White Etching Cracks in Bearing

 


Bearings that are used in large industrial gearboxes, train applications, paper mills, crusher mill gearboxes and lifting gear drives are subjected to a wide variety of operating conditions that can push them beyond their limits. Such conditions can result in bearing failure, often called white etching cracks or white structure flaking. 


What are white etching flakes?

White etching cracks are cracks within a bearing. White etching area refers to the white appearance of the altered microstructure of a polished steel sample. The affected areas usually contain ultra-fine, nano-recrystallised, carbide-free ferrite with carbide particles. These areas appear white under the optical microscope due to their low-etching response to the etchant. White etching areas are usually 10-50% harder than the surrounding unaffected microstructure. 


What causes white etching cracks to develop?

Two physical parameters accelerate rolling contact fatigue.

  • Stresses higher than anticipated - Stresses affecting the bearing can be higher than expected. Heavy loads can be caused by unexpected dynamics or temperature effects. Structural stresses in the bulk material of bearing are usually caused by deviations, misalignments or other factors which increases the stress in the materials. Increased stress on the raceaway can also cause severe tribological conditions.  

  • Strength lower than anticipated -  The material strength of bearings can be negatively influenced by environmental factors that are suspected to generate hydrogen. These could include water contamination, corrosion, electrical stray currents etc. Moderate loading conditions can lead to premature failure. 

Reasons of White Etching cracks in bearings 

Bearing rolling contact failures can be caused by several things, like material flaws, lubrication problems, contamination, poor handling or installation. Below are some types of bearing failures. 

  • Fatigue failure - The most frequent rolling contact failure is fatigue failure. It happens due to the bearing being loaded and unloaded repeatedly in cycles which can lead to material fatigue.  

  • Wear - Metal to metal contact between rolling elements can cause wear, resulting in material loss and modification in material geometry. This can result in more friction and worse bearing performance.    

  • Corrosion - Corrosion is a condition that can be brought on by exposure to chemicals and moisture. It can result in surface flaking, which can eventually cause the bearing to fail.   

  • Brinelling - Brinelling is caused by indentation failure that happens when a bearing is exposed to static loads, including during installation or transportation.  

  • Spalling - Spalling is separation of tiny flakes or particles of material from a bearing’s surface. It could be caused by poor lubrication, unloading or material flaws. Increased friction, vibration, and eventual bearing failure can cause spalling.  

  • Fretting - Fretting is a type of wear brought on by oscillations of modest amplitude between the rolling components and raceway.  Particularly in parts of the bearing that experience significant stress can result in surface damage. 

To avoid such situations and get the right assistance, you can contact Premier Bearings, one of the leading INA bearing suppliers in India. To get more details, visit our website - https://www.premierbearing.com/


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