| Continuous casting technology plays an important role in the field of metallurgical technology,which has a significant impact on the production of iron and steel.Whether there is a defect in the continuous casting billet is also one of the important conditions to determine the quality of the billet.The defect detection of the billet is an urgent problem to be solved due to its bad environment.In this paper,the electromagnetic ultrasonic transverse wave is used to detect the continuous casting billet,mainly to explore the location and quantity of the internal defects of the continuous casting billet,and to image the cross-section defects,so as to provide reference data for the process researchers to improve the cooling process system,so as to improve the quality of the billet and save energy consumption.The test object of this paper is high temperature billet at the end of continuous casting,the temperature is about 800 ?.In the simulation experiment,30 mm * 200 mm Q235 small billet sample is set as the tested object.The finite element simulation model of the electromagnetic ultrasonic transducer is established by using the finite element simulation software COMSOL multiphysics,which is composed of two parallel spiral coils on both sides of the cylindrical permanent magnet.A kind of electromagnetic ultrasonic transducer different from the general structure is given.The simulation results show that the smaller the diameter of the cylindrical permanent magnet is,the more uniform the magnetic field intensity is.According to this phenomenon,the size parameters of the cylindrical permanent magnet are optimized.The size and exciting signal frequency of the spiral coils on both sides of the cylindrical permanent magnet are given.The eddy current intensity of the sensor on the surface of the measured body reaches the eddy current intensity of the flat coil under the same excitation signal.The simulation results show that when the bias magnetic field is provided by the permanent magnet and the high frequency current is applied to the coil,the ultrasonic wave is excited in the measured body.The electromagnetic ultrasonic transducer with this structure can successfully excite and receive the electromagnetic ultrasonic shear wave on the surface of the high temperature continuous casting billet.The influence of the young's modulus change in the continuous casting billet on the propagation speed of ultrasonic wave at different time and position in the tested billet and at high temperature was calculated.This paper studies thefeasibility of electromagnetic ultrasonic transverse wave in the detection of high temperature continuous casting billet.Two kinds of defects,i.e.cracks and bubbles,are set in the billet.The propagation of electromagnetic ultrasonic wave and the generation of image are calculated when the cracks are 5mm wide * 1mm high and 1mm wide * 1mm high,the bubbles are 2mm radius and 5mm radius in different positions of the billet under test.The solution of the positive problem of electromagnetic ultrasonic layer analysis imaging is completed.Using matla software and data generated from electromagnetic ultrasonic tomographic forward problem in COMSOL,image inversion calculation is carried out,and binary logic back projection algorithm is used to generate the image of the measured billet cross section.The results show that the new structure of the electromagnetic ultrasonic transducer can excite and receive the electromagnetic ultrasonic transverse wave on the surface of the high temperature billet with the surface temperature of 800?.The simulated electromagnetic ultrasonic tomographic imaging system can detect the location,number and size of the cracks with the width or thickness greater than 1mm in the cross section of 30 mm * 200 mm billet,and generate the internal cross section of the continuous casting billet. |
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