Method for bending pipes

Abstract

Method for bending pipes (T) or similar elongated elements in a pipe bending machine includes a seat for positioning the pipe (T) to be bent, a forming roller (R) having a predetermined radius (RR) around which the pipe is bent and appropriated devices for seizing and moving the pipe.

1 . Method for bending pipes or similar elongated elements in a pipe bending machine said machine comprising a seat for positioning the pipe to be bent, a forming roller of predetermined radius around which the pipe is bent and appropriated means for seizing and moving the pipe, comprising the following steps:
 a) providing a test pipe having the same characteristics as the actual pipe to be bent in the seat,   b) performing on the test pipe, a pair of bendings setting the predetermined theoretical angles (AT 1 , AT 2 ), on the machine and measuring the resulting bending angles (AR 1 , AR 2 ),   c) calculating starting from the set theoretical and measured actual bending values on the test pipe a proportional springback (RP) defined as the value of the angle to be added to each degree of theoretical angle (AT) set to obtain the correct bending angle of the pipe to be set in the machine (API),   d) calculating starting from the calculated proportional springback and from the theoretical and measured actual bending values on the test pipe the fixed springback (RF) defined as the value of the angle to be added to the theoretical bending degrees to obtain the correct bending angle of the pipe to be set in the machine (API),   e) calculating the correct bending angle of the pipe to be set in the machine (API) adding to the theoretical bending angle (AT) the value of the fixed springback (RF) and the proportional springback (RP) multiplied by the theoretical bending angle (AT),   f) providing the actual pipe to be bent in the pipe bending machine,   g) setting the correct bending angle of the pipe in the machine (API),   h) performing the bending of the pipe around the forming roller of the bending machine;   
       wherein to perform subsequent bendings performing the following steps:
 i) calculating the radius of curvature (RA) of the pipe starting from the radius of the roller (RR) on which the bending has been performed and from the proportional springback (RP), 
 j) recalculating the length of the rectilinear section between the two curves replacing the radius of the forming roller (RR) with the radius of the pipe (RA) calculated in the previous step, 
 k) calculating a backward movement factor (Y) defined as the circular arc whose radius is the radius of the forming roller (RR) and whose angle is the fixed springback (RF), 
 l) setting on the pipe bending machine the actual forward movement calculated by subtracting the backward movement factor (Y) from the recalculated forward movement value (X) of the pipe, 
 m) repeating the steps e) to h) to perform further bendings. 
 
     
     
         2 . (canceled) 
     
     
         3 . Method according to  claim 1 , wherein such calibration measurements are performed starting from theoretical bending angles one smaller and one greater than 90°, in such a manner to simulate a bending of an acute angle and an obtuse angle. 
     
     
         4 . Method according to  claim 1 , wherein such proportional springback (RP) is calculated according to the following formula: RP=((AT 1 −AT 2 )−(AR 1 −AR 2 ))/(AR 1 −AR 2 ), where AT 1  and AT 2  are the predetermined theoretical angles and AR 1  and AR 2  are the bending angles resulting from the test bendings. 
     
     
         5 . Method according to  claim 1 , wherein the fixed springback (RF) is calculated according to the following formula: RF=AT−AR(I+RP), where AT is used to indicate a set theoretical angle and AR is used to indicate a measured actual angle resulting on the pipe upon setting such theoretical angle on the pipe bending machine. 
     
     
         6 . Method according to  claim 1 , wherein the bending radius of the pipe (RA) is calculated according to the following formula: RA=(1+RP)*RR, where RR represents the radius of the roller of the pipe bending machine and RP is the proportional springback. 
     
     
         7 . Method according to  claim 6 , wherein the backward movement factor (Y) is calculated according to the following formula: Y=RA*RF 2π/360, where RA is the bending radius of the pipe and RF is the fixed springback. 
     
     
         8 . Method according to  claim 1 , wherein the test angles are respectively 30° and 120°.