Injection Molding
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PMMA Internal Stress Cracking
Fenómeno del problema
Products crack along gates and corners during storage or use, and cracking is significantly aggravated after contact with solvents such as alcohol.
Análisis de la causa
High injection pressure and low mold temperature result in high residual internal stress; PMMA is sensitive to stress cracking, and solvents invade stress concentration areas to induce and propagate silver-streak-like cracks.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solución
①Raise mold temperature to 70~80℃ to promote stress relaxation; ②reduce injection and holding pressure; ③anneal products at 80~90℃ for 2~4 hours; ④avoid sharp corner design.
Conclusión clave
Internal stress is the number one cause of PMMA cracking; high mold temperature plus annealing is the standard elimination method, and stress control and verification must be done in solvent-contact applications.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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