Molding Process
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Brittle edges and crumb shedding of PP products
Problem Phenomenon
The edges of PP products are brittle and crack, shed crumbs, whiten at trimming areas, and have poor edge strength.
Cause Analysis
Sudden wall thickness changes at the edge or excessive holding pressure cause high internal stress at the edge, which cracks brittlely under external force; material degradation (too much regrind, long heat history) also makes the edge brittle; dull trimming tools aggravate edge chipping.
Solution
①Make fillet transitions at edges and avoid sudden wall thickness changes; ②appropriately reduce the holding pressure and internal stress; ③check the melt temperature and residence time to prevent degradation; ④control the regrind ratio; ⑤keep trimming tools sharp and optimize the trimming angle.
Key Takeaway
PP brittle edges = check both 'stress + degradation': first reduce stress (fillets, holding pressure), then control degradation (temperature, regrind), and finally manage trimming tools well; edge problems are often a barometer of the stress state of the whole part.
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