Molds & Tooling
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Sticking of PP products to the mold (difficult demolding)
Problem Phenomenon
The product tightly wraps the core or adheres to the cavity, is scratched and deformed during demolding, requires manual prying, and seriously affects cycle time and appearance.
Cause Analysis
PP shrinks greatly and has a strong gripping force on the core; excessive holding pressure and high melt/mold temperature make the gripping force even greater; insufficient draft angle, poor cavity polishing or local galling, and the vacuum suction effect of deep cavities all significantly increase the demolding resistance.
Solution
①Reduce the holding pressure and melt temperature to reduce the gripping force; ②ensure a sufficient draft angle (generally ≥1°, larger for grained surfaces) and polish along the demolding direction; ③demold only after sufficient cooling; ④provide air intake/anti-vacuum structures for deep-cavity parts; ⑤balance the ejection system to avoid one-sided force.
Key Takeaway
For PP mold sticking, first 'reduce pressure and temperature' to lessen gripping, then 'fix draft and polish' to reduce resistance, and finally deal with deep-cavity vacuum suction; the polishing quality of the mold along the demolding direction often affects the feel of 'easy or hard to demold' more than the draft angle.
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