新型圆坯结晶器铜管结构模拟优化设计

为优化设计新型圆坯结晶器铜管结构,提高结晶器寿命和铸坯质量,利用商业有限元软件ANSYSTM建立二维连铸结晶器内钢水凝固传热及弹塑性应力有限元瞬态分析模型,铸坯传热边界采用与气隙相关的热流密度修正函数,建立与温度相关的热物性参数、力学性能和屈服函数,并利用多场间接耦合的方式对不同工况下的4种圆坯在结晶器内的凝固收缩变形过程进行数值模拟.结果表明,钢种和工况条件对铸坯边界凝固收缩过程影响显著,6瓣模型为4种计算模型的最优形状,依据铸坯边界凝固收缩曲线和新型结晶器设计准则,新型结晶器铜管结构设计采用凸型花瓣状内腔和大锥度设计.     

异型坯结晶器与铸坯热力耦合数值模拟

为研究异型坯连铸结晶器内铸坯凝固和变形过程,采用ABAQUS软件建立了异型坯连铸结晶器和铸坯的二维瞬态热力耦合有限元模型,编制ABAQUS用户自定义子程序GAPCON实现结晶器内壁和铸坯之间的传热模拟.计算模型中考虑了铸坯的凝固和热变形、气隙对传热的影响以及铸坯与结晶器之间的接触应力.分别对2种不同水缝设计结晶器进行了数值模拟,数值分析结果表明,小孔水缝设计的结晶器温度峰值较低、热面温度分布更均匀,因而比大孔水缝设计结晶器具有更长的使用寿命和更优的铸坯质量,这一结论与现场试验结果一致.     

FTSC薄板坯连铸结晶器内的热/力行为研究

基于SPHC钢在H2结晶器内的凝固过程,利用有限元软件ANSYS中的单元生死技术,通过改变薄板坯单元的状态建立其在结晶器内随时间变化的二维非稳态模型。模拟出薄板坯在结晶器不同部位处的温度场及应力场分布情况,其结果可为优化结晶器锥度及改善薄板坯质量提供理论依据和技术基础。     

连铸方坯温度场数值分析中的几个问题

本文针对连铸方坯的凝固特性,对铸坯在结晶器及二冷区的边界传热模型进行了修正,取得了与实验相符的结果。本文还就计算坯壳厚度的临界条件进行了讨论,并首次提出有效坯壳厚度的概念,讨论了结晶器冷却能力、拉速等对坯壳厚度的影响。     

不锈钢／普碳钢复合连铸技术及模拟研究

利用长、短水口结合电磁制动技术在同一结晶器内连铸复合钢坯是刚刚发展的一项新工艺。本文发展一种数学模型分析该工艺过程结晶器内两种异质钢液流动及分布特征。采用低Reynolds数湍流模型计算湍流参数，并以虚拟凝固壳来代替实际的凝固计算。通过与文献中的实验结果对比和较系统的数值分析，证明了模型的可靠性和所提方法改善工艺的作用。     

基于ANSYS的TA2板材等离子弧焊接有限元分析

采用ANSYS有限元软件模拟了4 mm厚TA2板材等离子弧焊接过程,计算分析了焊接过程中瞬态温度场分布特征,并在温度场的基础上采用热-应力耦合方法计算分析了TA2等离子弧焊接头应力场分布和焊件的变形特征。结果表明,接头焊缝形貌与实际焊接过程基本吻合,温度场分布呈椭圆形特征,并且在近焊缝处具有较高的温度梯度;焊件中应力呈现拉应力和压应力共存,在焊接过程的瞬态应力场中,热应力为主要因素,而在残余应力分布中,塑变应力为主要因素;焊接完成后的变形呈现角变形特征,最大变形量2.3 mm。     

连铸坯的凝固与传热过程研究

凝固过程实质是传热过程,钢水的凝固实际上是一个强制冷却、加速钢液传热的过程。钢水从结晶器开始凝固,使铸坯形成均匀且具有一定厚度的坯壳,保证足够的强度。凝固过程是在凝固温度区间液体转变为固体的加工过程,已凝固坯壳的冷却是经历形变"热处理"过程。     

电磁超声横波测量连铸钢坯壳厚度

为解决连铸坯壳厚度在线检测问题,提出采用电磁超声横波反射法检测连铸坯壳厚度。对电磁超声横波换能器的激发和接收过程进行模拟仿真,分析横波在连铸坯中的传播情况,获得横波在连铸钢坯内固液两相区分界面处的反射回波。以坯壳厚度为10～50 mm的Q460连铸小方坯为研究对象,通过有限元仿真软件COMSOL,仿真得出温度在800～1300℃范围内时横波速度随温度的变化曲线。根据被测对象内部的温度场分布,得出坯壳内平均声速。利用回波时间与平均声速计算坯壳厚度。实验证明,上述方法可用于测量连铸坯壳厚度,当声时测量误差在1～2μs时,厚度测量误差为2～5 mm。     

混凝土安全壳的LOCA温度场分布与温度内力分析

在混凝土安全壳的结构设计中,LOCA事故下的温度效应是不容忽视的问题。由于其温度变化具有较强的瞬时特征,温度场在壳壁内的分布也具有显著的不均匀性,导致其内力计算较为复杂。而我国现行的安全壳设计规范并没有对LOCA温度效应的计算与设计提出具体的方法。该文基于传热学分析方法计算得到了LOCA事故下不同时刻安全壳壳壁内的温度场分布,可作为安全壳进行温度内力分析的基础;基于弹性力学理论,忽略结构底端的约束效应,提出了安全壳结构在LOCA温度作用下的内力简化分析方法;采用有限元软件ANSYS对安全壳结构在LOCA各时刻温度场作用下的应力、位移、内力等进行了详细分析,并与理论分析结果进行了比较,结果表明两者在一定范围内吻合得较好。     

显式有限元方法求解二维壳体塑性大变形接触问题

本文系统论述了二维壳体塑性大变形接触问题的显式有限元求解方法，包括退化壳单元理论、弹塑性本构方程、应力回映算法、接触搜寻法及计算接触力的拉格朗日乘子法。本文方法已成功地应用到薄板成形过程的有限元分析之中，文中给出了几个计算实例，计算结果与实验结果相当吻合。     

铸型涂层对熔体过冷度和凝固组织的影响

利用溶胶－凝胶方法,在铸型内表面玻璃涂层上制备ＳｉＯ２晶态和非晶态薄膜涂层,将深过冷的Ｃｕ７０Ｎｉ３０合金熔体浇入两种涂层铸型中,分别获得９０Ｋ和１９８Ｋ的过冷度。提出了用重合密度和重合原子中心偏离度分析涂层结构对合金熔体形核惰性影响的模型。用ＢＣＴ模型分析过冷熔体凝固过程中枝晶生长与过冷度的关系,结果表明,８０Ｋ为临界冷度,△Ｔ〈８０Ｋ时,枝晶生长受成分过冷控制;△Ｔ〉８０Ｋ时,受热过冷控制。在深过冷范围内,凝固组织为细密挺直枝晶。     

Thermophysical Property Measurements on Mold Materials: Thermal Expansion and Density

In order to optimize casting processes, computational models of solidification have proven to be very valuable to foundrymen. It is experimentally proven that the casting defects are primarily related to mold properties. During the eutectic growth the temperature rises, which is commonly referred to as recalescence. This has a strong effect on the mold walls, and mold wall movement can occur. The huge pressures generated at this time can block voids if mold is rigid. In green sand molds the moisture content will be reduced and mold wall will expand easily. According to previous research results, a distribution of thermophysical properties of the mold in the mold cavity, and the movement (expansion or contraction) of the mold and the metal interface are crucial for formation of many defects. The thermal expansion and bulk density of selected mold materials (olivine sand and zircon sand) and silica sand cores in transient regimes were determined in this study using a computer-controlled dual-pushrod dilatometer.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al–13% Si alloy

For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al–13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing.     

Molding and casting behavior of ferro chrome slag as a mold material in ferrous and non-ferrous foundry industries

In the present investigation, efforts are made to use Ferro Chrome (Fe-Cr) slag as a mold material for the replacement of silica sand in the foundry industry. The sodium silicate-Fe–Si process is adopted for evaluating the same. The process parameters considered for this investigation are % of sodium silicate, % of Fe–Si powder as a binder, and mold setting time. A series of sand tests are carried out on sand, slag individually, and for various combinations of these two. Three types of molds are made with sand, slag individually, and combination of these two with 6% sodium silicate and 1.5% Fe–Si. Various ferrous and non-ferrous castings are performed on these newly developed slag molds. The results reveal that the Fe-Cr slag with mold permeability, compression, and shear strength is a suitable candidate for either partial or full replacement of silica sand. During casting neither fusing, dripping, nor collapse of the mold walls is observed in slag molds; this is true for both ferrous and non-ferrous castings. Castings with good surface finish and no surface defects are made by slag molds. Faster heat transfer in slag molds enable to obtain castings with enhanced metallurgical and mechanical properties.     

Fabrication, properties and application of porous metals with directional pores

This paper reviews the recent development of fabrication methods, various properties of porous metals with directional pores and its applications. This porous metals are fabricated by unidirectional solidification in pressurized gas atmosphere such as hydrogen, nitrogen and oxygen. The pores are evolved from insoluble gas when the melt metal dissolving the gas is solidified. The nucleation and growth mechanism of the directional pores in metals are discussed in comparison with a model experiment of carbon dioxide pores in ice. Three fabrication techniques, mold casting, continuous zone melting and continuous casting techniques, are introduced. The latter two techniques can control the solidification velocity and the last one possesses a merit for mass production. The porosity and pore size are able to be controlled by solidification velocity and ambient gas pressure, while the pore direction can be controlled by solidification direction. Not only metals and alloys but also intermetallic compounds, semiconductors and ceramics can be produced by this method. Anisotropy in the mechanical and physical properties is resulted from anisotropic pore morphology. The experimental results on the anisotropy in the elastic property and electrical conductivity are consistent with those calculated with an effective-mean-field theory. The anisotropic behaviors of tensile, compressive and fatigue strength are explained in terms of the dependence of stress concentration on the pore orientation. This porous metals exhibit good sound absorption and vibration-damping properties. Several possible applications are in progress for heat sink, golf putter, biomaterials and so on.     

SCM435钢大方坯凝固过程组织的模拟

为了模拟不同冷却状态下的连铸坯的凝固组织,利用反算确定了SCM435钢325 mm×280 mm连铸坯的换热系数,采用有限元法模拟了连铸传热过程,获得了连铸坯的温度场及冷却速率,在此基础上与元胞自动机耦合模拟了连铸坯的凝固组织.研究发现,表面细晶区很大,且在连铸结晶器中完成形核并长大形成,而柱状晶开始形核于结晶器末端.降低形核数,晶粒密度、最大晶粒面积、平均半径存在不同程度的改变,其中晶粒的最大截面积增加了2.7倍,而微调成分对晶粒密度与平均半径影响较小,但同样凝固条件下晶粒不均匀程度有所加剧.     

Investigation on the transferability of algorithms for the numerical optimization of cooling channel design in injection molding on metal gravity die casting

The thermal mold design and the identification of a proper cooling channel design are primordial steps in the development of complex molds for injection molding. In order to find a suitable cooling channel system, a lot of effort is needed to avoid part warpage after solidification. In current research, a simulative procedure to optimize the cooling channel layout iteratively is being developed at the Institute of Plastics Processing. These algorithms are transferred to the metal gravity die casting process, which has several similar requirements to the mold. Effectively, the simulation is simplified to a heat conduction problem. Instead of water, high temperature resistant oil is deployed and the casted material is a A356 aluminum alloy instead of semi‐crystalline plastics. The algorithm is adapted to these changed boundary conditions and the calculation of the optimized heat distribution is performed. Aim of this procedure is the construction of a mold producing parts with less warpage than a conventional mold.     

Finite element numerical simulation on thermo-mechanical behavior of steel billet in continuous casting mold

The thermo-mechanical behavior of a thin, growing shell during the early stages of solidification in a continuous casting mold is very important to the ultimate quality of the final billet. A two-dimensional, transient finite element model has been developed to treat the heat flow and deformation of the solidifying shell in the continuous casting billet mold as a coupled phenomena. The major application of the model is to predict the extent of the gap between the mold and the shell and focus on the influence of mold taper on the thermo-mechanical behavior of the steel billet to help to understand the formation of off-corner cracks and break-outs in the solidifying shell. The calculations indicate that the gap is initially formed at the corner of the billet, where heat transfer is greatly reduced. Insufficient mold taper contributes to a hot spot in the off-corner region, which corresponds to the lowest shell thickness. At the same time, the solidifying front on the diagonal of the billet is subjected to an excessive mechanical strain, which causes the off-corner cracks and even the break-outs.