Molds & Tooling
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PET melt temperature too high causing degradation
Problem Phenomenon
The preforms turn yellow, IV testing shows a decline, the AA value rises, and carbonized black specks can be seen during barrel cleaning, confirming that the processing temperature exceeds the range the material can withstand.
Cause Analysis
When the melt temperature stays above the 290℃ upper limit for a long time, PET thermo-oxidative degradation accelerates; the superposition of screw shear heat and hot runner overshoot can also make the actual melt temperature exceed the set value.
Solution
①Adjust the temperatures of all zones back to the 270~290℃ window; ②actually measure the melt temperature to calibrate the thermocouple; ③reduce the screw speed to reduce shear heat; ④clean the hot runner to eliminate dead corners.
Key Takeaway
PET thermal degradation simultaneously produces the triple hazards of yellowing, AA increase, and IV decline; regularly measuring the actual melt temperature rather than only looking at the display is a basic requirement of temperature control management.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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