The Mechanical Handling and Storing of Material

& THE MECHANICAL HANDLING OF MATERLAL 164 coal face, where all mechanical devices are more roughly used, and more subject to injury than in any other industry. The principle is simplicity itself, and one wonders why it has not been employed before. Such conveyors consist of an open sheet-iron fiat- bottomed trough with slanting sides, or the trough may be semicircular, which is supported by chains from the timbering, or from trestles, or by rollers from below. A reciprocating motion is imparted to such troughs either by hand or motive power, and as the original conveyors were inclined, being used in inclined seams, the material moved or slid forward and downward at the down-stroke, whilst it remained stationary at the up-stroke. The speed of travel depends on the method of support, the stroke, and the incline. The oldest form is the suspended trough conveyor. With this system it must be borne in mind that the stroke must come to a stop when the supporting chains or links are in a vertical position, that is to say, the stroke must not extend equally on either side of the points of suspension, as then there would be no forward motion, at least not in a horizontal conveyor. The action is therefore as follows : When the conveyor is at rest all the supporting links or chains hang vertically down; as the stroke begins the trough is lifted, as it moves on the path of an arc described by the suspended links. During this motion the coal in the trough remains stationary ; as the end of the stroke is reached the trough will be in its highest position, and it then begins the forward stroke. During this the coal likewise remains stationary, that is, moves the trough, but as soon as the lowest point is reached the motion is reversed, and the cycle of motions repeated, but owing to the velocity imparted to the coal during the downward motion it slides on and does not come to rest till the trough has nearly completed its backward stroke. This motion is repeated again and again, and it is obvious that the length of the stroke and the incline, if such should be available, will materially affect the speed at which the coal travels in the trough. The links supporting the trough, it will thus be seen, do not travel at the forward stroke beyond their vertical position, and it is regulated by the stroke of the pneumatic engine, which does not permit an extension of the movement. The aforesaid refers to conveyors suspended on chains or links either from the timbering of the roof or from special trestles. If the trough is supported from beneath on rollers, and a sufficient fall should be available, the rollers may move on the floor of the seam, or parallel with it on short lengths of upturned channel iron ; but if the seam is level, or nearly so, these rollers must move on a path similar to that indicated by the suspended links, that is, short sections of rails or wedge-shaped wooden blocks must be provided, which begin at one end with a gentle incline and which become steeper towards the end of the stroke. If a number of pairs of rollers are attached, running on such inclined rail sections, the behaviour of the coal in the trough will be the same as in the suspended conveyor, and it will be conveyed in the same way. The troughs of these conveyors are best made of Siemens-Martin steel sheets from 2 to 4 mm. thick (14 to 9 B.W.G.), and joined up out of lengths of 10 ft. each. As to the width of these troughs, when first introduced there was a tendency to make them rather large, 24 to 28 in. wide and 12 to 13 in. deep, but these have been found unnecessarily large, and the best size has been found to be 16 to 20 in. wide and from 5 to 8 in. deep. Coal face conveyors should work with as little noise as possible, and it has been found that small troughs well filled work more quietly than wider ones with a thinner load. It has also been found that conveyors of the smaller dimensions are quite capable of coping with the output of the seams, that is, keep pace with the men who load them. At first most of the troughs were made of 2 mm. (about 14 B.W.G.) sheets, but it was found that they soon wore out, and if the plates were 3 to 4 mm. (about 10 to 9