Electromagnetic testing emt-mft chapter 9b

Another area in which the flux leakage method has been successfully
implemented is the inspection of rolling-element antifriction bearings. A
schematic illustration of the method as applied to an inner bearing race is
shown in Fig. 9. In this application, the part is magnetized by an
electromagnet, as indicated in Fig. 9(a). The race is then rotated by a spindle,
and the surface is scanned with an induction coil sensor. Typically, the race is
rotated at a surface speed of about 2.3 m/s (7.5 ft/s), and the active portion of
the raceway is inspected by incrementally indexing the sensor across the
raceway. Magnetizing fields are applied in the radial and circumferential
orientations. It has been shown that radial field inspection works best for
surface flaws, while circumferential field inspection shows greater sensitivity
to subsurface flaws. Data have been collected on a large number of bearing
races to establish the correlation between leakage field signals and inclusion
depths and dimensions determined by metallurgical sectioning.
Charlie Chong/ Fion Zhang