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To facilitate compliance with title 30 CFR 75.1001-1(b), which requires testing and calibrating of trolley line automatic circuit interrupting devices at intervals not to exceed six months. Approach Calibration of a circuit breaker ideally implies the passage of the expected fault current through the sensing circuit, and observing a successful circuit interruption at the preset level within a specified time. On trolley lines, the required current may be a few thousand amperes, with maximum duration well exceeding one-tenth of a second. Any method of obtaining this calibration current Involving the trolley wire can contribute to wire sagging and other permanent damage to the haul-age system due to the high energy dissipated during the test. Also, control to assure that exactly the required level and duration of current flow is obtained implies the use of equipment which is simply not available In the ordinary mine. Under a Bureau of Mines contract, a circuit to achieve the necessary calibration pulse was conceived and built. How It Works Two prototype units were fabricated and have been field tested by MSHA technical support engineers in under-ground mines. The equipment consists of an electronics Package 20 x 24 x 8 inches and weighing 93 pounds, including a side-mounted circuit breaker, with a set of 8 foot long detachable, AWG #4/0 leads with plier-type clamps. The total lead assembly weighs 21 pounds.

Jan 1, 1981

By E. J. Gleim

The construction of explosion-proof electric mine equipment for operation in gassy coal mines of the United States was begun as early as 1903. In 1.906, similar equipment with special protective devices was built for export. An investigation of explosion-proof motors was conducted by the United States Bureau of Mines during 1910 and 1911. In other words, this was among the first efforts of the Bureau directed toward the saving of life and property subsequent to its establishment by act of Congress in 1910. In these early motors, those with special devices for relief of explosion pressures predominated. At that time it was generally considered that, by providing for pressure relief, the enclosures could be made lighter in weight because of the lower explosion pressures developed within.

Jan 1, 1954

By Earl R. Maize

This is the first of a series of reports dealing with development of a method of strengthening bituminous-coal-mine roof. Later reports will describe the progress made with injecting high cohesive and adhesive bonding agents into bedding planes and mine tests of roof strata strengthened by the bonds formed. The concept of strengthening roof strata in coal mines by inserting steel rods in the form of bolts has been widely accepted by the coal industry. The benefits of increased production and safety derived from this type of roof support has more than justified the increased cost of roof bolting. However, not all coal-mine roof structure is amenable to this type of support, and failures occur owing to the heterogeneity and variable character of mine-roof strata.3/

Jan 1, 1957

By Edward F. Divers

The Bureau of Mines recently tested a sideboard device that is designed to act as an extension of conventional brattice, thus improving face ventilation of developing room-and-pillar-type coal mining. In these laboratory tests, an 8-foot-long rigid sideboard was mounted vertically along the left fender of a full-scale-model ripper-type continuous mining machine, rising to the mine roof to provide an air seal. It extended from the auger support frame pivot point outby along the fender. A novel water spray manifold was used to form an air seal between the sideboard and brattice. Tests showed improvement in face ventilation with the prototype device, and also demonstrated that water sprays can form an effective air seal over a fairly wide pressure range. Based on this preliminary study, subsequent improvements may make the sideboard concept much more effective, thus affording a simple, inexpensive technique to improve the effectiveness of face ventilation.

Jan 1, 1979

By Joseph Cervik, Gerald L. Finfinger

The Bureau of Mines conducted an experimental degasification project in Island Creek Coal Co.'s Virginia Pocahontas No. 5 mine. Methane from the over- lying Pocahontas No. 4 coalbed was entering mine workings in the Pocahontas No. 3 coalbed through fractures in the roof rock. Small-diameter (1-5/8-inch) holes were drilled into the overlying coalbed to reduce the gas pressure and intercept methane flows, which were piped to the surface through an under- ground 6-inch-diam steel pipeline. The total methane flow rate from the vertical holes averaged 150,000 ft3/day for the first month. Methane flows into the mine were reduced by 47 pct, thereby demonstrating the effectiveness of this form of degasification in reducing ventilation requirements and providing a safer working environment.

Jan 1, 1979

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 E. D. Gardner

This paper is one of a series on milling methods being published by the United States Bureau of Mines. Atlanta is in Elmore County, Idaho, about 80 miles from the railroad at Mountain Home, Idaho. The concentrator is at an elevation of, 6,000 feet and located in a timbered, well-watered region of relatively heavy snowfall. The snow, however, does not seriously affect local operations. The track road to Mountain Home, which passes over a mountain range, is closed each winter from about November 1 to June 15. During this period concentrates are stored and bullion is shipped by airplane. Power is generated by a Diesel engine and by an auxiliary hydroelectric plant. Gold is the principal metal produced; the or also contains an able quantity of silver.

Jan 1, 1935

By C. E. Jordan

The Bureau of Mines conducted laboratory studies on methods to increase the recovery of brine from slime produced by operating potash plants. The slime was comprised of 80 percent brine saturated with KCl and NaCl, and 20 percent solids. A variety of settling techniques, filtration methods, continuous centrifugation, and novel processing techniques were investigated. Vacuum filtration recovered 6S percent of the brine at 47 gallons of brine per square foot per day. Pressure filtration, on the other hand, recovered 74 percent of the brine at 40.9 gallons of brine per square foot per day. Centrifugation in a 6-inch-diameter continuous decanter-type separator resulted in 42 percent recovery of the brine at a treatment rate of 542 gallons of brine per day. Vertical drains proved to be the most promising novel debrining technique investigated. With this method, 45 percent of the brine was recovered in 3 days.

Jan 1, 1977

By Tobias W. Goodman, Joseph Cervik

This Bureau of Mines report investigates the horizontal trajectory of boreholes drilled in coalbeds using the rotary drilling technique. Test holes drilled in coalbeds showed that the path of a borehole in the horizontal plane depends on drilling assembly configuration, drill bit rotation, and coalbed geologic features. An assembly that contained an 18-ft (5.53) long drill collar and two centralizers had the best horizontal stability evidenced by trajectories that deviated less than 16 ft (4.9 m) from a target at 1,000 ft (305 m). Removal of one of the centralizers resulted in a loss of control of hole trajectory in the horizontal plane. Generally, holes tended to turn to the right, presumably because of right-hand rotation of the bit. Deviations from the original bearing line were as much as 200 ft (61 m) or more at a depth of 1,000 ft (305 m).

Jan 1, 1988

By E. R. Cole

A lead smelting process that appears to present minimal pollution problems has been developed at the Bureau of Mines, Rolla Metallurgy Research Center. Ten and 100 g samples of PbS mill concentrates were vaporized at 1,000° to 1,100° C in a furnace with an inert gas atmosphere during a 2-hour period. The PbS vapor was transported by the inert carrier gas to the reduction zone of the furnace where it was reduced at the same temperature with excess hydrogen to metallic lead. Lead of 99.9 pct purity was produced. The H2S formed can be decomposed into elemental sulfur and water vapor by a modified Claus process. Approximately 90 pet of the Cu and 70 pct of the Ag and Zn remain in the residue and are potentially recoverable. More than 98 pct of the lead in the concentrates was extracted.

Jan 1, 1974

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, approved by the American Engineering Standards Committee. December 30, 1925. It is specified that the dust to be used is of a elm 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. Thus the coarsest size of dust and the minimum proportion of fine dust are specified, but the specification does not indicate whether a larger proportion of fine dust would be desirable. There have been advocates of the use of that size of rock dust of which the particles would all approach 200-mesh in fineness. Explosion tests were made in the Experimental mine in the earlier period of testing which indicated that the finer rock dust is somewhat more effective under test conditions, but not sufficiently so to Justify the cost of finer grinding of the dust; also there are some disadvantages of finer dust described hereafter.

Jan 1, 1930

By R. S. Olsen

The Bureau of Mines is engaged in a continuing research effort toward the recovery of alumina from kaolinitic clay and other nonbauxitic domestic minerals. Hydrochloric acid extraction of calcined clay is among the acid processes under consideration. Although aluminum is easily leached from calcined clay, the presence of fines and slimes in the leached residue has hindered the application of this and other acid leaching processes. A clay feed preparation method was therefore developed that eliminated the slimy nature and the separation problems normally associated with leached clay residues. The preparation process consists of crushing the raw clay to minus 20 mesh, dampening the crushed clay with a fine water mist while tumbling on a rotating disk, and calcining the misted clay at 750° C. The misting process increases residue settling rates threefold to 9 cm/min (18 ft/hr) and filtration rates by two orders of magnitude. Leaching-kinetics were determined for misted clay feeds in a batch, stirred-tank reactor. Rapid leaching occurred during the first 85 to 90 pct of the extraction. The linear relationship of extraction to time during this initial phase corresponded to a zero order reaction with a rate constant of around 10 pct/min.

Jan 1, 1981

By Paul Sands

Single- and two-stage tests were made with 6-inch, coal-cleaning hydrocyclones to determine the effect of hydrocyclone geometry, operating conditions, and feed composition on performance. Most of the testing was conducted in an open-circuit pilot plant that had a maximum capacity of about 9 tons per hour. The coals used in the investigation had top sizes of 1/4 inch and 28 mesh. Considerable latitude was found in the range of geometry variables that could be used without affecting performance adversely, although a certain minimum ratio of overflow to underflow openings had to be maintained for best operation. Two-stage cleaning proved distinctly better than operation with a single hydrocyclone, because clean coal lost in the refuse product of the primary unit can be partly recovered in the secondary. There is an unusually great difference in the specific gravities at which the individual sizes of the feed are separated in the hydrocyclone. This militates against high efficiency because maximum yield occurs when all sizes are cleaned at the same specific gravity. The size composition of the feed and, more particularly, the size composition of the impurity have a greater influence on the efficiency attainable in the hydrocyclone than in most other types of fine-coal cleaners.

Jan 1, 1968

By A. F. Colombo

In an effort to maintain an adequate supply of iron to meet national economic and strategic needs, the Bureau of Mines, U.S. Department of the Interior, is conducting research on methods for beneficiating the oxidized taconite resources located on the western Mesabi range in Minnesota, thus expanding domestic iron ore reserves. The selective flocculation and cationic flotation process was investigated in a pilot plant using an ore feed rate of 410 kg/hr (900 1b/hr) and 88 percent recycled water. Lime and a cationic flocculant were used to clarify the waste slurries treated in the water reclamation circuit. An oxidized taconite assaying approximately 36 percent Fe yielded concentrates averaging 63.5 percent Fe and 4.3 percent SiO2 and having an average iron recovery of 84.4 percent. The estimated reagent cost per tonne of concentrate was approximately $1.10. In an attempt to recover more of the iron lost in the flotation tailing, wet high-intensity magnetic (WHIM) separation was incorporated in the pilot plant circuit. The flotation concentrate grades obtained from beneficiation circuits with and without WHIM scavenging were similar, but when WHIM separation was used the overall iron recovery was increased by 2 to 9.5 percent, depending on the iron assay of the flotation tailing.

Jan 1, 1978

By L. A. SCHOLL, J. K. CLEMENT

Among the problems investigated by the Bureau of Mines the coal- dust problem has received much attention. Several of the bureau's publications deal specifically with the subject. Bulletin 20° contains an account of preliminary experiments of the bureau to determine the explosibility of coal dusts as well as a review of pertinent literature. Bulletin 50 is a report of a laboratory study of the inflammability of coal dust. The first series of coal-dust explosion tests in the bureau's experimental mine at Bruceton, Pa., is described in Bulletin 56, and Technical Paper 56 presents notes on the prevention of dust and gas explosions in coal mines, and Technical Paper 84 discusses the causes of such explosions and describes methods and apparatus devised by engineers of the bureau for preventing and checking them. The present paper is a report of a detailed study of the bituminous dusts of Illinois mines, and is a part of the investigations conducted by the bureau in cooperation with the Illinois State Geological Survey and the department of mining engineering of the University of Illinois./ It is well known that bituminous coals like those found in Illinois yield dusts that may give rise to explosions of great violence. In order that proper methods might be devised for preventing dust explosions in Illinois mines it was considered desirable to obtain accu- rate information on the quantity and character of these dusts. Ex- periments and tests of dust explosions in an experimental mine as well as in a large steel gallery comparable in area of cross section to mine entries have been made by the Bureau of Mines. Similar experi- ments have been made in Austria, England, France, and Germany. Experiments under conditions similar to those of actual mining prac- tice are obviously more conclusive than tests made in a laboratory. On account, however, of the expense, time, and quantity of dust re- quired, it is not practicable to conduct large-scale tests in studying a large number of dusts and recourse must be had to laboratory apparatus and methods. Laboratory,devices for the study of coal-dust explosions have been devised by a number of investigators. Most of these were intended for qualitative tests only. Quantitative methods have been devised by investigators of the English and French mining-experiment stations." In the experiments described in this report, laboratory tests of inflam- mability were made with an apparatus devised by Dr. J. C. W. Frazer, formerly a chemist of the Bureau of Mines. Laboratory tests of inflammability have been made on more than 500 samples of dust from 100 representative Illinois mines. As a result of these tests it may be stated that: 1. The coals of Illinois when ground fine enough yield highly inflam- mable dusts which when suspended in air may give rise to violent explosions. 2. In the majority of the mines of the State the dusts adhering to the ribs are inflammable. In about one-fourth of the mines the quantity of rib dusts present in the entries is sufficient to form an explosive mixture with air. 3. Most of the road dusts are inflammable when ground to a suffi- cient degree of fineness.

Jan 1, 1916

By Richard J. Mainiero

The Bureau of Mines investigated coal-mine-type short-delay electric detonators marketed by three domestic manufacturers to determine the accuracy of delays and the probability of overlap between adjacent de- lay periods. The Winzer index was computed and compared with the probability of overlap. A close agreement between the Winzer criterion and overlap probability was demonstrated. A permissible blasting unit capable of delivering a maximum firing energy of 4.0 J and a digital oscilloscope were used to measure the delay time with an accuracy of 20.25 ms. Another oscilloscope and a pulse transformer were used to record firing current. Experimental data indicated negligible overlap probability in detonators of shorter delay periods: periods 1 to 4, which correspond to 25 to 250 ms. However, a significant probability of overlap was detected in some detonators of longer delay periods: periods 5 to 9, which cor- respond to 300 to 500 ms.

Jan 1, 1985

By Edward Thimons, William A. Hertbrink

The effect of wind speed upon aerosol penetration into an idealized enclosure was studied The idealized enclosure was a painted plywood box that was 1 2X1 2 XI meters in volume Two fans supplied 1 7 m3 /min of filtered air to this enclosure at a static pressure of 2 8 mm of water The enclosure had a 7 5 cm diameter vent port which was isolated from the air flow around the enclosure To simulate holes in real enclosures, three 16-cm diameter holes were drilled on the front and back sides of the enclosure This simulated enclosure was placed in a tunnel-like structure The air flow from an ultra-light air craft was directed at the front of the enclosure The air speeds were varied between 14 and 36 km/hr as measured by rotating vane anemometer Static pressure in the enclosure was measured with an electronic manometer Two optical particle counters measured the particle number concentration of particles between the 0 35 to 0 5 µm inside and outside of the enclosure Aerosol penetration into the enclosure was computed as the ratio of the aerosol concentration inside the enclosure to the concentration outside of the enclosure The enclosure static pressures measured increase from 2 8 to 3 4 mm of water (P=00001) Aerosol penetration into the enclosure increased linearly with air velocity above 20 km/hr Theoretically estimated penetrations were correlated with observed penetration into the simulated enclosure When simple linear regression was used to model the observed penetration as a function of the estimated penetration, the value of the slope was 0 69±0 12 and the P value for the regression model was less than 0 0001 These results indicate that enclosure static pressure needs to be higher than the wind's velocity pressure in order to minimize aerosol penetration into these enclosures

Jan 1, 1999

By M. Kanda, J. W. Adams

A system for measuring amplitude probability distributions (APD’s) of electromagnetic noise in coal mines is described and typical APD’s from an underground coal mine are presented. The APD is a basic statistic required for the design and analysis of communication systems, especially those intended for use in noisy environments, and where neither overdesign nor underdesign is acceptable. The rms and average field strengths are obtained by integration of the APD, and examples are shown at several frequencies. All field strength levels are given in absolute units. Selected frequencies cover the range from 10 kHz to 32 MHz.

Jan 1, 1973

The Navajo Nation is the largest Indian tribe in the United States and occupies a reservation encompassing about 16 million acres in northeastern Arizona, southeastern Utah, and northwestern New Mexico, with three satellite reservations in western and west-central New Mexico. Coal mining is conducted on a commercial scale at four large surface mines: two are in northeastern Arizona and the other two are in western and northwestern New Mexico. The principal coal-bearing region in Arizona is the Black Mesa coal field, which underlies about 3,200 square miles in the northeastern part of the state. The Black Mesa coal field lies within the boundaries of the Navajo and Hopi Indian Reservations and makes a significant contribution to the economies of both tribes. Coal reserves in this field are estimated to be 352 million tons, less than one-tenth of one percent of U.S. coal reserves. This coal was first mined by prehistoric Indians as fuel for cooking and heating. It has been estimated that the Indians removed more than 100,000 tons between 1300 and 1600 A.D. The coal-bearing region of the Navajo Reservation in New Mexico is located in the San Juan Basin. The Navajo Mine, which supplies coal for the Four Comers Power Plant, is located in this area. The Office of Surface Mining's Albuquerque, New Mexico, Field Office is responsible for regulating mining and reclamation on Navajo land. The Navajo Abandoned Mine Land Program was approved May 16,1988.

Jan 1, 1992

By L. J. Douglas, A. G. Kim

Methane and other hydrocarbon gases, byproducts of coalification, are emitted from coal at widely varying rates and often present ventilation problems during mining. The air in some coal mines apparently contains no methane. To determine if coals from mines which had no history of detectable gas emission contained adsorbed methane, samples of coal at the shaft bottom and at an active face were obtained and placed in sealed metal cylinders. The atmosphere around the coal was sampled and analysed by gas chromatography. Methane, ethane, ethylene, propane, propylene, and butane were found to have been desorbed from these coals. Hydrogen and helium were also detected. An estimate of the amount of residual gas per ton of coal indicated that coal samples from the active face generally contained more adsorbed gas than coal samples obtained from the shaft bottom, although in both instances the total amount of gas was relatively small.

Jan 1, 1973