Process Design and Validation of High-Speed Punch Disc in Ductile Iron Casting

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This paper presents a comprehensive methodology for producing large-scale ductile iron castings through the case study of a 38-ton punch disc. The chemical composition design, casting process optimization, and digital simulation verification demonstrate effective solutions for overcoming challenges in thick-section ductile iron production.

1. Chemical Composition Design

The chemical formula for carbon equivalent (CE) is critical for ductile iron casting quality:

$$ CE = C + \frac{1}{3}(Si + P) $$

For punch discs requiring QT500-7 properties, the optimized composition is:

Table 1: Chemical Composition Requirements (wt%)
Element Base Iron After Treatment
C 3.5-3.7 3.4-3.6
Si 1.4-1.5 2.0-2.4
Mn 0.35-0.45 0.35-0.45
P ≤0.02 ≤0.02
S ≤0.01 0.006-0.01
Mgres – 0.035-0.055

2. Casting Process Design

The solidification time (t) for thick-section ductile iron casting follows Chvorinov’s rule:

$$ t = k \left(\frac{V}{A}\right)^n $$

Where:
k = mold constant (1.0-1.2 for resin sand)
V = casting volume
A = cooling surface area
n = 1.5-2.0 (empirical constant)

Table 2: Process Parameters for Ductile Iron Casting
Parameter Value
Pouring Temperature 1300-1330°C
Mold Material Furan resin sand
Gating Ratio 1:1.2:0.8
Cooling Rate 15-25°C/min
Inoculant Addition 0.6-0.8%

3. Digital Simulation Verification

The fluid dynamics equation for mold filling analysis:

$$ \frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \mathbf{v}) = 0 $$
$$ \rho \left(\frac{\partial \mathbf{v}}{\partial t} + \mathbf{v} \cdot \nabla \mathbf{v}\right) = -\nabla p + \mu \nabla^2 \mathbf{v} + \rho \mathbf{g} $$

Key simulation results:

Table 3: Mold Filling Simulation Data
Stage Filling Time (s) Velocity (cm/s) Oxide Content (g/cm³)
14% Filled 12 160 4.2
40% Filled 26 51 3.8
Complete 43 28 3.58

4. Production Validation

The final ductile iron casting achieved:

$$ \sigma_b = 535\ MPa,\ \delta = 5.5\% $$

Microstructure parameters:

Table 4: Metallurgical Test Results
Parameter Requirement Actual
Graphite Sphericity ≥90% 95.42%
Nodule Count ≥100/mm² 125/mm²
Pearlite Content ≤20% 15%

5. Process Optimization Guidelines

For successful ductile iron casting production:

$$ \text{Cooling Rate} = \frac{T_{\text{pour}} – T_{\text{solidus}}}{t_{\text{solidification}}} $$

  1. Maintain Mgres = 0.035-0.055% with Y-based rare earth treatment
  2. Implement multi-stage inoculation: 0.6% pre-inoculation + 0.2% stream inoculation
  3. Control CE = 4.0-4.2 through precise C/Si ratio adjustment
  4. Optimize gating design using velocity criterion: 50-150 cm/s

This methodology demonstrates that proper control of metallurgical parameters combined with advanced simulation techniques enables reliable production of heavy-section ductile iron castings for high-stress applications.

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