1. Impurities in grease;

2. Insufficient lubrication (oil level is too low and improper storage leads to oil or grease leakage through the seal);

3. The clearance of the bearing is too small or too large (problem of the manufacturer);

4. Impurities such as sand or carbon particles are mixed into the bearing to play the role of abrasive;

5. Dirt such as water, acid or paint is mixed into the bearing to corrode;

6. The bearing is flattened by the seat hole (the roundness of the seat hole is not good, or the seat hole is not straight);

7. The sizing block on the bottom surface of the bearing seat is uneven (resulting in seat hole deformation and even crack of the bearing seat);

8. There are sundries in the bearing seat hole (residual chips, dust particles, etc.);

9. Eccentric sealing ring (contact with adjacent parts and friction);

10. The shaft bears additional load (the shaft bears axial tightness, or there are two fixed end bearings on one shaft);

11. The fit between the bearing and the shaft is too loose (the diameter of the shaft is too small or the tightening sleeve is not tightened);

12. The clearance of the bearing is too small and it is too tight during rotation (the tightening sleeve is too tight);

13. Bearing noise (caused by roller end face or steel ball slipping);

14. The thermal elongation of the shaft is too large (the shaft bears static and indeterminate axial additional load);

15. The shaft shoulder is too large (touching the seal of the bearing and causing friction);

16. The shoulder of the seat hole is too large (it distorts the seal of the bearing);

17. The clearance of labyrinth seal ring is too small (friction with shaft);

18. The teeth of the lock washer are bent (touching the bearing and rubbing);

19. The position of the oil slinger is inappropriate (touching the flange cover and rubbing);

20. There are pressure pits on the steel ball or roller (caused by knocking the bearing with a hammer during installation);

21. Bearing noise (interference from external vibration source);

22. The bearing is discolored and deformed by heating (caused by removing the bearing by heating with a spray gun);

23. The shaft is too thick, which makes the actual fit too tight (resulting in excessive bearing temperature or noise);

24. The diameter of the seat hole is too small (resulting in excessive bearing temperature);

25. The diameter of the bearing seat hole is too large and the actual fit is too loose (the bearing temperature is too high - the outer ring slips);

26. The bearing seat hole becomes larger (the bearing seat hole of non-ferrous metal is supported larger, or becomes larger due to thermal expansion);

27. The cage is broken.

28. The bearing raceway is rusty.

29. Wear of steel ball and raceway (unqualified grinding or bumping of products).

30. The ferrule raceway is unqualified (manufacturer's problem).