Paper Sheet Rewetting In Press Section
Paper sheet rewetting in paper machine press section is a transfer phenomenon of capillary water, so how the paper sheet rewetting in paper machine press section appear?
Paper Sheet Rewetting Reasons
1. Paper sheet rewetting in press nip: When the press pressure starts to drop in press process, it immediately produces the back-wetting effect. Basically, the paper sheet rewetting is unrelated to paper basic weight and speed, its size is mainly controlled by felt and wet paper capillary thickness, wet paper and felt swelling recovery speed and felt moisture content.
Paper sheet rewetting is also affected by the fine fluff fiber on felt surface, so the capillary diameter of paper machine felt should be close to the capillary size of the pressed wet paper. In order to achieve this requirement, felt is better with flat fine hairs, uniform surface. When the press pressure is relieved, the wet paper starts to swell and absorbs water from the felt surface.
2. Paper sheet rewetting after press nip: The paper sheet rewetting increases with the increase of residence time, wet paper dryness and roughness degree of felt surface.
In order to shorten the felt contact time, it can be solved from the extraction angle of the press felt, so that the felt is separated immediately after wet paper sheet leaving press section.
In addition, using even surface felt can also help to reduce paper sheet rewetting. In the same conditions, the paper machine with using even surface felt, wet-back water only is about 5g/m2, if the use of rough surface felt, wet-back water can be more than 15~20g/m2.
