Mechanics of Creping Process in Tissue Making: Modeling and Experiments, PaperCon2017

While the demand for printing and writing paper has declined over the years, the demand for tissue products is growing, with rapidly expanding markets in Asia and South America. However, scientific knowledge of tissue manufacturing processes, particularly dry creping, is scattered and still in its embryonic stage. Intense competition in this industry sector precludes the sharing of scientific knowledge gained by each manufacturer from painstaking experimentation. In the creping process periodic folding microstructures in the tissue are formed, which can significantly increase the quality of tissue (bulk, softness, absorbency).1 During creping section, first a continuous wet web is pressed and adhered onto the surface of Yankee dryer with the help of adhesive chemicals. After being dried by the hot steam and air around the drum, the web is scraped off from the surface by a doctor blade and folding structures are formed, shown as Fig.1. Many control parameters have effects on the creping such as Yankee surface speed, adhesion and blade geometry.2 However, most of tissue companies are trying to optimize the creping process by trial and error on commercial or pilot tissue machine, which is very costly and time consuming. Thus a comprehensive and quantitative study about creping is necessary.

In this work the fundamental mechanics of creping is studied by experiments and modeling. First a lab-scale apparatus is built to mimic the creping process. High speed imaging study is performed to directly observe the creping process and the micro-fold to macro-fold transition mechanism is confirmed. Next a particle dynamics model is developed to simulate the creping of tissue. Specifically, the web is modeled as a series of discrete particles connected by spring-damper systems, shown as Fig.2.3 The adhesive layer is described by a cohesive zone model.4 The creping simulation results show that there are three typical stages during the formation of micro-fold, as Fig.3 shows. The effects of various control parameters on the tissue structure has also been identified.   

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