Effect of Pass Schedule on Cross-Sectional Shapes of Circular Seamless Pipes Reshaped into Square Shapes by Hot Roll Sizing Mill

Abstract

A heavy gauge square steel pipe is manufactured by a hot roll sizing process, in view of difficulty in manufacturing such a pipe with sharp corners by cold roll forming. In this paper, the effect of pass schedule on a cross-sectional shape is discussed by referring to experimental measurements, and results calculated by the rigid-plastic finite element method. The experiment was carried out at the last step of the sizing process for seamless pipes. The corners of a product become sharper as the magnitude of total reduction increases. In the case of a two-roll type roller, the corner near the roll flange becomes sharper than the corner near the groove bottom. The hollow depth at the sides is small when the incremental reduction at each sizing stand is high at the early reshaping stage with a large bending curvature ((D₀/2)/R_i, R_i: bending radius, D₀: initial external diameter of a circular seamless pipe) and low at the late reshaping stage with a small bending curvature.