Mini-Encyclopedia of Papermaking Wet-End Chemistry
Part Three: Equipment & Unit Operations

Couch

The function of couch roll (pronounced "cooch") of a paper machine is to remove water by application of vacuum. It also serves as the final "wrap" where the wet web exits the forming fabric on its way to the wet-press section. The surface of the couch roll is covered with rows of small holes. Baffles within the interior of the couch roll direct the vacuum toward that segment of the roll where the wet web is on the fabric. Unlike vacuum boxes, an increase in vacuum does not increase the power needed to drive the forming fabric. However, too high an application of vacuum at the couch is likely to produce visible suction-hole "shadows" due to movement of fines within the sheet.

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This page is maintained by Martin hubbe, Associate Professor of Wood and Paper Science, NC State University, m_hubbe@ncsu.edu .