A part of a papermaking machine, following the press section, in which steam-heated cast iron cylinders evaporate as much residual moisture from the paper web as possible. The paper web snakes through a series of cylinders (as many as thirty in some systems) which alternately expose the web's wire side and felt side to the heated cylinders, so as to ensure consistent drying on both sides of the paper. It is necessary to keep the paper web under tension, so as to prevent distortion and shrinkage. A paper's water content is about 60:70% before entering the drying section, and ranges from 2:8% at the end of the drying section, depending on its end-use requirements. In general, about two pounds of water are evaporated for every pound of paper produced. Different desired paper characteristics can also vary the drying method used. (See Yankee Dryer and Air Drying.) Surface sizing is also performed in the drying section. (See Size Press.) After drying, the paper web is sent to the next and final section of a traditional papermaking machine, the calender, which controls various surface characteristics of the paper.
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