Material Drying
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Bubbles/pores on the surface of polyolefin plastomer extruded products
Fenómeno del problema
Bubbles or pores appear on the surface or cross section of the extrudate, and the product density decreases.
Bubbles not only affect the appearance but also reduce the mechanical strength and pressure resistance of the product, and are common in pipe and profile extrusion.
Análisis de la causa
（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 low molecular volatile content in the raw material is high
Solución
（1）Fully dry the raw material, with the moisture content of the polyolefin plastomer controlled below 0.02%
（2）Check the venting section design, and use a vented extruder when necessary
（3）Appropriately lower the barrel temperature to a reasonable value within the range of 180-230°C
（4）Reduce the screw speed to increase the residence time of the material in the venting section
（5）Select raw material grades with low volatile content
Conclusión clave
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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