Extrusion & Post
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Bending Deformation of High-Density Polyethylene Extruded Pipes
Problem Phenomenon
The pipe bends after extrusion, and the straightness is out of tolerance.
Bending deformation affects pipe installation and use, and is particularly prominent in long pipe production.
Cause Analysis
（1）The cooling on each side in the extrusion direction is uneven, and the shrinkage is inconsistent
（2）The haul-off device is not concentric with the die
（3）The cooling water tank is installed incorrectly or the water temperature is uneven
（4）Uneven pipe wall thickness causes different shrinkage in all directions
（5）The support after extrusion is improper, and the pipe's own weight causes bending
Solution
（1）Check the cooling system to ensure uniform cooling on all sides of the pipe
（2）Align the centerline of the haul-off device with the center of the die
（3）Correct the position of the cooling water tank and control the water temperature to be uniform
（4）Adjust the concentricity of the die and mandrel to ensure uniform wall thickness
（5）Add pipe support rollers to reduce self-weight deformation
Key Takeaway
Pipe bending is caused by non-uniform cooling or haul-off eccentricity, and needs to be solved from cooling uniformity and equipment alignment.
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