| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface crack detection method and a surface crack detection device which detect a surface crack of a mandrel bar used in a mandrel mill on a circulation conveyance line accurately without erroneous detection.SOLUTION: A stroboscopic light source 7 irradiates a mandrel bar 3, which is being conveyed on a circulation conveyance line, with stroboscopic light for illumination at a plurality of times. Reflected stroboscopic light, which the stroboscopic light for illumination reflects on a surface crack, is received by a camera 8, and a slit laser light source 15 irradiates a field of view of the camera with linear slit laser light vertically to a traveling direction of the mandrel bar. Reflected laser light, which the slit laser light reflects on the surface of the mandrel bar, is received by the camera and an image is captured. The image is transmitted to an image processing device to analyze the image, and a diameter of the mandrel bar is calculated by image analysis of the reflected laser light in the image, and then presence/absence of the surface crack is determined by image analysis of the reflected stroboscopic light within a range of the diameter.SELECTED DRAWING: Figure 1 |
