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How did the good paper roll up? Whats good, whats the reason?

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How did the good paper roll up? Whats good, whats the reason?

Release date:2018-06-11 Author:山东海天造纸机械有有限公司 Click:

  

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At present, a large number of modern high-speed paper machines have been introduced into the domestic paper industry, especially the high-speed news paper machines, which are characterized by the use of single-row dryer, which can better solve the problem of the broken head of the paper page in the dryer, so as to greatly increase the speed of the paper machine, without the risk of cylinder stopper and process spare parts damage. However, the paper produced by the single-row dryer will appear to curl. Curling (not the same as warping) of paper is a common but difficult problem to solve. It will make the paper absorber not run normally during printing, and affect the printing quality and the reading and preservation of printed products.



The type of paper pages that curl



According to the reasons, paper can be divided into three types: mechanical crimp, structural crimp and moisture crimp (also called dry and wet crimp).



A. mechanical crimp:



Mainly in the process of production, storage and processing, the paper amplitude is mechanically stretched, a surface under stress exceeds its elastic limit. For example, the water content on both sides of the paper is different in the calender, and the elongation on both sides is different after the calender. When the paper is stretched on a sharp edge, the paper produces different degrees of permanent deformation. The paper amplitude is stored in the form of a reel and is in tension for a long time.



B. structural crimp:



A lot of crimp is structural crimp, it is to point to a kind of crimp that is caused by stress - strain when paper page is dry. The main reason is that the two sides of the paper frame have different structures and compositions. Because in the forming process of wet paper, the two sides of the paper width fibers are arranged in different directions, the content of fillers is different, and the time to reach the critical water point is different when the two sides reach the critical water point when the paper is dry, resulting in the two sides of the shrinkage imbalance and curly.



C. water curls:



Water crimp occurs when more fibers cross on one side of the page than on the other. When the moisture content changes, the balance is destroyed, causing crimp.



The cause of the paper page crimp and the factors influencing the crimp



There are many reasons why pages curl. They do not exist independently, but interact with each other, causing different forms and types of crimp. However, its causes can be summarized in the following aspects:



- crimp is related to the properties of the fiber itself;



- crimp is related to the thickness, softness, porosity, length of fiber, pulping method and bleaching degree of paper pages;



-- changes in the proportion of the amount of damaged pulp in the pulp will lead to different crimp degree of the paper pages;



-- the different fiber anisotropy of the front and back of the paper page, i.e. the two sides of the paper page cause curly;



- the fiber interleaving direction of the inner layer and the surface of the paper is different, which will cause curls.



- the curly shape is related to the interwoven arrangement of fibers when the paper materials are connected to the Internet to form the paper pages;



- in the dry part, the strength of the inner layer and outer layer of fiber under heat has a great influence on the curl;



- the crimp is related to the nature of the dry net used in the dry part;



- the crimp is also related to the degree of dry net tension in the dry part;



-- the unreasonable drying curve causes the paper to curl;



-- the unreasonable adjustment of speed difference of each part leads to the crimp of the paper page;



-- the change of the tightness of the paper page leads to different crimp degree, and the thickness direction of the paper page tends to crimp;



-- the water distribution on both sides of the page is closely related to the crimp;



-- finally, the surface with the water removed will have inner curl;



- curling is related to the ash size of the paper and the moisture content of the paper;



- curling is related to the use of auxiliary materials and auxiliaries;



- the curl is related to the ambient temperature, humidity and the degree of external force;



In summary, the occurrence of paper page curl is closely related to three factors, namely, raw materials, copying process and environmental conditions.



The solution to curling



In the process of copying paper, the main reason for the paper width curling is that there are two sides of the paper itself, coupled with the improper control of drying conditions, unreasonable drying curve, inconsistent drying rate on both sides, imbalance of shrinkage on both sides and other factors. Therefore, raw materials, copying process and environmental conditions can be adjusted.



1. The raw material



-- the ratio of slurry can be adjusted, and slurry with low wet expansion coefficient can be selected;



- appropriately reduce the amount of slurry to reduce the wet expansion coefficient of paper pages;



2. The forming



In the forming process, the internal structure of the paper, especially the structure and composition of the two sides, should be adjusted to make it close to each other, so as to reduce the tendency of curling. It can be adjusted according to practical experience.



- adjust the speed ratio of slurry network;



-- adjusting the outlets;



-- adjust the injection Angle;



-- adjust the vacuum of the forming element;



- adjust the dewatering amount of the dehydrating element;



- adjust the performance parameters of the forming network;



3. Press



By gradually increasing the pressure to alleviate the dehydration, a more uniform z-direction paper structure can be obtained. For example, the compression of boots and keeping the upper and lower woollen cloth clean are beneficial to reduce the curl. Select the appropriate middle height of the roller.



4. Dry



The drying process is an important external factor for the finalization of crimp degree.



-- reduce the speed difference of each drive section appropriately;



- adjust the drying curve;



- adjust the dry net tension properly;



-- adjust the vacuum degree of Vac roller properly;



-- increase the stable ventilation of the hood;



- reduce the paper temperature of the dryer;



5. Burnish the steam box



Calendering steam box is a way to relieve the paper leaf curl. Under the precondition that the forming part and the dry part form the potential curl, the steam box is used to spray the steam uniformly, so that the dry paper surface can be wet again, reducing the difference of stress-strain between two sides, and the top and bottom of the paper page tend to be the same, so as to overcome the disadvantages brought by a single row of dryer. However, it is only a passive defense, and the practical application effect is not ideal, and its internal factors should be eliminated in the forming and drying parts.


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