The Mechanical Handling and Storing of Material

INTRODUCTORY REMARKS 41 just the opposite consistency, almost dead, as, for instance,, cement, and if conveyed in a push-plate conveyor have a tendency to lie at the bottom of the trough and let the scrapers travel over the top. Then, again, there is a difficulty in handling fine materials on account of the tendency of fine particles to enter the working parts of the conveyor, and if the material is of a sharp and cutting nature this is one of the principal drawbacks, as such parts are soon destroyed by wear and tear. It will thus be seen that for the conveying by mechanical means of fine materials the utility of the existing types of conveyors is considerably restricted. Belt conveyors can be used if the material can be fed on and off without causing dust, and also if the belt travels sufficiently slowly. Whilst all conveyors with agitators can only be used when running slowly or when completely covered in, this is sometimes difficult, particu- larly with push-plate conveyors, the general construction of which would not permit of covering without complications. The Zimmer conveyor of reciprocating type appears to be very suitable for handling fine material, because the trough can easily be covered with a dust-tight lid, and there are no stirring or pushing elements to create dust or which are subject to wearbut again there is an objection, and that is that with this type of conveyor fine material can only be conveyed satisfactorily in a very thin layer or stream, and then preferably on a slightly downward gradient, so that here the same objection holds good as with the belt conveyor. Both can be mads to do the work, but the capacity is small on the belt conveyor on account of tli6 slow speed, and on the Zimmer conveyor on account of the thin feed, so that both these types, if used for fine material, would have to be made rather wider, and therefore more expensively, for capacities which could be conveyed on smaller conveyors if the material were coarser. As a résumé of the foregoing, push-plate, belt, and Zimmer conveyors cannot be looked upon as the best means of handling fine material under general conditions, so there is only the worm conveyor left. This can be fitted with a dust-tight lid, inlets and outlets, and it has a moderate capacity. It does the work well if the material is not of a cutting nature, and is inexpensive in first cost, but for long distances and large capacities it presents drawbacks which make it not much better than the other types. The driving power consumed is higher than for any other conveyor, and with sharp and cutting stuff the wear and tear on the ordinary intermediate bearings, which must of necessity work surrounded by the material to be conveyed, is very great.