Introduction to the basic structure of paper machine
According to the needs of the papermaking process, the paper machine has various structural forms, which are generally composed of flow, forming, pressing, drying, finishing, coiling and transmission components and auxiliary systems and other supporting equipment.
It is composed of headbox, chest roll, forming net, water suction tank and couch roll. The headbox distributor will spray the slurry from the flow system to the forming net evenly, and the slurry speed shall match with the net speed. The main factor of choosing headbox type is to control the speed of pulp and net. The fully closed hydraulic headbox adjusts the speed of the pulp by adjusting the delivery pressure of the pulp pump, which is suitable for high-speed paper machine; 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 in the box, which is suitable for medium speed paper machine; the open compartment headbox is suitable for low-speed paper machine. The forming net is an endless ring-shaped net. Between the chest roll and the couch roll, a horizontal or slightly inclined flat net surface is formed. As the working section of pulp dehydration, it is often called a net table, so it is called a long net. If the endless forming mesh is placed on the circular mesh cage, it becomes the arc-shaped dehydration forming working section, which is called the circular mesh. If a steel mesh drum with holes is used to draw vacuum from the shaft end to accelerate the dehydration of the pulp on the forming mesh surface, it is called vacuum round mesh or vacuum forming mesh. If the pulp is held by two long nets, and the two nets are dehydrated at the same time, it is called a net clamping formator (Figure 2). These shapers adopt different dehydration elements to accelerate the dehydration of pulp on the web. There are three types of components: static, rotating and both. Static components such as dehydration plate, curved surface vacuum box, etc., rotating components such as case roll, vacuum forming roll, etc. In addition to using a single formator to group long web machine, round web machine, and web clamping machine, there are also forming parts composed of long web, multi round web, multi web clamping and multi forms of long web hybrid formators.
The formed wet paper is further dehydrated by means of pressure. It consists of two rollers with hard and soft surface, such as stone roller and rubber roller to form a group of press. The pressing part is composed of the same or different pressing groups, and conventionally includes a vacuum suction device. When pressing, the paper page is supported by a suitable specification of wool cloth, which can evenly distribute the pressure and take away some of the water squeezed out by the press, and can enhance the pressure and improve the dehydration capacity of the press. The line pressure of 20-60kn / M is usually used for low-speed paper machine, and the line pressure of 210kN / M is used for high-speed paper machine. When high-speed paper machine is used for pressing, for example, the line pressure of 350kn / M can be used for wet paper machine; The rubber covered roll is made into vacuum press roll, groove press roll, lining press roll, blind hole press roll, etc. in order to take the press water out of the press zone more effectively. These are all new technologies adopted since the 1950s to improve the efficiency of press dehydration. After that, a double press structure is used to form a closed paper guide. It is composed of two or three groups of pressing. The wet paper is peeled off from the forming net by the vacuum suction roll and sent to the composite press by the wool cloth support. After that, the paper page is transferred between the rollers, so as to eliminate the phenomenon that the paper page is broken due to the traction of self weight and other factors in the past. Since the 1980s, there has been a wide press area technology, strong rubber belt or rubber roller, which deforms under strong pressure, thus having a line pressure of up to 750kn / M and a wide contact surface, obviously prolonging the dehydration time and greatly improving the press dehydration capacity, and the effect is more prominent in high-speed paper machine. The paper dryness can be increased from 30-37% to 43-45%, some even to 50%. The surface quality of the paper is affected by the number of times that the paper contacts the smooth hard roll surface or the number of times that the rough rubber surface is contacted and the amount of water loss on each surface. If the treatment is reasonable, the difference of smoothness on both sides of the paper can be reduced obviously, otherwise, the difference of smoothness on both sides can be increased.
A plurality of drying cylinders driven by gears or by woolen cloth are a group, and a plurality of groups of drying cylinders form a drying part. The linear speed of each drying cylinder can be adjusted separately, and the micro speed difference between each drying cylinder can be maintained to compensate the shrinkage of the paper in the drying process. The dryness of the paper out of the drying section is generally about 92-94%. At the end of the drying part, a cold cylinder is generally equipped to make the water gas condense on the cold cylinder surface. Condensed water can wet the surface of the paper to get better surface smoothness in finishing. Diameter of drying cylinder 1.5m The effect is good. One side glossy paper can get higher one side glossiness by using large diameter drying cylinder with high hardness and high finish. The diameter of large diameter drying cylinder is generally 3 ~ 7.5m 。
Surface finishing department
Multi process treatment is used to obtain good surface quality. Most of the paper is calendered by mechanical calender after the paper machine, so that the paper surface is flat and consistent. The mechanical calender is made of several cold cast iron rollers, which press the paper surface with the self weight or additional pressure of each roller. If higher surface smoothness is required, the super calender shall be used for calendering. It is generally composed of paper meal roll and cold cast iron roll arranged alternately. According to different requirements, some varieties need surface sizing to improve the surface quality; some need surface coating to improve the appearance quality or printing quality. The surface sizing and coating can be processed outside the paper machine by the sizing machine and coater, or the sizing machine and coating equipment can be combined inside the paper machine for machining.
Connect all parts of the paper machine to operate synchronously, so that the mechanical and electrical components are integrated. It is composed of mechanical decelerating device, speed regulating and stabilizing device, partial transmission device, etc., all powered by electric power