Extrusion & Post
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Uneven Wall Thickness of Polypropylene Extruded Pipe
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 under pressure, the thin-wall side breaks first, seriously affecting the use safety of the pipe.
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 discharge 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 a circumferential gap error not exceeding ±0.05mm
(2) Check the distribution of the die heating bands to ensure the circumferential temperature difference does not exceed ±3°C (range 200-280°C)
(3) Check the plasticization stability of the extruder to ensure uniform discharge
(4) Adjust the center line of the haul-off device to align with the center of the die
(5) Check the sizing sleeve; replace it if it is severely worn, and ensure concentricity during 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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