The principle of magnetic particle testing and its main characteristics

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After a ferromagnetic material workpiece is magnetized, when the direction of the defects is at an angle to the direction of the magnetic field, the local distortion of the magnetic flux lines caused by these defects leads to some of the magnetic flux lines escaping from the surface of the workpiece, thereby creating a leakage magnetic field. This occurs especially when the discontinuities are located on the surface or near the surface of the component. The leakage magnetic field attracts the magnetic particles applied to the surface of the part, resulting in magnetic traces that are visible to the eye under appropriate lighting, indicating the location, shape, and size of the discontinuities. Magnetic particle inspection is used to detect surface cracks; compared with ultrasonic testing and radiographic testing, it features high sensitivity, simple operation, reliable results, good repeatability, and easy identification of defects. However, this method is only applicable to detecting surface and near-surface defects in ferromagnetic materials.