Views: 0 Author: Site Editor Publish Time: 2022-05-11 Origin: Site
There are many factors restricting the high-speed operation of the paper machine, but they are all technical and management details defects and the lack of knowledge and use of equipment. "Constraints" can be summarized from the following aspects
The cleaning mentioned here is in a broad sense, not only the workshop environment, but also the pulp system (especially the sizing system of the paper machine), the equipment of the auxiliary material system and the inner wall of the pipeline, the wet end frame, the rollers, the mesh and other parts. Dirt accumulation and scaling are not allowed.
Of course, the same is true for the drying section and other non-wet parts. Paper wool and paper chips are not allowed to fly around, and paper dust and oil stains accumulate on the surface of the dryer wire and drying cylinder.
Any flocculation in the wet end (fibers, fillers, foreign matter, dry pulp, etc.) can cause paper defects such as holes or paper breaks in different parts.
It is very important to reduce or promptly remove the build-up of flocs and flocs. The surface in continuous contact with the slurry must be smooth and regular cleaning is necessary.
The proportion of slurry, beating quality and slurry concentration should be stable.
Stable pulp can keep the process parameters of the paper machine stable (such as the vacuum degree of the wire part, the dryness of the wire part, the wet strength of the press part, the speed difference and tension of each part, etc.), and the paper machine can run stably.
In addition, stable operation of the entire paper machine is also important.
There are a lot of topics related to stability. Interested fans can check the previous related content, so I won’t say more.
The pulp flowing from the headbox to the wire must be uniform in the transverse direction of the paper machine, including the consistency of the thickness of the pulp layer, the consistency of the turbulence of the pulp exiting the nozzle, the consistency of the consistency, and the consistency of the speed.
The consistency of the thickness of the slurry layer is determined by the consistency of the nozzle opening;
The uniformity of turbulence depends on the uniformity of the smoothness of the inner surface of the headbox and the uniformity of the interference of the lip slats;
The consistency of concentration depends on the sufficient uniformity of dilution water and slurry mixing;
The consistency of the speed depends on the design of the speed matching of the headbox. If the speed at the end of the step diffusion cannot be effectively attenuated, the shotcrete speed will be inconsistent.
Dewatering of the mesh evenly
This means that the dewatering rate of the pulp is the same at any longitudinal position at each point in the width direction of the wire, otherwise the retention rate will be different.
This mainly depends on the quality of the dewatering elements of the mesh, that is, the quality of the mesh and its uniform contamination or cleaning, the straightness, angle, and leading edge accuracy of the wiper.
Uniform quantitative means that the absolute dry basis weight of the paper is uniform in the lateral direction, which can be understood as the absolute dry basis weight of the paper sheet exiting the press section is uniform in the lateral direction. Even if the two mentioned above are done well, the quantification of the banner is not necessarily uniform.
Because the dehydration uniformity of the press section will also affect the quantitative uniformity, the uneven air permeability and cleanliness of the felt will affect the quantitative uniformity. Where the felt has been washed, the basis weight is low and the thickness is thin.
The dewatering rate of the wire section determines the length of the wire section and the speed of the paper machine. The higher the dewatering rate of the wire section, the better. For the single fourdrinier section, if the dewatering rate is too high, the problem of flying and skipping will occur.
Under high-speed conditions, the influence of air resistance on the surface of the pulp layer is also manifested. Therefore, the running speed of the single Fourdrinier paper machine is restricted by the wire section, and the speed of the machine is not easy to exceed 1000m/min. The clipping section (top clipping, horizontal clipping, vertical clipping) is dewatered on both sides, and the dehydration rate is high, which can avoid the problem of a single fourdrinier section, and can meet the requirements of higher vehicle speeds.
Common compound press dewatering rates are determined by the press roll, felt and vacuum. The width of the vacuum area, the width of the press area, and the surface opening ratio of the vacuum press roll are important factors, followed by the quality of the felt. A good felt has the characteristics of good air permeability and suitable bulk, and it is not easy to harden and dehydrate after long-term operation. .
The diameter of the press roll determines the effective width of the nip. The larger the diameter, the larger the effective width and the better the dewatering effect.
The optimized ordinary compound press can support the speed of more than 1200m/min.
A paper machine with a higher speed must be equipped with a shoe press, and the vacuum sealing thread between the press section and the dryer section is required.
(1) Slurry degassing equipment. The pulp containing a lot of air is not easy to dewater, and the pulp is unstable, which restricts the increase of the vehicle speed and has a great impact on the quality of the paper.
(2) A headbox of dilution water type, no air cushion, and controlled fiber orientation.
The contact of pulp with air will inevitably produce foam and fiber flocculation. The fiber orientation of the edge part determines the fiber structure, and also determines the wet strength, dry strength, tensile strength, and stretchability of the paper sheet. The headbox is equipped with side flow (gill flow) to supplement the stock, control fiber orientation, and facilitate high-speed operation.
(3) Vacuum feeding rolls, vacuum press rolls, large diameter blind hole or groove rolls, stone rolls with wide vacuum area, and felt net scrubbers that can wash evenly.
(4) Web stabilizer. Whether in the wet end or the dryer end, the web (especially in the low tenacity period) cannot run free-flowing. The function of the web stabilizer is to make the paper sheet run stably against the felt or dry wire to meet the needs of high speed.
(5) Film transfer sizing coater. The traditional pond press sizing is not suitable for high speed due to the violent movement of the glue. To complete surface sizing under high speed conditions, film transfer sizing coaters are used.
In short, in order to make the paper machine run at a high speed, in addition to what the editor said, there are many other factors that need to be considered. I hope everyone can work together.