1. Selection and control of shaft and housing tolerances

After a bearing is pressed into its housing, it must rotate flexibly without any locking. If obvious inflexibility is observed, it indicates that the shaft diameter is too large and the tolerance should be reduced. If the bearing is pressed onto the shaft and a noticeable “rustling” sound is felt when rotating by hand, the shaft tolerance may be too large or its roundness insufficient. Therefore, when controlling shaft and housing tolerances, roundness must also be checked. Currently, many domestic manufacturers only control tolerances and ignore roundness.

2. Bearing assembly method

Bearings are high‑precision components; incorrect assembly can easily damage the raceway and lead to bearing failure. During assembly, special tooling must be used – do not strike the bearing arbitrarily. When pressing onto a shaft, apply force only to the inner ring; when pressing into a housing, apply force only to the outer ring. Assembly requires pneumatic or hydraulic pressure, and the upper and lower fixtures must remain level. If tilted, the force may damage the raceway and cause abnormal bearing noise.

3. Preventing foreign matter ingress during assembly

When a bearing is mounted on a rotor for dynamic balancing, iron chips generated during the balancing process can easily enter the bearing. For this reason, dynamic balancing must be completed before installing the bearing. Some manufacturers apply a small amount of oil or grease to the bearing housing during assembly to facilitate installation, but operators often find it difficult to control the correct quantity. If oil or grease accumulates in the bearing housing, it can easily seep into the bearing along the shaft during rotation.

⚠️ Important: The bearing housing should not be lubricated with oil or grease. If absolutely necessary, ensure that no accumulation remains inside the bearing housing.

4. Preventing paint rust (corrosion from insulating varnish)

Paint rust is often seen in sealed motors. During assembly the motor sounds perfectly fine, but after being stored in a warehouse for some time, abnormal noise becomes very noticeable, and bearing rust is found when disassembled. Many manufacturers used to blame the bearings, but after continuous communication, motor manufacturers now understand that this is primarily an issue with the insulating varnish. The problem arises because acidic substances released from the insulating varnish, under certain temperature and humidity conditions, form corrosive compounds that attack the bearing raceway and lead to bearing damage. The solution is to select a high‑quality insulating varnish and, after the varnish has dried, allow prolonged ventilation before assembly.

2026-05-09