Processing Machinery
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Rough Inner Wall of High-Density Polyethylene Extruded Products
Problem Phenomenon
The inner wall of the pipe or profile is rough and uneven, with visible stripes or particles.
A rough inner wall affects the fluid resistance and hygiene performance of the pipe, and bacteria may breed in water supply pipes.
Cause Analysis
（1）The mandrel temperature is low, and the melt undergoes stick-slip flow on the mandrel surface
（2）The mandrel surface finish is insufficient or worn
（3）The compressed air pressure is insufficient (during internal pressure sizing)
（4）The melt temperature is low, and the flowability is poor
（5）The screw plasticization is insufficient, and there are unmelted particles in the melt
Solution
（1）Appropriately increase the mandrel temperature to match the die temperature (180-260°C range)
（2）Polish the mandrel surface to Ra≤0.2μm, and chrome-plate when necessary
（3）Check the compressed air system to ensure stable pressure
（4）Appropriately increase the barrel temperature to a reasonable value within the 180-260°C range
（5）Optimize the screw design and rotation speed to ensure sufficient plasticization
Key Takeaway
A rough inner wall is caused by low mandrel temperature or poor surface condition, and needs to be solved from temperature control and mold maintenance.
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