Lifetime and discard for multi-layer spooling in cranes
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. Du ring 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. To facilitate rope endurance predictions and, thereby, predictions on the reliability of ropes experimental research is the only method. ln the past 75 years, investigations resulting in a high degree of certainty into the life time and discard of ropes with a view. to stress on ropes running over sheaves have been made at the IFT in Stuttgart. This work is based on over ten thousand tests. Unfortunately, there are still extensive areas in the fields of rope technology and rope applications which lack systematic tests and, thus, construction and dimensioning approaches. On the other hand it is indispensable, especially in a sensitive and crucial area such as rope technology, to continually verify existing and novel calculative approaches with the help of serial testing. Only by way of statistically proven tests it is possible to come up to and improve the required safety and reliability standards. The following paper, based on the latest investigations by the IFT, undertakes to prove the necessity of experimental research:
- influence of multi-layer spoolings on the lifetime of ropes
- influence of fleet angle on the lifetime of ropes running over sheaves
- ropes under fluctuating tension
Due to the time limit imposed on the speakers, the lecture will exclusively centre around the research subject of "Influence of Multi-Layer Spoolings on the Lifetime of Ropes".
Author(s): Wehking, K-H.