Troubleshooting
- A downhill design minimizes end distortion. Although the word downhill implies that each pass is lower than the preceding pass, this isn't the case. In a downhill design, the midpoint of the metal profile is at the same height in every forming pass. A downhill design has less longitudinal elongation and less forming moment than a conventional uphill design (in which the midpoint of the metal rises progressively). A downhill design minimizes end distortion at the design stage.
- A long profile transition region—the region that comprises the noncontact and contact forming regions—has less angle increment per length, less forming moment, and less end distortion than a short profile transition region. A large bottom roll has a longer profile transition region and less end distortion than a small bottom roll.
Figure 5
Using side rolls can help to prevent end distortion. When forming prenotched materials, side rolls prevent the notches from hitting the rolls in the forming passes. They should be set up to form 50 percent to 100 percent of the forming angle of the next forming pass.
Figure 6
Post-treatments include counterforming, straightening, and a combination of counterforming and straightening.
- A pair of side rolls mounted before the forming pass (Figure 5) is a common method for preventing end distortion. These side rolls increase the profile transition distance, reduce the angle increment per length, and reduce the forming moment. Side rolls reduce the surface stresses in the profile transition region (forming zone) and therefore reduce the residual moment and residual surface stress and minimize end distortion. Setting up the side rolls to form about 50 percent of the forming angle for the following forming pass helps to reduce end distortion.
