Analysis of oil supply phenomena by sintered porous reservoirs

Different ways of supplying a liquid film with lubricant initially contained in a porous structure have been investigated experimentally: centrifugation, creeping by roughness or thermal effects. Observations and measurements concerning sintered porous materials (polyimide, stainless steel) impregnated with conventional lubricants for space applications (MAC or PFPE) are presented and discussed in this paper. Centrifugation caused the release of lubricant from the porous structure when a threshold in rotational speed had been reached, proving consistent with an analytical model in which the threshold is a function of oil surface tension and pore radius. We also observed some leakage from porous samples deposited on rough stainless-steel substrates. But the lost volume did not depend on surface roughness. On the other hand, a temperature gradient representative of the temperature distribution in running ball bearings proved unable to make the oil spread out from the tank, although capillary effects due to roughness did.