Magnetic particle inspection is a commonly used non-destructive testing method, widely used in the fields of aeronautics and astronautics, rail transportation, shipping, pressure vessels, and other areas. It is used to detect defects on the surface and near the surface of ferromagnetic materials. The sensitivity is one of the important indicators for measuring the effectiveness of magnetic particle inspection, determining whether the detection system can accurately identify small cracks or other defects. Therefore, improving the sensitivity of magnetic particle inspection is of great significance to ensure product quality and safety.



1. Choose the appropriate magnetization method



Different magnetization methods have a significant impact on sensitivity. Common magnetization methods include longitudinal magnetization, circumferential magnetization, and composite magnetization, etc. Circumferential magnetization is suitable for detecting longitudinal defects, while longitudinal magnetization is suitable for detecting transverse defects. To improve sensitivity, the magnetization method should be reasonably selected according to the shape, material characteristics, and expected defect direction of the inspected workpiece. Composite magnetization can detect defects in different directions simultaneously, which is suitable for complex workpieces and an effective means to improve sensitivity.



2. Optimize the magnetization current parameters

　　The size and type of magnetization current directly affect the strength and distribution of the magnetic field. Generally, appropriate high current can produce a stronger magnetic field, which is helpful to excite the leakage field of minute defects. However, excessive current may lead to magnetic saturation, which反而降低灵敏度. Alternating current is suitable for detecting surface defects, while direct current or half-wave rectified current is suitable for detecting near-surface defects. In actual operation, the current parameters need to be adjusted according to the material thickness, defect depth, and detection requirements.



3. Rational use of magnetic particles and magnetic suspension solution

　　The particle size, color, magnetism, and dispersibility of magnetic particles have a direct impact on sensitivity. Fine-grained magnetic particles are more easily adsorbed by the leakage field, improving the detection capability of minute defects. In addition, using the appropriate magnetic suspension solution (aqueous or oil-based) and controlling its concentration is also very important. Excessive concentration can conceal defect displays, while insufficient concentration affects sensitivity. Regular stirring and replacement of the magnetic suspension solution to maintain its uniformity and effectiveness are the key to improving the detection quality.



4. Strengthen surface treatment and lighting conditions



The roughness of the workpiece surface or oil stains can affect the adhesion of magnetic particles, reducing the detection sensitivity. Therefore, pre-treatment such as cleaning, deoiling, and derusting should be carried out on the workpiece before inspection. In addition, good lighting conditions (especially when using fluorescent magnetic particles) are helpful to observe weak magnetic trace displays, thereby improving the ability to identify.



5. Adopt advanced detection equipment and technology



Modern magnetic particle inspection equipment is constantly upgrading, such as automatic magnetization devices, fluorescent magnetic particle detectors, and image recognition systems, which can significantly improve sensitivity while improving detection efficiency. For example, fluorescent magnetic particles have higher contrast and visibility under ultraviolet light, which can clearly display minute defects.



6. Standardize the operation process and personnel training



The influence of human factors on the test results should not be ignored. Only by strictly following the standard operating procedures can the reliability of the test be ensured. At the same time, strengthening the technical training of the testing personnel and improving their ability to identify magnetic traces are also important links to improve the overall sensitivity.



Conclusion



To improve the sensitivity of magnetic particle inspection, it is not only necessary to select appropriate magnetization methods and parameters, but also to consider multiple aspects such as material treatment, equipment selection, and operational specifications. With the continuous advancement of technology, the sensitivity of magnetic particle inspection will continue to improve, playing a greater role in ensuring the quality and safety of industrial products.