PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 4, Number 2, 2018
INCREASED SERVICE LIFE DESPITE HIGH TEMPERATURE DIFFERENCE AT CALENDER APPLICATIONS by Dipl.-Ing. (FH) Torsten Bellaire, Application Engineering SchäferRolls Paper finishing or calendering is one of the most demanding processes in the paper machine from a roll cover point of view. Especially when high temperature differences delta T result in frequent cover damages and high impacts from deposits on the cover surface.
Since the first introduction of polymer based covers in the calender more than 20 years ago, the basic strength and durability of covers have improved significantly and an outstanding dynamic mechanic property is a basic requirement. Most state of the art covers can withstand the high line load and speed in a modern calender. Even an incidental impact can be accommodated by most modern cover materials. Today’s challenge at a modern calender position (Fig. 1) is maximizing the service life in best balance with web quality. The service life of calender covers is normally limited to a certain level of barring, which is related to systematic wear or surface fatigue initiated by a system vibration. One major step towards extended service life is the increased strength and
stiffness of the basic polymer matrix employed in cover manufacturing. A novel nano and copolymer technology makes it furthermore possible to combine high stiffness with outstanding toughness and strength. The combination of the improved properties of these new cover materials require less reinforcing fibres, which leads to significantly improved cover homogeneity with controllable influence on the desired smoothness or gloss of the web. However, difficult positions such as the 2 stack soft calender with 380 kN/m and temperatures up to 200°C challenge engineers.
Fig. 2: conventional cover with high temperatures at the edges ∆T 32°C
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