Stainless Steel Paper Machine Vacuum Suction Box

The low vacuum / high vacuum suction box used in the paper forming part

After the slurry is formed on the net and preliminary dewatering, its dryness and tightness gradually increase, and the resistance to dehydration increases. To continue dewatering on the net, a method of high pressure difference must be used. The vacuum box is a device that uses the higher pressure difference inside and outside the box to enhance dehydration. The wet paper sheet has a dryness of about 2-3% before the vacuum box, and can reach 10-14% after passing through the vacuum box. At the same time, the tightness of the paper sheet has also increased.

1. Structure: The vacuum box is composed of a box body and a panel.

Cabinet: commonly used for welding stainless steel;

Amplitude modulation device: There are amplitude modulation devices at both ends of the box to adjust the width of the suction port, but most paper machines do not change the copy width often. Therefore, after the closed position of the two ends of the suction box is adjusted once according to the copy width, it is fixed.

Suction port: one end of the box has a suction port connected to the vacuum system,

Panel: The width of the vacuum panel is generally 250-300 millimeters. Panel material: Polyethylene is now used more and more, and ceramic panels are used, mainly to reduce the wear of the forming mesh.

2. The shape of the opening of the panel: it should ensure that the wet paper sheet is dehydrated evenly, and it will not increase the wear and tear of the forming net and deviate. There are generally three types of openings: round holes, long holes, and slits. The area of ​​the openings is 25-45% of the total area of ​​the panel. The effective area of ​​the long holes and slits is relatively large, and the friction area is relatively small. However, the long holes tend to deform the forming mesh as it passes, and the slits will cause the forming mesh to be corrugated and undulated, resulting in severe wear of the forming mesh. Panel pass mostly use oblique long holes or herringbone long holes

3. Dewatering process: The test shows that the dewatering of the wet paper web on a vacuum suction box can be roughly divided into three stages.

3.1 Free dehydration stage: The water content of the wet paper web is very high, and the water is filtered and discharged under the pressure difference caused by the vacuum;

3.2 Compression dehydration stage: The wet paper web is compressed under the action of pressure difference, and compression dehydration occurs;

3.3 Aerodynamic dehydration stage: The air begins to penetrate the paper web, and a part of the water between the fibers is brought into the suction tank with the air flow, forming the so-called aerodynamic dehydration. The main dehydration process is the first two stages. The amount of aerodynamic dehydration is not large, but it can absorb the water under the net and the mesh with the help of air flow, which is beneficial to the dehydration of the next vacuum suction tank, which is necessary in the actual dehydration process of the vacuum suction tank.

4. The number of vacuum boxes: usually a large number, narrow width, close arrangement, which is conducive to dehydration. The actual number of vacuum suction tanks required for a paper machine depends on the type of paper produced.