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| Figure 1 The roll forming process results in surface residual tension and residual moment. As the term implies, the residual moment is a force that remains in the roll formed profile. Cutting the product releases this force and can cause distortion. |
Figure 2 The leading ends of these three products show three possible outcomes: toed in, flared out, and no distortion. |
Sources of Distortion
The bending moment is the result of two forces. The top roll exerts one of these forces by pushing down on the channel's center. The bottom roll exerts the other force, pushing up on the channel's flanges. Cubes are helpful in illustrating the processes that result in end distortion (see Figure 1). The first cube shows the bending moment. On the front side of the cube, the bending moment is clockwise. On the back side of the cube, the bending moment is counterclockwise. The bending moment twists the channel flanges up in both the air bending region and the contact forming region and settles to the residual moment after the material comes out of the forming rolls. The second cube shows the residual moment. On the front side of the cube, the residual moment is counterclockwise. On the back side of the cube, the residual moment is clockwise.
