Preliminary Study On Numerical Simulation Of Gas Production And Diffusion In Core During Sand Casting

Porosity is one of the most common defects in casting, it affects the mechanical properties and reliability of castings, serio usly, and restricts the improvement of casting quality. Because the sand core heating up fast, having a long exhaust path, and the amount of gas generated by binder decomposition is large, in the process of sand mold casting that core gas is an important factor of porosity. Compared with traditional methods, using computer simulation techniques to study the core gas can take factors such as temperature, pressure, environmental conditions etc. couples to study the core gas. Besides the complexity of the core geometry can also be taken into consideration. All the advantages talked above can provide conveniences for us to explain the causes and course of gas generation and transportation in core during casting process. In this study, a mathematical model of the core gas production and diffusion is built and a preliminary study on numerical simulation of gas production and diffusion in core is carried.Based on the theory of chemical kinetics- Arrhenius equation the decomposition amount of binder during the casting solidification process is calculated. And the amount of gas generated by the decomposition of binder from core is acquired according to the mass conservation law. According to the ideal gas state equation, acquired gas density and temperature the pressure distribution within the core is calculated with. And the gas velocity distribution is obtained by the application of porous media Darcy's law.In the article an improved model is built to predict behavior of gas generation and diffusion by resin sand. Effect of speed on the permeability coefficient in the fluid dynamics model is considered in, which is a factor less consideration in the previous model. For discrete, finite volume method mathematical model is used here, and the SIMPLE algorithm is used to calculate and solve mathematic equations. Using SIMPLE algorithm can not only guarantee the accuracy of the results of numerical solution, and it can also avoid the time-consuming problem as well as applying a small amount of memory. Besides this artic le ensures the accuracy and stability of measurement results with the sub time step and sub-grid.Four examples are simulated and analysis to verify the feasibility and accuracy of the model; Gas enters into the cast mainly in the early stages. By comparing the impact of the vent, illustrates that during the design process, the porosity can be reduced and the quality of casting products can be improved through the rational design of vent. Therefore, with the simulation of core gas generation and diffusion, pores defect can be predicted accurately. The simulation can also provide a reference for the actual production process, has great practical value in optimizing production process, and improving the performance and productivity of the casting.