Finite element analysis of tilting of metal in bar rolled with three-roll mill

Boiled metal bars and rods often exhibit tilting, which is rotation of the material around the pass line under rolling. Tilting may result in a defective shape. High dimensional accuracy is demanded in 3-roll rolling because 3-roll rolling is used for finishing passes. Therefore, the design of calibers and a rolling sequence that can reduce tilting is important from industrial aspects. In this study, three-dimensional FE analysis is applied to the prediction of metal tilting under 3-roll rolling in an oval-round pass and a hexagon-oval pass. The difference in the characteristics of tilting according to the contact contour between metal and the roll is investigated by classifying the characteristics of tilting into two modes, with the aim of clarifying the threshold for the occurrence of overturning and restoration resulting from tilting. Predicted results agree well with the experimental measurements of tilting, and the validity of method for analyzing tilting is confirmed. Moreover, it is found that the mechanism of tilting differs according to the contact contour. In an oval-round pass that is of a convex contact type, the bar tilt angle is difficult to decrease once tilting has occurred. In a hexagon-oval pass that is of a concave contact type, although the bar tilt angle tends to increase when the entrance cross section is constrained strongly, the bar tilt angle tends to decrease after constraint becomes relatively small.