Design Of Magnetic Flux Leakage Detector For Rail Top Surface Defects

With the rapid development of high-speed rail and subway,the mileage and the scale of operation of domestic rail transit have increased year by year.The reliability of rails is of great significance to ensure the safety of rail transport.Due to the repeated extrusion,friction and impact of wheel sets,the rail will produce cracks,which are concentrated on the top of the rail at the initial stage and exist in the form of small cracks.This paper focuses on the nondestructive detection technology of rail top crack,develops a detection system based on magnetic flux leakage,designs the software and hardware of the system,verifies the effectiveness of the system through experiments,and provides a set of effective technical means for the detection of rail top crack.In this paper,the formation mechanism and magnetic field distribution of leakage field are studied by theoretical analysis and simulation.Aiming at the problem that the early natural cracks will appear on the top and side of the rail head,a double-plate structure was designed,that is,a detecting plate containing sensor array was used to measure the cracks on the overhead and lateral surface of the rail,which effectively reduced the lift off under the premise of less complicated structure.According to the characteristics that the leakage magnetic field decreases rapidly with the increase of lift off a new bearing detection structure is designed for the continuous vibration of the train in the process of running.The lift off of sensor probe is effectively reduced and the lift off stability is maintained as much as possible by the sliding boots probe.On the basis of double-plate structure and sliding boots probe bearing mechanism,a set of rail surface cracks detection system is designed.For the artificial and natural cracks on the top of the rail,the turntable,trolley,and electric double-track detection vehicle are used to test the system,which verifies the effectiveness and reliability of the designed system.According to the test results,a cracks detection method of vertical array sensor is proposed.Instead of the previous method of identifying cracks by the absolute magnitude of the amplitude of the signal acquisition,the relative size of multiple sensor outputs is used to identify cracks,and the best distance between each sensor is deduced.The experiment shows that this method can effectively suppress vibration and improve the identification accuracy of a single crack.