Press section of paper machine

The press section of the paper machine further dewaters the formed wet paper sheet under pressure. It consists of two rollers with hard and soft surfaces, such as stone rollers and rubber rollers, to form a set of presses.

The press section of a paper machine is composed of press groups of the same form or different forms, which conventionally also includes a vacuum suction device. When pressing, the paper sheets are supported by the appropriate specifications of felt, which can evenly distribute the pressure and take away part of the water squeezed out by the squeezing, and can increase the pressure and increase the dewatering capacity of the press. Low-speed paper machines usually use 20-60kN/m line pressure, high-speed paper machines use up to 210kN/m line pressure, when high-impact presses are used, such as wet paper presses can be as high as 350kN/m line pressure; Vacuum press rolls, groove press rolls, net-lined press rolls, blind hole press rolls, etc., to more effectively take the press water away from the press zone, these are new technologies used to improve the efficiency of press dewatering since the 1950s. After that, a compound press structure is used to form a closed threaded paper. It is composed of two or three sets of presses and combined. The wet paper is peeled from the forming wire by a vacuum suction roller, and fed into the composite press with a felt support. Later, the paper is transferred between the press rollers, thus eliminating the need for paper sheets in the past. The squeezing is caused by the traction of its own weight and other factors, resulting in the phenomenon of broken ends.

Since the 1980s, wide-nip pressing technology has appeared in the press section of paper machines. The tough rubber belt or rubber roll deforms when subjected to strong pressure, resulting in a line pressure of up to 750kN/m and a wide contact surface. The extended dewatering time greatly improves the dewatering capacity of the press, and the effect is more prominent on the high-speed paper machine. The dryness of the pressed paper sheet can be increased from 30 to 37% in the past to 43 to 45%, and some even reach 50%. The number of times the paper sheet touches the smooth hard roller surface or the number of rough rubber surfaces and the amount of dehydration on each side will affect the surface quality of the paper sheet. Proper handling can significantly reduce the difference in smoothness on both sides of the paper, and vice versa, it can also increase the difference in smoothness on both sides.