GB1397065A - Defect detection - Google Patents

Abstract

1397065 Ultrasonic probes; ultrasonic inspection devices BRITISH STEEL CORP 9 June 1972 [18 March 1971] 7198/71 Headings H4J and H4D In coupling a moving strip or sheet 4 (Fig. 1) with an ultrasonic transducer arrangement 1, a member 8 movable relative to a housing 3 is resiliently urged into contact with the strip or sheet 4 and coupling liquid is fed through a nozzle 16 and into passageways 15, 14 to flood the region between the transducer arrangement 1 and strip or sheet 4. The housing 3 comprises a cylindrical outer easing 5. Screws 6 secure an annular support 7 to which in use a detector 2 is attached. Member 8 is annular, is slidably mounted within outer casing 5 and is resiliently urged by three adjustable springs 9 away from annular support 7. Member 8 has a cylindrical extension 11. Support 7 has a cylindrical extension 12. The two extensions 11 and 12 are joined by a flexible tube 13 to define an inner chamber for the transducer arrangement 1 and detector 2. In use, this inner chamber is filled with water or other liquid which surrounds the transducer arrangement 1 and provides the acoustic coupling. The liquid is pumped through the nozzle 16 and passes through an opening 17 via an outlet elbow 18. The liquid may be recirculated by the pump or may merely pass out of the elbow 18. The device may utilize two transducers 22 (Fig. 2) of radius 10 mm. and three transducers 23 of radius 6 mm. They may cover an area of width 25 mm., each being coupled to a separate amplifier, all amplifiers having the same gain. Transducers 23 produce a defect signal when covered by a defect whose greatest dimension is 3 mm. whereas the same signal will be produced by transducers 22 only for a defect whose greatest dimension is at least 5 mm. Thus the transducers 23 are more sensitive than transducers 22 and may be used to test the edge of a strip or sheet where small defects are important, e.g. if a strip is to be welded at the edge.