Effect of gripping conditions and strip oscillations on vibrations originating at cold rolling

Abstract

The process of continuous rolling is subjected to non-stationarity, accompanied by oscillations of not only basic technological and power parameters, but also parameters in the hearth of deformation. Non-stationarity at the rolling accounting high dynamic of the process results in origination of negative vibration effects. To prevent the vibrations originations the rolling speed is decreased, which prevents the reaching of the designing parameters of rolling mills operation. The study of influence of non-stationarity of the rolling technological process on gripping conditions and origination of dangerous oscillations was carried out. Characteristics of rolling mode of strip of 2.0–0.45 × 970 mm dimension, accompanied by vibration was presented, as well as graphs of the strip oscillations in the process of stationary rolling and under conditions of vibrations origination presented. An assumption made, that during vibrations origination the gripping conditions of the strip by rollers are disturbed. It means that provision of the grip stationarity will decrease the risk of the vibrations originating at the rolling. The assumption was confirmed by the studies of the cold rolling at five-stand mill 1700 of Cherepovets steel-works. The calculations of the hearth of deformation parameters were made by application of an elaborated dynamic model of the rolling process. The higher probability of vibrations originating at the rolling of strips of smaller thickness explained. It was shown, that due to the strip length, the rolling of the thinner metal is accomplished at higher speeds, comparing with the rolling of thicker metal. In addition, it was shown that the friction coefficient value at that would promote increase of risk of non-stationary rolling mode originating. The support of stable friction conditions in the hearth of deformation is promoted by usage of chrome-plated working rollers and asymmetrical rolling.