Metal Forming Study during Pipe Reduction on Three-High Rolling Mills

Abstract

Pipe rolling units (PRU) with three-high screw rolling mills are used to produce hot-rolled seamless pipes. Two units with rolling mills are operated in Russia: one is the TPA-160 mill at Pervouralsk Novotrubny Plant, JSC (Pervouralsk, Sverdlovsk oblast, Russia) and the second is the TPA-200 mill at Volzhsky Pipe Plant, JSC (Volzhsky, Volgograd oblast, Russia). Currently, increasing the technological capabilities of these PRUs is one major problem. It is necessary to expand the size and grade range, as well as utilize a non-traditional application of the sizing and rolling mills for screw rolling. To resolve these problems, the processes of reducing or plugless rolling of pipes on three-high screw rolling mills with increased reduction in diameter up to 25% are studied. The results of computer finite element simulation using QForm software are presented. The objective is to study the effect of the rolling process with increased diameter reductions on metal forming in the deformation zone and on changes of geometrical dimensions when reducing the capped blanks with different wall thickness on experimental-industrial mills. The capped blank ovality is quite important during metal forming when screw rolling. The ovality is the ratio of the feed radius when the metal comes in contact with the roll and the radius under the roll in the deformation zone cross section. The ovality characterizes the resistance of capped blank to deformations in inter-roll space. Reducing the thin-wall capped blanks is accompanied by large values of ovality, which makes the deformation process less stable. Therefore, the formation of shape defects (faceting) and end defects is possible during the plug rolling process. The rolling process ovality on the plug increases more intensely as compared with plugless rolling. The presence of plug limits the metal displacement in the axial direction and promotes metal displacement in the gaps between rolls. During plug rolling, it is necessary to use the rolls with shoulder, which make it possible to carry out the main reduction in the wall, thereby localizing the reduction zone on the plug and then decreasing the ovality of capped blanks.