Bearing is a vital part of modern machinery production activities, if in the assembly, test and use process fails to operate in accordance with the requirements, it is likely to let the bearing produce too much “pressure”, resulting in bearing deformation;  Or fall apart completely, or even more seriously.

Foreign particles (contaminants), such as chips and burrs, have entered the bearing causing indentation when the raceway rolls into the rolling element. The indentation particles are not necessarily hard. Even thin sheets of paper and cotton thread used for drying are harmful.

By bearing failure (inner ring rotating towards you, rolling parts away from you). V shape is the typical sign of indentation damage of ball bearing. The initial spalling spreads out in a V shape to the back.

If the lubricating oil contains contaminant particles, there is a risk of severe indentation to the surface during rolling contact. Bulging materials, due to plastic deformation, cause fatigue. This is due to the concentration of loads at the convex edges around the indentation.

When fatigue reaches a certain level, it causes premature spalling from the far end of the indentation (see figure below).

Spalling begins with cracks in the surface and occurs more quickly than normal. That’s why it’s called premature.

The life of the impact of the indentation requires the addition of a correction factor. The most important operational data required for calculation are bearing type and size, rotational speed, bearing load, oil viscosity at operating temperature, and size, hardness, and concentration of pollution particles. Cleanliness of lubricants and careful handling during installation are of course important factors in preventing severe indentation.

Below is a good picture of indentation failure (spherical roller bearing).

Rotate from right to left. A sizable contaminant was trapped on the runway and spilled. At the bottom of the dent, the abrasion line is still clearly visible, as is the raised edge around the dent. To the left of the dent, there is a large spalling (black) and the material is missing. There are also some cracks and these materials are going to peel off.

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