金属喷射成型的最新发展态势

传统粉末冶金工艺，难以制造形状复杂的零件。受塑料喷射成型的启发，在20世纪80年代后期，金属粉末界也开始探索喷射成型技术。经过10多年的探索、研发，金属喷射成型技术取得了很大的进展。从国外的统计资料来看，欧洲、亚洲、美洲金属喷射成型生产都已初具规模，详见表。     

宝钢建成国内钢铁业首台自主集成喷射成型设备

最近，由宝钢自主集成的100kg（可扩展至300kg）多功能喷射成型中试机组完成安装。这是国内钢铁行业第一台自主集成的喷射成型装置，对宝钢今后开发高合金、高附加值钢铁产品具有积极意义。[第一段]     

喷射成型锭坯形状的数值模拟研究

建立了描述喷射成型过程中沉积坯外轮廓动态生长的三维数学模型，该模型考虑了喷射成型过程中各种工艺参数的影响，这些工艺参数包括喷嘴的雾化特性值、偏心距离、沉积盘的旋转速度和下拉速度，在计算后进行数据处理得出了锭坯生长的三维外形轮廓，通过与实际喷射成型设备成形的锭坯对比，两种结果符合较好，并可用此模型来预测不同工艺条件下锭坯的外形生长轮廓。     

喷射成型圆棒生长机制的数值模拟

喷射成型过程中沉积物的生长模型是基于法向表面的增长速度，该模型揭示了过程变量对沉积物形状变化的影响，在喷射过程中，沉积物形状经过一个最初的瞬时区域，最终将达到一种稳定状态，达到稳定状态的条件是收集器的后退速度Ｖ＜ａｃｏｓΦ     

光固化快速成型工艺的精度研究

光固化快速成型是目前世界上研究最深入、技术最成熟、应用最广泛的一种快速成型方法.文章对影响光固化快速成型精度的因素进行了理论分析及确定,并对各因素对成型精度产生的影响进行分析.     

不同成型工艺下钕铁硼模压成型过程的力学行为分析

为了优化钕铁硼粉末模压成型工艺, 通过离散元软件EDEM建立模压成型过程的离散元模型, 分析不同成型工艺条件(压制速度和摩擦系数)对压坯力学特征(压制力和压坯内应力)的影响, 为优化钕铁硼成型工艺提供理论参考。结果表明: 在成型过程中, 钕铁硼粉末位置状态基本保持与布粉时一致, 只有靠近模冲区域的粉末发生较大位移; 压坯成型时会出现应力松弛现象, 不同速度压制成型对压制力峰值影响不同, 但压制力最终均会收敛至相近的平衡值; 添加润滑剂能改善压坯内部受力状态, 减小压制力, 但是也会减小压坯相对密度; 对于大尺寸压坯成型宜采用双向压制方式。     

喷射成型沉积坯组织及机械性能分析

喷射成型是近年来发展极其迅速的一种崭新的金属和合金成型技术，它不仅具有快速凝固的优点，可以生产低偏析、细晶粒、高致密度和近终形尺寸的坯料，而且简化了生产工序，从而比一般粉末冶金生产工艺降低了成本。用光学显微镜和扫描电子显微镜观察喷射成型制造的GCr15沉积坯，分析其组织结构和晶粒度的分布状况。同时，对沉积坯的密度、硬度进行测定分析。结果表明，沉积坯具有细小的等轴晶粒，化学成分比较均匀。在此基础上提出了一些改进微观组织和性能的措施。     

管材电磁成型机理与实验研究

对管材电磁成型机理进行了分析，推导出的脉冲磁场压力函数式，能准确反映管材电磁成型过程中磁场压力随时间的变化，在管材成型实验研究中，探索出管材的变形规律及各工艺参数的成型质量的影响规律，为该项技术应用提供了理论依据，有效地指导了实际生产。     

板材电磁成型实验研究

对板材的电磁成型进行了较全面的实验研究，探索了各种参数对板材成型效果的影响及板材变形规律。实验结果表明，只要选取合理的参数，就能获得高质量的产品。电磁成型效率大约为１２％，高于其他成型方法。     

粉末注射成型工艺及其特点

粉末注射成型是一项新型近净尺寸成型技术,被用于生产较小尺寸及复杂外形与表面的制品.与传统的加工工艺相比,粉末注射成型技术成本优势明显.结合该工艺的特点,文章论述了包括混料、注射成型、脱脂、烧结4道工序中涉及的工艺参数对制品质量的影响.粉末注射成型工艺在陶瓷、金属材料方面得到了很好的应用.     

Analysis of Mould,Spray and Radiation Zones of Continuous Billet Caster by Three‐dimensional Mathematical Model based on a Turbulent Fluid Flow

An analysis of mould, spray and radiation zones of a continuous billet caster has been done by a three‐dimensional turbulent fluid flow and heat transfer mathematical model. The aim was to reduce crack susceptibility of the billets and enhance productivity of the billet caster. Enthalpy‐porosity technique is used for the solidification. Turbulence is modelled by a realizable k‐ε model. The three‐dimensional mesh of the billet is generated by Gambit software, and Fluent software is used for the solution of equations. In various zones, different standard boundary conditions are applied. Enhanced wall treatment is used for the turbulence near the wall. In the mould region, Savage and Prichard expression for heat flux is applied. In the spray cooling zone, the heat transfer coefficient for surface cooling of the billet is calculated by knowing the water flow rate and the nozzle configuration of the plant. The model predicts the velocities in the molten pool of a billet, the temperature in the entire volume of billet, the heat transfer coefficient in the mould region, the heat flux in the cooling zone and radiation cooling zone, and the shell thickness at various zones. The model forecasts that the billet surface temperature up to the cutting region is above the austenite‐ferrite transformation temperature (which is accompanied by large volume change). The model predicts a temperature difference of maximum 700 K between the centre and surface of the billet. The entire solidification takes place at 11.0 m length at 3.0 m/min. For the same casting arrangement, increasing the casting speed up to 4.0 m/min has been explored. Based on the simulation results, recommendations to alter the spray water flow rate and spray nozzle diameter are presented to avoid a sudden change of temperature.     

纳米Al_2O_3陶瓷粉料喷雾干燥制粒

利用喷雾干燥技术对纳米Al_2O_3粉体进行造粒,研究了浆料固含量、粘结剂含量及分散剂含量对喷雾干燥粉体颗粒形貌、结构、松装密度和流动性的影响。结果表明:当料浆固相含量为50%,分散剂和粘结剂分别为固相质量的0.04%和1.0%时,浆料具有合适的粘度和最佳的分散稳定性,喷雾造粒得到的粉体为球形,表面光滑致密,具有较高的松装密度和流动性,能满足各种压制成型的需要。     

GCr15钢喷射成形沉积坯孔隙形成及致密度的分析

GCr15钢(1.01%C、1.48%Cr)经100kg中频感应炉熔化至1 580℃,金属液流经炉底导液管喷嘴处被高压氮气流在雾化室雾化成微米级液滴,在基底形成沉积坯。通过使用金相显微镜、扫描电镜对GCr15钢喷射成形试样的孔隙分布、微观组织和密度进行比较分析。结果表明,沉积坯截面上有宏观孔隙,在整个截面上也存在一些形状不规则的孔隙;沉积坯整体平均相对致密度为85.51%。     

喷流式连续加热炉数学模型的研究

本文讨论了喷流预热装置对连续加热炉的意义,并根据喷流段内钢坯的受热情况,建立了合理的数学模型,采用数值计算方法,借助于计算机求解钢坯温度随着炉内喷流预热装置的长度的变化而变化的温度曲线,最终确定了连续加热炉内喷流预热装置的合理长度范围和最佳长度.     

车轮钢圆坯表面温度和坯壳厚度的数值分析

采用分段线性的结晶器和二冷拉矫段热流密度表示方法,对车轮钢圆坯的宏观凝固过程进行了流场、温度场和凝固的耦合数学模拟.计算结果与实测数据吻合,表明数学模型可靠准确地反映了实际情况.由于拉速变化引起计算空间内质量流量的变化,圆坯的表面温度和坯壳厚度受拉速强烈影响.二冷拉矫段热流密度的变化反映了散热方式随温度变化进行的自我调节.保温段对圆坯表面温度回升有明显影响,并将凝固终点推后大约1 m.     

Influence of Melt Feeding Scheme and Casting Parameters During Direct-Chill Casting on Microstructure of an AA7050 Billet

Direct-chill (DC) casting billets of an AA7050 alloy produced with different melt feeding schemes and casting speeds were examined in order to reveal the effect of these factors on the evolution of microstructure. Experimental results show that grain size is strongly influenced by the casting speed. In addition, the distribution of grain sizes across the billet diameter is mostly determined by melt feeding scheme. Grains tend to coarsen towards the center of a billet cast with the semi-horizontal melt feeding, while upon vertical melt feeding the minimum grain size was observed in the center of the billet. Computer simulations were preformed to reveal sump profiles and flow patterns during casting under different melt feeding schemes and casting speeds. The results show that solidification front and velocity distribution of the melt in the liquid and slurry zones are very different under different melt feeding scheme. The final grain structure and the grain size distribution in a DC casting billet is a result of a combination of fragmentation effects in the slurry zone and the cooling rate in the solidification range.     

圆坯凝固末端电磁搅拌作用下的流动与传热行为

以特殊钢圆坯连铸为研究对象, 建立了研究凝固末端电磁搅拌作用效果的三维耦合数值模型.利用分段计算模型获得末端电磁搅拌区域钢液流动与凝固的实际状态, 并采用达西源项法处理凝固末端钢液在糊状区的流动, 研究了不同电磁搅拌工艺参数下的电磁场分布及钢液的流动与传热特征.通过测量搅拌器中心线磁感应强度和铸坯表面温度验证了模型的准确性.研究结果表明: 电流强度每增加100 A, 搅拌器中心磁感应强度增加19.05 mT, 电磁力随着电流强度的增加显著增大.在20~40 Hz范围, 随着电流频率的提高, 中心磁感应强度略微下降, 但电磁力仍有所增加.在搅拌器区域, 液相穴内的钢液在切向电磁力的作用下旋转流动, 其切向速度随着电流强度和频率的增加而变大.末端电磁搅拌可促进钢液在圆坯径向的换热, 随着电流强度和频率的提高, 铸坯中心轴线上的钢液温度降低, 同时末端搅拌位置处的中心固相分率增加.      

Effect of Nozzle Angle on Flow Field and Temperature Distribution in a Billet Mould when using Swirl Flow

Recently, interesting effects have been noted in studies of swirl flow, particularly regarding billet moulds when considering a specific divergent angle of the immersion nozzle. Therefore, in the present work a numerical analysis and water model study of the mould region of a continuous casting apparatus are performed with changing the outlet divergent angles of the immersion nozzle using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mould. To make our studies consistent with the previous research, which was done based on a square billet, this time we investigate round billets. The results show that the distance from the meniscus of the centres of both the lower and upper circulation loops decreases systematically with increasing the divergent angle. This, in turn, leads to: (i) a more active heat and mass transport near the meniscus (particularly over 100°); (ii) a gradual change from a concentric circulation to a more clearly logarithmic spiral from the mould wall to the nozzle on the meniscus, which leads to more active heat and mass transfer; (iii) a decreased penetration depth of nozzle outlet flow (even at a comparatively small divergent angle such as 20°) and a superheat dissipation in the melt.     

六流方坯连铸中间包结构优化水模实验

 通过六流方坯连铸中间包水模实验,研究了不同控流装置对其流动特性的影响。采用笔者提出的多流中间包流动特性分析模型及各流流动特性一致性的分析方法进行了定量描述。结果表明,带横墙和不带横墙的“V”型挡墙均能明显改善各流流动特性的一致性,与不带横墙的“V”型挡墙组合挡坝的数量、高度均对流动特性有影响,在较优的“V”型挡墙与挡坝组合控流装置基础上加入抑湍器后控流效果更佳。通过实验研究,提出了优化方案。     

Modeling of porosity during spray forming: Part II. Effects of atomization gas chemistry and alloy compositions

In this article, the effects of gas chemistry and alloy composition on the level of porosity in deposited materials are investigated by using a porosity model established in Part I of this article. The calculated results reveal that atomization gas chemistry has a significant influence on the level of porosity during spray forming, which can be rationalized on the basis of the influence of gas properties such as gas density, viscosity, and gas constant on the melt flow rate. The alloy properties that predominantly affect the variation of porosity with melt flow rate include melt viscosity, density, surface tension, solvent melting point, liquidus temperature, and equilibrium partition coefficient. A material property factor, μ _mγ_m/ρ ² _m , plays an important role in determining the processing conditions required to attain a minimum amount of porosity in deposited materials.