Molds & Tooling
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PP Ejector Whitening and Cracking
Fenómeno do problema
White round spots and radial white marks appear at ejector pin positions; in severe cases, puncture or ejection cracks occur—high incidence in deep-cavity and thin-walled parts.
Análise das causas
PP's crystallization shrinkage generates large gripping force on the core with high demolding resistance; small ejection area, insufficient cooling time (part still hot with low strength), insufficient draft angle, and unbalanced ejection all make local ejection force exceed the part's bearing capacity, causing stress whitening or even ejection cracking.
Solução
①Extend cooling time to lower part temperature at ejection; ②increase ejector pin count, enlarge pin diameter, or use stripper plates/blocks to disperse ejection force; ③reduce holding pressure and gripping force; ④ensure sufficient draft angle and polish the core; ⑤optimize ejector pin layout to place ejection points at high-rigidity locations.
Conclusão principal
The main control line for PP ejector whitening/cracking is 'reduce gripping force + disperse ejection force + sufficient cooling': first extend cooling, then enlarge ejection area, finally reduce holding pressure; whitening itself is an alarm of excessive ejection force—disperse the force to eliminate it.
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