The causes of abnormal noise in bearings are diverse, including lubrication issues, improper fit selection, contamination by foreign particles, corrosion effects, assembly problems, and other factors.

Causes of Abnormal Bearing Noise and Damage, and Their Impact on Bearing Life

Specifically, potential causes include:

• Improper selection of lubricating oil or grease, leading to inadequate lubrication.

• Insufficient lubrication, possibly due to low oil level or grease leakage through seals.

• Excessive bearing clearance, potentially due to improper fit selection.

• Contamination by foreign particles such as sand or carbon dust, which act as abrasives and accelerate wear.

• Exposure to corrosive substances like water, acids, or paint, which can damage bearings.

• Bearing distortion due to poor roundness or misalignment of the housing bore.

• Uneven shims under the housing base, causing housing deformation or even cracks.

• Debris in the housing bore, such as residual chips or dust particles, affecting normal operation.

• Eccentric sealing rings causing friction with adjacent components.

• Additional loads on bearings, such as axial binding or improper installation of two fixed-end bearings on one shaft.

• Loose fit between the bearing and shaft, possibly due to undersized shaft diameter or improperly tightened adapter sleeves.

• Insufficient bearing clearance causing tight rotation, potentially due to overtightened adapter sleeves.

• Noise caused by roller end face or ball slippage.

• Excessive thermal expansion of the shaft leading to indeterminate static axial additional loads.

• Oversized shaft shoulder rubbing against bearing seals.

• Oversized housing shoulder deforming bearing seals.

• Insufficient clearance in labyrinth seals causing shaft friction.

• Bent lock washer teeth contacting bearings.

• Improperly positioned oil slingers rubbing against flange covers.

• Dents on balls or rollers, potentially from hammer strikes during installation.

• External vibration sources causing bearing noise.

• Thermal discoloration and deformation, possibly from torch heating during disassembly.

• Oversized shaft diameter creating excessive tightness, leading to overheating or noise.

• Undersized housing bore diameter causing elevated temperatures.

• Oversized housing bore diameter creating excessive clearance, potentially causing overheating or outer ring slippage.

• Enlarged housing bore, possibly from deformation of non-ferrous housings or thermal expansion.

• Bearing noise (fretting corrosion).

Potential Causes of Abnormal Bearing Noise

• Contaminated grease affecting lubrication performance.

• Insufficient lubrication due to low oil level or poor sealing causing leakage.

• Improper bearing clearance, potentially from manufacturing issues.

• Abrasive particles like sand or carbon dust accelerating wear.

• Exposure to corrosive materials damaging bearings.

• Housing bore distortion due to poor roundness or misalignment.

• Uneven base shims causing housing deformation or cracks.

• Bore contamination affecting normal operation.

• Eccentric seals rubbing against adjacent parts.

• Extra loads from axial binding or dual fixed-end bearing installation.

• Loose shaft fit from undersized diameter or loose adapter.

• Tight rotation from insufficient clearance or overtightening.

• Noise from roller ends or ball slippage.

• Excessive shaft expansion creating additional axial loads.

• Large shaft shoulder contacting seals.

• Oversized housing shoulder deforming seals.

• Inadequate labyrinth seal clearance.

• Bent lock washer teeth.

• Misaligned oil slingers.

• Impact marks from installation tools.

• External vibration-induced noise.

• Heat damage from disassembly methods.

• Overshafting causing overheating.

• Undersized housing bore raising temperature.

• Oversized housing bore causing slippage.

• Bore enlargement from material issues.

• Cage fracture affecting stability.

• Raceway rust impairing lubrication.

• Worn components from manufacturing defects.

• Substandard raceway quality.

Manufacturer Information
Operational Worldwide, Dragon Soars. From the East, Rising Supreme. Dragon三类Self-Aligning Roller Bearings Lead Industry Innovation. Liu Xingbang CA CC E MB MA, Building a Brilliant Future Together.

Technical Note
Bearings, as critical machine components, facilitate shaft rotation by reducing friction while maintaining precision and providing protection. However, various operational damages can significantly impact both bearing service life and overall machine performance.

Causes of Bearing Damage and In-Depth Analysis

Bearing failure can arise from various causes, primarily including material fatigue, inadequate lubrication, contamination, installation issues, and improper handling. To explore these causes and their effects in detail, we will analyze bearing damage from seven key aspects:

1. Dents on Raceway and Roller Surfaces
These typically result from contamination during installation, including particles from the cage and wear on the raceway surfaces. During installation, cleanliness must be maintained, fresh grease should be used, and seal integrity must be carefully inspected.

2. Wear Due to Improper Lubrication
Surface wear appears mirror-like and turns blue or brown, mainly caused by insufficient lubrication. The lubrication interval should be reevaluated, and oil seals must be inspected.

3. Dents from Improper Installation
Dents spaced at intervals equal to the roller diameter on the working surfaces of the inner and outer rings are often due to installation errors, such as incorrect striking of the ring, excessive pushing, or static overload.

4. Dents Caused by Foreign Particles
Dents covering the working and roller surfaces may stem from foreign particles introduced during installation, contaminants in the lubricant, or environmental factors. Bearings should be thoroughly cleaned before installation, using clean lubricant and inspecting oil seals.

5. Scuffing on Roller End Faces
This is usually caused by excessive axial loads or inadequate lubrication. Lubricants with higher viscosity should be prioritized.

6. Scoring of Rollers and Raceways
Scuffing and localized discoloration at the entry zone of the raceway load area occur mainly due to sudden acceleration when rollers enter the load zone. Solutions include selecting higher viscosity lubricants or reducing bearing clearance.

7. Scoring on External Surfaces
Scratches and localized discoloration on the inner ring bore or outer ring surface are typically due to relative movement between the ring and the shaft or housing. To prevent this, increase the interference fit between the ring and shaft/housing to avoid relative rotation. Axial braking or clamping may not resolve this issue.

Surface Pitting
Small, shallow pits on raceways, rolling elements, or large cross-sections, exhibiting a crystalline fractured appearance, are often due to poor lubrication—such as oil starvation or viscosity changes from temperature rise—preventing effective oil film separation and causing instantaneous contact wear.

Fretting Corrosion
Fretting corrosion occurs when there is relative movement between the bearing ring and the shaft or housing, primarily due to a loose fit or housing deformation.

Electrical Erosion
Dark brown or gray-black streaks or pitting on rolling elements or surfaces result from electrical arcing across bearing components when current passes through. To prevent electrical erosion, ensure no current can flow through the bearing.

Spalling at Symmetrical Positions on Rolling Surfaces
If pronounced load marks with skin peeling are observed at radially symmetric positions on one ring, it may be due to housing deformation or oval compression. The housing should be remanufactured.

Spalling from Axial Loads
Clear load marks with skin peeling on one side of a ring or one raceway of a double-row bearing may result from improper installation, excessive preload, or jamming of non-located bearings. Installation should be checked and adjusted to ensure proper axial load application.

Spalling from Indentations
Raceway surface spalling with indentations spaced at roller intervals is typically caused by excessive static load from incorrect installation. Carefully review the installation process to ensure accuracy.

Cracks from Rough Installation Handling
Chipped fractures occurring only on one side may result from forceful striking transmitted through rolling elements to the ring end face. Avoid directly striking bearing rings during installation.

Cracks from Excessive Press-Fitting
Full-Section Fractures
When cracks penetrate the entire cross-section of a bearing ring, it is usually due to excessive interference fit between the inner ring and shaft, or over-tightening on a tapered shaft.

Transverse and Circumferential Cracks
Fretting corrosion produces transverse cracks on inner rings and circumferential cracks on outer rings, mainly due to loose fits or non-standard housing shapes.

Spalling Phenomenon
Spalling on the ring raceway due to fretting corrosion, with corroded marks on the external surface, is often caused by a loose fit or incorrect housing shape.

Factors Influencing Bearing Service Life

Different bearings have varying service lives, influenced by multiple factors:

• Material Selection: High-carbon chromium bearing steel is commonly used for rolling bearings. The purity of its chemical composition significantly impacts lifespan.

• Surface Roughness: Fatigue cracks often originate at surfaces, making roughness a critical factor. Surface treatments that alter hardness and residual stress distribution in the surface layer can significantly extend bearing life.

• Temperature: Operational temperature rise affects lubrication effectiveness and thermal deformation, thereby influencing running accuracy and lifespan.

• Lubrication Technology: Appropriate lubricants and methods are crucial for significantly extending bearing life.

• Operating Speed: This is another key factor affecting bearing life.

Impact of Operating Speed on Bearing Life

Operating speed primarily affects the instantaneous contact time—the time a rolling element takes to roll over the contact ellipse width on the raceway under maximum load. As speed increases, this contact time lengthens, leading to reduced fatigue life. Conversely, bearings operating at lower speeds exhibit longer life in terms of revolution cycles. Furthermore, the duration of instantaneous contact time indirectly affects surface residual stress, further influencing fatigue life.

Impact of Load on Bearing Life

Research shows that rolling element parameters and curvature coefficients significantly affect the fatigue life of deep groove ball bearings. Specifically, increased load directly raises the maximum rolling element load, thereby shortening fatigue life.

Note on Bearing Life Calculation Methods

Different calculation methods can yield different results. Two commonly used methods are:

• L-P Theory Algorithm

• ISO International Standard Theoretical Algorithm

The ISO standard algorithm is a simplified version of the L-P theory. It assumes the supporting ring is rigid, whereas actual rings are non-rigid. Furthermore, under the same load, ball bearings experience greater contact deformation. Consequently, results from these two methods may differ in practical applications.