Noise and Vibration

Bearing rings and balls are not perfectly round and the balls and raceways, even after extensive fine grinding and polishing, are not perfectly smooth. There are machining imperfections in the form of rough or uneven surfaces which will cause one ring to move or oscillate radially in relation to the other. The amount and speed of this movement contributes to the amount of bearing vibration and bearing noise.  The smoothness or quietness of a bearing can be checked by accelerometers which measure bearing vibration at the outer ring, usually with the inner ring rotating at 1800 rpm.

Vibration is potentially damaging to a bearing and the equipment it is used in, increasing the rate of fatigue and shortening bearing life. Displacement measurements do not tell us enough. Vibration in a bearing or a machine will usually occur at many different frequencies and they all contribute to fatigue so we need to take all of these frequencies of vibration into account in our measurements of vibration.

A low noise/vibration rating is achieved by paying particular attention to the surface finish of the raceways and balls, the roundness of the rings and balls and correct cage design.

To help reduce noise levels even further, low noise greases are available and the choice is now greater as improved manufacturing techniques mean these greases are more finely filtered and contain fewer, smaller solid particles. These particles generate noise when they pass between the balls and raceway.

External factors such as surrounding vibration can affect bearing noise. Another problem, particularly with smaller and thin-section bearings, is ring distortion caused by poor shaft or housing roundness. Dirt or dust contamination will also increase noise and vibration levels. Poor fitting practice or incorrect handling is sometimes to blame, causing shock loads which, in turn, create scratches or dents in the raceway.

tolerance date for vibration of one bearing

maximum vibration acceleration of one bearing