There are many ways to generate noise from the motor casing, including electromagnetic induction noise, mechanical noise and pneumatic noise. Among them, friction, collision, imbalance and structural resonance of a part of the motor will cause mechanical noise. Mechanical noise includes bearing noise, rotor unbalance noise caused by customization of motor housing, noise caused by axial force of assembly line, etc. The noise value caused by bearing noise in the production of motor casing is closely related to the specification accuracy, roughness and dimensional tolerance of steel balls, inner and outer ring pipe trenches, etc. Bearing noise can be reduced by:

(1) The assembly line needs a strict demagnetization cleaning process to remove oil and iron feet;

(2) Select sealed bearing to avoid dust entering; The mutual fit between the outer side of the bearing and the bearing cavity and the mutual fit between the inner hole and the shaft should not be too tight;

(3) In order to clear the radial clearance of the rotor, the appropriate working pressure must be released on the bearing; Ductile sealing ring, with reasonable fluid tightness, properly add lubricating fluid to reduce friction;

(4) Motors with special noise regulations shall adopt low noise bearings; When the load is not very large, the oil-bearing can be selected.