Generation mechanism of polygonal wear of work rolls in a hot leveler and a countermeasure by dynamic absorbers

This paper deals with the polygonal deformation phenomena of work rolls in a reversible hot plate leveler. According to the measurements of deformed rolls and the vibration measurement, a simple model regarding the polygonal deformation as unstable vibration caused by time retardation accompanied by wear on the surfaces of the rolls is proposed. Also, the modal analysis is applied to a general system with time retardation accompanied by wear in order to obtain the equations of motion for each mode and to derive some important parameters. Furthermore, a countermeasure for the polygonal deformation by using dynamic absorbers is considered. The optimal design of a dynamic absorber mounted on a single degree-of-freedom system where the polygonal wear is generated is discussed by applying the optimal design procedure of a dynamic absorber for forced vibration to this self-excited vibration system. As a result, a design in which the system is perfectly stabilized is obtained. This result is applied to a hot leveler as a two degree-of-freedom system through the modal analysis. By numerical analysis, it is confirmed that the hot leveler changes into a perfectly stable system by two dynamic absorbers, and the polygonal wear is not generated at all.