Why do bearings fail? The main causes and how to prevent them
Most bearings fail earlier than their calculated life, and nearly always for a reason that can be found and fixed. Here are the main causes and where to read about each.
The main causes
| Cause | Share of premature failures (commonly quoted) | What happens | Read more |
|---|---|---|---|
| Poor lubrication | about 36% | The film breaks down, the surfaces touch and wear, smear or overheat | Lubricant failure (starved, over-filled, mixed or worn-out), Overheating & lubricant breakdown, Adhesive wear (smearing & skidding) |
| Fatigue | about 34% | Flakes break from the raceway at the end of life, or early if the bearing is overloaded | Subsurface-initiated fatigue, Surface-initiated fatigue (surface distress) |
| Mounting and handling | about 16% | Dents, misalignment, wrong fits and loose seats | Handling and installation damage, Misalignment & distorted seats (edge loading), Ring creep and loose fits |
| Contamination | about 14% | Dust, grit and water grind the surfaces or corrode them | Abrasive wear, Moisture corrosion, Indentations from particles |
Indicative published figures. They vary by industry and by how a failure is counted.
Electrical and other causes
Motors fed by variable frequency drives can pass current through the bearing, leaving a fluted pattern (Current leakage erosion (fluting)). Standstill vibration leaves marks without any overload (False brinelling). A cracked ring points to shock or poor support (Forced fracture).
How to find the real cause
| Step | What to do |
|---|---|
| 1. Keep the evidence | Do not clean the bearing. Photograph the raceways, rolling elements, cage, shaft and housing before anything is changed. |
| 2. Read the damage | Match the pattern to a failure mode on the failure modes page, or upload photos to Bearing Autopsy. |
| 3. Check the history | Running hours against calculated life, last lubrication, recent repairs and changes in load or speed. |
| 4. Fix the cause | Replacing the bearing without changing the cause brings the same failure back. |
Questions
What is the most common cause of bearing failure?
Poor lubrication is the most commonly quoted cause, followed by fatigue, mounting and handling errors, and contamination.
Do bearings fail because they are low quality?
Rarely. Most early failures trace back to overload, lubrication, contamination, misalignment or mounting problems rather than the bearing itself.
How long should a bearing last?
It depends on load, speed and conditions. Calculated life is a statistical value, and bearings that are well lubricated, clean and correctly mounted often exceed it.
How can I tell why a bearing failed?
Match the damage pattern to the failure modes in ISO 15243, then check the running conditions and history. A photo of the damage is a useful first clue.