Numerical simulation of filling and solidification of permanent mold castings

Filling of a mold is an essential part of the permanent mold casting process and affects significantly the heat transfer and solidification of the melt. For this reason, accurate prediction of the temperature field in permanent mold castings can be achieved only by including simulation of filling in the analysis. In this work we model filling and solidification of a casting of an automotive piston produced from an aluminum alloy. Filling of the three-dimensional mold is modeled by using the volume-of-fluid method. Fluid mechanics and heat transfer equations are solved by a finite element method. Comparisons of numerical results to available experimental data show that the formulated model provides a solution of acceptable accuracy despite some uncertainty in material properties and boundary and initial conditions. This implies that the model can be a viable tool to design permanent molds.     

Numerical simulation of the casting process of a wind turbine rotor hub

An integrated numerical model was applied to simulate the mold filling and solidification process as well as predict the occurrence of relative casting defects for a rotor hub casting. The goal was to conduct a numerical experimentation to obtain an optimal alloy design of ductile cast iron for the rotor hub casting. A computer‐aided engineering software based on the finite element method was employed in this study. Numerical simulations were conducted for the rotor hub casting with two different types of alloy composition for ductile cast iron. The mold filling and solidification process were examined to predict the occurrence and extent of casting defects and a better alloy design was then proposed based on the simulated results to alleviate casting defects of the rotor hub casting. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical prediction of turbulent flow and heat transfer with phase change in crystallizer of inverse casting

horoductionInverse casting is a technique for Producing nearnet-shape cast strips. T'he main idea of this technique isdeveloped from a successful inveshgation['], in which ithas been Proved that the inverse cashng teclmiquewould be applicable to produce the steel strip with aabackness of 0.5-3 nun, with a good material prOPertyand with a lower energy consumption in contrast withconventional conhnuous cashng process. The POssibilitytO p~ce composite strips is also one of the mostattrachve pro…     

The study on polymer melt front,gas front and solid layer in filling stage of gas-assisted injection molding

The algorithms are developed to predict the polymer melt front, gas front and solid layer in gas-assisted injection molding. The simulation of two-dimensional, transient, non-isothermal and high viscous flow between two parallel plates with the generalized Newtonian fluid is presented in detail. During solidification while an injection mold fills, a solid-liquid interface moves and a two-phase zone exists; an enthalpy model is used to predict this interface in the two-phase flow problem. The model takes into account the three-phase flow including the effects of the gas front, solid layer and polymer melt front.     

Numerical Method for Calculation of Complete Casting Processes—Part I: Theory

This article presents a method for calculation of the complete casting process, including the pouring of the liquid metal into the mold, its solidification, the deformation of the solidified cast, the formation of airgaps between the cast and the mold and their influence on the heat transfer, and the residual stresses. An original phase-change procedure is developed, valid for an arbitrary number of pure metals and/or alloys. A collocated version of a segregated finite-volume method is used to calculate both the liquid metal flow and the deformations and stresses in solids.     

Simulation of Slag-Skin Formation in Electroslag Remelting Using a Volume-of-Fluid Method

A modified volume-of-fluid method is implemented in a fixed-grid, finite-volume model simulating transport phenomena, solidification, and electromagnetics. The VOF model agrees well with published results, and the complete model is used to investigate process variations in the electroslag remelting process, in which liquid metal is melted from a consumable electrode immersed in an electrically resistive slag. The molten metal sinks through the slag cap floating on the liquid metal pool while a slag skin freezes to the mold. Here a VOF tracks slag skin formation and its effects on melt rate with different current levels and ingot diameters.     

FTSC结晶器内钢渣两相运动行为的数值模拟

利用VOF方法建立两相湍流瞬态流动模型对FTSC结晶器内钢-渣界面运动和钢液流场分布进行了数值模拟计算,考察了水口结构、拉速对钢液流动及钢渣界面运动行为的影响作用。计算结果表明：采用不同结构的4孔水口进行浇注时,在结晶器内宽面方向一侧形成数量不等、位置不同的回流区;结晶器内的钢渣界面形状及出现液面裸露的位置由于水口结构的不同均有所差异。     

Melt cavitation at its volumetric crystallization

It is shown that at volumetric crystallization of the undercooled melt the high negative pressures are generated in this melt; they are caused by matter shrinkage at solidification, what leads to intensive cavitation of uncrystallized melt. The mechanisms are studied and the kinetic model of this process is presented here. Considerable dependence of cavitation intensity on the cooling rate is shown. Numerical solutions to the problem are found at the example of cavitation of crystallizing metal melts. The sizes of crystalline grains and formed cavitation inclusions in the solidified material are determined.     

Studies on turbulent momentum, heat and species transport during binary alloy solidification in a top-cooled rectangular cavity

A two-dimensional transient fixed-grid enthalpy-based numerical method is developed to analyze the effects of turbulent transport during a binary alloy solidification process. Turbulence effects are introduced through standard k-ε equations, where coefficients are appropriately modified to account for phase-change. Microscopically-consistent estimates are made regarding temperature-solute coupling in a non-equilibrium solidification situation. The model is tested against laboratory experiments performed using an NH₄Cl-H₂O system in a rectangular cavity cooled and solidified from the top. Particular emphasis is laid on studying the interaction between Rayleigh-Benard type convection and directional solidification in the presence of turbulent transport. Numerical predictions are subsequently compared with experimental results regarding flow patterns, interface growth and evolution of the temperature field, and the agreement is found to be good.     

离心铸造太阳电池硅片液态成形机制的研究

为了将离心铸造技术成功地移植到低成本超薄多晶太阳电池硅片的成形工艺上，提出了ＥＬＣＣ技术的硅片液态成形方法，即将铸模型腔预热至硅熔点以上温度，过热的硅液被浇注到型腔后，在离心力的作用下始终保持液态充型。这种成形机制易于实现厚度小于１ｍｍ的硅片的完整成形，而且对模具转速、硅液过热度等要求较低。采用该方法，硅片的成形与结晶不会同时发生，可以在硅片液态成形后，采用定向凝固的方法获得粗大的定向柱晶组织，提高硅片的光伏性能。采用理论分析、计算机模拟与工艺实验相结合的方法，对ＥＬＣＣ技术硅片液态成形机制进行了研究，为进一步对硅片凝固过程组织控制的研究奠定基础。     

Modeling and simulation of heat transfer phenomena during investment casting

Determining the heat transfer phenomena during casting processes is an important parameter for measuring the overall performance of process. It gives information about the properties of the metal being casted and its possible behavior in the mold during casting process. Improper determination of heat transfer phenomena and use of improper molding materials and casting conditions leads to defects such as misruns, cold shuts, shrinkage, pin holes, air holes and porosity in final product. A mathematical model was developed using standard transport equations incorporating all heat transfer coefficients to calculate the time for solidification of metal in casting and computer simulation of the model was carried out in C++ to validate the model. The metal used was pure iron casted in investment molds of silica sand with zircon coating. It was shown that airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. So, the changes in heat transfer coefficient also contribute towards time of solidification. The time calculated was found to be in good agreement with experimental values.     

一种燃机叶片试板定向凝固过程的研究

明确铸件定向凝固过程中的温度变化规律．可以避免重型燃气轮机定向叶片铸造中出现的一些缺陷。文章选取了与某重型燃机第1级涡轮动叶尺寸相近的试板．采用定向凝固高温合金DZ445．研究了该试板在实际工业生产用定向结晶炉中的定向凝固过程,结果表明：在距离水冷铜盘位置〉50mm后固液界面形态将发生大的转变,温度梯度逐渐变小,〉100mm后温度梯度基本保持不变．这为后续制定叶片抽拉工艺给出了参考。该实验还通过热电偶获得的定向凝固过程中温度一时间曲线与ProCAST模拟结果基本一致．验证了模拟边界条件和设置参数的准确性．后续可以用于模拟结构复杂的叶片定向凝固过程．指导实际生产工艺.     

Numerical and Experimental Investigation of Solidification Shrinkage

The solidification heat transfer, melt convection, and volume shrinkage in the casting of an energetic material are analyzed through numerical modeling and experimental investigation. The shrinkage resulting from phase change is considered through the volume-of-fluid method. The model is validated against an analytical solution and then applied to study the volume contraction during the casting of trinitrotoluene (TNT). Good agreement is obtained between experimental results and predictions of temperatures at selected locations as well as shrinkage shape. New casting conditions are suggested based on the analysis, and improved results are observed both numerically and experimentally.     

Suppression of melt convection in a proposed Bridgman crystal growth system

Numerical simulations are performed for Bridgman crystal growth of several semiconductor materials, such as InAs, InSb, GaSe, CdTe, PbTe, and GaP. For materials with low Prandtl and low Grashof numbers, melt convection is weak and the traditional Bridgman technique is a suitable growth process. For the materials with high Prandtl numbers in their melt status and the growth system with high Grashof number, the temperature field and the growth interface are significantly influenced by melt flow, resulting in the complicated flow pattern and curved interface shape. A new Bridgman crystal growth system is proposed to suppress convection and improve solidification interface shape by cooling of the top melt. The results obtained from the proposed design demonstrate that melt convection may be controlled by adjusting the design parameters. Further, parametric studies are performed to determine the influence of the control parameters on melt flow and solidification interface.     

Three—Dimensional Flow Characteristics in One Ceramic Candle Filter

INTRODUCTIONThe stringent regulation of CO2, SOx or NOx,which are the main cause of the environmental contamination, is getting strengthened to save earth.Since it has influence on the energy industries, Integrated Gasification Combined Cycle (IGCC) amongthe clean coal technologies has attracted the increasing attention to meet restrictions on the environmental contamination and to promote high efficiency. TheClean Coal Technology (CCT) requires a competenthot-gas cleanup facility …     

Filling-box process during solidification of a liquid hypoeutectic binary solution

Solidification of binary solutions often occurs in many industrial applications, including the casting of binary alloys. In this study we consider the effect of a side cooling wall on the development of double-diffusive convection during solidification of a hypoeutectic aqueous ammonium chloride (NH₄Cl–H₂O) solution. To study flow development during solidification of this solution, we used the shadowgraph technique, particle image velocimetry, and a thermochromic-liquid-crystal slurry. In addition, the transient temperature distribution within the test cell was measured by type-T thermocouples. The results of these experiments revealed that the filling-box process originated from the bottom of the test cell to the top. This process induced several double-diffusive layers and counterclockwise roll cells in the melt, mainly caused by double-diffusive convection. Consequently, the filling-box process may cause serious V-segregates and material defects in solidified ingots.     

Transient freezing of liquids in forced flow inside convectively cooled tubes

The aim of this investigation is to study the characteristics of solidification of a liquid flowing through a convectively cooled pipe under different flow situations. A mathematical model is developed by establishing an energy balance. The amount of heat transferred from the liquid layer to the freeze-front in a tube section is directly proportional to the convective heat transfer coefficient and the difference between the average temperature of the fluid at the section and the freezing point. The limiting conditions for the commencement of the solidification process are stated. The formulated set of conjugated heat transfer equations is analysed for both laminar and turbulent flows. The governing equations are solved numerically for a specific range of parameters and their characteristics of the process discussed.     

Modeling and Measurements of Heat Transfer Phenomena in Two-Phase PbSn Alloy Solidification in an External Magnetic Field

The main aim of this work is to study numerically the influence of an external magnetic field on the solidification processes of two-component materials. Based on the continuum model of two-phase flow a mathematical model for the directional solidification of a binary alloy in a magnetic field is presented. The model includes mass, momentum, energy and species mass conservation equations written in compressible form and additional relationships describing the temperature-solute coupling. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The macroscale transport in the solidification of alloys is governed by the progress of the two-phase mushy zone, which is treated by means of a porous medium approach. The volume fraction of liquid and solid phases, respectively, is calculated from a 2D approximation of the phase diagram. The results of calculation are compared with experimental data.     

Mathematical model for turbulent flow,heat transfer,and solidification

A steady‐state, two‐dimensional numerical model has been used to describe coupled liquid steel's turbulent flow and heat transfer with solidification for Fe‐C binary alloy in a crystallizer of inverse casting. The solid‐liquid phase change phenomena have been modeled by using continuum formulations and considering the mushy zone as porous media. The turbulence flow in the crystallizer has been accounted for using a modified version of the low‐Reynolds‐number κ?ε turbulence model. The flow pattern in the liquid zone and the temperature distribution in the solid, mushy, and liquid regions have been predicted. The numerical analysis indicates that the residence time of the mother sheet in the crystallizer is one of the key parameters. The effects of some other main parameters on the solidification behavior have also been studied, such as the thickness and the initial temperature of the mother sheet, and the superheat degree of liquid steel. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(7): 582–592, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10112     

Analysis and Suppression of Base Separation in the Casting of a Cylindrical Ingot

This paper presents a comprehensive numerical investigation of the influence of cooling conditions on base separation, void formation, and thermally induced stresses during the solidification of a high Prandtl number energetic melt in a cylindrical enclosure. Numerical models have been developed to simulate the heat and mass transfer processes in melt casting as well as analyze the base separation and thermal stresses induced during solidification. Two models are dynamically coupled, and the numerical predictions are validated against experiments. Based on the numerical analysis, modified cooling conditions are suggested that are shown to reduce base separation.