On the Characteristics and Mechanism of Rolling Instability and Chatter

A nonlinear model describing the dynamical interaction between work rolls and metal sheets and the initiation of fifth octave rolling chatter is presented. The model, which comprises a work roll sub-model and a metal sheet roll-bite sub-model, enables the instability of strip rolling to be qualitatively and quantitatively studied as a function of rollstack stiffness, rolling speed, inter-stand tension, roll-bite entry and exit thickness, and the sheet force resulted from the interactive action of the work roll with the plastic deformation of the rolled strip. It is concluded that, even though the governing dynamics is highly nonlinear, rolling chatter instability is none other than mode excitation or beating, and thus linear. Analyzed results correspond well with what have been observed in physical rolling mills. Specifically, the natural frequency predicted for a 4-H rolling stand fits the fifth octave chatter at 550∼650 Hz and there is a critical rolling speed (2.54 m/sec for the material and sheet configurations considered in the paper) beyond which rolling instability will occur. This research establishes the fundamental knowledge base required for the understanding of chatter characteristics and mechanism, and thus provides the essential bases for effective control of rolling instability and chatter-free roll mill design.