Sep. 30, 2020
3 Filter installation device
Under normal circumstances, the installation method of the filter device is: the roughest filter is facing the protective plate, and the finest filter is facing the extruder.
For example, the arrangement of the filter screen from the protection plate to the extruder may be 20 mesh/40 mesh/60 mesh, because this arrangement can prevent the filter from being blocked and "blow" impurities into the protection plate. Inside the opening.
If the finest filter screen is 80 or more meshes, in order to prevent the filter screen from being blocked by the rotating movement of the molten material or large impurities, you can put a coarse filter screen in front (such as 20/100/60/ 20 mesh arrangement). Because this type of device looks the same from both sides, in order to ensure that they will not be reversed, sometimes a symmetrical arrangement (20 mesh/60 mesh/100 mesh/60 mesh/20 mesh) is used.
Some deliberately set the filter upside down, so that the coarse filter first filters out larger particles on the upstream surface. They believe that this method can allow more side molten material to pass through and make the material on the upstream surface of the protective plate less decomposed.
4 Notes on the filter
As extruder screens are prone to rust, avoid moisture during storage, otherwise rust will appear in the extrudate. What's more serious is that the rusty filter screen is easy to break and leak the filtered impurities. Therefore, the filter screen should be stored in a plastic bag or rust-proof paper.
When blowing and cleaning the protective plate, it is easy to reverse the phenomenon, which will damage the sealing surface and make the sliding surface mismatch, resulting in leakage. In this way, not only will the cleaning work be time-consuming, but the leaked molten material may affect the value of the thermocouple, damage the heater, and sometimes even cause a fire.
For a single-exhaust, two-stage extruder, if the back pressure at the filter becomes larger, the output of the second stage will decrease, but the output of the first stage will not be affected. When the back pressure increases to approximately 2500lb/in2 (1lb=0.4536Kg, 1in=25.4mm), the molten material from the first stage begins to slowly leak into the exhaust hole. In order to avoid this kind of phenomenon, the filter must be replaced when the pressure is low. In addition, the gear pump behind the filter device also has the effect of preventing the molten material from leaking into the exhaust hole.
If a custom Single Extruder Screen filters out large pieces of debris (such as paper), it will suddenly and completely fail, which will cause the pressure of the extruder to quickly peak. Therefore, in order to prevent the above situation from happening, there must be a safety system such as a safety diaphragm, a safety pin or an alarm connected to a pressure gauge.