Mechanism of Nano-Scale Thickener Deposited Film in Starved Grease Lubrication

The behaviour of grease lubricating film in and the micro-scale migration of lubricant around a point contact under starved condition was studied by using relative optical interference intensity method. Under laboratory conditions, the contact would experience fully flooded phase – starving phase – deposited film lubrication phase – bled oil lubrication phase, successively. By using atomic force microscope (AFM), the deposited film was detected. It was formed from the sheared thickener debris during the rolling process and was of nano-scale. Infrared measurement showed that bled oil was basically base oil which was gradually squeezed out of the bulk grease during the operation. In the very beginning of the experiment, the initial grease reservoir around the contact was lost due to starvation, however, bled oil would reform a second phase oil reservoir to replenish the contact in the long run. Thickener deposited film would increase the contact angle of bled oil on the rolling surface which prevented bled oil from replenishing the rolling track. But this deposited film would be consumed during overrolling, after which the bled oil would reflow back to the contact. Evidence showed that the nano-scale thickener deposited film contributed to protecting rolling surface when bled oil was insufficient.