May 20, 2013
Plate Rolling for Wind Towers
The three-roll method provides numerous benefits over the four-roll system in the fabrication of wind towers.
With the available and untapped wind resources in the United States, wind power is all but guaranteed to be a boon to its economy for quite some time to come. This represents a great opportunity for manufacturers of the component parts necessary to build and erect them, such as the towers themselves. Three-roll translating geometry style plate rolls are suitable, as well as the “more efficient than popular four-roll machines” for fashioning the conical plate sections used in the construction of wind towers. The following descriptions and illustrations provide a summary of the details and advantages to using the three-roll plate system for wind tower production.
First, the plate is placed on a supporting, motorized rollway and introduced into the three bending rolls (see Fig. 1). The plate is then aligned with the help of two hydraulic side arms. One is positioned on the opposite side of the material infeed, and the other acts as a rollway. Because the plate will become a circular section with a ring shape, the side that will become the small diameter of the cone must possess 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 (Fig. 2). 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 be prebent. With a three-roll machine with variable axis the material can be presented to the rolls on an angle, rather than parallel to the top roll axis.
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 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 or exceedingly long “scissor lift” table are needed to lift and reposition the plate.
Once the plate is prebent, it continues its clockwise rotation. The left hydraulic side arm with double articulation supports a medium to large diameter and leads it up to the hydraulic central arm (Fig. 3). To get a good bend, the plate should be closed for 80-90 percent of its final diameter during this first cycle. 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 plates that have the same dimensions. The panel may give other information as well, such as the presence of anomalies or alarms, diagnostics of all electro valves, and monitoring of automatic lubrication.
The trailing edge of the plate is prebent in the same manner as the leading edge (Fig. 4). 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. Next, the plate is closed by rotating it counterclockwise. The two side arms with double articulation and the central arm provide support for the plate.
is a senior application specialist at the Carell Corporation. To learn more call (251) 937-0948 or go to (www.carellcorp.com).