Injection Molding
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Uneven Surface Gloss of High-Density Polyethylene Injection-Molded Products
Fenómeno del problema
The gloss of different areas on the product surface differs obviously, with local dull or high-gloss areas appearing, affecting appearance consistency.
Uneven gloss is usually related to the melt flow direction and differences in cooling conditions, and is especially common in large flat products.
Análisis de la causa
(1) The surface finish of the mold cavity is inconsistent, with local wear or uneven polishing
(2) The melt temperature is uneven, and temperature differences at the flow front lead to different surface replication effects
(3) The mold cooling system design is unreasonable, and the cooling rates of various parts differ greatly
(4) The injection speed is improper, the melt flows unsteadily in the cavity, and different textures form on the surface
(5) Too much release agent is used or it is uneven, affecting the surface gloss of the product
Solución
(1) Check and re-polish the mold cavity to ensure consistent surface finish, with roughness Ra≤0.4μm
(2) Optimize the barrel temperature setting to ensure uniform melt temperature, with the temperature difference controlled within ±5°C (range 180-260°C)
(3) Improve the cooling water channel design to ensure uniform cooling of all parts of the cavity, with a temperature difference not exceeding 5°C
(4) Adjust the injection speed and adopt multi-stage injection to make the melt fill the mold smoothly
(5) Reduce the amount of release agent or switch to a silicone-free release agent to ensure uniform coating
Conclusión clave
Uneven gloss reflects the inconsistency of the 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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