One of the most important functions of polyester forming fabrics is dehydration.Generally speaking, the size of the dewatering capacity depends on the ratio of the slurry, the beating condition, the auxiliary materials and the model of the paper machine. For the forming fabrics itself, the dewatering capacity is mainly determined by the weave, structure, thread diameter and weft density of the forming net.
The polyester forming fabrics is heat-set to elongate the warp threads and shrink the weft threads. Therefore, the geometry of the net structure has changed, and the interweaving point has also changed.
From the surface, the void volume of the forming fabrics is correspondingly smaller than that of the copper mesh, and the water filtration is also poor. However, as an object in a two-dimensional space, the dewatering performance is explained by the projected opening area, that is, the polyester forming fabrics is regarded as directly dewatering vertically according to the projected opening.
In fact, there are many factors for net dehydration, not only the size of the opening rate, but also the thickness of the net, the wettability of the net and other conditions.
According to the filtering theory, the net actually has a three-dimensional fabric. The factors that affect the water filterability include: the void volume of the forming mesh, the total wetted surface and the surface energy. Therefore, the production of polyester forming fabrics must consider expanding the void and volume, and adopting the multi-heald weaving method to improve the water filtration performance of the polyester forming fabrics.
In the papermaking process, the use of finer polyester forming fabrics can increase the retention rate of fine fibers and auxiliary materials, but to use a finer mesh, first consider the dewatering capacity of the forming mesh, rather than unilaterally considering the retention rate.
Changing the polyester forming fabrics from a single layer to a multilayer mesh can also increase the retention of fine fibers and auxiliary materials.
However, the conditions of the paper machine must be considered, such as water pressure, panels and other conditions.
The wet paper sheet is formed in the wire section of the paper machine and most of the water has been removed, and it already has a certain strength, but the wet paper sheet has to be passed to the next process, which is insufficient.
In order to achieve the purpose of transferring the wet paper to the next process, open threading, sticky paper threading, vacuum threading, etc. are commonly used at present, but no matter which threading method is used, the bottom line is that the adhesion between the paper and the net is required. Keep it as low as possible, that is, the paper is easy to peel off the net.
There are many factors that affect the peeling of wet paper. The difficulty of peeling off the polyester forming mesh depends on the flatness of the mesh surface and the tightness of the mesh structure, that is, the larger the T value (T value-warp thread density plus weft thread density), the smaller the number of fibers extending into the holes of the forming mesh. The wet paper sheet is also easier to peel off, that is, the polyester forming fabric with a larger T value is easier to peel off the paper sheet.
From the characteristics of polyester monofilament, we know that the elongation of polyester monofilament is greater than that of metal wire. Although the polyester forming mesh undergoes a heat setting process in the weaving process, the elongation of the polyester mesh is still greater than that of the copper mesh. Therefore, the use of polyester forming nets should consider the elongation of the nets on the machine, and whether the net tightening device can play the role of net tightening.
Under the conditions of the production paper type permit, a thicker or more warp polyester forming fabric has better longitudinal stability, and the same is true in the transverse direction. Therefore, the dimensional stability of the multilayer net is better than that of the single-layer net.
Because the rigidity of polyester monofilament is not as good as that of metal wire, it is relatively soft, so the horizontal and vertical stiffness of the mesh is not as good as that of copper mesh. However, after heat setting, a polyester forming fabric with a larger T value can improve the stiffness of the forming fabric.
The polyester forming mesh has high tensile strength, fatigue resistance, abrasion resistance, and chemical corrosion resistance. Therefore, the service life of the polyester forming mesh is 3 to 5 times that of the copper mesh, and the longest can be more than 10 times.
The polyester forming fabric has good corrosion resistance. Soak in 5% hydrochloric acid or 20% sulfuric acid and 2.5% NaOH solution for 2h at room temperature, the strength will not be affected. Organic solvents such as acetone, ethanol and gasoline do not harm the net.
The polyester forming Fabric has good abrasion resistance and good elasticity. It is not easy to deform the plastic due to wrinkles and collisions during the process of handling and setting the net, so that the net cannot be used.
