The function of vacuum roll on Fourdrinier paper machine

The vacuum roll on the paper machine is mainly dehydrated by vacuum suction. Its advantages are convenient operation, high dehydration rate, less wear of the net, and convenient paper threading. The use of vacuum rolls in the paper machine can increase the dryness of the wet paper to more than 20%, and the high-speed paper machine can reach 27%.

The vacuum roll of the paper machine is composed of two parts: the vacuum chamber and the roll shell. The roller shell is generally made of tin bronze centrifugal casting. When using plastic mesh, in order to prevent electrostatic corrosion, use copper shell encapsulation or stainless steel roller shell. The holes in the contact part of the shell and the copper mesh are all countersunk round holes. The round holes are small inside and large outside to facilitate the inhalation and throwing of white water. In order to give full play to the role of the vacuum roll, the holes on the roll shell must be kept clean. In order to meet the needs of screen changing work, the vacuum roll can be designed as a cantilever type. When in normal production, its two ends are still supported on the bearing seat.

The dewatering principle of the vacuum roll of the paper machine is similar to that of the vacuum suction box. The vacuum roll is dehydrated through its internal vacuum chamber. Its dehydration strength mainly depends on the degree of vacuum in the vacuum chamber. The dehydration time and the amount of air passing through the wet paper are only secondary factors. The increase of the vacuum degree has a significant impact on the dewatering capacity of the roll, if the vacuum degree is increased by 5.3kPa, the dryness can be increased by 1%-1.5%. The dehydration time on the roll is very short.

When the vehicle speed is low, water and air enter the roll and enter the vacuum chamber of the roll. In this case, a water-gas separator system must be used to separate air and water, so that white water does not enter the vacuum generation system. At higher speeds, most of the moisture escaping from the wet paper has no time to enter the vacuum chamber inside the roll. Usually 70%-80% of the water remains in the small holes on the roll surface or in the mesh of the forming wire.

The higher the vehicle speed, the less water enters the vacuum chamber. The moisture remaining in the roll hole is thrown out by the air stream that rushes into the small hole at a high speed at the moment after the roll hole passes through the vacuum box. Therefore, a white water pan and a water baffle plate must be installed to prevent the thrown water from returning to the entrance side of the meshing area between the bending roller and the forming wire or splashing on the screen driving roller with the white water pan.