To understand the answer to this question, you need to understand how vibration works and its parameters: displacement, velocity and acceleration. Put your thinking caps on, it’s about to get technical.
Vibration describes a movement or mechanical oscillation around a starting point. Displacement is the distance or amount of oscillation in a vibrating object, defining how far away from the starting point an object has moved. The entire oscillation movement is called a cycle.
The number of times a complete cycle of motion takes place during one second is called the frequency and is measured in hertz (Hz) or can be expressed as cycles per second (CPS).
Vibration velocity, which is calculated by multiplying displacement and frequency, tells us how quickly the bearing is moving away from the central point, and in turn, how noisy the bearing will be. The higher the vibration velocity measurement, the noisier the bearing. Vibration velocity can be measured using a bearing vibration tester or an Anderon Meter.
Although vibration velocity is a useful tool in calculating the fatigue potential of a bearing, it doesn’t factor in the strength of the force powering the movement. Vibration force can be very damaging at high frequencies, even where velocity readings may be low.
For this reason, vibration acceleration calculations are useful for bearings that will experience frequencies above 2000Hz. The sum works out the increase in velocity, which provides useful force data in Newtons.
Why does it matter?
Knowing a bearing’s vibration rating isn’t much good if you don’t know how to interpret the results or why it’s important.
Bearings are not perfectly round and even after being machined to fine tolerances, the balls and raceways exhibit uneven surfaces. Excessive vibration will increase bearing noise and can significantly shorten the life of a bearing, leading to premature equipment failure.
To achieve a low vibration rating, you must pay attention to the surface finish of the raceways and balls, ensure the correct cage design is used and consider using a finely filtered, low noise grease. We’d recommend continual monitoring of vibration and machine condition.
Vibration sensors
To determine the quietness of a bearing, you can use a vibration measurement system to monitor the bearing vibration at the outer ring. Most commonly, vibration is measured using a piezoelectric sensor or accelerometer, but other vibration sensors can also be used for specific parameters.
For further information, visit the ball bearing noise and vibration technical area of our website.
If you would like more help, give the SMB Bearings team a call. We have years of experience supplying small and miniature bearings to a range of industries. Call our experts today on +44 (0) 1993 842 555 or e-mail sales@smbbearings.com.