Abstract: Friction properties of micro journal bearings are investigated with special developed test-rig. The bearings with journal diameter of several hundreds of micro meter are subjected to a small contacting load of several milli-Newton. Three kinds of bearing materials including mild steel, copper and cemented carbide are tested against the journal made of high-carbon steel under different contacting load and rotation speed. It is found that the material hardness and the surface roughness of the bearing have obvious influence on the friction coefficient. The change of rotation speed (100~1 200 r/min) has small influence on friction coefficient. The change of contacting load (5~70 mN) only result in slight decrease of friction coefficient. Among the three pairs of micro bearings, the copper bearing against high-carbon steel journal exhibits best friction performance.

Key words: Material hardness Surface finish, Micro bearings, Small load Fraction performace