It is mainly shown that, from their basic origin, vibration rotor modes are following a fixed pattern which has been theoretically analyzed. Various perturbation effects related to geometrical or physical defects are evaluated. Three main classes of modes are distinguished which correspond to different origins: global “outside” modes, “static” rotating rotor deformation modes, and real dynamic excited deformation modes representing the only power sink strictly related to rolls deformation. Good agreement is found for measurements from an industrial paper mill plant operating unit and for experimental observations from a laboratory experiment with large mode coupling. In both cases, most of observed modes are belonging to the first two classes, which can be cured aside by appropriate respective frame shielding and roll grinding. For the last class, a continuous three parameter transformation group is constructed so that the industrial unit and the university apparatus both belong to it, allowing to study properties of the first one on the more manageable second one. Because the modes are sharply peaked due to metal stiffness and weak damping, there exists broad rotation frequency windows where the total mode amplitude is small enough for the system to be preferentially operated.

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