Until now, tension levellers have been the most commonly used means to eliminate shape defects of strips. Their levelling effect is achieved by combining strip bending and longitudinal strip tension. High strip tension is required to set the necessary wrap angle of the strip deflected around the levelling rolls and to support plastification of the strip for achieving the desired levelling effect.

  Fig. 1                                                                Fig. 2 

The new form-fit-bending machine developed by BFI avoids the disadvantages associated with tension levelling. Its rolls are arranged in such a manner that the strip is forced into shape around the bending rolls (Fig. 1). This principle makes it possible to perform the bending process at markedly reduced tension rates.

Form-fit-bending machines are installed in the bright annealing line at the Krefeld plant of ThyssenKrupp Nirosta (Fig. 2) and in the continuous pickling line for medium sized strip at ThyssenKrupp Hoesch Hohenlimburg (Fig. 3). These lines process steels featuring tensile strengths of up to 1,600 MPa at speeds up to 300 m/min. Strip thickness is between 0.5 and 6.0 mm, strip width between 500 and 1,300 mm.

The new technology of form-fit-bending has considerable advantages in terms of lengthbow and crossbow correction of strips as well as elimination of strip flatness defects.

Based on the technique of reverse bending, bow shaped faults can be objectively influenced by asymmetrical adjustment of the bending rolls arranged in the two roll cartridges. In addition the variably adjustable positions of the form-fit-bending cartridges enable the adjustment of the desired elongation value over the complete strip length.

            

 Fig. 3