Method for bend straightening

Abstract

Method for bend straightening in which a steel pipe having a bend is placed in a state where the steel pipe is convex upward, the steel pipe is pressed from above by a press unit at a target load value, whereby the steel pipe is straightened, the method including: (a) measuring a bottom-dead-center load value Pk when the press unit is at a bottom dead center in the pressing; (b) measuring an amount of change 46 in amount of bend between an amount of bend of the steel pipe before the pressing in step (a) and an amount of bend of the steel pipe after the pressing in the step (a); (c) repeating step (a) and step (b) a plurality of times to create a relational expression Pk=(Δδ); and (d) determining a target load value for next pressing from the relational expression Pk =(Δδ).

1 . A method for bend straightening in which a pipe body having a bend is placed in a state where the pipe body is convex upward, the pipe body is pressed from above by a press unit at a target load value, whereby the pipe body is straightened, the method comprising:
 measuring a bottom-dead-center load value when the press unit is at a bottom dead center in the pressing;   measuring an amount of change in amount of bend between an amount of bend of the pipe body before the pressing and an amount of bend of the pipe body after the pressing;   repeating measuring the bottom-dead-center load value and measuring the amount of change a plurality of times to create a relation between the bottom-dead-center load value and the amount of change in the amount of bend; and   determining a target load value for next pressing from the relation.   
     
     
         2 . The method for bend straightening according to  claim 1 , further comprising:
 measuring the bottom-dead-center load value when the press unit is at the bottom dead center in a case where the pressing is performed at the target load value determined in the step (d);   measuring an amount of change in amount of bend between an amount of bend of the pipe body before the pressing performed at the target load value and an amount of bend of the pipe body after the pressing performed at the target load value; and   updating the relation using the bottom-dead-center load value measured when the pressing is performed at the target load value and the amount of change in the amount of bend measured.   
     
     
         3 . The method for bend straightening according to  claim 1 , further comprising
 measuring a residual amount of bend of the pipe body after the pressing, wherein   when the target load value is determined, the target load value is determined from the relation and the residual amount of bend.   
     
     
         4 . The method for bend straightening according to  claim 3 , wherein when the residual amount is measured, after the pressing, the pipe body is rotated about an axis direction, a rotation amplitude value of the pipe body is measured, and from the rotation amplitude value, the residual amount of bend is measured. 
     
     
         5 . The method for bend straightening according to  claim 1 , wherein measuring the bottom-dead-center load value, measuring the amount of change, repeating measuring the bottom-dead-center load value and measuring the amount of change, and determining the target load value are repeated until an amount of bend of the pipe body after the pressing is equal to or less than a threshold value. 
     
     
         6 . The method for bend straightening according to  claim 1 , wherein the pipe body is a steel pipe.