Extrusion & Post
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Uneven wall thickness of linear low-density polyethylene extruded pipes
Problem Phenomenon
Pipe wall thickness is uneven in the circumferential direction, showing eccentric wall phenomenon.
Uneven wall thickness affects pipe pressure resistance; the thin-wall side ruptures first under pressure, seriously affecting pipe safety in use.
Cause Analysis
(1) The die and mandrel are not concentric, and the gap is uneven
(2) Melt temperature is uneven, and the temperature difference in the circumferential direction of the die is large
(3) Extruder output is uneven and melt pressure fluctuates
(4) 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 mandrel, with circumferential gap error not exceeding ±0.05mm
(2) Check die heating band distribution to ensure circumferential temperature difference does not exceed ±3°C (190-250°C range)
(3) Check extruder plasticization stability to ensure uniform output
(4) Align the center line of the haul-off device with the die center
(5) Check the sizing sleeve; replace 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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