Round-to-square section drawing through flat idle rolls

Abstract

Cold drawn metal bars of regular polygonal section are industrially produced by direct drawing from round stock using either a round-to-polygonal section converging die or a drawing head comprising an adjustable set of symmetrically arranged flat idle rolls. In the present work a solution is obtained to determine the roll load and drawing force for steady state direct cold drawing of square section from round stock through flat idle rolls. The results obtained have shown that the drawing force in a case of fair lubrication condition amounts to about 40% of that required for drawing through converging dies, which allows using a drawbench of lower load capacity. The drawing stress is highly influenced by the friction conditions at the roll surface and to a lesser extent by the area reduction ratio and roll diameter, indicating the need for good quality finish and adequate lubrication for the rolls contact surface. The ratio of the drawing stress to the roll mean pressure is independent of friction and increases almost linearly with the increase of area reduction ratio.