The frictional properties of several polytetrafluoroethylene (PTFE) coatings versus a 70 Shore D polyether polyurethane valve seat material were evaluated in ambient air, dry mica, and water immersion conditions. Plots were made of coefficient of friction versus time. The frictional properties of one of the coatings was dependent on its thermal history during curing. Of particular interest was the maximum and reversal in coefficient of friction noted for some of the coatings. From the data obtained in the mica immersions an estimate of the comparative wear life of the coatings was made. The mechanism involved in visco-elastic friction is discussed.

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