Bearing damage

Each of the different causes of bearing failure produces its own characteristic damage. Such damage, known as primary damage, gives rise to secondary, failure-inducing damage - flaking and cracks. Even the primary damage may necessitate scrapping the bearings on account of excessive internal clearance, vibration, noise, and so on. A failed bearing frequently displays a combination of primary and secondary damage.
The types of damage may be classified as follows
  • Primary damage
    Wear
    Indentations
    Smearing
    Surface distress
    Corrosion
    Passage of electric current
  • Secondary damage
    Flaking
    Cracks
    Cage damage
The primary and secondary damage listed above can be split into various causes:
  • Wear
    Wear caused by abrasive particles
    Wear caused by inadequate lubrication
    Wear caused by vibration
  • Indentations
    Indentations caused by faulty mounting or overloading
    Indentations caused by foreign particles
  • Smearing
    Smearing of roller ends and guide flanges
    Smearing of rollers and raceways
    Raceway smearing at intervals corresponding to the roller spacing
    Smearing of external surfaces
    Smearing in thrust ball bearings
  • Surface distress
  • Corrosion
    Deep seated rust
    Fretting corrosion
  • Passage of electric current
  • Flaking (spalling)
    Flaking caused by preloading
    Flaking caused by oval compression
    Flaking caused by axial compression
    Flaking caused by misalignment
    Flaking caused by indentations
    Flaking caused by smearing
    Flaking caused by deep seated rust
    Flaking caused by fretting corrosion
    Flaking caused by fluting or craters
  • Cracks
    Cracks caused by rough treatment
    Cracks caused by excessive drive-up
    Cracks caused by smearing
    Cracks caused by fretting corrosion
  • Cage damage
    Vibration
    Excessive speed
    Wear
    Blockage
    Other causes of cage damage

Securing evidence before and after removal

When a bearing is removed from a machine due to failure the cause of the failure should be classified as well as the means to avoid future failures. To obtain the most reliable results possible it is helpful to follow a systematic procedure when securing and inspecting the bearing.
The following points should be considered when investigating bearings:
  • obtain operating data, analyse records and charts from bearing monitoring devices;
  • extract lubricant samples to determine lubrication conditions;
  • check bearing environment for external influence including equipment problems;
  • assess bearing in mounted condition;
  • mark mounting position;
  • remove bearing and parts;
  • mark bearing and parts;
  • check bearing seats;
  • assess bearing;
  • examine individual bearing/bearing parts
  • consult experts or despatch bearings to experts together with full results from the above check points as required.
Important factors necessary to find the causes of failure may be lost if the procedure selected is incorrect.
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