A surface inspection system for hot continuously cast slabs has been developed. The system was designed so as to automatically detect harmful longitudinal cracks, with a width over 0.5 mm and a length over 50 mm, discriminating them from longitudinal dents. The principle of crack detection is based on the fact that a shadow is produced only at a crack by an appropriate lighting condition. Longitudinal cracks are automatically recognized, using an image processing technique, from the image of slab surface obtained by a line scan camera under the lighting condition.
Prototype equipment was manufactured and provided to experiments in order to confirm the performance of the system. On-line experiments showed good results under the good surface condition, namely, the system could inspect harmful longitudinal cracks on the slab surface travelling at a speed of 60 m/min in a real-time manner.
Based on these experimental results, the on-line equipment inspecting longitudinal cracks is now planned to be installed in Fukuyama Works of NKK.
