National University of Science and Technology “MISiS” (Moscow Russia):

A. S. Budnikov, Assistant, Post-graduate., Metal Forming Dept., e-mail: fiar128@yandex.ru
E. A. Kharitonov, Cand. Eng., Associate Prof., Senior Researcher, Metal Forming Dept., e-mail: haritonov45@mail.ru
A. S. Aleshchenko, Cand. Eng., Head of Metal Forming Dept., e-mail: judger85@mail.ru

Pervouralsk New Tube (Novotrubny) Works (Pervpuralsk, Russia):
R. V. Iskhakov, Leading Engineer Technologist, e-mail: iskhakov@chelpipe.ru

In order to improve the technological capabilities of three-roll calibration rolling mills for helical rolling, a study was made of the process of deforming hollow products and pipes without the use of a mandrel. Such a process may be applicable in the preparation of small-diameter pipes from a continuously cast billet, while at the same time it will be possible to exclude the roll of the billet to a smaller diameter. An important issue when using this process is to obtain a pipe with a given wall thickness. Solving this issue, a method was proposed for estimating changes in pipe wall thickness, based on the laws governing the intensity of wall thickness changes with various parameters of the deformation process and the deformation zone. The article discusses the effect of rolling without rolling or reducing pipes with a reduction in diameter of 5–25% in a three-roll helical rolling mill. The developed method for estimating the intensity of changes in the thickness of the liner wall at the deformation zone, characterized by the angle τ, is presented. The technique allows to determine the final value of the wall thickness during unwinding rolling in a wide range of values τ of the total reduction, the geometrical parameters of the original liner (the ratio of the diameter to the wall thickness) and the calibration of the work rolls. The results of experimental rolling without liners with D/S = 5–10 on the MISiS semi-industrial mill 130 are described. A relationship has been established between the angle τ, the D/S ratio of the original liner, and the total reduction in diameter. A test was carried out to assess the intensity of wall thickness change in industrial conditions at TPA 160 of JSC «PNTZ», where the effect of roll calibration and the total diameter reduction on angle τ was noted. Based on the experimental rolling without rolling, a finite element model of the process was built and implemented in the DEFORM 3D program, which allows you to expand the possibilities for studying the intensity of wall thickness changes by a pronounced angle τ, to determine the relationship with the main deformation parameters of the reduction process. The developed method of estimating the change in wall thickness can also be applied in conditions of screw rolling of tubes on a mandrel. In the areas of reduction of the deformation zone with increased compression in diameter, the assessment of the change in wall thickness allows you to more accurately study the conditions of pipe deformation, and choose the most rational modes of pipe rolling.

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