| 摘要 |
PURPOSE:To inspect a surface flaw, by a method wherein 90 deg. is divided to provide a probe group allowing ultrasonic beam to be incident at an angle equal to more than a critical angle and the same probe group separated by a predetermined dimension in an axial direction on a plane parallel to the axis of a material so that a flaw detection point becomes one and the coincidence of the flaw signals of the probes of the same angle is detected. CONSTITUTION:A columnar material moves while rotates from the right to the left at a high speed. A rear probe group 24 of probes 16, 18, 20, 22 is placed so as to be separated from a front probe group 14 of probes 6, 8, 10, 12 by a distance L. The probe groups are respectively recorded on recorders 72-78 through transmitter-receivers 25-38, gate circuits 40-50, AND circuits 56-62 and switch circuits 64-70 and, when there is an echo signal wherein even one point exceeds a predetermined level, said signal is processed by a signal processing circuit 80. Since 90 deg. is divided to arrange the probes and beam is incident at a critical angle or more, a flaw in any direction can be detected with high sensitivity and, only when the flaw signals of the same places of two probes in the same direction coincide with each other, a flaw is detected and, since the columnar material rotates at a high speed and air bubbles or contaminants are scattered, erroneous detection is reduced. |
