What are the main causes of paper machine malfunctions?

　　1. Wear and tear: Reason one is the wear and tear of components and equipment that come into contact with copper mesh, woolen cloth, pulp, and formed paper for a long time, such as pulp pumps, pulp crushers, desanders, vacuum box panels, press rollers, calendering rollers, etc; Reason 2: Parts that move relatively frequently between components, such as scrapers, inlet heads, cylinders, vacuum rollers, vacuum pumps, etc.　　2. Lubrication: Mechanical rotation cannot be separated from bearings. Paper machines, mainly composed of rotating rollers, have a wide variety of types and quantities of rollers, with hundreds of different types of bearings. Therefore, lubrication management work is very important, especially affected by water, high temperature, and heavy loads. Lubricating oil (grease) is prone to loss, evaporation, and aging, which can damage the lubrication effect, cause bearing damage, and shaft head wear. Therefore, regular inspections and refueling are essential.　　3. Fatigue: Heavy load and continuous operation of machinery are prone to fatigue failure. On paper machines, due to the constraints of mechanical structure and operating principles in certain parts, the design strength of components (such as mesh table shaking spring plate, electromagnetic clutch suction cup, coupling overload prevention pin, etc.) should not be too large to avoid damage. The solution can be taken through measures such as maintenance and technological improvements.

Introduction to the Basic Classification of Paper Machines

　　Traditionally, the paper machine is divided into long mesh, circular mesh, sandwich mesh, and mixed long circular mesh models according to the type of paper forming machine used; There are also cultural paper machines (including newsprint), 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 produced paper, it can be divided into thin paper machines, cardboard machines, and conventional paper machines.

What are the main characteristics of a paper machine?

　　A paper machine is a collective term for a complete set of equipment that forms a paper web for pulp, including a main unit such as a pulp box, a mesh unit, a pressing unit, a drying unit, a calendering machine, a paper rolling machine, and a transmission unit, as well as auxiliary systems such as steam, water, vacuum, lubrication, and heat recovery.　　A machine that produces paper by dewatering the pulp water suspension that meets the requirements of papermaking through a filter, mechanical extrusion dewatering, and drying processes. 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, pulp and white water circulation, vacuum, ventilation and exhaust, paper loss treatment and lubrication, and self-control. The specifications of paper machines are often expressed by the width of the finished paper they produce (referred to as the width of the paper), the width of the copper mesh, and the preferred operating speed. The width of modern large paper machines can reach 11m, the working speed of the machine 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 developing countries and some specialty paper production, with a width of 1-3m and a working speed of tens of meters to 200 meters per minute.

Introduction to Mesh Lining Pressing of Paper Machines

　　Mesh lining pressing includes two methods, namely lining mesh pressing and sleeve mesh pressing.　　1. Lining net pressing　　Mesh pressing is the process of lining a large plastic mesh inside a pressed blanket, in order to reduce fluid pressure in the pressing area and facilitate dehydration. The use of lining mesh pressing can achieve the goal of increasing the pressure in the pressing zone, improving the dryness of wet paper width, and increasing the speed of the paper machine. However, due to the plastic mesh used for lining and pressing being packed inside the blanket, loading and unloading are more complicated and prone to damage. At the same time, the effect is limited. Therefore, it has not been widely promoted and used.　　2. Net pressing　　Net pressing is the process of placing a net cover on a flat pressing rubber roller or vacuum roller below, and fixing the two ends of the plastic net cover with block or whole ring pressure rings.　　The hardness of the adhesive layer of the net roller should be slightly higher than that of ordinary rubber rollers, generally 95-96 Shore hardness, and the hardness should not be less than 88-90. If the adhesive layer is too soft, the mesh sleeve is prone to deformation. In addition, both ends of the rubber roller should be machined into a circular arc shape with a radius of no less than 12.5mm to prevent cracks or scratches on the mesh sleeve.　　The mesh sleeve used for net pressing is made of double-layer woven single filament plastic mesh with a thickness of 2.25mm, a quantitative amount of about 900g/m2, and a void volume of about 1500cm/m. The dehydration mechanism of net pressing is basically the same as that of groove pressing. Because the mesh sleeve is made of single filament double-layer weaving, the side in contact with the blanket has enough mesh gaps to accommodate the pressed water, and the bottom layer has a channel for flowing water, so the water extracted from the wet paper during pressing is dehydrated in a vertical flow manner.

Introduction to Flat Roll Pressing of Paper Machine

　　Both regular pressing and regular pressing use flat roller pressing. The structure of flat roller pressing is that the upper roller is a stone roller and the lower roller is a rubber roller, both of which have flat and smooth roller surfaces.　　Stone roller is a common type of flat press roller. Stone rollers are usually made of materials that are easy to peel off from paper, mostly using granite. The main characteristic of granite is that there are many small pores in its tissue, which store a certain amount of air and are conducive to the peeling of wet paper pages. Its disadvantages are high cost and easy brittleness. During operation, if the speed is too fast or the load is too high, it may cause overheating of the shaft head, resulting in axial or annular cracks on the surface of the stone roller. Severe high-temperature expansion can cause the shaft center to fall off.　　With the increase of paper machine speed, the limitations of granite rollers are becoming increasingly apparent. Nowadays, most artificial stones made by mixing rubber and quartz sand are used instead of natural granite as upper pressure rollers.　　The lower roller of the flat roller press is a cast iron roller with rubber coating. In addition to providing the corrosion resistance of the pressure roller, the most important thing is to provide good elasticity and ease the pressing effect of the upper pressure roller on wet paper and blankets, thereby extending the service life of the blankets and reducing the "compression" of wet paper. The elastic rubber wrapping lower roller can also give the two rollers a good indirect contact and uniform dehydration effect, and compensate for the high errors in the lower pressing roller.　　When producing general paper, the rubber hardness of the rubber roller is usually 70-90 Shore hardness. The hardness of the rubber rollers used for each pressing line in the pressing department increases accordingly with the increase of pressure on each pressing line.

The working principle and characteristics of the tensioner

　　Tensioner is a commonly used holding device in belt and chain transmission systems. Its characteristic is to maintain the appropriate tension of the belt and chain during the transmission process, thereby avoiding belt slippage or preventing synchronous belts from jumping or falling off teeth and dragging out. Or it can prevent the chain from loosening or falling off, and reduce the wear of sprockets and chains.　　In terms of effectiveness, tensioners using spring structures are generally used due to their simple construction and low cost. However, tensioners using rubber components have a longer lifespan than springs due to the good elasticity of rubber. However, they have higher requirements for rubber performance and are relatively expensive, so they are less commonly used and are usually used in mechanical equipment.

Introduction to the Fault Characteristics of Paper Machines

　　When a device or system loses its specified function or reduces efficiency during use, resulting in shutdown, it is called equipment failure. There are two main types of downtime faults in paper machines: inherent production faults and equipment faults.　　(1) Characteristics and patterns of production inherent fault shutdown　　This type of shutdown is mainly carried out to ensure product quality and meet production process requirements, especially in the production of cultural paper. The main reasons for the shutdown are: firstly, the brushing work, the wet end filtration and dehydration components (or materials), after a certain period of use, their functions decline, and the dehydration and filtration cannot achieve the initial effect, requiring regular cleaning. The second is to replace the main process equipment, such as copper mesh and woolen cloth, which need to be replaced regularly after reaching their service life; The rubber roller and stone roller are worn by contact with paper and scraper, causing changes in the height of the roller surface, which can affect product quality and require regular repair.　　(2) Characteristics and analysis of equipment failure shutdown　　Due to the particularity and complexity of the paper machine production process, equipment failures have the following characteristics:　　1. There are multiple equipment failure points, and frequent equipment failures and shutdowns occur;　　2. Some components have a short service life and a higher frequency of replacement parts;　　3. The difference between the failure cycle and the maintenance time occupied is significant and difficult to manage. The reasons for equipment failures in paper machines are multifaceted.

Introduction to the Basic Structure of Paper Machines

　　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.