DOI: 10.14489/td.2015.04.pp.053-055

D'jakov P.A., Durnov F.Yu.
METHOD OF AUTOMATED ULTRASONIC INSPECTION OF STEEL SHEET WITH TRACES OF ABRASIVE MACHINING ON THE SURFACE
(pp. 53-55)

Abstract. The article deals with the problems of increasing the noise immunity of ultrasonic inspection using electromagnetic acoustic transducers (EMAT). The surface defects of rolls such as seam, prints, etc. are often detected in the production of sheet metal. Rolled surface, in this case, is treated with rough abrasive wheels. The cause of the noise in ultrasonic testing are metal particles remaining on the sheets after abrasive cleaning. These particles are difficult to remove from the surface of the sheets. Metal particles, being in the constant magnetic field of the EMAT, re-emit electromagnetic waves of self-resonant frequency. Since the resonant frequencies of the particles are being in the range of frequencies used in the inspection of sheet metal, these electromagnetic waves are fixed by EMAT. As a result, testing results contain noise that can block the signals from the real defects. The authors propose to suppress mechanical vibrations of the particles in a liquid layer. A layer of liquid sharply reduces the quality factor of mechanical vibrations, that leads to a considerable reduction of the oscillation amplitude. The signals of these oscillations do not interfere the carrying out of control on the required sensitivity and they are not fixed by an ultrasonic system.

Keywords: electromagnetic-acoustic probe, abrasive machining, ultrasonic inspection, noise cancellation, steel sheet.