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By M. S. Moats, W. C. Hartzell

The stable domestic supply of gallium, indium, and germanium has been identified as a critical need for the United States. Electric arc furnace dusts, processed to recover zinc, produce a residue that could be a potential source of these critical materials. An industrial zinc leach residue was characterized to determine its particle size, chemical composition, and predominant mineral phases. Heated, atmospheric, agitated leaching using sulfuric acid and hydrochloric acid was examined to determine the extractions of gallium, indium, and germanium as a function of concentration and temperature. Extractions of gallium were found to be similar to iron in all experiments. The maximum percentage of Ga, Ge, and In leached into solution were 71%, 63%, and 48%, respectively.

Feb 1, 2023

By Nathaniel White, Todd Kilduff, Justin Laviolette, Dan Laviolette, Randy Zeigler, Sean Sundermann

The Mitchell Point tunnel is a part of several ongoing efforts to connect the 12-mile-long Historic Columbia River trail between Mitchell Point Outlook to Mitchell Point Drive. The tunnel lies inside the Mitchell Spur entablature basalt geologic feature, extending 647 linear feet utilizing a typical horseshoe section with a height of 14.5 feet. The Oregon Department of Transportation (ODOT) required proper vibration control to minimize potential impacts to Interstate 84 and Union Pacific rail immediately below the tunnel excavations and sensitive, rare plants. The method of designing the vibration monitoring program and the results of its implementation show the iterative process of using monitoring to improve blast design as excavation proceeds, such as reducing air overpressure and COVID-related supply chain-constraints.

Dec 1, 2022

By III Westbrook

Although calcium sulfate dihydrate, commonly referred to as gypsum, has been utilized for some time in fiberglass reinforced polyester (FRP) applications, it does not have the fire retardant filler recognition of ATH. Gypsum is more commonly known for application in cement, soil and water treatment, plaster, and wall-board. Inherent characteristics of gypsum limit its use to low temperature and, until recently, non-aqueous applications. However, as a plentiful, naturally occurring hydrated mineral, the cost effectiveness of calcium sulfate dihydrate has prompted development and yielded success in the areas of FRP spray-up and latex carpet backing.

Jan 1, 1993

By M. L. Harris, J. Organiscak, S. Klima, I. E. Perera

"The National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) conducted underground evaluations in an attempt to quantify respirable rock dust generation when using an untreated rock dust and a rock dust treated with an anti-caking additive. Using PDM 3600s and 3700s, these evaluations measured respirable rock dust levels arising from a flinger-type application of rock dust on rib and roof surfaces. Rock dust with a majority of the respirable component removed was also applied in NIOSH’s Bruceton Experimental Mine (BEM) using a bantam duster. The respirable dust measurements obtained downwind from both of these tests are presented and discussed. This testing did not measure miners’ exposure to respirable coal mine dust under acceptable mining practices, but indicates the need for effective continuous administrative controls to be exercised when rock dusting to minimize the measured amount of rock dust in the sampling device. INTRODUCTION Two factors have combined to renew concern regarding respirable dust measurements and compliance. This renewed recognition is due to two regulations that have modified operators’ rock dust schedules. First, the 80% incombustible requirement in intake entries has increased both on-section and outby-the-section rock dusting. Secondly, the recent respirable dust regulation change that has increased the number of respirable dust samples taken per sampling cycle. Previously, when only 5 samples were needed bi-monthly, rock dusting could be scheduled to not interfere with the respirable dust sampling schedule. The significant number of samples now required under new regulations combined with the need to maintain 80% total incombustible content in active mining areas require the schedules for respirable dust sampling and rock dusting to intermix. This raises concerns about the amount of rock dust that potentially is included in the sampler weight gain. Additionally, the respirable dust maximum was lowered from 2.0 mg/m3 to 1.5 mg/m3 (effective August 1, 2016) increasing concern that rock dust contamination may be an issue. Currently, the acceptable practice is to apply administrative controls such as keeping the miners upwind during rock dust application or to schedule rock dusting during a maintenance shift when the number of miners present is lower. NIOSH’s research examining the quality of rock dust has led to the development of hydrophobic rock dusts."

Jan 1, 2017

By G. Frey, D. Scott, C. Pritchard

Controlled recirculation has been used in the metal/nonmetal mining industry for energy savings when heating and cooling air, in undersea mining and for increasing airflow to mining areas. For safe and effective use of controlled district recirculation, adequate airflow to dilute contaminants must exist prior to implementation, ventilation circuit parameters must be accurately quantified, ventilation network modeling must be up to date, emergency planning scenarios must be performed and effective monitoring and control systems must be installed and used. Safety and health issues that must be considered and may be improved through the use of controlled district recirculation include blasting fumes, dust, diesel emissions, radon and contaminants from mine fires. Controlled recirculation methods are expected to become more widely used as mines reach greater working depths, requiring that these health and safety issues be well understood. The U.S. National Institute for Occupational Safety and Health (NIOSH) conducted two controlled recirculation tests over three days at a Wyoming trona mine, utilizing an inline booster fan to improve airflow to a remote and difficult-to-ventilate development section. Test results were used to determine the effect that recirculation had on air qualities and quantities measured in that section and in other adjacent areas. Pre-test conditions, including ventilation quantities and pressures, were modeled using VnetPC. During each test, ventilation quantities and pressures were measured, as well as levels of total dust. Sulfur hexafluoride (SF6) tracer gas was used to simulate a mine contaminant to monitor recirculation wave cycles. Results showed good correlation between the model results and measured values for airflows, pressure differentials, tracer gas arrival times, mine gasses and dust levels.

Jan 1, 2013

By K. T. Brashear

Since the MINER Act of 2006, the minimum static load of in-situ underground mine seals has been increased from 20-psi to either 50-psi if monitoring is conducted or 120-psi if left unmonitored. These minimum strength requirements in seals must be designed, built, and maintained throughout the lifetime of the seal. Due to this, it has become necessary to assess the effectiveness of non-destructive testing (NDT) technologies to determine seal integrity, which in this case, are explored using sonic waves and tracer gases. Through both small and large scale testing, two NDT methods will be evaluated for their abilities to determine integrity of the seal. A sonic wave technique to observe a change in wave velocity to identify faults within the seal material. As a NDT method, tracer gases may be used as a potential indicator of a connection between both sides of the seal material through a series of faults and cracks within the material itself. This paper reviews the history of underground mine seals and discusses the overall assessment of sonic waves and tracer gases to serve as NDT methods for estimating the integrity of these seals.

Feb 23, 2014

By Jeffrey Peterson, John Beesley, Martino Scialpi, John Cassidy

The DC Clean Rivers Project is DC Water's ongoing program to capture and treat combined sewer overflows (CSOs) during rainfall before they reach the District waterways. The Anacostia River system was designed to reduce CSOs into the Anacostia River and includes the Blue Plains Tunnel, Anacostia River Tunnel, First Street Tunnel, and Northeast Boundary Tunnel. A portion of the Anacostia River system was commissioned in March 2018 and the final component, the Northeast Boundary Tunnel, was placed in operation on September 15, 2023. This paper provides a summary of the experience gained during construction of this +$2.9 billion project, an overview of the system performance since its activation in 2018, and a look-ahead to the next phase of the DC Clean Rivers program: the Potomac River Tunnel.

Jun 23, 2024

By Judson C. Higgins

The paper addresses changes in surface transportation methods in the Industrial Minerals business starting with history, the changes to present time including such areas as energy costs, improved highways, changes in regulations and deregulation, and attempts to project future transportation trends. Transportation methods such as rail, piggyback, truck and barge are compared, and their impact on Industrial Minerals producer's costs and profits examined. The customer impact on our businesses due to deregulation is also discussed.

Jan 1, 1983

By P. Zhang

This paper gives a review of promising technologies for phosphate processing, and covers flotation, analysis and process control, as well as tailings treatment and utilization. Air bubbles of less than a µm in size, combined with relatively large bubbles, have been demonstrated, both in the lab and on a pilot scale, to improve flotation dramatically, by reducing reagent use while improving product grade. Innovative use of polymers has allowed rapid dewatering of fine tailings with a final product that does not segregate. The first online laser-induced breakdown spectroscopy (LIBS) analyzer was created, allowing rapid analysis of wet samples using the laser technology. Many large commercial projects are successfully pursuing the utilization of phosphogypsum.

Feb 1, 2012

By W. G. Pariseau

"BACKGROUND The Crandall Canyon Mine (CCM) is located in the Wasatch coal field in central Utah. Extensive longwall mining at CCM preceded a decision to recover coal left in barrier pillars on each side of a set of main entries extending far into the mine. During mining in March, 2007, a major bump occurred that led to cessation of mining in the barrier pillar on the north side of the mains and to begin mining in the south barrier pillar. Subsequent loss of ground control in August, 2007, through coal pillar bursts had tragic consequences with loss of six miners and shortly afterwards three rescue team members. An MSHA report describes the events in detail (MSHA, 2008). An important lesson to be learned from CCM is the need to select a computer program suitable for pillar design. Computer programs are engineering tools; selecting the right tool for the job is essential. In this regard, a minimum program requirement is capability for computing stress distribution within a pillar and adjacent roof and floor strata. The reason is simple: strength of rock is stress dependent; both vary from point to point in pillars and adjacent strata. Preferably, one should follow the evolution of stress as the mining plan is executed from start to finish to assure safety or to warn of a potentially hazardous situation developing as mining progresses. The approach to the problem posed by barrier pillar mining at CCM is conventional in the sense of applying well known finite element modeling techniques to analysis of a proposed mining plan. The engineering purpose is to evaluate the mining plan with respect to ground control questions including roof, floor and pillar safety. Results of previous two dimensional finite element analysis indicated pillar safety was by no means assured (1, 2, 3). Geometry of barrier pillar mining is limited in two-dimensions, for example, crosscuts are not seen in vertical cross sections. While three dimensional analyses are preferred, even moderately sized regions often lead to very large problem sizes that exceed computer capabilities. However, a recent development in finite element modeling of tabular deposits allows for whole mine analysis in three-dimensions. This technique involves a dual node – dual mesh concept. Both have been used separately in much earlier work, but are only now are used in combination. Estimation of subsidence at a kilometer scale and details of stress, strain and displacement about barrier pillars, main entries and pillars, and so on at a meter scale are possible (4). No compromise involving empirical formulas or similar guess work is required. Indeed, all calculations are based on first principles: physical laws, kinematics, and material laws. Effects of joints and in situ variability or uncertainty in strata properties, elastic moduli and strengths, may be included for greater realism. An important objective of the present study is to assess the role of three-dimensional pillar geometry in arriving at conclusions regarding barrier pillar mining versus two-dimensional results."

Jan 1, 2015

By L. B. Hales

December 3, 1972, James Wm. White presented the results of an instrumentation and process control survey which was sponsored by the Anaconda Company at the annual Tucson Subsection AIME meeting.(1) Twenty-six responses were obtained from questionnaires sent to 48 operating plants throughout the world. The survey results were discouraging in that there were more failures and problems than examples of success. The following quotes are taken from the text of the paper. "We run our mill by the seat of our pants." 'If these blue sky Ph.D.'s (in the instruments and controls area within research) had some operating experience they wouldn't make a lot of the suggestions they do."

Jan 1, 1981

By Louis H. Meece

The romance of the River lives on in the tales of Mark Twain; and many Americans still think of the Mississippi River in terms of the steamboats loaded with passengers, gamblers and cotton. Yet for many years, coal has been a major cargo on the American waterways. Currently, about 100 million tons a year of coal is handled in some part of its journey from mine to destination by barge. The bulk of this traffic has been on the Ohio River System and the Upper Mississippi River System in years past. Now we have a new entry. Over the past 10 years various movements of coal have developed down the Mississippi River to power plants at Memphis and along the Gulf Coast, and a small amount of metallurgical coal has moved down the Mississippi River for export to Japan since 1970. But in 1980 a brand new player came on the scene. 1980 was a momentous year for the American coal business. Historically, we have exported about 50 million tons a year of metallurgical coal to the world's steel mills. Just before and after World War I, we also had a fairly healthy export trade in steam coal; and again in the late forties, we supplied large amounts of coal to Europe until domestic production could recover from the ravages of World War II. But since the early fifties, the name of the export game has been metallurgical coal. Starting in the mid seventies, something began that was almost totally missed by the American coal industry; and that was the growth in the use of coal first in Europe and now in the Far East as a steam product and as an alternative to petroleum products. As these world coal markets began increasing, the U.S. at first was thought to be noncompetitive because ocean rates were still very low. For example, as recently as 1977, Australian coal could be moved all the way from Australia to the Gulf Coast for $12.50 per metric ton. Coal exporting countries were Poland, Australia and South Africa, except for the continuing exports of U.S. high quality metallurgical coal. But then came the second oil shock, and all of the sudden that $12.50 rate from Australia to the U.S. Gulf became $25.00. And then suddenly and almost unrecognized by the American industry, American coal was in fact competitive at overseas destinations because of the drastic change in trade patterns brought on by the doubling and tripling and quadrupling of bunker fuel prices for ships.

Jan 1, 1982

By Barrie A. Wigmore

There are two aspects of financing western coal development -- whether there is going to be enough money to finance the prospective large development of the industry, and the specific techniques of raising money for that development. To take the first question of whether there is going to be enough money around to finance your industry, I think it is quite clear that the restrictions on the development of western coal are going to be non- financial. Environmental impact problems are creating the greatest delay in coal mine development, at the moment; but getting enough personnel, mining equipment, railroad equipment, and failure of the Department of Interior to act on leasing federal coal lands all appear likely to create significant bottle- necks in the development of western coal -- larger bottlenecks than financing. Financing appears straightforward for the industry. There are many projections of the financing required to meet Project Independence goals. The National Academy of Engineers estimated that development of 500 million tons per annum of western coal would be necessary by 1985 to meet the Project Independence goals which might require $20 billion of capital spending. It is generally agreed that 500 million tons a year is not a realistic possibility. Carl Bagge?s estimate of production of 250 million tons a year by 1983 appears a more reasonable projection. Development

Jan 1, 1976

By Barbara B. Newlin, Emily Rosenberg, Marianne Snedeker

Whose longwalls perform best in Eastern underground mines? What is the latest legislation affecting slurry pipelines? What are the trace element constraints on magma genesis? How can process set points be controlled more economically without affecting product quality? Where can I get a paper presented at the Australian Coal Preparation Conference? If answers to questions like these can help with your management decisions, exploration plans, or market positioning, your firm should know about Information on Demand. Information on Demand, Inc. (IOD) is a research service available to SME members to help them get the facts needed to develop business plans. IOD can function as a research staff and data bank specialist for geologists, planning specialists, production managers, and engineers in all levels of the mining industry. Just dial 415-549-3259 and ask IOD for a copy of an obscure article, a comprehensive literature search, or a background report on a company, a process, or a product. Within a short time, IOD will have the information you need delivered to your office or worksite. Information on Demand has a bank of dial-up terminals that provide access to more than 200 business and technical data bases, including Lockheed's Dialog, CompuServe, InfoLine, The New York Times Information Bank, and other systems. These data banks contain more than 95% of the world's technical literature published in the last 10 years. There is no input required from individuals or companies. The data bases are maintained by publishers and are constantly updated with abstracts of articles, reports and reviews, and other text appearing in more than 5,000 engineering publications, as well as thousands of other trade and technical publications. The data bases are organized by subject and offer a speedy comprehensive survey of world literature. One data base, called Compendex, provides worldwide coverage of engineering publications, meetings, and reports. The Metadex data base abstracts literature on the science and practice of metallurgy, and can be accessed by commercial, compositional, and numerical alloy designations. PatSearch and Claims data bases enable IOD to determine what patents have been filed by a given entity, what international patents are equivalent to a US patent, and other vital patent information. In the non-technical arena, the Commerce Business Daily has daily updates of federal procurement information. The Federal Register is abstracted on-line in a data base, and ABI/Inform is a data base full of marketing and management information for all industries. IOD offers a free pamphlet listing these and other data bases. A typical literature search from IOD will produce 60-200 references with abstracts, and can be printed out off-line and mailed or transmitted directly to an electronic mailbox. Abstracts will often give all the information needed by the reader. At times, when the complete article or technical report is needed for further study, IOD will send a photocopy of the full text for a small additional fee. Patents, books, securities exchange filings, standards, and specifications can also be supplied by means of IOD's network in major libraries, such as Harvard, MIT, and The Library of Congress. A technical translation service is available for foreign

Jan 12, 1983

By A. Noble

For the past 30 years, process flowsheet design has been accomplished largely through modeling and simulation. This approach provides circuit designers the freedom to test various separation approaches while minimizing physical and human resource requirements. The Limn® software provides a unique approach to process simulation, through a Microsoft Excel interface. While the software comes with standard process models for numerous unit operations, the Excel calculation environment and the accompanying VBA platform provide a convenient interface for custom model integration, even for non-experienced programmers. This feature is especially useful for university students in introductory process modeling and simulation-assisted flowsheet design courses as well as experienced practitioners with proprietary process models. This paper shows how the Limn® software may be used to solve basic process engineering problems as well as more comprehensive circuit design challenges. Industrial examples as well as opportunities for training and education are presented.

Feb 23, 2014

By Randall J. Weege

Nickel laterites throughout the world are similar in their gross aspects, but vary significantly in detail. The deposits occur in two separate and distinct geologic settings --those formed over ultramafic rocks which were mechanically emplaced, and those formed over ultramafic rocks that were intruded as melts. The source of the primary nickel in the parent rock may occur both as ionic replacement in silicate lattices and as nickel sulfides. Factors controlling the degree of laterization and nickel enrichment are dependent upon the parent rock characteristics as well as chemical and climatic conditions. Two chemically and physically distinct zones (oxide and saprolite) are commonly present in the laterized rock, but one or the other may be extremely thin or absent. Cobalt and copper may be present in recoverable amounts. Geologic, geophysical and geochemical methods are all utilized in exploring for these deposits. These methods are compared, evaluated and illustrated in the paper. Drilling patterns and ore reserve calculations are also discussed. In contrast to many ore deposits, processing costs are much higher than mining costs. The most efficient processing method is directly dependent upon the chemical composition of the ore. This variation in the chemical and physical characteristics of nickel laterites requires a detailed test program of the metallurgical response to representative samples and blends of ore. Detailed laboratory and bench-scale metallurgical tests are necessary prior to a full scale pilot plant test.

Jan 1, 1978

By P. Eger, D. Green

"The Soudan Mine was Minnesota’s first iron mine, operating from 1882 to 1962. The mine was donated to the State of Minnesota in 1963 and became a state park in 1965. The mine discharge contains elevated copper and cobalt concentrations and has been treated with an ion-exchange-resin-based system since 2009. The system includes flow equalization tanks, bag and cartridge filters, a carbon tank and two commercial ion exchange tanks. Although effective, the system’s high cost, inefficient removal of suspended material and substantial maintenance have been ongoing and troublesome issues.In November 2012, we initiated a pilot test using a peat-based sorption media. This media is produced from raw reed-sedge peat through a patented, low-temperature carbonization process that produces a hardened granular sorption material. The granules are uniform, have high hydraulic conductivity and maintain the high metal affinity of natural peat.Mine water was pumped through the peat-based sorption media without any pretreatment. Copper input concentrations typically ranged from 30 to 60 µg/L but increased to a high of 364 µg/L in the summer of 2013. Since startup, more than 60 million L (16 million gal or 32,000 bed volumes) have been treated, with average removal rates of 75 percent for particulate copper and 60 percent for dissolved copper. Backwash is required at about 4,000 bed volumes, but with a combination of air sparging and high-flow backwash, the suspended material is removedfrom the media.One tank of the peat-based sorption media was found to remove copper similarly to the first four components of the existing system. By reducing size and complexity, reductions in operation and maintenance costs are possible. A comparison of the estimated costs indicate that replacing the four initial components with the single media tank has the potential to reduce annual operating costs by more than half from around $163,000 to $70,000."

Jan 1, 2015

By A. A. Zatout, G. H. Sedahmed, T. M. Zewail, M. H. Abdel-Aziz, B. S. Ibrahim, E-S. Z. El-Ashtoukhy

In this work, the possibility of intensifying the cementation process in stirred vessels was studied by using the perforated baffles as turbulence promoters; the cementation reaction of Cu+2 on Zn was selected as a model. Zn was used in the form of a sheet lining the inner wall of an agitated vessel. Parameters considered are initial concentration of Cu+2, solution temperature, impeller rotation speed, and impeller geometry. Within the present range of parameters studied, the rate of cementation was found to increase with increasing initial concentration of Cu+2, solution temperature, and impeller rotation speed. At the same rotational speed, a flat turbine gave a higher rate of cementation than a 45° pitched turbine. The present suggested that baffles’ geometry gave superior performance in terms of mass transfer of copper cementation compared to the conventional baffle geometry. All parameters that affect the rate of cementation were correlated in the form of dimensionless equations suitable for the design and performance prediction of the agitated vessel. Potential applications of the obtained results in the field of hydrometallurgical processes and wastewater treatment were discussed.

Jan 12, 2021

By P. T. Bissert, T. J. Lutz, J. A. Yonkey, G. T. Homce

"Underground refuge alternatives require an air source to supply breathable air to the occupants. This requires pressure relief valves to prevent unsafe pressures from building up within the refuge alternative. The U.S. Mine Safety and Health Administration (MSHA) mandates that pressure relief valves prevent pressure from exceeding 1.25 kPa (0.18 psi), or as specified by the manufacturer, above mine atmospheric pressure when a fan or compressor is used for the air supply. The U.S. National Institute for Occupational Safety and Health (NIOSH) tested a variety of pressure relief valves using an instrumented test fixture consisting of data acquisition equipment, a centrifugal blower, ductwork and various sensors to determine if the subject pressure relief valves meet the MSHA requirement. Relief pressures and flow characteristics, including opening pressure and flow rate, were measured for five different pressure relief valves under a variety of conditions. The subject pressure relief valves included two off-theshelf modified check valves, two check valves used in MSHA-approved built-in-place refuge alternatives, and a commercially available valve that was designed for a steel refuge alternative and is currently being used in some built-in-place refuge alternatives. The test results showed relief pressures ranging from 0.20 to 1.53 kPa (0.03 to 0.22 psi) and flow rates up to 19.3 m3/ min (683 scfm). As tested, some of the pressure relief valves did not meet the 1.25 kPa (0.18 psi) relief specification.IntroductionThe Mine Improvement and New Emergency Response Act of 2006 (MINER Act) was enacted in the United States in the wake of three mine explosions/fires that claimed 19 lives that year. Intended to help improve underground coal mine accident preparedness, the MINER Act includes provisions that target mine safety issues in areas such as emergency response planning, adoption of new technology, training and education, and mine safety standards enforcement (U.S. Mine Safety and Health Administration, MSHA, 2006). Section 13 of the MINER Act specifically directed the U.S. National Institute for Occupational Safety and Health (NIOSH) to provide for research into the effectiveness and viability of refuge alternatives for underground coal mines. This mandate culminated in the 2009 adoption of changes to Title 30 of the Code of Federal Regulations (30 CFR) mining health and safety regulations, requiring underground coal mines to provide mine emergency refuge alternatives and associated components, to provide a life-sustaining environment for persons trapped underground. Such refuge alternatives can be either self-contained mobile units or built-inplace facilities. The regulatory changes also include provisions establishing requirements for MSHA approval of refuge alternatives and their components, and among these provisions are numerous criteria for providing a safe breathable atmosphere under positive pressure within the refuge alternatives. One specific criterion for maintaining a safe refuge alternative atmosphere requires the inclusion of an air pressure relief valve that will activate at a maximum of 1.25 kPa (0.18 psi), or at a pressure above mine atmospheric pressure, in the refuge alternative, as specified by the manufacturer when the breathable air is supplied by a fan or compressor (MSHA, 2008)."

Jan 3, 2018

By D. C. Torre

Ever since the early '60's there have been efforts to develop and produce reliable continuous haulage systems capable of taking the full output of a continuous miner and transporting it, in one continuous flow, from the face to the tipple. The majority of the continuous haulage systems which have been most successful to date were placed in operation in the early '70's and were all of the bridge conveyor type, usually consisting of bridges and mobile bridge carriers attached at the inby end to the continuous miner and at the outby end to the panel conveyor itself. These successful bridge conveyor type continuous haulage systems were, and continue to be, either of the belted or chain type. Undoubtedly, the most successful belt type continuous haulage systems are those manufactured and marketed by the Long-Airdox Company. Until early 1977, the most successful chain conveyor type haulage systems were manufactured and marketed by Jeffrey Mining Machinery Division. In 1977, Long-Airdox reentered the market with a chain type system to complement its belted system. I say "reentered" because the original bridge type continuous haulage system was introduced to the coal mining industry in the early '60's by the old Long Company, a predecessor of the current Long-Airdox Company, and those original units were of the chain conveyor type.

Jan 1, 1981