Material Drying
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PET Preform Excessive Drying Crystallization
Fenómeno del problema
The preform surface is locally whitened, and after blowing there is fixed-position thick haze.
Análisis de la causa
Drying temperature too high (over 165℃) or a single batch statically baked too long causes the preform surface to crystallize in advance and become brittle; during '2079851475616104457 the crystallized zone cannot be oriented and stretched, and it is amplified into white haze.
Solución
①Control drying temperature at 140~160℃, strictly prohibit exceeding 165℃; ②shorten the single-batch drying cycle to avoid static baking; ③turn the material in the hopper to prevent local overheating; ④downgrade whitened preforms for use.
Conclusión clave
Drying is not the longer the better; over-drying = pre-crystallization.
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