Injection Molding
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PET shear rate and brittleness
Fenómeno del problema
After excessive injection speed, PET products become brittle and fail impact tests in batches
Análisis de la causa
Excessive injection speed creates excessive shear rate; shear degradation of PET melt breaks molecular chains; the product appearance is normal but brittleness increases and mechanical properties quietly deteriorate
Solución
① Control injection speed so that shot filling is completed within 3-5 seconds; ② gate design avoids high-shear narrow slits; ③ perform impact sampling verification on brittle parts; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Conclusión clave
PET shear embrittlement is a hidden defect; 3-5 second shot time is the empirical upper limit, and impact sampling is the fallback verification; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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