Extrusion & Post
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HDPE Melt Fracture Sharkskin
Problem Phenomenon
Extruded product surface shows periodic rough texture like sharkskin, with loss of gloss
Cause Analysis
When HDPE extrusion speed exceeds the critical shear rate, the melt surface fractures; low die lip temperature increases melt viscosity and wall shear stress, making sharkskin appear earlier
Solution
①Reduce extrusion speed below the critical shear rate; ②increase die lip temperature to reduce wall shear stress; ③add fluoropolymer processing aid to promote wall slip; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Sharkskin is a shear critical phenomenon in HDPE extrusion; reducing speed, increasing mold temperature, and adding PPA work together; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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