To provide a method capable of detecting the existence, kind, shape and direction of flaw or defect on the surface of a metal part or a metal product except a rolling trace, using one detection device.
Optical fiber bundles 3, 5 are arranged concentrically around spot light of a laser beam, and reflected scattered light is allowed to enter the inside optical fiber bundle 3, and diffracted light is allowed to enter the outside optical fiber bundle 5. Each optical fiber bundle 3, 5 is divided in numbers in the circumferential direction respectively, and photodetectors 8a, 8b...8l, 9a, 9b...9l are installed in each block, and light-receiving quantities are measured, and the mean value is determined from the total amount thereof by operation means 11a, 11b. A determination means 12 detects the existence and the kind of flaw in each block, by comparing the light receiving quantity in each block with the mean value, and the shape and the direction of the flaw from a light-receiving pattern in each block. The photodetector for detecting the rolling trace is determined, beforehand from a spot having no flaw, and the data of the photodetector is set excluded.
IMAIDE MASAAKI
ITANI MASARU
SHIMAZUTSU YUZO
NIPPON SYSTEM DESIGN
SHINEI IND
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