Discarding the economics of wire ropes

This paper discusses the discard criterion of a wire rope. The discussion indicates that choice of the discard criterion of a rope is governed by the dispersion of its service and by the ratio of the rupture losses to the initial cost of the cope. The service life dispersion is determined by the mechanical properties of the rope and by the adopted control procedure. The index of exploitation of the service life can be optimized with the aid of the condition of minimum total cost. A complete solution of the problem is hampered by lack of both economic and technical data on the dispersion pattern of the service life, and on its analytical relationship with the control procedure and frequency. However, even before the necessary studies have been completed, it is possible - in the light of the above, and in view of the flatness of the cost curve near the minimum - to categorize the rope exploitation index according to the relative dispersion on 2-3 classes and to the degree of liability represented by the rupture losses. In either case 3-4 categories would suffice for practical purposes. Where multiple-rope systems are involved, the rupture probability is much lower, and an improved exploitation index becomes an economic possibility. Control of the tension can also contribute in this respect. While at the outset this control should ensure uniform distribution of the load among the ropes, the distribution should gradually be adjusted so as to reduce the share of weakened ropes.