Views: 0 Author: Site Editor Publish Time: 2022-09-19 Origin: Site
There are many factors affecting the forming of a paper machine, some of which are factors affecting dehydration, and some factors are "congenital" to the forming process, such as the characteristics of fibers in the pulp, the ratio of pulp, etc. Some factors are Due to the characteristics of the former, such as shaking, double-sided dehydration of the mesh, etc., some factors can be adjusted during the production process. The editor of Zibo Tianyang Paper Machinery Co., Ltd. will share the following
1) Pulp concentration
Low pulp concentration can increase the mobility of the fibers. When the turbulence and shear disappear, the time required for the fibers to form a flocculated state in low-concentration pulp is also longer than that in high-concentration pulp. Groundwood pulp with shorter fibers Fiber as an example, when the concentration is 1%, the flocculation time is about 100 milliseconds after the influence of disturbance disappears, only 1 millisecond when the concentration is 4%, and about 500 milliseconds when the concentration is 0.5%, so the low concentration has Conducive to better dispersion of fibers.
The reduction of pulp concentration on the Internet also enhances the activity of fine substances, and the loss of fine substances also increases when the initial water discharge is fast. , forming a net.
During the deposition process, the higher the content of fine fibers and fine substances in the laminate near the mesh surface, the better the surface of the laminate and the undulations and concavities of the mesh surface, that is, the clearer the net marks reflected by the laminate. , the net marks are strengthened. It can be seen from the above situation that when the pulp concentration on the net is low, the opportunities for fine fibers and fine substances to move to the net surface increase, so the net marks also tend to be strengthened.
2) Dewatering speed of paper machine
The influence of dewatering speed on the forming process and forming quality is multi-faceted. The initial dewatering speed of pulp feeding on the web is very different from the speed of dewatering of the free suspension above the layup in the later stage of the forming process through the formed layup.
When the initial dewatering speed is high, the defects in the fiber distribution caused by the flow section will be quickly fixed, the loss of fibers and fine particles will increase, and the web marks of the wet paper web will be enhanced. The result of passing through the layers.
Except for some thin papers, measures are usually taken to slow down the initial dehydration speed, so that the dehydration in the early stage of the forming process is relatively gentle, and at a relatively gentle initial dehydration speed, the orientation of the fibers in the lower part of the laminate can be easily controlled. , reducing the tendency of fibers to be arranged in the direction perpendicular to the forming mesh surface, which is conducive to better dispersion of fibers in the drainage.
3) Speed difference of pulp wire of paper machine
The speed difference of the pulp web is a measure to apply directional shearing. The speed difference of the pulp web is large, the directional shearing in the longitudinal direction is also large, and the orientation of the fibers in the longitudinal direction is also strong. The further away from the forming wire, the weaker it is.
The directional shear produced by the speed difference between the pulp and the web also has a good effect on the dispersion of the fibers in the undrained free suspension. The pulp speed is slightly faster or slower than the web speed, which reflects the improvement of fiber uniformity during the forming process. The effect of too large speed difference between pulp and web on forming is bad.
4) Paper machine forming wire
The forming wire is an essential element involved in the forming process, and the dewatering of the fiber suspension on the forming wire is related to the effective flow area and mesh size of the forming wire.
The effective circulation area refers to the sum of all mesh areas in the unit forming mesh area, and the mesh size is the specific size of a single mesh. The effective circulation area is related to the number of meshes and the diameter of the warp and weft threads. In a single-woven net, the effective circulation area is usually smaller for those with more meshes, because the warp and weft lines increase. When the effective flow area is more than 80 meshes per inch, the effective flow area usually increases with the increase of the mesh. Under the conditions of the same pressure difference and flow resistance, when the effective flow area is large, the dehydration speed is also higher. The effective flow area is the same but the mesh number is higher. For a long time, it means that the size of the mesh is small, and the dehydration speed will decrease due to the increase of flow resistance.
5) Pulp temperature
The increase of pulp temperature can reduce the viscosity of the water in the suspension and increase the dehydration speed. The fiber suspension is originally a three-phase suspension, because there will inevitably be more or less air in it, increasing the pulp temperature. It is conducive to the rapid escape of the gas phase in the suspension under the condition that the volume increases rapidly, so that the flow conveying part or the attached degassing device has a better degassing effect. However, the increase in pulp temperature also creates favorable conditions for bacterial reproduction, and it is easy to form viscous pulp in the pulp and form fouling in pipes and machines, reducing the quality of pulp or causing secondary waste in paper production. When the white water closed circulation system, the above problems caused by the increase of pulp temperature are more likely to occur.