In the plastic injection industry, one of the most common visual defects that directly affect product quality is gray or silver streaks. In technical literature, this problem is also known as “splay.” These streaks appear on the product surface as lines, spots, or gloss marks and are generally considered an aesthetic defect. Especially in sectors with high quality expectations, such flaws may become unacceptable.
In this article, we at Vincita Plastik share the causes of gray and silver streaks and their lasting solutions, drawing on years of production experience.
What Are Gray and Silver Streaks?
In injection-molded plastic parts, fine, wavy, shiny, or hazy lines appearing on the surface are called gray or silver streaks. These marks typically form due to gas, moisture, or additive residues within the molten plastic. While they do not directly affect the mechanical properties of the product, they significantly reduce visual quality.
What Are the Main Causes of Gray and Silver Streaks?
- Granules that have not been properly dried release steam when heated during injection, causing microscopic explosions inside the mold.
- It is especially common in hygroscopic materials such as PA (polyamide), PET, PC, and ABS.
- Excessive speed and pressure cause turbulent flow of the material, creating gas marks on the surface.
- Incorrect mold design or ventilation; if the mold lacks adequate air venting channels, trapped air can create silver streaks.
- Material degradation or burning.
- Excessive heating of the material or prolonged residence in the mold can cause degradation within its structure.
- Incompatible or poorly dispersed additives (such as pigments) can cause splay.
Prevention and Solutions for Gray and Silver Streaks
- The material should be dried at the appropriate temperature and duration according to its properties. For example, for PA, drying at 80–90°C for a minimum of 4 hours is recommended.
- Check the calibration of your drying equipment.
- Adjust the injection speed and pressure without exceeding recommended limits.
- Optimize the machine parameters.
- Reduce the back pressure to minimize air bubbles within the material.
- Review the mold ventilation.
- If the mold has insufficient ventilation, additional venting channels should be added.
- During mold maintenance, the venting channels should be cleaned.
- Low-quality or high-recycled-content raw materials are more prone to such surface defects.
- At Vincita Plastik, we make sure to use first-class raw materials in every production process.
- Especially during production transitions, any residual material left in the nozzle must be cleaned.
Standardize Quality with Vincita Plastik
Vincita Plastik offers not only high-quality products but also solutions that help optimize your production processes, leveraging industry expertise and engineering support. You can work with our experienced team to minimize potential surface defects in the injection process.
Conclusion
The gray and silver streak problem is one of the challenges of injection production; however, it can be easily prevented with proper analysis and production parameters. Vincita Plastik is always by your side to help improve your production processes and enhance the quality of your final products.
You can contact us for more technical information and support.
No comments yet.