Processing Machinery
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LLDPE screw speed
Problem Phenomenon
After increasing screw speed, LLDPE sharkskin becomes severe
Cause Analysis
LLDPE is highly sensitive to shear rate, increasing speed immediately exceeds the critical value; when troubleshooting on site, verify item by item according to this mechanism to 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
Control speed by the melt fracture critical value; add PPA to widen the window; large die gap; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability; change only one variable at a time and record parameter changes to facilitate locating effective measures
Key Takeaway
LLDPE speed management is stricter than LDPE; 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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