Some open questions in boundary lubrication

Bowden and Leben, in 1938, showed that there was a critical temperature limit for smooth boundary friction. This, Frewing showed in 1942, could be analyzed by the van 't Hoff isochore. Next, the 150 degrees C critical temperature of mineral oil was found to be due to its surfactant component, which also followed the van 't Hoff rule. This temperature was the same as Kelley and Lemanski's 300 degrees F limit for involute gears. Research needs in boundary lubrication are: the theory of boundary friction, the cause of the Borsoff effect, the fraction of vacant adsorption sites at scuffing, the reason for chain matching and how load and surface roughness alter the critical temperatures. When physisorption changes to irreversible chemisorption, a micron-sized thick film forms, giving a thick boundary lubricating film. A mercury displacement rig can be used to show if and when such a thick film occurs on metal surfaces. We have developed a high frequency rig (HFR) with reciprocating motions to study the temperature ranges that this thick lubricating film is formed. Another issue is that deciding if the absence of an organic layer covering the asperities or Dyson's failure mechanism of the EHL film is the effective cause of scuffing, is still very much an open question.