122

SHOP TOOLS.

rising and falling with, the ram. The beam or jib has the ladleat one end, and a counterweight at the other. The horizontalmotions are obtained either by hydraulic power, or by hand-gearing.

Sir Henry Bessemer originally gave considerable attention tothe arrangement of the maehinery for the pits of steelworksfor his process, and,, in principle, this remains the same now.Attention has been of late years directed to effecting economiesin the production of hydraulic power, by employing compoundengines, and by saving water during the working of the crane,-when the loads to be raised and lowered vary. Also by mini-inising the effect of the great leverage of the weighted ladle onthe beam. In the original forms of crane one centre ram wasmade large enough to lift both the ingot and its own weight,together witli that of the top and jib of the crane, and to actalso as a guide. A more modern arrangement is shown byPlate 21, which is a “Hydraulic Centre Crane” by Messrs.Tannett, Walker, & Co., of Leeds, capable of lifting 12 tons.The radius is 17 feet, and the stroke or vertical lift is 7 feet.There are two rams AA (9 inches in diameter), in communi-cation with the accumulator, nearly balancing the dead load ofthe rams, jib, ladle, &c. Sufiicient margin is allowed to admitof the crane descending and forcing back into the accumulatorthe water that is displaced by this ram. A third ram B (12Jinches in diameter) is under the control of the worlanan bymeans of a valve, which can be placed either close to the craneor at a distance from it. In this case the turning is done byhand, but it is offen perforined by a hydraulic engine. Thetwo side rams effect a saving of water-power, and enable thecrane to be made of any desired strength, without involvingthe loss of power that occurred in the old form of crane.

Mr. Thomas Wrightson has designed a good form of balancecrane to meet the diffieulty of dealing with the strains in aheavy 15-ton casting crane. This is shown by fig. 36. Thecrane post revolves on a pivot, and carries the cylinder with it,in its horizontal rotation, by means of a key. Frames for the