| 摘要 |
PURPOSE:To enable the high-sensitive detection of an internal defect of an object to be inspected, by a method wherein the object to be inspected is AC-excited, and is charged with a pulse current at an arbitrary point of time of a period during which the ultrasonic current attains a peak value or in the proximity of the peak value. CONSTITUTION:A magnet 1, consisting of U-shaped core 1a and a coil 1b coiled around the core, is placed so that the core 1a faces a passage band of a SB, and a magnetic flux, emanating from a magnetic pole surface 2 of the magnet 1 through the excitation of the coil 1b with an AC current of about 100Hz, enters into a magnetic pole surface 3. An AC magnetic field, directing perpendicualrly to the movement direction of the billet SB, is produced on the upper surface of the billet SB. Probes 10 and 20 are located above the billet SB and between the magnetic pole surfaces 2 and 3, and flat square cylindrical transmitting and receiving coils 12 and 20 are housed in a case 11 of the probe 10. The transmiting coil 12 for generating ultrasonic waves is connected to a pulse oscillator via a connector 15, and the receiving coil 13 is joined to an amplifier via a connector 16. |
