Some open questions in boundary lubrication

Bowden and Leben, in 1938, showed that there was a criticaltemperature limit for smooth boundary friction. This, Frewingshowed in 1942, could be analyzed by the van 't Hoff isochore.Next, the 150°C critical temperature of mineral oil was foundto be due to its surfactant component, which also followed thevan 't Hoff rule. This temperature was the same as Kelley andLemanski's 300°F limit for involute gears. Research needs inboundary lubrication are: the theory of boundary friction, thecause of the Borsoff effect, the fraction of vacant adsorptionsites at scuffing, the reason for chain matching and how load andsurface roughness alter the critical temperatures. Whenphysisorption changes toirreversible chemisorption, a micron-sized thick film forms,giving a thick boundary lubricating film. A mercury displacementrig can be used to show if and when such a thick film occurs onmetal surfaces. We have developed a high frequency rig (HFR) withreciprocating motions to study the temperature ranges that thisthick lubricating film is formed. Another issue is that decidingif the absence of an organic layer covering the asperities orDyson's failure mechanism of the EHL film is the effective causeof scuffing, is still very much an open question.