Injection Molding
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Low Hardness of High-Density Polyethylene Injection Molded Products
Problembeschreibung
The surface hardness test value of the product is lower than the standard requirement, and the surface is easily scratched or indented.
Low hardness affects the wear resistance and surface scratch resistance of the product, and affects the service performance in products requiring surface hardness.
Ursachenanalyse
（1）The mold temperature is low, and the crystallinity of the high-density polyethylene is low, resulting in decreased hardness
（2）The barrel temperature is high, the material is partially degraded, and the molecular weight is reduced
（3）The holding pressure is insufficient, and the product density is low
（4）The cooling time is insufficient, and the crystallization process is not completed
（5）The material grade is improperly selected, and the hardness index does not meet the requirements
Lösung
（1）Appropriately increase the mold temperature to a higher value within the 30-80°C range to increase the crystallinity
（2）Control the barrel temperature at a reasonable value within the 180-260°C range to avoid overheating
（3）Increase the holding pressure to 80-120MPa to ensure the product is compact
（4）Extend the cooling time to ensure sufficient crystallization
（5）Select a suitable grade, and add a nucleating agent when necessary to increase the crystallinity
Wichtigste Erkenntnis
Low hardness is mainly caused by insufficient crystallinity or material degradation, and needs to be improved by increasing the mold temperature and holding pressure.
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