Causes and Solutions for Silver Streaks in Injection Molded Products
Silver streaks, or flow marks, are common defects in injection molded products that can affect both the appearance and performance of the final part. These defects typically manifest as silver-colored lines or streaks on the product's surface or interior.
Material-Related Factors:
Drying Process: Most plastic materials are hygroscopic. Excessive moisture in the material can vaporize during the injection molding process, causing moisture-related defects like silver streaks. Different materials have varying drying requirements. Ensure that drying equipment is functioning correctly and regularly inspect heating and ventilation systems. Malfunctioning temperature sensors can lead to inadequate drying.
Material Selection and Cleaning: Impurities such as dust or paper can contaminate materials during transportation or storage, affecting the melt flow and causing defects. Materials should be screened using equipment like vibrating sieves before processing. Additionally, the storage environment should be clean to prevent contamination.
Injection Process Factors:
Injection Speed Adjustment: Excessive injection speed can create turbulence in the melt, entrapping air and causing silver streaks. Reducing the injection speed can help mitigate this issue.
Injection Pressure Control: Excessive injection pressure can also lead to air entrapment. Lowering the injection pressure can reduce the likelihood of air being drawn into the melt. For example, reducing pressure from 100 MPa to 80-90 MPa may improve the situation, but this should be carefully evaluated as it may affect part quality.
Melt Temperature Adjustment: Low melt temperatures can reduce melt fluidity, increasing the likelihood of defects. Increasing the melt temperature can improve flow and reduce defects.
Venting: Insufficient venting in the mold cavity can lead to air entrapment and the formation of silver streaks. Implementing venting channels or using porous steel can improve venting.
Mold-Related Factors:
Gating and Runner System: Insufficiently sized gates or poorly designed runners can hinder melt flow and cause defects.
Mold Cleaning and Maintenance: Residues such as mold release agents and plastic degradation products can accumulate in the mold, affecting melt quality and flow. Regular cleaning with appropriate mold cleaners is essential. Additionally, inspect the mold surface for scratches, wear, or other defects that may impact part quality.
