According to the needs of the copying process, paper machines have various structural forms and are generally composed of components such as flow, forming, pressing, drying, finishing, coiling, and transmission, as well as supporting equipment such as auxiliary systems.
Forming department
Composed of a headbox, chest roller, forming net, suction water tank, and pressure roller, etc. The headbox distributor evenly sprays the slurry sent by the flow system onto the forming mesh, and the slurry speed should match the mesh speed. Controlling the jet and mesh speeds is the main factor in selecting a headbox type. The fully enclosed hydraulic headbox adjusts the slurry speed by adjusting the slurry pressure of the flushing pump, suitable for high-speed paper machines; The air cushion headbox adjusts the speed by adjusting the air cushion pressure, while the open high-level headbox adjusts the speed by adjusting the height of the pulp level inside the box, suitable for medium speed paper machines; The open compartment flow box is suitable for low-speed paper machines. The formed net is an endless circular net, which forms a horizontal or slightly inclined flat net surface between the chest roller and the bed roller. As a working section for pulp dewatering, it is commonly referred to as a net table, and therefore is called a long net. If the endless formed mesh is placed on a circular mesh cage to form an arc-shaped dehydration forming working section, it is called a circular mesh. If a steel mesh drum with drilled holes is used to draw vacuum from the shaft end to accelerate the dehydration of pulp on the formed mesh surface, it is called a vacuum circular mesh or vacuum formed mesh. If the pulp is clamped between two long nets and dehydrated simultaneously, it is called a clamp net Former (Figure 2). These shapers use different forms of dewatering elements to accelerate the dehydration of pulp on the web. There are three types of components: stationary, rotating, and dual-use. Static components such as dewatering boards, curved vacuum boxes, etc., while rotating components such as table rollers, vacuum forming rollers, etc. In addition to using a single form forming machine to form long mesh paper machines, circular mesh paper machines, and clamp mesh paper machines, there are also forming parts that combine long mesh, multi circular mesh, multi clamp mesh, and various forms of long circular mesh mixed forming machines.
Pressing department
Further dehydrate the formed wet paper pages by applying 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 pressing section is composed of pressing groups of the same or different forms, which in practice also includes a vacuum suction device. When pressing, a suitable specification of woolen cloth is used to support the paper pages. It can evenly distribute the pressure and take away some of the water squeezed out by pressing, and can enhance the pressure and improve the dewatering ability of pressing. Low speed paper machines often use a line pressure of 20-60kN/m, while high-speed paper machines use a line pressure of up to 210kN/m. When using high impulse pressing, such as wet paper mills, the line pressure can reach up to 350kN/m; Making the glue wrapping roller into vacuum pressure roller, groove pressure roller, lining mesh pressure roller, blind hole pressure roller, etc., in order to more effectively remove the pressing water from the pressing area, these are new technologies adopted since the 1950s to improve the dewatering efficiency of pressing. Afterwards, a double pressing structure was adopted to form a closed paper guide. It is composed of two or three sets of pressing and merging. The wet paper is peeled off from the forming net by vacuum suction rollers, supported by a woolen cloth and sent to the composite pressing. Afterwards, the paper pages are transferred between the various pressing rollers, thus eliminating the phenomenon of paper pages being pulled by self weight and other factors during pressing and causing breakage. Since the 1980s, wide press pressing technology has emerged, where strong and tough rubber belts or rollers deform under strong pressure, resulting in a line pressure of up to 750kN/m and a wider contact surface. This significantly prolongs the dewatering time and greatly improves the dewatering ability of the press, making it more effective on high-speed paper machines. The dryness of the pressed paper can be increased from 30-37% in the past to 43-45%, and some even reach 50%. The number of times a paper page comes into contact with a smooth hard roller surface or a rough adhesive surface, as well as the amount of water removed from each surface, will affect the surface quality of the paper page. Reasonable handling can significantly reduce the difference in smoothness between the two sides of a paper page, while conversely, it can also cause differences in smoothness between the two sides.
Drying department
A group of several drying cylinders is formed by gear transmission or driven by a woolen cloth, and the drying section is composed of several groups of drying cylinders. The linear speed of each group of drying cylinders can be adjusted separately to maintain a slight speed difference between each group of drying cylinders to compensate for the shrinkage of the paper during the drying process. The dryness of the paper leaves from the drying section is generally around 92-94%. At the end of the drying section, a cold cylinder is generally equipped to allow water and gas to condense on the surface of the cold cylinder. Condensed water can moisten the surface of the paper to achieve better surface smoothness during decoration. The effect is better when the diameter of the drying cylinder is 1.5m. Single sided glossy paper can achieve higher single-sided glossiness by using a large diameter drying cylinder with high hardness and high smoothness. The diameter of the large diameter drying cylinder is generally 3-7.5m.
Surface finishing department
Use multiple processing steps to achieve good surface quality. Most paper is processed by a mechanical calender after the paper machine to achieve a smooth and consistent surface. The mechanical calender is made of several cold cast iron rollers, which flatten the paper surface with their own weight or additional pressure. If higher surface smoothness is required, a calender should be used for polishing. It is generally composed of paper pulp rollers and cold cast iron rollers arranged alternately. According to different usage requirements, some varieties need to be surface glued to improve surface quality; Some require surface coating to improve appearance or printing quality. Surface gluing and coating can be carried out on finished paper outside the paper machine through gluing and coating machines, or they can be combined inside the paper machine for internal processing.
drive system
Connect and operate the various parts of the paper machine synchronously, so that the mechanical and electrical components are integrated. It is composed of mechanical deceleration device, speed regulation and stabilization device, and segmented transmission device, all of which use electricity as the power source.
White water system
It is a recovery, treatment, and reuse system for the dehydration of the paper machine forming section. The entire system includes equipment for collecting, conveying, filtering or precipitating white water, air flotation, etc., to separate and recover fibers and reuse fillers, as well as to recycle clean white water in the papermaking process.
Auxiliary system
It consists of electrical system, vacuum system, lubrication system, workshop steam supply and exhaust system, damaged paper treatment, compressed air system, steam supply, water supply and drainage system, etc., which are matched with the paper machine.
