VIDEO RECORDINGS OF AN EHD POINT CONTACT LUBRICATED WITH GREASE

Optical interferometry has been used to study the film thickness of an EHD point contact lubricated with grease. The greases used were two lithium, two lithium complex and two sodium greases, all with NLGI grade two, the most common grade. They were based on one mineral oil of naphthenic type and one synthetic polyalphaolefin. The contact was lubricated without a continuous supply of grease and thus the film thickness decreased with time as the grease was gradually squeezed away from the contact area. The film thickness fluctuated during the measurement. To overcome this problem, the contact point was recorded with a video camera and the results evaluated after the tests. The video camera proved to be a powerful help in this evaluation. The test were run at 20-degrees-C and under pure rolling conditions at a rolling velocity of 0.055 m s-1. The results from all greases showed a decreasing film thickness that tended to stabilize on about 0.2-mu-m after 40 cycles. The lithium and lithium complex greases showed strong local film thickness variations inside the lubricated contact, deviating from the normally horseshoe-shaped contact, during the first 20 to 40 cycles.