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The cause of die swell in plastic mold

Plastic mold in the melt at the inlet side of the pressure drop in the export side of the phenomenon of expansion known as the end effect, also known as the inlet effect and the mold expansion effect.


When the polymer melt flows out of the conduit, the ambient pressure is greatly reduced or even completely disappears, which means that the macromolecules within the polymer suddenly become free, so that the elastic deformation energy stored in the macromolecules in the preceding flow is Released, resulting in the flow of deformation has been extended in the macromolecular chain to re-curl, the molecular chain spacing increases, resulting in increased free space within the polymer, so the volume corresponding to the expansion.


The inlet effect and the mold expansion effect are usually unfavorable to the molding of the plastic, especially in the injection molding, extrusion molding and drawing processes, which may lead to product deformation and distortion, reduce the dimensional stability of the plastic parts and may Internal stress generated within the body to reduce the physical and mechanical properties of plastic parts.


Increasing the length of the straight portion of the tube or die, appropriately reducing the pressure at the time of molding and increasing the molding temperature, and pulling or stretching the extrudate at an appropriate speed are all advantageous for reducing or eliminating the adverse effects of the end effect influences.




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