Injection Molding
2 views
General-purpose polyethylene injection molded products surface flow marks
Problem Phenomenon
Concentric circular or wavy stripes centered on the gate appear on the product surface, i.e. flow marks.
The surface at the flow marks is rough, the color may differ slightly, affecting product appearance quality, mostly seen in high-gloss products.
Cause Analysis
（1） The flow front temperature repeatedly rises and falls when the melt flows in the cavity, forming alternating hot-cold flow marks\
（2） Injection speed too slow or unstable, the melt front stagnates intermittently during filling\
（3） Mold temperature too low, the melt cools rapidly after contacting the mold wall forming a cold material layer\
（4） Barrel temperature set improperly, nozzle temperature too low producing cold slug\
（5） Mold gate size too small, shear heating and pressure loss occur when the melt passes through the gate
Solution
（1） Increase injection speed, adopt multi-stage injection, maintain a stable speed front during filling\
（2） Increase mold temperature to the higher value within the 30-80°C range, reduce melt temperature drop\
（3） Increase nozzle temperature to be consistent with or 5-10°C higher than the front barrel section temperature to prevent cold slug\
（4） Enlarge the gate size, reduce shear and pressure loss when the melt passes through the gate\
（5） Appropriately increase barrel temperature to the higher value within the 160-260°C range
Key Takeaway
Flow marks are a manifestation of an unstable melt flow front, stabilizing the flow front by increasing injection speed, mold temperature and melt temperature.
Was this helpful?
0 people found this helpful
Thank you for your feedback!