Abstract
In this paper, the principle of ac magnetic flux leakage (referred to as MFL) detection is presented by analyzing the formation of ac magnetic flux leakage and how it is collected. It is found that ac excitation frequency is a very important equipment parameter for ac magnetic flux leakage detection of steel rod. High-frequency current not only stabilizes the penetration depth of ac magnetic field under the rod surface and leakage magnetic field of defects, but also improves the ability to detect defects and adapts to higher detection speed. It is concluded that the lift-off effect is the fundamental reason affecting the reliability of MFL detection of steel rod, and there is an inherent signal amplitude deviation from the irremovable probe bouncing on the surface of steel rod. Then, the factors that aggravate the lift-off effect are analyzed synthetically, and the corresponding countermeasures are put forward. It provides an effective basis for improving the test reliability and reasonably controls the quality risk of the rod.
Highlights
The surface finish of hot rolled steel rod is poor, better signal-to-noise ratio and greater detection depth can be obtained by using MFL detection method which is superior to Eddy current detection method [1,2,3] 126
We began to discuss the principle of MFL detection of steel rods, during which we found that ac magnetization frequency is a very important equipment parameter in MFL detection; the encouraging result is that we find that the lift-off effect is the root cause that affects the reliability of test signals during detection
1) In this paper, the Principle of ac MFL detection of bar is given, and it is found that ac excitation frequency is a very important equipment parameter for MFL detection of steel rod
Summary
The surface finish of hot rolled steel rod is poor, better signal-to-noise ratio (referred to as SNR) and greater detection depth can be obtained by using MFL detection method which is superior to Eddy current detection method [1,2,3] 126. The large diameter rod detection line MFL detection equipment is used to detect steel rods with diameters of Ф70 ~ 180 mm. The steel rod is driven by a V-shaped roller and determines that the central line is being tested; The magnetic leakage device of the small diameter rod detection line is used to detect steel rods with a diameter of Ф20 ~ 80 mm. The steel rod is driven by a three-claw roller and the central line is determined to detect the steel rod. We began to discuss the principle of MFL detection of steel rods, during which we found that ac magnetization frequency is a very important equipment parameter in MFL detection; the encouraging result is that we find that the lift-off effect is the root cause that affects the reliability of test signals during detection. We comprehensively analyze various factors that aggravate the lift-off effect and put forward corresponding countermeasures to ensure the reliability of testing and effectively control quality risks
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