The Mechanical Handling and Storing of Material

12 THE MECHANICAL HANDLING OF MATERIAL Where grain elevators are concerned this is of little consequence, but in elevators handling coal, minerals, and other material of varying size, it is desirable to keep an even space between the buckets and the bottom of the well to prevent jamming, as shown in Fig. 11. In this case the elevator well is designed to go down with a sprocket wheel when the chain is tightened, and vice versa, whilst the bracket supporting the elevator well remains a fixture. This is only applicable to elevators handling small pieces ; for coarser material no elevator wells are used. There is a third way of tightening elevators without interfering with either the feed or the delivery end, and this is by means of a separate tightening or jockey pulley arranged at some convenient points on their length, in a similar manner to the pulley shown in Fig. 11 (although in this particular instance the pulley is for ano’ther purpose). As a rule, especially with grain elevators, the tightening gear is made as part of the elevator well; but for larger elevators, particularly those which are used for heavy material, the tightening gear is separately mounted on the supporting girders of the elevator framing, and the well is entirely dispensed with. Figs. 3 to 6 show two such tightening gears. Both have an adjustment which will allow of holding the bearing in position after tightening. The construction is so simple that it explains itself. The gear shown in Figs. 3 and 4 allows of an adjustment to suit elevators at a variety of inclines. (See also Tightening Gears, page 191.) To Prevent Choking-.—The buckets should be made large enough to cope readily with the feed, and at the same time due allowance must be made for the largest pieces to be elevated. In addition to this, the elevator must be fed correctly. For instance, if fed from a large accumulation of material, say from a stock heap or from a bin or hopper, it would not do to feed the elevator by an ordinary spout or shoot. In such a case the elevator should preferably be fed by a mechanical feeding device, such as an oscillating feed shoot, making between 30 and 60 oscillations per minute, which deposits at each backward and forward stroke a quantity corresponding to the capacity of the elevator. This precaution is, however, only necessary when dealing with minerals of uneven size (see Feeding Devices, page 202), and would not be necessary when handling grain or seeds. The choking in such cases, if ordinary spouts are used, is due to one of two causes. Either the rush of feed is too great, and is therefore more than the elevator can take up, or else a few large pieces of material have found their way to just above the feed spout and arch it over, thus stopping the feed flowing to the elevator. Feeding devices will obviate both. They will not allow an undue