Dynamic torque characteristics of disk-drive spindle bearings

Dynamic torque characteristics of ball bearings for hard disk drives are investigated. The use of a generalized Stribeck curve reveals distinctive tribological regimes for the bearings during dynamic conditions. Below a transition speed, the bearing's dynamic torque is dominated by viscosity effects so that (a) torque scales with bearing speed to the 0.66-th power and (b) torque values affected strongly by the operating temperature. Above a transition speed, the bearing's dynamic torque is primarily affected by the EHD lubrication film between the ball and race-ways. Consequently, bearing dynamic torque has a maximum value (Mmax) during spinup that is several times higher that in the steady-state operation (Mss). Furthermore, both Mmax and Mss vary little with applied axial load and appear independent of bearing speed. It is this kind of disparity in tribological characteristics that precludes a uniform scaling of bearing torque on operating parameters.