Jebel Ali Free Zone, Dubai,
United Arab Emirates.

Bearing Defects & Preventive Measures

Bearings must be carefully handled, mounted, and maintained in order to operate properly. Care and attention must be used during and after installation to increase the work life of the bearing, prevent bearing defects, and reduce the cost of repair and replacement.

In case of poor performance or breakdown, the cause of failure must be determined to prevent repetition. There are three types of data which should be gathered to enable the correct diagnosis of bearing problems:

  • Time of occurrence
  • Symptoms during operation
  • Condition of Bearings

Time of Occurrence 

Time of Occurance / CauseBearing SelectionDesign or Manufacture of other drive partsLubricant Type, System or AmountDefective BearingBearing InsallationSeal Failure
Soon After Installation
Soon after periodic disassembly
Soon After Re-lubrication
After replacement or repair of other parts
During normal operation

Symptoms During Operation

Operation ConditionCauseRemarks
Ever-changing soundChange of clearance by temperature rise Defect in progress on raceway
Low Level Metallic SoundImpression on Raceway
High Level Metallic SoundLoss of Clearance, Poor Lubrication
Irregular SoundExcess clearance, contaminants, defect of rolling element surface, improper lube
Abnormal temperature riseLoss of clearance, creep, insufficient or excess lubricant, excess loadUse a surface thermometer.
Reduction in accuracyRaceway or rolling element broken by impurities, or insufficient lubricantLathe: stick-slip marks
Grinder: wavy pattern
Cold roll mill: occulting wave pattern
Contaminated lubricantPoor lubrication, foreign matter, wear
Unstable operationBroken raceway, rolling element Foreign matter
Excess clearance
Example: vibration

Condition of Bearings & Prevention Methods

(1) Premature Flaking
The repeated heavy stress cycle between the bearing raceway and rolling element surface results in fatigue cracks which become loosened from bearing materials.PREMATURE FLAKING
CausesCounter Measures
Abnormal axial load or excessive load caused by expanded shaft.Clearance fit for the outer ring of one bearing to allow the floating end to move freely axially.
Deflection or misalignment of shaft.Correct alignment of shaft and bearing housing.
Poor parallelism of inner and outer rings.Improve mounting and alignment.
Poor lubrication.Carefully clean and handle shaft and housing.
Rusting, Nicks, Galling from dirt, etc.Review type and quantity of lubricant.
(2) Seizure
Bearing is seized up by excessive heat. Discoloration, softening and fusion of raceway and rolling element.BEARING SEIZURE
CausesCounter Measures
Loss of clearance.Review fitting and bearing clearance.
Operating over limiting speed.Review type of bearing.
Poor or improper lubricant.Select a proper lubricant, and feed it in proper quantity.
(3) Breakage
Splits and cracks in the inner/outer ring or rolling element.BEARING CRACKS BREAKAGE
CausesCounter Measures
Excessive interference fit.Check fits. Finish shaft and sleeve to higher accuracy.
Bearing seat has larger corner radius than bearing.Make shaft corner radius smaller than that of the bearing.
Excess clearance during operation.Check fits and bearing clearance.
Excess impact load.Re-check load conditions.
(4) Indentation
Brinelling, indentation and pear skin of bearing raceway and rollingBEARING INDENTATION
CausesCounter Measures
Impact applied during mounting.Carefully handle the bearing.
Impact from dropped bearing.Clean shaft and housing.
ContaminationImprove the sealing.
Load applied to bearing at rest in excess of static load rating.Re-check load conditions.
(5) Fretting
Occurs when a small relative motion is repeatedly caused in non-rotating bearing. Fretting surface wear produces red colored particles at fitting surface.BEARING FRETTING
CausesCounter Measures
Vibration applied to bearing at rest (e.g. during shipment).Fit the shaft and housing during shipment.
Swing with smaller amplitude.Apply a preload. Use oil for lubrication.
Minute clearance on fit surface.Increase the interference.
Slight sliding during operation as a result reduced interference under a load.Apply oil.
(6) Scoring
Metal to metal contact of bearing raceway, flange face, rolling element and retainer due to destruction of oil film.BEARING SCORING
CausesCounter Measures
Incorrect lubrication.Review type and quantity of lubricant.
Contamination by foreign matter.Improve sealing and component cleaning.
Deflection or misalignment of shaft. Excessive axial load.Correct mounting errors. Review load conditions.
Sharp speed increase at startup.Change to smooth acceleration.
(7) Smearing
Metal to metal contact due to the destruction of oil film. Sliding motion between outer/inner ring and rolling element.Bearing Smearing
CausesCounter Measures
Excess axial load.Correct mounting errors.
Misalignment of bearing.Review the load condition.
Poor lubrication.Select a proper lubricant, and feed it in proper quantity.
Intrusion and galling caused by foreign matter.Improve the sealing.
High acceleration on start-up.Clean shaft and housing.
Avoid sharp acceleration.

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