The film forming behavior at high speeds under oil−air lubrication

•EHL film thicknesses were measured up to 30 m/s under oil−air lubrication.•The minimum film thicknesses decrease linearly against speed in starved regime.•A defined parameter η shows 30 times higher under oil−air lubrication at 30 m/s.•The roles of micron-order oil droplets were verified and discussed.

The film forming behavior has been investigated under oil−air lubrication, compared with that under oil−jet lubrication in present work. Images of microscopic oil reservoir and interference were obtained up to 30 m/s. A parameter η describing the oil supply effects is 30 times higher and the film thickness reduces in starved regime much slower under oil−air lubrication compared with that under oil−jet lubrication. The contribution of micron-order oil droplets on film forming is discussed. More micron-order oil droplets can spread onto the disc while less of them are driven away by centrifugal effects. As a result, the oil supply efficiency of oil−air lubrication is improved. The high pressure compressed air can blow off the oil and intensify the film oscillation.