Investigating effectiveness of changing calibration of input cone of rolls and lines of a piercing mill with tapered rolls using computer modeling

Abstract

Screw piercing of a workpiece is a process with complex cyclical nature of metal flow in deformation center. Setting up the deformation tool and its calibration, as well as the accuracy of the workpiece feed and release of the hollow billet from deformation zone, have a significant impact on the quality of the hollow billet: dimensional accuracy and presence of defects on its inner and outer surface. In the paper, a technical solution was proposed to increase the stability of piercing a continuously cast workpiece on screw rolling mills. Implementation of the idea involves the use of an improved calibration of the piercing mill tool. For both in order to achieve the workpiece alignment and its stable feeding along rolling axis of the piercing mill, it was proposed to add a special thickening (hump) on the roll input cone and to change calibration of its input section on the ruler in order to meet the workpiece with the rolls earlier: before the initial capture of the workpiece by the rolls, that is, before deformation of metal of the continuously cast workpiece by the rolls. To check and correct the proposed solution, the tasks of FEM-modeling of screw piercing process with a modified design of the tapered roll and ruler were set and solved using the QForm 3D software package. Results of the finite element modeling (FEM) showed that the use of improved tool calibration makes it possible to improve the alignment of the workpiece and ensure its stable position along the rolling axis of the piercing mill, thereby reducing the runout of the workpiece in the deformation center and thereby reducing the force on the rolls from 8 to 5 MN. The results of measurements of the hollow billets’ geometric parameters obtained by FEM showed insignificant relative deviations that fit within the regulatory limits.