Injection Molding
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PET shear rate and brittleness
Problem Phenomenon
After excessive injection speed, PET products become brittle and fail impact tests in batches
Cause Analysis
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
Solution
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
Key Takeaway
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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