Lifetime and discard for multi-layer spooling in cranes
Technical Meeting Experiences with Ropes – Lenzburg 2003
Owing to the helical structure of both wires in strands and strands in ropes, complex stress conditions are produced during rope bending processes with the ropes running over sheaves or under fluctuating tension. This stress in the rope is superimposed with friction, the extent of which is a consequence of various parameters as well as of manufacturing factors. ln the course of the last decades, stress factors on rope wires have been meticulously predetermined by way of calculation by various researchers - the latest eminent contributions coming from scientists like Leider, Schiffner and Wiek. This has been undertaken for ropes subjected to fluctuating tension as well as for ropes running over sheaves, while taking the rather complex influence of friction into account. Even for standard load conditions it has, however, been impossible to determine the lifetime of a rope until breakage or discard from the calculated wire stresses, and this is for various reasons such as, for example, manufacturing quality or discrepancies in the test quality of different laboratories. During practical operation, ropes are exposed to additional stress which cannot be deduced mathematically. Owing to the multitude of parameters acting on the rope during practical operation, it is impossible to determine the lifetime of a rope exclusively from the calculated stress values for its wires.
Author: K-H. Wehking