Transverse ribbing on single-cell reversible cold rolling mills

One of the problems with cold rolling of thin strips is the self-oscillation that occurs at rolling speeds above 20 m/s. The vibration amplitude increases so quickly that it is necessary to reduce the rolling speed or stop the mill completely. During cold rolling, transverse ribbing may occur. Transverse ribbing occurs during self-oscillation with a low vibration level, while the thickness of the rolled strip varies according to the harmonic law and the thickness change exceeds the permissible values. The reason for the appearance of self-oscillations is the synchronous oscillations of the last crates of the multicellular mill. Transverse ribbing is also possible in two-ring reversible cold rolling mills. The reason is the synchronization of the oscillation of the crates of the mill. The frequency of self-oscillations is equal to the natural frequency of the bed of the mill crates, approximately 100-120 Hz. On single-cell reversible mills, transverse ribbing occurs during single-pass rolling directly from the uncoiler to the right winder. The vibration parameters of a single-cell mill were determined in an industrial experiment using a wireless, mobile vibration diagnostic system. The natural oscillation frequencies of the crate bed are determined. The frequency of the first form is 108 Hz. Harmonics up to and including the 7th harmonic are present in the spectrum. The natural frequency of the decoiler was determined by a non-stationary method using DIAMEH vibration equipment and a vibrator in the rotation frequency range from 300 to 5000 rpm. The natural frequency of the decoiler pressure roller obtained experimentally: “DIAMEСH” - 17 Hz, “VIBRATOR” - 14-15 Hz, Mobile diagnostic system - 11 Hz. The dependence of the change in the frequency of self-oscillations on the change in the rolling speed has been experimentally obtained. Moreover, the frequency of self-oscillations is three times higher than the rotation frequency of the working rolls and, accordingly, the frequency of forced oscillations. A nonlinear model is obtained separately for the crate and for the decoiler of the mill. The boundaries of synchronization and the zones of almost periodic oscillations are determined.