Common failure modes and countermeasures for bearings

1. Spalling at the extreme position of one side of the raceway

 The spalling of limit position on one side of the raceway is mainly occurs at the junction of the raceway and the ring rib，where it is the severe spalling zone. The reason is that the bearing is not installed properly or bust axial overload during operation. The countermeasures are to ensure that the bearing is installed in place or the outer ring on the free side to be changed fit into clearance fit, in order to compensate the bearing when it is overloaded.

2. The raceway spalling at a symmetrical position in the circumferential direction

The spalling at the symmetrical position of the inner ring is the spalling of the surrounding belt, while the outer ring shows spalling at the circumferential symmetrical position (i.e. the short axis direction of the ellipse), which is mainly caused by the housing bore of ellipse too large, or the two-half separated housing bore structure, which is particularly obvious in camshaft bearings used in motorcycles. When the bearing is pressed into the larger elliptical housing bore, or tightened in the two-half separated housing bore, the outer ring of the bearing is elliptical, and the clearance in the short axis direction is significantly reduced, even negative clearance. Under the action of load, the spalling marks are produced circumferentially by the rotation of inner rings, while the spalling marks are produced symmetrically by the outer ring in the direction of short axis. This is the main reason for the early failure of the bearing. The inspection on failure parts of the bearing shows that the roundness of the outer diameter of the bearing has changed from 0.8μm to 27μm under the original process control. This value is much larger than the radial clearance value. Therefore, it is certain that the bearing is running under severe deformation and negative clearance, and abnormal sharp wear and spalling are easily formed early on the working surface. The countermeasures are to improve the processing accuracy of the housing bore or do not to use the housing bore structure with two halves separated as far as possible.

3. Inclined spalling of raceway

There is inclined spalling ring belt on the bearing working surface, indicating that the bearing is working in an inclined state, when the inclination angle reaches or exceeds the critical state, it is easy to form abnormal sharp wear and spalling in early stage. The reasons are mainly due to poor installation, shaft deflection, low accuracy of journal and housing hole, etc. Countermeasures are taken to ensure the bearing installation quality and improve the axial runout accuracy of the shaft shoulder and housing bore shoulder. 

4. Broken ring

Ferrule fracture failure is generally rare, and is often caused by sudden overload. The causes are more complex, such as bearing material defects (bubbles, shrinkage holes), forging defects (overburn), heat treatment defects (overheating), machining defects (local burns or surface microcracks), host defects (poor installation, poor lubrication, Instantaneous overload), etc., once subjected to overload, impact load or severe vibration, the ferrule may break. Take countermeasures to avoid overload impact load, select appropriate interference, improve installation accuracy, improve service conditions and strengthen quality control in the bearing manufacturing process.