Analysis of influence of billet torsion on formation of surface defects

The paper describes the effect of billet torsion on the formation of surface defects (such us captivity and chink) on sleeves and pipes, as well as the formation of inhomogeneously deformed structure. To produce such analysis, maximum possible angles of billet torsion are calculated assuming of absence of slippage on the boundary between the billet and the work roll. Calculation method is briefly described in the article. Results of calculation of billet torsion are provided for 460 and 600 mm diameter billets when decreasing, not changing and increasing diameter. It follows from these results that calculated torsion angles are small and located at different angles to the surface than captivities and other surface defects, which means that torsion cannot cause the formation of surface defects and grain inhomogeneity.