Consideration of multi-coil type magnetizer for detection of omnidirectional crack in magnetic particle testing

In a rotating-magnetic-field-type magnetizer using a three-pole (three-phase) coil, omnidirectional cracks can be detected via a single test. However, the rotating magnetic field ultimately experiences non-homogeneous distribution in an area far from the centre of the magnetizer. In this study, a multi-coil-type magnetizer that widely obtains uniform rotating magnetic fields was hence developed. Distributions of rotating magnetic flux densities in test object were evaluated using finite-element analysis, and the utility of the multi-coil was confirmed. In addition, the technique for omnidirectional magnetization on whole surfaces of 3D-shaped test object was considered via implementation of the subject multi-coil magnetizer.