DYNAMIC FRICTION MEASUREMENTS OF MOS2 COATED BALL-BEARING SURFACES

The friction behavior of MoS2 coated bearing surfaces operating under ultra-low-speeds with velocity reversal is investigated. Forty-two set s of exclusively ultra-low-speed operating conditions were examined th at include rotational speeds in the range of 0.1-1 deg/s, normal loads varying from 81.6 to 185.4 N per ball, silicon nitride (Si3N4) and st eel ball bearing elements and MoS2 coating thicknesses of 4000 Angstro m and 10000 Angstrom. The friction torque of coated bearing surfaces w as found to exhibit Dahl hysteresis behavior. General trends for the t wo unknown parameters of Dahl's model, the rest slope, sigma, and the steady torque. Ts, were established for MoS2 solid lubricant films. Th e results of the coated friction measurements were compared to that of oil-lubricated bearing operating under similar conditions. In additio n, a series of experiments were conducted to examine the film behavior at operating speeds from 0.1-50 deg/sec. Under the conditions tested, the coated friction torque was found to be relatively invariant with velocity. Implications to the field of controls, as applied to precisi on positioning and tracking instruments are discussed.