A Novel Sensing System Used for Detecting Magnetic Shots Inside Conductive Tubes Based on Low Frequency Eddy Current Testing

Shot peening is often applied into the surface strengthening. However, a portion of magnetic shots tend to remain in the tubes and disable the workpiece. In order to detect the magnetic shots in conductive castings, we have found it in extensive experiments that a feature parameter, the response of imaginary part of impedance, exhibits a great difference between magnetic and non-magnetic conductors, for a double-coil eddy current testing system with super low frequency exciting. Subsequently, the research confirmed this finding with samples of steel and aluminum alloys. Based on this different low-frequency response, this paper proposed a sensing system, it could efficiently find out the magnetic shots from aluminum alloy tubes.