A Dynamical Model of a Paper Calendering Unit with Surface Wear

Abstract eng:
Calendering is one of the last steps in the manufacturing process of paper. The operation is performed by passing the paper web through a nip formed by two rotating cylinders pressed against each other. Considering printability and appearance, very fine surface properties have to be achieved. There are different types of calendering units varying in the number of cylinders. In modern soft calenders usually one of the cylinders has a steel core with a plastic coating while the other cylinder is not coated but heated. A main problem that sometimes interferes with the calendering process is called barring. It can lead to grooves which in extreme cases arise within days on the plastic coated rolls, resulting in short operation times and high operating costs. It is commonly believed that the grooves arise due to wear. Obviously there exists an interrelation between the dynamical behavior of the system and the wear in the contact area. For certain production speeds, self-enhancing effects are observed. Here the worn surface causes varying contact forces such that an internal resonance occurs. Within the framework of this paper, a dynamical model of a calendering unit is developed. The model features a simplified description of the contact area as well as the modeling of surface wear. By performing a stability analysis, production speeds corresponding to an internal resonance are identified. Also a design approach for influencing barring is simulated.

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