Views: 0 Author: Site Editor Publish Time: 2025-06-25 Origin: Site
A cold runner is a channel system that delivers molten plastic from the injection molding machine nozzle to the mold cavities. Unlike hot runners, cold runners cool and solidify with the part, requiring ejection and separation (usually trimmed manually or automatically).
✔ Simple design – Easy to maintain and repair.
✔ Lower cost – No heating elements or complex controls.
✔ Material flexibility – Works with most thermoplastics.
✖ Generates waste – Runner scrap must be recycled or discarded.
Structure: Consists of two plates (fixed + moving).
Ejection: The runner and part are ejected together, requiring trimming.
Common Gates:
Sprue Gate – Direct injection; leaves a visible mark.
Edge Gate – Side entry; easy to remove but may leave marks.
Structure: Adds a middle plate to separate runners automatically.
Gates:
Pin Gate (Point Gate) – Small, clean break; ideal for multi-cavity molds.
Submarine/Tunnel Gate – Hidden gate for better aesthetics.
Fan Gate – Wide entry for uniform filling (e.g., flat parts).
Diaphragm Gate – Used for cylindrical parts (e.g., bottle caps).
| Factor | Cold Runner | Hot Runner |
|---|---|---|
| Cost | Lower initial cost | Higher (heating system) |
| Waste | Generates scrap | Minimal waste |
| Cycle Time | Longer (cooling) | Faster (no runner cooling) |
| Maintenance | Simple | Complex (heater maintenance) |
Best for Cold Runner:
Small to medium production.
Low-budget projects.
Materials sensitive to heat (e.g., PVC).
Best for Hot Runner:
High-volume production.
Critical surface finish (e.g., medical parts).
1️⃣ Balance the Runner – Ensure even filling in multi-cavity molds.
2️⃣ Gate Design Matters – Choose the right gate type for part aesthetics.
3️⃣ Recycle Runner Scrap – Grind and reuse material to reduce waste.
Cold runner systems remain a cost-effective and versatile choice for injection molding, especially for prototypes and low-to-medium production runs. While they generate some waste, proper design and recycling can minimize inefficiencies.
For high-volume or precision parts, hot runners may be preferable, but cold runners still dominate many applications due to their simplicity and reliability.
