Surface Defects Inspection For Continuous Casting Slab By Pulsed Eddy Current

Until now, it is still one of the obstacles need to overcome for effective and of high quality development of metallurgical industry technique that noncontact online nondestructive surface defects detection of continuous casting slab. Pulsed eddy current(PEC),which has been received much attention by its potential in noncontact quantitative determination for surface and sub-surface of the measured body, is a developing nondestructive detection technique in recent years. However, the product applied to online surface defects inspection in the high temperature of casting slab haven't successfully developed domestic and overseas by using PEC alone. Therefore, in this paper, works are carried out as follows to aim at reaches on surface defects detection of continuous casting slab.①Develop a PEC testing system related to lab study. By analyzing theory of PEC technique applying to continuous casting slab, the influence factors of the PEC testing system is brought up, an experimental equipment for the PEC testing system is developed, which includes a computer, a signal generating circuit, a sensors, a measured sample, a drive generator, a signal modulate circuit, an oscilloscope and so on.②Researches on extraction method of PEC signal features. First, using signal equalization method makes the signal stable; then smooth the signal by average filter, and evaluate the application to surface defects detection of continuous casting slab by comparing different features of smoothing signal. The time-to-zero, time-to-peak, peak-to peak value, peak value and difference of peaks are use to evaluate response condition of detecting signal, which effectively avoids signal distortion caused by local temperature difference, and the volume information of defects are reasonably evaluated.③Optimization design of PEC testing sensor. By analyzing influencing factors of detection probe, combining with physical experiment the waveform and feature value of signals are comprehensive evaluated, and the structural parameters of a probe can be optimized, then the probe become more suitable for continuous casting slab. The optimized probe used in this paper is: double deck and synchronous winding way, inside diameter is 5.0mm, outside diameter is 5.8mm, height is 25mm, and probe wounds 200 turns. PC40 ferrite is put in the probe as a magnetic core; excitation frequency is 29KHZ. ④Primary surface defects detection of slab. By analyzing influence of complex environment of continuous casting slab to signal, the influence degree of environment factors to signal are evaluated, anti-interference methods aiming to environment factors are brought forth initially. combining with response of signal to feature value , surface defects can be initially distinguish in continuous casting slab.