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By Thomas M. Barczak

Longwall roof behavior is characterized by strata displacements in both the face-to-waste (horizontal) and roof-to-f1oor (vertical) direc-tions. The roof support structure provides resistance to this motion by translation of these displacements into vertical and horizontal support loading. Observations indicate that the shield reacts with both a vertical and horizontal force to uniaxial convergence (displacement). However, there are different magnitudes depending on whether the displacement is vertical or horizontal. This makes it possible to use supports as monitors of strata activity and loading. The Bureau of Mines examined this behavior using a linear elastic model of the support structure with two degrees of freedom. Vertical and horizontal load reactions were related to associated displacement actions of the strata. This was done by determining the stiffness of the shield under controlled vertical and horizontal displacement motions in the Bureau's mine roof simulator. This report provides example predictions of strata convergence and isolation of horizontal support loading due to vertical roof convergence using the linear elastic shield model. The report also examines efforts to determine strata behavior by direct measurement of support displacement.

Jan 1, 1987

Capture airborne coal dust generated by a continuous mining machine to reduce workers? dust exposure and to improve face visibility. Approach Develop a low-profile dust collector system which can be mounted on the boom of a continuous miner. How It Works When coal is mined with a milling head continuous miner, a substantial amount of coal dust (respirable and non-respirable) escapes the dust suppression sprays at the cutter head. This can cause poor visibility around the cutting head and can expose the workers to high levels of respirable dust. A practical means of removing this dust is with a scrubber mounted directly on the mining machine. Under a Bureau of Mines contract, a low-profile, machine-mounted dust collector (MMDC) was developed to avoid adding extra height to the continuous

Jan 1, 1983

By M. J. Sapko

The Bureau of Mines conducted laboratory-scale flammability experiments to investigate the possible use of water spray systems for inerting or quenching mine-gas ignitions, such as those encountered at the working face of a coal mine. The inerting results for premixed methane-air-water mixtures indicated that water droplets of less than 10 µm tend to be as effective as the vapor. Water requirements for inerting such mixtures were much smaller than those for quenching the sustained flame propagation by the application of water sprays. The minimum water mass concentration for quenching methane-air flames increased linearly with increasing droplet diameter (surface weighted mean) and decreased with increasing spray temperature, whereas the droplet surface area required per unit volume was essentially constant for a given gas mixture composition. Data extrapolations indicated that a quenching system may be feasible for the longwall mining application.

Jan 1, 1977

By L. B. Pankratz

Low-temperature heat capacities, high-temperature enthalpy increments, and the enthalpy of formation at 298° K were determined calorimetrically for vanadium subnitride (VN0.465). The low-temperature investigation gave S°298.15 = 6.379 ±0.005 cal/deg mole, and a combustion calorimeter investiga¬tion provided ?Hf°298.15 = -31.80 ±0.60 kcal/mole. The two quantities were combined with the high-temperature data to give standard values of enthalpies of formation and free energies of formation above 298° K. These and related thermodynamic functions were tabulated to 1,800° K. Similar data are included in the range of 298° to 1,600° K for the mononitride, VN.

Jan 1, 1971

Provide reasonably priced, reliable fire protection for large walking draglines. Approach Fire hazards on large draglines were analyzed, then appropriate automatic fire sensing and suppression systems developed and in-mine tested. How It Works Five fire hazard areas identified for special attention are: electrical control room, high voltage transformer enclosures, circuit breaker rooms, collector ring/roller path area, and the automatic lubrication rooms. Automatic fire sensing and suppression systems were separately designed for each area. The design of each system was tailored to the hazards and equipment protected. Spot thermal sensing and Halon 1301 suppression were specified for the electrical

Jan 1, 1981

By Maria I. De Rosa

Table 10 and figure 4 show the number of fires and fire injuries occurring at the surface of underground coal mines by state during 199&1999. Table 10 also shows by state the risk rate, employees' working hours, and lost workdays. A total of 65 fires occurred in 10 states. Thirteen of those fires caused 12 injuries and 1 fatality (the yearly average was 6.5 fires and 1.2 injuries). Four fues and one fire injury involved con- tractors. The Ewhr value was 97 x l O6 hr (Irr = 0.025); the LWD value was 6,206. Pennsylvania had the most fues (20 fues and 5 injuries), followed by West Virginia (1 6 fires and 1 fatality) and Kentucky (1 5 fires and 3 injuries). Among these states, Pennsylvania had the highest injury risk rate value (Irr - 0.095). Table 1 1, partly illustrated in figure 5, shows by time period the number of fires, fire injuries, and fire fatalities; risk rates; employees' working hours; and lost workdays. The number of fires and fire injuries show a decrease followed by an increase during the five time periods, accompanied by a decline in employees' working hours throughout the periods (see table 11 and figure 5). The Irr values follow patterns similar to those shown by the injury values. Tables 12- 17 show the number of fires by ignition source, method of detection and suppression, equipment involved, location, and burning material by time period. Figure 6 shows the major variables during 199&1999. Table 18 shows the number of fire injuries per number of fires causing injuries and total fires by year, ignition source, equipment involved, and location.

Jan 1, 2004

By David S. Yantek

A-weighted sound levels around vibrating screens in coal preparation plants often exceed 90 dB(A). The National Institute for Occupational Safety and Health (NIOSH) is actively developing noise controls to reduce noise generated by horizontal vibrating screens. A 121-microphone, 3.5-meter-diameter array was used to perform beamforming to determine locations of significant noise radiation on the screen. Below about 1 kHz, the screen body was found to be the most significant noise source. The beamforming contour maps showed several key locations on the sides of the screen and the feedbox are the most significant contributors. Operating deflection shape (ODS) analysis was used to examine the screen behavior under actual operating conditions. This information is helpful in determining how to modify the screen body to reduce the noise radiated by the screen below 1 kHz. The analysis showed modal vibration patterns on the sides and feed box were the main contributors to noise. The results show several areas on the screen sides and feedbox that can be modified to reduce noise.

Jan 1, 2009

By Robert A. Jankowski

Through laboratory and underground studies, the Bureau of Mines has evaluated the use of passive barriers (dust shields) to help confine dust generated by longwall shearers to the face area. Laboratory studies focused first on selection of the optimum barrier design, which proved to be a simple, gobside barrier (made of conveyor belting), coupled with a headgate splitter arm, which was found necessary to prevent the dust cloud from entering the walkway at the headgate end of the shearer when cutting tail to head. Further laboratory testing was done to determine whether using passive barriers in combination with different water-spray dust-reduction methods, including the shearer-clearer system developed by the Bureau, would improve dust reduction over that from using the water sprays alone. It was found that the combination of gobs ide passive barriers plus the full shearer-clearer system was most effective, and surmised that this would be especially useful in thicker seams. However, underground testing revealed that the shearer-clearer system alone was 35 pct more effective in reducing dust contamination than when used with the gobside passive barriers, and far more effective than using passive barriers with a conventional water spray system. For such an effective system as the shearer-clearer; the reduction in avail-able space over the top of the machine actually impeded system performance; this was shom1 in both eastern and western mines. But when used with comparatively inefficient water spray systems, the passive barriers, used in combination with a headgate splitter arm, provide consider-able help in reducing dust levels in the walkway.

Jan 1, 1986

By G. S. Rice

The recommendations of the Bureau of Mines on rock-dusting practices are embodied, except in a few details, in the Recommended American Practice for Rock-Dusting Coal Mines to Prevent Coal-Dust Explosions,5 approved by the. American Engineering Standards Committee,6 December 30, 1925 It is specified that the dust to be used is of a size that all will pass through a sieve having 20 meshes per linear inch and that 50 per cent or more will pass through a sieve having 200 meshes per linear inch.

Jan 1, 1930

By Wilson Blake

The Bureau of Mines used a mathematical model based on the finite element method of stress analysis to calculate stresses and displacements surrounding an open pit mine in a gravity-loaded rock mass. Comparison of the finite element solution for a semicircular notch in a gravity-loaded plate with the theoretical solution for a semicircular notch in a plate under uniform compression parallel to the free boundary demonstrates the inapplicability of the latter method to openings at the free surface of a gravity-loaded medium. High stress concentrations are formed at irregularities along the boundary of an open pit in a gravity-loaded continuous competent rock; however, for this type of rock the magnitudes of the stresses are too low to be considered a major factor in open pit slope stability. High stress magnitudes will occur if, in addition to the gravity stress field, a large horizontal stress field exists.

Jan 1, 1967

By J. B. Janus

This report, the 25th in a series, lists analytical data of coal samples collected by the Bureau of Mines in connection with the purchase of several million tons of coal for various Government agencies during fiscal year 1975. Tipple samples were collected by Bureau of Mines engineers at tipples as coal was being loaded into railroad cars or trucks. Ultimate analyses are given for these coalbeds only. The delivered coal was sampled at destination in accordance with instructions furnished by the Bureau of Mines, and all samples were analyzed in the Bureau laboratory at Pittsburgh.

Jan 1, 1976

By Paul M. Tyler

Graphite is chemically identical with diamond, both being crystallized allotropic forms of carbon. Graphite obviously differs greatly from diamond in physical properties and is easily recognized by its blackness, its softness (1 to 2 on Mohs' scale), and its slick feel when rubbed between the fingers. Strictly speaking, all graphite is crystalline, but grades in which the individual grains cannot be distinguished with the naked eye are commercially classed as amorphous. Natural mixtures of the two varieties occur in all proportions, and the classification of a given sample as "amorphous" or "crystalline" graphite is based largely upon trade practice. Until recently different varieties of vegetable or animal charcoal, lamp black, soot, gas carbon, and coal ware considered strictly amorphous, but modern examination by X-ray methods indicates that even these materials possess the same internal crystalline structure as graphite, differences in physical properties being perhaps explained by porosity or presence of combined hydrogen or other impurities.

Jan 1, 1941

By D. Harrington

Research in connection with occupational diseases, including silicosis or, more definitely, pneumoconiosis, has been prosecuted much more actively in North American countries during the past 5 or 10 years than in any other known period. This applies particularly to the United States, owing largely to the fact that in recent years compensation for ill health presumed to be caused by industrial work of certain kinds is being paid to a far greater extent in this country than previously. Most other countries have had occupational-disease laws for many years. Court rulings in the United States, which started 5 or 6 years ago, have given a few heavy verdicts in connection with ill health or death caused, or alleged to have been caused, by some phase of occupational work other than traumatic injury, and these have called attention to the fact that ill health and even incapacitation can be caused by some kinds of employment. With the onset of the world-wide financial depression, which resulted in permanent abandonment of many business or industrial enterprises (among them mines) in the United States, the workers frequently believed that they could expect nothing in the future from their former employers, hence they felt free to demand monetary benefits or damages because of ill health which they suffered, or thought they suffered, because of their previous employment. The result was a flood of lawsuits and. compensation claims for occupational disease, particularly where dust was involved.

Jan 1, 1938

By John Gross

The modern practice of grinding ores so that often 80 per cent or more of the product is finer than 200 mesh makes it desirable to supplement sieve sizing so as to extend considerably the range of sizing. Moreover, the fact that the material finer than sieve size represents the major part of the work done in grinding emphasizes thick need in can investigation of crushing efficiency. A method based on the settling rate of particles in grater appeared to be most practical for sizing; finely ground ores. There are two possible methods of utilizing this principle: one based on free settling or sedimentation; and the other on separation by means of a rising; current of water, or elutriation. In sedimentation, mechanical entanglement causes material at the start to settle in a mass, and this persists throughout. As this feature is largely eliminated by elutriation, which permits a comparatively clean separation of the various sizes, the elutriation method was adopted.

Jan 1, 1929

By D. B. Dow

"Natural gas-gasoline is made by collecting in the liquid state the condensable hydrocarbon vapors that exist in different natural gases in varying amounts. In the richer type of natural gas the gasoline is generally recovered by compression and cooling. If exceedingly high pressure or low temperature is used, there is dissolved in the gasoline a large amount of very volatile material, which evaporates rapidly at atmospheric temperature and pressure.In the leaner type of natural gas, the gasoline vapors are selectively absorbed from the permanent gases by passing the natural gas through an absorbing oil. The gasoline is recovered by distilling the saturated oil, and as compared with ""compression"" gasoline is of high Baume' gravity and low vapor pressure. Before a volatile gasoline can be transported in tank cars, it is necessary to decrease its volatility in order to lessen the risk of fire or explosion, as well as to prevent excessive evaporation in transit. This can be accomplished either by weathering the gasoline, or by blending it with a more stable material, naphtha being commonly used in the weathering process the more volatile portions of the gasoline are allowed to evaporate and the losses in volume are very large, therefore, blending is preferable, wherever possible.It is very difficult, however, to produce by blending, in gasoline plants, a motor fuel which is equal to straight-run refinery gasoline. In order to make a blended motor fuel of a grade equal to straight-run gasoline, only a small percentage of natural gas-gasoline can be blended with the naphtha, consequently it is customary to blend the gasoline with only enough naphtha to enable It to be shipped to an oil refinery when the material is again blended to form a finished motor fuel."

Sep 1, 1921

By Robert L. Crosby

The Bureau of Mines investigated the substitution of cement copper powder for commercial copper powder in an Fe-7 pct Cu-l pct C powder metallurgy alloy. Copper powders from six different commercial cementation operations were separately upgraded by screening and hydrogen reduction. They were then mixed with commercial iron and graphite powders to form the Fe-7 pct Cu-l pct C alloy. Various chemical and physical properties were determined on the upgraded cement copper and the alloy powders. Mechanical, physical, and chemical properties were determined on green and sintered specimens made from the alloy powders. Mean tensile and bending strength of sintered specimens were significantly lower than the means from specimens made from commercial metal powders. The lower strengths are apparently related to poor sinterability.

Jan 1, 1970

Continuous remote sensing of methane concentration in underground mines. Approach A methane transducer, developed as a fixed point rib-or face-mounted operating device, measures ambient levels of methane and produces a signal that is proportional to the measured concentration. How It Works The methane transducer, developed under contract for the Bureau of Mines, uses a catalytic-type sensor which will detect methane concentration. The transducer is mounted vertically, as shown. This type of mounting minimizes dust accumulation on the sensing element, which might cause degraded operation. The unit must not be located in an area where water can continuously drip or run on It. The transducer generates an electrical signal proportional to methane concentration at the sensor. A sensor failure output indicates the status of the sensing element A circuit within the methane transducer detects whether the sensing element is shorted or open. A high signal (approximately 8 Vdc) on the failure output Indicates the sensor element is operating In Its normal range. A low output (less than 1 Vdc) indicates an element fault. The methane transducer, enclosed in a stainless steel

Jan 1, 1982

By A. L. Engel

This publication describes further research by the Federal Bureau of Mines in beneficiating domestic manganese ores. The ores selected for treatment were typical of many manganese deposits in California and Nevada in that they have not been economical to mine because they are low grade or contaminated with siliceous minerals and are not amenable to physical concentration.3 4/ It would be desirable to develop a simple treatment method resulting in nearly complete extraction of manganese from these ores and applicable to small-scale operations. Sulfation reduction appeared to be such a method. The studies reported in this publication were directed toward sawdust or lignin-sulfonates as reducing agents. Sawdust, as waste from lumbering, and lignin-sulfonates, byproducts of woodpulp papermaking, are comparatively cheap and may be available in areas where manganese ores are found. Sugar, oils, and coal were also tried as reducing agents.

Jan 1, 1960

By S. E. Khalafalla

The Bureau of Mines investigated the metallothermic reduction of copper oxide as a function of temperature, reactant proportions, form of reductant, and gaseous environment, using iron and steel scrap reductants. The reaction proceeded rapidly with powdered iron at temperatures above 560° C, attaining over 95 percent copper metallization within 3 hours. The importance of inter-reactant contacts on the extent of the reaction was evident from the variable, but usually lesser, degree of metallization obtained with iron from tin cans and automobile steel scrap. Reduction decreased as the molar ratio of copper to iron increased between 1 and 3. The most favorable gaseous environment for the reaction was a static helium atmosphere containing about 0.6 percent water vapor. Ferrothermic extraction of copper from its oxides appears to be essentially a "solid-state cementation" process. While ordinary cementation processes must be preceded by leaching, the ferrothermic method avoids this generally slow step and also the water pollution caused by the leaching agents. Sulfidic copper concentrates could likewise be reduced with metallic iron following their complete oxidative roasting.

Jan 1, 1969

By John Durkin

Field studies have been conducted in a large number of coal mines throughout the U.S. to determine the effectiveness of electromagnetic techniques in locating men trapped underground following a mine disaster. Data from these tests have been used to generate models of expected signal and noise distributions as found above mines throughout the coal fields. These distributions have aided in placing the expected performance of a through-the-earth electromagnetic communications technique into a probabilistic framework. Results indicate an expected 45% probability of detecting a miner's signal from a depth of 1,000 ft, a depth which exceeds 903 of the coal mines within the U.S. and a 90% probability at a depth of 500 ft, a depth which exceeds 50% of the mines.