ROLL FORMING PROCESS

1. Plate Infeeding and Alignment
First, the plate is placed on a supporting, motorized rollaway and introduced into the three bending rolls.
The plate is aligned with the help of two hydraulic side arms. One is positioned on the opposite side of the material infeed. The other hydraulic arm acts like a rollaway.
Because the plate will become a circular section with a ring shape, the plate side that will become the smaller diameter of the cone must have a smaller amount of curvature. Therefore, the plate must be aligned at its central axis and fed into the rolls at a slight angle, rather than fed parallel to the rolls.
This conical section is where three-roll bending with a variable axis offers an advantage over four-roll bending. The four-roll configuration requires that the material always be presented parallel to the rolls for the entire leading edge to be prebent. If the plate were presented to a four-roll bender at an angle, the corner of the plate would not get prebent. With a three-roll machine with variable axis, the material can be presented to the rolls on an angle—not parallel to the top roll axis.
Next, the material is aligned at its central axis at the top roll. Material can be presented to the three-roll bender rolls at an angle.
Then, the plate is prebent. It is taken through the rolls’ rotation, up to the center of the top and left side rolls. At the same time the top roll comes down, pressing and bending the plate. The top roll presses the leading edge of the plate, leaving the remaining metal plate in a horizontal position on the rollaway.
2. First Prebending: Leading Edge
Next, the leading edge of the plate is prebent. The plate is taken through the rolls' rotation, up to the center of the top and left side rolls. At the same time the top roll comes down, pressing and bending the plate. The top roll presses the leading edge of the plate, leaving the remaining metal plate in a horizontal position on the rollaway. To allow the plate to slide, the side rolls must be tilted at the cone angle.
The prebending stage is another area in which three-roll bending with variable axis offers an advantage over four-roll bending for wind tower sections. With a three-roll bender, the prebending can be done on the tilted edge of the plate. In contrast, a four-roll machine uses the top and central rolls to pinch the plate, while its side roll lifts the plate to perform the prebending. Because the plate for a wind tower is very long, a bridge crane is needed to lift and reposition the plate.
3. First Bending
Once the plate is prebent, it continues its clockwise rotation. The left hydraulic side arm with double articulation supports a medium- to large-diameter pipe and leads it up to the hydraulic central arm. To get a good bend, the pipe should be closed for 80 percent to 90 percent of its final diameter during this first cycle.
Once the plate is prebent, it continues its clockwise rotation. The left hydraulic side arm with hydraulic double articulation supports a medium- to large-diameter pipe and leads it up to the hydraulic central arm.
To facilitate and speed up all operations, three-roll benders can be equipped with a control that shows the position of the rolls and the lateral roll's tilting. The panel helps the operator move the rolls. In addition, it retains memory of the operation so that it can repeat the operation with pipes that have the same dimensions. The panel may give other information as well, such as the presence of anomalies or alarms, diagnostics of all electrovalves, and monitoring of automatic lubrication.
4. Second Prebending: Trailing Edge
The trailing edge of the plate is prebent in the same way as the leading edge. While the plate ends its rotation, the top roll presses on the last section of the plate to prebend it. The lateral rolls are in the same position they were in for the leading edge; just inverted.