Material Drying
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Bubbles or silver streaks in PET preforms
Fenómeno do problema
In injection-stretch-'2079851475616104457, bubbles and silver streaks appear inside or on the surface of PET preforms, transparency decreases.
Análise das causas
Insufficient drying; moisture content exceeds 30ppm (0.003%); at high temperature moisture hydrolyzes with PET producing gas.
Solução
Use a dehumidifying dryer, drying temperature 160-170°C, time 4-6h, dew point ≤-40°C, test moisture after drying, prevent re-moistening.
Conclusão principal
Strict PET drying is the prerequisite for preform quality; moisture control must reach ppm level.
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