How to tell what motor bearing noise means?

What does motor bearing noise mean? Motor bearing noises vary, and people can tell if there is a serious defect in the bearing by the noise. But do you know how to tell? In fact, motor bearing noises generated inside the motor are common in rolling bearings, because the rolling elements need to roll in the raceways to ensure the normal operation of the bearing. But usually, these noises can be ignored. However, if the noise is loud and can be clearly heard, it usually means that there is a problem.
Below are common noises generated by motor bearings (most of which can be detected by a noise meter). Each noise indicates a different motor bearing performance, and how to eliminate each noise. If you hear a continuous and soft sound, it is the basic noise of the rolling bearing, which occurs when the raceways and rolling elements touch each other. It is smooth and continuous. The faster the running speed, the louder the sound, and if the radial clearance is reduced, the sound will also increase. The higher the lubrication viscosity, the lower the sound, and the higher the housing stiffness, the lower the amplitude of the sound.
It is impossible to completely eliminate this noise, but it can be minimized by improving the quality of the motor bearing. Clicking is more likely to occur in large bearings under radial load. It is generated at low speeds and when the rolling elements and the cage or inner ring collide. Applying preload is an effective countermeasure to mitigate this type of noise. In another case, the noise is loud and sounds like metal sliding on metal. Contrary to expectations, this may not indicate a problem. Using relatively large motor bearings under radial loads can cause squealing noise. Friction between the outer ring and the rolling elements is believed to be the cause of the squealing noise. Generally, reducing the radial clearance and using very shallow grooves in the outer ring raceway can solve it.