For a continuous sintering furnace with a 6-inch-wide belt: 5-15 m³/hour of hydrogen or hydrogen-nitrogen blend. For a batch furnace: 2-5 air changes per minute of the hot zone volume. The flow must be sufficient to maintain a dew point below -40°C at the furnace exit — this is the real acceptance criterion, not the flow rate itself.
Recommended flow rates by furnace type:
| Furnace Type | Hot Zone Volume | Recommended Gas Flow | Air Changes/Hour | Dew Point Target |
|---|---|---|---|---|
| Small batch (0.1 m³) | 0.1 m³ | 0.3-1.0 m³/hr | 3-10 | <-40°C |
| Medium batch (0.5 m³) | 0.5 m³ | 1.5-4.0 m³/hr | 3-8 | <-40°C |
| Continuous (6" belt) | — | 5-15 m³/hr | — | <-40°C |
| Continuous (12" belt) | — | 10-30 m³/hr | — | <-40°C |
| Large continuous (18" belt) | — | 20-50 m³/hr | — | <-40°C |
| Flow Rate Relative to Minimum | Dew Point | Effect on Part Quality |
|---|---|---|
| 2-3x minimum | <-50°C | Excellent — no oxide issues, high density |
| 1-2x minimum | -40 to -50°C | Good — standard production quality |
| At minimum | -35 to -40°C | Acceptable — requires clean input gas |
| Below minimum | -20 to -35°C | Marginal — oxidation risk, reduced density |
| Well below minimum | >-20°C | Poor — parts will oxidize, density below 95% |
For a batch furnace: Minimum flow (m³/hr) = Hot zone volume (m³) × 2 air changes/hr
For a continuous furnace: Minimum flow is determined empirically by measuring dew point at the furnace exit at different flow rates and selecting the rate that achieves <-40°C.
Troubleshooting high dew point (indicating insufficient flow):- Check gas supply pressure and regulator function
- Verify gas purity (should be >99.995% for H₂)
- Check for leaks in furnace shell or gas lines
- Verify gas dryer/desiccant is not saturated
- Increase flow rate by 25% and re-measure dew point