Bearing Failure Analysis: What a Failed Bearing Can Tell You

A failed bearing is usually treated as a maintenance event.

Remove it.

Install a replacement.

Put the machine back into production.

But a bearing can provide valuable information about the condition of the equipment around it. The damage pattern on the bearing may help identify the actual mechanism that caused the failure.

That makes bearing failure analysis a useful tool for improving equipment reliability.

Don't Throw Away the Evidence

Before disposing of a failed bearing, inspect it.

Look at the races, rolling elements, cage, seals, lubrication, and mounting surfaces.

Ask:

• Where is the wear concentrated?

• Is the damage symmetrical?

• Is there evidence of overheating?

• Is the lubricant contaminated?

• Are the races showing localized damage?

• Is there evidence of impact?

The answers can point toward the root cause.

Misalignment

Misalignment can produce uneven loading across the bearing.

Instead of distributing the load appropriately, portions of the raceway may experience excessive contact stress.

The resulting wear pattern can be very different from normal fatigue.

Misalignment can originate from:

• Improper shaft alignment

• Housing misalignment

• Bent shafts

• Distorted machine frames

• Incorrect installation

If a replacement bearing fails quickly after installation, alignment should be high on the troubleshooting list.

Lubrication Problems

Both insufficient and excessive lubrication can create problems.

Insufficient lubrication can increase friction and temperature.

Too much grease can also increase operating temperature in certain applications because the rolling elements must move through excess lubricant.

Contamination is another major concern.

Dust, water, metal particles, and other contaminants can damage bearing surfaces and degrade lubrication.

Overloading

Bearings are selected based on expected loads and operating conditions.

If equipment is modified without reevaluating those loads, an existing bearing may be operating outside its intended conditions.

For example, changing a conveyor configuration or increasing material throughput can alter radial or axial loading.

The machine may still operate, but the bearing life can decrease significantly.

Installation Matters

A new bearing can be damaged during installation.

Improper force applied through the rolling elements can create brinelling or other damage.

Incorrect fits can also cause problems.

A bearing mounted too loosely can experience unwanted movement. An excessively tight fit can create undesirable internal loading.

The correct installation method depends on the bearing, shaft, housing, and application.

Look Beyond the Bearing

One of the most important principles in reliability engineering is that components don't operate independently.

If a bearing is failing because the shaft is bent, replacing the bearing doesn't solve the problem.

If the bearing housing is moving because the mounting structure is cracked, replacing the bearing doesn't solve the problem.

If contamination is entering through inadequate protection, replacing the bearing doesn't solve the problem.

The bearing may simply be the component that happens to fail first.

Final Thoughts

A failed bearing should be treated as evidence.

Its condition can provide clues about alignment, lubrication, loading, contamination, installation, and the overall health of the machine.

That information can be more valuable than the replacement bearing itself.

Lesson from the Shop Floor

One of the worst maintenance habits is throwing away failed components immediately. If a bearing fails unusually early, I want to know why. A five-minute inspection of the old bearing can sometimes save months of repeated replacement. The failed component has already done its job as a diagnostic tool—you just have to look at it.

Call to Action

CCI Machine can help manufacturing facilities investigate recurring mechanical failures and develop replacement components, modifications, and fabricated solutions that address the underlying equipment problem.