Fffects of Humidity on the Dry Friction of Metals

Abstract

An experimental study has been made of the effects of humidity on the dry friction of metals. The sliding friction test was carried out in the atmosphere of a constant temperature (30°C) and a constant humidity (dry and relative humidity 80%).
Wear of iron slid against a hardened bearing steel ring under a load of 1 kg decreased sharply, when water vapour was contained in the atmosphere, particularly at a lower sliding speed. However, at a higher sliding speed (4 m/sec), no difference was observed in the wear of iron between the cases slid in dry atmosphere and in humid one. Wear of iron at 1 m/sec decreased with increasing water vapour pressure in the atmosphere.
Wear of 70/30 brass decreased in the presence of water vapour at a lower sliding speed, as in the case of iron.
However, in the case of leaded 60/40 brass which showed a severe wear, the presence of water vapour increased the friction and wear.
It was observed that in the friction of iron or 70/30 brass, fine wear debris cohered together and adhered to the frictional surface, and the presence of water vapour accelerated the cohesion and adhesion of wear debris to the surface. It is suggested that the fine wear debris (oxides) adhered to the metal surfaces protects the surfaces from metallic adhesion and reduces the wear.
A large wear debris was formed in the case of leaded 60/40 brass, and it appears that the adhesion of wear debris to the sliding surface increased by water vapour causes an increase of friction and wear.