This article presents a comprehensive study on the production of heavy-duty ductile iron castings for sand suction pump bodies, focusing on process optimization and defect control. The pump body discussed weighs 46,600 kg with maximum wall thickness of 355 mm, requiring strict quality control to prevent shrinkage porosity and ensure mechanical integrity.
1. Process Design Fundamentals
The casting process combines EPS (Expandable Polystyrene) pattern casting with furan resin sand molding, specifically developed for complex ductile iron castings. Key design parameters include:
$$H_p = H_{mold} + H_{cup} – \frac{C}{2}$$
Where:
$H_p$ = Metal static pressure head (mm)
$H_{mold}$ = Flask height (mm)
$H_{cup}$ = Pouring cup height (mm)
$C$ = Casting height (mm)
| Parameter | Value |
|---|---|
| Resin addition | 1.2% |
| Coating thickness | 0.4mm (2 layers) |
| Pouring temperature | 1,330-1,350°C |
2. Gating System Optimization
The multi-level gating system for ductile iron castings was designed using:
$$t = \sqrt[3]{G_L}$$
$$A_{choke} = \frac{G_L}{\mu \rho t \sqrt{2gH_p}}$$
Where:
$A_{choke}$ = Choke area (mm²)
$\mu$ = Flow coefficient (0.4)
$\rho$ = Density (7.3 kg/dm³)
| Component | Area Ratio |
|---|---|
| Sprue | 1.0 |
| Runner | 1.2 |
| Ingate | 0.8 |
3. Metallurgical Control
The composition control for ductile iron casting follows:
| Element | Pre-treatment | Post-treatment |
|---|---|---|
| C | 3.4-3.5% | 3.2-3.4% |
| Si | 1.5-1.6% | 2.3-2.5% |
| Mg | – | 0.035-0.055% |
Nodularization treatment parameters:
$$Q = W \times (1.05\% + 0.4\% + 0.15\%)$$
Where:
$Q$ = Total additive quantity
$W$ = Molten iron weight
4. Cooling Strategy
The solidification control for heavy-section ductile iron casting requires:
$$t_{solid} = \frac{V}{A} \times k$$
Where:
$t_{solid}$ = Solidification time (min)
$V/A$ = Modulus (cm)
$k$ = Solidification coefficient (1.2 for resin sand)
| Cooling Method | Application Area |
|---|---|
| External chill | Flange surfaces |
| Internal chill | Bearing housing |
5. Quality Verification
Mechanical testing results of ductile iron casting samples:
| Property | Requirement | Actual |
|---|---|---|
| Tensile Strength | ≥420 MPa | 460-490 MPa |
| Elongation | ≥5% | 7-11% |
| Hardness | 170-241 HB | 175-179 HB |
The successful production of this ductile iron casting demonstrates that proper gating design combined with advanced metallurgical control can effectively prevent defects in heavy-section components. The process optimization methods developed provide valuable references for similar large-scale pump castings in the industry.