Extrusion & Post
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Uneven Wall Thickness of High-Density Polyethylene Extruded Pipes
Problem Phenomenon
The wall thickness of the pipe in the circumferential direction is uneven, showing an eccentric wall phenomenon.
Uneven wall thickness affects the pressure resistance of the pipe; when pressurized, the thin-walled side breaks first, seriously affecting the safety of pipe use.
Cause Analysis
（1）The die and the mandrel are not concentric, and the gap is uneven
（2）The melt temperature is uneven, and the temperature difference in the circumferential direction of the die is large
（3）The extruder output is uneven, and the melt pressure fluctuates
（4）The haul-off speed is unstable or the haul-off center is not concentric with the die
（5）The pipe sizing sleeve is worn or installed incorrectly
Solution
（1）Adjust the concentricity of the die and the mandrel, with the circumferential gap error not exceeding ±0.05mm
（2）Check the distribution of the die heating rings to ensure the circumferential temperature difference does not exceed ±3°C (within the 180-260°C range)
（3）Check the plasticization stability of the extruder to ensure uniform output
（4）Align the centerline of the haul-off device with the center of the die
（5）Check the sizing sleeve; replace it if severely worn, and ensure concentric installation
Key Takeaway
Uneven wall thickness is caused by uneven die gap or uneven temperature, and needs to be solved from mold precision and temperature uniformity.
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