Injection Molding
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PMMA Stress Cracking
Problem Phenomenon
Products crack during assembly, solvent contact or after storage, often starting from sharp corners and screw bosses.
Cause Analysis
PMMA is brittle and sensitive to residual stress; high stress from fast injection, cold demolding, sharp corners and press fits cracks under solvent or load.
Solution
①Slow injection; ②Sufficient cooling and gentle demolding; ③Change sharp corners to rounds (25%~60% of wall thickness); ④Anneal at 70~80℃ for 2~4 hours; ⑤Avoid contact with incompatible solvents.
Key Takeaway
PMMA delayed cracking = the delayed detonation of internal stress, annealing is the insurance.
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