Study of the effect of kinematic tension coefficient on tube forming in groove taper during lengthwise rolling on a stub mandrel

An open joint-stock company “Sinarsky Pipe Plant” uses pipe-rolling mill PRM-140 to produce pipes made of carbon and alloy superduty steels: drill pipes, casting pipes, pipes for power plant engineering industry from 73 to 168 mm in diameter with wall thickness from 5 mm to 23 mm. To reduce the production costs it is important to master the production of the pipes of the 140 PRM from continuously cast billet that is 150 mm and 156 mm in diameter and to cease the production of rolled billet that is 120 mm in diameter. It is necessary to increase the elongation ratio on the automatic mill “tandem” to master continuous casting. At present the elongation ratio on the lengthwise pipe-rolling mill No. 1 ranges from 1.16 to 1.5 and the elongation ratio on the lengthwise pipe-rolling mill No. 2 ranges from 1.07 to 1.15. The increased elongation ratios of automatic mill “tandem” cause the increase of strap sizes and as a result the increase of the amount of waste at a “guide mark” defect. The way to reduce the probability of the formation of a “guide mark” defect due to the kinematic tension during rolling on a stub mandrel with rough tube preovalisation was researched. The influence of the kinematic tension on the forming tube in the groove taper during lengthwise rolling with rough tube preovalisation was studied. The possibility of increasing the elongation ratio on the automatic mill “tandem” is shown.