Hot Runner vs Cold Runner — Injection Molding Runner Systems
Compare hot runner and cold runner systems for injection molding. Cost, waste, cycle time, maintenance, and selection criteria.
Runner Systems Overview
The runner delivers molten plastic from the machine nozzle to the cavity gates. Two types: hot runner and cold runner.
Cold Runner Systems
- Pros: Lower mold cost, simpler design, easier color changes, less maintenance
- Cons: Material waste (15-50% regrind), longer cycle, requires separation equipment
Hot Runner Systems
The manifold keeps the runner molten via heater bands and thermocouples. Only cavity material solidifies.
- Pros: Zero runner waste, shorter cycle, better quality, ideal for multi-cavity
- Cons: Higher mold cost ($3,000-20,000+), complex maintenance, slower color changes
Selection Guide
| Factor | Cold Runner | Hot Runner |
|---|
| Volume | Under 50k | Over 50k |
| Material cost | Cheap materials | Engineering materials |
| Cavity count | 1-8 | 8-128 |
| Mold budget | $5k-20k | $20k-100k+ |
Hot Runner Types
- Externally Heated: Standard. Even heat, higher power.
- Internally Heated: Better thermal efficiency.
- Valve Gate: Mechanical pin shut-off. Best gate vestige.
- Thermal Gate: No moving parts. Simpler.