PJSC Novolipetsk Iron and Steel Works, Lipetsk, Russia:

V. A. Pimenov, Cand. Eng., Senior Researcher, Head of Technological Projects of the Directorate for the Development of New Process Technologies, e-mail: pimenov_va@nlmk.com

When rolling thin strips on a five-stand mill 2030, it was noted that increasing vibrations (chatter) occur at different speeds, the level of which significantly depends on the technical condition of the replaceable equipment: rolls, chocks, etc. It is shown that in the process of rolling the work roll chocks perform cyclic movements in the vertical and horizontal directions, and the amplitude of horizontal movements depends on the size of the gaps between the guide bars on chocks and stands. The stability of the position of chocks is determined by the balance of horizontal projections of the forces acting on chocks and rolls. Depending on the sign of the resulting force, which determines the pressing force against the bars, the chocks occupy a fixed position in the direction of rolling or against it. On the basis of the experimental data obtained on the 2030 mill, the load dynamics was studied and it was found that, depending on the mode, during the rolling of thin strips, the chocks of the work rolls of stand 5 can be in a state of unstable equilibrium. The spectral analysis of the pressing force showed the presence of strong periodic perturbations associated with the eccentricities of the backup rolls and transverse vibrations of the strip between the stands. A criterion for the stability of the chocks position is proposed, which makes it possible, on the basis of statistical characteristics of the rolling mode, to estimate the probability of their horizontal movement. A mathematical model of horizontal movements of chocks in the presence of gaps has been developed, taking into account the transverse vibrations of the strip in the interstand space and the displacements of the suspension points of the strip in the vertical and horizontal directions. The results of numerical simulation confirm the significant effect of gaps on tension fluctuations and the stability of the rolling process. Measures implemented taking into account the results obtained at mill 2030 made it possible to stabilize the technological process and increase the speed of rolling thin strips up to 5%.

NLMK employees A. V. Morozov, N. A. Dikarev, S. M. Krushinsky, M. E. Orekhov took part in organizing and carrying out work at mill 2030.

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