The Mechanical Handling and Storing of Material

146 THE MECHANICAL HANDLING OF MATERIAL which the hot coke is continually changing its position, thereby heating up the whole conveyor gradually and uniformly j whilst the former conditions depend on ths details of the construction of the chain and trough, and have been met in a variety of ways. It may be urged that a conveyor of the push-plate type requires more power to drive it, and causes more breakage of coke and greater wear of the trough than does a tray conveyor; but in the Author’s opinion the advantages of the push-plate type moie than counterbalance these defects. The wear of the trough of a conveyor of the push-plate type, caused by the action of the hot coke, is after all not so great, especially when the trough has once been worn smooth, if the conveyor chains are of small pitch, and if the polygon terminals are not less than eight- or ten-sided, so as to ensure a fairly uniform speed of travel. Moreover, there is practically no limit to ths thickness of the bottom plates of the troughs of these conveyors; there is, in fact, no reason why the bottom of the trough should not be of concrete slabs. The more modern hot coke conveyors in use in gasworks are all more or less of one type, consisting of substantial iron troughs, 2 ft. to 2 ft. 6 in. in width, in which scrapers are manipulated by a chain, or more often by two chains, travelling at a speed of 30 ft. to 60 ft. per minute. When two chains are used, they are either concealed in suitable channels in the sides of the trough, or placed outside the trough altogether. Conveyors of the plate or tray type, although they tend to protect the chains from the coke, and cause less wear of the trough, do not appear to have been so successful. In conveyors of this type the coke rests on the plates and moves with them, so that the plates become damaged by excessive heating, whilst the heat soon spreads to the chains, which must suffer considerably unless the trough in which the conveyor travels is filled with water up to the level of the plates. An attempt to prevent breakage of the coke, and at the same time to reduce the wear of the trough, has been made by constructing the push-plates in such a form that they support the coke to some extent, thereby preventing, wholly or partially, its contact with the trough. This type of conveyor may be termed a combination of the push-plate and the travelling-plate conveyor, and to some extent it protects the coke from breakage, but, on the other hand, the “ breeze ” which is always present will find its way between the pushing agents and the trough, so that the protection afforded to the latter is more or less inconsiderable. The chains employed in hot coke conveyors are nearly all of the long-link type, but differ widely in details of construction. Formerly the links were usually either forged or of malleable cast iron, but these have now to a great extent been superseded by links of Hadfield manganese cast steel, with forged pins of the same material. The advantages of this material are that it contains fewer blow-holes than ordinary cast steel, and is more durable under the severe conditions to which such chains are frequently exposed. The ultimate tensile strength of the chains is very much greater with this material, but it is not advisable to reduce the sectional area of the links in proportion, especially as the elastic limit of the manganese steel is rather low ; and although the material is suitable for general use on hot coke conveyors, it should not be employed when likely to be exposed directly to the action of the hot coke. The following are descriptions of nine conveyors used for handling hot coke. Of these, the first four are of the tray or plate type, in which the coke is carried on plates,, trays, gratings, etc.; the fifth, the West conveyor, is intermediate between this type and the push-plate type, as in it the coke is partly carried and partly pushed along; and the remainder are of the push-plate type. The New Conveyor Co.’s Hot Coke Conveyor.—This conveyor consists.