Injection Molding
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General-purpose polyethylene injection molded products uneven surface gloss
Problem Phenomenon
The gloss of different areas of the product surface differs significantly, with locally darkened 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 plate products.
Cause Analysis
（1） The 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） The mold cooling system design is unreasonable, with large differences in cooling rates at various parts\
（4） Improper injection speed, the melt flows unstably in the cavity, forming different surface textures\
（5） Too much or uneven mold release agent, affecting product surface gloss
Solution
（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 （160-260°C range）\
（3） Improve cooling water channel design, ensure uniform cooling at all cavity parts, temperature difference not exceeding 5°C\
（4） Adjust injection speed, adopt multi-stage injection, make the melt fill the mold smoothly\
（5） Reduce mold release agent dosage or switch to silicone-free release agent, ensure uniform coating
Key Takeaway
Uneven gloss reflects inconsistency between the mold surface state and melt flow, and needs improvement from three aspects: mold polishing, temperature uniformity and injection process.
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