Tube forming machine using three point bending

Abstract

A tube forming machine for making a tube from a sheet is disclosed. The forming rolls of this invention include various V-shaped rolls at least some of which are used as part of a three-point bending technique. The three-point bending technique entails the use of a V-shaped bottom roll and a narrow top roll. The sheet is shaped running the sheet through a gap between the narrow top roll and the V-shaped bottom roll. The technique allows a wide variety of tubing to be made from the same set of forming rolls, because the curvature obtained in a sheet can be varied by opening or closing the gap. A V-shaped forming roll disclosed herein is also used at a pinch roll stand with a second complementary V-shaped roll. The pinch roll stand of this invention creates an initial V-shaped sheet which facilitates the threading of the sheet at the start of a forming operation. Brimmed rolls are also disclosed. Brimmed rolls have a relatively sharp included angle, and are used to engage the edges of a sheet and to press the sheet against a single bottom roll in brimmed roll stand.