Key Takeaways & Executive Findings
- •• A novel gas generation and flow constitution model integrates temperature-dependent gas evolution with Darcy's law, enabling accurate simulation of gas pore formation in iron castings. • The virtual heat transfer method effectively identifies dangerous core regions by leveraging the analogy between heat and gas flow, reducing computational cost. • The model predicts gas pore risk based on gas pressure, melt viscosity, and state, validated by three distinct sand core designs in actual iron castings. • This approach provides a practical tool for optimizing sand core venting and reducing leakage defects in high-integrity castings like cylinder blocks and heads.
Abstract
In the production of castings, intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings, such as cylinder blocks and cylinder heads for engines. It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process. Therefore, a gas generation and flow constitution model was established, in which the gas generation rate is a function of temperature and time, and the flow of gas is controlled by the gas release, conservation, and Darcy’s law. The heat transfer and gas flow during casting process was numerically simulated. The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core. The gas pores in castings are predicted by the gas pressure, the viscosity and state of the melt for these dangerous points. Three distinct sand core structures were designed and used for the production of iron castings, and the simulated gas pore results were validated by the obtained castings.
1. Introduction
The casting method is widely used in critical sectors such as aviation, aerospace, automotive, equipment, and metallurgy industries. To ensure the quality of cast components, it is crucial to prevent the formation of gas pores during casting. Intrusive gas pores are mainly caused by insufficient venting of gases generated during the casting process due to the resin burn-off of sand cores. This phenomenon significantly causes leakage in air-tight required castings such as cylinder block, and cylinder head castings, undermines their mechanical properties and durability and even results in rejection in severe cases. Therefore, the prediction and control of the formation of gas pores is of paramount importance.
The formation mechanism of gas pores in castings is complex and related to numerous factors, therefore, numerical simulation of gas pore formation poses significant challenges. To date, there is still no software available for the prediction of gas pores in castings. Research related to gas evolution and venting in sand cores primarily focuses on the optimization of core structures and exhaust pathways, including the measurements of gas evolution characteristics in sand cores as well. The study of gas evolution performance in sand cores mainly focuses on the determination of gas volume, gas evolution rate, and permeability. There are typically two methods: One is to quantify the generated gas by heating sand samples in a furnace at a specific temperature [1-5]. The other method is to collect produced gases by a liquid metal pouring experiment [6-11].
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Ji-wu Wang, Xiao-long Wang, Yu-cheng Sun, Yu-hang Huang, Xiu-ming Chen, Xiong-zhi Wu, Na Li, Jin-wu Kang, Tao Jing, Tian-you Huang, Hai-liang Yu (2025). Prediction of intrusive gas pores caused by resin burning in sand core for iron castings. China Foundry. https://doi.org/10.1007/s41230-024-4091-9
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Frequently Asked Questions
What causes intrusive gas pores in iron castings?
Intrusive gas pores are caused by gases generated during the resin burn-off of sand cores that intrude into the casting, leading to leakage in high-integrity components like cylinder blocks.
How does the proposed model predict gas pore formation?
The model combines gas generation rate as a function of temperature and time with Darcy's law for gas flow, and uses a virtual heat transfer method to identify dangerous core regions, then predicts gas pores based on gas pressure, melt viscosity, and state.
What is the virtual heat transfer method?
It is a technique that exploits the similarity between heat transfer and gas flow in sand cores to quickly identify critical areas where gas pores are likely to form, reducing computational effort.
How was the model validated?
The model was validated by designing three distinct sand core structures for iron castings, comparing simulated gas pore predictions with actual castings produced.
What are the practical implications of this research?
The research provides a numerical tool to optimize sand core venting designs, reducing gas pore defects and improving the quality and reliability of castings used in automotive and other industries.
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