Experimental study of surface defects in continuous casting using developed laser scanning system

Abstract

Various methods of detecting surface defects are being used in automated industrial manufacturing environments. This work presents the design and development of a laser charged couple device (CCD) displacement scanning system. The surface defect detection method using a laser CCD displacement sensor is derived from an idea in which surface defects such as cracks, inclusions and holes of three‐dimensional morphology characteristics are compared to normal surface especially in continuous casting slabs. Some novel research methods have been applied to develop the surface defect detection system used: first, getting a one‐dimensional distance matrix along transverse direction and a two‐dimensional matrix combining with a certain moving speed through the laser CCD displacement sensor; second, obtaining the slab surface profile and mapping to a greyscale image and finally, obtaining the surface defect regions by an image processing and searching algorithm and quantitatively detecting slab surface defect shape and depth. The research results in the lab trials have shown that the methodology proposed is effective to detect two‐dimensional defect size and reconstruct a three‐dimensional surface defect shape. At the same time, it is also able to accurately locate and identify surface defects and realise automatic surface defect non‐destructive detection online, and provides a theoretical base and technology idea for further studying surface defects online inspection for hot continuous casting slab.

Keywords:

• Continuous casting
• Surface defect inspection
• Laser scanning
• Image processing

The authors wish to express their appreciation to the National Natural Science Foundation and Shanghai Baosteel joint project support (grant no. 5097415) and Chongqing Natural Science Foundation (grant no. CSTC, 2008BB0162). The authors also thank Engineer Limang and Professor Liang Xiangqian from Chongqing University for their assistance in taking some of the measurements.