THE MECHANICAL HANDLING OF MATERIALS 317 the chains are fitted with buckets which are suspended from a point above their centre of gravity, and are free to swing. Thus, whatever the position of the endless chain, the buckets always hang in an upright position whether they are travelling vertically or horizontally. For this reason the gravity-bucket system may be employed to perform the combined duties of elevator and conveyor. Delivery at any desired point is arranged for by interposing a device which tilts the bucket and discharges its contents. The driving gear is unique, and usually consists of a spur-geared engine operating two sets of panels which successively thrust the chain in the direction of its travel, engaging with both sides simultaneously. In this way the chain is puslied forward link by link. An essential feature of the system is the provision of some type of filling device, so that the material may "be delivered to the
Fia. 232.— The Gbavity-Bucket Conveyor.
buckets without undue spilling. The ordinary sprocket drive is, however, fitted in some of the more modem installations. The filler consists of a hollow casting securely keyed on a steel spindle. The casting is formed with five openings in its periphery, and these are arranged to centre with the buckets as the filler is rotating. The filler is driven direct by the conveyor chain engaging with an adjustable sprocket wheel bolted on the rotating hollow casting. The speed of the gravity bucket is necessarily low, the rate of travel normally vaiying between. 25 and 50 feet per minute. The capacity depends upon the size and speed of the buckets used, and installations may be erected capable of handling from 20 to 100 tons and upwards per liour. The power required is low in comparison with many other types of conveyor, but depends largely upon. the proportion, of elevating work which. is performed.
The following table gives the power required for varions sizes of gravity-bucket conveyors :—