Lubricated polymer-steel-systems

The effect of the interaction of thermoplastic polymers with lubricants on the tribological behaviour of a lubricated polymer-steel system was investigated with oscillatory tribometry and by determining the coefficient of friction (COF) at low gliding velocities, the surface hardness and the wear rate. The study focusses on elucidating how far surface- and interfacial energies of the frictional partners can give a first insight into the tribological behaviour. For a short-term contact of lubricant and polymer, the tendency of the lubricant to mobilise polymer chains near the surface, the “solving tendency”, influences the behaviour of the tribological system at the transition between sticking and gliding. The tendency of the lubricant to spread into the frictional contact correlates well with the COF at low gliding velocities. A long-term exposure of the polymer to the lubricant can result in a significant uptake of the lubricant by the polymer and to changes of the surface hardness (either by lubricant sorption or reactions of the polymer with the lubricant). The solving tendency gives a first insight into the extent of lubricant-uptake by the polymer. The formation of a lubricating film still influences the COF at low gliding velocities for polymers which do not show a significant sorption of the lubricant. For polymers with a strong sorption of the lubricant, the reduced surface hardness dominates the tribological behaviour. The wear rate correlates with the surface hardness of the polymer.