Detection of scratch defects for wire rod in steelmaking process

This paper presents an approach for the surface inspection of steel product. The research aims to detect surface defect of a wire rod. Scratch defect is caused by many reasons such as poor quality of raw material or malfunction of rolling process. The defects are very difficult to detect accurately due to the scale-covered background and uneven illumination. The inspection system is based on vision technology. Image processing algorithms are applied for detecting scratch defects of wire rod. The detection algorithm is mainly divided into three steps. First, wavelet transform is used to obtain the approximation subimage at resolution level one. Then, line segment detection method is applied to detect scratch defects from the images. But the complex backgrounds in images of wire rods inevitably result in false positive and false negative defects. Therefore, additional post-processing methods are applied based on detection results. Compared with previous methods, the proposed method provides the possibility to obtain better results on surface scratch detection.