1. Field of the Invention
The present invention relates to a method and an apparatus for the non-destructive testing for interior flaws of still well deformable steel by ultrasound waves emitted by an ultrasound probe at a roll used for rolling the steel.
2. Description of the Prior Art
Non-destructive testing by ultrasound has been known for a long time.
German patent No. 3,204,797, for example, describes a method in which a finished work piece, such as a pipe, is subjected to ultrasound waves, the ultrasound energy being transmitted from the probe to the work piece along a path passing through an aqueous coupling medium.
The detection of interior flaws in the work piece is accomplished in the so-called impulse-echo method, that is, the ultrasound waves emitted from the probe are reflected, on the one hand, from the surface and, on the other hand, from the back wall of the work piece after the waves have passed therethough. This produces two more or less sharp impulses with a certain amplitude in the test indicator. If the ultrasound wave impinges on a flaw in the work piece, such as a crack, an occlusion, etc., it is also reflected at this location, causing a third impulse, i.e. a flaw impulse, to be generated. Since the ultrasound energy passes back and forth several times between the location of the flaw and the probe, the cited German patent proposes a method for masking such additional impulses, which are of no interest, for instance impulses which result from possible impurities in the coupling medium. The test takes place on the finished work piece by the use of a liquid coupling medium which may contain foreign bodies which may disturb the testing.