Effects of Shaft Surface Wettability on the Friction of Oil-Impregnated Sintered Bearings

摘要

A shaft with a low oil-wettable surface was found to show lower friction than one with a highly oil-wettable surface when used in oil-impregnated sintered bearings. Both the highly wettable shaft and the low wettable shaft were made of hardened stainless steel, with the latter also being coated with PTFE transfer film. A projector was used to observe bearing clearances where a large amount of oil droplets was observed on the low wettable shaft as compared to the highly wettable shaft. This suggested an oil-rich environment in the sliding area, resulting in low friction of the low wettable shaft. The large stability of droplets on the low wettable surface - stemming from a large contact-angle hysteresis between the oil and the low wettable surface - is probably responsible for the abundance of oil droplets in the bearing clearance for the low wettable shaft.