Balance of Pulling Forces in Roll Piercing

In screw rolling, the workpiece is deformed by rolls rotating in the same direction, while friction forces impart rotational and translational motion to the workpiece. For the piercing process to be stable, the gripping condition, which is determined by the balance of pulling forces, must be met. This article examines the conditions for balancing pulling forces during piercing of a workpiece in two-, three-, and four-high screw rolling piercing mills, demonstrating the obvious advantages of three- and four-high piercing schemes over two-high piercing.