铝合金轮毂压铸模温度场数值分析

运用有限元分析软件ProCAST对压铸模进行了压铸过程模具温度场分析,研究了模具预热温度、浇注温度对模具温度场的影响。结果表明,模具型腔表面温度受金属液充填的影响较大,距型腔表面距离超过20mm后,模具温度受金属液的影响较小。模具预热温度影响模具内的温度梯度和升温速率,预热温度越高,型腔表面升温速率越小,模具内的温度梯度越小。浇注温度越高,模具型腔表面的升温幅度和升温速率越大。     

基于FLUENT的水射流冲击力影响因素仿真分析

基于水射流冲击模型,应用FLUENT流体分析软件对喷嘴射流冲击力数值模拟和仿真,得出不同的射流压强、喷距及喷嘴出口直径对射流冲击力及冲击作用区域的影响。结果表明:其他相关因素确定时,射流冲击力随着射流压强的增加而增大,随着喷距的增加先增大、后减小;不同喷嘴出口直径的射流冲击力的比值约为喷嘴出口直径的平方比,射流冲击的作用区域与喷嘴出口直径有关,其面积约为出口直径的2.9倍。     

基于辐射管内外耦合传热模拟带钢连退过程的温度均匀性

针对立式带钢连续退火炉内辐射管加热过程带钢温度均匀性问题，建立了W型辐射管管内流动、燃烧和管内外换热的耦合模型以及带钢内部非稳态导热模型，模拟研究了辐射管表面温度分布对带钢温度均匀性变化的影响。结果表明，在带钢升温过程中，其宽度方向温度呈凹状分布，这与辐射管两端温度偏高和炉墙的辐射绝热作用有关，该温差先增大后逐渐减小，宽度1200 mm的带钢在加热中段时最大温差可达13.6℃;带宽方向温差随着带宽的增大先缓慢增大后快速降低；带宽较小时，带宽方向温差随着功率的增加而增大，带宽较大时则相反。带宽接近辐射管长度时，带宽方向温差最小，可降至5℃以内；加热前期，辐射管表面温度最不均匀，加热中期，带宽方向温差最大。     

不同热装方式下铸坯温度分布研究

采用有限元软件对步进式加热炉内钢坯加热过程进行分析计算,建立铸坯加热温度场模型,计算不同热装条件下铸坯中心与表面的温度变化曲线。以铸坯1/4断面为研究对象,分析铸坯断面全流程温度分布,得到连铸坯表面温度、角部温度、心部温度的变化曲线。模拟分析不同热装方式装炉的铸坯在加热炉内的加热升温情况,提取铸坯表面和中心位置的加热曲线。模拟加热炉内加热过程,为降低铸坯断面温差、加热炉能耗以及提高生产效率提供依据。     

不锈钢重熔工艺瞬态热物理性能数值模拟

应用有限元方法对层流等离子体射流不锈钢表面重熔工艺中的瞬态热物理现象进行了数值模拟研究.针对不同加热距离,确定了材料熔化和凝固过程中的瞬态温度场、温度梯度和凝固率的时间和空间分布特征.通过引入等效温度面积密度概念,研究了不锈钢重熔热处理的适合条件.结果表明,9～13 mm的范围是较为适宜的加热距离,该结果与试验观察基本符合.     

等离子喷涂过程基体温度场分布的数值模拟

等离子喷涂的热源温度高,涂层成形区域温度梯度大、热量累积快,涂层中常存在较大的残余应力。研究通过数值模拟并辅以必要的试验测试研究了等离子喷涂过程基体表面热量累积行为：建立了二维静态喷枪加热模型,研究了在不同喷涂距离时基体表面温度场分布规律;建立了移动热源加热模型,研究了在不同喷枪移动速度和扫描遍数时基体热量累积规律。结果表明：在静态喷枪加热作用下,基体温度场呈中间高两端低的对称分布状态;随着喷涂距离减小,基体表面最高温度与平均温度显著升高,温度梯度变化明显,高温区域半径显著增大。在动态喷枪加热过程中,基体左右边界热量累积现象明显,且喷枪移动速度越快,基体表面热量累积越少,温度分布梯度越小;随着喷枪扫描遍数的增加,基体中心区域温度呈波浪式上升,温度增长幅度逐渐变小。     

马氏体耐热钢大型管坯加热工艺模拟

为优化马氏体耐热钢G115大型管坯的加热制度,通过有限元模拟,分析了加热工艺对钢锭温度场分布的影响。结果表明,升温过程中钢锭端部截面边缘处与管坯长度1/2截面中心处温差较大,最大约为93 ℃,钢锭加热温度越高,各部位温差越小;钢锭端部截面边缘处温度最高且升温速率最快,管坯长度1/2截面中心处温度最低且升温速率最慢。通过本文研究,推荐G115钢大型管坯的加热制度为炉温由300 ℃升高到500 ℃保温4 h,再升温到850 ℃保温4 h,升温到1000 ℃保温4 h后升温到1230 ℃保温20 h,可为其它工序的加热过程提供参考。     

30CrMnSiNi2A钢轴类零件感应热处理的数值模拟

利用Comsol软件对30CrMnSiNi2A钢的感应回火进行了模拟,利用控制变量法研究了感应加热过程中电源频率、电流以及线圈的结构和尺寸参数对工件内部温度均匀性的影响。结果表明,电流强度和电源频率越大,工件在感应加热过程中的升温速率越大,最终平衡温度越高,但其径向/轴向温差越大。线圈的匝数越多,工件的升温速率和径向/轴向温差越大,最终平衡温度越高。线圈半径的变化仅会对工件端部的升温速率产生影响,线圈半径越小,工件端部的升温速率越快,轴向温差越小。线圈截面外径和壁厚的变化对工件感应加热过程中的温度场没有影响。根据模拟结果的对比分析,提出了一种采用分段加热法与增设导磁体相结合的方法,对感应回火系统进行了优化。通过优化设计可使工件在感应加热过程中的径向温差基本消除,使轴向温差小于10℃。     

等离子喷涂流场分布及颗粒运动特性（英文）

考虑了化学反应及压力梯度力,对等离子喷涂流场分布及颗粒运动特性进行研究。利用Spray Watch-2i对飞行颗粒进行在线监测。结果表明:气流的最高温度为12000 K,最高速度为150 m/s。当载气流量在4 L/min时,颗粒能够很好的加热加速。当送粉流道与射流方向垂直时,颗粒分布在流场外围,而当送粉流道与流场垂直方向倾斜8°夹角后,颗粒的运动轨迹偏向流场中心。当颗粒直径为10μm时,颗粒能够被载气送入到射流中心位置。而当颗粒直径逐渐增大时,颗粒穿过射流中心分布在流场外围。颗粒的最大速度达到270.9 m/s,最大温度达到3939 K。最佳喷涂距离为80 mm。     

水射流冲击压力最佳喷距数值仿真及试验研究

基于水射流冲击模型,应用Fluent流体分析软件对喷嘴射流冲击力进行数值仿真,得出不同喷距对射流冲击压力的影响。结果表明：在低压连续水射流条件下,出口直径为2 mm的喷嘴在喷距为50 mm时产生的射流冲击压力最大;并通过实验验证射流仿真模型的正确性和有效性。     

Computational study and experimental comparison of the in-flight particle behavior for an external injection plasma spray process

A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the torch nozzle via the heating of the are gas by an electric are within the nozzle. The stochastic discrete model was used for the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance have been investigated. The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0 slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61 slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature. Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting, the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5–4.0 slm.     

Effects of spray conditions on coating formation by the kinetic spray process

The kinetic spray coating process involves impingement of a substrate by particles of various material types at high velocities. In the process, particles are injected into a supersonic gas stream and accelerated to high velocities. A coating forms when the particles become plastically deformed and bond to the substrate and to one another upon collision with the substrate. Coating formation by the kinetic spray process can be affected by a number of process parameters. In the current study, several spray variables were investigated through computational modeling and experiments. The examined variables include the temperature and pressure of the primary gas, the cross-sectional area of the nozzle throat, the nozzle standoff distance from a substrate, and the surface condition of nozzle interior and the powder gas flow. Experimental verification on the effects of these variables was performed primarily using relatively large-size aluminum particles (63–90 μm) as the feedstock material. It was observed that the coating formation is largely controlled by two fundamental variables of the sprayed particles: particle velocity and particle temperature. The effects of different spray conditions on coating formation by the kinetic spray process can be generally interpreted through their influences on particle velocity and/or particle temperature. Though it is limited to accelerate large particles to high velocities using compressed air or nitrogen as carrier gas, increasing particle temperature provides an additional means that can effectively enhance coating formation by the kinetic spray process.     

Nanoparticles Modeling in Axially Injection Suspension Plasma Spray of Zirconia and Alumina Ceramics

Suspension plasma spray (SPS) is a thermal spray method in which nanoparticles are injected into the plasma jet with the help of suspension droplets to achieve thin and finely structured nanocoatings. The nanoparticles experience three in-flight stages: injection within the suspension droplets, discharge of the nanoparticle agglomerates after the evaporation of the suspension solvent, and tracking of the nanoparticle or agglomerates during the momentum and heat transfer with the plasma jet before coating. A numerical model is proposed in this paper for nanoparticle injection, discharge, acceleration, heating, melting, and evaporation. Initial values of suspension droplet size and agglomerate size are selected according to typical experimental data. Noncontinuum effects on particle acceleration and heating, known as Knudsen effects, are considered, as well as the influence of evaporation on the heat transfer. After a comparison with the experimental data, this nanoparticle model is applied for zirconia and alumina axially injected into the suspension plasma spray. Trajectory, velocity, and temperature of the in-flight nanoparticles are predicted for different initial sizes ranging from 30 nm to 1.5 μm; the distributions of the particle characteristics for multiple particles in the spray are also presented. The effects of powder size and material, power input, plasma gas flow rate, and standoff distance on the nanoparticle characteristics have been investigated and discussed.     

等离子熔射过程中射流与粒子流的加热效应

采用CCD图像采集系统与图像处理技术提取等离子射流长度;以红外测温仪检测的单位时间内基体温度变化来衡量加热效应,研究不同熔射距离与射流长度条件下射流和粉末粒子流对基体的加热效应特点.结果表明,当熔射距离不大于射流长度时,基体温升主要来至于射流加热效应;随着熔射距离增大,射流对基体的加热效应迅速减弱;当熔射距离大于射流长度时,粒子流加热效应比较明显.提出射流长度可以作为合理选择熔射距离的特征评价指标,并通过不同熔射距离条件下熔射皮膜的截面尺寸以及形貌进行验证.     

Investigation on in-flight particle velocity in supersonic plasma spraying

0Introduction Asakindofsurfaceengineeringtechnology,thermal sprayingcanprovideprotectiveorfunctionalcoatings whicharewidelyusedinmanyindustrieslikechemistryin dustry,papermaking,electricengineering,powerplant, aviation,automobileproducing,steelmill,glass…     

A Study of Wire Breakup and In-Flight Particle Behavior During Wire Flame Spraying of Aluminum

Although wire flame spraying has been used for many years, there has been relatively little attention given to understanding the process dynamics. In this work, imaging of the molten wire tip, particle imaging using the Oseir SprayWatch system and particle capture (wipe tests) have all been employed to quantify plume behavior. Aluminum wire feedstock is melted and then breaks up close to the exit of the spray nozzle in a non-axisymmetric manor. The mean velocity and diameter of the particles detected by the SprayWatch system change little with standoff distance with values of approximately 280 m/s and 70 µm, respectively, for the spray parameters employed. The particle diagnostic system could not detect particles ?45 µm in diameter, and it is estimated that these account for no more than 53% of the sprayed material. Overall, wire flame spraying generates a surprisingly stable particle stream.     

面向等离子熔射成形技术的粉末飞行特性数值分析

粉末在射流场中飞行特性是影响熔射成形件质量的重要因素。通过所建立的粉末与射流相互作用的动量和能量传递方程，应用有限差分法，模拟计算和分析了粉末速度与温度分布规律及其对成形件质量的影响。结果表明：①粒径及密度越小，加(减)速度越快，而到达原模时的速度则不同；②热传导性越差，粒径越大，极值温度则越小，且逐渐向原模方向偏移；③粉末的力学行为和加热特性的匹配，可进一步提高熔射成形件质量。模拟结果为实现熔射成形质量控制及参数优化，提供了理论依据。     

Numerical Modeling of Suspension HVOF Spray

A three-dimensional two-way coupled Eulerian-Lagrangian scheme is used to simulate suspension high-velocity oxy-fuel spraying process. The mass, momentum, energy, and species equations are solved together with the realizable k-ε turbulence model to simulate the gas phase. Suspension is assumed to be a mixture of solid particles [mullite powder (3Al₂O₃·2SiO₂)], ethanol, and ethylene glycol. The process involves premixed combustion of oxygen-propylene, and non-premixed combustion of oxygen-ethanol and oxygen-ethylene glycol. One-step global reaction is used for each mentioned reaction together with eddy dissipation model to compute the reaction rate. To simulate the droplet breakup, Taylor Analogy Breakup model is applied. After the completion of droplet breakup, and solvent evaporation/combustion, the solid suspended particles are tracked through the domain to determine the characteristics of the coating particles. Numerical simulations are validated against the experimental results in the literature for the same operating conditions. Seven or possibly eight shock diamonds are captured outside the nozzle. In addition, a good agreement between the predicted particle temperature, velocity, and diameter, and the experiment is obtained. It is shown that as the standoff distance increases, the particle temperature and velocity reduce. Furthermore, a correlation is proposed to determine the spray cross-sectional diameter and estimate the particle trajectories as a function of standoff distance.     

Numerical Simulation of Temperature Field in Nanostructured Al2O3-13TiO2 Feedstock in Supersonic Plasma Spraying

Velocity and temperature of nanostructured Al2O3-13TiO2 feedstocks in supersonic plasma spraying was detected applying CCD thermal spray monitor.Based on the detect results,temperature field in the feedstock in spraying process was analyzed via finite element method.Result shows that the highest velocity of the flying particles exceed to 800m/s.With the increase of spraying distance,velocity decline parabolic.Surface temperature of the feedstock increase firstly and then decrease and the highest temperature exceed to 2600℃.Internal temperature of the feedstock is higher than the melting point when the distance reaches to 80mm.As the spraying distance increase,temperature gradient in the particle decreased gradually.     

An Investigation on Temperature Distribution Within the Substrate and Nozzle Wall in Cold Spraying by Numerical and Experimental Methods

During cold spraying (CS), heat exchange between the hot driving gas and the solid bodies, e.g., spray nozzle and substrate, results in the temperature redistribution within the solid bodies. In this study, numerical and experimental investigations on the heating behavior of the substrate and nozzle wall were conducted to clarify the temperature distribution within the solid bodies in CS. The results show that after heating by the hot gas, the highest temperature presents at the center point of the substrate and decreases toward the substrate back surface and edge. With increasing standoff distance or decreasing inlet temperature, the substrate temperature decreases gradually, but the temperature gradient within the substrate changes little. The numerical results are consistent with the experimental measurements. Besides, it is also found that increasing the substrate size (diameter) can lead to the gradual increment in the substrate temperature. Moreover, the numerical study on the temperature distribution within the nozzle wall reveals that the highest temperature presents at the throat section of the nozzle and that the nozzle material significantly affects the temperature distribution within the nozzle wall.