The Mechanical Handling and Storing of Material

COAL FACE CONVEYORS 165 B.W.G.), the total weight of the trough was naturally increased from 50 to 100 per cent., which made more powerful motors necessary. It was also found that the middle of the bottom of a flat-bottomed trough wore through first, so that the troughs had to be scrapped when the sides and a portion of the bottom were still good. A middle course was then adopted by some of the best makers, and the troughs were manufactured out of specially rolled sheets, which were thin at the sides and gradually thickened in the middle, and in the proportion in which the wear has been observed. Semicircular troughs were made of similar sheets, fortified similarly by an extra thickness at the points where the wear was found to be most prominent. This method has the advantage that the weight of the trough is brought to a minimum and its lasting qualities to a maximum, and that the whole trough wears uniformly. The methods of coupling up the different lengths of the trough of one long conveyor are very numerous. At first the practice was adopted of making the ends flanged, and bolting the units together with a narrow kind of fish plate on each side of the flanged joint, but these loose parts were constantly lost by the men, and the process had the disadvantage of being too slow. More modern methods include few or no loose parts, and allow a slight flexibility at the joints, so that slight curves in the level of the seam may be followed by the conveyor. In suspended conveyors the weight of the trough itself has been utilised for tightening the joints by combining the links of suspension with a coupling device. The details of the supports, both hanging and rolling, vary more or less in the machines of different makers, but the essential principle is the same, so that it is not proposed here to give much space to them, as the number of varieties is so great that it would require many pages to do them all justice. The motors are nearly all of the compressed air type. Attempts have been made to use electricity as motive power, but the pneumatic principle is so obviously the most suitable that it is not to be wondered at that it has held its own. To use an electro-motor, a quick rotary motion has to be converted into a slow reciprocating motion, whilst the movement of the pneumatic engine with its slow reciprocating motion is so similar to that of the coal face conveyor that it may be coupled direct to it; therefore it is only those who have no pneumatic plant in their mine who will consider electric drives. Pneumatic engines are used either directly coupled to the conveyor trough by a connecting rod, the engine being fixed to the ground underneath, or they are coupled by the intervention of levers, rods, or cables; One of the latest methods is to fix the motor to the trough itself, and adjust the movement by a chain anchored at one end to the ground and at the other to the engine, which may be single or double acting. Direct-coupled motors generally occupy less room, and are more easily shifted as the face recedes, and the initial cost is less than that of the gear-coupled motor; on the other hand, the former are more noisy, being fixed with the conveyor close to the coal face instead of some distance away (probably in the gateway). They must be moved every time the conveyor is moved, and, being placed under the conveyor, have a tendency to occupy more height, which may be an objection in working small seams. Both types of motors vary in the number and length of the strokes. For conveyors on an incline, where gravity is one of the conveying powers, direct-coupled motors are generally and preferably single-acting with a long stroke, as their action gives the coal a greater momentum, and therefore a greater forward movement at the change of the stroke ; whilst for more horizontal conveyors, where gravity does not come into play, double-acting motors are better, with more frequent and shorter strokes. In order to adapt motors to all the conditions in the same pit some of the types have been made with adjustable strokes.