Injection Molding Defects And Solutions -- Surface Flow Marks

Blog

Categorías

nuevo blog

Etiquetas

Injection Molding Defects and Solutions -- Surface Flow Marks 2025-10-17

Surface Flow Marks (Flow Lines / Flow Ripples):
This defect appears as streaked patterns radiating from the gate on the surface of the molded part. It occurs when the molten resin does not flow smoothly along the cavity surface but moves in a semi-wavy manner. During flow, stagnant zones form, and the resin that initially enters the cavity cools too quickly, creating a boundary with the subsequently injected molten resin. This results in poor fusion between the cold and hot material, forming visible flow marks.

11.1 Causes	11.2 Solutions
11.1.1 Low melt, mold, or nozzle temperature.	11.2.1 Properly increase melt, mold, and nozzle temperatures.
11.1.2 Low injection pressure or slow injection speed.	11.2.2 Increase injection pressure and speed to slow down the temperature drop of the melt flow.
11.1.3 Improper cold slug well, presence of cold material.	11.2.3 Adjust cold slug well position or enlarge the cold slug well.
11.1.4 Low melt flow index or poor melt fluidity.	11.2.4 Use materials with higher melt flow index.
11.1.5 Improper mold cooling system.	11.2.5 Modify the mold cooling system.
11.1.6 Long runner system, small cross-section, or improperly positioned gates causing high flow resistance and fast cooling.	11.2.6 Redesign runner system and gate position, increase cross-section, reduce flow resistance.
11.1.7 Thin walls, large area, or complex part shape.	11.2.7 Increase wall thickness appropriately or modify runner/gate design to improve melt flow.
11.1.8 Insufficient feed.	11.2.8 Check for causes of insufficient feed and ensure adequate material supply.
11.1.9 Twisted or narrow runners with poor surface finish.	11.2.9 Redesign runners with larger cross-section and ensure smooth surface finish.
11.1.10 Low injection speed or low back pressure.	11.2.10 Increase injection speed and back pressure.
11.1.11 High screw rotation speed.	11.2.11 Reduce screw speed.
11.1.12 Short holding time.	11.2.12 Increase holding time.
11.1.13 Hot runner heater malfunction or low temperature setting.	11.2.13 Replace heater or reset hot runner temperature.