| 摘要 |
PURPOSE:To detect a non-metallic inclusion in small steel securely on-line by adopting an attenuation method transmitting an ultrasonic focusing beam vertically from a probe to a steel sheet and fetching the bottom surface echo succeeding to the 2nd bottom surface echo received from the sheet. CONSTITUTION:A liquid tank 20 is filled with a liquid 22 and the probe 24 and the steel sheet W are dipped into the liquid 22. The sheet W is arranged vertically to a beam axis. An ultrasonic focusing beam 24a projected from the probe 24 to be used for both transmission and reception is propagated in the liquid 22 and partially reflected on the surface of the sheet W to obtain a surface echo S. On the other hand, the transmitted beam is reflected by the inclusion 16 or the bottom to obtain defective echos F1-Fn and the bottom surface echos B1- Bn. When said method is to be applied to the sheet W having especially thin thickness, the bottom surface echo attenuating method setting up a gate range 28 to the echo succeeding to the 2nd bottom echo B2-Bn is devised. Consequently, a small non-metallic inclusion in the steel can be securely detected on-line. |
