Today's KNOWLEDGE Share : What Are Flow Lines in Injection Molding

 Today's KNOWLEDGE Share

🔹 What Are Flow Lines in Injection Molding — and Why Should You Care?

Flow lines are one of the most common (and frustrating) surface defects in plastic parts.

They appear as:

➖ Wavy streaks

➖ Discoloration

➖ Directional lines following the melt flow

These cosmetic issues don’t always affect function—but for customer-facing parts, they can ruin product aesthetics and perceived quality.

🔍 What causes flow lines?

🌡️ Material cooling too quickly in thin sections

🧊 Inconsistent mold temperatures

🌀 Flow hesitation around corners, holes, or sudden thickness changes

🐢 Injection speed too low or poor gate design

💡 How to reduce flow lines

✅ Optimize gate size & position

✅ Increase injection speed & pressure

✅ Improve mold temperature control

✅ Design smooth, even wall thickness transitions

source : SCSplastic