Recommendations to reduce premature failures

To find effective remedies for reducing premature bearing failures (see table below), it is important to begin by asking: 

  • Why are cracks initiated much faster in prematurely failing bearings? What are the drivers?
  • What can be done to make the  customer’s application and bearings more robust?


Drivers

Bearing system (Design process)

Bearing solutions

Higher stresses
(e.g. tensile structural stresses, brief, heavy loads, frictional stresses, etc.)

  • Correct bearing selection 
  • Dimensional and geometrical tolerances of bearing seats in line with SKF recommendations
  • Limited shaft and housing seat deformations (due to loads and / or thermal effects)
  • Correct clearance / preload setting
  • Verify dynamics / peak loads during extreme events

  • High compressive residual stresses (minimum for the inner ring)
  • Premium steels





Lower material strength
(e.g. corrosion, electrical current, mixed friction & slip, etc.)

  • Limit water in oil
  • Limit humidity during standstill 
  • Verify transport and mounting procedures
  • Avoid stray current
  • Limit vibrations    
  • SKF black oxide
  • Case carbonitriding
  • High-strength stainless steel 
  • Insocoat®, hybrid bearings
    (electrical current protection)


If you need further assistance, feel free to contact a SKF representative or click on contact (top right corner).


Advantages of SKF black oxide bearings

  • Improves running-in properties and reduces friction and bearing wear
  • Improved resistance against smearing damage
  • Improved resistance against surface distress, enhances performance in low-lubrication conditions (fig.8)
  • Reduced risk of chemical attack from aggressive oil additives on the bearing steel (fig. 9 and fig.10)
  • Increased oil and grease adhesion 
  • Enhanced corrosion resistance (fig.11)
  • Reduced hydrogen permeation in the bearing steel (fig.12

For more precise information, please read the article from the Evolution magazine Benefits of using black oxidized bearings in wind applications.



Strong field experience with black oxide bearings in wind turbine gearboxes

Since 2008, sales of black oxide bearings has significantly increased. This has provided SKF with the opportunity to develop strong field experience with black oxide bearings in wind turbine applications for more than 7 years, which is well beyond the typical time-to-failure of standard bearings suffering from premature failures.

Having largely been applied on cylindrical roller bearings (though possible for all bearing types), black oxide bearings can be found on all positions in the wind turbine gearbox or applied in all turbine sizes and supplied in various sizes.

Note that they have been mainly applied at the most critical positions in the gearbox (low speed planet and high speed shaft) known to be most sensitive to premature failures and WEC.

Result: To date, these black oxide bearings have no known issue and a failure rate below 100ppm  (fig.13).

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