The reason why plate processing enterprises are unwilling to use the filter screen: when the blocked filter screen is replaced in the plastic plate production equipment,the pressure will suddenly drop,and the temperature of the molten material may also drop, resulting in the continuous change of the product size. In order to maintain the same size of its own products, the screw speed of the extruder can be adjusted in time, and the linear growth rate of the extruder can also be effectively adjusted. When extruding round products, these data changes may not directly lead to serious problems, but when extruding flat or irregular products, the change process of molten material temperature may affect the overall dimensions of main products. For example, in a flat mold, the colder molten material may make the center of the sheet thinner and the periphery thicker. In this case, after the filter screen changer is equipped, the gear pump can fully ensure that the molten material enters the mold stably, which can prevent the occurrence of the above problems. However, the change of temperature environment of molten material after the replacement of filter screen still needs teachers to adjust the mold. At the same time, because the gear pump is easy to be damaged by hard impurities, the gear pump also needs to be protected by a fine filter screen.
Some hardboard processors do not want to use this kind of screen, because this kind of screen will raise the temperature of PVC melt material and is easy to degrade, which requires the material to have better thermal stability, thus increasing the cost of the material. If a PVC special filter screen converter is used, the cost will also be increased. Therefore, most UPVC processors either avoid using filters or use coarse filters without converters to filter only larger particles.
How to select the filter screen?
Steel wire is a commonly used metal filter material for extruders. Although the price of a stainless steel company is relatively expensive, it can be used to treat some PVC profile production lines or other workplaces to avoid rust. Nickel alloy filter screen is used in occasions that are inevitably corroded by fluoropolymer network or PVDC.
Most of the screen holes of the filter are woven with squares, and the number of lines in each direction is the same. The Dutch weaving
method uses thick lines in the horizontal direction and is defined as an even number, for example,32x120/in(1 in=25.4 mm). The filter screen obtained by the Dutch knitting method does not need to be equipped with a parallel screen in the filter device, which plays a fine filtering role.
Generally, in this case, the mesh size of the filter screen(or the number of wires per inch)is 20~150 or more. The structure of the filter screen with 20 sieve is relatively coarse; The filter screen material with 40~60 sieve is relatively fine; The filter screen with 80~150 sieve is very fine.