- 行业: Mining
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The U.S. Bureau of Mines (USBM) was the primary United States Government agency conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral resources.
Founded on May 16, 1910, through the Organic Act (Public Law 179), USBM's missions ...
These couplings are used where shafts intersect at any angle or where pivoted members must be driven. If there is an offset in the two shafts, or if one or both shafts must change location during operation, two of these couplings are used, and one is fitted with a splined joint mating with the connecting intermediate shaft to allow axial movement.
Industry:Mining
These cuts consist of one or several fully charged holes in which blasting is carried out towards the face of the tunnel, i.e., toward a free surface at right angles to the holes. These represent in principle a completely new type of cut and make use of the crater effect that is obtained in blasting a single hole at a free rock surface. The possibility of a uniform enlargement can be counted on. This means that if the scale is enlarged so that the diameter and depth of hole and length of the charge are all doubled, e.g., a crater of 769 double the depth will be obtained. The number of holes can be increased instead of increasing the diameter of the holes.
Industry:Mining
These differ from straight overcurrent relays in that they are primarily used for ground protection. They are designed to measure fault current in one or two sections. Whether faults will cause flow in one or two directions is determined by system conditions. The 599 two-directional relay is used on transmission lines where ground-fault currents flow in either direction. These relays provide directional as well as overcurrent protection. Other directional relays provide phase protection.
Industry:Mining
These explosives are employed to a certain extent in the form of a powder in cartridges, or as a light-running granulated mass, or as solid sticks. They have the disadvantage that the density of charging will be small, which means that the cost of drilling will be comparatively high.
Industry:Mining
These explosives are similar to the straight gelatins except that the main constituent is ammonium nitrate instead of sodium nitrate. Ammonium nitrate is a more active explosive ingredient than sodium nitrate; therefore it can be substituted for nitroglycerin in much larger quantities and still give explosives of high weight strength. The nitroglycerin content is usually 25% to 35%, and the ammonium nitrate content ranges from about 30% to 60%. Ammonium nitrate gelignites are characterized by plastic consistency; high densities of 1.5 to 1.6 g/cm<sub>3</sub>; medium velocity of detonation of 2,500 m/s; and good fume properties. The ammonium nitrate gelignites are useful all-purpose explosives and are widely used in metal mines, nongassy coal mines, quarries, tunneling, and construction work. Its wide range of strengths enables a suitable grade to be selected for blasting almost every variety of rock from hard to soft.
Industry:Mining
These explosives are sometimes referred to as straight gelatins. They are really modifications of blasting gelatin in which varying percentages of nitroglycerin are replaced by sodium nitrate and combustible material to give a range of gelatinous explosives of varying strengths. The nitroglycerin content may be from about 30% to 80%. Straight gelatins are characterized by their plastic consistency; high densities of 1.5 to 1.6 g/cm<sub>3</sub>; medium velocity of detonation of 2,500 m/s; good resistance to the effects of water, which also gives them good storage properties, and they possess fume characteristics suitable for underground workings. All the various requirements for metal mining, tunneling, and quarrying operations are covered by this wide range of gelatinous explosives. Their high resistance to water makes them particularly useful in wet conditions, and their relatively high density is advantageous where a powerful concentration of explosive energy is required.
Industry:Mining
These explosives consist of one simple chemical compound. The explosive heat is liberated with the breaking down of the molecules and the atoms recombining to form water, carbon dioxide, nitrogen and other gases, and possibly solid substances such as carbon. To this group belong explosives in the proper sense of the word, such as nitroglycerin, nitroglycol, nitrocellulose, trotyl, and cyclonite (RDX). Also includes "molecular explosives."
Industry:Mining
These fuses were designed so that electrical shotfiring methods could be used for initiating blasting powder. The powder fuse consists of a thick paper tube containing a small charge of blasting powder, with an ordinary low-tension fusehead fixed at one end. On passing electric current through the fusehead, it flashes and sets off the blasting powder in the tube, which can then initiate the main charge of blasting powder in the shot hole.
Industry:Mining
These include (1) a hydraulic classifier and (2) a flotation cell marketed as the Denver Sub A.
Industry:Mining
These include the cross-sectional area of a structural member, its moment of inertia, section modulus, and other geometrical properties essential for accurate design calculations.
Industry:Mining
