1. There are impurities in oil;

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

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

4. Sand or carbon particles are mixed into the bearing to play the role of abrasive;

5. Water, acid or paint are mixed into the bearing to cause corrosion;

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 bottom iron pad of the bearing seat is uneven (causing seat hole deformation and even bearing seat crack);

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

9. The sealing ring is eccentric (contact with adjacent parts and friction occurs);

10. The bearing bears extra load (the bearing bears axial tension, or there are two fixed end bearings on the root 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 when rotating (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 the static and indefinite 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 (the seal of the bearing is distorted);

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

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

19. The position of the oil slinger is not suitable (touching the flange cover and causing friction);

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

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

22. The bearing is discolored and deformed when heated (caused by dismantling the bearing with spray gun heating);

23. The shaft is too thick to make the actual fit too tight (causing too high bearing temperature or noise);

24. The diameter of the seat hole is too small (causing the bearing temperature to be too high);

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 enlarged 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 bruised product);

30. The raceway of the ring is unqualified (the problem of the manufacturer).