Supercalender, paper machine

By tradition and technical feasibihty, coating and supercalendering for surface quality improvement have been off-hne processes. Today both are increasingly integrated into the paper machine. The final activities in paper and board production are shtting of the full width reels into smaller rolls at the winder followed by packaging the rolls for shipment... 

In 1798, Nicolas Louis Robert invented the paper machine. It took more than fifty years, however, until calenders were installed in the paper machine. These calenders - also called machine calenders - consisted of at least two hard rolls. A decade later the supercalender appeared with a large number of alternating hard... 

Supercalenders are classic off-line machines as they have downtimes of 25-30% due to the fiUed roll change. To be able to keep pace with a high-speed paper machine at least two, sometimes even three, supercalenders were therefore required. This disadvantage of the supercalender led, at the begiiming of 1980, to the development of the soft calender. The soft calender consists of at least one heated roll and one resilient roll covered with synthetic material. Because synthetic rolls are much more resistant to marking than the filled rolls of the conventional supercalender, the soft calender was also able to be used on-line. In many cases, the online soft calender was very successful. However, not all quality demands on the paper surface could be met with it. For demanding papers, the supercalender equipped with filled rolls and which could therefore only be operated off-Hne remained the only alternative. 

Other parts of the paper machine vary according to the end use of the paper. These include the size press, calender, reel, and supercalender. 

Woodfree uncoated papers include, above all, office papers, which are in turn subdivided into writing and printing papers as well as copy papers. In the past, these papers were not supercalendered. Simple machine calendering was considered satisfactory. However, the demands made on the surface quality of these papers have now increased considerably. 

Wood-free, supercalendered natural printing papers with basis weights as described for machine-finished papers. 

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