This paper analyzes critical factors affecting the quality and efficiency of steel casting processes for large shell-type components through empirical case studies. By optimizing pouring positions and solidification control strategies, we demonstrate significant improvements in yield rates and defect reduction.
1. Technical Requirements and Process Challenges
The shell component (Fig. 1) features complex geometry with thickness variations from 18mm to 130mm. Key challenges include:
| Parameter | Specification |
|---|---|
| Chemical Composition | C:0.19-0.29%, Si:0.25-0.65%, Mn:0.40-0.80% |
| Mechanical Properties | Rm≥450MPa, Z≥18%, HB:130-170 |
| Quality Standards | ASTM E446 Level II/III, GB7233-2009 Level I |
The solidification modulus (M) varies significantly across sections:
$$M = \frac{V}{A}$$
Where V = volume (m³) and A = cooling surface area (m²). Critical sections show modulus ratios up to 7.2:1.
2. Initial Process Limitations
The original steel casting process with C-groove upward orientation exhibited several drawbacks:
| Parameter | Initial Process |
|---|---|
| Yield Rate | 41.0% |
| Pouring Weight | 5100kg |
| Defect Rate | 23% (sand inclusion/gas porosity) |
The Reynolds number during pouring reached critical turbulence levels:
$$Re = \frac{\rho v d}{\mu} > 4000$$
Where ρ = density (kg/m³), v = velocity (m/s), d = characteristic length (m), μ = viscosity (Pa·s).
3. Optimized Steel Casting Process
The modified process features C-groove downward orientation with bottom-gating system:
| Improvement | Technical Solution |
|---|---|
| Solidification Control | Exothermic risers (η=32%) vs. sand risers (η=14%) |
| Gating Design | 4-bottom gates with Fsprue:Frunner:Fgate = 1:2:3.38 |
| Process Yield | 61.5% (3400kg pouring weight) |
The Niyama criterion confirms improved feeding:
$$N = \frac{G}{\sqrt{\dot{T}}} > 1\,^{\circ}C^{1/2}/min^{1/2}$$
Where G = temperature gradient (°C/m), Ṫ = cooling rate (°C/s).
4. Defect Reduction Mechanism
The optimized steel casting process reduces turbulence energy by 68%:
$$E_t = \frac{1}{2}\rho v^2 < 150\,J/kg$$
Key improvements include:
- Entrained slag inclusion probability reduced from 0.42 to 0.07
- Gas porosity index decreased by 83%
- Dimensional accuracy improved to IT13-IT15
5. Production Efficiency Gains
The steel casting process optimization enables:
| Metric | Improvement |
|---|---|
| Pouring Capacity | 2 castings/ladle (7500kg) |
| Solidification Time | 65s (34% reduction) |
| Energy Consumption | 9.8kWh/ton (-27%) |
The thermal efficiency of exothermic risers follows:
$$Q_{exo} = m[\Delta H + c_p(T_m – T_a)]$$
Where m = riser mass (kg), ΔH = reaction heat (kJ/kg), cp = specific heat (kJ/kg°C).
6. Conclusion
This steel casting process optimization demonstrates that proper pouring position selection combined with scientific feeding system design can achieve:
- Yield rate improvement: 41.0% → 61.5%
- Defect rate reduction: 23% → 4.7%
- Production capacity doubling: 1 → 2 castings/ladle
The methodology provides valuable insights for similar steel casting applications requiring complex geometry and high quality standards.