Mechanical parts, plants and cross-linkages inspected with MT are typically complex 3D shapes. In the complex 3D shape portion, because a magnetizer often cannot be configured to the inspection portion and the test object cannot be appropriately magnetized, there is a possibility of overlooking a crack in such an instance. Thus, MT system development that was successfully able to detect omnidirectional cracks in 3D shape portions was considered in this study's trials. Two magnetizers were hence arranged face-to-face, and the magnetization of omnidirectional scenarios for all surfaces of 3D shape test object (arranged in between both magnetizers) was evaluated.

No 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.

The maximum magnetic flux leakage from a crack is obtained when the magnetic flux is distributed to the longitudinal direction of the crack in the orthogonal direction. 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 a three-pole coil (a three-phase alternating current), omnidirectional crack can be detected by a single testing. However, the rotating magnetic field becomes no homogeneous distribution at a position far from the center of the magnetizer, and the strong magnetic field is generated in a specific direction.In this research, the multi coil magnetizer that widely obtained uniform rotating field distribution was developed. The distribution of the rotating magnetic flux density on the steel plate was evaluated with a finite element method analysis. In addition, a prototype magnetizer was produced based on the analytical results, and the characteristic was evaluated.

No abstract