Views: 0 Author: Site Editor Publish Time: 2025-05-15 Origin: Site
A cold runner is a traditional injection molding system where the molten plastic flows through unheated channels (runners) before entering the mold cavity. The runners cool and solidify along with the part, requiring ejection and separation.
Plastic enters through the sprue, flows into runners, and fills the cavity via gates.
After injection, both the part and the runner solidify and are ejected.
The runner system is typically part of a two-plate or three-plate mold.
✅ Lower mold cost – Simpler design, no heating elements.
✅ Better for color/material changes – Easy to clean, no residual molten plastic.
✅ Suitable for heat-sensitive materials (e.g., PVC) – No risk of overheating.
❌ Material waste – Runners must be recycled or discarded.
❌ Longer cycle time – Cooling includes runners, slowing production.
❌ Post-processing needed – Separating runners from parts adds labor.
Small-batch production.
Frequent color changes (e.g., consumer goods).
Low-budget projects.
A hot runner system keeps the plastic molten inside heated channels, delivering it directly to the cavities without solidifying. This eliminates runner waste and improves efficiency.
A heated manifold maintains plastic in a liquid state.
Nozzles inject plastic directly into the cavities.
Only the part cools and ejects—no runner removal needed.
✅ No material waste – 100% material utilization.
✅ Faster cycles – Only the part needs cooling.
✅ Better part quality – Reduced shear stress, fewer defects (e.g., weld lines).
❌ Higher mold cost – Complex design with heaters and controllers.
❌ Maintenance challenges – Temperature control is critical.
❌ Difficult color changes – Requires thorough purging.
High-volume production (e.g., automotive parts, electronics).
High-precision components (e.g., medical devices).
Cost-sensitive materials (e.g., engineering plastics).
| Factor | Cold Runner | Hot Runner |
|---|---|---|
| Material Waste | High (runners discarded) | Minimal (no runners) |
| Cycle Time | Slower (cools runners) | Faster (only parts cool) |
| Mold Cost | Lower | Higher (heating system) |
| Maintenance | Simple | Complex (temp. control) |
| Best For | Small batches, color changes | Mass production, high precision |
Use Cold Runner if:
You need flexibility in material/color changes.
Budget is limited.
Production volume is low.
Use Hot Runner if:
Minimizing waste is critical.
High-speed production is needed.
Part quality and consistency are top priorities.
Some molds combine both systems (semi-hot runners) for a balance between cost and efficiency.
Both cold and hot runners have their place in injection molding. The right choice depends on production volume, material type, budget, and quality requirements. By understanding their differences, manufacturers can optimize efficiency and reduce costs effectively.
