On the torsional behaviour of triangular-strand hoisting rope

Owing to the helical construction of the wires and strands in a triangular-strand rope, a torque is generated when the rope is restrained and tensioned. When a rope is suspended vertically, there is a load differential along its length due to the self weight of the rope. This load differential gives rise to an initial torque differential in the rope. Since the rope is constrained only at the conveyance and sheave wheel, the torque along its length must be constant. In order to maintain equilibrium, a variation in lay length occurs so that the lay length at the conveyance end decreases, and the lay length at the sheave end increases, from the manufactured state. The tension-torsion testing of steel-wire ropes is discussed, and it is shown how the results of the tests can be used to predict static In-shaft torsional behaviour. The expected changes in strand lay length in very deep shafts (deeper than 2500 m) are calculated, and the associated problems and effects of severe changes in lay length on lope endurance and safety are discussed. Examples of current in-service rope distortions such as kinks and corkscrews are shown.