Injection Molding
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PMMA Stress Cracking
Fenómeno del problema
Products crack during assembly, solvent contact or after storage, often starting from sharp corners and screw bosses.
Análisis de la causa
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.
Solución
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.
Conclusión clave
PMMA delayed cracking = the delayed detonation of internal stress, annealing is the insurance.
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