Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this ...Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.展开更多
In this paper, an algorithm for simulating fluid flow and heat transfer for mold filling of shaped castings is presented. The main features of the algorithm include: 1) a simple but practical technique based on VOF me...In this paper, an algorithm for simulating fluid flow and heat transfer for mold filling of shaped castings is presented. The main features of the algorithm include: 1) a simple but practical technique based on VOF method to determine free surface, 2) an explicit scheme of enthalpy to solve the energy equation more efficiently, and 3) an effective treatment to modify the flux deviation due to pressure iteration. In order to verify these methods, well controlled experiments have been repeatedly done with both water analog and gray iron pouring experiments to record the flow patterns and temperature variations. The calculated results are in accordance with the experimental ones. For the applications, the simulated initial temperature distribution right after mold filling was used to analyse subsequent solidification and to predict shrinkage defects. Actual castings were poured and tested in a foundry plant. The reuslts show that the defects predication with considering fluid flow effects is more precise than that without considering the effects.展开更多
The effects of the binder composition, the powder loading, the thermal properties of feedstocks, and the injection molding parameters on the compact shape retention for metal injection molding 17-4PH stainless steel w...The effects of the binder composition, the powder loading, the thermal properties of feedstocks, and the injection molding parameters on the compact shape retention for metal injection molding 17-4PH stainless steel were investigated. The high-density polyethylene is more effective than ethylene vinyl acetate as a second component of the wax-based binder to retain compact shape due to its higher pyrolytic temperature and less heat of fusion. The compact distortion decreases with increasing the powder loading, molding pressure and molding temperature. There exists an optimal process combination including the powder loading of 68%, molding pressure of 120MPa and molding temperature of 150℃. Under this process condition, the percentage of distorted compacts is the lowest.展开更多
The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during productio...The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during production were explored. The results show that the solid volume loading of less than 50vol% and the surfactant mass fraction of 6wt% result in a perfect flowability of feedstock; this feedstock is suitable for injection molding. When the debinding time is 8 h at 40°C, approximately 50% of the wax can be solvent debinded. Defects detected during the preparation are traced to improper injection parameters, mold design, debinding parameters, residual stress, or inhomogeneous composition distribution in the green body. The bulk density, Vickers hardness, and fracture toughness of the gas-pressure-sintered Si3N4 ceramic reach 3.2 g/cm^3, 16.5 GPa, and 7.2 MPa·m^1/2, respectively.展开更多
Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established ...Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-ε model were applied to simulate the flow field of the three phases(steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab.展开更多
Facing the market economy and global challenge the development ofmanufacturing industry especially casting industry is critical to the national economy. To reformthe traditional casting industry by using computer tech...Facing the market economy and global challenge the development ofmanufacturing industry especially casting industry is critical to the national economy. To reformthe traditional casting industry by using computer technology is one of the hottest researchfrontiers studied by many researchers and engineers. Computer simulation of solidification processof shaped casting can assure the quality of casting, optimize the casting technology, shorten thelead time and therefore decrease the developing and manufacturing cost. Recently, numericalsimulation of mold-filling and solidification processes of shaped casting and prediction ofmicrostructure and property as well are extensively studied and put into application in many castingplants with many successful simulation cases.展开更多
文摘Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.
文摘In this paper, an algorithm for simulating fluid flow and heat transfer for mold filling of shaped castings is presented. The main features of the algorithm include: 1) a simple but practical technique based on VOF method to determine free surface, 2) an explicit scheme of enthalpy to solve the energy equation more efficiently, and 3) an effective treatment to modify the flux deviation due to pressure iteration. In order to verify these methods, well controlled experiments have been repeatedly done with both water analog and gray iron pouring experiments to record the flow patterns and temperature variations. The calculated results are in accordance with the experimental ones. For the applications, the simulated initial temperature distribution right after mold filling was used to analyse subsequent solidification and to predict shrinkage defects. Actual castings were poured and tested in a foundry plant. The reuslts show that the defects predication with considering fluid flow effects is more precise than that without considering the effects.
基金Project(2001AA337050) supported by the National High Technology Research and Development Program of China ject(81041) supported by the Huo Yindong Education Foundation project(200135) supported by the Chinese Excellent Dissertation
文摘The effects of the binder composition, the powder loading, the thermal properties of feedstocks, and the injection molding parameters on the compact shape retention for metal injection molding 17-4PH stainless steel were investigated. The high-density polyethylene is more effective than ethylene vinyl acetate as a second component of the wax-based binder to retain compact shape due to its higher pyrolytic temperature and less heat of fusion. The compact distortion decreases with increasing the powder loading, molding pressure and molding temperature. There exists an optimal process combination including the powder loading of 68%, molding pressure of 120MPa and molding temperature of 150℃. Under this process condition, the percentage of distorted compacts is the lowest.
基金financially supported by the National Nature Science Foundation of China (Nos. 51102024 and 21276028)
文摘The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during production were explored. The results show that the solid volume loading of less than 50vol% and the surfactant mass fraction of 6wt% result in a perfect flowability of feedstock; this feedstock is suitable for injection molding. When the debinding time is 8 h at 40°C, approximately 50% of the wax can be solvent debinded. Defects detected during the preparation are traced to improper injection parameters, mold design, debinding parameters, residual stress, or inhomogeneous composition distribution in the green body. The bulk density, Vickers hardness, and fracture toughness of the gas-pressure-sintered Si3N4 ceramic reach 3.2 g/cm^3, 16.5 GPa, and 7.2 MPa·m^1/2, respectively.
基金supported by the National Natural Science Foundation of China(No.51504020,and No.51404019)Beijing Key Laboratory of Green Recycling and Extraction of Metals(GREM)+1 种基金the Laboratory of Green Process Metallurgy and Modeling(GPM2)the High Quality Steel Consortium(HQSC)at the School of Metallurgical and Ecological Engineering at University of Science and Technology Beijing(USTB),China
文摘Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-ε model were applied to simulate the flow field of the three phases(steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab.
基金This project is supported by Natural Science Foundation of China(No.59990470-3)Ford-China R &D Project(No.9715509)and Significant Fundamental Research Project of State Ministry of Science and Technology of China(No.G2000
文摘Facing the market economy and global challenge the development ofmanufacturing industry especially casting industry is critical to the national economy. To reformthe traditional casting industry by using computer technology is one of the hottest researchfrontiers studied by many researchers and engineers. Computer simulation of solidification processof shaped casting can assure the quality of casting, optimize the casting technology, shorten thelead time and therefore decrease the developing and manufacturing cost. Recently, numericalsimulation of mold-filling and solidification processes of shaped casting and prediction ofmicrostructure and property as well are extensively studied and put into application in many castingplants with many successful simulation cases.
