NSK New Bearing Doctor

When a rolling bearing is damaged during machine operation, the entire machine or equipment may seize or malfunction. Since bearings that fail prematurely or unexpectedly cause trouble, it is important to be able to identify and predict failure beforehand, if possible, so that preventive measures can be adopted.

This pamphlet contains explanations about correct bearing handling, mounting, lubrication, and maintenance to prevent premature failure together with color photos of bearing failures. Most premature bearing failures can be avoided. Causes include improper mounting, mishandling, poor lubrication, entry of foreign particles/contamination and abnormal heat generation.

If all conditions are known both before and after the failure, including the application, operating conditions and the environment, then a countermeasure can be determined by studying the nature of the failure and its probable causes.

In general, if rolling bearings are used correctly, they will survive to their predicted fatigue life. Bearings, however, often fail prematurely due to avoidable mistakes. In contrast to fatigue life, this premature failure is caused by improper mounting, mishandling, poor lubrication, entry of foreign matter or abnormal heat generation.

If all conditions are known for the times both before and after the failure, including the application, the

operating conditions, and environment, then a measure can be determined by studying the nature of the failure and its probable causes. A successful measure will reduce similar failures or prevent them from happening again.

Bearing Damage and Countermeasures: Flaking

Damage Cond

Flaking occurs when small pieces of bearing material are split off from the smooth surface of the raceway or rolling elements due to rolling fatigue, thereby creating regions having rough and coarse texture.

Possible Cause

Excessive load
Poor mounting (misalignment)
Moment load
Entry of foreign debris, water penetration
Poor lubrication, Improper lubricant
Unsuitable bearing clearance
Improper precision for shaft or housing, unevenness in housing rigidity, large shaft bending
Progression from rust, corrosion pits, smearing,dents (Brinelling)

Countermeasure

Reconfirm the bearing application and check the load conditions
Improve the mounting method
Improve the sealing mechanism, prevent rusting during non-running
Use a lubricant with a proper viscosity, improve the lubrication method
Check the precision of shaft and housing
Check the bearing internal clearance

Part: Inner ring of an angular contact ball bearing
Symptom: Flaking occurs around half of the circumference of the raceway surface
Cause: Poor lubrication due to entry of cutting coolant into bearing

Part: Inner ring of an angular contact ball bearing
Symptom: Flaking occurs diagonally along raceway
Cause: Poor alignment between shaft and housing during mounting

Bearing Damage and Countermeasures: Flaking

Part: Balls
Symptom: Flaking of ball surface
Cause: Dents due to shock load while stationary

Part: Outer ring
Symptom: Flaking of raceway surface at ball pitch
Cause: Dents due to shock load while stationary

Part: Rollers of a cylindrical roller bearing
Symptom: Premature flaking occurs axially on the rolling surfaces
Cause: Scratches caused during improper mounting

Bearing Damage and Countermeasures: Flaking

Damage Condition

Possible Cause

Excessive load
Poor mounting (misalignment)
Moment load
Entry of foreign debris, water penetration
Poor lubrication, Improper lubricant
Unsuitable bearing clearance
Improper precision for shaft or housing, unevenness
in housing rigidity, large shaft bending
Progression from rust, corrosion pits, smearing,
dents (Brinelling)

Countermeasure

Reconfirm the bearing application and check the load conditions
Improve the mounting method
Improve the sealing mechanism, prevent rusting during non-running
Use a lubricant with a proper viscosity, improve the lubrication method
Check the precision of shaft and housing
Check the bearing internal clearance

Part: Inner ring of a spherical roller bearing
Symptom: Round shaped peeling pattern occurs on the
center of the raceway surface
Cause: Poor lubrication

Bearing Damage and Countermeasures: Peeling

Part: Convex rollers
Symptom: Round shaped peeling pattern occurs on the center of the rolling surfaces
Cause: Poor lubrication

Part: Outer ring of a spherical roller bearing
Symptom: Peeling occurs near the shoulder of the raceway over the entire circumference
Cause: Poor lubrication

Bearing Damage and Countermeasures: Scoring

Damage Condition

Scoring is surface damage due to accumulated small seizures caused by sliding under improper lubrication or under severe operating conditions. Linear damage appears circumferentially on the raceway surface and rolling surface. Cycloidal shaped damage on the roller end. Scoring on rib surface contacting roller end.

Possible Cause

Excessive load, excessive preload
Poor lubrication
Particles are caught in the surface
Inclination of inner and outer rings
Shaft bending
Poor precision of the shaft and housing

Countermeasure

Check the size of the load
Adjust the preload
Improve the lubricant and the lubrication method
Check the precision of the shaft and housing

Part: Inner ring of a spherical roller bearing
Symptom: Scoring on large rib face of inner ring
Cause: Roller slipping due to sudden acceleration and deceleration

Part: Convex rollers
Symptom: Scoring on roller end face
Cause: Roller slipping due to sudden acceleration and deceleration

Part: Cage of a deep groove ball bearing
Symptom: Scoring on the pressed-steel cage pockets
Cause: Entry of debris

Part: Convex rollers of Photo 3.5
Symptom: Scoring on the roller end face
Cause: Debris, which is caught in surface, and excessive axial loading

Bearing Damage and Countermeasures: Scoring

Damage Condition

Possible Cause

Excessive load, excessive preload
Poor lubrication
Particles are caught in the surface
Inclination of inner and outer rings
Shaft bending
Poor precision of the shaft and housing

Countermeasure

Check the size of the load
Adjust the preload
Improve the lubricant and the lubrication method
Check the precision of the shaft and housing

Part: Outer ring
Symptom: Smearing occurs circumferentially on raceway surface
Cause: Roller slipping due to excessive grease filling

Part: Convex rollers
Symptom: Smearing occurs at the center of the rolling surface
Cause: Poor lubrication

Bearing Damage and Countermeasures: Cracks

Damage Condition

Cracks in the raceway ring and rolling elements. Continued use under this condition leads to larger cracks or fractures.

Possible Cause

Excessive interference
Excessive load, shock load
Progression of flaking
Heat generation and fretting caused by contact between mounting parts and raceway ring
Heat generation due to creep
Poor taper angle of tapered shaft
Poor cylindricality of shaft
Interference with bearing chamfer due to a large shaft corner radius

Countermeasure

Correct the interference
Check the load conditions
Improve the mounting method
Use an appropriate shaft shape

Part: Outer ring of a double-row cylindrical roller bearing
Symptom: Thermal cracks occur on the outer ring side face
Cause: Abnormal heat generation due to contact sliding
between mating part and face of outer ring

Part: Roller of a tapered roller thrust bearing
Symptom: Thermal cracks occur at large end face of roller
Cause: Heat generation due to sliding with the inner ring rib
under poor lubrication

Bearing Damage and Countermeasures: Pitting

Damage Condition

The pitted surface has a dull luster which appears on the rolling element surface or raceway surface.

Possible Cause

Debris becomes caught in the lubricant
Exposure to moisture in the atmosphere
Poor lubrication

Countermeasure

Improve the sealing mechanism
Filter the lubrication oil thoroughly
Use a proper lubricant

› Improve the sealing mechanism
› Filter the lubrication oil thoroughly
› Use a proper lubricant

Part: Ball
Symptom: Pitting occurs on the rolling element surface

Bearing Damage and Countermeasures: Wear

Damage Condition

xWear is surface deterioration due to sliding friction at the surface of the raceway, rolling elements, roller end faces, rib face, cage pockets, etc.

Possible Cause

Entry of debris
Progression from rust and electrical corrosion
Poor lubrication
Sliding due to irregular motion of rolling elements

Countermeasure

Improve the sealing mechanism
Clean the housing
Filter the lubrication oil thoroughly
Check the lubricant and lubrication method
Prevent misalignment

Part: Outer ring of a spherical roller bearing
Symptom: Wear having a wavy or concave-and-convex texture on loaded
side of raceway surface
Cause: Entry of debris under repeated vibration while stationary

Part: Tapered rollers of Photo 10.3
Symptom: Stepped wear on the roller head and face
Cause: Fretting progression due to excessive load while stationary

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NSK New Bearing Doctor