Rubber steel friction in contaminated contacts

The effects of water, oil, and wear debris on the friction coefficient of rubber against steel were investigated. A pin-on-disk apparatus was used to simulate rubber tyres on track in a metropolitan transit system. Three methods of applying the water were used, and the results were compared with dry conditions. One method was to spray it, one was to drip it, and one was to use fully flooded conditions. The sprayed condition produced only a momentary drop in friction, but the fully flooded condition resulted in the lowest continuous reduction in friction. Oil and wear debris contaminants produced similar levels of friction. When dry sliding tests were conducted at a temperature of 200 °C, to simulate certain conditions observed in service, the friction coefficient exhibited values similar to those for oil and contaminants. This behaviour was correlated with the formation of blisters and thermal cracks on the rubber side, and the subsequent transfer of debris particles to the counterface as the softer rubber surface degraded.