Processing Machinery
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COC Residence Time Too Long Degradation
Fenómeno do problema
COC production stops midway and resumes, products show yellowing, black specks and embrittlement, returning to normal only after purging many shots, optical performance fluctuates obviously.
Análise das causas
COC maximum allowable residence time in the barrel is about 15 minutes, thermal degradation occurs when exceeded; high Tg grades have high processing temperature, degradation speed is faster; degradation products contaminate subsequent melt.
Solução
①Strictly control residence time within 15 minutes; ②reduce barrel temperature to 170℃ in advance when shutdown is expected; ③fully purge and replace before resuming production; ④match machine shot volume with product weight when scheduling production.
Conclusão principal
The 15-minute residence red line is a hard constraint of the COC process; shutdown cooling operation must be written into the work instruction; the weight matching of machine and product is often overlooked but is the main cause of degradation.
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