METHOD FOR DETECTING FLAW ON SURFACE OF METALLIC OBJECT

摘要

PURPOSE:To eanble the detection of the flaw on a surface with high S/N ratio and with good accuracy, by setting the angle between the incident angle of the irradiated light in the traveling direction of a specimen or from behind the same and the surface of the specimen at 35-75 deg.. CONSTITUTION:A laser light source 22 disposed forward in the traveling direction of a continuous casting slab 20 above the traveling line thereof irradiates external light in such a way that the angle theta1 between the surface of the slab 20 and the incident direction of the irradiated light attains 35-75 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 side opposite from the slab traveling line where the angle between the surface of the slab 20 and the reflected and photodetected direction 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 defect signal is thus made >=2.0 and the defect detection with high accuracy is made possible.