Effect of lubricants on micropitting and wear

Micropitting was studied using a three-contact disc machine having a central roller in contact with three harder, annular counter-discs (rings) of precisely controlled roughness. Roughness, running conditions, base stock and additive concentration were varied. The response of the same lubricants in a reciprocating sliding wear test operating in the boundary regime was also studied. Results of experimental studies of the rolling contact behaviour of carburised steel rollers are reported. All the tests with the additive present led to micropitting. However, severe micropitting wear was only observed when the calculated film thickness exceeded 12% of the centre-line average roughness of the rings. It was found that there was an approximately inverse correlation between the micropitting damage in the disc machine test and the mild wear in the reciprocating sliding test. This was attributed to the tendency of anti-wear additives to prevent running-in of the rough surface. (C) 2008 Elsevier Ltd. All rights reserved.