薄板坯连铸结晶器内钢液流动与传热及凝固耦合的数值模拟

针对断面为135 mm×1200 mm的薄板坯连铸结晶器,建立了4孔浸入式水口下薄板坯连铸结晶器内钢液流动、传热和凝固耦合的三维数学模型,引入F数评价薄板坯连铸结晶器内液面波动情况,分析结晶器内钢液流动、温度分布及凝固坯壳厚度的变化情况. 结果表明,用F数评价薄板坯连铸结晶器内液面波动可行,拉速由1.44 m/min增加到1.80 m/min时,钢液液面波动的F数由1.05增加到2.55,凝固壳厚度(dshell)与凝固时间(t)满足关系式dshell=18.92t1/2?1.05,模拟结果与文献实验结果基本一致.     

拉坯速度对结晶器内钢液流动和温度分布的影响

针对板坯连铸过程,建立了钢液流动、传热、凝固的三维耦合数值计算程序,计算分析了拉坯速度对结晶器内钢液的流动、凝固特征的影响.计算结果表明,拉坯速度对流动的影响主要表现在宏观速度的大小上,不会影响流动的形态.但对传热和凝固过程有重要影响,直接影响到凝固终点的位置.凝固终点的长度与拉坯速度成正比关系.     

板坯连铸凝固过程动态耦合数值模拟

基于实际生产测得的数据,采用连续动态三维耦合模型对板坯连铸凝固过程的流场、温度场和凝固进行模拟. 结果表明,由浸入式水口进入的钢液在结晶器内冲击形成上下两股回流,凝固促进了流动速度的衰减,提高拉速扩大了回流区域;结晶器内铸坯宽面偏角部100~150 mm处存在局部过热,在结晶器出口,拉速由0.02 m/s增加到0.025 m/s,坯壳厚度减小约3 mm.     

钢液对软接触结晶器内三维电磁特性影响的数值模拟

运用有限元程序,数值模拟了有、无钢液条件下电磁软接触结晶器内的三维电磁特性. 结果表明: 结晶器内的电磁特性与有、无钢液密切相关, 软接触结晶器内的电磁场对钢液面波动十分敏感, 线圈位置对电磁场的影响效果受有、无钢液所决定, 高频电磁场有利于弯月面的约束成形和减小电磁力对内部钢液的搅拌, 建议采用20 kHz以上的频率, 电磁场主要集中在铸坯外表面约10 mm厚度的范围内.     

电磁制动对连铸器内钢水流场的影响及表面检测

采用数值模拟与钢水表面插钉法,对电磁制动条件下薄板坯连铸结晶器内钢水流动进行研究,分析了不同磁场强度对结晶器内钢水流动及弯月面波动的影响.模拟结果表明,电磁制动能够明显抑制高速流动的钢水,减小对结晶器窄面的冲击及钢水表面卷渣的影响,磁场电流强度由180A增加到284A时,钢水表面速度最大值由无电磁制动的0.85m/s分别降低至0.5,0.16m/s.插钉法可作为一种经济有效的方法检测钢水表面速度,且测量值与模拟结果比较吻合.通过合理控制磁场电流强度约260A可以优化结晶器内钢水流动,进而改善铸坯质量.     

基于FLUENT对水平连铸结晶器凝固过程数值模拟

对圆柱形钢坯的水平连铸问题,采用轴对称二维传热模型,基于FLUENT软件,通过简化边界条件的方法,对初期坯壳生长规律作了计算分析,与射钉结果相比较得到很好验证.通过分析过热度和拉速对出结晶器坯壳厚度,液芯长度的影响,发现40Cr拉速提高0.1 m/min,出结晶器坯壳减薄0.91 mm,过热度每增加10℃,出结晶器坯壳减薄1.4 mm等凝固特点,降低过热度有助于提高拉速.由凝固曲线看出,在刚开始的0～2 m内,曲线斜率大,说明冷却强度大,圆坯在凝固后期有个加速凝固阶段.     

连铸FC结晶器电磁参数的优化

为了优化国内某钢厂FC(Flow Control)结晶器电磁制动参数以适应生产需要,研究了不同电磁参数下的磁场对结晶器内钢液流动形态的影响. 结果表明,FC结晶器内最大磁场强度与电流成正比;电流在一定范围内(I<665 A)变化可控制表面流速大小,超过该范围则主要影响钢液表面流速大小的位置分布;流股撞击深度随电流增加而减小,窄面撞击压强在电流为665 A时达到最大值1890 Pa;下部磁场位置变化与表面流速最大值成正比,且比上部磁场位置变化对钢液表面流速的影响更大,钢液表面流速随上衔铁位置变化的最大波动值为0.010 m/s,而随下衔铁位置变化的最大波动值为0.025 m/s;FC结晶器内流场形态是上、下磁场大小及位置共同作用的结果.     

板坯连铸结晶器内流场的数值模拟

针对某钢厂板坯连铸机结晶器的结构和工艺参数,建立了描述结晶器内钢液流动的三维数学模型,用商用软件FLUENT,运用湍流动能Κ方程和湍流动能散耗率ε方程的Κ-ε方程模型在给定的数值计算条件下,对板坯连铸结晶器内钢液的流场进行了模拟.通过模拟浇注初期钢液的流动状态,分析了结晶器内流场的基本特征.同时模拟计算了浸入式水口的出口倾角、插入深度以及拉速对钢液流动的影响.得出了满足断面要求的合理工艺参数:水口倾角为向下15°,插入深度为200mm,拉坯速度为1.3 m/min.     

矩形钢坯结晶器浸入式水口结构设计与优化

以某公司矩形钢坯连铸机结晶器为研究对象,利用数值模拟和物理模拟相结合的方法,对结晶器内钢液流动及温度分布进行系统分析,分别计算不同浸入式水口倾角、浸入深度、拉速等条件下结晶器内钢液流动状态及热流分布,并对相应的工艺参数进行优化. 结果表明,对于断面为150 mm′330 mm的矩形坯,最优的结晶器浸入式水口侧开孔形状为跑道形,内径30 mm,侧开孔角度25o.     

超宽板坯结晶器内流场和温度场的耦合数值模拟

以南钢3250超宽板坯结晶器为研究对象,基于商业软件FLUENT,建立了超宽板坯结晶器三维有限体积模型,对结晶器内钢液流动状况和传热行为进行了耦合数值模拟,研究了超宽板坯结晶器流场和温度场特征,考察了水口结构参数和结晶器宽度尺寸、水口倾角、水口插入深度、拉速、过热度及冷却强度对超宽板坯结晶器流场和温度场的影响,多组对比模拟计算结果表明,当浸入式水口出口倾角为15°,插入深度为120～150mm,拉速为1.2～1.4 m/min时,结晶器自由液面速度和湍动能分布以及注流冲击点深度均较为适宜,流场较为合理;同时结晶器内钢液的温度分布相对均匀,有利于坯壳的均匀形成.数值模拟结果可为优化南钢超宽板坯结晶器浸入式水口结构以及确定合理工艺参数提供理论依据.     

吹氩板坯连铸结晶器内夹杂物去除的数值模拟

针对吹氩板坯连铸结晶器内非金属夹杂物去除问题,采用准单相模型和离散相模型描述了水-空气-夹杂模拟物体系和钢液-氩气-夹杂物体系的粒子行为和去除效率.结果表明,吹氩有利于夹杂物上浮去除,同一气量(6.0L/min)下夹杂物在拉速1.3m/min时去除率最低.同一拉速(1.2m/min)下存在临界气量9.0L/min,小于临界气量,吹氩可增加夹杂物上浮率,减小进入铸坯率;大于临界气量,夹杂物上浮率减少,进入铸坯率增大.准单相模型和离散相模型能较好地模拟夹杂物在气液两相中的运动和去除.     

板坯连铸中电磁制动方式对结晶器中钢液流场的影响

以水银模拟钢水,研究了板坯连铸电磁制动过程中不同拉速下,不同电磁制动方式[单条型电磁制动(EMBr-Ruler)和流动控制结晶器(FC Mold)]对结晶器内钢水流动的影响规律. 实验表明,(1) FC Mold可有效抑制结晶器内液面流及其波动行为(拉速0.52 m/min时最大液面流速和湍流度分别为无电磁制动时的1/5和1/6); (2)两种电磁制动方式均会压缩水口出流的扩张空间,结晶器窄壁附近向下液流的竖直流速剧增[拉速0.41 m/min时最大竖直流速由0.030 m/s(无电磁制动)增至0.066 (EMBr-Ruler)和0.057 m/s (FC Mold)],不利于快速形成活塞流;(3)高拉速(如2.0 m/min)时FC Mold电磁制动可获得较好的流场形态(液面最大流速为0.028 m/s),中拉速(如1.3 m/min)时EMBr-Ruler电磁制动所得流态较好,而低拉速(如1.0 m/min)时2种电磁制动方式均未获得预想的效果,甚至会恶化结晶器内原有的流态.     

Advanced injection molding mold and molding process for improvement of weld line strengths and isotropy of glass fiber filled aromatic polyester LCP

An advanced injection molding tool for measurement of mechanical strength and anisotropy of liquid crystal polymers (LCP)/mineral filler composites was developed. The mold produces thin‐walled LCP specimens that can be used by water cutting technique for production of an injection molded flow direction test bar, a transverse‐to‐injection molded flow direction test bar, a test bar for knit line strength measurement, and a test bar for butt weld line strength measurement. This tool and its use for molding experiments were optimized by experimental research and by computational calculations based on experimental parameters obtained by molding of several LCP test materials. Different pressure profiles and different injection speeds were tested as well as application of mold overflow phenomenon in production of test specimens. It was observed that a pressure controlled X‐melt technique and on the other hand fast injection speeds with overflow in conventional molding methods gave the best strength and isotropy properties for the test specimens. Results indicate that the mold developed is useful for determination of anisotropic and weld line strength properties of LCP composites. When developing “isotropic LCP” by different possibilities of nanotechnology this tool significantly reduces time of LCP material and process development. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

CaO/Al2O3比对高铝钢连铸保护渣凝固结晶行为的影响

针对目前高铝钢用常规结晶器保护渣中SiO2易被钢液中Al还原导致连铸坯质量缺陷及非反应性保护渣消耗量偏低和润滑差的问题,基于CaO-SiO2-Al2O3三元系相图设计了SiO2含量为20%(w)的CaO-SiO2-Al2O3连铸保护渣,并采用热丝法模拟研究了CaO/Al2O3比对该渣系凝固结晶行为的影响. 结果表明,随CaO/Al2O3比的增加,保护渣的结晶性能增强;CaO/Al2O3比在0.7~1.3范围内其凝固固相分数较小,与现用工业渣具有相似的润滑作用. 综合考虑保护渣的传热和润滑作用,高铝钢保护渣中CaO/Al2O3比范围应为0.7~1.3.     

Analysis of a liquid‐assisted molding process for coating microchannels with an ultraviolet curable polymer

Injection molding can be altered to form hollow parts by partially pre‐filling a mold with polymer melt and then injecting a gas into the mold before cooling. The gas will core the center section and in the process force melt into the unfilled portions of the mold. This process is called gas‐assisted injection molding (GAIM) and is a thoroughly studied polymer processing technique. Liquid‐assisted molding follows the same principles as GAIM, except the coring fluid is a liquid of low viscosity. Liquid‐assisted molding of an ultraviolet (UV) curable polymer can be used to coat microchannels, the benefit of which being a smooth and circular cross‐section. Presented here are experiments of the controlled microchannel flow of a long, immiscible liquid thread through a viscous UV curable polymer. The roles of channel geometry and bubble velocity are discussed for square, rectangular, and circular microchannels. Finally, a quasi‐analytical model for calculating the Newtonian coating fluid thickness, when the coring fluid is driven by a constant pressure, was developed using the equation for Poiseuille‐like flow within a square channel. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Modeling and simulation of fiber‐reinforced polymer mold‐filling with phase change

A gas‐solid‐liquid three‐phase model for the simulation of fiber‐reinforced composites mold‐filling with phase change is established. The influence of fluid flow on the fibers is described by Newton's law of motion, and the influence of fibers on fluid flow is described by the momentum exchange source term in the model. A revised enthalpy method that can be used for both the melt and air in the mold cavity is proposed to describe the phase change during the mold‐filling. The finite‐volume method on a non‐staggered grid coupled with a level set method for viscoelastic‐Newtonian fluid flow is used to solve the model. The “frozen skin” layers are simulated successfully. Information regarding the fiber transformation and orientation is obtained in the mold‐filling process. The results show that fibers in the cavity are divided into five layers during the mold‐filling process, which is in accordance with experimental studies. Fibers have disturbance on these physical quantities, and the disturbance increases as the slenderness ratio increases. During mold‐filling process with two injection inlets, fiber orientation around the weld line area is in accordance with the experimental results. At the same time, single fiber's trajectory in the cavity, and physical quantities such as velocity, pressure, temperature, and stresses distributions in the cavity at end of mold‐filling process are also obtained. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42881.     

板坯连铸电磁制动下结晶器内金属流场的研究

以水银为实验工质,通过物理模拟实验研究电磁制动下,板坯结晶器内钢水流动规律. 实验通过超声多普勒测速仪获取不同电磁制动方式[单条型电磁制动(EMBr-Ruler)和流动控制结晶器(FC Mold)]、水口浸入深度和结晶器宽度下的液流特征. 结果表明,在EMBr-Ruler或FC Mold II电磁制动下,结晶器窄壁处形成"液流通道",不利于结晶器内快速形成向下的活塞流. 水口出口距下区磁场越近或被磁场所覆盖,则通道效应减弱; 结晶器宽度增大,亦可降低该通道内液流的冲击效果. FC Mold II下,液面流速和湍流度比EMBr-Ruler时低[液面水平流速最大值分别为0.155 (Case 1)和0.134 m/s (Case 2)],且加大水口浸入深度,可降低液流撞击结晶器窄壁的水平流速[其最大值0.071 (Case 2)和0.068 m/s (Case 3)]. 结晶器宽度的变化不改变水口浸入深度对结晶器流场的影响规律.     

Use of sensors and actuators to address flow disturbances during the resin transfer molding process

In Resin Transfer Molding a fiber preform is placed in a mold, the mold is closed and a thermoset polymeric resin is injected through gates into the mold to saturate the preform completely. The resin flow rate is controlled by actuators, which are usually injection machines. When one places the preform into the mold, the gap between the preform and the mold walls can create race tracking channels and provide the resin flow paths that can severely influence the flow patterns and drastically change the flow history. As this gap is unavoidable and not reproducible, one could have different strengths of this disturbance from one part to the next, some of which will cause incomplete saturation of the fibers by the resin. Hence, an active control of the filling stage is necessary that can detect and characterize the race tracking and provide the control action to redirect the flow with the aim to saturate the preform without resin starved regions (macro voids or dry spots). A methodology is proposed that intelligently places sensors in the mold to detect the resin arrival times at these locations. This information is used to determine and quantify the strength of the disturbance and used as an input parameter for the actuators to redirect the flow. This paper demonstrates this methodology on a simple mold configuration, and outlines how this technique can be generalized to any mold geometry or disturbance set in an automated RTM environment. Numerical simulations are used to establish the control methodologies, and all of the efforts are confirmed in a laboratory setting. The proposed methodology should prove useful in increasing the yield of Resin Transfer Molded parts.