Injection Molding
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PET Preform Neck White Spot Crystallization
Problem Phenomenon
White crystallization spots appear on the threaded neck of the preform, affecting the neck appearance and sealing fit; after blowing, the white spot area is still white.
Cause Analysis
Too slow injection speed causes the melt front to cool and crystallize at the neck; sudden injection speed changes, melt viscosity too high or low mold temperature at the neck area all make the melt unable to fill quickly.
Solution
①Increase injection speed to avoid front cooling; ②keep the injection speed curve stable; ③appropriately raise the melt temperature to reduce viscosity; ④raise the mold temperature in the neck area.
Key Takeaway
Neck white spots reflect improper filling speed or temperature management; the neck no longer deforms in the blowing process, and defects from the injection stage are retained as-is, so they must be controlled at the source.
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