Material Drying
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Bubbles appear inside or on the surface of extruded products
Problem Phenomenon
Bubbles appear inside or on the surface of extruded products, voids visible in pipe or profile cross-sections
Cause Analysis
Raw material moisture content exceeds standard, vaporizing at high temperature
Extrusion temperature too high (exceeding the upper limit of 170-230°C), thermal degradation
Insufficient screw venting section, poor venting
Poor die venting
Regrind contains moisture
Solution
Fully dry the raw material under 75-85°C/3-4h conditions
Lower the extrusion temperature to a reasonable value of 170-230°C
Ensure the screw venting section is effective
Add die venting
Fully dry the regrind
Key Takeaway
Extrusion bubbles need to be addressed from drying and venting
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