The screen is an industrial fabric which is woven with raw materials such as silk, metal wire or synthetic fiber, has uniform and stable vent holes on the surface, and has screening and filtering functions. The mesh of the screen is customarily called. The size of the screen is often expressed in terms of the number of holes per unit length (mesh) and also the width of each hole. China's national standards are expressed in terms of the number of holes per centimeter, such as 20 holes/cm.
The filter screen is a group of wire meshes of different meshes supported by the sieve plates before the material of the extruder, and its function is to filter the melt flow and increase the flow resistance, thereby filtering out mechanical impurities and improving the effect of mixing or plasticizing. If the filter is filtered into large pieces of debris (such as paper), it will suddenly fail completely, which will quickly bring the pressure of the extruder filter to a peak. Therefore, in order to prevent this from happening, there must be a safety system such as a safety diaphragm, a safety pin or an alarm connected to the pressure gauge.
For a single-exhaust, two-stage extruder, if the back pressure at the filter becomes larger, the second stage of production will be reduced, but the production of the first stage will not be affected. The molten material from the first stage begins to leak into the vent. To avoid this, be sure to replace the filter when the pressure is low. In addition, the gear pump behind the filter device also prevents the molten material from leaking into the vent hole.