Innovative visual rope inspection method for maintenance
When in operation for example in aerial ropeways, cranes or mines the ropes run over rollers and are deflected by sheaves. On the one hand the rope is subjected to tensile and bending loads and to torsion, and on the other hand additional stresses occur due to the helix-shaped structure of the rope. Running ropes of ropeway plants, cranes and mines have a finite service life. For this reason safe operation is only possible when the ropes are tested regularly and damage which necessitates the replacement of the rope is recognized reliably and in time before a hazardous operating state is reached. According to the specifications of the European Regulations for ropeways (EN 12927-1 to -8  for example), the ropes of aerial ropeways must be checked at regular intervals by visual and magnetic induction tests. According to EN 12927-7 , the main carrying ropes must be inspected visually every month with a maximum speed of around 0.5 m/s (examination speed). The visual checks serve to determine external wire breakages, lightning strikes, corrosion and wear, loosening of wires, changes of the rope’s lay length, changes of the rope diameter and other changes in the rope structure. In contrast to this, the magnetic induction test which must also be carried out regularly, serves to determine the internal state of the rope. In order to ensure safe operation of a rope system, both the visual and the magnetic induction test are necessary. As already mentioned, the visual inspection enables the ropes to be removed from service in time. The visual check helps to recognize weak points in the rope drive and to take measures to prevent repeated occurrence of such damage. Above all loosening of wires and other changes in the rope structure, as well as widespread lightning strikes or rope derailments are difficult to detect by means of magnetic induction test procedures or radiographic tests, thus making a visual rope inspection indispensable. The visual inspection is time-consuming and, for various reasons, not unproblematic with regard to the sure recognition of damages. Research projects which support the visual inspection of ropes have been undertaken jointly with the BG BAHNEN (Highways and Railways Trade Association) [3-6].
Author(s): Winter, S., Moll, D. & Wehking, K-H.