The Mechanical Handling and Storing of Material

CONVEYING BY GRAVITY ^97 cases from a top floor to the cellar of a London warehouse. The cases or casks are started at the top on a short length of roller runway, and vary in size up to 2 ft. 6 in. cube, and in weight up to about 4 cwt. The time taken on the journey down the shoot of course varies with the size of the case, but the maximum time does not exceed about 10 sec. On the last run of the shoot near the basement the speed of the cases is broken by several large steel spring brakes, and at the extreme end there is a plated upward incline to a small platform upon which the cases land. Inclined Roller Runways or Gravity Conveyors.1—For materials in sacks, cases, or parcels, or individual loads of more or less uniform size, roller runways are often used. During the past ten years roller runways, as shown in Fig. 267, have been largely adopted for moving boxes of regular shape having smooth bottoms, especially in bottling fac- tories. As auxiliary appliances, these, gravity conveyors are very convenient and easy to apply. Their attractive- ness lies in their cheapness and in their applicability where no running shafting or electric power is available. Another valuable feature is. the ease with which they can be led round curves. The carrying capacity of a roller runway, however, is much less than that of a continuous power- driven conveyor, and the useful length is, as a rule, limited according to the height available at the feeding point. In the case of an ordinary in- clined shoot of wood or steel plate, there is considerable friction between the sliding body and the surface of the shoot. A roller runway is an artifice to reduce the friction to a Fig. 264. Spiral Gravity Shoot of Timber. minimum, by substituting freely-revolving rollers for the shoot bottom. The usual dia- meter of the rollers is about 2| in. and the pitch from 4 in. to 6 in., according to the size of the box. The rollers are made of thin solid-drawn steel tubing, and mounted 1 W. H. Atherton, “Continuous Package Conveyors for Factories.”