Production of tissue products is one of the most sophisticated processes in the paper industry. Very low basis weights, often produced at operating speeds of far above 2,000 m/min, dried in less than one second pass through a range of creping, reeling, rewinding, and converting processes. Only when these challenging demands on designers and operators of tissue manufacturing and converting equipment have been met, is the packed final product ready for delivery. But the difficulties don’t end there. Tissue manufacturers are faced with increasing demand for more efficient use of resources and cost effectiveness in production, without affecting product quality. As the pressure to enhance machine performance intensifies, hand-in-hand with the desire to meet customer quality standards, this drives continual efforts to optimise tissue product manufacturing.
The choice of roll cover plays a significant part in the manufacturing process, as it directly affects the dewatering performance and the runnability of the equipment as well as the bulk and softness of tissue products. In times of growing cost and performance pressure, it’s more important than ever to select the right roll cover – one which best fulfils the specific demands of the manufacturing system and machine operator.
SchäferRolls is a leading name in the industry, renowned for its precision, technical expertise and solid track record
Pressure roll position – a real challenge
Drying the tissue paper web with the heated Yankee cylinder and the hot air hood is an extremely energy-intensive process. Considering the constant growth in energy costs, all efforts are made to reduce energy consumption by enhancing mechanical dewatering. An increase in dry content after the pressing process has an immediate impact on reduction of energy costs and a resultant increase in system efficiency when producing tissue paper. Suction pressure and pressure rolls are expected to dewater the paper web as efficiently and gently as possible. Yet the roll covers are used in very difficult operating conditions, creating certain challenges defining the optimal nip geometry of the roll covers, primarily due to the extreme diameter/length ratio of the Yankee cylinder, the related dynamic deformation of the cylinder under internal steam pressure, temperature and linear loads.
Low roll diameters and high operating speeds witnessed in modern tissue machines result in high linear loads and nip frequencies. As a consequence, the roll covers are exposed to extreme thermodynamic loads. Compared to suction pressure rolls, pressure rolls face substantially higher loads. Since there is no water flow to regulate the temperature for tissue pressure rolls, this leads to an increase in self-heating in the roll cover due to high nip frequencies and increased internal friction, which can quickly result in material fatigue in case of lack of cooling.