Views: 1 Author: Site Editor Publish Time: 2021-12-03 Origin: Site
The forming plate (also called the tissue plate) is the first element under the net behind the breast roll of the Fourdrinier paper machine, and it plays the role of supporting the net and controlling the dehydration of the net section.
As the width of the paper machine increases, the diameter of the breast roll increases. If the slurry flow is still near the center line of the breast roll, there will be a considerable distance from the mesh point to the first roll. If the speed of the paper machine is high, a large amount of dehydration will occur at the breast roll, which is suitable for some thin papers, but for some other paper machines, the severe dehydration during the initial forming is extremely unfavorable for the formation of the paper web. . It will make the fibers stand up and affect the strength of the paper; it will cause a large number of small fibers to leak out, causing poor performance on both sides of the paper; it will promote the initial deposition of the fiber layer to be too tight, which will affect the further smooth formation and dewatering of the pulp; even on the chest The rolls cause the copper mesh to sink, and the phenomenon of skipping on the mesh surface occurs, which affects the formation of the paper web. Therefore, a forming plate is installed behind the breast roll to slow down the dehydration of the pulp layer on the web, so that the initial sheet forming can be carried out without violent suction.
The most common forming boards are several long wooden flat plates. The first one is 100-200mm wide, and the others are narrower, usually 65-100mm wide with a spacing of 40-50mm.
On a modern high-speed Fourdrinier paper machine, the forming board is usually a box composed of a wide flat beam board and several small inclination chopping boards. The landing point of the slurry flow is on the plane near the front edge of the beam. After the slurry flows on the Internet, the slurry flow can be stabilized due to the slow dehydration of the plane beams. Then there are cutting board blades with an inclination angle of about 1° to cause low-intensity turbulence and proper dehydration to prevent the fibers from re-flocculating.
The design and use of forming plates are very important. To make the pulp maintain a stable longitudinal flow rate in the grid section without impact, firstly there must be a ground or planed forming plate; secondly, it must be strictly ensured that it is parallel to the lip plate; the distance between them must be adjusted to eliminate the leading edge of the forming plate The effect of backflow recoil; in addition, the front edge of the forming plate should be slightly inclined downward to overcome the impact of the pulp when sprayed on the surface of the forming plate, otherwise, the pulp will produce ridges on the forming plate. If the forming plate is too much lower than the net, it will cause the under-net water to backwash the net and destroy the stability of the pulp. The degree of inclination of the forming plate depends on the specific situation.
The surface layer of the forming plate must be made of anti-wear materials to reduce the wear and damage to the forming net. Generally, hardwood, polyethylene, phenolic laminates, rubber sheets containing molybdenum disulfide, polytetrafluoroethylene, high-density polyethylene, ceramics and other non-deformable wear-resistant materials can be used. The first four are mostly used in paper machines with a speed of about 300m/min, and the latter three can be used in higher-speed paper machines.
The formed plate made of alumina sintered ceramic panel has good performance. It is very wear-resistant, has a smooth surface, and can be made into a straight and sharp front edge to avoid forcing water back to the net and destroying the initial deposited fiber layer . Sintered ceramics have no affinity with most resins and can be kept clean for a long time without slurries or clogging, and there is very little maintenance work. However, it is difficult to manufacture and process, and the price is more expensive.
The above is the function of the forming plate on the Fourdrinier paper machine.