Experimental study on quantitative surface defect depth detection based on laser scanning technology in continuous casting

Abstract

In this paper, a scanning laser system based on an array couple charged detector (CCD) has been developed to detect and measure quantitatively the morphology and depth of defects on continuously cast billet (CC billet) surface at high temperatures. The technique, based on a linear light scattering method, employs a low power He–Ne laser and a conventional CCD probe and enables a narrow line array laser beam to be projected on the test surface across the width direction on the CC billet surface. In the relative scanning direction between the test surface and the CCD probe, the one-dimensional linear surface image acquired by the CCD sensor at a given shutter time, which exhibits the curvature change of the laser scanning line, can be used to determine the distance morphology according to triangulation principles. Combining with casting speed, a linear laser beam image can be spliced into a two-dimensional surface image that constructs the billet surface profile and detects surface defect shape and depth. Furthermore, it can reconstruct a three-dimensional morphology for the billet surface defects in the high temperature condition. Proof of concept experiments have been performed through online measurement of different size defects, and quality tracking on the hot CC billet surface has been implemented.