Lubricating properties of cotton transfer films studied with a pin-on-disc apparatus

In cotton spinning machines fibres are twisted to a yarn by the high-speed revolution of a traveller on a ring. Wear of the ring–traveller system is thought to be attenuated by the lubricating properties of cotton fibre, but few experimental studies of the phenomenon have been reported. A new methodology has been developed to study both the formation of a cotton transfer film on a steel disc and the effect of such films on the tribological behaviour of a steel-on-steel contact. A ball-on-disc tribometer placed in a controlled humidity chamber was used. Cotton transfer films were produced reproducibly by rubbing a cotton pad on a steel disc. The chemical composition of the films analysed by IR was similar to that of films formed on the ring during operation of an industrial spinning machine. In addition to the cotton peaks the IR spectra contained a peak attributed to cotton wax. The film coated steel discs were subjected to rubbing against a steel ball at different relative humidity. In all cases, the measured friction coefficient in presence of the cotton film was lower than in absence of a film. The transfer films produced at a relative humidity of 30% were thicker than those produced at 50 or 75% relative humidity and presented no case of failure during the tribological tests. The wear volume of the steel ball was found to be negligible in the presence of the transfer film compared to the wear obtained during the rubbing after the destruction of this transfer film.