Investigation of fibre interaction with a forming fabric

The forming stage of the papermaking process plays an important role in shaping the quality of final paper sheets. This thesis focuses on studies of fibre motion in the forming section. Wire mark was investigated both numerically and experimentally. Initial sheet forming was simulated with hundreds of fibres of random initial distribution placed into the flow above the fabric and advected onto the fabric. The surface roughness of the resulting fibre mat was calculated. The results show that during initial formation, topographic wire mark is caused in part by fibre bending and in part by the geometry of the fabric. For the specific fibres and sinusoidal forming fabric examined, more than 50% of topographic wire mark was caused by fabric geometry, with the remainder caused by fibre bending. In the experiments, the surface roughness of paper sheets made from different fibre properties was studied using an X-ray tomography device. Light-weight fibre mats were made in a handsheet former machine. A surface map of the wire side of the paper was produced via image analysis. The results reveal that increasing fibre coarseness decreases the surface smoothness of paper. As fibre length increases, surface roughness decreases slightly. Both fine and coarse forming fabrics were used in the sheet forming section. The surfaces of fibre mats made from finer forming fabrics were found to be smoother. The fibre orientation distribution of final paper sheets is closely dependent on the physical properties of the sheets. Fibre orientation in the forming section was studied numerically. In the simulations, one end of each fibre was held by the wire/fibre mat, with the other end carried in the flow. In the uniform flow, analyzed solution from the analysis was obtained. The fibre angle after deposition was only found to be a function of flow direction and initial fibre position. In the shear flow, a dimensionless group of γL/u_z was defined. As the value of γL/u_z increases, fibre mats increase in anisotropy. Fibre properties such as flexural rigidity and aspect ratio were found to have a insignificant effect on fibre orientation.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat