Do You Know The Dehydration Principle of Paper Machine Wet Section?

Dehydration Mechanism of Wet End of Paper Machine

The constant function of the forming section, press section, and dryer section of the paper machine is dehydration. In the wet section, mechanical methods are often used for dehydration, while in the dryer section, evaporation is used for dehydration. The relative cost of extracting 1 ton of paper is as follows: forming section: press section: dryer section=10:12:78; Therefore, papermaking workers must strive to improve the dehydration efficiency of the wet section, especially the efficiency of the press section, in order to reduce the evaporation load of the dryer section, and the horizontal dehydration should be uniform and consistent.

The dehydration of paper is the process of solidification, forming a network in the forming section. Only by using vacuum action can the dryness of the paper roll reach 18-23%. Within this moisture range, most of the free water has been removed, and further dehydration needs to be achieved by pressing to compress the paper structure and increase the internal water pressure to achieve outward dehydration. After remove out the water from the paper sheet during the paper sheet pressing process, the void volume of the paper sheet decreases, and a certain degree of fiber compression occurs at the contact between fibers. The applied pressure helps to distribute the moisture evenly throughout the entire paper sheet.

Pressing and dehydration are divided into four stages: the pressing pressure is the sum of water pressure and mechanical pressure, and the wet pressing zone is divided into four stages based on the interaction between water pressure and mechanical pressure.

In the first stage, the paper and felt are purged of air until the paper reaches saturation with moisture and there is no residual air. In this stage, the paper sheet didn't take a pressure, so the dryness of the paper sheet didn't change.

in the second stage , the paper sheet is fulled with water, the water pressure of paper sheet increased, so that the water are transfered from paper sheet to the felt. When the felt also water saturation, the water will remove out from the felt. The second stage reach to middle of press zone, and the total pressure is the maxium.

In the third stage, the pressure zone seam begins to expand, and further dehydration is carried out until the water pressure in the paper drops to zero, at which point the dryness of the paper is at its maximum.

In the fourth stage, the paper and felt begin to expand, and the paper becomes unsaturated. At this time, the paper returns to the paper through capillary action, internal vacuum, or void wetting mechanism, and some water returns to the paper. The pressed export paper should be separated from the felt as soon as possible to reduce the moisture regain effect.