UBC Theses and Dissertations
Modeling the creping process in tissue making Pan, Kui
Creping is a key operation in the manufacturing of low-density tissue paper. In this process, a wet web is pressed and adhered onto a drying cylinder (Yankee) rotating at a high speed, dried on Yankee, and then scraped off by a doctor blade. This controlled and violent interaction between the web moving at a high speed with the stationary blade creates a series of invisible micro-folds, and explodes the thickness of the web through inter-fiber debonding. Various parameters govern creping and finding their optimal combination is currently limited to experience or costly trials. A one-dimensional particle dynamics model is developed to study nonlinear deformations in the creping process, and to understand the underlying mechanisms. Specifically, the web is modeled as a single layer of discrete particles connected by visco-elasto-plastic elements. A mixed-mode discrete cohesive zone model is embedded to represent the adhesive layer. Self-contact of the web is incorporated by a penalty method. First, a systematic parametric study is reported to assess the relative impact of various process parameters on the crepe structure and hence the tissue quality. Then, the model is extended to a multi-layered web to investigate the “sheet explosion”. A phase diagram for the creping regimes is constructed. Next, the effects of inhomogeneities on the creping process are investigated. Three common inhomogeneities are considered separately: the forming fabric pattern; the non-uniform basis weight; and the non-uniform adhesion. Finally, a series of experiments have been conducted on an existing lab-scale creping apparatus to validate the proposed model, and qualitative agreement is observed. The model can serve as a tool to investigate the process-structure-property correlation in tissue making, and the findings in this thesis offer practical guidance to the industry in the choice of forming and creping process parameters.
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