Material Drying
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General-purpose polyethylene injection molded products surface bubbles/voids
Problem Phenomenon
Round or elliptical bubbles of various sizes appear inside or on the surface of the product, with bulges or depressions visible on the surface.
Bubbles not only affect appearance, but also significantly reduce product density and mechanical strength, especially severe in thick-wall products.
Cause Analysis
（1） The raw material is not fully dried, moisture vaporizes at high temperature producing water vapor bubbles\
（2） Injection speed too fast, air in the cavity has no time to escape and is drawn into the melt\
（3） Holding pressure insufficient or holding time too short, voids produced by shrinkage at thick-wall parts are not fed\
（4） Barrel temperature too high （exceeding the 160-260°C upper limit）, material thermally degrades producing gas\
（5） Air is drawn in during screw retraction, and insufficient back pressure causes inadequate venting
Solution
（1） Fully dry the raw material, general-purpose polyethylene dried at 60-80°C for 2-4h, moisture content controlled below 0.02%\
（2） Adopt multi-stage injection, slow-fast-slow, reduce injection speed at the initial and final filling stages to reduce gas entrainment\
（3） Increase holding pressure to 80-120MPa, extend holding time to 15-25s, ensure thick walls are fully fed\
（4） Appropriately lower the barrel temperature to a reasonable value within the 160-260°C range to avoid thermal degradation\
（5） Increase back pressure to 5-10MPa, ensure adequate venting during screw pre-plasticization
Key Takeaway
Bubbles and voids are mainly caused by moisture vaporization, gas entrainment or insufficient feeding, and need to be systematically solved from raw '2079851475616104451, injection process and holding pressure parameters.
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