The Mechanical Handling and Storing of Material

2Ö THE MECHANICAL HANDLING OF MATERIAL likely to be discovered as in the case of a number of elevators driven singly, for whereas- in the latter case the driving belt would come off as soon as the choke took place, in the foimei the main belt driving ths line of elevators would probably, being much stronger, remain in its place, with this result, that the elevator pulley would continue to revolve against the elevator band, which would be held stationary through the accumu- lation of material. 1 his has frequently been the cause of fires in flour mills, as the friction between the pulley and the band would be sufficient to cause the latter to ignite. The only advantage of having the elevators in one line and driven by one shaft is the saving of expense, and on that account this practice is too often followed,, but to drive elevators singly or in pairs is far preferable. Cable-chain Elevators.—Elevators for handling rough and uneven material are sometimes driven by ordinary grooved pulleys and cable chains. Details of such an elevator are shown in Figs. 19 to 21. The illustration shows the general arrangements of the elevator, with driving gear at the top and tightening gear at the bottom. The chain and one bucket with its skidder bar are shown to a larger scale, while a cross section shows the angle iron against which the skidder bars of the buckets run. A Type of Simple Mineral Elevator.—Fig. 22 shows a type of construc- tion which is much in favour, the elevator well in this case being a masonry structure and not a complete iron well. This illustration is more intended to show the construction of the elevator itself, which consists of a pair of T girders braced by stays and rods. 1 he two terminals are fitted to the girders in the usual way, the lower one being, as usual, the tightening one. The elevator chain and buckets, instead of being fitted with slats running upon guides, are here supported and held in a straight line by a series of guide rollers, the bearings of which are bolted to the girders on either side. 1 he elevator here illustrated is used for loading a suspended railway by means of a hopper and shoot. Gear Drives for Elevators.—For very large elevators, especially in cases where the available space does not admit of the internal elevator pulleys (sprocket or polygon wheels) being of large diameter, spur or bevel wheels having a ratio of 1 :2 to 2 :3 should be employed, together with a suitable countershaft. Power Required for Elevators.—This depends, of course, on the height of the elevator and on the weight to be lifted, but for practical purposes not less than twice the theoretical H.P. should be allowed. Archimedean Screw Elevators.—These are sometimes used, in which case the screw or worm fits fairly tightly into a cylindrical receptacle. Such elevators must be driven 25 to 50 per cent, faster when used for elevating than when used for con- veying on the level. 1 here is no special feature about this particular type of elevator beyond that which will be found under the head of worm conveyors, with the exception that the worm must be of the continuous type, and that the pitch must not be more than half the diameter of the worm. Such elevators can be driven from top or bottom by bevel gear, the latter being the more general arrangement. Such a driving gear is shown in Fig. 23. The upright worm is erected within a receiving hopper, and the -grain is admitted from the hopper to the worm by two or more inlets. Spouts and Shoots.—The spouts and shoots which receive the feed from elevators in immediate proximity to the latter, should always be made of stout wrought iron, or better still, cast iron. For smaller grain elevators, wood, with a sheet-iron lining, will be found sufficient. It is surprising how quickly even cast-iron shoots are worn through