Asymmetry of the roll gap as a factor improving work of the hydraulic gauge control in the plate rolling mill

Abstract

Plate mill in the Steel Plant Czȩstochowa has been recently equipped with the hydraulic gauge control system. Analysis of the work of the mill after the modernisation has shown an increase of the loads by about 20%. Additionally, changes in the geometry of the stand resulted in about 35% increase of the stress in the upper traverse of the stand and about 20% increase of the stress in the lower traverse and in the poles. These additional loads are due to the work of the hydraulic gauge control system which, on the other hand, decreases the variations of the thickness along the plate and improves the flatness of the plate. Investigation of the possibilities of the decrease of the rolling loads is the main objective of the present project. An assumption is made that an introduction of the asymmetrical rolling may be one of the ways of solving that task. Research on the practical aspects of the implementation of the asymmetrical rolling in the plate mill Czȩstochowa were carried out. The asymmetry was introduced by varying the angular velocities of the upper and lower rolls. In the present work, the theoretical analysis of that problem has been performed using the finite-element code Elroll. The code uses rigid-plastic flow formulation coupled with the numerical solution of the general heat diffusion-convection equation. It has been earlier successively applied to the simulation of the metal flow and heat transfer during rolling of the bimetalic plates. In the present project program Elroll has been used for the calculation of the loads in the symmetrical and asymmetrical rolling of steel plates. Analysis of the results obtained for the rolling of eight different carbon-manganese steels has shown that asymmetrical rolling results in a decrease of the rolling loads in the last finishing passes ranging from few to more than 70%, depending on the process parameters. It is shown that an application of the asymmetrical rolling in the stands with the hydraulic gauge control leads to: i) an improvement of the flatness of the plate, ii) a decrease of the thickness variations along the plate, iii) an improvement of the transverse profile of the plate.