A common question regarding steel plate rolling is whether the raw material, the steel blank, should be cut to length or provided with extra material to be trimmed during and/or after the rolling process.
Another question related to the blank size is whether the plate to be rolled can be provided cut to length with the ends beveled.
The answer is that if the plate ends can be bent prior to rolling, then no extra material is required. This process is called “pre-bending.” Pre-bending can be done with a radius die in a press brake or done in a three-roll, plate roll. How thick a plate you can pre-bend is controlled by the maximum pressure that can be applied by the top roll of the machine.
Why need pre-bending?
In the plate rolling process, you have the unbent flat section at the leading and trailing edges. It’s usually barely noticeable, especially in sheet metal and plates rolled to a large diameter. But they’re there, and they’re unavoidable because the pinch rolls need a place to hold the material.
The unbent flat section of the plate rolling process
Same as the section bending machine, the three rolls of the symmetrical 3-roll plate rolling machine are arranged in an isosceles triangle, so during the rolling process, an unbent flat section must be left at both ends of the workpiece.
The length of the unbent flat section is about half the distance between the centers of the two lower rolls. This part of the straight line is where the plate roller cannot roll, which is the biggest disadvantage of the symmetrical three-roll plate bending machine.
Pre-bending of the heavy plate with a 3-roll plate roller
An operation called pre-bending minimizes the flat sections on the plate’s leading and trailing edges. In a typical setup, the operator performs the prebend to the leading and trailing edge, usually leaving an unbent flat 1.5 to 2.5x the material thickness, depending on the application and material.
For critical-dimension cylinder rolling, an operation might opt to roll the cylinder, weld the longitudinal seam, grind it down, then reroll to eliminate the unbent flat. But in most cases, that small unbent flat section remains.
More specifically, the capacity of a three-roll plate roll machine is defined by the maximum thickness and the minimum radius combinations that can be pre-bent for a given plate of maximum width. Pre-bending saves time. You do not have to cut then roll, cut then roll, etc. Pre-bending also eliminates flat spots and material waste.
What about beveling or chamfering the edges at the ends of the plate? (Beveling or chamfering the sides on the width of the plate as it is put into the machine is not an issue—that process works well.) With pre-beveled and pre-bent plates, the rolling process can again provide uniform plate curvature with minimal material waste and no need for extra trimming.