SchäferRolls GmbH

Overcoming frontiers: optimized tissue pressure roll position with SchäferRolls tisQ.R cover

Application example WEPA Hygieneprodukte GmbH Marsberg-Giershagen, Germany.

Author: Frank Kretschmer, Product Manager SchäferRolls GmbH & Co. KG

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.

 

tisQ.R, view tender side.
tisQ.R, infrared image.

Tough and reliable:
WEPA has overcome frontiers with the tisQ.R roll cover

WEPA Hygieneprodukte GmbH was originally founded as the trading company, “Westfälische Papierfabrik“, in Arnsberg, Germany, in 1948. In 1953 the company expanded to become a manufacturing plant and since 1958 the WEPA Group has enjoyed international success in its core business of producing tissue paper. The company operates 22 paper machines and more than 90 processing machines for rolled and folded tissue paper products at locations in Germany, France, Italy, Poland, Netherlands and Great Britain, achieving a market share of approx. 8% (25% in Germany).
Four paper machines are operated at WEPA in Marsberg-Giershagen (Pic. 2), on which toilet paper and kitchen towels are produced.

The PM 7 produces toilet paper and is equipped with a suction pressure and pressure roll position (Cover), with paper weight range 15-20 g/m²; operating speed 1,630-2,000 m/min; operating width 2.710 mm. In the past, WEPA experienced unacceptable limits at the pressure roll position due to an increase in vibrations which had a negative impact on product quality and which reduced the running time intervals. Since the cooling system of the pressure roll is not fitted with a syphon system, water content of the roll could not be regulated. Customer suspected a negative impact because operation conditions could not be exactly defined. To optimise performance at this position, SchäferRolls GmbH & Co. KG was requested to meet the following requirements relating to a roll cover: roll cover must be operable without cooling in order to ensure definable operating conditions; targeted running time 1 year; Vmax 2,000 m/min.

 

Solution proposed by SchäferRolls

Graph 1. Loss factor tan delta.

The tisQ.R material optimized for application in pressure roll positions has a very low loss factor tan delta, an indication of its excellent elasticity and the low heat build-up inside the cover (Graph 1). This material property enables use without energy-intensive operation of a cooling system for internal cooling of the roll covers. The special metal bonding system provides excellent reliability for the bonding of the roll cover to the core. An application-specific multi-layer structure ensures the transfer of loads under high dynamic stress. Outstanding wear properties and high hardness stability deliver long running time intervals and stable operating conditions.

 

Initial practical experience with tisQ.R on the PM 7

On initial operation in January 2018, the roll was not operated with cooling, which reduced the weight of the roll in operation by one ton. Start-up of the machine was successful with the following parameters: paper weight 18 g/m²; start-up speed 1,500 m/min, as a result of new felt installation; no vibrations. After reaching the full dewatering performance of the felt, machine speed could be increased to 2,000 m/min on production of even 16 g/m² tissue paper over a long time. The vibration level was very low during the entire running time and had no negative impact on product quality and machine efficiency.

The roll was replaced in accordance with plan in November 2018 after a running time of 10 months. Based on data from the grinding records, the material already confirms its excellent wear properties, i.e. very low wear: delivery diameter 957 mm; diameter after grinding 956 mm.
Uwe Bigge, Technical Manager at WEPA Marsberg-Giershagen, confirms the success of initial application: “After 10 months running time, we have removed the pressure roll as planned. The roll recorded no problems during the entire running time“.

 

 

It’s the rolls that make the paper. With over 25 years in the paper industry, we know what’s on our customers’ minds

Pic. 2 - WEPA Marsberg-Giershagen, Germany.

 

 

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