The Mechanical Handling and Storing of Material

311 AERIAL CABLEWAYS OR CABLE-CRANES that it supports the hoisting rope at a point always midway between tower and carriage This reduction of the unsupported span to one half is sufficient for the successfu operation of most cableways, though similar travelling carriages geared to one-fourth and three-fourths speed have been used for unusually long spans. Slippage, if. it should occur, causes no trouble, as the carriers are forced together by the main carriage when ever it approaches close to the tower, and are thus brought back occasionally to the common starting point. . . , . Still another system of supporting the hoisting rope is in occasional use. In this an endless hoisting line is provided strained initially to support itself with the same sag as the main cable. At a point on this line there is attached the end of the fall rope which supports the buckets from the carriage. By advancing the endless hoisting line and holding back on the endless travelling rope the fall rope is drawn out and the bucket hoisted. There-are at least two objections to this system 1 he load cannot be hoisted close to the tail tower, as a branch rope leading to the fall-blocks would foul the tower sheaves. With a three or four part line and a high lift this prevents the use of a portion of the cableway. The wear on the hoisting line is as great as on the traversing line since both must slide across their spool drums as they are overhauled, and any attempt at high speed will cause the endless hoisting line and branch fall rope to twist up and foul. . . . . • With a single hoisting line, the only practicable form of bucket is a single s p filled by hand and dumped by unlatching it and allowing it to turn over, or lowering it on to inclines which tilt it to liberate the contents, or by setting it down until the chain supporting one end can be unhooked either by hand or automatically, and hen hoisted again for emptying. For rapid excavation, dredging, or unloading, self-filling and self-dumping buckets with two hoisting lines are required. One of these lines may lift and the other close an “ orange-peel ” or “ clam-shell ” bucket; or one may be attached to each end of the skip, the contents of which are dumped by hau mg up one end or letting down the other. The two cables must be wound up together and at the sa speed for hoisting, or separately actuated for filling and dumping so that the manner of operating them in connection with the engine is o muc in eres ■ - . . that the skip may be dumped either by lowering the open end or by raising the o , this may be accomplished by winding both lines on a single drum with special accesso . To dump by lowering one end of the skip the hoisting drum is slopped after theload has been raised, the dumping line is clamped by a steel power brake a"d the drum ,s allowed to run down until the skip is inclined sufficiently. Ihe dumping 1 "e brake and drum slackens during the progress and tends to pile up on itself "hen drum is again started forward, which might damage the wire rope by bending crushing where the coils cross. To dump by raising.the back of the skip Ihe> dump line must be wound up at a faster rate than the ho.st.ng line One way to acconipl s this is to provide an enlarged central portion on the drum whose two ends car the hoisting and dumping lines respectively, and a slotted flange between Ih.s porBon and the portion carrying the dumping line. By a suitable sh.fter th.s hne can be thrown against the flange, and entering one of the slots be passed over to the large, where it is wound up faster than the hoisting line on the smaller diameter, a the end of the skip as desired. ... , The limitations on the two systems of dumping just described are that one will only dump while the skip is going down, and the othei while it is g0,nS UP-, available head room between the skip and the top of the spoil bank or the sack: of the hopper or railway car into which the load is to be dumped, is diminished by the y