Material Drying
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Bubbles/pores on the surface of cross-linked polyethylene extruded products
Problem Phenomenon
Bubbles or pores appear on the surface or cross-section of the extrudate, and the product density decreases.
Bubbles not only affect appearance but also reduce the mechanical strength and pressure resistance of products, and are common in pipe and profile extrusion.
Cause Analysis
(1) Raw material moisture content exceeds standard, water vaporizes at high temperature producing bubbles
(2) Screw venting poor, air entrained in the melt
(3) Barrel temperature too high, material thermal degradation produces gas
(4) Screw rotation speed too fast, venting time insufficient
(5) High low-molecular volatile content in raw material
Solution
(1) Fully dry raw materials, control cross-linked polyethylene moisture content below 0.02%
(2) Check venting section design, use a vented extruder if necessary
(3) Appropriately reduce barrel temperature to a reasonable value within 170-220°C
(4) Reduce screw rotation speed to increase material residence time in the venting section
(5) Select raw material grades with low volatile content
Key Takeaway
Bubbles are caused by water vaporization or gas entrainment, and need to be solved from raw '2079851475616104451 and the venting system.
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