Injection Molding
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Uneven surface gloss of random copolymer polypropylene injection molded products
Fenómeno del problema
Gloss differences are obvious in different areas of the product surface, with locally darkened or high-gloss areas, affecting appearance consistency.
Uneven gloss is usually related to melt flow direction and cooling condition differences, and is especially common in large flat products.
Análisis de la causa
(1) Mold cavity surface finish is inconsistent, with local wear or uneven polishing
(2) Melt temperature is uneven; temperature differences at the flow front cause different surface replication effects
(3) Mold cooling system design is unreasonable, with large cooling rate differences across areas
(4) Improper injection speed; melt flows unsteadily in the cavity, forming different surface textures
(5) Excessive or uneven use of release agent affects product surface gloss
Solución
(1) Check and re-polish the mold cavity to ensure consistent surface finish, with roughness Ra≤0.4μm
(2) Optimize barrel temperature settings to ensure uniform melt temperature, with temperature difference controlled within ±5°C (190-260°C range)
(3) Improve cooling water channel design to ensure uniform cooling of all cavity areas, with temperature difference not exceeding 5°C
(4) Adjust injection speed, using multi-stage injection to make the melt fill the mold smoothly
(5) Reduce release agent dosage or switch to silicone-free release agent, ensuring uniform application
Conclusión clave
Uneven gloss reflects inconsistencies in mold surface condition and melt flow and needs to be improved from three aspects: mold polishing, temperature uniformity and injection process.
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