1. Grease with impurities;
2. Lack of lubrication (oil level is too low, due to improper preservation of oil or grease leakage through seal);
3. Bearing clearance is too small or too large (manufacturer`s problem);
4.Mixed with sand or carbon particles to play the role of abrasive;
5. Extruder bearing mixed with water, acids or paint and other dirt react corrosion;
6.Bearing holes are clamped flat (block hole roundness is not good, or block hole distortion is not straight);
7. The bottom iron uneven surface of bearing seat (lead to the seat hole deformation and even bearing seat cracks);
8. Bearing seat hole has debris (residual debris, dust grains, etc.);
9. Sealing ring is eccentric (touching adjacent parts and friction);
10. Additional load on bearing (bearing axial - tight, or a shaft with two fixed end bearing);
11.With the loose between bearings and shaft (shaft diameter is too small or not screwed tight sets);
12. Bearing clearance is too small, too tight (rotating locking sleeve is screwed too much);
13. Bearing with noise (end face of roller or steel ball);
14.The axis of the thermal elongation is too large (shaft bearing to statically indeterminate axial additional load);
15. The shaft shoulder is too large ;
16. Holes of retaining shoulder is too large (the bearing of the seal is distorted);
17. Labyrinth seal ring clearance is too small (friction with the shaft);
18. Lock the teeth of the lock ring (the bearing and friction);
19. Position is not suitable to swing the oil ring (hit the flange cover and friction);
20. The pressure hole on steel ball or roller (caused by installation with a hammer beat );
21. Bearing noise (external vibration interference);
22. Bearings are heated and deformed (using the spray gun to heat the removal of the bearing);
23.The axis is too thick to make the actual tight matched (caused by bearing temperature is too high or make noise);
24.The diameter of the holes is too small (the temperature of the bearing is too high);
25.The bearing seat hole diameter is too large, too loose to the actual size (high temperature ,bearing outer ring - slip);
26.The bearing seat hole is enlargement (bearing hole of nonferrous metal is up, or due to thermal expansion and change);
27. Holding frame with fracture.
28. The rolling way of bearing is rust.
29. Steel ball and roller are wear (grinding or substandard products are damaged).
30.The raceway is unqualified (manufacturer`s problem).