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 by setting the angle between the incident direction of the incident light having a prescribed plane of polarization from a laternal side and the normal on the surface of a specimen at 15 deg.-55 deg. and detecting the prescribed polarization component of the specular reflected 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 the external light having a linear polarization characteristic 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 deg.-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 26 through a rotator 24 for the plane of polarization. On the other hand, a photodetection camera 30 which is disposed in the position on the opposite side of the slab traveling line equal to the angle theta1 between the normal on the surface of the slab 20 and the detection direction of the specular reflected light and has a polarization filter 28 detects the prescribed polarization component of the specular reflected light, and a signal processing circuit 32 outputs a defect signal.