Effect Of Extruder Filter On Plastic Extrusion

  Effect of Extruder Filter on Plastic Extrusion

  During the extrusion of the extruder, the molten material is conveyed through the filter to the mold. The filter allows the material to be filtered and improves the mixing effect of the material. However, the filter can also cause fluctuations in the process, resulting in back pressure and molten material temperature rise, and sometimes will be reduced.

  The filter of the extruder is fixed to a protective plate of a porous or trough so that a seal is formed between the extruder and the mold. Clean the pressure generated by the filter is small, may only 50 ~ 100lb / in2 (1lb = 0.4536Kg, 1in = 25.4mm). As the pressure increases, the amount of impurities in the resin retained on the filter becomes more, thereby blocking the filter.

  The filter will affect the temperature of the molten material

  When replacing the blocked filter, the pressure will suddenly drop, the temperature of the molten material may also be reduced, resulting in product size changes. In order to maintain the same size of the product, you can adjust the screw speed of the extruder, you can also adjust the linear speed of the extruder. These changes may not cause serious problems when extruding round products, but changes in the temperature of the molten material may affect the dimensions of the product when extruding flat or irregularly shaped products. For example, in a flat mold, the cold melt material may make the center of the sheet thinner, leaving the periphery thicker. This can be corrected by automatic or manual adjustment of the mold.

  Behind the filter converter is equipped with a gear pump that ensures that the molten material stably enters the mold, which prevents the above problems from occurring. However, the temperature change of the molten material after the replacement of the filter still needs to be solved by adjusting the mold. At the same time, since the gear pump is easily damaged by hard impurities, the gear pump also needs to be protected by fine filters.

  Some hard PVC processors do not want to use the filter because the filter will make the PVC melt material temperature and easy to degrade, which requires better thermal stability of the material, thereby increasing the cost of materials. If you use PVC-specific filter converter, will increase the cost. So most hard PVC processors either avoid using the filter or use a coarse filter without a converter to filter only larger particles of impurities.