Extrusion & Post
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PVC Pipe Extrusion Melt Fracture
Fenómeno do problema
Pipe outer surface periodically rough, sharkskin-like.
Análise das causas
Exit shear exceeds critical; low die temperature, high speed; PVC high-viscosity melt is prone to melt fracture at high speed; during on-site troubleshooting, verify item by item according to this mechanism, avoid blindly adjusting the machine based solely on experience.
Solução
①Increase die temperature by 3~5℃ to reduce exit shear; ②Reduce injection speed to reduce shear heat and flow disturbance; ③Polish die lips to reduce exit resistance; ④Optimize internal/external lubrication balance to improve plasticization and surface quality; ⑤Evaluate adding processing aids (such as PPA).
Conclusão principal
PVC melt fracture = 'shear exceeding limit': raise temperature, reduce speed, polish, optimize lubrication; PVC is heat-sensitive, raising temperature must be cautious — lubrication and speed adjustment are often safer.
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