Processing Machinery
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HDPE film sharkskin melt fracture
Problem Phenomenon
Periodic rough ripples appear on the film surface, similar to sharkskin, and the gloss decreases.
Cause Analysis
When the melt passes through the die gap, the shear stress exceeds the critical value and melt fracture occurs; low die gap temperature, small gap or low melt index of the resin will all aggravate it.; when troubleshooting on site, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Raise the die head temperature by 10~20℃; ②widen the die gap; ③add PPA processing aid; ④switch to a high melt index or broad distribution resin.; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Sharkskin is the signature defect of shear instability; the three moves of heating up, widening the gap and PPA can quickly eliminate it, and adjust the resin if necessary.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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