Extrusion & Post
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PVDF Extrusion Melt Fracture Sharkskin
Problembeschreibung
【Problem phenomenon】After speeding up extrusion of PVDF pipes and cables, periodic rough sharkskin patterns appear on the surface and gloss is lost
Ursachenanalyse
When the shear rate exceeds the critical value, the melt alternately sticks and slips on the die wall surface, causing melt fracture; both Avient and LG Chem materials record that special processing aids can induce wall slip to eliminate sharkskin and increase speed
Lösung
Add PVDF-specific processing aids (PPA type) to reduce wall stress; increase the die temperature or lengthen the die lip land; speed reduction is a fallback measure, while aids allow the line to speed up
Wichtigste Erkenntnis
Sharkskin is eradicated with special PPA aids; speed reduction is only a stopgap measure; 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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