The Mechanical Handling and Storing of Material

CONVEYORS A—APPLIANCES CONSISTING OF A STATIONARY TROUGH IN WHICH THE MATERIAL IS CONVEYED BY MEANS OF A CONTINUOUS PUSHING DEVICE CHAPTER IV WORM OR ARCHIMEDEAN SCREW CONVEYORS The worm or Archimedean screw is undoubtedly the oldest type of mechanical conveyor, and it has long been the only one for fine materials. This simple mechanism, with all its good and bad points, has been practically unsurpassed till within comparatively recent years. The history of the worm conveyor is difficult to trace, and it is probable that the flour miller was the first user of this labour saver. Whatever purpose the worm conveyor might have served at the time of its supposed invention by Archimedes (287-212 b.c.) Fig. 40. Earliest Construction of Worm Conveyor. we know for certain that a crude form of it was employed in flour mills over 250 years ago. The nature of the worm conveyor is such that only comparatively fine material can be conveyed satisfactorily, and at the time when this conveyor was the only mechanical one, all materials consisting of pieces too large for this type of conveyor were debarred, and had to be moved by hand labour. Worm conveyors are of the simplest possible construction. They consist of a continuous or broken-bladed screw fixed to a revolving spindle, and the whole is mounted in a suitable trough, so that the revolving screw propels the material fed in at one end of the trough slowly to the other end. The first specimens of worm conveyors were made of soft wooden octagonal spindles into which round holes were bored, and into these holes were driven hard wood blades with square pegs or shanks. Such a worm is illustrated in Fig. 40. In course of time this construction was improved upon by cast-iron spiral sections being threaded on a square iron shaft, which was turned for suitable bearings at intervals from 6 to 10 ft. 42