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By K. Hebbar, R. G. Reddy

The viscosities of various FeO-SiO2 slags were calculated using a previously developed structural-based model. Using hole theory and the atomic pair model, an expression was derived to relate the viscosity to temperature and the fraction of the bridging oxygen in silicate melts. The deduced equation was successfully applied to predict the viscosities of FeO-SiO2 slags in the composition range of 0.1 < XSi02 < 0.423 for several temperatures. The calculated data agree well with the experimental viscosity data.

Jan 1, 2002

By D. R. Taylor, R. G. Goss

The use of clay granules as carriers for pesticides dates from the early 1940&apos;s and by the present day represents a business conservatively estimated at between 200 - 300 thousand tons / year in the U.S. alone. Aside from economic and specific target pest efficacy advantages, the use of clay granules as pesticide carriers also delivers a number of environmental benefits which will be reviewed. Topics to be discussed will include: 1) drift control (versus liquid sprays), 2) mobility (in the environment), 3) worker safety, and 4) transportation (spill) safety.

Jan 1, 1999

By John W. Greene

For the past two years, Tenneco Minerals Company has been evaluating a refractory, pyritic, carbonaceous gold deposit, Results from agitated biological oxidation reactor tests show the gold extraction was increased from 15 to 90 percent using microbial oxidation, Also, no preg robbing occurred after complete microbial oxidation. Three column biological oxidation tests were then initiated on minus 1/2 inch ore. Biological oxidation was discontinued in two of the three tests, These columns then were leached with cyanide. The maximum gold recovery was 62 percent. No preg robbing was observed,

Jan 1, 1990

By J. L. Waldron

This paper presents a theoretical tool used to analyze gold recovery problems at Dee Gold Mining Co. The first step in addressing the problem was realizing that lower gold extraction was linked to high silver grades, and could not be correlated to either the carbonaceous or sulfidic content of the ore. Analyses of metallurgical testwork, blasthole, and mill recovery data demonstrated that decreases in gold extraction correlatP� well to increases in silver extraction. Figure 1 illustrates this for 1991 mill operations. This was the starting point for the work described in this paper.

Jan 1, 1992

By J. D. Miller

Reaction kinetics for gold dissolution in acid thiourea solutions were investigated using formamidine disulfide as an oxidant. For the conditions studied it appears that a surface reaction limits the rate of gold dissolution. The rate was found to be first order with respect to thiourea concentration and half order with respect to the concentration of formamidine disulfide; the apparent activation energy for the reaction was 10.40 kcal/mol (43.40 kJ/mol); and the reaction rate was independent of pH for the pH range 1.0 to 3.0.

Jan 1, 1999

By Charles E. Mergentime, J. Marshall Dean

Mergentime/Loram&apos;s extension of the Washington, DC Metro Subway System includes construction of dual 1,770-foot tunnels in soft ground, a crossover structure, a fan structure and pumping station, and other related work. This paper describes the overall construction requirements of the Contract, including subsurface conditions; Mergentime&apos;s value engineering of the tunneling and compressed air contract requirement; selection of the tunnel boring machine and backup equipment; installation of the compressed air plant; the manufacture, use and evaluation of the tunnel liners; and the tunneling performances during construction of the first tunnel.

Jan 1, 1985

By H. Bogart

The Golden Sunlight Underground Mine located near Whitehall, Montana was portalled from the bottom of the existing Golden Sunlight Pit in July 2002. Gold was mined by sublevel stoping in the larger ore zones and longhole back stoping in the narrower ore zones. The stopes varied from 30 feet to 100 feet in width, extended up to 200 feet in height, and were completely unsupported. Underground production averaged 1,500 tons per day with a staff of35 people. The mine operated with a break-even cut-off grade of0.080 ounces per ton.

Jan 1, 2004

By Sue W. Wells, James J. Moore, Stephen D. Lynch, R. Hunter White

This paper describes the products and services that Phelps Dodge Corporation desires from solvent extraction reagent suppliers and the partnering relationship that Phelps Dodge wishes to develop with these suppliers. Product topics include: 1) manufacturing concerns, 2) product and process quality control reporting and 3) reagent customizing to meet individual plant needs. Service subjects include distribution, delivery time, emergency re-supply, terms, and tailoring technical support. The partnering relationship discussion reviews mutual benefits, communications, reliability, cross-functional teams for problem solving and developing new opportunities, and long-term commitment.

Jan 1, 1994

By David G. Chedgy, Edward A. Zawadzki, Robert D. Stoessner

Extensive research and testing in commercial facilities has clearly demonstrated that heavy medium cyclones are the most effective process for cleaning a 0.6 x 0.15mm (28 x 100 Mesh) coal at low separating gravities, less than 1.35. This paper describes testing performed to deter- mine system characteristics at these lower gravities and the type of circuitry required to maximize performance. The results of these studies include both pilot and commercial scale tests of cleaning 0.6 x 015mm (28 x100M) coal.

Jan 1, 1988

By J. P. McDonnell, L. A. Beckett, K. Y. Hammy

Dangerously high stress areas can be controlled by proper mine planning and/or destressing. This paper reviews practical methods to detect and destress high-stress zones along coal faces. The US Bureau of Mines investigated stress-related burst problems and destressing efforts at a cooperating mine. Laboratory tests of the drilling yield method for high stress detection were conducted to determine the correlation between the volume of cuttings obtained and the magnitude of the applied stress. A three- dimemiom1 computer modeling program was used to evaluate the effectiveness of stress relief methods.

Jan 1, 1987

By J. Tuzson, H. McL. Clark

Introduction Wear of pumps, wet cyclones and pipelines by suspended solid particles will impact their operating economies by limiting their useful life, reducing their reliability and increasing the amount of servicing. Erosion is considered a materials problem. The empirical solution consists of testing different materials in field applications. Such tests are time consuming and expensive. The prediction of localized wear rates, life estimates and appropriate material selection demand a better understanding of the slurry wear process in environments corresponding to those found in working equipment. Key words: Wear, Slurry abrasion, Coriolis erosion tester The slurry wear process Solid particles suspended in liquid generally move with the flow, but such particles deviate under the centrifugal and Coriolis forces encountered in pumps. The concentration of particles will increase, and a solid layer or bed may accumulate if the acceleration is directed against the flow passage wall. Large particles in dilute suspensions may impact the wall. dissipating their kinetic energies and removing material. However, particles smaller than about 11)(1 µm encounter great drag when moving through the liquid. and such par¬ticles have little kinetic energy left when they reach the wall. They cannot penetrate the stagnant boundary layers present in pumps. Therefore, small particles tend to form beds that slide along the wall, removing material by a process that could he called sliding erosion or wet abrasion. Wear by impact erosion from large particles in dilute slurries can he predicted by appropriate analytical and empirical methods. However, laboratory tests and calculations of wear rates that correspond to sliding erosion are more likely to correlate with field experience from wear under similar conditions. Specific energy Data from laboratory slurry erosion experiments have shown that the amount of material removed is approximately in proportion to the energy expended in the erosion process. Thus. the specific energy-energy expended in removing by erosion a unit volume of material-offers a simple, practical measure for the erosion resistance of materials. The concept was found to also apply to sliding erosion (Clark et al.. 1997). Generally, the study of the material-removal process in slurry erosion continues to remain a subject of research. Conceptually, if the flow velocities and accelerations could be calculated in a pump or pipeline, the energy dissipated at the passage walls could also be estimated, and the material removal rate would become known from the specific energy determined by laboratory tests. Slurry erosion testing Laboratory devices made specifically for slurry erosion testing may be grouped into the following: jet erosion devices, slurry pots and the Coriolis test machine (Pagalthivarthi and Helmly, 1992). Jet erosion devices use a slurry pump and nozzle to produce a high-velocity slurry jet that is directed at a flat material specimen, either perpendicularly or at some acute angle. Combined impact and sliding erosion are produced. but the processes cannot be separated, and the wear is difficult to assess except by weighing. Slurry pots consist of a cylindrical vessel containing the slurry of interest. In the slurry pot, test specimens are attached to a rotating arm. The samples are rotated in the slurry and experience local flow conditions that result in combined impact and sliding erosion. Wear depth measurements from detailed laboratory experiments have been successfully correlated with results from an analytical model of the process, and specific energy values have been calculated (Wong and Clark, 1995). In industrial use, the samples are weighed to determine the total material loss. Materials are ranked with respect to some reference material. The Coriolis erosion tester (Tuzson, 1984) consists of a rotor with a central cavity, from which two opposing radial passages lead out (Fig. 1). The slurry is fed to the centerof the rotor in one pass from a stirred overhead tank. The slurry particles are subjected to the Coriolis acceleration as they flow out through the radial passages. The material specimens are mounted into the radial passage walls facing the direction of rotation and are eroded by the particles that are pressed against them as they flow out radially. A narrow groove is worn into the sample within a few minutes, using a few gallons of slurry. Material removal is estimated accurately from profilometer traverses across the wear scar at different locations. The energy dissipated by the particles can be estimated, which leads to a well-defined experimental value for the specific energy.

Jan 1, 2000

By Roger A. Kauffman, Dean Van Dyk

Feldspar is the earth&apos;s most abundant mineral group. The feldspars are aluminum silicate minerals belonging to the tectosilicate class. Feldspars are the most widespread of any mineral group and are estimated to constitute 60% of the earth&apos;s crust. They make up a large percentage of the exposed rocks as well as soils, clays, and other unconsolidated sediments. Feldspars are widely used in the glass and ceramic industry and are principal components in rock classification schemes. Feldspar minerals and their production are important contributors to the domestic and world economies and standard of living. In 1990, the United States produced 630 kt of feldspar minerals, and world production was estimated to be more than 5 Mt. Feldspar mineral production in the United States has a long and interesting history (Feitler, 1967, Rogers Jr. et al., 1983). The first commercial production in the United States occurred in about 1825 and came from pegmatite bodies located in Connecticut, where feldspar was mined, hand sorted, and shipped to England. Feldspar production grew during the 19th and 20th centuries with important developments in production location, integrated mine and processing facilities, and the development of the flotation process for feldspar by the US Bureau of Mines and the feldspar industry. The first commercial feldspar flotation plant began operations-in Kona, NC, in 1946, some six years after this process had been developed. In 1990, the domestic feldspar industry consisted of 12 operating companies with mines and processing plants located throughout the United States (see Table 1). During the last 25 years, the domestic feldspar industry has been dynamic, marked by new plant construction and capacity expansion at older plants. The industry has also seen plant closures, changes in ownership of existing operations, the consolidation of the Canadian nepheline syenite industry, and the increase of imported feldspar products. The industry has been affected by contractions in its major end-use markets brought about by economic cycles, product substitution, and environmental effects, such as recycling, land-use controversy, and air and water pollution. Despite problems, the industry remains mature and highly competitive. GEOLOGY Mineralogy The common feldspar group of minerals form a single crystalline phase or solid solution series of minerals. Fig. 1 is a ternary phase diagram that shows the feldspar mineralogy-KAlSi,O8, NaAlSi3O8, and CaAl2Si2O8. The end-member compositions are also referred to as potassium, sodium, and calcium feldspar. The feldspars whose chemistry ranges between the potassium and sodium end-members are known as alkali feldspars, while those between the sodium and calcium end-members are plagioclase feldspars. These feldspar groups can be further subdivided based on structural and compositional features within the alkali or plagioclase feldspar series. The distinction between and the proportion of members of the two feldspar groups are important to the classification of igneous rocks (Deer et al., 1966). Perthites are the exsolution product of an initially homogeneous potassium-sodium feldspar solid solution which forms (in an environment of decreasing temperature) a heterogeneous intergrowth of sodium-rich feldspar lamellae in a host crystal of potassium feldspar. Antiperthites are exsolution products in which the host mineral is sodium-rich plagioclase feldspar and the intergrowths are potassium-rich feldspar.

Jan 1, 1994

By E. P. Fahrenthold, K. E. Gray

Introduction Brine reservoirs along the Texas and Louisiana Gulf coasts are currently under study to investigate the technical and economic viability of production wells designed to extract methane gas in solution. The effect of well pressure drawdown on reservoir rock and associated overburden material is important to well performance predictions and the analysis of potential subsidence problems. Consequently a series of compaction tests have been conducted on sandstone and shale cored from a test well drilled near Hitchcock, Texas, in order to determine the variation of mechanical properties to be expected over the producing life of the formation. Previous Work The referenced tests are part of an extended study of geopressured-geothermal reservoir behavior, including compaction (Jogi, Gray, Ashman, and Thompson, 1981 and Jogi, Kalra, Gray, and Thompson, 1981) and creep (Thompson, Jogi, Gray, and Richardson, 1981) tests of reservoir rock and related reservoir performance studies (Rago, Okhuma, Seperhnoori, and Thompson, 1985). Recent work has considered the nonlinear constitutive behavior of sandstone (Fahrenthold and Gray, 1985 and 19861, while additional experimental work is reported here. Geological structure and composition of the Hitchcock field from which the core samples were obtained is discussed by Light (1985). Experimental Procedure Compaction tests were conducted on cylindrical cores, nominally 2.75 inches in length and 2 inches in diameter, with independent control of the axial, confining, and pore pressures. Axial and radial deformation of the samples were measured in tests over a range of effective stress states expected to develop over the reservoir lifetime. The term effective stress as used here refers to the algebraic difference of the total stress and pore pressure, with compression taken as positive. Three types of compaction tests were conducted on the sandstone. In the uniaxial tests, axial total stress and radial strain were held constant as the pore pressure was reduced, similating one dimensional compaction which may occur during reservoir depletion. In the triaxial tests, radial total stress and pore pressure were held constant as the axial total stress was increased, duplicating conventional rock compaction test procedures. In the pore pressure drawdown tests, axial and radial total stresses were held constant while the pore pressure was reduced, in order to investigate differences in sample response to mechanical and pore pressure loading. Compaction tests were also conducted on shale material obtained from the reservoir overburden. The field coring process provided few consolidated shale sections sufficiently large to allow preparation of samples with the dimensions described above. With additional attrition during sample preparation of this brittle material, ultimate yield of the coring effort was limited. The few available samples were tested in uniaxial and triaxial tests similar to those described above. The use of displacement transducers to measure sample deformation avoided the difficulty of strain gauge installation on this material. Test Results The sandstone and shale both demonstrated nonlinear stress-strain behavior, with hysteresis and residual strain present upon unloading. Polynomial interpolation of the stress-strain curves was used in the calculation of incremental values for the loading and unloading moduli. Figures 1 and 2 show example axial effective stress-axial strain curves for triaxial tests conducted on sandstone and shale samples. The figures plot incremental stress and strain variables, defined as deviations from the state of prestress to which the sample was subjected. The state of prestress was varied between tests in order to investigate material behavior over the entire stress and strain space of interest. Tables 1 and 2 give the incremental moduli (Young&apos;s modulus and Poisson&apos;s ratio) as a

Jan 1, 1986

By J. M. W. Mackenzie

Three major developments have dominated the recovery of gold from ores, viz; 1846 Elsner's studies of gold solubility in aerated alkaline cyanide solutions 1887 MacArthur and Forrest's process based on zinc precipitation 1980+ Large scale development of the CIP process The brevity of this list for a metal whose extractive metallurgy has been as widely studied as any metal reflects the fact that the chemistry of the gold recovery process, as opposed to the engineering has seen few significant breakthroughs in over a century of application. to The purpose of this paper is introduce a new chemistry for gold recovery which may, in the future, add significantly to the technology of gold recovery. This new chemistry is based guanidine functionality - (R2R2N) 2 C = N R2 on the In developing the use of the guanidine functionality for the recovery of gold as the aurocyanide anion from leach solutions and pulps, Henkel has, as its objective, the development of an effective gold selective ion exchange resin. As will be seen, the initial investigation of the properties of the guanidine functionality in the solvent form for gold recovery lead to some significant metallurgical developments of their own but, the foremost objective was, and remains, the development of a resin for gold recovery. As a part of this development project, Henkel has entered into association with Mintek, South Africa, and this ongoing association has the potential to develop RIP/RIS technology for the gold industry. More details on Henkel's gold recovery technology and Mintek's role in this programme are given in (1). an The application of ion exchange resins to gold recovery is not new and many reviews have been published on the advantages of this process, and on the current state of the art of gold recovery by ion exchange resins. (2)(3)(4) Widespread application of ion exchange resin based processes for gold recovery has, however, not occurred to date. Fleming and Cromberge (5), described some significant pilot plant RIP trials in South Africa and the partial success of these pilot plant trials held out the tantalising possibility of a breakthrough in gold recovery based on RIP technology. Despite this pioneering work, only two really significant applications of RIP technology for gold recovery exist today. These are the Golden Jubilee Plant in the Eastern Transvaal South Africa and the widespread, although in some respects technically backward, use of ion exchange for gold recovery in the former USSR. There are two main reasons for the current scarcity of RIP and RIS plants used for gold recovery. These are: 1. 2. The perceived problems of engineering RIP plants The lack of a resin having suitable chemistry for both gold loading and gold elution The problems of engineering RIP plants have been largely overcome in the last 25 years. Much of the development in RIP plant design took place in the uranium industry during the rapid expansion of that industry in the mid 1970's. In addition, the development of CIP engineering systems has lead to the development of in-pulp solid extractant based metallurgical plant designs which can, with limited modification, be adopted to RIP. The lack of a resin having suitable chemical properties has almost certainly been the main reason for RIP/RIS not being introduced into the gold industry over the past decade. Attempts to use RIP/RIS have focussed on either conventional we ak base or conventional strong base resins. The weak. base resins have the disadvantage that they

Jan 1, 1993

By George J. Simchuk

The selection of a stripping method and subsequently, the stripping equipment, are two of the most important decisions confronting a project engineering staff during the initial feasibility study of a new coal stripping operation. The selected stripping units average from 60 to 70 percent of the total capital outlay for mine equipment and their selection will affect the type, size, and quantity of the attendant equipment, such as loading shovels, drills, haulage trucks, and bulldozers. This paper is intended to report on an in depth study by Utah&apos;s Technical Services Staff regarding the selection of stripping equipment for the Goonyella Coal Mine in Queensland, Australia. We will touch briefly, on the objectives considered in this selection; the various alternatives which were explored; the general assumptions that were followed throughout the engineering and design of an appropriate stripping system; and computations necessary to determine the amount and size of stripping equipment. INITIAL EXPLORATION Utah Development Company (presently 90% owned by Utah Construction & Mining Co. and 10% by Australian investors) commenced systematic geological studies of the Bowen Basin coal fields of Central Queensland in 1961. The Blackwater Mine as shown in Figure 1 has since been established in this area and is now producing 3.0 million tons per annum of washed coking coal. Geological reconnaissance was then extended to the northern part of the Bowen Basin and in 1963 Utah&apos;s coal prospecting area covered 2444 square miles of Central Queensland. The authority to prospect north of Blackwater has since been trimmed to 810 square miles by relinquishments to the State.

Jan 1, 1971

By William Lodding

That grinding may change a crystalline material both in a physical and in a chemical sense has been shown by a number of authors in recent years. Thus Mackenzie (1) and Bartha (2) reported the effects of careful grinding on muscovite, quartz, gypsum, dolomite, etc. Increase in specific surface produced by grinding implies increase in total energy of a system. Newly produced surfaces are chemically more reactive; dislocations may be introduced during grinding, and existing strain may be released by the same process, as shown by Holt et el. (3) All these changes are easily detected by thermal analysis, but it is not easy to separate the multiplicity of effects registered and to arrive at quantitative interpretations. This paper is an attempt to analyze by the use of thermal analysis some effects produced in grinding. In differential thermal analysis (DTA) one measures all thermal changes occurring in a substance during heating or cooling. Chemical changes, such as decompositions, synthesis, oxidation, reduction, etc., and physical changes such as phase transformations, changes in specific surface and in thermal conductivity, strain release, etc. By thermo gradmetric analysis (TGA) on the other hand only chemical changes involving weight loss or gain are recorded. Similarly gas evolution analysis (GEA) will register only reactions involving gas evolution, including water vapor, and oxidation-reduction. By performing two or all three of these thermal methods of thermal analysis simultaneously and on the same specimen one can separate the different effects registered and by difference evaluate their magnitude.

Jan 1, 1966

By Guy T. McBride

Mr. Chairman, Fellow Keynoters, Ladies, and Gentlemen: It is purposed to consider the theme of this meeting, "The 1970&apos;s - Pivotal Decade for the Mineral Industries," from the particular -- some would say peculiar -- point of view of one engaged in mineral engineering education, and this coign of vantage prompts the textbookish subtitle, "Problems and Solutions (?) in Undergraduate Mineral Engineering Education." Three interrelated problems, or problem areas, will be presented and discussed, and where solutions seem to be emerging or seem worthy to be suggested, they will be identified. The three problems are: 1. The goals, and therefore the course requirements, of the undergraduate curricula are in question, 2. The unit costs of undergraduate education appear excessive to those who bear the charges, and 3. The social ambience of the day affects for the worse the work attitudes and the career motivation of both prospective and in-course students. The Need. - Any discussion of these problems must bottom upon recognized national needs for minerals and a technologically sound minerals industry staffed by competent engineers, particularly at the exploration, development, and production levels, Fortunately, these needs have been recognized and to some extent quantified, and they are even now under further intensive study by some of the most competent members of our society and profession. The latter reference is, of course, to the current work of the National Commission on Materials Policy (U.S.A.) under the executive directorship of Dr. James Boyd. Predating this, and perhaps to some extent

Jan 1, 1972

By R. L. Roller

In recent years, there have been many articles and papers written on the use of specially designed belt conveyor systems in mining operations, either economic studies or actual experience. These papers generally conclude that the use of these systems can reduce overall costs from 10% to 40% over conventional methods using general purpose equipment (truck/shovel, scrapers, etc.). However, they also generally conclude that conveyor systems are inflexible and capital intensive. With the increasing cost of mobile equipment, the capital cost conclusion is losing steam, particularly when the costs of maintenance shops, road and ramp construction and other related start-up costs are thrown in. Attention here will be focused on answers to flexibility related questions, but first, a look at costs in general. Basic production economics tell us that when we have a small job to do, it is cost effective to use simple, low cost, general purpose tools which will have a minimum impact on total cost. It also tells us that when we have a large project, we can employ methods using special, relatively expensive production tools. Figure 1 illustrates what occurs on projects, of different sizes, with various quantities of production. With small quantities of work, the cost per unit of work starts out much lower using general purpose equipment, rather than using special purpose methods and equipment. However, at a relatively low quantity of work, the cost hits a lower limit and, regardless of how great the quantity of work, the unit cost can never go any lower.

Jan 1, 1985

By Charles W. Merrill

The price records of 7 representative mineral commodities for the 68-year period 1890 through 1957 have been compiled and analyzed for significant trends. When reduced to real prices in terms of dollars of constant purchasing power or to the purchasing power of industrial wages at average rates, a substantial overall fall in prices is revealed. This downtrend contradicts the widely held concept that, heavy drafts on a mineral resource must lead to scarcity, reflected in rising prices. Three metals (aluminum, copper, and pig iron), two fuels (bituminous coal and petroleum)&apos;, and two nonmetals (sulfur and cement) have been chosen because of their preeminence in their respective categories, their significance in an industrial economy, and the ready availability of their price records. It might be added that these seven commodities. were selected before any price figures were compiled, none was selected or rejected to substantiate any preconceived notions as to price trends, The overall importance of the seven is demonstrated by the fact that, taken together, they composed over three-fourths of the value of all minerals produced in the United States in 1957. The first step in the analysis was to reduce the price records to a basis for significant comparisons, Two such comparisons have been made: (1) The quantities of each of the commodities that could have been purchased for an average hour&apos;s wage in each year; and (2) the unit price of each commodity through hhe years in terms of deflated dollars. These data are set forth in the accompanying table and two charts.

Jan 1, 1959

By Robert A. Haney

During the last ten years, longwall mining systems have undergone many changes. Panel widths and lengths have increased. Longwall faces have become more automated. Average production from individual longwall panels has increased from 1,000 to 3,600 tons per shift. To control the dust generation resulting from the higher production, longwall dust control systems have integrated various dust control techniques. Systems designed to control dust generated at the crusher/stageloader, shearer, and supports are common to most longwall faces. A survey was made of the dust controls that are currently in place on all the longwalls in the U.S. This survey addressed the types of controls used to reduce dust generated at the crusher/stageloader, shearer and roof support movement. Additionally, information on face ventilation rates, cutting cycle and level of automation was obtained. The purpose of this paper is to review the dust control practices that have been implemented throughout the United States and to identify those controls that are being used on high production longwall faces. Additionally, a model is used to demonstrate how ventilation and automation affect occupational exposure. Automation of roof support movement can offer some of the greatest reductions in occupational dust exposures. While technically feasible, its full benefit has not been fully realized by the industry. Until technology to fully automate longwall mining systems becomes more reliable, future dust control systems must rely on increased ventilation, application of headgate dust collectors, improved shearer dust controls and improved shield dust suppression systems.

Jan 1, 1995