Research On EMAT Transmitting System Used In Train Wheel On-line Flaw Detection

At present, people usually use the static way or disassembly way to detecttrain wheel flaws, these methods are low efficiency and high cost.Electromagnetic ultrasonic surface wave can be used in train wheel tread on-lineflaw detection, which improves detection efficiency and save manpower andresources. EMAT transmitting system which is used to excite electromagneticultrasonic surface wave is an essential part of the flaw detection system. Theimprovement of its performance can significantly compensate for poortransduction efficiency and sensitivity to the environmental. Hence, the researchon EMAT transmitting system used in train wheel tread on-line flaw detection isof great significance.Take needs of train wheel flaw detection into account, this paper providedthe technical specifications of the transmitting system, made the overall programof the transmitting system, and improved the plan of train wheel on-line flawdetection.EMAT design method based on the experiment was provided. This methodutilized the finite element method to model EMAT and calculated EMATequivalent circuit parameters. Aiming at enhancing ultrasonic echosignal-to-noise, coils were tested by orthogonal experiments and results wereanalyzed by range method. The excellent detection EMAT was found and theecho signal-to-noise increased by about24%compared to the old one. Theconnections between coil equivalent impedance and liftoff were got bysimulation.A high-frequency and high-power transmitting circuit was designed. Whenthe operating frequency of the transmitting circuit was in the range of0.1MHz to5MHz, the maximum output power was up to10kW. Using the finite elementmethod and the method of least squares fitting, the transmitting circuit modelwas established. Trough the circuit simulation, the operating point oftransmitting circuit was determined and the reliability of the transmitting circuitwas improved.we designed an experiment setup of the transmitting system. The experimentsetup consists of a low noise receiver circuit, a data acquisition circuit and a PC.It can complete functions of receiver, data acquisition and signal processing. Inthe static experiment, results were consistent with simulation results. We usedthe transmitting system and experiment setup in dynamic wheel flaw detection,and results indicated that the transmitting system could effectively detect20mm long and2mm deep axial crack on the wheel tread. The EMAT transmittingsystem studied by this paper laid the foundation of the on-line flaw detectionsystem for train wheels.