On the Origin of Torsional Vibrations in Hot Rolling Mills and a Possible Remedy

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Abstract
Hot rolling mills suffer from severe torsional vibrations in particular working conditions (thin thickness). These vibrations are often explained as the result of an exogenous disturbance amplified by a resonance effect. In this paper, we show that these vibrations are in fact produced by the interaction between the kinematic chain and the phenomenon of the plastic deformation of the strip occurring in the roll bite. Precisely, the vibrations are the expression of an unstable limit cycle due to the combination of the dynamics associated with these two effects. Starting from this key observation, the vibration attenuation control problem is studied. First of all, by investigating the observability and controllability properties, it can be seen that there is a basic controllability problem in the standard configuration of the plant. To circumvent it, it is proposed to modify some mechanical characteristics so as to ensure the system controllability. Then a suitable active control system based on frequency domain concepts can be designed. The proposed control system neutralizes the torsional vibration, and therefore it allows one to preserve the system integrity while increasing plant efficiency and productivity.

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