Polymer Wear Modes.

Abstract

Abstract : This work originated with frequent observation that polymers wear less under severe conditions of sliding than under mild conditions of sliding. An investigation was conducted with a view to deriving mathematical models for the wear behavior of polymers. It was found that the physics of the wearing process is not sufficiently understood to write mathematical models at this time. The investigation included rubbing various polymers against steel surfaces in a circular track while continuously monitoring the gases in the vicinity of rubbing. The following conclusions were reached: The conventional equations for temperature rise on rubbing surfaces are of limited value. This was found by comparing the gases evolved from the sliding process with gases evolved from polymers heated to various temperatures. The wear rate is controlled primarily (if not exclusively) by the tendency to form or not form a stable transfers film on the metal surface. Severe wear always occurs if there is no transfer film or if the transfer film is readily removed, and the wear rate is proportional to rubbing severity. Where a stable transfer film forms very little wear occurs until a surface temperature is reached that is 50 C above the temperature at which severe wear begins in the case where no transfer film forms or is retained. The nature of the transfer film depends upon the severity and time (number of passes) of sliding, and severity excursions through all ranges of severity. The exact nature of this dependence has not been explored. Surface cleanliness influences wear rate far more than surface finish does.