What kind of noise is normal for motor bearings?
Motor bearing noise has always been a problem that troubles many engineers. As mentioned in the previous article, the noise of motor bearings cannot be described in words, so it often brings trouble to motor technicians in judging.
However, after a long period of on-site practice, coupled with the mastery and analysis of motor bearing knowledge, many useful on-site judgment criteria will be obtained. For example, what kind of "noise" is the "normal noise" of the bearing.
Are there bearings without "noise"?
People often ask how to eliminate the noise of bearings. The answer to this question is that it is impossible to completely eliminate it. Because the operation of the bearing itself will definitely have some "noise". Of course, this mainly refers to the state of the bearing when it is operating normally, including:
Are there bearings without "noise"? Collision between rolling elements and raceways in the non-load zone 01
The rolling elements of the bearing run in the bearing raceway. When the rolling elements run in the non-load zone, the rolling elements will collide with the raceway in the radial or axial direction. This is because the rolling element itself comes out of the load zone and has a certain linear speed. At the same time, the rolling element has a certain centrifugal force. When it rotates around the axis, it will collide with the raceway, thus generating noise. Especially in the non-load zone, when residual clearance exists, such collision noise is particularly obvious.
Are there bearings without "noise"? Collision between rolling element and cage 02
The main function of the cage is to guide the operation of the rolling element. The collision between the rolling element and the cage is also a source of noise. Such collisions include circumferential, radial, and possibly axial. From the perspective of motion state, it includes the collision when the rolling element actively pushes the cage inside the load zone; the collision when the cage pushes the rolling element in the non-load zone. The collision between the rolling element and the cage in the radial direction due to the centrifugal force. Due to disturbance, the collision between the rolling element and the cage during axial movement, etc. Are there bearings without "noise"? Rolling element stirring grease 03
When the bearing is filled with grease, the operation of the rolling element stirs the grease. This stirring will also produce corresponding noise.
Are there bearings without "noise"? Sliding friction of rolling elements in and out of the raceway 04
There is a certain amount of sliding friction between the rolling element and the raceway when it enters the load zone. There may also be a certain degree of sliding friction when it leaves the load zone.
Are there bearings without "noise"? Other movements inside the bearing 05
The friction of the bearing lip with seals can also cause noise.
In summary, it is not difficult to find that these rolling bearings running under normal conditions will inevitably produce some "noise". Therefore, the answer to the opening question is: For rolling bearings, the inherent "normal noise" is impossible to eliminate.
So, what is the normal sound of motor bearings?
From the previous analysis, we can see that these motion states generate noise due to collision and friction. For a normal and qualified bearing, it is not difficult to find that these noises are closely related to the speed. For example, the friction when the rolling element enters and exits the load zone, the collision of the rolling element with the cage inside and outside the load zone, the stirring of grease, the friction of the seal lip, etc., will change with the change of speed. When the motor is at a constant speed, these movements should be in a stable state. Therefore, the excited bearing noise at this time should be a stable and uniform sound. From this we can infer that a normal noise of a bearing should have a basic characteristic, that is, stable and uniform. The stability and uniformity mentioned here are not a continuous sound. Because many motion states, such as collisions, occur one after another, so these sounds are a stable small-cycle sound. Of course, some continuous sounds are also included, such as the sound of seal friction. In actual working conditions, such as when there are certain interferences, the noise will also appear to be stable and uniform to a certain extent. However, this type of noise often does not sound like the frequency that the bearing should have. Therefore, when judging bearing noise on site, in addition to stability and uniformity, it is often necessary to add a frequency without abnormalities (hearing sensation).