Introduction to the Vacuum Suction Box of Fourdrinier Paper Machine

The vacuum suction box of the paper machine is a traditional vacuum dewatering element. When the pulp reaches the vacuum suction box, the consistency has reached 2%-3%. Generally, on a low-speed paper machine, the pulp concentration can reach about 11% after passing through the vacuum suction box; on a high-speed paper machine, the pulp concentration after the vacuum suction box can reach more than 15%. On different paper machines, the number of vacuum suction boxes varies from 2 to 10, and the number of assemblies mainly depends on the type of paper. The number of vacuum suction boxes for high-quality paper or high-speed paper machines is relatively large. The vacuum range is 10-33kPa. The vacuum degree on the main pipe of the vacuum suction box is generally less than 40kPa, and it is as high as 80kPa on the high-speed paper machine.

The structure of the vacuum suction box:

The vacuum suction box is composed of a box body and a panel. The body of the vacuum suction box is generally made of wood, cast iron, steel plate or cast aluminum. The vacuum suction box on the small paper machine is made of wood. The larger paper machine adopts the structure of welded steel or cast iron. Modern paper machines mostly use silicon-aluminum alloy or stainless steel welded boxes.

The material of the vacuum suction box panel is the same as that of the forming plate. Low-speed paper machine, the material covering the surface of the vacuum box is generally high-density polyethylene. High-speed paper machines use hard materials such as silicon carbide or alumina. The panel is required to be processed smoothly, the orifice is smooth, and the flow of water in the box is smooth. There are three types of opening shapes: round holes, long holes and slits. Generally, the wet vacuum suction box has a slit-shaped opening, and the dry vacuum suction box can have a slit or hole shape, depending on the type of production. In the production of fine (high-grade) paper and coated paper, it is best to use a slit-shaped surface, because the hole-shaped surface produces a pulp channel in the paper and forms streaks in the paper. The slit width of the dry vacuum box is different from that of the wet vacuum box, and the wet vacuum box is slightly wider, about 25mm. The slit width of the vacuum box in the middle is 16mm, and the width of the high vacuum vacuum box is 13mm.

There are movable sealing baffles at both ends of the vacuum suction box. When the position of the baffle is moved by threaded transmission, the suction width of the vacuum suction box can be adjusted to adapt to the width of the paper made. Generally, the sealing edges at both ends of the vacuum chamber are 10-20mm wider than the paper edges.

The water and air sucked in by the vacuum suction box are usually discharged from the transmission end of the box, and the air and water are separated by the relevant separation system. The air and water mixture flows out from the back of the vacuum suction box and enters a water vapor separator containing a baffle. The white water continues down, and the air goes up to the vacuum header. There is a valve on the top of each vacuum water leg, which can control the vacuum degree of the vacuum box. The air pressure water leg pipe from each separator enters the water seal tank, preventing air from escaping from the system. The length of the air pressure water leg pipe must be greater than the length of the water column with the highest vacuum degree used by the system.

In order to stabilize and adjust the vacuum degree in the vacuum suction box of the paper machine, a diaphragm type vacuum regulator can be equipped on the exhaust pipe of the vacuum suction box. The sensor element of this regulator is a rubber membrane. The upper part of the diaphragm is in communication with the atmosphere, the lower cavity is connected with the exhaust pipe of the vacuum box, and the diaphragm and the valve body of the vacuum valve are connected as a whole. The position of the diaphragm rises and falls with the fluctuation of the real degree in the suction box, thereby opening and closing the vacuum valve, automatically maintaining the stability of the vacuum degree in the box. The vacuum degree is adjusted by turning the adjusting handwheel to change the pressure of the regulator spring on the diaphragm.