By Alex Dahm08 January 2009
For lifting applications fibre-only ropes may not be robust enough to withstand handling during installation and maintenance operations. Deterioration on multi-layer drums will also be a limiting factor. The solution to the problem would seem to lie between the two: composite steel-fibre ropes which would combine the robustness of a steel rope with the weight saving properties of fibre ropes.
The paper given at the conference was concerned with the development of such composite ropes for lifting applications, some of the background concept of which has been previously reported. The term "composite" is taken to mean a rope which is a steel fibre combination rope where the fibre in the rope is an integral load bearing member, rather than just acting as a support for the outer strands. The type of fibres under consideration here are of the aramid type, e.g. Twaron, Technora (an aramid copolymer) or Kevlar, which have a very high breaking strength associated with low stretch and low densities, compared with steel, as well as dimensional stability over a wide temperature range.
The idea of combining high-strength fibres with steel wires in a rope construction has been previously considered. In 1977 a UK patent was filed entitled "wire rope with load-carrying core fibres" which described a steel wire rope incorporating a core of aromatic polyamide fibres which act as load-carrying elements. Several years later Klees described a composite steel wire in their US patent which is similar to the configuration discussed here, but with some significant differences.An extension to the idea of the composite rope is the tapered mass rope proposed by McKenzie with the application of deep mine - drum winder - hoisting in mind. The tapered mass rope involves progressively removing steel from the rope to reduce its mass, and breaking strength, while maintaining the overall rope diameter. The motivation for this design is that in deep vertical shafts less rope strength is required at the conveyance end than at the head sheave as a result of the suspended rope mass. In theory a rope could be constructed that would have varying metallic cross-sections and the wires in the strands are progressively replaced by polymer fibres or rods. Unfortunately the practical problems of manufacturing such a rope and ensuring its integrity during operation has prevented one ever being manufactured. It would appear that in general, a composite rope like that proposed by Klees and others, is a more realistic solution for a light weight rope."