Development of Magnetic-Particle Testing Magnetizer for Generation of Uniform Rotating Magnetic Field in Wide Area

Abstract

The maximum magnetic flux leakage from a crack is obtained when the direction of the magnetic flux is orthogonal to the longitudinal direction of the crack. In magnetic-particle testing with a yoke method, since we usually cannot predict the direction of the crack to be detected, it is necessary to perform the testing at least two times by changing the direction of magnetization. In a rotating magnetic field type magnetizer using three-pole coils (three-phase alternating current), omnidirectional crack can be detected by a single testing. However, directions of the weak magnetic flux density appear at positions far from the center of the magnetizer, and the rotating magnetic field becomes no homogeneous distribution. In this research, it was considered to split each magnetic pole in the magnetizer to generate the uniform rotating magnetic field. The distribution of the rotating magnetic flux density was evaluated with a finite element method analysis, and an optimal disposition angle of the split coil was discussed. In addition, a multi coil magnetizer was developed to generate the uniform rotating magnetic field more widely.