Publish Time: 2026-01-06 Origin: Site
Configuration requirements for the press section of the paper machine:
When designing a new paper machine or retrofitting an existing one, one will inevitably encounter the issue of configuring the press section of the paper machine. Configuring the press section involves the schematic design of the press section, primarily entailing the selection of the paper pick up method, the number of press zone, and the form of each press zone.
1. Principle of configuration for the press section
The configuration of the press section primarily depends on three major factors: the type and quality of paper, the type and ratio of pulp, and the speed of the press. When considering the configuration of the press section, one can start from its function and task, and combine general technical and economic requirements. This can be summarized into the following principles:
(1) Under the premise that the dewatering process conforms to the dewatering characteristics of the papermaking pulp, the maximum possible dewatering efficiency and dewatering amount should be achieved, in order to attain the highest possible paper web dryness.
(2) Meet the requirements of various processing or treatment processes needed for the characteristics of paper.
(3) The paper web transfer method and route shall comply with the requirements of safe and convenient operation, without affecting the quality of the paper, and shall be suitable for the design speed range of the paper machine.
(4) The structural form, basis weight, and material of the press felt meet the requirements for dewatering or paper-carrying, and can have a longer service life. Felt with the same structural form and basis weight should have the same length to reduce the storage quantity of valuable materials.
(5) The accessories for the press felt can effectively keep the felt clean and in an appropriate condition, and the types of accessories should be as simple and uniform as possible to reduce maintenance work.
(6) The disposal of damaged paper is convenient, with no concern of accumulated damaged paper.
(7) The frame structure and layout design facilitate the replacement of felt, as well as observation, inspection, and maintenance.
(8) The control system is simple to operate and convenient to handle, aiming to achieve centralized operation at specific points or overall centralized operation as much as possible.
(9) Adopt standardized components as much as possible to enhance interchangeability and reduce the number of spare parts.
In addition, the consistency with the forming section, dryer section, etc. should also be considered in terms of the level of mechanization and automation of the configuration.
2. Selection of press method and number of press zone
The form and number of presses are determined based on the dewatering characteristics and certain quality requirements of the paper, taking into account the existing configuration of the press section of the paper machine or the results of intermediate tests, according to the raw material ratio of the paper.
(1) The press section of a typical cultural paper machine employs three dewatering presses. Sometimes, a fourth press is added to enhance dewatering or improve the uniformity of both sides of the paper sheet. For pulp that is easier to dewater, a high-efficiency, high-line pressure press form and fewer press passes are used. For viscous pulp, dewatering is achieved through multiple press passes at lower line pressure. The former often uses one or two vacuum presses on older paper machines, while newer press sections employ a compound press consisting of vacuum press rolls and grooved press rolls. The latter previously used three to five vacuum presses, ordinary positive presses, and reverse presses to form the press section. Alternatively, three to four passes of vacuum press, corrugated press, separation press, or hot press can be used for dewatering.
(2) When a good bulkiness (low tightness) of the paper is required, lower linear pressure, larger diameter of the press roll, and fewer press zones are needed. For example, most sanitary paper machines only have one roller press, sometimes supplemented by another press, and sometimes equipped with two roller presses. As the machine speed increases from low to high, the types of rollers can be selected in order as flat rubber coated press rollers, grooved press rollers, vacuum press rollers, shoe press rollers.
(3) The first press has the highest dewatering capacity, and the felt is also the most prone to soiling. Embossing is likely to occur on the first press, and it is often a key part that limits the increase in vehicle speed. Therefore, priority should be given to selecting a press with high dewatering efficiency, such as vacuum press, and equipping it with an efficient felt washing device.
(4) When both sides of the paper sheet require good smoothness, various types of counter-nip presses are often equipped in the press section to reduce the difference in smoothness between the two sides of the paper web caused by squeezing and dewatering during pressing, or to eliminate or reduce the difference in smoothness between the two sides of the paper web formed by the former. For some paper grades that require high smoothness on both sides, smoothing presses are also equipped.
(5) For thick paper or paperboard with high basis weight, double-felt presses or double-felt vertical flow high-efficiency dewatering presses are often used as the first press. For thin paper with low basis weight, the phenomenon of rewetting on both sides is relatively prominent in double-felt presses, so double-felt presses are generally not used.
(6) Paper machines that produce paper with low wet strength and operate at high speeds often adopt compound pressing. For cultural paper machines and corrugated paper machines, compound pressing has become a standard configuration for medium-to-high speed paper machines. This is because compound pressing moves the first open-type traction of the paper web to the third or fourth press zone, allowing the paper web to have sufficient wet strength to withstand the tension generated by open-type traction at high speeds.
(7) For large high-speed paper machines or board machines, it is advisable to equip them with a closed-end, straight-through press section, and the pressing method can be either large-diameter roller pressing or shoe pressing.
3. Selection of paper pick up method and device
The selection of the transfer device for transferring the paper web from the forming fabric to the press section is related to the basis weight and machine speed of the paper web. For low-speed fourdrinier machines producing paper grades with high wet strength, ordinary open-type traction paper can be used to simplify the structure and reduce operating and maintenance costs.
For cylinder mould paper machines and board machines, the traditional lapping method is generally used. When the machine speed is slightly high, a vacuum return roller is required to ensure that the paper web does not fall off when the felt turns. Low-basis weight tissue paper is also often produced using the lapping method on low-speed paper machines.
Currently, newly designed fourdrinier paper machines are generally equipped with vacuum suction paper pick up devices when the machine speed exceeds 200m/min. For paper machines producing low-basis weight paper grades, such as fourdrinier tissue machines, suction boxes with simple and compact structures can be adopted.
A paper guide rope device is often required for both anti-squeezing and smooth squeezing.