| 摘要 |
PURPOSE:To detect a true defect of an external surface deformed metallic material with high sensitivity by placing plural detecting coils at the same gap as the external surface of a metallic material to be inspected, and also, by inclining them in the longitudinal direction of the metallic material to be inspected. CONSTITUTION:In case when a metallic material to be inspected is, for instance, a hexagonal steel bar 1, hexagonal annular coils 2A, 2B are placed in an inclined state in the longitudinal direction. As for the detecting coils 2A, 2B, its ground position is invariable, and the steel bar 1 is moved by a carrying roll group being a moving means. At the time of detecting a flow, in a signal processor 3, a short flaw is detected by a level discrimination by which a level exceeding some level is regarded as a defect, based on a difference of the impedance of the detecting coils 2A, 2B. A long flaw is detected by detecting a difference of the impedance of the oil to all keys and executing a level discrimination, while catching a variation of a signal of the detecting coil 2A.
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