Cranein Engineering

Crane, in Engineering, is a machine much employed at docks, wharves, warehouses, and elsewhere, for raising and lowering various materials. Cranes may be worked by hand, steam, high-pressure water, or, a plan which has recently been adopted, by electromotors. The simplest form consists essentially of a vertical pillar, a long oblique arm or jib springing from the base of the pillar, its upper extremity reaching to the maximum height required; and a lifting-chain passing from a drum on the crane-post over a pulley at the top of the jib, and bearing at its other extremity the load to be lifted. Rotation of the drum produces upward or downward motion of the load, and is effected by hand or machine. The crane admits of rotation about the vertical post, this motion being produced by auxiliary apparatus. A direct-acting steam-engine, with small vertical boiler attached, is frequently mounted on the carriage that supports the crane, and is adjusted in position so as to balance the load lifted. The necessary force to lift the load might be too great to be applied directly at the drum; so a smaller force is made to effect this by a combination of spur-gearing. The crane being mounted upon a carriage possesses the advantage of being able to carry a load from place to place, and lines of rails are frequently laid down to facilitate this. The jib is to stand compression, and should therefore be designed so as to resist buckling. It is frequently hollow, or, in heavier types, of lattice-girder pattern. Armstrong's hydraulic cranes employ water at a pressure of 700 lbs. to the square inch, and the power is multiplied by a system of pulleys. The foundations supporting heavy machines must be carefully and substantially built, loads of fifty to a hundred tons, such as are lifted by the heavier cranes, being sufficient to crush weak foundations.