After the bearing is installed, when the outer ring or shaft of the bearing is rotated by hand, the rotation is not flexible. The main reasons are as follows:

1) Scale, dust and other dirt enter the bearing, resulting in pad pressure and grinding;

2) Moisture, acid, alkali and other corrosive media enter the bearing, causing the bearing to rust;

3) The bearing clearance is too small, or the inner ring expands too much due to temperature rise when the bearing is working;

4) The lubricant is insufficient, too much or has dried out;

5) The manufacturing precision of the journal, shaft shoulder and bearing seat is too low or deformed during use;

6) The installation seal is not correct, such as the seal is too tight or the seal has friction with related parts;

7) Deformation of the cage;

8) For preloaded bearings, the axial preload is too large.