Numerical analysis of the vertical vibrations of rolling mills and their negative effect on the sheet quality

Vibrations in the frequency range (120–180 Hz) are among the phenomena causing the most critical profile defects of the final product (metal sheet). These defects are caused by the backward self- and parametrically excited movement of the working rolls. The equation of motion of the strip has been derived in taking into account the transportation motion with an average feed velocity. It is demonstrated that the strip feed velocity plays a crucial role in the excitation and intensity of vibrations. A broader picture of the phenomenon has been obtained compared to the results discussed in the earlier literature. It has turned out that apart from vibrations taking place at a constant amplitude, the beating and chaotic oscillations can get excited. At high strip feed velocities an unstable increase of vibrations can take place, resulting in the rupture of the strip. The velocity–frequency characteristics have been considered, taking the maximum vertical displacements of the roller axes as the measure of the excited vibrations.