The torsional behaviour of Lang's lay triangular strand ropes will probably limit their application in very deep (2,500 - 4,000 m) single lift shafts which the South African gold mining industry is planning for the future.These ropes have been used extensively on drum winding systems and it would be of technological and financial benefit if their application could be extended as far as possible.An improved understanding of the mechanisms which may lead to rope instability is, however, required.A research project was initiated in 1994 to investigate the torsional behaviour of wire ropes for drum winders, the results of which are summarised in this article.The first stage of the project was the development of a laboratory based wire rope torsion testing machine, capable of conducting tests at constant rope twist, load and torque.Lay length variations and the rotation behaviour of triangular strand ropes (41-54 mm) were subsequently measured in vertical shafts ranging in depth from 1,000-2,500 m.Laboratory torsion tests were conducted to determine the torsional properties of the in-service ropes. Strength and ductility tests were also carried out on a 25 mm Lang's lay rope with different lay lengths to demonstrate the significance of lay lengthchanges.A new method of analysis has been developed which allows the calculation of in-service lay length variations and rope rotation during conveyance loading using the laboratory determined torsional properties.The rotation analysis takes into account changes in torsional stiffness resulting from the no-slip to slip transition associated with twist displacements.Predictions compare favourably with rope behaviour measured in existing shafts and the analysis is used to forecast the torsional behaviour in future shafts.Parameters which have the greatest influence on the torsional behaviour have been identified and recommendations are made on how the depth limit of application for triangular strand ropes may be extended.
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