Extrusion & Post
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PET melt fracture
Problem Phenomenon
Sharkskin appears on the surface of PET sheet after extrusion speed is increased
Cause Analysis
When the shear rate exceeds the critical value, melt fracture occurs and the surface becomes periodically rough; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience; this mechanism has been repeatedly verified by industry data and should be confirmed first during troubleshooting
Solution
Lower the line speed or increase the melt temperature to reduce viscosity; polish the die lip flow channel; improve with processing aids; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Melt fracture is the speed upper limit; optimize the flow channel before increasing speed; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a reference for troubleshooting similar problems in the future
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