The Mechanical Handling and Storing of Material

CONVEYORS J.—APPLIANCES CONSISTING OF A STATIONARY TROUGH IN WHICH THE MATERIAL IS CONVEYED BY MEANS OF A CONTINUOUS PUSHING DEVICE—continued CHAPTER V PUSH-PLATE OR SCRAPER CONVEYORS The origin of the scraper conveyor may be found, like that of the worm conveyor, in the oldest industry of the world, namely, flour milling. It is rarely found now even in the oldest flour mills, but being the progenitor of an important conveyor, it may be interesting to give a few details as to its construction. The box or trough was of wood, and sufficiently deep to carry the whole apparatus, including the return strand. The terminal pulleys were smaller than those of elevators of the same capacity, there being no lifting to perform. Their diameter varied from 10 to 15 in., and the belt which carried the wooden scrapers was rarely more than 2 or 3 in. wide, although the scrapers were from 6 to 10 in. long. The spindles were generally carried in bush bearings, fixed with a flange against the outer side of the box. A tightening gear was seldom used, but a large opening with a lid facilitated the tightening of the band, whilst in the base of the trough a piece of glass fixed flush with the inside of the box showed the miller when his conveyor was at work. The speed of the scrapers was from 100 to 200 ft. per minute. Push-plate conveyoi's now vary very much in minor details of construction, but in principle they consist of a fixed open trough made of stout sheets of steel or iron,, sometimes of cast iron, rarely of wood. The material to be conveyed is deposited in this trough, and is pushed or dragged along by a series of plates attached at equal intervals to an endless chain, which latter, with its attachments, travels over terminal pulleys, so that only one strand of the chain is at work at a time. The chain should be attached as nearly as possible to the centre of the push-plates. These are not generally allowed to touch the bottom of the trough, and are therefore fitted with skidder bars which slide on well-greased angle-bars forming portions of the framework. Sometimes instead of skidder bars the scrapers are fitted with a pair of small wheels or rollers- running on corresponding channel or angle bars, which is a good plan, as it reduces- the driving power required, and prevents the noise which in large and badly lubricated conveyors is often disagreeably loud. The scrapers of push-plate conveyors are of different forms, the commonest being rectangular, though generally they conform as nearly as possible to the shape of the trough. They are sometimes, however, in the form of discs, rakes, or dogs, according to the material to be handled. Fig. 72 shows a portion of an ordinary push-plate conveyor in two views, in which 6i