Method of and apparatus for eliminating crossbow in metal strip

Abstract

Crossbow in metal strip in a strip processing line is eliminated immediately upstream of a strip processing device by measuring the crossbow and controlling response to the measured value penetration depth of a correcting roller into strip while the latter is supported by a pair of support rolls. The device is provided immediately upstream of the processing unit.

We claim:  
     
         1 . A method of eliminating crossbow in metal strip in a strip processing, comprising the steps of: 
 (a) passing metal strip along said strip processing line through a strip processing device;    (b) detecting crossbow in said strip; and    (c) immediately upstream of said strip processing device, pressing a correcting roller against said strip between two support rolls to a variable depth determined by a detected degree of crossbow    
     
     
         2 . The method defined in  claim 1  wherein respective correcting rollers are provided between respective support rolls on opposite sides of said strip for displacement of respective variable depths for eliminating crossbow in opposite directions in said strip directly before said strip enters the strip processing device.  
     
     
         3 . The method defined in  claim 1  wherein said cross bow is eliminated downstream from a strip processing device having a negative effect on strip planarity.  
     
     
         4 . The method defined in  claim 1  wherein in step (b) the crossbow of the strip is measured and a measured value of the crossbow is compared with a setpoint value to generate an error signal determining the depth to which said correcting roller is displaced against said strip between said support roll thereby eliminating the crossbow in said strip.  
     
     
         5 . The method defined in  claim 1 , further comprising the step of minimizing an effect of waviness in said strip in measurement of crossbow thereof by integrating measured values of said crossbow over a predetermined time period.  
     
     
         6 . The method defined in  claim 1 , further comprising the step of minimizing an effect of waviness in said strip in measurement of crossbow thereof by forming a sliding mean value filtering out the effect of waviness.  
     
     
         7 . The method defined in  claim 1 , further comprising the step of filtering out an effect of strip camber on measurement of the crossbow during a computer correction of an inclined position of the measured crossbow across the strip width.  
     
     
         8 . The method defined in  claim 1  wherein said strip processing line includes a strip leveler and another strip processing device traversed by said strip prior to detection of crossbow and upstream of the correcting roller and the support roll.  
     
     
         9 . A strip processing line comprising at least one strip processing device traversed by metal strip susceptible to crossbow upstream of said strip processing device; 
 a sensor for detecting crossbow in said strip upstream of said strip processing device;    a pair of support rolls engaging said strip at one side and a correcting roller on an opposite side of said strip between said support rolls and adapted to be pressed to a variable depth against said strip between said support roll and determined by a detected degree of crossbow to at least partially deform said strip plastically and eliminate the crossbow immediately before the strip enters said strip processing device.    
     
     
         10 . The apparatus defined in  claim 9  wherein said sensor generates a measured value signal representing the crossbow in said strip, said apparatus further comprising a circuit for comparing said measured value with a setpoint value and generating an error signal for controlling depth of penetration of said correcting roller between said support roll.  
     
     
         11 . The method defined in  claim 10 , further comprising another pair of support rolls on said opposite side of said strip and a correcting roller on said one side of said strip capable of being pressed to a variable depth against said strip whereby crossbow in said strip in opposite directions is eliminated before said strip enters said strip processing device.