Injection Molding
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Bubbles/Voids Appearing on the Surface of Low-Density Polyethylene Injection Molded Products
Problembeschreibung
Round or elliptical bubbles of various sizes appear inside or on the surface of the product, and bulges or depressions are visible on the surface.
Bubbles not only affect the appearance, but also significantly reduce the product density and mechanical strength, and are particularly severe in thick-walled products.
Ursachenanalyse
（1）The raw material is insufficiently dried, and the water vaporizes at high temperature to produce water vapor bubbles
（2）The injection speed is too fast, and the air in the cavity has no time to be discharged and is involved in the melt
（3）The holding pressure is insufficient or the holding pressure time is too short, and the voids produced by the shrinkage of the thick-walled parts are not compensated
（4）The barrel temperature is too high (exceeding the 160-220°C upper limit), and the material thermally degrades to produce gas
（5）The screw sucks in air when retracting, and insufficient back pressure leads to insufficient venting
Lösung
（1）Fully dry the raw material; low-density polyethylene is dried at 60-80°C for 2-4h, and the moisture content is controlled below 0.02%
（2）Adopt multi-stage injection, slow first, then fast, then slow, and reduce the injection speed at the beginning and end of mold filling to reduce gas involvement
（3）Increase the holding pressure to 80-120MPa and extend the holding pressure time to 15-25s to ensure sufficient shrinkage compensation of the thick walls
（4）Appropriately reduce the barrel temperature to a reasonable value within the 160-220°C range to avoid thermal degradation
（5）Increase the back pressure to 5-10MPa to ensure sufficient venting during screw pre-plasticization
Wichtigste Erkenntnis
Bubbles and voids are mainly caused by water vaporization, gas involvement, or insufficient shrinkage compensation, and need to be systematically solved from raw '2079851475616104451, injection process, and holding pressure parameters.
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