The Mechanical Handling and Storing of Material

SLAT CONVEYORS ioi Metal plate conveyors are principally used for conveying coal, and have the great advantage of handling it so gently as to avoid breakage, provided of course that the delivery is at the terminal. There may be one drawback to the use of these conveyors beyond the keeping in repair of numerous small wearing parts, and that is that the driving gear must always be at the delivery terminal of the conveyor to make the upper or working strand the tight side of the conveyor. / SLAT CONVEYORS Chain and Wood Slat or Lattice Conveyors are most useful for conveying bales and packages in factories, also for sulphate of ammonia in bags. A typical example is given in Figs. 130, 131, and 132, showing elevation, plan, and cross section. Slat conveyors are used largely to carry substances in bags, also general merchandise packed in boxes and crates, or made up in pieces or bales. They can be made partly horizontal and partly inclined, and with either a single or double strand of chain, to which are bolted a series of narrow boards or slats (usually from 1 to in. thick), forming a continuous travelling platform. The terminals consist of one or two pairs of chain wheels; the bearings of those forming the tail end sliding in slotted frames, in order to permit of the extension of the chain being taken up by tension screws from, time to time. Cast-iron supporting rollers or idlers about 9 in. diameter are provided at intervals of 3 ft. or more, the shafts running in plain or bushed bearings fitted with Stauffer grease lubricators. The outer rollers have a single guide flange; the inner rollers are plain. The bearings of the idlers are usually bolted to continuous channel steel beams. A conveyor on similar lines has been erected by the Chain Belt Engineering Co. It is 204 ft. long, the slats are 24 in.; it travels at 50 ft. per minute, and handles 600 sacks of sulphate of ammonia of 2 cwt. each per hour. The chain used is No. 500 Gray Chain, 6 in. pitch. In an alternative design of slat conveyor (Fig. 133) the slats are furnished with brackets and travelling wheels or rollers of small diameter, running on angle-iron tracks. This design has the advantage of avoiding the slight up-and-down movement of the packages in passing over fixed supporting rollers, due to the sag of the chain. Also the slats need not necessarily be close together, but can be spaced a foot or two apart in some cases. On the other hand, there is more difficulty in lubricating numerous travelling wheels than fixed bearings, and they are less secure and durable. Moreover, rollers revolving in contact with wood slats work more quietly than cast-iron wheels running on angle-iron tracks. A conveyor on these lines, built by the Chain Belt Engineering Co., is worthy of note. It is 470 ft. centres, moving 2 cwt. bags of sugar at a large sugar refinery. It is driven by a 20 H.P. 3-phase motor at a speed of 70 ft. per minute. In this case the hard wood slats are 30 in. long and bolted to two strands of chain. The main lattice steel girders of the conveyor bridge are 7 ft. 6 in. deep, and are supported 20 ft. above the yard level by lattice steel towers and cross girders. Double Service Chain and Slat Conveyors are also sometimes used. The special feature of this type of conveyor is that the return strand of chain and slats is not led back empty, but the two strands travel on the same plane in opposite directions, generally side by side, and both are utilised for carrying material. In this case the terminals are, of course, also placed horizontally. This conveyor is extremely useful for moving open crates, bottles, jars, tins and other goods needing careful handling. If the articles are not taken off they simply go round the circuit again and cannot be thrown off (see Fig. 254 on page 189).