Operational observation of paper roll polygonization due to rolling contact vibration

The paper winder creates the customer paper rolls at the end of paper machine. Winding is a cyclic process, where the paper roll diameter and mass change constantly, while surface speed is kept constant. Currently the machine operational speeds are limited by severe self-excited vibrations arising from the paper rolls. One of the proposed causes for these vibrations is the polygonization of the paper rolls, where the paper roll shape is no longer cylindrical. The polygonization results from the plastic deformation caused by rolling contact between the paper roll and nip roller used to support the paper roll. Measurement of paper roll roundness profile during the winding process is almost impossible, and therefore there has been no experimental proof for the polygonization. In this study the polygonization of the paper rolls are experimentally observed from full scale vibration measurement during normal winder operation. The acceleration data from the static machine parts are transferred to frequency domain, which shows that there are notable side bands in the response spectra. The observed sidebands occur at multiples of the integer difference between the rotational speeds of the machine. These sidebands are identified from the measurements using nonlinear least squares method. The results show that the method can be used to extract the measured side band frequencies, and that the observed sidebands vary between the measurements. The knowledge can be used to estimate paper roll defects due to polygonization.