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Anti-wear
Table of Contents
Physical & Chemical Properties
Anti-wear additives are those which reduce or control wear. They form organic, metallo-organic, or metal salt films on the surface. Sliding or rolling occurs on top of, or within, the films thus reducing metal-to-metal contact. Anti-wear additives only reduce the rate of wear, which still occurs, but without a catastrophic failure. The films are sacrificed so that the wear fragments in the oil are primarily the film material.
Anti-wear performance is measured on numerous bench lubricant testers operating under moderate conditions, where the volume or weight of material removed is measured.
An example is the 4-ball wear test. Also, the pin-on-disk apparatus is used and run under conditions described in ASTM G 99. The types of anti-wear additives are zinc dialkyldithiophosphates (ZDDP), carbamates, organic phosphates such as tricresyl phosphates, organic phosphates and chlorine compounds. The most common anti-wear additive is ZDDP, which decomposes to deposit metallo-organic species, zinc sulfide or zinc phosphate, or reacts with the steel surface to form iron sulfide or iron phosphate. Operating conditions control the specific film material.
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