Extrusion & Post
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Bamboo-node pattern/melt fracture appears on the surface of polyolefin plastomer extruded products (Variant: strengthened measures)
Problembeschreibung
Periodic coarse ripples or bamboo-node-like undulations appear on the extrudate surface, and in severe cases the extrudate shape is distorted.
Melt fracture is a serious defect in the extrusion process and directly leads to product scrapping.
Especially on the original basis, additional attention is needed, and this problem is more prominent and requires key attention.
Ursachenanalyse
(1) Extrusion speed exceeds critical shear rate, melt flow unstable
(2) Die temperature too low, melt viscosity high
(3) Die sizing section length insufficient, melt not fully relaxed
(4) Resin molecular weight too high or molecular weight distribution too wide
(5) Improper die entrance angle, melt entrance flow unstable
(6) On the original basis, additional attention is needed: process parameter fluctuations or equipment state changes aggravate this problem
Lösung
(1) Reduce extrusion speed below the critical shear rate
(2) Increase die temperature to the higher value within 180-230°C to reduce melt viscosity
(3) Increase die sizing section length, generally 10-20 times the die diameter
(4) Select grades with moderate molecular weight distribution
(5) Optimize die entrance design, entrance angle 30-60°
(6) Add a small amount of processing aid (fluoroelastomer) to improve fluidity if necessary
(6) And strengthen process monitoring; on the original basis, additional attention is needed, paying special attention to parameter stability
Wichtigste Erkenntnis
Melt fracture is flow instability caused by extrusion speed exceeding the critical value, and the speed needs to be reduced, the temperature increased and the die design optimized.
Targeted preventive measures need to be taken in different production scenarios.
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