Technical>Discord sound testing
Discord sound testing

dB noise testing is a traditional noise measurement which can only give a general idea of bearing quality by their noise level. Vibration measurements are of great importance for high-quality bearing production which is applied widespread over the world famous bearing manufacturers. HCH’s bearings are 100% tested by noise and vibration measurements.

However, besides waviness, roundness and non-adequate lubrication etc., a noise application can lead the unreliable bearing performance which can also be caused by local defects, dirt particles and cage problems. In addition, HCH is also implementing 100% discord sound testing of bearings, which can test and detect all of these bearing quality issues. Following table lists common types of discord sound, their causes as well as countermeasures.

Causes of discord sound and countermeasures

discord sound
Cause Countermeasure
Squeak This is a dense and strident squeak just like noise when steel is sawed by saw blade and the wave crest occurs rhythmically. It will be specific reflected by BVT-1 equipment via high band: the pointer will rise and fluctuate. The amplitude is changing according to the intensity of noise. This kind of noise is the most deleterious. It is mainly caused by surface bumping (knocking) between the ball and raceway. 1. Choose the ball with surface strengthened.
2. Strictly control the quality of ball’s surface (flaw, stripe, black spot and surface scuffing).
3. Strictly control the bumping (knocking) hurt of inner and outer raceway.


This kind of noise is arrhythmic noise when grease or impurity is rolled. Sometimes it occurs and sometime it’s gone. When this noise appears, the high band’s pointer of BVT-1 equipment rises suddenly. The amplitude is changing according to the intensity of noise. It is closely related to the cleanliness of bearings, anti-rust oil and impurity of grease.
1. Do the inspection and control of bearing cleanliness.
2. Choose the anti-rust oil and grease with low impurity(namely high cleanliness anti-rust oil and grease).
Hum When hum appears, normally the read of the low band of BVT-1 equipment is high. Louder the noise is, higher the read will be. This sound is closely related to the noise rising of the machine. It is related to the roundness and accuracy of bearing’s inner and outer raceway. Strictly control roundness of raceway.
Ripple A kind of high-frequent noise which is symmetrical, ringing and continuous. The read of high band of BVT-1 equipment is a little bit higher which will increase the noise of the finished products. It is related to the raceway’s chatter mark. reflecting the defect of the raceway waviness. Strict control inner and outer race’s undulation variation (monitor by Roundness & Waviness meter).
Grease stirring Sounds like the clop. Check the characteristic of grease. If the grease used is with high viscocity, it is normal agitating sound. But if the grease used is with low viscocity, please check the quality of the grease.

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