Method and device for descaling a scaled metal strip

Abstract

The invention relates to a method for descaling a scaled metal strip, in particular a hot-rolled metal strip with a thickness of more than 1 mm, for example 1.2 mm to 16 mm. The strip is guided around at least two straightening rollers which are arranged one behind the other in the strip running direction and undergoes an alternating bending in the process. At least one of the straightening rollers can be positioned transversely to the strip running direction. The method is characterized in that the strip is unstressed or is under a low tensile stress of less than 10% of the yield strength of the strip on the inlet side upstream of the straightening rollers, and the diameter of the straightening rollers, the spacing between same in the strip running direction, and the positioning of the rollers transverse to the strip running direction are selected while taking into consideration the strip properties such that expansions and compressions of at least 2%, preferably at least 3%, are produced in the course of a first plastic bending process and a second plastic bending process on the strip upper face and on the strip lower face for the purpose of descaling.

1 . A method of descaling metal strip, in particular a hot-rolled metal strip having a thickness of more than 1 mm, the method comprising the steps of:
 guiding the strip upstream and downstream straightening rolls arranged one downstream of the other in the travel direction of the strip such that the strip undergoes an alternate bending, at least one of the straightening rolls being movable transversely to the travel direction of the strip;   maintaining the strip tension-free upstream of the straightening rolls at the upstream end or at a low tensile stress of less than 10% of the yield strength of the strip; and   using straightening rolls of such a diameter and spacing in the travel direction of the strip as well and positioning the straightening rolls transversely to the travel direction of the strip under consideration of the strip properties such that in the course of a first plastic bending at the upstream straightening roll and of a second plastic bending on the downstream straightening roll, elongations and compressions of at least 2% are generated for descaling on the upper face and the lower face of the strip.   
     
     
         2 . The method as claimed in  claim 1 , further comprising the step of:
 providing an idler roll upstream of the upstream straightening roll;   providing a transversely positionable idler roll downstream of the downstream straightening roll;   transversely positioning at least one of the idler rolls and spacing the straightening rolls and idler rolls in the travel direction such that in the course of the plastic bending, elongations and compressions of at least 2% are generated on the upper face and the lower face of the strip.   
     
     
         3 . The method as claimed in  claim 2 , further comprising:
 selecting the spacing of the straightening rolls and of the idler rolls and the positioning of the straightening rolls and the idler rolls such that in its tension-free condition on the straightening rolls, the strip can adopt a maximum circle diameter that corresponds to a maximum of three times the straightening roll diameter.   
     
     
         4 . The method as claimed  claim 1 , wherein the bending radii are the same or substantially the same in the course of the first plastic bending and of the second plastic bending. 
     
     
         5 . The method as claimed in  claim 1 , further comprising the step of:
 generating a strip tension at the downstream end that exceeds the strip tension at the upstream end at least by the extent of deformation losses.   
     
     
         6 . The method as claimed in  claim 2 , further comprising the step of:
 setting the spacing between the roll surfaces of two immediately adjacent straightening rolls or idler rolls to be always greater than the strip thickness.   
     
     
         7 . The method as claimed in  claim 1 , further comprising the step of:
 providing a positionable bending roll downstream of the last straightening roll so as to correct any residual curvature.   
     
     
         8 . The method as claimed in  claim 1 , wherein the straightening rolls have a diameter that is less than fifty times the smallest band thickness. 
     
     
         9 . The method as claimed in  claim 1 , further comprising the step of:
 subjecting the strip to a tensile stress of less than 25 MPa upstream of the straightening rolls.   
     
     
         10 . The method as claimed in  claim 1 , further comprising the step of:
 aspirating or flushing away scale broken up on the straightening rolls.   
     
     
         11 . The method as claimed in  claim 1 , further comprising the step of:
 bracing each of the straightening rolls the strip is guided around by at least two respective backup rolls.   
     
     
         12 . An apparatus for descaling a hot-rolled metal strip having a thickness of more than 1 mm, the apparatus comprising:
 at least one upstream straightening roll;   a downstream straightening roll downstream thereof;   an idler roll upstream of the downstream straightening roll;   an idler roll downstream of the downstream straightening roll,   drive means for maintaining the strip tension-free at the upstream end upstream of the straightening rolls or at a low tensile stress of less than 10% of the yield strength of the strip, the diameter of the straightening rolls and the spacing thereof in the travel direction of the strip as well as the positioning thereof transversely to the travel direction of the strip being such that, under consideration of the strip properties, in the course of a first plastic bending and of a second plastic bending on the upper face and the lower face of the strip, elongations and compressions of at least 2% are generated.   
     
     
         13 . The apparatus as claimed in  claim 12 , wherein the idler rolls have a larger diameter than the straightening rolls. 
     
     
         14 . The apparatus as claimed in  claim 12 , further comprising:
 respective upstream and downstream pairs of backup rolls supporting the straightening rolls.   
     
     
         15 . The apparatus as claimed in  claim 14 , wherein a ratio between the backup roll diameter and the straightening roll diameter amounts to a maximum of 1.5. 
     
     
         16 . The apparatus as claimed in  claim 12 , wherein the idler rolls have a diameter of 150 mm to 600 mm. 
     
     
         17 . The apparatus as claimed in  claim 12 , further comprising:
 a positionable bending roll downstream of the last straightening roll and capable of effecting a correction of any residual curvature.   
     
     
         18 . The apparatus as claimed in  claim 12 , further comprising;
 at least one supply coil and one finish coil and respective drive units upstream and downstream of the straightening rolls at the upstream end and at the downstream end.   
     
     
         19 . The apparatus as claimed in  claim 12 , further comprising:
 respective upstream and downstream straightening roll pairs the straightening rolls of the upstream straightening roll pair having a different diameter from that of the straightening rolls of the downstream straightening roll pair, at least one of the straightening roll pairs being positionable.