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  • Bearing Failures and Countermeasures

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


    For instance, the causes of rib scoring, as one example of premature failure, may include  insufficient lubrication, use of improper lubricant, faulty lubrication system, entry of foreign matter, bearing mounting error, excessive deflection of the shaft, or any combination of these. Thus, it is difficult to determine the real cause of some premature failures.


     
    If all the conditions at the time of failure and previous to the time of failure are known, including the application, the operating conditions, and environment; then by studying the nature  of the failure and its probable causes, the possibility of similar future failures can be reduced.

     

            Type of Failure

        Probable Causes

    Countermeasure

    Flaking

    Flaking of one-side of the raceway 

    of radial bearing.

    Abnomal axial load.

    A loose fit should be used
    when mounting the outer 

    ring of free-end bearings 

    to allow axial expansion 

    of the shaft.

    Flaking of the raceway

     in symmetrical patterm.

    Out-of-roundness of the 

    Housing  bore.

    Correct the faulty housing.

    Flaking pattern inclined

     relative to the raceway
     in radial ball bearings. 

    Flaking near the edge 
    of the raceway and rolling 

    surfaces in roller bearings.

    Improper muonting, deflection 

    of   shaft, inadequate tolerances 

    for shaft and housing.

    Use care in mounting 

    And centering, select a 

    bearing with a large 

    clearance, and correct the 

    shaft and housing shoulder.

    Flaking of <, /SPAN>raceway with 

    same spacing as rolling 

    elements.

    Large shock load 

    during mounting,
    rusting while bearing 

    is out of operation for

     prolonged period.

    Use care in mounting 

    and apply a rust 

    preventive when 

    machine operation 

    is suspended for a 
    long time.

    Premature flaking of raceway

     and rolling elements.

    Insufficient clearance, 

    Excessive load, 

    improper lubrication, 

    rust, etc.

    Select proper fit, bearing 
    clearance, and lubricant.

    Premature flaking of duplex 

    bearings.

    Excessive preload.

    Adjust the preload.

    Scoring

    Scoring or smearing 

    between raceway and 

    rolling surfaces.

    Inadequate initial lubrication,
    excessively hard grease and 

    high  acceleration when starting.

    Use a softer grease 

    and avoid

    rapid acceleration.

    Spiral scoring or smearing 

    of raceway surface of thrust 

    ball bearing.

    Raceway rings are not parallel
    and excessive speed.

    Correct the mounting, apply

     a preload, or select another 

    bearing  type.

    Scoring or smearing between

     the end face of the rollers 

    and guide rib.

    Inadequate lubrication, incorrect 
    mounting and large axial load.

    Select proper lubricant and 
    modify the mounting.

    Cracks

    Crack in outer or inner ring.

    Excessive shock load,

    excessiveinterference in

    fitting, poor surface

    cylindricality, improper sleeve

    taper, large fillet radius,

    development of thermal 
    cracks and advancement 

    of flaking.

    Examine the loading 

    conditions, modify

    the fit of bearing and 

    sleeve. The fillet radius 

    must be smaller than 

    the bearing chamfer.

    Crack in rolling element. 

    Broken rib.

    Advancement of flaking, 

    shock  applied to the rib during 

    mounting  or dropped during 

    handling.

    Be carefull in handling 

    and mounting.

    Fractured cage.

    Abnormal loading of cage due

     to incorrect mounting and

     improper  lubrication.

    Reduce the mounting 

    error and review the 

    lubricating method 

    and lubricant.

    Indentat

    ions

    Indentations in raceway

     in same pattern as 

    rolling elements.

    Shock load during mounting or
    excessive load when not rotating.

    Use care in handling.

    Indentations in raceway 

    and rolling elements.

    Foreign matter such as metallic 
    chips or sand.

    Clean the housing, 

    improve the seals, and 

    use a clean lubricant.

    Abnorm

    al Wear

    False brinelling 
    (phenomenon similar

     to brinelling)

    Vibration of the bearing without
    rotation during shipment or 
    rocking motion of small 
    amplitude.

    Secure the shaft and housing,

    use oilas a lubricant 

    and reduce vibrationby 

    applying a preload.

    Fretting

    <, /TD>

    Slight wear  of  the fitting surface.

    Increase interference and 
    apply oil.

    Wearing of raceway, rolling 
    elements, rib, and cage.

    Penentration by foreign matter, 
    incorrect lubrication, and rust.

    Improve the seals, clean the 
    housing, and use a clean 
    lubricant.

    Creep

    Insufficient interference or 
    insufficient tightening of sleeve.

    Modify the fit or tighten 

    the sleeve

    Seizure

    Discoloration and melting 
    of raceway, rolling 

    elements, and ribs.

    Insufficient clearance, 
    incorrect lubrication, or 
    improper mounting.

    Review the internal clearance 

    and bearing fit, supply an

     adequate  amount of the

     proper lubricant and improve

     the mounting method and 

     related parts.

    Electric Burng

    Fluting or corrugations.

    Melting due to electric arcing.

    Install a ground wire to stop 

    the flow of electricity or

     insulate the beaning.

    Corrosion & Rust

    Rust and corrosion of 
    fitting surfaces and

     bearing interior.

    Condensation of water from the 
    air, or fretting.

    Penetration by corrosive 
    substance(especially 
    varnish-gas, etc).

    Use care in storing and 

    avoid high temperature and 

    high humidity,treatment for

    rust prevention is 

    necessary when operation

    is stopped for long time. 

    Selection of varnish and grease.