Daily production of 5 tons of toilet paper papermaking machine, 1880 toilet paper machine production line

A paper machine is a collective term for a complete set of equipment that enables the formation of paper pulp into a web, including a headbox, a mesh section, a pressing section, a drying section, a calender, a paper rolling machine, and a transmission section, as well as auxiliary systems such as steam, water, vacuum, lubrication, and heat recovery.

A machine that produces paper from pulp water suspensions that meet the requirements of papermaking through processes such as dewatering through a filter screen, mechanical extrusion dewatering, and drying. The paper machine consists of three main parts: forming, pressing, and drying, which complete the above process. It is equipped with necessary finishing, coiling, and transmission devices, as well as auxiliary systems such as pulp supply, slurry and white water circulation, vacuum, ventilation and exhaust, paper damage treatment and lubrication, and automatic control. The specifications of a paper machine are often expressed by the width of the finished paper (referred to as the width of the paper), the width of the copper mesh, and the preferred working speed. The width of modern large paper machines can reach 11m, the speed of the working car can reach over 1000m/min, the daily paper production can reach hundreds of tons, and the weight of the entire machine can reach over a thousand tons, reaching over a hundred meters. Small paper machines are commonly used in the production of general developing countries and some specialty papers, with a width of 1-3m and a working speed of tens of meters to 200 meters per minute.

Traditionally, the paper machine is divided into long mesh, circular mesh, sandwich mesh, and mixed long circular mesh models based on the type of paper forming machine used; There are also cultural paper machines (including Xinwei paper), cardboard machines (including packaging paper), toilet paper machines, and special paper machines based on their main product varieties; Or according to the thickness of the paper produced, it can be divided into thin paper machines, cardboard machines, and conventional paper machines.

According to the needs of the manufacturing 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.

Paper machine:

It is composed of a headbox, chest roller, forming mesh, suction tank, and couch roller. The headbox distributor evenly sprays the slurry from the flow system onto the forming wire, and the slurry speed should match the wire speed. Controlling the jet speed and wire speed is the main factor in selecting the headbox type. The fully enclosed hydraulic headbox adjusts the pulp speed by adjusting the feeding pressure of the pulp pump, suitable for high-speed paper machines; The air cushion headbox adjusts the speed by adjusting the air cushion pressure, while the open high position headbox adjusts the speed by adjusting the height of the pulp level inside the box, suitable for medium speed paper machines; The open compartment headbox is suitable for low-speed paper machines. The formed net is an endless circular net that forms a horizontal or slightly inclined flat net surface between the breast roller and the couch roller. As a working section for pulp dewatering, it is commonly referred to as a net table, hence it 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 extract 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 the two nets are dehydrated simultaneously, it is called a clamp net shaper (Figure 2). These shapers use different forms of dewatering elements to accelerate the dehydration of pulp on the wire. There are three types of components: stationary, rotating, and both. Static components such as dewatering boards and curved vacuum boxes, while rotating components such as table rollers and vacuum forming rollers. In addition to using a single form forming machine to form a long mesh paper machine, a circular mesh paper machine, and a clamping mesh paper machine, there is also a forming part that combines long mesh, multi circular mesh, multi clamping mesh, and various forms of long circular mesh mixed forming machines.

Pressing department:

Further dehydrate the formed wet paper 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 traditionally include vacuum suction devices. When pressing, a suitable specification of woolen cloth is used to support the paper sheet. It can evenly distribute the pressure and take away some of the water squeezed out by the press, and enhance the pressure and dehydration capacity of the press. 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 machines, the line pressure can reach up to 350kN/m; Making rubber covered rollers into vacuum pressure rollers, groove pressure rollers, lining mesh pressure rollers, blind hole pressure rollers, etc., in order to more effectively remove the pressing water from the pressure zone, these are new technologies that have been adopted since the 1950s to improve the efficiency of pressing and dehydration. Afterwards, a double press structure was used 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 a vacuum suction roller, supported by a cloth and fed into the composite pressing. Afterwards, the paper sheets are transferred between the pressing rollers, thereby eliminating the phenomenon of paper sheets being pulled apart by factors such as self weight during pressing in the past. Since the 1980s, there has been a wide pressure zone pressing technology, where strong and tough rubber belts or rollers deform under strong pressure, resulting in a line pressure of up to 750kN/m and a wide contact surface. This significantly prolongs the dewatering time and greatly improves the dewatering capacity of the pressing process, especially 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 sheet touches a smooth hard roller surface or a rough adhesive surface, as well as the amount of water removed from each surface, can affect the surface quality of the paper sheet. Reasonable handling can significantly reduce the difference in balance between the two sides of a paper page, while conversely, it can also increase the difference in smoothness between the two sides.

Drying department:

Driven by gears or a cloth, several drying cylinders form a group, 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 best effect is to use a diameter of 1.5m for the drying cylinder. 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 processes to achieve good surface quality. Most paper is calendered by a mechanical calender after the paper machine to ensure 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 super calender should be used for calendering. It is generally composed of paper pulp rolls and cold cast iron rolls arranged alternately. According to different usage requirements, some varieties need to be surface coated to improve surface quality; Some require surface coating to improve appearance or printing quality. Surface gluing and coating can be processed using paper outside the paper machine through a gluing machine and coating machine, or by combining the gluing machine and coating equipment inside the paper machine for internal processing.

Transmission system:

Connect and synchronize the various parts of the paper machine to make the mechanical and electrical components integrated. It is composed of mechanical deceleration devices, speed regulating and stabilizing devices, and segmented transmission devices, all of which use electricity as the power source.

White water system:

The recovery, treatment, and reuse system for the dehydration of the paper machine forming section. The entire system includes equipment for collecting, conveying, filtering or settling 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 the 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. that are matched with the paper machine.

Schematic diagram of paper machine structure

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