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 sets of exclusively ultra-low-speed operating conditions were examined that include rotational speeds in the range of .01–1 deg/s, normal loads varying from 81.6 to 185.4 N per ball, silicon nitride (Si₃N₄) and steel ball bearing elements and MoS₂ coating thicknesses of 4000 Å and 10000 Å. The friction torque of coated bearing surfaces was found to exhibit Dahl hysteresis behavior. General trends for the two unknown parameters of Dahl’s model, the rest slope, σ, and the steady torque. Ts, were established for MoS₂ solid lubricant films. The results of the coated friction measurements were compared to that of oil-lubricated bearings operating under similar conditions. In addition, a series of experiments were conducted to examine the film behavior at operating speeds from .01–50 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 precision positioning and tracking instruments are discussed.