Process Optimization and Production of Large Stainless Steel Volute Castings

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This article focuses on the production process of large stainless steel volute castings. It details the product characteristics, mold design, casting process, simulation analysis, and production verification. By optimizing various process parameters and using advanced techniques, the goal is to produce high-quality castings that meet the design requirements. The study provides valuable insights and references for the production of similar castings in the field of casting engineering.

I. Introduction

In the field of aviation engine development, the accurate detection of various parameters of combustion gases requires the use of specialized detection devices with complex internal cavity structures, such as the stainless steel volute . The stainless steel volute casting has strict quality requirements, as it needs to withstand high-temperature gas erosion for a long time without any internal defects such as cracks, pores, shrinkage cavities, and slag inclusions. This poses significant challenges to the casting process. Therefore, this study aims to optimize the casting process to ensure the quality and performance of the volute casting.

II. Product Introduction

The stainless steel volute casting is made of ZG12Cr18Ni9Ti, with a weight of approximately 3.2 t and a maximum size of 3800 mm. The wall thickness is 20 mm, which is a typical thin-walled structure. There are 30 partitions in the volute cavity, each with a wall thickness of 20 mm and a height of 200 mm. The chemical composition of the material is shown in Table 1. The complex structure and uneven wall thickness make the overall casting of the volute prone to deformation and casting defects, requiring careful design of the casting process.

III. Production Process

A. Mold Design

  1. Symmetry and Design: Considering the symmetry of the upper and lower structures of the casting and the presence of local control valve flanges and installation bosses, the mold design incorporates these parts as movable blocks. A single wooden model board can be used for molding both the upper and lower sand boxes.
  2. Shrinkage Rate: The is set at 3 mm, and the overall shrinkage rate of the steel liquid is designed as 2.5%. The shrinkage rate of the inlet and outlet flanges of the volute is specifically designed as 1.0%. A machining allowance of 15 mm is provided.
  3. Sand Core Design: The sand core weighs about 3 t, calculated based on the density of at 2.0 g/cm³. To prevent deformation and drift during pouring, a core bone structure reinforced with steel bars is designed. The center plane of 1/2 symmetry is used as the, and sawdust and straw ropes are added to increase .
  1. Riser Placement and Connection Methods
    • Location Impact on Solidification Pattern
      • The location of the riser has a significant impact on the solidification process of the casting. If the riser is placed improperly, it may not be able to effectively feed the areas that need it most during solidification. For the stainless steel volute casting, placing the riser at the thickest or most critical hot spots can help to ensure that the molten metal is supplied in a timely manner to prevent shrinkage defects. For example, near the connections between the partitions and the main body of the volute where the heat concentration is relatively high.
    • Connection Method and Metal Flow
      • The connection method between the riser and the casting also affects the flow of molten metal during solidification. A proper connection should ensure a smooth flow of metal from the riser to the casting, without causing any obstruction or turbulence. In the case of the easy-to-cut riser seat used in the casting process, it provides a convenient and effective way to connect the riser and the sand mold, while also allowing for easy removal of the riser after casting. The design of the bottom liquid inlet of the exothermic insulating riser and its connection with the riser seat needs to be carefully considered to ensure optimal metal flow and feeding efficiency.

VIII. The Role of CAE Simulation in Casting Process Optimization

CAE (Computer-Aided Engineering) simulation plays a crucial role in the optimization of the stainless steel volute casting process. It allows engineers to predict and analyze various phenomena that occur during the casting and solidification processes, providing valuable insights for process improvement.

  1. Defect Prediction
    • By simulating the filling and solidification processes, CAE can predict the possible locations of defects such as porosity, shrinkage cavities, and cracks. In the case of the stainless steel volute casting, the simulation results showed the areas where there was a higher risk of shrinkage defects (as shown in Figures 9 and 13). This enables the design team to take preemptive measures, such as adjusting the riser size, location, or adding cold iron and chromium ore sand to improve the local solidification conditions and reduce the defect occurrence.
  2. Process Parameter Optimization
    • The simulation can help optimize various process parameters, including pouring temperature, filling speed, and cooling rate. For example, by adjusting the pouring temperature from the initial setting, the simulation can show how it affects the temperature distribution and solidification pattern in the casting. A suitable pouring temperature can be determined to ensure that the molten metal fills the mold cavity smoothly while minimizing the formation of defects due to excessive temperature gradients or rapid solidification. Similarly, the filling speed can be optimized to prevent air entrapment and ensure a uniform filling of the complex volute cavity.
  3. Design Validation and Improvement
    • CAE simulation provides a way to validate the casting process design before actual production. By comparing the simulation results with the desired quality and performance criteria, any deficiencies in the design can be identified and corrected. In the process of optimizing the stainless steel volute casting, the simulation results led to the modification of the pouring system design (from Scheme 1 to Scheme 2 with some adjustments in the riser and inner pouring channel design) and the addition of measures to enhance the casting density and prevent defects. This iterative process of simulation and design improvement helps to achieve a more reliable and efficient casting process.
  4. Cost and Time Savings
    • Conducting physical experiments and trials for different casting process designs can be time-consuming and costly. CAE simulation allows for multiple scenarios to be tested virtually, reducing the need for extensive physical prototypes. This saves both time and resources in the development process. For example, instead of building and testing different pouring system configurations in the actual foundry, the simulation can quickly provide an indication of which design is likely to perform better, allowing the engineers to focus on the most promising options and make necessary adjustments before proceeding to actual production. This significantly accelerates the product development cycle and reduces the overall cost of bringing the stainless steel volute casting to market.

[You can insert some screenshots or visualizations from the CAE software to demonstrate the simulation results and how they are used for analysis and optimization. For example, a color-coded temperature distribution map during solidification or a graph showing the pressure changes during filling.]

IX. The Importance of Material Selection and Composition Control in Stainless Steel Volute Casting

  1. Material Properties and Performance Requirements
    • The choice of ZG12Cr18Ni9Ti stainless steel for the volute casting is based on its excellent resistance to high temperatures and corrosion. In the context of the aviation engine喷气检测装置, the volute needs to withstand the harsh environment of high-temperature gas erosion for a long time. The specific chemical composition of the material, as shown in Table 1, determines its mechanical properties, such as tensile strength, yield strength, and elongation. These properties are crucial for ensuring the structural integrity and reliability of the volute during operation.
    • The chromium content in the stainless steel provides good corrosion resistance, while the nickel addition enhances its ductility and toughness. The titanium addition helps to stabilize the microstructure and improve the resistance to intergranular corrosion. The proper control of these alloying elements is essential to achieve the desired material properties and meet the performance requirements of the volute casting.
  2. Effect of Composition Control on Casting Quality
    • Nitrogen Content Control: In the melting process, the control of nitrogen content is important. Titanium is highly reactive and easily forms TiN with nitrogen, which can lead to the formation of slag on the steel liquid surface and affect the quality of the casting. By reducing the addition ratio of stainless steel pouring and riser return materials and controlling it within 40% – 50%, and adding titanium iron after proper脱氧, the nitrogen content in the steel liquid can be effectively reduced. This helps to prevent the formation of TiN and improve the cleanliness and quality of the molten metal, reducing the risk of defects such as inclusions and porosity.
    • Melting and Solidification Behavior: The composition of the stainless steel also affects its melting and solidification behavior. The appropriate control of the alloying elements can ensure a more homogeneous microstructure during solidification, reducing the occurrence of segregation and shrinkage cavities. For example, a proper titanium content can help to refine the grain size and improve the mechanical properties of the casting. At the same time, during the solidification process, the difference in the solidification rates of different components can lead to internal stress and potential cracking. By carefully adjusting the composition and process parameters, these issues can be minimized.
  3. Quality Inspection and Assurance
    • After the casting is completed, the quality of the stainless steel volute needs to be inspected to ensure that it meets the design requirements. This includes not only the detection of surface defects such as cracks and slag inclusions but also the evaluation of the internal microstructure and mechanical properties. The tensile test results on the随炉试棒, with a tensile strength of 490 MPa, a yield strength of 215 MPa, an elongation of 28%, and a reduction of area of 35%, indicate that the material properties of the casting are within the acceptable range. However, continuous quality monitoring and improvement are necessary to ensure the consistency and reliability of the casting quality. This can involve the use of advanced non-destructive testing methods, such as ultrasonic testing and X-ray inspection, to detect internal defects more accurately. In addition, regular analysis and adjustment of the melting and casting process parameters based on the quality feedback can help to further optimize the casting process and improve the quality of the stainless steel volute castings.

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