For handling heavier weights, and for lifting weights to bigger heights, tower cranes are necessary and for those companies, which do not have their own tower cranes, tower crane hire is available. Factories and constructions sites have to handle a stream of heavy objects day in and day out hirein. These heavy materials might have to be moved from one place to another, loaded into waiting trailers, unloaded from the larger vehicles that have brought them in, or fitted correctly into an existing structure. At times, such operations are to be performed at substantial heights. All these are managed by a lifting tackle or a tower crane. In fact a tackle functions as a unit of a large tower crane itself, for a tower crane lifts and places heavy objects at the required points with the help of such a gear.
Independent lifting tackles that are mounted on different types of frames are used for handling lesser weights. A tackle may be mounted on an A frame, an H frame, a portal frame, or a tripod. In an A frame, the two arms of the frame converge at the top as in the alphabet A and a pulley block sheave is fixed at the point of convergence. A hook sheave is suspended from this pulley, equipped in different sizes and shapes to lift different types of weights. In an H frame, the arms of the frame are parallel, and there is a horizontal cross bar connecting the two arms, to which the pulley is attached. A portal frame is very similar to an H frame, except in that the cross bar connecting the two arms is fixed at the top of the vertical parallel arms. A tripod frame consists of three members in space converging at one point, from which point the pulley block is suspended.
A lifting tackle is a small piece of machinery which many companies own, but a tower crane hire becomes necessary quite often. A tower crane is a monster of a machine, and consists of a central mast, to the top of which is attached what is known as a slewing jib, which can be rotated a full 360 degrees. The base of the central mast remains anchored to a concrete foundation at the work site. To keep the jib balanced, appropriate counterweights are provided on the opposite side of the jib. As objects have to be lifted pretty high by using a tower crane, there is provision for increasing its height with the addition of extra modules of the mast.