Sheet forming studies using layered orientation analysis: Can lead to a better understanding of the drainage process

The layered structure of a paper sheet contains information about the flow dynamics of the fibre suspension during the sheet forming process. This work discusses how the drainage process can be studied using analysis of the layered orientation of the paper sheet. For this purpose a method based on image analysis of layered paper strips, has been developed to measure the anisotropy and orientation angles in each layer. By using a simple theory of inclined filtration together with dewatering rate measurements, the hydrodynamic mechanisms like orientated shear can be estimated during the sheet forming. As a result, the response of different forming sections, as weil as the adjustable process parameters influencing layered orientation structure, can be studied. This review includes comparisons of results between different mill scale studies in normal running conditions together with some pilot plant trials.