The Mechanical Handling and Storing of Material

I 92 THE MECHANICAL HANDLING OF MATERIAL the respective machinery is driven by spur gear and countershafts. It will be seen from the illustrations that the tightening gears consist of two bearings movable in a sliding frame, the two bearings being movable together in the correct position corresponding to the radii of the spur gears, so that when the chain requires tightening both terminal Fig. 258. Type of Tightening Gear for Conveyors with Spur Gears. wheel and countershaft can be moved at the same time. These types are the designs of Commicbau. SPEED-EQUALISING GEARS FOR LONG-LINK CHAINS DRIVEN FROM HEXAGONAL TERMINALS The extremely limited speed at which long-link chain conveyors can be run, as compared with a leather or fabric one, and the consequently limited output, is due to the irregularities in speed imposed upon the chain by the necessarily non-circular form of driving tumbler. To take the special case of a five-sided tumbler, it may be of interest to point out that the velocity of the belt, when the tumbler is rotating at uniform angular speed, varies as much as 25 per cent, during the cycle caused by the passing of a single cant of the tumbler, or with an hexagonal tumbler as much as 15 Fig. 259. Another Type of Tightening Gear for Conveyors. sating accurately for this, enables the permissible per cent. This imparts a pulsating or jerky motion to the chain. It will thus be seen how rattle and consequent wear take place, and how the strain on the chain as well as the driving power is hereby considerably increased. This difficulty has practically limited the speed of long-link chain conveyors to 100 ft. per minute, and the speed-equalising gear, by compen- velocity in some cases to be practically double, with the result that a conveyor of half the sectional area will do the work when provided with this gear. It will thus be seen that not only is the conveyor itself much cheapened but a great lightening of the supporting structure results from the decreased weight of unit length of conveyor. The Toogood Gear.—The equalising gear, introduced by Mr H. J. Toogood, ensures uniformity of speed of the conveyor chains even when long-linked chains and hexagonal terminals are employed, and enables lighter chains, with long links, to be