Material Drying
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Bubbles/pores on the surface of low density polyethylene extruded products
Problem Phenomenon
Bubbles or pores appear on the extrudate surface or cross-section, reducing product density.
Bubbles not only affect appearance but also reduce mechanical strength and pressure resistance; common in pipe and profile extrusion.
Cause Analysis
(1) Raw material moisture content exceeds standard; moisture vaporizes at high temperature producing bubbles
(2) Poor screw venting; air entrained in the melt
(3) Barrel temperature too high; material thermal degradation produces gas
(4) Screw rotation speed too fast, insufficient venting time
(5) High low-molecular volatile content in raw material
Solution
(1) Fully dry the raw material; control low density polyethylene moisture content below 0.02%
(2) Check venting section design; use a vented extruder when necessary
(3) Appropriately reduce barrel temperature to a reasonable value within the 160-220°C range
(4) Reduce screw rotation speed, increase material residence time in the venting section
(5) Select raw material grades with low volatile content
Key Takeaway
Bubbles are caused by moisture vaporization or gas entrainment; they need to be solved from raw '2079851475616104451 and the venting system.
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