Abstract
The article delves into the challenges faced in producing gas explosion sand adhesion-free clay sand casting parts, specifically focusing on the surface defects observed in flywheel shell castings. By utilizing MAGMA simulation software, a comprehensive analysis of the gas distribution during the casting process was conducted. This study identifies the root causes of poor exhaust and severe gas explosion sand sticking, leading to the development of effective countermeasures that significantly reduce the occurrence of these defects. The findings highlight the value of simulation tools in enhancing casting quality and process optimization.
Introduction
The production of high-quality sand casting parts, particularly those involving complex geometries and critical applications, presents numerous challenges. One such challenge is the persistent issue of gas explosion sand adhesion, particularly in clay sand casting processes. This phenomenon can significantly impair the surface quality of castings, leading to increased finishing costs and potential product rejection.
In this study, we examine the case of flywheel shell castings produced using a clay sand static pressure line process. These castings have consistently exhibited surface gas explosion sand adhesion defects, despite various attempts at process improvement. To address this issue, we leveraged MAGMA simulation software to analyze the gas distribution during the casting process and identify the underlying causes of the sand adhesion problem.
Background
The flywheel shell (model 7274) is a critical component of the engine system, serving as a crucial component in power transmission. Produced from HT250 grey iron with a raw weight of 20.5 kg, this casting requires tight dimensional control and excellent surface finish to ensure optimal performance. However, surface defects such as sand adhesion and, more specifically, gas explosion sand adhesion, have plagued the production process.
Casting Process
The casting process for the flywheel shell involves a clay sand static pressure line and a coated sand core production process. The molding is achieved through an upper and lower mold setup, with sand cores placed inside the mold cavity to form internal features.
Despite rigorous quality control measures, surface defects such as local sand adhesion and severe gas explosion sand adhesion have persisted.
Previous Improvement Measures
Several attempts were made to mitigate the sand adhesion issues, including:
- Reducing Bentonite and Moisture Content: To improve exhaust and reduce gas generation.
- Increasing Ventilation Holes: To facilitate better gas escape during the casting process.
- Adjusting Pouring System Design: To optimize filling velocity and flow patterns.
While these measures led to some improvement, the results were inconsistent and not sustainable for large-scale production.
MAGMA Simulation Analysis
To gain a deeper understanding of the gas dynamics during casting and identify the root causes of gas explosion sand adhesion, MAGMA simulation software was employed. The simulation focused on analyzing the gas flow, distribution, and accumulation during the filling process.
Simulation Setup
The simulation model included detailed representations of the mold, cores, and pouring system. Key parameters such as sand permeability, metal pouring temperature, and mold preheating temperature were accurately calibrated based on actual process conditions.
Key Findings
The MAGMA simulation revealed several critical issues contributing to the gas explosion sand adhesion:
- Uneven Filling Velocity: Local regions experienced high filling velocities, leading to turbulence and increased gas entrainment.
- Poor Ventilation at Critical Areas: The simulation highlighted inadequate ventilation at the casting’s top regions, causing gas accumulation and subsequent explosion.
- Gas Entrapment and Expansion: The rapid gas generation from sand additives and moisture combined with poor ventilation resulted in high-pressure build-up, triggering gas explosions.
Process Improvement Based on MAGMA Analysis
Guided by the MAGMA simulation results, targeted improvements were implemented in the casting process:
Improved Pouring System Design
- Adjusted Runner and Gate Sizes: Runner cross-sections were optimized to ensure a more uniform filling velocity, reducing turbulence and gas entrainment.
- Modified Gating System: The number and size of gates were increased to facilitate smoother metal flow and reduce localized high velocities.
Enhanced Ventilation
- Additional Ventilation Holes: New ventilation holes were drilled at strategic locations, particularly at the casting’s highest points, to improve gas escape.
- Redesigned Mold Parting Lines: Complex parting lines were simplified to reduce gas entrapment zones and facilitate better gas release.
Material and Process Parameter Optimization
- Reduced Bentonite and Moisture Content: Further reductions in bentonite and moisture levels were implemented to minimize gas generation during casting.
- Controlled Sand Properties: The sand mix was adjusted to ensure optimal permeability and collapsibility, reducing the likelihood of gas entrapment.
Verification of Improved Process
The revised casting process was verified through trial production runs. The results demonstrated a significant reduction in gas explosion sand adhesion defects.
Quantitative Comparison
| Process Parameter | Original Process | Improved Process |
|---|---|---|
| Bentonite Content (%) | 7.5 – 9.0 | 7.0 – 7.5 |
| Moisture Content (%) | 3.4 – 3.6 | 2.95 – 3.15 |
| Number of Ventilation Holes | 6 (Φ14 mm) | 8 (Φ18 mm) |
| Gate Cross-Section (mm²) | 90 (30 x 3 x 3) | 135 (45 x 3 x 4) |
| Defect Rate (Gas Explosion Sand Adhesion) | High (frequent) | Low (occasional) |
Broader Application and Future Work
The success achieved in resolving the gas explosion sand adhesion issue in flywheel shell castings has prompted the application of similar improvements to other clay sand casting parts with similar geometries and processes. Similar defect reduction trends have been observed in 8428 and 0415 flywheel shell castings, demonstrating the widespread applicability of the findings.
Future work will focus on further refining the casting process and simulation models to achieve even higher levels of defect-free production. Additionally, the integration of real-time monitoring and feedback mechanisms during casting will be explored to enhance process control and further reduce defect rates.
Conclusion
The study underscores the importance of utilizing advanced simulation tools such as MAGMA in identifying and mitigating casting process issues. By leveraging the simulation results, targeted process improvements were implemented, resulting in a marked reduction in gas explosion sand adhesion defects in flywheel shell castings. The successful application of these findings to other similar casting parts demonstrates their broad applicability and underscores the value of simulation-driven process optimization in the sand casting industry.