After being magnetized, the magnetic field of the discontinuous part of the material is distorted, which will form part of the leakage of magnetic flux on the surface of the product, and then attract the magnetic powder to form the accumulation of magnetic powder in the defective part, which is the magnetic trace in the industry. The position and shape of the defect are directly revealed, and the magnetic particle accumulation is observed and explained to realize the magnetic particle inspection.

The magnetic particle inspection is a non-destructive testing method for detecting the surface defects of ferromagnetic materials or near parts by the accumulation of magnetic particles in the leakage magnetic field near the defect. The characteristics of this flaw detection method are that it is simple and more intuitive, and the speed is faster, the sensitivity is high, it can enlarge the defect, and it is also convenient for the post-processing of the steel castings, such as kiln supporting rollers, kiln tyres, etc. This is the reason why many manufacturers prefer this kind of flaw detection.