To provide high-performance overloading of loose cargoes, metal scrap, charge and other materials, grabs are applied.
The construction of grabs differs depending on the type of the overloaded material, volume, control method and the intensity of works they are involved in.
Overhead grabbing reloaders of ore and coal are characterised by application of double-jaw four-rope grabs. Operation of the grab is provided in these cranes using two installed lifting mechanisms – lifting/closing of the grab jaws.
For portal (harbour) grab reloaders, double-jaw and orange peel double-rope grabs are generally used (and draglines in specific cases). Two lifting winches are installed in the machinery compartment of grabbing portal cranes.
Motor (with the built-in closing mechanism) or single-rope (lifting is interchanged with closing) grabs found their application during reequipment of the general-purpose lifting machine (hook cranes) for the grabbing mode. When installing such type of a grab, the control system must be modernized: grab power supply management and the crane safety appliances system – the overload limiter installation. The mechanisms and the crane metal structure are recalculated as to the possibility of operating under extremely heavy-duty conditions.
Grabbing cranes are developed for operation under extremely heavy-duty loading conditions and must be equipped with an OVERLOAD LIMITER with the “black box” parameter recorder.