Consideration of Lubricants for Temperatures above 1000 F

Abstract

A study has been made of the various solid and liquid lubricants which could be considered for use to temperatures above 540 C. This study consisted of a literature survey to isolate temperature-stable, low shear strength compounds, and some experimental work to evaluate the most promising materials. Many of these compounds were effective at high temperatures and the results can explain the compatibility of certain metals at high temperatures. These compounds were not effective at lower temperatures. A more detailed study was made of the sliding characteristics of metals when lubricated with silver and molten boric oxide. The results show that, for silver, a number of factors such as choice of bearing materials, strength, and impurities affect the frictional behavior. Boric oxide, under conditions of boundary lubrication, showed a large increase in friction when the viscosity increased above 2400 poise. Variations in the friction could be explained by independent variations of viscosity and shear area. No lubricants were isolated which could be considered completely effective for a temperature range from 27 C to above 540 C. The choice of bearing materials and designs will have to be made to minimize these deficiencies.