Synchronized assessment ofcompression of corrugatedboard : Mechanics and visualization

Abstract: Flexographic printing involves driving a paper substrate through the gap between two cylinders, where one of the cylinders has a print form layer covered in ink. The ink transfer from the print form to the paper is dependent on the pressure between the paper substrate and the cylinders. Knowledge about how the paper substrate reacts to compression is therefore important when aiming for high quality flexography printing. In this project the paper substrate in focus is corrugated board consisting of a top liner, a bottom liner and a fluted paper material in between the liners. To gain knowledge about the compression dynamics of the boards they are subjected to compression experiments with and without print form. The compression experiments are filmed and the videos are then analyzed using thresholding and tracking methods. The developed thresholding method is able to measure the thickness of each material separately in each frame while the developed tracking method is able to track the movement of the top and bottom metal blocks compressing the materials. The strains calculated from the image analysis measurements are then used as input values to the Maxwell spring-dashpot model with the intention of modelling the stress. Analysis of the compression experiment videos shows that the material properties of thecorrugated board may not be constant for the duration of the compression. This is because the fluting changes its shape when being compressed. Comparing the modelled stress to the stress measured by the press used in the experiments shows that the Maxwell spring-dashpot model is not able to model the stress accurately when the corrugated board goes through multiple stages of compression. The model works better for compression where the shape of the fluting is not significantly changed.