Molds & Tooling
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PP Dimensional Post-shrinkage Drift
Problem Phenomenon
PP parts continue shrinking 24~72 hours after demolding, causing precision assembly out of tolerance.
Cause Analysis
Semi-crystalline PP continues crystallizing and shrinking after demolding (post-crystallization), more obvious in high-temperature environments; inconsistent measurement aging may be misjudged as process fluctuation.
Solution
①Extend in-mold cooling for more sufficient crystallization; ②appropriately raise mold temperature to promote in-mold crystallization; ③unify measurement aging (24 hours after molding); ④if necessary, anneal at 60~80℃ for 1 hour to accelerate stabilization.
Key Takeaway
PP dimensions should be managed by 'post-aging dimension'.
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