Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/88

08 C A L [MINING. suitable projections for working into and propelling a chain or band. Beneath or to the side of the frame (or both) is fixed temporarily or otherwise a lever, the extremity of which is constructed to carry a wheel called the ter minal wheel, marked II H ; a chain or band is made to pass round the driving and terminal wheels, and by means of the driving wheel FF it is made to revolve. Into the chain are fixed cutters of different forms (see the parts marked, figs. 4, 5, 6, and 7), which, when the machine is in action, revolve with it, and upon being pressed or drawn against the coal, erode and excavate the same. The dis tance of the excavation from the face of the coal is governed by the dimensions of the machine, and by the length of the lever and the distance between the driving and terminal wheels. The arrangements of the lever allow it to revolve, and to excavate any given range ; see dotted lines fig. 1. If found necessary, two or even three levers may be in operation at the same time, and arranged to cut in any direction. Other parts of the machine not particularly de scribed are capable of elevating and depressing the front part of the machine, marked V, T, U, W ; and those marked X, Y, Z, and K are capable of propelling the machine whilst at work, by acting against the prop. The Gartsherrie machine of Messrs Baird is of the same character, but the chain of cutters works round a fixed frame or jib projecting at right angles from the engine car riage, instead of traversing upon a centre, an arrangement which makes it necessary to cut from the end of the block of coal to the full depth, instead of holing into it from the face. The forward feed is given by a chain winding upon a drum, which hauls upon a pulley fixed to a prop about 30 yards in advance. This is one of the most compact form of machines, the smaller size being only 20 inches high. With an air pressure of from 35 to 40 ft> per square inch, a. length of from 300 to 350 feet of coal is holed, 2 ft, 9 in. deep, in the shift of from 8 to 10 hours. One of the simplest forms of coal-cutting machines is that of Messrs Winstanly & Barker (fig. 14), which is driven Fro. 14. Winstanly & Barker s Coal-cutting Machine Plan. by a pair of oscillating engines placed on a frame run ning on rails in the usual way. The crank shaft carries a pinion which gears into a toothed wheel of a coarse pitch, carrying cutters at the ends of the teeth. This wheel is mounted on a carrier which, being movable about its centre by a screw gearing worked by hand, gives a radial sweep to the cutting edges, as in the machine figured in Plate V. When at work it is slowly turned until the carrier is at right angles to the frame, when the cut has attained the full depth. The forward motion is given by a chain-winding upon a crab placed in front, which is worked by a boy who hauls it slowly forward. With 25 R) pressure it will hole 3 feet deep, at the rate of 30 yards per hour, the cut being only 2| in. high, but it will only work on one side of the carriage. Another kind of application of machinery to coal mining is that of Messrs Bidder & Jones, which is intended to replace the use of blasting with gunpowder for bringing down the coal, a practice which in fiery collieries is often attended with considerable danger from the flash of the ex plosion firing the gas given off the coal. It consists of a small hydraulic press, which forces a set of expanding bits or wedges into a bore-hole previously bored by a long screw augur or drill, worked by hand, the action of the press being continued until a sufficient strain is obtained to bring down the coal. The arrangement is, in fact, a modification of the plug and feather system used in stone quarrying for obtaining large blocks, but with the substitution of the powerful rending force of the hydraulic press for hand -power in driving up the wedges. This apparatus has been used at Harecastle in North Staffordshire, and found to work well, but with the disadvantage of bringing down the coal in unmanageably large masses. The use of gunpowder in very fiery mines is always attended with danger, and a method of wedging down coal sufficiently perfected to be of general application would add greatly to the security of the colliers in work ing such mines. The removal of the coal when broker from the work- ing faces to the pit bottom or to the main levels is effected mainly by hand labour when the mine is small, and the distances to be traversed inconsiderable, and in mines of greater extent by horse or steam traction. The simplest method is that of loading the broken coal on to a sledge, which is dragged along the floor to the level, but now the practice of carrying railways to the face is almost universal. The old form of flat rail or tram is still largely used, the waggons having sharp- edged disc wheels, but probably edge rails and flanged wheels are now more general. The class of rail used is generally a flat-bottomed or bridge section, weighing from 15 to 25 ft> per yard, laid upon cross sleepers, which, in roads that are intended to be kept open for some time, are fixed down firmly, but are laid in a temporary manner along the working faces, and in similar positions where it is necessary to be continually shifting them, as, for instance, wheie coal-cut ting machines are used. The arrangement of the drawing roads at the face of a long-wall colliery is seen in the plan fig. 12, where the rails are brought to the face upon a smooth iron plate, upon which the trams can be easily handled by turning on the flanges of the wheels. The names applied to the vehicles in which the coal is carried vary considerably, as do also their size and capacity. The word " corf " or " corve," representing the old basket sledge, is one of the most generally used, as are " tram," signifying a tram waggon, and " tub," of the same signification as the last, but a representative of the old method of drawing in wooden buckets. In South Staffordshire and other Midland districts, a contrivance called a "skip" is the representative method of conveyance ; this consists of a platform with tram wheels, upon which the coal is built up to a consider able height, the large pieces round the sides being kept to gether by loose rings of sheet iron, and the intermediate spaces packed full with small coal, the whole arrange ment representing a kind of cask. This, however, like most of the similar primitive methods, is giving way to the more improved system of tubs or trams. These are small railway trucks, generally with flanged wheels and square- sided bodies, either of wood or wrought iron, varying in capacity from 4 cwt. in thin seams to 10 or 12 cwt. in thicker seams. In the removal of the coal from the workings the first portion of the journey .is generally performed by hand- Coal wedging Under- g r undc

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