2025 Volume 97 Issue 3 Pages 154-163
Spheroidal graphite cast iron is a material with excellent mechanical strength and strong resistance to corrosion. However, shrinkage cavities may be generated inside this material during manufacturing. In this research, we propose a non-contact measurement method for detecting shrinkage cavity inside the cast iron using electromagnetic force vibration. In this proposed method, electromagnetic vibration is generated inside the cast iron from the static magnetic field, and the eddy current by the alternating exciting coil. When the cast iron is vibrated, the spatial magnetic field between the proposed sensor and the cast iron fluctuates. The fluctuation of the spatial magnetic field is detected by the Hall element. If there is a shrinkage cavity inside the cast iron, it presence will change the vibration intensity as well as the fluctuation intensity of the spatial magnetic field subsequently. Therefore, the shrinkage cavity is estimated by the fluctuation intensity of the spatial magnetic field between the sensor and cast iron. In this paper, the electromagnetic vibration and displacement inside the cast iron are calculated by 3-D nonlinear electromagnetic FEM analysis and displacement FEM analysis. The phenomenon of this proposed method is clarified using these FEM analysis methods and verification experiments. These calculations and verification experiments show that the shrinkage cavity can be evaluated from the fluctuation intensity of the spatial magnetic field.
