Views: 0 Author: XINYITE PLASTIC Publish Time: 2025-07-30 Origin: Site
When injecting certain engineering plastics, i.e ABS V0, PA6 GF30, PP GF30 etc, we might face the problem of flow marks while injecting. Now, Let's break down the causes.
The most common causes of flow marks (flow lines) in injection molding can be grouped into the following key categories:
Cause： | Why It Happens： |
Low mold temperature | Causes rapid surface freezing, forming a skin layer that later melt must flow over, leaving visible marks |
Too-slow injection speed | Allows melt to cool at cavity walls, creating temperature gradients and uneven flow |
Small or poorly placed gate | Restricts flow and causes turbulence or jetting, especially if the gate faces a deep cavity |
Poor melt flow (low MFI) | High-viscosity materials or poor lubrication resist smooth filling, leading to staggered flow fronts |
Inadequate venting | Trapped air disrupts melt front, causing irregular cooling and surface streaks |
Quick Fixes in Practice：
Increase mold & melt temperature (first-line fix for most cases).
Use multi-stage injection speed (start fast, slow near end).
Enlarge gate size or relocate it to avoid jetting.
Check material drying & MFI; switch to higher-flow grade if needed.
Add or clean vents to eliminate air traps.
These five causes account for the majority of flow mark issues seen in day-to-day injection molding production. If you have any other questions regarding injection of engineering plastic compounds, please kindly contact us for more discussion.
