The pulp concentration is between 2 and 3%, and the dewatering capacity of the chopping board and the vacuum board is significantly reduced. The dewatering here must be done with a vacuum suction box with a vacuum ranging from 10 to 33 KPa.
When the net passed through the vacuum suction box, it began to remove moisture from the paper, but then the air also passed through the screen, and the air and water were pumped into the vacuum suction box. Where there is much moisture, the light reflects strongly. Like the mirror, the air penetrates the layer, which is called the “waterline” and is sometimes called the “dryer line”.
Generally, the water line is about 7% thick. In high-speed new double-layer (multi layer, Nip Wire Machine, etc.) paper machines, the waterline moves forward and is not see on the suction box.
The dewatering of the suction box is based on the suction of the vacuum pump, which creates a high pressure difference between the upper and lower sides of the paper, and forcibly dewatering the wet paper. It is hoped that the paper can be transferred to the press section with a high dryness. The vacuum cannot be used to force the dewatering. This accelerates the wear of the fabrics, increases the driving force of the fabrics, improves the tension of the fabrics, and has a long life for the fabrics. Bad effects.
The number of vacuum boxes varies according to the type of paper, the model of the paper machine, and the speed of copying. Generally, it is 7~9. In the multi layer,or Nip Wire Machine, the wetness of the wet paper is greatly improved. The number is greatly reduced, usually only 2~5, or even not used. In order to adapt to the change in the wetness of the wet paper, the vacuum of the suction box should be gradually increased.
Under the suction of the vacuum pump, the air mixture of water in the suction box is withdrawn from the suction box, enters the vertical pipe connected with the suction box, and the water is separated from the air under the action of gravity, and the white water is lowered to the water sealing groove. The air merges with the manifold and is pumped away by a vacuum pump.