| 摘要 |
PURPOSE:To enable accurate discrimination of a surface and underskin defects, by a method wherein two kinds of ultrasonic waves different in the angle of refraction is made incident into a material to be inspected and ultrasonic echoes reflected on the same defect is detected to compare heights thereof. CONSTITUTION:Probes 10A and 10B differ in the angle of refraction from each other and the angles of refraction thereof 10A and 10B are set at about 40 deg. and 60 deg.. Then, the probes 10A and 10B perform an ultrasonic angled beam flaw detection turning about a round bar 14 conveyed straight. Defect echo level signals detected by this flaw detection are amplified with detectors 18A and 18B and inputted into an arithmetic unit 20, which then, performs a positioning of defect echo level signals inputted from a tracking circuit 22 and a difference DELTAEH between the defect echo levels EH1 and EH2 positioned is calculated therefrom to be compared with a preset value DELTAEH0. As a result of the comparison, when DELTAEH>DELTAEH0, a defect detected is a surface defect. When DELTAEH<DELTAEH0, it is identified as underskin defect and an identification signal is outputted.
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