Evolution of grease lubrication regimes and surface damage during reciprocation-oscillation transformation

Abstract

The responses of two kinds of lithium greases during the transformation from reciprocating motion to oscillation were firstly studied on a ball-on-disk test rig using optical interferometric technique. Although in pure rolling motion, after a long run a thin film lubrication (TFL) state is formed on the track, in simple sliding motion an interior boundary lubrication (BL) region is quickly developed in the contact after only tens of working cycles and the region increases with the increase of the radius stroke ratio. Microstructure of the thickener fiber makes a difference in the formation of the inside BL region. By an SRV tester, grease lubricated wear tests were carried out using samples with smooth surfaces, textured surfaces and textured + diamond like carbon (DLC) coated surfaces in simple sliding reciprocating and oscillating motion. It is seen that lubrication using grease with thinner and evenly distributed thickener fibers produces less severe surface damage. The smooth or textured surface is soon worn out, causing severe surface damage. The application of DLC coating onto the textured surface can protect the surface well but increase the friction coefficient a little bit.