Material Drying
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Bubbles/Pores on the Surface of Polypropylene Extruded Products
Fenómeno do problema
Bubbles or pores appear on the surface or cross-section of the extrudate, and the product density decreases.
Bubbles not only affect appearance but also reduce the mechanical strength and pressure resistance of the product, and are common in pipe and profile extrusion.
Análise das causas
(1) The moisture content of the raw material exceeds the standard, and the moisture vaporizes at high temperature to produce bubbles
(2) The screw venting is poor, and air is entrained in the melt
(3) The barrel temperature is too high, and the material thermally degrades to produce gas
(4) The screw speed is too fast, and the venting time is insufficient
(5) The content of low-molecular volatiles in the raw material is high
Solução
(1) Fully dry the raw material, and control the moisture content of polypropylene below 0.02%
(2) Check the venting section design, and use a vented extruder when necessary
(3) Appropriately reduce the barrel temperature to a reasonable value within the range of 200-280°C
(4) Reduce the screw speed to increase the residence time of the material in the venting section
(5) Select a raw material grade with low volatile content
Conclusão principal
Bubbles are caused by moisture vaporization or gas entrainment, and need to be solved from raw '2079851475616104451 and the venting system.
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