Surface Roughness and Load in Boundary Lubrication

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Abstract
Using the Bowden-Leben apparatus, the effects of load and surface roughness on the frictional behavior of various steels are studied over a range of temperature and of additive concentration. Cetyl amine and long-chain acids were used as surfactants, cetane and squalane being the carriers. The critical temperatures associated with sharp rises in friction and in track width decreased linearly with increasing load. When extrapolated to zero load, these temperatures corresponded to the temperature at which serious surface damage occurred. An explanation of this effect is given in terms of a desorption work term. Thermodynamic analysis is shown to be very powerful using the Langmuir adsorption model. The heat of adsorption and entropy changes were found to be functions of surface roughness for all the steels investigated. Optimum adsorption occurred at about 15 microinches CLA. This offers an additional thermodynamic explanation for the known danger of having machine parts too smooth.

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