False brinelling is fretting occurring in bearings

When fretting wear occurs in bearings, it is referred to as false brinelling.  A bearing will experience false brinelling when it is not turning but subjected to vibrations of some sort.  Because the bearing is not turning, the grease or oil will be gradually removed from the ball or roller contacts ending in metal to metal contact.  Next wear takes place and the damage will cause the bearing to fail sooner after start up.

False brinelling is different from true brinelling.  Brinelling is caused by a large impact on a bearing which causes the rolling elements to leave large dents in the raceway.  False brinneling leaves a very similar wear scar, but it comes from a series of small impacts instead of one large impact.  False brinelling marks are usually wider than brinelling marks and there may be two marks for each roller because of the slip zones occurring on either side of the roller.

Bearings often experience false brinelling damage in an assembled machine in storage.  Only very small vibrations are needed for false brinelling to take place and usually vibration is not considered while deciding upon where to leave a machine.  If a machine it stored near where it will be used, it is very likely that there will be vibrations present from the machine it will replace.

False brinelling caused one of the most famous cases of fretting.  Automobiles in the 1930s were being shipped from Detroit to the west coast on trains.  During shipment, their storage location–a train car–experienced vibration leading to the failure of wheel bearings.  Unfortunately, similar mistakes have been be made many times since.

False brinelling causes bearings to fail because the rolling element and raceway come into metal-on-metal contact.  When the asperities touch one another both wear and oxidation take place.  This is bad on for several reasons:

  • The wear debris formation leaves a wear scar in its wake which will interfere with the normal rotation of the bearing when a machine is started.
  • Because bearing races and rolling elements are very hard, hard wear particles are formed which cause abrasive wear.
  • Because the bearing is not turning, the particles remain in the contact area instead of being distributed evenly or removed by a filter.

False brinelling is a failure due to fretting wear not fretting fatigue.  A bearing will fail due to the geometric changes of the wear scars not from fatigue cracks nucleating at the rolling-element contacts.

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6 Comments

  1. David Benyon says:

    Will someone explain how this can happen with bearings that are oil filled or lubricated with super-greases which are extremely adherent. One can only assume that the grease used in the 1930s was not much better than lard.

    • Al Lupinc says:

      I believe the wheel bearings on cars transported by train where failing because the axel was chaned to the car deck (to prevent the cars from moving). This extra pressure on the wheel bearings led to false brinelling and subsequent bearing failure.

  2. Ben says:

    Thanks for the comment David, I am not an expert on different types of greases. I have read that metal to metal contact takes place in various different articles about false brinelling, but it is possible that the authors had ignored the existence of a mono-layer or two of grease separating the surfaces.

    I do know that bearing manufacturers are concerned about false brinelling today. Whenever you have a stationary bearing there is no converging surface, so the lubricant film goes away. Whenever the film thickness is less than the RMS roughness of the surfaces you will have boundary lubrication where there is significant asperity interaction.

  3. Selina says:

    Will someone provid some equipement that can test the false brinelling about the lubricant gease?
    I find some on the net but can not find the manufacturer.

    http://www.tri.hs-mannheim.de/falsebrinelling.htm

  4. B. Leonard says:

    Hello Selina,

    Thanks you for the comment. I have not purchased a commercial fretting testing machine, but I know that Falex sells a fretting testing machine. This machine would appear to be adequate for your desired tests.

    http://www.falexint.com/functions/list.asp?Lid=2&pnav=;3;10;&item=23

  5. Ricardo Hein says:

    The ASTM D-7594 is the standard to test greases for false brinneling. It runs on the SRV at 400N for 4 hours and 0.3 mm vibration.

    Greases when under pressure and without a movement to renew the film, they separate the oil from the thickener and loose all lubricity. Normal greases cannot prevent fretting. Greases with very high content of the right solids (called pastes) are the best films for prevent fretting. Let me know if you need some help in selecting these lubricants.

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