Injection Molding
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Whitening in the gate area of PET preforms
Problem Phenomenon
A white opaque area appears near the gate of the PET preform, with reduced strength, sometimes accompanied by cracks.
Cause Analysis
Excessively high shear rate at the gate causes stress-induced crystallization, producing micro crystal grains that scatter light; gate size is too small or injection speed is too fast.
Solution
Increase gate diameter to ≥0.8-1.2mm; reduce injection speed (multi-stage injection); increase mold temperature in this area.
Key Takeaway
PET gate whitening is the result of stress-induced crystallization; reducing shear is the fundamental measure.
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