Builders' Hoisting Machinery; Simple Lifting Tackle; Winches; Crabs; Cranes; Travellers; Motive Power for Hoisting Machinery baixar o livro de graça

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...the power is transmitted by means of a longitudinal line of shafting running down one wall of the shop, in a line with the fixed gantry. This drives a square shaft along the traveller girder on which the crab moves, and operates the motions of the crab through worm gearing or bsvel wheels. This movement is the reverse of that in which the crab is made to drive a travelling gantry, and there is little essential difference in the methods by which these movements from traveller to crab, or from crab to traveller, are transmitted. Instead of using a square shaft along the gantry, a cotton rope running at a high speed is a favourite method employed to transmit power from a distance to the traveller. When electricity is used as the motive power, then the dynamo is situated in any convenient locality away from the traveller, and a rod conveys the current thence alongside the gantry, whence it is taken up by a brush on the crab connected to the electric motor. Then belt gearing is used to reduce the speed as required. The motions of many overhead travellers are operated from one end, from levers brought to a cage within which the attendant sits. The method is applied to crabs actuated by square shafts and cotton ropes, and to jenny crabs operated by either method. The advantages are that the maximum of head room is obtainable in this way, more especially when a jenny is used, and that the attendant can from his cage see the work below much better than from a platform on crab or traveller. Such an arrangement consequently is used very extensively. CHAPTER IV. CRANES AND TRAVELLING CRABS: THEIR DETAILS OF CONSTRUCTION. The framework of a traveller consists of main beams or girders with, or without truss rods, and end cradles with their attachments....