In the field of equipment manufacturing, the reliability of mechanical systems heavily depends on the quality of critical components, such as bearing seats. These casting parts serve as supports for bearings, ensuring proper lubrication, sealing, and load distribution. For medium to large-sized casting parts, achieving high integrity without defects like shrinkage porosity is a significant challenge. This article presents a comprehensive casting process design for the upper half of a gray iron front bearing seat, focusing on optimizing the工艺 through numerical simulation. The casting part is made of HT250 gray iron, which has favorable casting properties but requires careful design due to its complex geometry and varying wall thicknesses. We will explore every aspect of the process, from initial analysis to final validation, emphasizing the use of simulation tools to enhance efficiency and quality. Throughout this discussion, the term “casting part” will be frequently used to underscore the focus on the铸件 itself, and we will incorporate tables and formulas to summarize key data.
The casting part in question is an upper half bearing seat for a turbine assembly, with a轮廓尺寸 of 1,095 mm × 910 mm × 380 mm and a net weight of 566 kg. After accounting for machining allowances and non-cast features, the final casting part has an average wall thickness of 25 mm, with a minimum of 20 mm and a maximum of 153 mm. This disparity in wall thickness, nearly an 8-fold difference, creates hot spots that are prone to shrinkage defects. The casting part features internal cavities, multiple bearing mounts with flanges, window structures on the sides, and a narrow, curved oil injection hole—all of which complicate moldability. The technical requirements specify no allowable shrinkage porosity, gas holes, or sand inclusions that could impair performance. Therefore, our goal is to design a casting process that ensures directional solidification and defect-free production. We will use furan resin self-hardening sand for mold and core making, with alcohol-based graphite coatings, and employ gravity sand casting in a one-piece-per-mold setup for small-batch production.
To begin the casting process design, we first analyze the casting part’s structural characteristics and castability. The casting part’s geometry necessitates a curved parting surface to minimize the number of sand cores, simplifying the overall process. We selected a pouring position where the larger flat surfaces are oriented upward, facilitating riser placement for feeding, and the critical machined surfaces for bearing fits are positioned to ensure quality. The parting line follows a曲面, enabling two-part mold assembly and reducing core usage to just two sand cores: one for the front bearing mount and another for the oil hole and adjacent mount. This approach streamlines production and lowers costs. The casting part’s material, HT250 gray iron, exhibits self-feeding properties due to graphite expansion during solidification, but this must be balanced with riser design to prevent defects. We will detail these elements in subsequent sections, using tables to summarize dimensions and formulas to calculate key parameters.
For the gating system, we opted for a closed bottom-pouring design to ensure smooth filling with minimal turbulence and slag entrapment. The cross-sectional area ratio is set as follows: ΣAsprue : ΣArunner : ΣAingate = 1.4 : 1.2 : 1. The pouring temperature is 1,350°C, and the pouring time is calculated using an empirical formula for iron castings. The effective pouring time \( t \) (in seconds) is given by:
$$ t = 2.5 \sqrt[3]{G_{\text{件}}} \cdot \delta $$
where \( G_{\text{件}} \) is the net weight of the casting part in kg (573 kg after adjustments), and \( \delta \) is the main wall thickness in mm (20 mm). Substituting the values:
$$ t = 2.5 \sqrt[3]{573} \cdot 20 \approx 35 \text{ s} $$
Using the choke section method, the total choke area ΣA阻 is calculated as 26.4 cm². With 8 ingates, each with a trapezoidal cross-section, the area per ingate is 3.3 cm². The sprue area is 37 cm², and the total runner area is 32 cm², split into two channels. Table 1 summarizes the gating system dimensions.
| Component | Cross-Sectional Area (cm²) | Dimensions (mm) | Number |
|---|---|---|---|
| Sprue | 37 | Circular, diameter ~68.7 | 1 |
| Runner | 32 (total) | Rectangular, 40 × 80 each | 2 |
| Ingate | 3.3 each | Trapezoidal, heights 20-30 | 8 |
To validate this design, we performed numerical simulation using ProCAST 2021. The casting part was meshed with 1,138,332 volume elements, and boundary conditions included a heat transfer coefficient of 1,000 W/(m²·K) between the casting part and sand, and 2,000 W/(m²·K) between the casting part and chills. The filling process simulation showed that metal enters from the bottom, rising steadily without splashing or air entrapment, completing in approximately 35 s. However, defect analysis of the bare casting part (with only the gating system) revealed significant shrinkage porosity in thick sections, particularly at the 153 mm thick area and elliptical bosses, due to lack of feeding. This underscores the need for risers and chills to achieve directional solidification for this casting part.
Based on the simulation results, we designed a riser system comprising one visible top necking-down riser, two insulation risers, and four vent risers. The risers are placed atop hot spots to feed shrinkage. Using the modulus method and empirical ratios, we determined their sizes. For example, the modulus \( M \) of a riser is calculated as:
$$ M = \frac{V}{A} $$
where \( V \) is volume and \( A \) is surface area. For the main thick section of the casting part, with a modulus of approximately 5 cm, the riser dimensions were set to ensure it solidifies last. Table 2 lists the riser specifications.
| Riser Type | Dimensions (mm) | Location on Casting Part | Quantity |
|---|---|---|---|
| Visible Top Riser | Diameter 150, height 200 | Elliptical boss | 1 |
| Insulation Riser | Diameter 180, height 250 | Main thick section | 2 |
| Vent Riser | Diameter 30, height 100 | Various hot spots | 4 |
Simulation with risers showed reduced shrinkage, but defects persisted in peripheral areas like circular bosses and window regions. To address this, we added external chills to accelerate cooling in these hot spots. Five chills were designed: three conformal chills for the main thick area and two circular chills for small bosses. The chill dimensions are based on the casting part’s geometry, with thicknesses chosen to extract heat efficiently. Table 3 provides details.
| Chill Type | Dimensions (mm) | Thickness (mm) | Location on Casting Part | Quantity |
|---|---|---|---|---|
| Conformal Chill #1 | Curved, matching part | 150 | Main thick section | 1 |
| Conformal Chill #2 | Rectangular, 200 × 100 | 150 | Window areas | 2 |
| Circular Chill | Diameter 50 | 20 | Small bosses | 2 |
The final casting process scheme, incorporating risers and chills, was simulated again. The results showed complete elimination of shrinkage porosity in the casting part, with directional solidification achieved: distant sections solidify first, followed by the elliptical boss, and finally the main thick section fed by insulation risers. The total solidification time was around 8,635 s, and the casting part exhibited no internal defects. The process yield, calculated as the ratio of casting part weight to total poured weight, reached 85%. This optimization demonstrates how numerical simulation can refine the casting process for complex casting parts.
In conclusion, we have developed a robust casting process design for the upper half of a gray iron front bearing seat. Key elements include a curved parting surface to simplify molds, a closed bottom-pouring gating system with a calculated pouring time of 35 s, and a combination of risers and chills to ensure directional solidification. The use of ProCAST simulation allowed us to iteratively improve the design, eliminating shrinkage defects and enhancing the integrity of the casting part. This approach not only shortens production cycles but also reduces costs, making it valuable for manufacturing high-quality casting parts in the equipment industry. Future work could explore other alloys or larger scales, but the principles remain applicable. Throughout this study, the casting part’s requirements guided every decision, underscoring the importance of tailored process design in achieving defect-free components.
To further illustrate the concepts, we can summarize the key formulas used in this design. The pouring time formula ensures proper filling, while the modulus method aids riser sizing. For gray iron, the self-feeding effect due to graphite expansion can be approximated by a feeding efficiency factor \( \eta \), often taken as 0.5 for HT250, but in our design, we relied on risers for safety. The heat transfer during solidification can be modeled using Fourier’s law, but in simulation, it’s handled numerically. Overall, this project highlights how integrating traditional calculations with modern simulation leads to optimal outcomes for demanding casting parts.