Processing Machinery
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PC Thermal Degradation Yellowing
Problem Phenomenon
After the melt temperature is too high or the residence is too long, the whole product turns yellow, and black specks appear in the sprue
Cause Analysis
PC undergoes thermo-oxidative degradation above 320°C or during long residence in the barrel, with molecular chain scission and generation of chromophoric groups; shear heat superimposed on the set temperature makes the actual melt temperature exceed the standard without being noticed
Solution
①Control the melt temperature not to exceed 320°C; ②if the machine stops for more than 15 minutes, empty the barrel and lower the temperature; ③produce small parts on small machines to control the melt residence time; after adjustment, take samples continuously to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Yellowing is the first signal of PC thermal degradation; dual management of the temperature upper limit and residence time, and shutdown handling specifications must be written into the work instruction; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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