Formation of Particulate Contaminants (Brown Sugar) in Miniature Bearings.

There have occasionally been field reports of miniature bearing failures attributed to particulate contaminants which, because of their appearance under low-power magnification, have been given the descriptive term brown sugar. This study examines the formation of particulates under both dynamic and static conditions. The lubricants include diesters, polyol esters, a silicone, and mineral oil the bearing surfaces or substrates were 52100 steel, 440C steel, and Pyrex. Particulate formation was readily achieved under boundary lubrication. The resultant films adhered tenaciously and resisted rinsing or wiping. Surface analysis by X-ray photoelectron spectroscopy and Auger electron spectroscopy indicated the presence of iron oxides and probably iron-organics soap compounds. Under static conditions exposure of thin films of lubricants to light or heat 100 C did not generate lubricant-derived particulate products. This exposure did have one adverse effect, viz. the complete depletion of several antioxidants after only a few hours. Author