Molds & Tooling
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Brittleness Caused by Too Low Mold Temperature of PEEK
Problem Phenomenon
PEEK products are brittle after demolding, with obviously low notched impact strength; they break brittlely under stress, with flat fracture surfaces without ductile deformation features, and a cold crystallization peak can be seen in DSC testing.
Cause Analysis
When the mold temperature is below the 143℃ glass transition temperature, the melt is quenched to form an amorphous structure rather than a crystalline structure; PEEK's mechanical properties and wear resistance depend on the support of 30~35% crystallinity.
Solution
①Raise the mold temperature above 160℃, and up to 180~200℃ for thick-wall parts; ②Verify by testing crystallinity with DSC; ③Confirm that the mold heating system has sufficient power — a high-temperature oil temperature controller is essential equipment.
Key Takeaway
PEEK crystallinity is the mother of performance; products produced with mold temperature below Tg are essentially nonconforming; the DSC cold crystallization peak is direct evidence of insufficient crystallization and should serve as the standard method for dispute determination.
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