Injection Molding
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Strength Decrease of PE Injection Molded Products
Problem Phenomenon
PE parts fail mechanical tests and are brittle, yet show no obvious appearance abnormality.
Cause Analysis
An excessive regrind proportion brings molecular weight decrease, too long heat history causes degradation, weld lines happen to pass through stressed areas forming weak bands, and water-containing regrind triggers internal microvoids; these factors all quietly weaken strength without changing the appearance, which appearance inspection simply cannot detect.
Solution
①Control the regrind proportion and re-dry it; ②Stabilize heat history (melt temperature, residence time); ③Keep weld lines away from stressed areas; ④Investigate internal microvoids; ⑤Carry out sampling inspection of mechanical properties.
Key Takeaway
PE 'strength decrease with normal appearance' = a material history problem: regrind, heat history, and weld line position are the three major suspects; strength must be guaranteed by process data and sampling inspection, not by appearance alone.
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