Adhesive friction and wear of micro-pillared polymers in dry contact

Abstract

Elastomers are currently used intensively in various industrial applications. However, their deployment in dry tribological contact is normally inhibited by their poor dry sliding friction behaviour due to their intrinsically high adhesive characteristics. This problem is normally addressed in the industry by using various fluid (greases or oils) or solid (coatings or lacks) lubricants. Alternatives to the use of lubricants for tribosystems involving elastomers exist in the form of modifications of the elastomer composition or by reducing their effective nominal contact area by using surface texturing. The latter approach of reducing the adhesive nature of elastomers by surface structuring is the main focus of the present study.Two different micro-sized structures (consisting of micro-pits) were produced on thin Al inlays using a microscopically scaled punching process. These inlays were thereafter glued onto laboratory-scale injection moulds. These micro-pitted moulds were subsequently used to produce injection moulded micro-pillared Liquid Silicone Rubber (LSR) pads.The present study was focused on three different aspects: 1. Determination of the degree of replication of microstructures from injection moulds to the surface of LSR pads; 2. Evaluation of any possible friction reduction induced by a decrease of the nominal contact area through micro-texturing of LSR pads in dry tribological tests; and 3. Evaluation of the wear resistance of micro-pillared LSR pads under dry conditions.The results have shown that successful production and relatively accurate replication of micro-pitted structures from injection moulds onto LSR pad surfaces in the form of micro-pillars may be achieved. Furthermore, it was shown that a decrease of the effective nominal contact area through micro-pillars may enable a reduction of friction in comparison to the benchmark (unstructured LSR pads), but only for low normal loads where the adhesive component of friction is playing a determining role. Finally, wear tests have shown that the wear resistance of both micro-pillared structures produced on LSR pads under dry conditions against Al or PA6.6-GF30 was relatively poor. Both structures exhibited extensively worn regions after a testing distance of 11 m: structure 1 showed a larger worn area ratio than structure 2 (ratio worn area/total area ~45%–60% for structure 1 and ~30% for structure 2).