Technology of On-line Surface Inspection for Hot-rolled Steel Strips and Its Industrial Application

Surface of hot-rolled steel strips is different from surface of cold-rolled steel strips, because it has high-temperature and intense radiation.Moreover, there are waters, scales, uneven illumination on hot-rolled steel strips.Line-scan CCD cameras are introduced to capture images, and green linear lasers are applied for illumination.Radiation of hot-rolled steel strips is filtered by narrow-band filter lens, and contrast of defects is improved.According to the characteristics of hot-rolled steel strips, a new algorithm of defect detection and classification is developed.A step of defect detection for four different types of detects is added to remove false defects caused by waters, scales, etc., and false detection is decreased while detection rate of defects is not worsen.Results of industrial application show that the technology can be applied to on-line inspection, and detection rate of defects is higher than 95% while classification rate of defects is higher than 85%.