Jebel Ali Free Zone, Dubai, U.A.E.
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  • 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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