| 摘要 |
PURPOSE:To increase the S/N ratio of a defect signal and to make the remedy for heat resistance of a light projector and a photodetector easy, by setting the angle between the incident direction of the irradiated light from the lateral side of a traveling line for a specimen and the normal of the surface of the specimen at 15-55 deg.. 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 in the position on the lateral side opposite from the slab traveling line where the angle between the normal on the surface of the slab 20 and the photodetection direction of the reflected light is equal to theta1 detects the specular reflected light, and a signal processing circuit 28 outputs a defect signal. The S/N ratio of the detect signal is thus made >=2.0 and the distance between the camera 26 and the slab 20 is taken large, whereby the remedy for heat resistance is made easy. |
