Service Life Testing of Railroad Bearings with Known Subsurface Inclusions: Detected with Advanced Ultrasonic Technology

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Steel cleanliness is of the utmost importance in the production of tapered roller bearings used in the railroad industry. Impurities in the steel can make it vulnerable to fatigue initiation because they act as stress concentration sites in the fabricated parts, especially when these impurities are located in regions of susceptibility for rolling contact fatigue (RCF). Impurities present near the rolling surfaces (e.g., raceways in bearings) are referred to as subsurface inclusions. These subsurface inclusions make the steel susceptible to the initiation of fatigue cracks that can propagate towards the surface leaving a cavity called a “spall”. Spalls occurring on the rolling surfaces of bearings can have detrimental effects that may lead to overheated bearings, loss of full service life, and in extreme cases, can lead to derailments if not addressed in-service by early detection methods. The study presented in this paper investigates the effects of subsurface inclusions present beneath the surface of the bearing cup (outer ring) and cone (inner ring) raceways.

New bearing components were scanned using a unique ultrasonic technique in order to detect and identify potentially detrimental subsurface inclusions present in the RCF regions of the rolling surfaces. Two service life tests of these components were then carried out: one to examine subsurface inclusions found on cone raceways, and one to explore subsurface inclusions present on cup raceways. The test results indicate that the service life of components containing subsurface inclusions is reduced compared to controls for which no subsurface inclusions were detected. Moreover, subsurface inclusions on bearing cups appear to accelerate spall development relative to those present in bearing cones. This paper summarizes the findings of the experimental study performed on ultrasonically scanned bearing components, and emphasizes the need to establish more refined methods to inspect railroad rolling stock. These results are anticipated to be of great value to fatigue life prediction models relevant to the railroad industry.


© Saxe-Coburg Publications, 2013

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International Journal of Railway Technology