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Detection of small inclusions in thin steel sheets by magnetic flux leakage technique

 
: Yashan, A.; Becker, R.; Klein, A.

European Federation for Non-Destructive Testing -EFNDT-; Spanish Society for Non-Destructive Testing:
8th European Conference on Nondestructive Testing 2002. CD-ROM
Madrid, 2002
European Conference on Nondestructive Testing (ECNDT) <8, 2002, Barcelona>
Englisch
Konferenzbeitrag
Fraunhofer IZFP ()
flux leakage technique; MFL technique; cold rolled strip; magnetic field sensor

Abstract
One of the reasons for rejection of the products manufactured of the thin steel sheets are the steel inclusions. Therefore, the inclusions cleanliness is an important factor of steel quality and trade acceptance.
The comprehensive online detection of the defects and inclusions in the thin steel sheets can be realised by magnetic flux leakage technique (MFL technique) using a magnetisation system in combination with several hundreds of magnetic field sensors.
In this study, the detectability of the small size (0.2 mm) inclusions in the steel sheets with a thickness more than 0.5 mm was tested. The developed measurement arrangement is described.
The resolution capability of the used technique was investigated on the test specimen of thickness 0.8 mm. The drilled holes with a diameter of 0.2 mm with various depths were used as test defects. In order to model the detection of hidden (internal) inclusions, the magnetic field sensor was placed at the opposite side of the specimen to the surface with the drilled holes. An important point of the design optimisation was to increase the air gap between the inspected steel sheet and the sensor (sensor lift off).
As the present results shown, the drilled hole with a diameter of 0.2 mm and depth 0.2 mm at the back surface of the test specimen of thickness 0.8 mm can be detected with the sensor lift off 1.5 mm.

: http://publica.fraunhofer.de/dokumente/N-10059.html