Molding Process
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HDPE large-diameter pipe sag (Sag)
Problem Phenomenon
For large-diameter thick-walled pipes above 630mm, the wall thickness is severely thin at the top and thick at the bottom, with material accumulation at the bottom, and concentricity and ovality deteriorate.
Cause Analysis
The inner wall of the thick-walled pipe remains molten for a long time, and the material flows from top to bottom before cooling and sizing to form sag; the larger the pipe diameter, the thicker the wall, and the lower the line speed, the more severe the sag.
Solution
①Preset the die gap with a wide top and narrow bottom eccentric compensation before startup; ②select low-sag bimodal PE100 material; ③strengthen sizing with internal and external double-sided cooling; ④use four-point ultrasonic thickness measurement with segmented heating for fine-tuning.
Key Takeaway
Sag is the core challenge of large-diameter thick-walled pipes; die eccentric compensation plus low-sag material plus double-sided cooling is the industry standard combination, and thickness measurement feedback can reduce trial-and-error times.
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