Contamination is the cause of about 50% of bearing failure. Inner-ring hoop stress may be the root cause of your bearing failures.
Consider this: stress concentrations occur when the inner ring expands, especially so at high operating temperatures. As the rolling elements pass over these areas, hairline fractures form at or near the raceway surface.
These fractures expand until the inner ring cracks and bearing failure occurs. Dryer journals and heated calendar rolls are very typical applications of this failure type. However applications where heat is inherent are not the only places that failure occurs.
Failure rates are even worse in highly contaminated environments. Contamination is the cause of about 50% of bearing failures.
Now special steels and heat treatment are available that strengthen the inner ring of spherical roller bearings against inner ring cracking. NSK has developed a line of Tough Steels for difficult applications such as these.
With built-in compressive stress, NSK's TL steel (for Tough and Long Life) has increased surface hardness, while maintaining dimensional stability for continuous operation at 200 degrees C. This proprietary process differs from case-carborizing.
Compressive stress of the TL bearing acts to minimize the formation of fractures and further restricts their propagation, a process inherent to bearings used in papermaking.
An additional benefit of TL steel is its increased hardness and the ability to perform well in contaminated conditions. This steel, actually 'controls' the damage to the raceways caused by contaminants. 'Controls' means a steel with a micrstructure that provides harder and tougher surfaces that minimizes stresses arond indentations caused by debris in the lubrication. Hence TL steel is suitable for use in steel rollings mills, vibratory equipment, mining equipment, transmissions and industrial gearboxes.