Rolling bearing vibrations—The effects of geometrical imperfections and wear

The geometrical shape and surface properties of the components of rolling bearings will always deviate to some extent from their theoretical design. For bearings of standard tolerances these deviations are large enough to cause measurable levels of vibrations when the bearing is in operation. The purpose of this paper is to show in some detail how these surface irregularities are related to the vibration characteristics of the bearing. The study is restricted to radial bearings, having a radial load and a positive clearance. The approximate methods used render the results useful mainly for lightly loaded bearings operating at low and moderate speeds. Attention has been focused on the effects of inner ring waviness and non-uniform diameters of the rolling elements. A mixed theoretical and experimental impedance approach has been used to treat the bearing when fitted in a simple machine structure, thereby showing how resulting vibrations of the bearing pedestal can be calculated, with account taken of the effects of bearing, rotor and foundation properties. During operation bearings undergo progressive surface and subsurface deterioration. These alterations of geometrical and surface properties of bearing components will always be accompanied by some degree of change of the vibrations characteristics of the bearing. Two common modes of surface deterioration—spalling fatigue and abrasive wear—have been studied, the practical objective being to highlight some possible methods of condition monitoring and prediction of impending bearing failure.