Abstract: This paper introduces the structural characteristics and quality requirements of the intercooler seat tube made of nodular cast iron. It focuses on the casting process through the rational selection of the parting surface, sand core segmentation, core support structure, chilled iron design, and pouring system. The anti-error technology is adopted to improve the dimensional accuracy of the castings and eliminate the shrinkage cavity and porosity defects, achieving the purpose of simplifying operations and improving product quality.
1. Introduction
The intercooler seat tube is an innovative design for large internal combustion engines, integrating functions such as diesel engine air intake and water intake. This component belongs to the thin-walled box-type casting category, with stringent requirements in terms of structure, material, and quality.
Table 1: Product Specifications of the Intercooler Seat Tube
| Attribute | Value |
|---|---|
| Material | QT500-7 Nodular Cast Iron |
| Dimensions (mm) | 2154 × 506 × 232 |
| Weight (kg) | Approximately 235 |
| Main Wall Thickness (mm) | 10 |
| Flange Back Tabs (mm) | 50 × 50, evenly distributed |
| Wall Thickness Tolerance (mm) | ±0.405 |
2. Quality Requirements
- Hydraulic Test: After processing, the entire internal cavity and side pipelines of the intercooler seat tube must maintain a pressure of 0.5 MPa for at least 5 minutes without any leakage. The machined surfaces must be free from porosity, shrinkage, and other casting defects.
- Surface Quality: High surface quality is required, with no sand adhering, iron penetration, or other defects. The inner and outer walls must have a smooth transition, and the surface roughness must meet specified requirements after shot peening.
- Dimensional Accuracy: The wall thickness of the casting must be inspected and must not exceed the tolerance range. The finished weight is required to be 225 kg.
3. Casting Process Design
Table 2: Casting Process Overview
| Step | Description |
|---|---|
| Molding Process | Two-box core assembly molding is adopted. The supplementary sand cores on the side lower mold are enlarged to the top surface of the casting. To fully utilize existing sand boxes and simplify the mold structure, the lower mold pattern is only made up to the center of the water pipes. |
| Pouring System | A bottom-return pouring system is set at the bottom of the internal cavity of the intercooler seat tube. It ensures stable mold filling and effective slag blocking. |
| Sand Core Error Prevention | Positioning is added between the upper and lower layers of the inner cavity sand cores to ensure accurate positioning. Anti-error designs are implemented for similar sand cores to prevent misplacement. |
| Core Support and Chilled Iron | Core supports with a 2 mm thick iron sheet and a shape consistent with the sand core outer circle are used to enhance stability. Chilled iron is placed at the thick tabs to balance the solidification speed and prevent shrinkage porosity defects. |
3.1 Molding Process
Adopting the two-box core assembly molding method simplifies molding operations and reduces mold manufacturing costs.
3.2 Pouring System Selection
The bottom-return pouring system ensures stable mold filling, prevents slag entry, and reduces defects such as cold shuts.
3.3 Sand Core Error Prevention Design
Positioning devices are added to prevent sand core misplacement, effectively avoiding casting scrap.
3.4 Core Support and Chilled Iron Design
Enhanced core supports improve sand core stability, and chilled iron placed at thick sections eliminates shrinkage porosity defects.
4. Process Implementation Results
After adopting this process, the quality of the intercooler seat tube castings significantly improved. Defects such as slag holes and cold shuts were completely eliminated. The rate of shrinkage porosity and leakage defects was greatly reduced, with a waste rate below 3%. The workload of molding and mold closing was reduced, and production efficiency was increased.
5. Conclusion
- For castings with large through-holes, setting a bottom-return pouring system ensures stable mold filling and effective slag blocking.
- Core supports with consistent shapes and increased thickness improve sand core stability and reduce floating.
- Setting chilled iron at localized hot spots eliminates shrinkage porosity defects.
- Changing from a three-box to a two-box molding process simplifies operations and improves casting dimensional accuracy.
This research provides valuable insights into the casting process of nodular cast iron intercooler seat tubes, contributing to the improvement of product quality and production efficiency.