Search Documents

By Gabriel Esterhuizen

Observations of pillar conditions in limestone mines showed that the presence of weak bands in the limestone can result in pillar damage at stresses that are lower than one would otherwise expect. The objective of this National Institute for Occupational Safety and Health study was to investigate the mechanism of failure caused by the presence of weak bands by using a series of numerical models based on realistic physical properties. The effect of the weak bands on pillar strength was also investigated by developing a series of pillar models with different width-to-height ratios and determining their strength by simulating a servo-controlled loading condition. The material properties of the bands and the limestone were varied and their effects on pillar strength were determined. Model results demonstrated failure development similar to the pillars observed in the field. The weak bands were seen to develop tensile stresses in the limestone as they extrude under increasing stress. The limestone fails in tension at a much lower stress than its expected uniaxial compressive strength. The results showed the load bearing capacity of the pillars can be reduced significantly by the presence of multiple thin weak bands. The degree of strength reduction is largely dependent on the compressive strength, the frictional resistance and the thickness of the weak bands. Single weak bands do not affect pillars as severely as multiple bands. However, the model results show that a single thick weak band, which comprises more than about 2 percent of the pillar height, can cause a significant reduction in pillar strength. The weakening effect of the bands become less severe as the pillar width-to-height ratio is increased. Field observation of spalling and failure associated with weak bands in limestone pillars show that the failure mechanism in the models resembles the observed failure. The model results provide insight into the important factors affecting pillar strength in the presence of weak banded materials.

Jan 1, 2007

By Sidney Katell

This study estimates capital investment, operating costs, and selling prices for four underground bituminous mines producing coal with annual production ranging from 1.06 to 4.99 million tons. It is assumed that the mines have a 20-year life. Wages and union welfare payments are considered as of November 12, 1973, under the Bituminous Wage Agreement of 1971, and costs for material and equipment are based on 1973 indexes. Initial capital investment ranges from $12,540,700 for the 1.06-million-ton-per-year (MM tpy) mine to $44,720,500 for the 4.99 MM tpy mine. Total capital investment ranges from $21,850,700 to $75,693,500 for the same mines. Corresponding selling prices for the coal range from $8.76 to $7.53 per ton, assuming a 12-percent discounted cash flow rate of return after Federal income taxes.

Jan 1, 1974

By A. B. Hooker, J. W. Paul

"There was a time when any suggestion that the Davy flame (safety) lamp be discarded, would have evoked unlimited, criticism. However, that time is past.Investigations both here and abroad have shown conclusively that the Davy lamp does not have the necessary factor of safety against ignitions of mine gas, and England, the lost stronghold of the Davy lamp in Europe, has eliminated this lamp and substituted safer types.In the United States there are companies who still use the Davy lamp in spite of all that has been said and published as to the dangers connected with its use.Recently the purchasing agent of an anthracite coal company requested the Department of the Interior, Bureau of Mines, to pass upon the safety of some braise gauzes for use in a shielded Davy lamp. A shielded Davy lamp is an ordinary Davy safety lamp equipped with a circular brass shield that is attached to the lamp posts. This shield extends about one-half way around the gauze and one-half of the gauze height. The main purpose of the shield is to prevent the lamps being extinguished by a sudden increase in the velocity of the air current past the lamp.The brass gauzes submitted for this test represented two grades of brass - a yellow brass and a red brass. The analysis of these brasses was not determined. Two shielded Davy lamps that were submitted for the tests each had a steel gauze. These steel gauzes were also tested. Tests were made in horizontally moving mixtures of Pittsburgh natural gas and air at velocities of 400 to 1,000 feet per minute. The gas percentages used were 7%, 8.6%, and 11%. Tests were made with the lamp shield in two positions relative to the lamp and direction of flow of the gas-and-air mixture. In one position the shield was between the gauze and flow, as normally used. In the other position the shield was on the downstream side of the lamp. The tests were continued until one or more failures or gas explosions been obtained with each of the six gauzes. The results of these tests summarized as follows:"

Jun 1, 1923

The first metal-mine accident-prevention course was prepared and published in 1942-45 as a series of seven miners' circulars (Nos. 51-57). The scope of the course has been broadened, revised, and brought up to date and is being published as a similar series of seven miners' circulars (Nos. 51-57, revised) on accident prevention in metal and nonmetallic mines. These circulars are: Accident Statistics (Miners' Circular 51), dealing with general statistics on accidents and injuries at metal and nonmetallic mines, including causes, costs, and the use of investigations and reports of all accidents.

Jan 1, 1957

By A. H. Cronk

This paper is one of a series being prepared by the United States Bureau of Mines on mining methods and costs in the different mining districts. The mining methods described in this paper are employed by one of the large mines in the Illinois fluorspar district. The mine is located at Rosiclare, Ill., and shipments are made over the Illinois Central Railroad: and by barge on the Ohio River.

Jan 1, 1930

By V. F. Parry, J. B. Goodman

The low-rank coals containing 10 to 50 pet natural bed moisture represent over half of the tonnage reserve of the available solid fuels of the United States, but only about 2 pet of United States coal production is derived from these fuels. Increased utilization of these large reserves will result if the bed moisture can be removed at the mine in high-speed low-cost processes. This paper presents a theoretical and experimental study of the factors affecting high-speed drying of coal dusts. The time required to heat particles of coal is proportional to the square of their diameter, and it is calculated that the probable time in minutes is equal to 6D2. In other words, a 11 a in. coal particle should be heated to drying temperature in 1.5 to 2.0 sec. Likewise, 1/8 in. particles should be heated in about 6 sec. The net heat required to dry subbituminous coal and lignite varies from 240 to 375 Btu per pound, depending upon the moisture removed, and this heat can be obtained from 42 to 61 cu ft of hot gases at 600°F.

Jan 1, 1949

By R. J. Wensley

THE use of small substations for the supplying of 275-volt energy to the locomotive and cutting machines in coal mines is a well-established practice. A few years ago, when labor costs were lower, these substations were located as near to the load as possible, and an operator was provided for each station. This practice has now become so expensive that substations are being located with reference to other mining machinery, such as hoists or pumps, so that one operator can look after both. Some-times the substation is operated by one whose duties make him traverse quite a large area. In such cases the interruption of alternating-current supply may produce a long interruption in the direct current, as the station cannot resume service until this man reaches it. Such interruptions interfere seriously with production and may easily counterbalance the supposed saving gained by such operating methods. The grouping of substations for convenience in operating may also result in excessive copper loss and consequently poor trolley voltage, with its attendant evils of low locomotive speeds and increased locomotive motor maintenance. The speed of the coal-cutting machines will also be reduced. By relieving the substation of its, burden of the operating labor cost, the most economical location, from an electrical standpoint, may be chosen. The matter of machine insurance should also be considered. If an attendant is caring for several kinds of equipment, he cannot watch the machine continually for signs of trouble; therefore, continued overload, phase failure, low alternating-current voltage, bearing trouble, etc. may result. Some partly automatic equipments have been installed; these have protection against low voltage, reverse current, and bearing trouble and are provided with automatic reclosing circuit breakers. This is a step in the right direction but it does not go far enough to give first-class machine insurance.

Jan 9, 1921

By F. Ernest Brackett

Much new data on the flow of gases have been discovered by recent experiments by the United States Bureau of Mines and others. Although additional investigation is still desirable, the information now collected seems sufficient to attempt a tentative coördination of the friction factors. This study is confined entirely to fluid friction when the density throughout the duct is so nearly constant that it may be so considered. In the subsequent discussion the following notation is used: v = mean velocity of fluid in duct, feet per second. v' = mean velocity of fluid in duct, meters per second. R = hydraulic radius of duct, feet. R' = hydraulic radius of duct, meters. S = the hydraulic slope. P = pressure absorbed by friction, pounds per square foot. p = pressure absorbed by friction, pounds per square inch. p' = pressure absorbed by friction, kilograms per square centimeter. A = sectional area of duct, square feet. O = perimeter of duct, feet. L = total length of duct, feet. L' = total length of duct, meters. d = diameter of a cylindrical duct, inches. w = density of the fluid, pounda per cubic foot. g = specific gravity of the fluid compared with water = w % 62.4. C, k and B, coefficients for formulas using English measures. C' = metric coefficient, v' = C'R'S. n = coefficient of roughness for English or metric units. The basic formula for the flow of all fluids at constant density appears in the three following forms, which may be denominated: (a) The slope formula, v = CRS (b) The ventilation formula, " n = (c) The pipe formula, C is Kutter's coefficient, which is extensively applied to the flow of water in ducts and channels of all kinds; E is Atkinson's coefficient, used principally with air in ventilation problems; B is a coefficient conveniently adapted to studying the flow of water, gases and vapors in pipes. 312

Jan 1, 1927

By Fred V. Seibert

The Functions and the Responsibilities of the Institute The Canadian Institute of Mining and Metallurgy is unique. ln addition to the welfare of its members, it has a real interest in the welfare and promotion of one of Canada's largest and most important basic industries. It is because of this that the membership is composed of both individual and corporate members. The individual members are both technical and non-technical (Members and Associates). Both Members and Associates have the same status in the Institute and all are interested in the welfare of the mineral industry. The aims and objects of the Institute 11re twofold. The education and welfare of its individual members and the sound promotion and welfare of the mineral industry. Perhaps it might be well if we reviewed these aims and objects as stated in our Constitution: "First - To promote the arts and sciences connected with the economical production of valuable minerals and metals, by means of meetings for the reading and discu11ion of technical papers, and the subsequent distribution of such information as may be gained throo.gh the medium of publications". It cannot be denied that we have do ne a good job in this particular phase of our work. Nevertheless, there is still room for improvement. It has been suggested that we might have more discussion and, on occasions, more criticism of our papers and programmes. This can best be done if the authors will have their papers prepared in sufficient time to permit of preprints being made availa1ble before the meeting at which they are to be presented.

Jan 1, 1950

By Donald Bruce

The three types of specifications which are used for micropile work are: ? Performance Specifications: The contractor is permitted control over certain design and/or construction procedures but must demonstrate to the owner through testing and/or certification that the final product meets the specified performance criteria. This method allows and encourages the contractor to provide a competitive and/or innovative micropile design within the framework of the overall design requirements. The responsibilities for the work are shared between the owner and the contractor. ? Open Specifications: These leave the scope and design of the installation up to the micropile contractor. This method is the most common for securing bids on temporary micropile work. The responsibility for design and performance is clearly placed on the contractor. Open specifications are not recommended for permanent applications. This method allows the contractor to select the most economical micropile system. ? Prescriptive Specification: The Owner describes specific procedures that must be followed, but which may not necessarily describe the objective of the work. When prescriptive specifications are used, the owner is responsible for the proper performance of the system. The contractor is responsible for satisfying the details of the specifications. Performance specifications are the most common and best reflect the challenges and interests of micropile technology and applications.

Jan 1, 2004

By Joint Micropiles Committee

"The three types of specifications which are used for micropile work are: • Performance Specifications: The contractor is permitted control over certain design and/or construction procedures but must demonstrate to the owner through testing and/or certification that the final product meets the specified performance criteria. This method allows and encourages the contractor to provide a competitive and/or innovative micropile design within the framework of the overall design requirements. The responsibilities for the work are shared between the owner and the contractor. • Open Specifications: These leave the scope and design of the installation up to the micropile contractor. This method is the most common for securing bids on temporary micropile work. The responsibility for design and performance is clearly placed on the contractor. Open specifications are not recommended for permanent applications. This method allows the contractor to select the most economical micropile system. • Prescriptive Specification: The Owner describes specific procedures that must be followed, but which may not necessarily describe the objective of the work. When prescriptive specifications are used, the owner is responsible for the proper performance of the system. The contractor is responsible for satisfying the details of the specifications.Performance specifications are the most common and best reflect the challenges and interests of micropile technology and applications.The owner, designer and contractor will together be responsible for the tasks associated with the design, installation, acceptance, and performance of the micropiles. The installation of micropiles requires specialized equipment, techniques, and appropriate workmanship. Not every detail of the work can be specified, and not every potential problem can be anticipated. Therefore, a contractor who has demonstrated experience in micropiles must be selected to execute the work required."

Jan 1, 2004

By T. W. West

During the design and construction of a coal preparation facility, there are many items that can cause serious problems if not properly handled in the early stages of a project. These problems can be a detriment to smooth owner/ contractor relationships, the designing of a flow sheet, the selection of equipment, the design of the facility, the maintenance of schedule and budget, and a smooth start-up. It is the purpose of this presentation to identify some of these problems and to suggest steps that can be taken to reduce or eliminate their impact.

Jan 1, 1977

By Joan C. Biordi

A molecular beam-mass spectrometer-low pressure flat flame apparatus has been constructed for the purpose of examining the chemical microstructure of normal methane-oxygen-argon flames and those inhibited with Halon extinguishants. Details of construction and performance of this apparatus and of related flame temperature measurements are given. Particular attention is paid to the empirical characterization of the perturbation to the flame caused by the sampling probes. The composition profiles obtained for normal flames are compared to those of flames inhibited by CF3Br. In addition to the usual stable species (CH4, O2, CO, CO2, H2O, H2, and H2CO), the inhibitor, its products and intermediates associated with its reactions could be followed. In particular, hydrogen bromide, bromine atoms, hydrogen fluoride, and carbonyl fluoride were observed. The relatively rapid disappearance of inhibitor and early appearance of fluorinated reaction products suggest a short lifetime for the CF3 radical in this system. Observation of COF2 suggests that CF3Br is effective as an inhibitor, at least in part, by virtue of its interference with the oxygen containing species of the normal chain reaction. Profiles of the 17+ peak at low electron energy suggests that the hydroxyl radical may also be sampled, but the profiles obtained are not yet sufficiently accurate to determine the effect of inhibitor on this important flame radical.

Jan 1, 1973

By Christopher C. Jobes

Computer-aided control of a mining machine requires a guidance system to aid remote positioning of the machine by determining its position and heading. The mechanical position and heading system (MPHS) developed by the U.S. Bureau of Mines provides such navigation information during face maneuvers. This report describes the required theory, which yielded a reliable algorithm for calculating machine position and heading, and implementation of this theory in hardware and software design, which made surface testing of the MPHS possible. Analysis of the errors and test results showed that the MPHS provides reliable results and can, therefore, provide useful guidance information for face navigation.

Jan 1, 2010

The Australian Gas Light. Company was established in 1837, the first gas being sent out from the Kent Street Works, then the headquarters, in 1841. Mortlake Works were opened in 1886, and has since grown to the vast undertaking inspected by members of the Institute.The Kent Street Works were closed in 1921. The area of the, company's property at Mortlake is 117 acres.Some interesting figures from the statistics of the company's activities for 1937 are:-

Jan 1, 1938

By Jay F. Colinet

Longwall mining in lower seam heights may necessitate the use of single-drum shearers to overcome size constraints associated with standard double-drum shearers. To avoid the operational problem of clearance in the tailgate entry with one single-drum shearer, two single-drum machines can be operated on the same face, with each shearer responsible for mining a predefined portion of the face. However, utilization of two shearers on the same face necessitates the positioning of one shearer operator and a jacksetter in the return air of the upwind shearer, thus complicating respirable dust control on the longwall. In an effort to evaluate the unique dust control problems associated with this type of mining, the U.S. Bureau of Mines conducted dust surveys on two multiple-machine longwall operations. Sampling was done to quantify major sources of respirable dust and to identify potential solutions to problem areas. Sampling results indicate that the cutting sequences utilized on multiple-machine faces may have to be designed to minimize dust exposure, as opposed to optimizing productivity or facilitating operational requirements. Also, state-of-the-art dust control techniques typically found on double-drum shearer longwalls must be employed to help minimize the exposure of all face personnel to traditional dust sources.

Jan 1, 2010

By Noel N. Moebs

This report summarizes a U.S. Bureau of Mines study on the application of geotechnology to identify and minimize ground control hazards in talc mining operations in northwest Georgia. The major ground control hazard is pillar sloughing attributed to the steeply dipping orientation of a pronounced foliation in the talc ore body. The sloughing problem, which gradually reduces the effective support area of a pillar through attrition, can be minimized by appropriate artificial support, as determined by a rock classification system, and by a more uniform pillar design. A boundary element model confirmed the advantages of using a uniform pillar design to avoid excessive loads on portions of irregular pillars. Instrumentation to measure roof convergence and pillar loading was installed at selected locations in an active talc mine but failed to detect any significant changes, suggesting that the gneiss hanging wall constitutes a strong roof that probably can support large spans between pillars and permit high extraction ratios. This interpretation also is supported by a rock classification of the hanging wall gneiss.

Jan 1, 2010

By Charles Vaught, Michael J. Brnich, Roberta A. Calhoun

This document contains most of the materials needed to use the exercise. The main part of the document is the instructor's copy. It tells how to use the exercise, presents the objectives, the master answer sheet, the scoring key, and discussion notes to be used following the exercise. The next section summarizes results from field tests of the exercise, and reports the miners' evaluation of the activity. The last part of this document is three appendices. Appendix A is the exercise problem booklet. This booklet can be duplicated locally. The booklets are reusable. One is needed for every person in the classroom. Appendix B is the answer sheet. Copies of this answer sheet must have the latent image (invisible) ink answers that appear in Appendix C printed on them.2 Answer sheets are consumable. One is needed for each person or each small group of persons who work the exercise. Exercise Summary Read this section first. It determines if the exercise is appropriate for your classes. If you choose to use the exercise, examine the table of contents and review the remainder of this document. Type: Latent image Audience: Underground coal miners Length: 9 questions (30 minutes for administration and 30 minutes for discussion) Skills: Mine fire escape strategies/procedures Use of emergency breathing apparatus Knowledge of sensations experienced when wearing breathing apparatus Communication Location: Underground coal mine section, average 60 inch seam height Problem: You are the section foreman on the 17 Left longwall development section at the Paula Ann No. 3 mine. The section has been driven about 4,000 feet from 4 West Mains. One of the shuttle car operators took a call from the fireboss saying that there was smoke from an unknown source coming into your section. You attempt to contact someone to find out where the smoke is coming from but get no response. You assemble the crew and start riding out of the section on the mantrip when you encounter heavy smoke. At this point, you decide to take your crew and travel on foot in the belt entry that is on a neutral split of air. After traveling about 6 crosscuts in the belt entry, you encounter heavy smoke at which time you and your crew don your person-wearable SCSRs (PWSCSR). After donning the apparatus, you and your crew continue traveling outby in the belt entry. Near the mouth of the section, one miner in the group starts to have trouble breathing from his SCSR. Because breathing resistance is increasing with the length of time the apparatus is worn, the miner is "outbreathing" the device since his oxygen requirements are greater that what the PWSCSR can supply. Although you slow

Jan 10, 1999

By C. Feng, W. Song, B. Moudgil, P. Zhang, W. Xiao

Separation of dolomite from phosphate is the most challenging problem in phosphate mineral processing. Over 50% of the future phosphate reserves in Florida contains too much dolomite to process using the current industry practice. The FIPR Institute has collaborated with worldwide experts in the field to address this issue. As a result, the industry is now offered with three feasible options. Optional 1 involves crushing and grinding of high-dolomite phosphate pebbles followed by dolomite flotation at slightly acidic pH using a new collector that does not require phosphoric acid as a phosphate depressant, achieving a final concentrate analyzing less than 0.9% MgO at about 87% P2O5 recovery. Option 2 offers three methods for reducing MgO content in the concentrate from the Crago process, including adding a dolomite depressant in the rougher flotation step, dolomite flotation of the cleaner concentrate, and scrubbing the cleaner concentrate in quartz sand. These methods could reduce MgO content in the final concentrate by 20-40%. Option 3 is a gravity separation technique using an innovative separation jig, and may well be the ultimate solution to the problem. INTRODUCTION Magnitude of the Dolomite Problem With the depletion of the higher grade, easy-to-process Bone Valley deposits, the central Florida phosphate industry has moved into the lower grade, more contaminated ore bodies from the Southern Extension. The phosphate deposits in the Southern Extension may be divided into two zones: an upper zone and a lower zone. The upper zone is readily processable using the current technology, but the lower zone is highly contaminated by dolomite. Geological and mineralogical statistics (Hassan and Bogan, 1994) show (Table 1) that more than 50% of the phosphate resource would be wasted if the lower zone is bypassed in mining, and about 13% of the resource would be wasted if the dolomitic pebbles in the lower zone were discarded.

Jan 1, 2019

By M. Somerville, S. Sun

The liquidus temperature and viscosity of a range of melter slags produced in South Africa were determined. Drop-quench experiments were carried out on the supplied plant samples to determine the liquidus temperature and phase relations at sub-liquidus temperatures. The temperature measurement range covered 1300°C to 1630°C. Results from these experiments show liquidus temperatures for the melter slags to be in excess of 1500ºC with the chromium containing spinel as the primary crystalline phase. At lower temperatures, an olivine or pyroxene phase co-existed with the spinel phase. The viscosity of the slags was determined over a temperature range of 1350 to 1550°C, under a controlled atmosphere. Results show two orders of magnitude variation in the viscosity (0.2 to 20Pa s) with strong effects of slag chemistry and temperature. Slags with lower SiO2and Cr2O3concentrations were more fluid. Slags with the lowest FeOx and highest SiO2concentrations were the most viscous. These observations are in accord with general behaviour of silicate slags. While the presence of a spinel phase may have an effect on the viscosity of the melter slags, results obtained to date indicate a much stronger effect due to the presence of an olivine or pyroxene phase at lower temperatures. Keywords: phase equilibria, liquidus, viscosity, slags, olivine, spinel, pyroxene

Jan 1, 2004