Research On Magnetic Testing Methods And Their Application To Longitudinal Cracks Of Steel Bars

The longitudinal crack of steel bar is the main factor that influences its quality. In modern industry, the requirement of product's quality is higher and higher, accordingly, it is important and urgent to test the longitudinal cracks in steel bar. With the view of improving product's quality, lowering the labor intensity, and minimizing industrial application accidents, it is of great significance to design an automatic crack testing system. After analyzing the status quo of non-destructive testing methods and systems both in China and abroad, the author puts forward the blue print of a speedy and sensitive magnetic flux leakage (MFL) testing system according to practical testing requirement and features of the cracks. Trough the analysis of various factors that influences magnetic flux leakage field in longitudinal crack testing, such as the magnetizing strength, magnetizing clearance, and planning of the magnetic source, it is found that there exist many problems when using the traditional longitudinal testing methods to test the cracks of steel bars, Such as the decentralization of magnetization, the lack of magnetizing intensity and poor stability of the system. Then further analysis and experiments are conducted to find out the causes that arouse those problems and finally by alternating the magnetizing measures and testing the maximum sensitivity of different methods the author finds an effective testing method for longitudinal cracks, that is the flaky magnet magnetizing method. Based on this method, the author has designed the structure of testing sensor and the control system. This testing system has been proved to be of excellent function, reliable testing accuracy and high sensitivity by practical application.