METHOD FOR DETECTING FLAW ON SURFACE OF METALLIC OBJECT

摘要

PURPOSE:To enable the detection of the defect on a surface with high S/N ratio, by setting the angle between the incident direction of the irradiated light from the lateral side and the normal of the surface of a specimen at 15-55 deg. and detecting the scattering light of <20 deg. the angle to the incident direction of the irradiated light. CONSTITUTION:A laser light source 22 disposed in the diagonal direction intersecting orthogonally with the traveling direction of a continuous casting slab 20 on the lateral side of the traveling line of said slab irradiates external light in such a way that the angle theta1 between the normal on the surface of the slab 20 and the incident direction of the irradiated light attains 15-55 deg.. The laser light 22a is expanded to a belt shape up to the necessary visual field on the slab 20 by a cylindrical lens 24. On the other hand, a photodetection camera 26 disposed on the same lateral side as the light source 22 of the slab traveling line detects the scattered and reflected light of <20 deg. angle theta2 to the incident angle of the irradiated light and a signal processing circuit 28 outputs a defect signal. The S/N ratio of the defect signal is thus made >=2.0 and the defect detection with high accuracy is made possible.