Burn marks (also known as burn marks or scorching) in injection molded parts are a common defect, primarily caused by poor mold venting, excessively high injection speed, overly high melt temperature, or trapped air/gases being compressed and ignited.
To effectively prevent burn marks in injection molded parts, optimize from the following aspects:
- Optimize mold venting: Add vent slots (depth 0.01–0.03 mm) at the mold ends and areas prone to gas entrapment to ensure smooth gas escape. Regularly clean vent channels to prevent blockages.
- Adjust process parameters: Reduce injection speed (especially using slower filling in the final stage), lower melt temperature by 10–20°C, and appropriately decrease injection pressure to avoid excessive air compression.
- Material handling: Ensure raw materials are thoroughly dried (moisture content <0.2%) to prevent moisture vaporization from generating gases. Select resins with moderate flowability.
- Mold design improvements: Reasonably position and size gates to avoid sharp corners or dead zones. When necessary, adopt vacuum venting or gas-assisted injection molding.
By implementing these preventive measures, you can significantly improve the surface quality of injection molded parts and reduce scrap rates.