Transition Temperatures in Sliding Systems

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Abstract
A pin-on-disk type of apparatus is used to study the effect of operating variables on transition temperatures with dilute solutions of pure fatty acids in pure paraffinic hydrocarbons and with a straight paraffinic mineral oil. It is found that the temperature at which the sudden transition from low to high friction and wear occurs increases with sliding speed, decreases with load, and is otherwise independent of operating variables. Empirically, the reciprocal of the absolute transition temperature varies linearly with the logarithm of the ratio of load to speed. The absence of conventional hydrodynamic lubrication in this system is demonstrated. It is concluded that these results are inconsistent with the widely accepted concept that boundary lubricants must form a “solid” adsorbed film to be effective. It appears necessary to adopt a modified view of the role of the boundary lubricant, in which rheological and other diverse physical characteristics must be considered, and not simply the state of matter in which it exists. In addition, it appears necessary to consider the interrelated kinetics of boundary film formation and welding between asperities.

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