In modern industrial applications, ductile iron castings are widely used due to their excellent mechanical properties, such as high strength, good ductility, and superior wear resistance. The centrifugal casting process is particularly advantageous for producing cylindrical components like cylinder liners, as it enhances material density and reduces defects. However, optimizing this process for large-scale ductile iron castings requires a deep understanding of the fluid flow, temperature distribution, and pressure fields during casting. In this study, we employ numerical simulation to analyze the centrifugal casting process of large ductile iron castings, focusing on the coupling effects of temperature, flow, and pressure fields. Our aim is to provide insights that can improve the quality and efficiency of producing ductile iron castings.
We used advanced simulation software to model the centrifugal casting process, segmenting the model to accurately capture the gravity-driven and centrifugal flow stages. The geometry of the casting and mold was discretized into finite element meshes, with a total of approximately 1.28 million elements. The material properties for ductile iron were incorporated into the database, with key parameters including a solidus temperature of 1150°C and a liquidus temperature of 1200°C. The mold material was set as H13 steel, preheated to 200°C, and the pouring temperature was maintained at 1400°C. The rotational speed was set to 700 rpm, and the filling time was 90 seconds. These parameters were chosen to reflect typical industrial conditions for ductile iron castings.
The simulation results revealed that the metal fluid filled the mold in a laminar flow pattern, taking 90.3 seconds to complete. The velocity field showed that the fluid initially spread radially along the mold wall, with the flow direction aligning with the rotation. As the filling progressed, the fluid thickness increased uniformly from the inlet side to the opposite end. The temperature field indicated that the outer surfaces cooled faster due to direct contact with the mold, leading to directional solidification from the outside inward. The solidification sequence followed a layered pattern, with the final solidification occurring at the mid-thickness region of the thicker sections. The pressure field exhibited a concentric distribution, with higher pressures at the outer surfaces due to centrifugal forces. The maximum pressure reached 0.5063 MPa, enhancing the feeding capability and reducing shrinkage defects.
To quantify the material behavior, we analyzed the thermal and mechanical properties using mathematical models. The heat transfer during solidification can be described by the Fourier equation: $$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T $$ where \( T \) is temperature, \( t \) is time, and \( \alpha \) is thermal diffusivity. For ductile iron castings, the latent heat release during solidification was accounted for in the simulation, leading to temperature plateaus observed in cooling curves. The centrifugal force acting on the fluid is given by: $$ F = m \omega^2 r $$ where \( m \) is mass, \( \omega \) is angular velocity, and \( r \) is radius. This force significantly influences the pressure distribution and fluid flow, as confirmed by our simulations.
The following table summarizes the chemical composition of the ductile iron used in our study, which is critical for achieving the desired mechanical properties in ductile iron castings:
| Element | Content (wt%) |
|---|---|
| C | 3.2–3.6 |
| Si | 2.0–2.5 |
| Mn | 0.3–0.5 |
| Mg | 0.04–0.06 |
| Fe | Balance |
In terms of flow field analysis, we observed that the metal fluid entered the mold and adhered to the inner wall, rotating synchronously with the mold. The velocity vectors demonstrated a gradual increase in fluid thickness, with the filling rate reaching 100% at 90.3 seconds. The laminar flow pattern minimized turbulence, which is beneficial for reducing inclusions in ductile iron castings. The temperature distribution was non-uniform, with higher temperatures near the inlet and lower temperatures at the distal ends. This gradient influenced the solidification morphology, leading to the formation of columnar grains in the outer regions and equiaxed grains inwardly. The solid fraction evolution showed that complete solidification occurred at 808 seconds, with the last solidifying areas prone to defects like shrinkage porosity.
The pressure field analysis highlighted the role of centrifugal forces in enhancing the integrity of ductile iron castings. The pressure difference between the outer and inner surfaces reached 0.317 MPa, while the variation along the axial direction was 0.023 MPa due to gravitational effects. These pressures contributed to improved feeding during solidification, reducing the likelihood of defects. We also examined the effects of rotational speed on the process; higher speeds increased the pressure but could lead to element segregation if excessive. Thus, an optimal speed range is essential for high-quality ductile iron castings.
To validate our simulation results, we compared them with actual production data from industrial-scale centrifugal casting of ductile iron castings. The optimized process parameters, derived from the simulation, were applied to produce cylinder liners with diameters of 400 mm and 580 mm. The castings exhibited full filling, uniform microstructure, and minimal defects, confirming the accuracy of our numerical model. The table below outlines the final process parameters for a 400 mm diameter ductile iron casting:
| Parameter | Value |
|---|---|
| Mold Temperature | 200 ± 50°C |
| Metal Weight | 760 ± 3 kg |
| Pouring Temperature | 1410 ± 20°C |
| Pouring Time | 100 ± 20 s |
| Rotational Speed | 540 ± 20 rpm |
Furthermore, we investigated the mechanical performance of the ductile iron castings post-solidification. The yield strength and tensile strength increased with higher cooling rates, while elongation was influenced by the solidification morphology. The simulation data allowed us to predict these properties accurately, facilitating the design of robust ductile iron castings for demanding applications. The integration of numerical simulation into the production process not only reduces trial-and-error costs but also enhances the consistency of ductile iron castings.
In conclusion, our numerical simulation of the centrifugal casting process for large ductile iron castings provides a comprehensive analysis of the coupled temperature, flow, and pressure fields. The results demonstrate that laminar flow filling, directional solidification, and centrifugal pressure are key factors in achieving high-quality ductile iron castings. The validation with industrial production confirms the reliability of our approach, offering a valuable tool for optimizing the manufacturing of ductile iron castings. Future work could explore the effects of alloying elements on the simulation outcomes to further improve the performance of ductile iron castings.