Injection Molding
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Uneven surface gloss of homopolymer polypropylene injection 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, especially common in large flat products.
Análisis de la causa
(1) Inconsistent mold cavity surface finish, local wear or uneven polishing
(2) Uneven melt temperature; flow front temperature differences cause different surface replication effects
(3) Unreasonable mold cooling system design, large cooling rate differences in various parts
(4) Improper injection speed; unstable melt flow in the cavity, different textures formed on the surface
(5) Excessive or uneven use of mold release agent, affecting product surface gloss
Solución
(1) Check and re-polish the mold cavity, ensure consistent surface finish, roughness Ra≤0.4μm
(2) Optimize barrel temperature settings, ensure uniform melt temperature, temperature difference controlled within ±5°C (200-280°C range)
(3) Improve cooling water channel design, ensure uniform cooling of cavity parts, temperature difference not exceeding 5°C
(4) Adjust injection speed, adopt multi-stage injection, make melt fill the mold smoothly
(5) Reduce mold release agent dosage or switch to silicone-free release agent, ensure uniform application
Conclusión clave
Uneven gloss reflects inconsistency of mold surface condition and melt flow; it needs to be improved from three aspects: mold polishing, temperature uniformity, and injection process.
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