1. Introduction
In the landscape of modern energy, wind power has emerged as a crucial player in the pursuit of sustainable development. Wind power castings, especially suspension beams, are vital components in wind turbines. Their quality directly impacts the stability and lifespan of the entire wind power generation system. However, the traditional use of low – grade and low – elongation ductile nodular iron in wind power castings is being challenged by the increasing demand for higher performance. This has spurred the need for in – depth research into the casting process design and optimization of wind power suspension beams.
2. Structure and Requirements of Wind Power Suspension Beams
2.1 Structural Characteristics
The wind power suspension beam is a complex – shaped component. As shown in Figure 1, its maximum external dimensions are 670 mm×250 mm×250 mm, and it weighs 138 kg. The significant difference in wall thickness across the casting poses challenges in the casting process. For example, areas with thick walls cool more slowly than thin – walled areas, which can lead to issues such as shrinkage porosity and non – uniform microstructure if not properly addressed.
| Structural Feature | Details |
|---|---|
| Maximum Dimensions | 670 mm×250 mm×250 mm |
| Mass | 138 kg |
| Wall Thickness | Varies significantly |
2.2 Material Requirements
The material chosen for the wind power suspension beam in this study is QT500 – 14. This ductile iron grade has specific chemical composition requirements, as presented in Table 1. The carbon (C), silicon (Si), manganese (Mn), sulfur (S), and phosphorus (P) contents need to be precisely controlled. For instance, the C content in the range of 3.0 – 3.5% affects the graphite formation and the overall mechanical properties of the casting. A proper balance of these elements is crucial for achieving the desired mechanical and metallurgical properties.
| Element | Content (mass fraction/%) |
|---|---|
| C | 3.0 – 3.5 |
| Si | 3.7 – 4.3 |
| Mn | ≤0.50 |
| S | ≤0.025 |
| P | ≤0.05 |
| Fe | Bal. |
Table 1 Chemical composition of QT500 – 14
In addition to chemical composition, the mechanical properties of QT500 – 14 are also strictly specified. The casting must meet requirements for tensile strength, yield strength, elongation, and hardness, as well as having a specific nodularity and pearlite content. These properties ensure that the suspension beam can withstand the complex mechanical loads during the operation of the wind turbine.
3. Initial Casting Process Design
3.1 Molding Method and Sand Core Design
The initial casting process adopts a resin – sand manual molding line, with one casting per mold. Given the complex shape of the suspension beam, a sand core is designed in the middle hole where it is impossible to remove the mold. This sand core not only helps in forming the internal structure of the casting but also affects the flow of molten metal during casting. The proper design of the sand core can prevent issues like misruns and ensure the integrity of the casting’s internal cavity.
3.2 Pouring System Design
The pouring system is placed on one side of the casting and consists of 4 inner gates. An open – type pouring system is chosen, with the cross – sectional area ratio of the sprue, runner, and inner gate being 直相内. This ratio is designed to ensure a proper filling speed. A too – slow filling speed may cause cold shuts and sand inclusions, while a too – fast speed can lead to turbulent flow, which may entrain air and result in porosity defects. The pouring system also includes filters on both sides of the sprue to effectively trap slag and prevent it from entering the casting cavity.
3.3 Riser Design
Based on the casting modulus method, the riser size is calculated with the riser modulus set as 1.2 times the casting modulus. The riser is placed at the top of the casting. Its main function is to provide additional molten metal to compensate for the shrinkage that occurs during solidification. A well – designed riser can help in reducing shrinkage porosity and ensuring the internal and external quality of the casting. However, an oversized riser can lead to a decrease in the casting yield and an increase in production costs, while an undersized riser may not be able to provide sufficient feeding, resulting in internal defects.
4. Casting Simulation Analysis of the Initial Process
4.1 Simulation Setup
To evaluate the reliability of the initial casting process, MAGMA simulation software is utilized. The casting, riser, and pouring system are converted into STL format files and imported into the MAGMA simulation system. The components are then meshed, with the grid size of the pouring system being larger than that of the casting part to speed up the calculation without sacrificing accuracy. The total number of nodes is 2,099,766, and the number of units is 472,057. The chemical composition is controlled according to the mid – values in Table 1. The pouring temperature is set at 1340 °C, the sand mold temperature at 25 °C, and the final pouring time at 15 s. The main simulation parameters are summarized in Table 2.
| Parameter | Value |
|---|---|
| Casting material | QT500 – 14 |
| Mold materials | Resin sand |
| Initial pouring temperature/°C | 1340 |
| Pouring time/s | 15 |
Table 2 Setting of simulation parameters
4.2 Simulation Results and Analysis
The simulation results for the solidification, shrinkage porosity, and hot spots of the wind power suspension beam are shown in Figure 2. When the iron liquid solidifies to 99.5%, the casting is not fully solidified, indicating that the riser’s feeding capacity is insufficient. The presence of independent liquid phases inside the casting and below the riser, as well as hot spots in the casting, suggest a high risk of shrinkage porosity or shrinkage holes. This implies that the existing riser may be too small. Although increasing the riser size can potentially solve the feeding problem, it will lead to a lower product yield and higher production costs.
5. Process Optimization
5.1 Optimization Strategy
To address the issues identified in the initial simulation, a process optimization strategy is proposed. Instead of simply increasing the riser size, cold irons are added to the thick – walled areas far from the riser. This approach aims to increase the riser’s feeding distance and enable the use of a smaller riser for effective feeding. Additionally, due to the high Si content in QT500 – 14, which can cause coarse graphite in the casting structure and affect elongation, the use of cold irons can help in refining the structure and ensuring the casting’s elongation.
5.2 Cold Iron Design
According to the casting structure, chilling effect, and process – ability principles, two types of cold irons are placed in the lower mold of the thick – walled area. The dimensions of the cold irons are calculated using the formula , where is the cold – iron mass, is the cold – iron density, and is the cold – iron contact area. The calculated dimensions of cold iron 1 are 130 mm×100 mm×60 mm, and those of cold iron 2 are 130 mm×60 mm×60 mm.
| Cold Iron | Dimensions (mm) |
|---|---|
| Cold Iron 1 | 130×100×60 |
| Cold Iron 2 | 130×60×60 |
Table 3 Dimensions of cold irons
5.3 Effect of Cold Iron on Casting Solidification
Cold irons have a high thermal conductivity. When the molten metal is poured into the mold, the cold irons quickly absorb heat from the adjacent metal. This causes the temperature of the metal near the cold irons to drop rapidly, increasing the temperature – field gradient and accelerating the cooling rate. As a result, the metal near the cold irons solidifies first, changing the original solidification sequence of the casting. The solidification now progresses from the cold – iron areas to other parts of the casting, achieving a sequential solidification pattern. This effectively transfers shrinkage porosity and shrinkage holes to the riser and other feeding areas, improving the casting’s density and reducing internal defects.
5.4 Simulation Results of the Optimized Process
The simulation of the optimized process shows significant improvements. As shown in Figure 3, there is no independent liquid phase inside the casting, and all the remaining liquid is concentrated in the riser and pouring system. The casting also has no internal hot spots, indicating that the risk of shrinkage porosity and shrinkage holes has been effectively eliminated. The optimized process also ensures a stable filling process, with the inner gates remaining full during filling, preventing gas from entering the cavity and reducing turbulence.
6. Experimental Materials and Methods
6.1 Melting Process
The furnace charge consists of 10% (mass fraction) pig iron, 60% return material, and 30% scrap steel. After being dried, the materials are melted in a 1 – t ABP medium – frequency coreless induction test electric furnace. The molten iron is heated to 1500 – 1530 °C, then powered off and allowed to stand for 5 – 10 minutes before slagging. This melting process is crucial for ensuring the uniform distribution of elements in the molten iron and removing impurities.
6.2 Inoculation and Pouring
During the melting process, the ball – forming agent Elmag5932 is used. For in – ladle inoculation, a silicon – barium inoculant is added at a rate of 0.6%, and a silicon – strontium – zirconium inoculant is added at a rate of 0.05% during the pouring process. The pouring temperature is controlled at (1340 ± 10) °C. After pouring, the casting is cooled for 10 hours before being removed from the mold. Once cooled to room temperature, the surface of the casting is cleaned. These inoculation and pouring parameters play a significant role in controlling the graphite morphology and the final mechanical properties of the casting.
6.3 Sample Preparation and Testing
Samples are taken from the casting body. After grinding and machining, the samples are made into 金相试样 (10 mm×10 mm), hardness specimens (10 mm×30 mm), and tensile test bars (φ14 mm). The graphite shape and size are observed using a German Leica DMi8 C metallographic microscope. The tensile strength is tested using an American MTS SHT4305 micro – computer – controlled electro – hydraulic servo universal testing machine, and the hardness is measured using a Chinese Huayin HB – 3000B – 1 Brinell hardness tester. Each sample is tested at 3 points, and the average value is taken. The sampling locations are shown in Figure 4, and the chemical composition and performance requirements are presented in Table 4.
| Element | Content (mass fraction/%) |
|---|---|
| C | 3.2 – 3.4 |
| Si | 3.8 – 4.0 |
| Mn | ≤0.25 |
| S | ≤0.015 |
| P | ≤0.05 |
| Fe | Bal. |
7. Experimental Results and Discussion
7.1 Analysis of Casting Shrinkage Porosity Defects
The casting produced using the optimized process is cut into 10 – mm slices and subjected to PT inspection. The results, as shown in Figure 5, indicate that the internal structure of the casting is dense. No red areas are observed, which means there are no shrinkage porosity or shrinkage hole defects. This validates the effectiveness of the optimized casting process in eliminating internal defects.
7.2 Microstructure and Mechanical Properties
The metallographic structure of the QT500 – 14 suspension beam is shown in Figure 6. Using image – analysis software, it is determined that the nodularity of the casting is greater than 90%, and the pearlite content is 1% (area fraction), which meets the casting’s metallographic structure standards. In terms of mechanical properties, as shown in Table 5, the tensile strength at two sampling locations is 526 and 556 MPa, the yield strength is 415 and 456 MPa, the elongation after fracture is 18.5% and 14%, and the average hardness value is 189 HBW. These values meet the casting standards, demonstrating good strength – toughness properties.
| Tensile test bar | Ultimate tensile strength/MPa | Yield strength /MPa | Elongation 1% | Hardness (HB) | Nodularity 1% | Area fraction of pearlite/% |
|---|---|---|---|---|---|---|
| 1 | 526 | 415 | 18.5 | 185 – 188 – 194 (average: 189) | 90 | 1 |
| 2 | 555 | 456 | 14 | |||
| Technical criteria | ≥480 | ≥390 | ≥12 | 170 – 200 | =80% | ≤5% |
8. Comparison with Traditional Processes
8.1 Defect Reduction
Compared with traditional casting processes for wind power suspension beams, the optimized process in this study shows a significant reduction in internal defects. Traditional processes often struggle to control shrinkage porosity and shrinkage holes, especially in complex – shaped castings with varying wall thicknesses. The use of simulation – based optimization and the addition of cold irons in this study effectively address these issues, resulting in a higher – quality casting.
8.2 Improvement in Mechanical Properties
The optimized process also leads to improved mechanical properties. The precise control of chemical composition, along with the refined microstructure achieved through the use of cold irons, results in better – balanced strength, elongation, and hardness values. In contrast, traditional processes may produce castings with inconsistent mechanical properties, which can affect the performance and reliability of wind turbines.
8.3 Cost – Benefit Analysis
Although the initial investment in simulation software and the design of optimized processes may seem high, in the long run, the optimized process offers cost – savings. By reducing the number of defective castings, the yield is increased, and the cost of rework or scrap is minimized. Additionally, the improved mechanical properties of the castings can lead to a longer service life of the wind turbine components, reducing maintenance and replacement costs.
9. Challenges and Future Research Directions
9.1 Challenges in Current Processes
Despite the success of the optimized casting process, there are still challenges. The accurate control of cold – iron placement and size requires precise manufacturing and process monitoring. Any deviation in cold – iron installation can affect the solidification sequence and lead to defects. Moreover, the simulation results are based on certain assumptions and models, and there may be discrepancies between the simulation and actual production, especially in complex industrial environments.
9.2 Future Research Directions
Future research could focus on further improving the accuracy of simulation models. Incorporating more complex physical phenomena, such as the interaction between the molten metal and the mold material, into the simulation can provide more reliable results. Additionally, exploring new materials and alloying elements for wind power suspension beams can potentially lead to better performance and cost – effectiveness. Research on advanced manufacturing techniques, such as 3D printing for sand cores and molds, may also offer new opportunities for optimizing the casting process.
10. Conclusion
In conclusion, this study presents a comprehensive approach to the casting process design and simulation of wind power suspension beams. Through the analysis of the structure and requirements of the suspension beam, the initial casting process was designed. Simulation analysis of the initial process identified potential problems, which were then addressed through process optimization, specifically the addition of cold irons. Experimental results verified that the optimized process can effectively eliminate internal defects, meet the mechanical and metallurgical property requirements, and produce high – quality QT500 – 14 wind power suspension beams. The comparison with traditional processes shows the superiority of the optimized process in terms of defect reduction, mechanical property improvement, and cost – effectiveness. However, challenges remain, and future research directions are proposed to further enhance the casting process for wind power suspension beams. This research provides valuable insights and technical support for the development of the wind power industry.
