Ultrasonic Testing Methods for Inspection of Large Diameter Bearing Balls

Metallic spherical balls are typically used as rolling mechanisms in rotary motion components such as ball bearing, tooling etc. to limit the rotational friction. Material and manufacturing defects in metal balls affect the proper functioning of the ball bearing during its service for intended load carrying capacity. Hence, it is essential to qualify the ball before putting it into service. The surface defects can be qualified by surface non-destructive examination (NDE) techniques such as liquid penetrant testing, magnetic particle testing and eddy current testing. For volumetric examination ultrasonic testing is preferred over radiography testing due to geometry. Conventional contact ultrasonic testing method has some limitations due to curved nature of surface. Hence, some non-contact method needs to be evolved to inspect the spherical objects which can cover the full the volume of the object with high probability of detection. In the present work, a procedure has been developed by using conventional immersion ultrasonic testing (UT) technique to examine the volumetric defects in large diameter spherical bearing steel balls. An immersion ultrasonic inspection set up and procedure has been evolved for the inspection of spherical steel ball of diameter 95 mm by conducting initial scanning trails using different frequencies and depth of focus. Steel balls with and without defects have been scanned and compared in order to evaluate the defects. The volumetric mapping and sizing of defects for spherical steel balls are discussed in this paper.