Flaking, pitting, wear and fretting: causes and countermeasures
Four of the most common surface failures: what each one is, why it happens early, and what to change.
Flaking and pitting
Flaking is when the surface turns scaly and peels off after repeated contact stress in the raceway and rolling surfaces. It shows that the end of the bearing life is near. Pitting is small holes, about 0.1 mm deep, made by rolling fatigue. Both can start early in life, and then the cause must be found.
Why flaking and pitting start early
- Internal clearance became narrower than specified while running.
- The bearing ring was mounted at an angle.
- A flaw was made during mounting (brinelling, nicks, rust).
- Shaft or housing is not a true circle, or has dents on the surface.
Countermeasures for flaking
- Choose a bearing with a higher rated load.
- Check whether an abnormal load is being generated.
- Improve lubrication to form a better oil film, for example with a higher viscosity.
- If found early, take the measures above after investigating the cause.
Countermeasures for pitting
- Raise viscosity of the lubricant to build a better film.
- Take care: foreign matter can look like holes caused by brinelling or corrosion.
Wear
Wear is mainly caused by sliding on parts such as the roller end face and rib, cage pockets, the cage itself and the guiding surface of the ring. Dirt and corrosion can also wear the rolling surfaces.
Wear: causes and fixes
| Cause | Countermeasure |
|---|---|
| Wrong lubricant or too little lubricant | Review the lubricant and the lubrication method |
| Dirt and foreign matter | Filter the oil, improve sealing |
Fretting
Fretting is slight sliding repeated on the contact surface. On a fitting surface it makes a rust-like powder. If the bearing sees vibration at rest or in operation, small movements happen between the rolling element and the ring from elastic distortion, and false brinelling follows.
Fretting: causes and fixes
| Cause | Countermeasure |
|---|---|
| Vibration load | Find and reduce the source of vibration |
| Slight movement on the fitting surface under load | Increase interference, make the shaft stiffer |