| 摘要 |
PURPOSE:To discriminate exactly existence of a flaw without being influenced by whether an adhesion density of a magnetic powder is high or low, by dividing the surface of a part of a steel into a lot of small areas, measuring a luminance value of each area, and using a luminance value of the vicinity of a boundary of groups of a low luminance value and a high luminance value, as a reference value. CONSTITUTION:When a steel 5 is fed to a prescribed position of a flaw detecting device 3, ultraviolet rays are irradiated from a black light 8, light of a fluorescent magnetic powder adhering onto the surface of the steel 5 is made incident to a TV camera 10, and a signal processing circuit 11 divides a front part of the camera 10 of a detected picture into a lot of small areas and measures a luminance of each area. Its luminance value passes through an A/D converter 12 and is stored in a storing circuit 13. A counter 14 counts separately the number of storage values corresponding to a luminance value set in advance, and an SH level determining circuit 15 determines a luminance value of the vicinity of a boundary value of groups of a low luminance value and a high luminance value, as a reference value, compares the reference value and the storage value by a comparing circuit 16, and decides a flaw. Accordingly, existence of a flaw is decided exactly irrespective of whether an adhesion density of a magnetic powder is high or low.
|
