Nine Common Causes of Bearing Failure

Bearing failures during operation are common, so there is no need for undue concern. When a failure occurs, proper diagnosis and corrective action are essential. Today, we'll explain the common causes of bearing failure.

Excessive bearing temperature may be caused by: lubricating oil that does not meet specifications or has deteriorated, oil with excessively high viscosity, overly tight assembly (insufficient clearance), improper bearing fit, rotation of the bearing race on the shaft or in the housing, excessive load, or damage to the bearing cage or rolling elements.

1. Severe Raceway Wear: This may be caused by foreign matter entering the raceway, insufficient lubrication, or the use of an unsuitable lubricant.
2. Excessive Bearing Temperature: A certain amount of heat is normal during operation. When touching the outer shell by hand, it should not feel hot. If it does, the bearing temperature is likely too high.
3. Cage Fragmentation: Causes include insufficient lubrication, damage to the rolling elements, or misalignment of the raceways.
4. Abnormal Bearing Noise: Rolling bearings may produce a slight running noise during operation. However, excessive noise, abnormal sounds, or impact noises typically indicate a fault.
5. Plastic Deformation: If uneven pits appear on the contact surface between the raceway and rollers, it indicates plastic deformation. This is usually due to local stress exceeding the material's yield limit under a heavy static or impact load. It generally occurs in low-speed rotating bearings.
6. Bearing Burn: Burn marks (tempering colors) on the raceway and rolling elements are signs of bearing burn. Common causes include inadequate lubrication, poor lubricant quality or deterioration, and overly tight assembly.
7. Raceway Surface Peeling: Periodic pulsating loads on the rolling elements and raceways produce contact stress. After many stress cycles, fatigue peeling may occur. Excessive bearing load, improper installation, or shaft deflection can also accelerate peeling. This reduces bearing accuracy and causes vibration and noise.
8. Bearing Race Cracks: Cracks may result from overly tight fits, loose inner or outer rings, deformation of bearing components, or poor surface preparation of the mounting area.
9. Cage Metal Adhesion to Rolling Elements: This can occur if the rolling elements become stuck in the cage or if there is insufficient lubrication.

Causes of Rolling Bearing Noise (Summary):

1. Worn Bearing Fit Surfaces: Wear can destroy the fit between the bearing and its housing or shaft, causing axis misalignment and abnormal noise at high speeds. Fatigue on the bearing surface can also lead to increased radial clearance and noise.
2. Poor Lubrication: Insufficient lubrication, dry friction, or crushed bearings can result in abnormal noises.
3. Worn or Loose Bearings: A loose or damaged cage due to wear can also produce noise and lead to bearing failure.

When inspecting a disassembled rolling bearing, the cause of failure can often be determined by examining the damage.