Multilayer Spooling of High Performance Synthetic Fibre Ropes. Experimental investigations of rope properties and stresses in winch drums

Abstract

Winch drums can appear as relatively simple mechanical components. However, accurate quantification of loads in multilayer winch-rope systems depends on a complex interaction between rope and drum. As vital parts of lifting appliances and other handling systems, usually with no redundancy measures, proper load assessment is essential for structural integrity and optimized design.

This thesis addresses the loads induced in multilayer winch drums by high-performance synthetic fibre ropes (HPSFRs) and a comparable steel wire. Experiments with nine ropes are carried out on two winch drums equipped with strain measurements. The ropes are spooled in multiple layers with different rope tensions, and effects of rope properties as deformation under load, friction and stiffness are investigated. Further, the accuracy of classification rules and calculation methods considered as state-of-the-art are assessed against measurements.

Experiments prove that multilayer spooling of HPSFRs can induce considerably higher stresses in drum structures than steel wire rope. HPSFRs also require many more layers until stable tangential stress levels occur. The stresses are dependent on rope tension, spooling speed, and rope properties such as deformation, friction, ratios between longitudinal and transverse stiffness and between drum and rope diameters.

Rope packages of HPSFRs appear as much stiffer than quantified from single ropes or multiple ropes in linearly stacked arrangements. The actual physics behind this stiffness- increasing effect is yet to be fully understood and requires further investigation. However, it is assumed that the higher loads induced by HPSFRs are related to the more significant rope deformations and contact conditions between ropes and between fibres. Possibly, this creates a more compact rope package with limited space for further deformations resulting in increased stiffness. A novel method measuring relative stiffness between rope layers directly on the drum indicates that a higher relative increase in rope package stiffness for the fibre rope than for the steel wire is possible.

Comparing results from this study with stress calculation methods show that the procedures specified by classification societies can considerably underestimate the actual stresses in multilayer winch drums with HPSFRs. A calculation method denoted as the " modified Dietz"-method takes both rope deformation and stiffness into account and is considered state-of-the-art. The radial pressure on drums with multiple layers of steel wire rope is predicted with reasonable accuracy by applying this method with the transverse stiffness determined from a single rope. It is shown that, unless empirically accounting for an increased rope package stiffness, this method fails to predict radial pressure for multilayer winch drums with HPSFR.

A calculation method for the maximum tangential stress level in multilayer winch drums with HPSFRs is proposed. This method is based on factors derived from the experiments and significantly improve calculations compared to classification rules.