Method and apparatus for detecting flaws in strip

摘要

A flaw detecting method and apparatus for continuously testing a strip (1) that is continuously conveyed through a liquid (6) includes features for reducing air bubble generation in a liquid. The apparatus includes a liquid, conveying rolls (7-10) for passage of the strip through the liquid, and ultrasonic testing probes (20) arranged in the liquid for testing the strip. A conveying roll (8 or 9) in contact with the liquid is fully immersed. Air bubble generation is inhibited to improve the testing reliability by at least one of: (a) shielding (16) the liquid dropping from the portion of the strip leaving the liquid; (b) reducing the dropping force of the liquid onto the liquid surface (6a) by inclining the strip; (c) installing the fully immersed conveying roll (8 or 9) at a depth of at least 5 mm in the liquid; and (d) using a carrying speed of less than about 200 m/min. Upon manufacturing steel strips, testing is carried out at the stage of the hot-rolled steel sheet, or, preferably, in the pickling equipment.