Research On Online Detection System Of Wheel Tread Based On Electromagnetic Acoustic Technique

Rail transportation plays a more and more important role in the developmentof national economy, and higher requirements of the safety of rail transport havebecome more necessary. As the important part bearing trains, the wheel is proneto such flaws as wear, cracks and scratches during operation, which seriouslyaffect the safe operation of trains. In this paper, an online flaw detection systemfor wheel tread based on electromagnetic ultrasonic technology is developed.The system can achieve online detection without affecting the normal operationof trains, and has the advantage of high detection efficiency.The mechanism of Lorentz force and magnetostriction force has beenstudied, the testing methods of electromagnetic ultrasonic surface wave arestudied, and the technical specifications and overall scheme are designed basedon the characteristics of electromagnetic ultrasonic surface wave and the actualdetection requirements.The mathematical models of EMATs based on Lorentz force andmagnetostriction force are proposed in this paper, and a two-dimensional finiteelement model for surface wave electromagnetic acoustic transducers working onplates has been presented. The simulation results show that the surface wavesignal due to Lorentz force is about6.4times of that due to magnetostrictionforce. Therefore, the influence of magnetostriction force can be ignored in thefinite element model, which can greatly reduce the simulation time. Based on thetwo-dimensional model, transmitting and receiving coils with various parametershave been simulated. The influence of parameters on the performance oftransducers have been analyzed and compared, supplying basic rules fortransducer design. By comparative analysis, the transmitting and receivingperformance of skeleton coils is superior to that of PCB coils.In order to enhance the flaw detection ability of electromagnetic acoustictransducers, the common types of wheel flaws have been studied. These flaws aredivided into three types, including rectangular flaws, triangle flaws andsemi-elliptical flaws. The equivalent simulation models for these flaws have beenestablished according their characteristics. Eight parameters of transmitter coiland receiver coil, including slot number, conductor number of one layer, layernumber and wire diameter, have been chosen to conduct orthogonal test. TheEMAT coil parameter combination, with comprehensive optimal detectionperformance to three types of flaws, has been obtained, and the significance of the parameters, affecting the performance of the transducer detection, has beendetermined.The hardware, software, and machinery of the wheel online detection systemhave been designed in this paper. Offline experiment of the train wheel afterdisassembling and online experiment using the detection system have beenperformed. The test results show that the wheel online detection system designedin this paper can detect the flaws in the wheel effectively, verifying thefeasibility of the system.