Permanent magnet and pulsed eddy current composite magnetic flux leakage detection method

Abstract

The invention relates to a permanent-magnet and pulsed-eddy-current composite magnetic flux leakage detection method. With the method provided by the invention, defects on inner and outer surfaces can be effectively identified. The method belongs to the field of nondestructive test. With the effect of a permanent magnet, a ferromagnetic material requiring detection is magnetization into a local saturation state; if a detected magnetic flux leakage signal is larger than a preset intensity threshold B1, the ferromagnetic material has a defect; a reverse narrow pulse signal is applied to a excitation coil, such that the excitation coil generates a pulsed magnetic field, and pulsed eddy current is formed on the inner surface of the ferromagnetic material below two poles of a U-shaped magnetic yoke; at the time, if a detected leakage field intensity pulsation value is larger than a preset pulsation threshold B2, the defect is positioned on the inner surface of the ferromagnetic material; otherwise, the defect is positioned on the outer surface of the ferromagnetic material. The method provided by the invention has the advantages of simple hardware structure, low energy consumption, and convenient and fast signal processing.

Description

technical field [0001] The invention proposes a magnetic flux leakage detection method, especially a magnetic flux leakage detection method combined with permanent magnets and pulsed eddy currents, which realizes the discovery of surface defects of ferromagnetic materials and the identification of inner and outer surface defects, and belongs to the technical field of nondestructive testing. Background technique [0002] With the development of science and technology, there are more and more non-destructive testing methods, which are suitable for different testing occasions, but the most commonly used are the five conventional testing techniques of radiographic testing, eddy current testing, magnetic flux leakage testing, ultrasonic testing and penetration testing. As one of the five conventional nondestructive testing techniques, magnetic flux leakage testing is widely used in the testing of ferromagnetic materials. Compared with other non-destructive testing methods, it has...

AI Technical Summary

Problems solved by technology

DC magnetic flux leakage detection adopts DC signal or permanent magnet for excitation. It is a relatively mature detection method in magnetic flux leakage detection technology. Its magnetic flux leakage signal is strong and the detection results are reliable. The biggest disadvantage is that it cannot distinguish the defects on the inner and outer surfaces.

The AC excitation magnetic flux leakage detection technology uses AC signals for excitation, which is very sensitive to surface defects. The disadvantage is that the frequency is single, and due to the skin effect, its penetration depth is very limited, and it can only detect surface and near-surface defects.

Using the magnetic flux leakage detection method to distinguish whether the defect is located on the inner surface or the outer surface of the ferromagnetic material has always been a technical problem in the field of magnetic flux leakage detection, and the research at home and abroad is relatively rare.

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