Charge generation and bleed-off in spindle motors with ceramic ball bearings

A disussion about charge generation and bleed-off in spindle motors with ceramic ball bearings is presented. It is found that as compared to high-carbon chromium steel ball beaarings, hybrid ceramic bearings with high precision silicon nitride rolling elements and steel races exhibit smaller thermal expansion, good wearability and higher rigidity. The voltage is determined by the equilibrium between the charge generation in the bearings and the charge bleed-off in the ferro-fluid seal of the motor.