A basic principle of the roll forming process is that the strip is bent in a straight line in the longitudinal direction. However, the pressure generated during the bending deformation combined with the residual stresses present in the strip often deviates the strip from the cold bending equipment. To describe the degree of deviation of the strip from the next forming roll, commonly used words are: side bending - horizontal bending, warping - vertical bending, twist - spiral. To solve this problem, a straightening mechanism should be used at the end of the roll forming machine.
The basic principle of the straightening mechanism is that for the profiles with side bending, warping and other defects, the correcting mechanism should exert sufficient pressure in the opposite direction to deform them. If the amount of deformation in the opposite direction is suitable, the profile can be completely straightened after springback. If the profile is twisted in one direction, the straightening mechanism sequence rotates the profile in the opposite direction, resulting in plastic deformation. If the angle of rotation is suitable, after springback, the profile will no longer twist.
For straightening of bends or twists, roll forming machines are usually performed between the last forming roll and the cutting die. If the last roll cannot effectively support the profile, the entire profile section must be supported when entering the side of the straightening mechanism. Straightening of asymmetric profiles is that torsional deformation may occur at the same time as straightening. At this time, it is necessary to perform bending and torsional straightening in the opposite direction of profile deformation. During the straightening process, the profile will move up and down, left and right, so the gap between the straightening mechanism and the profile is required to be relatively loose. There can be a certain gap between the straightening mechanism and the surface of the profile, and the commonly used straightening mechanism is the Turkish correction head.