The surface of the roll is tested before use with rotating eddy current sensors. Cracks with a depth more than 0.2 mm have to be detected. To repair these cracks, the whole surface has to be grinded until no indications of cracks are detectable. Small areas of cracks can be repaired by moulding.

The testing of the outer shell of the roll for internal flaws will be done by ultrasonic. With a sensitivity of about 1 mm flat bottom whole single indications as well as areas with multiple indication were registered. If these regions grow above a limited area, the roll cannot be used any more and has to be repaired if possible.

The experience from the manually testing show, that to find out roll damages in a stage as early as possible it is necessary to test the roll surface as well as the outer shell for internal flaws. Due to these tests damages of roll stands and rolls caused by breaking of backup rolls had been reduced to a great extend since the beginning of manually testing.

This positive results from the manually testing were used for the construction of a fully automatically testing device for work- and backup rolls integrated in a grinding stand. The work rolls are tested within the different grinding stages for surface cracks only by eddy current, the backup rolls after grinding with ultrasonic and eddy current. As result the defects are indicated within a map of the roll surface where the depth of the ultrasonic indications is shown within the axial and circumferential section of the outer shell. The ultrasonic flaws are additionally sorted in critical and no critical flaws. The results will be discussed.