Film formation and shear properties in screw tightening lubricant PIB under oil starvation condition

Abstract

This paper describes that the film formation and shear properties of screw tightening lubricant PIB (Polyisobutylene) under the oil starvation condition. The point contacted pure sliding tests were conducted, and the film thickness was measured using the interferometry method with the spacer layer. The result showed that the starvation region occurred at the inlet of the conjunction becomes large with time. It was also shown in the initial time of the test that the film thickness decreases due to the oil starvation, however, the thickness is thicker than the value equivalent to surface roughness. The friction coefficient depended on the starved area, and that showed the constant value of 0.16-0.17 in the fully starved condition. The relationship between the friction coefficient and the shear rate suggested that the coefficient in the high shear rate condition is the constant value, that revealed the film may be changed to the solid like film with the high shear strength in the fully starved condition. The long term test showed that the breakdown of film is appeared at about 120 s and then the wear area expands in the remainder of the test. The test results suggested that the PIB lubrication film has the high shear strength and enable to protect the contact surface in the tightening screw from the direct contact and the wear.