Web instability at open draw and its impact on paper machine efficiency
Abstract
Paper machine efficiency is mostly affected by machine down time, resulting from maintenance work and web breaks. One of the main factors affecting breaks is the web instability at open draws on paper machines, especially at the wet-end between last press roll and dryer section. Web instability at the open draws can originate from different sources, from web properties variations to machine equipment to pulp quality. Often, the root cause of the instability can be difficult to identify because of the lack of information or tools that could help to understand the relation linking web instability to paper breaks and paper machine efficiency. Some studies in the literature have shown the importance of reducing paper properties and machine variability at the open draw to maintain good runnability and reduce breaks. Although many studies or specifically developed equipment have aimed at understanding and improving web runnability at the open draw, the means can be either too costly or too complex for papermakers. Hence, the development of accessible, simple and affordable tools to monitor and characterize open draw stability became of high interest. One of the objectives of the work presented in this paper is to actually quantify the open draw stability through some key parameters identified as such in the literature: release angle, paper solids and draw variations. There are probably additional parameters that will affect open draw stability, but we have decided to focus first on these ones and see if lower variability of release angle, paper solids and draw variations would contribute to fewer web breaks and better machine runnability. Empirical studies completed in paper mills are presented to assess variability of these key parameters at different types of open draws. When possible, links could be made between reduced variability at open draws and the amount of web breaks following these changes.
Citation
Parent, F. (2015, June). Web instability at open draw and its impact on paper machine efficiency. Paper presented at the Thirteenth International Conference on Web Handling (IWEB), Stillwater, OK.