential alternative market, the direct use of concentrates in the glass and ceramics industry, did not at the time justify the cost of constructing a new plant."

Jan 1, 1986

By D. Spindler

Pursuant to the Federal Surface Mining Act of 1977 and the Illinois Surface Mining Act of 1980, Illinois has adopted revegetation success standard regulations that include the Agricultural Land Productivity Formula. The Formula establishes yield goals and standards to measure the success of meeting yield goals for reclaimed prime farmlands. The formula compares the quality of the pre-mining soils in the permit area and the county, to the crop production achieved on the reclaimed permit area and the county crop yield in a given crop year. The regulations also specify acceptable crops, erosion control requirements and time frames for demonstrating success.

Jan 1, 1986

By F. D. Huntley

Raw materials used by the Flat Glass Industry are known in the Industrial Minerals geology sector as Specialty Products. These pro- ducts must meet specification limits usually not the same for all glass manufacturers. Evolving new glass compositions will require mineral concentrates of consistent purity being produced within economic limits that will assure market viability of the resulting glass product. The amount of success the Flat Glass Industry will achieve by developing and maintaining domestic production centers will be determined by many economic factors which affect the costs of doing business. Technological developments by mineral processors must continue in order to achieve more efficient production of high quality glassmaking raw materials.

Jan 1, 1986

By R. L. Grayson

As the total cost of labor has significantly increased over the past ten years, older underground mines have found it more difficult to compete- in a limited demand coal market. Many of the older mines were developed extensively into a reserve requiring a large number of workers to maintain and rehabilitate extensive track haulages and/or belt conveyor systems. Often, a large number of fans were required to maintain minimal airflows in areas where poor conditions and huge leakages prevail. This paper focuses upon problems which beset one such coal mine and projects undertaken to restore it to potential profitability.

Jan 1, 1986

By R J. Hill

Blasters are well aware of the problems and expense faced when trying to load in wet bore holes; problems of poor coupling and poor density, as well as the expense of higher priced cartridge product. In answer to these problems, I developed a system for dewatering using nozzles with lay -flat plastic liners which I have used successfully over the last few years. I found the system not only gave me better shots than I could have expected in the circumstances, but also dramatically decreased costs. The system has been adopted by two large roading contractors and a quarry operation in Eastern Canada.

Jan 1, 1986

By Chan. C. L., Zehr. R., M. M. Chen, J. Mazumder

"Two three-dimensional models of a surface tension gradient driven flow during laser surface heating are developed. The first model is based on a perturbation solution. The basic solution corresponds to the stationary axisynwnetric case and perturbation is based on a small scanning velocity. The advantage of seeking a perturbation solution, as it turns out, is that the three-dimensional flow is modeled by two sets of two-dimensional equations which are presumably much more tractable than the original three-dimensional equations. Numerical solutions are obtained and discussed. The second model is a full three-dimensional numerical solution of the Navier-Stokes equations, using a point-by-point partially vectorized iteration scheme. Surface shape is also determined in a self-consistent manner. The effect of the presence of convection on pool geometry, cooling rate and solute redistribution is presented and discussed.IntroductionThe existence of fluid flow and convection and their effects were first reported in the fifties (1,2). The role of convection in controlling pool geometry such as pool shape, undercut and ripples, and defects such as variable penetration, porosity and lack of fusion and weld properties such as weld homogeneity and bead formation is studied by a number of researchers and is reviewed by the authors in a recent paper (3).Recently, surface tension gradient driven flow has been identified as one of the forces responsible for convection within the molten pool (4,5). It is postulated that surface tension gradient driven flow is responsible for the surface ripple formation in the weld pool (6-8). Oreper, et al. (9) developed a two-dimensional convection model. Buoyancy, electromagnetic and surface tension gradient forces were considered. The formulation was based on a specified pool profile. It was found that the surface tension gradient is the dominant force in most cases. However, the solid-liquid interface is not known a priori. In fact, the solid-liquid interface, i.e. the pool shape, is a piece of information that the model should be able to predict. A two-dimensional transient self-consistent (i.e. the solid-liquid interface is solved as part of the solution] model for laser surface melted pool was first developed by Chan, Mazumder, and Chen (3)). This model predicted a non-uniform cooling rate, hence non-uniform microstructure. Depending on the Prandtl number (i.e. material) and surface tension number, the shape of the molten region as well as the cooling rate changes. It was also predicted that the recirculating velocity is of one or two order of magnitude higher than that of the scanning velocity. This model provides the detail of the flow field and heat transfer on a plane perpendicular to the scanning direction. However, the front-to-back motion and its effect on heat transfer also play important roles in the physical process, especially for the fact that the recirculating velocity is so much higher than the scanning velocity. Such a motion cannot be obtained from two-dimensional models."

Jan 1, 1986