Injection Molding
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Whitening in the gate area of PET preforms
Fenómeno del problema
A white opaque area appears near the gate of the PET preform, with reduced strength, sometimes accompanied by cracks.
Análisis de la causa
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.
Solución
Increase gate diameter to ≥0.8-1.2mm; reduce injection speed (multi-stage injection); increase mold temperature in this area.
Conclusión clave
PET gate whitening is the result of stress-induced crystallization; reducing shear is the fundamental measure.
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