EMAT/EC Composite Detection Technology And Application For Continuous Casting Slab With Defect

In recent years,with the development of continuous casting hot and hot rolling and direct rolling in continuous casting process,higher requirements of the quality of slab production have been put forward.At present,there are many methods of quality inspection of continuous casting billet,such as machine vision method using 2D and 3D optical imaging technology,eddy current detection method based on electromagnetic induction principle,electromagnetic ultrasonic method based on high frequency mechanical vibration in medium.But none of these methods are ideal.This paper takes the quality of continuous casting billet as the research object and makes a comprehensive use of eddy current in the detection of surface defects and the detection of electromagnetic defects.It proposes to study and analyze the surface defects and internal defects of the slab with the method of EMAT/ EC combined detection.What's more,the research results can lay the theoretical foundation for the continuous casting billet on-line quality inspection system development and industrial applications.At the beginning of this paper,the mechanism of EMAT and EC composite detection is studied.The magnetic field,eddy current field,secondary magnetic field,Lorentz force field and displacement field distribution are carried out by using the rectangular magnet,the spiral coil and the tested sample mathematical modeling and finite element analysis.The influence of excitation current and coil size on the magnetic field is analyzed to optimize the design of the composite detection probe and lay a solid foundation for the subsequent EMAT/EC composite detection.According to the principle of EC,we extra the real resistance and imaginary part inductance of the eddy current detection coil impedance as characteristic signal.By analyzing the variation of real resistance and imaginary inductance,defects of the continuous casting slab surface could be detect.In view of the principle of EMAT detection on the surface defects of the slab,we extract the echo time and the echo amplitude as the signal characteristics to realize the accurate positioning of the lower surface defects.In the EMAT feature signal extraction,we first preprocess the echo signal by wavelet denoising and Hibert transform extraction envelope algorithm,and then use the expectation maximization algorithm to estimate the arrival time of EMAT echo.After we obtained the arrival time of echo signal,the interpolation function isused to obtain the echo amplitude at the corresponding echo time point.In this paper,we focus on the eddy current characteristic signal and the electromagnetic ultrasonic characteristic signal by BP neural network,and finally through the defect inversion to realize the detection of the slab defect in this area.In view of the surface defects of the slab,we use the coil impedance distribution variation,the surface of the slab for amplitude and phase imaging,through 3-D imaging technology to achieve real time monitoring of slab surface defects.For the defect of the lower surface of the slab,the thickness of the defect estimated by parameters is taken as the image brightness information to 3-D imaging by EMAT,and finally on line real time monitoring of the upper and lower surfaces of the slab is realized.