Pressure build-up at the metal delivery tube orifice in ultrasonic gas atomization

The effects of geometry (diameter and tip design) and position (relative to the gas nozzles) of the metal delivery tube in an ultrasonic gas atomization (USGA) device on the pressure condition in the gas-metal interaction zone at the tube orifice have been studied. Simulation of ultrasonic gas (argon or nitrogen) atomization has been conducted, both at low (3.5 to 14 atm) and high (15 to 75 atm) atomization pressures. Low gas atomization pressures are generally used in spray deposition processes such as liquid dynamic compaction (LDC), while high pressures are used for powder production. Depending on the experimental conditions, i.e. the shape and angle of the taper at the metal delivery tube orifice or its position with respect to the nozzles' gas exit common plane, either partial vacuum (equivalent to downward aspiration of the melt) or overpressures (equivalent to back-pressurization of the melt) at the metal delivery tube was detected. Underpressure and overpressure effects were found to increase with gas atomization pressure. The maximum pressure differences measured with respect to the atomization chamber pressure were about 0.15 to 0.25 atm for the low-pressure experiments, and 0.50 to 0.60 atm for the high-pressure experiments. Underpressures or overpressures of these magnitudes have a large effect on the metal flow rate during gas atomization, either enhancing or reducing it, and thus changing significantly the gas to metal flow ratio. Because this is a crucial parameter for both the USGA and the LDC processes, the state of pressure at the delivery tube's orifice has to be monitored carefully, in order to ensure optimal processing conditions.     

Effects of process parameters on surface morphology of metal powders produced by free fall gas atomization

There are a number of process parameters which affect the characteristics of metal powders produced by free fall gas atomization. In the following work effects of various process parameters like apex angle of atomizer, focal length of atomizer, number of nozzles, diameter of nozzles, diameter of liquid metal delivery tube, superheat of liquid metal and type of metal etc. were studied on their surface morphology. It was observed that shape of powder particles depends on apex angle, superheat of liquid metal, type of metal and particle size range within a powder collective. Other parameters like focal length of atomizer, number of nozzles, diameter of nozzles and diameter of liquid metal delivery tube were found to have no effect on the shape of powder particles. However, Surface porosity and solidification shrinkage were observed on almost all types of metal powders.     

Low-pressure gas atomization of aluminum through a Venturi nozzle

A new concept of powder atomization based on the venturi phenomenon is presented in the current work. In the proposed method, the working gas speeds-up while flowing into the venturi nozzle. Under the low static pressure developing at the narrow part of the venturi, liquid metal is sucked and mixed perfectly with the gas. By controlling the operating parameters, metal powder of different sizes and shapes can be produced. Carbon dioxide and pure aluminum were mixed in the nozzle and the effect of different operating gas pressures on the produced particle size and shape were thoroughly investigated. Most of the particles were found to average to almost 150 μm, however, even sub-micron aluminum particles were produced at low mass fractions. With the increase of the gas pressure from 0.5 bar to 4 bar, finer aluminum particles are produced. One of the most attractive features of the proposed method is the low gas pressure required to cause melt atomization, which in certain cases may be up to 30 times lower compared to current industrial atomization methods.     

Impact of process flow conditions on particle morphology in metal powder production via gas atomization

Additive manufacturing processes as for instance selective laser melting or electron beam melting are becoming more common and just turning into standard manufacturing processes for metal components. Nevertheless, these processes are still new compared to classic powder metallurgy manufacturing routes such as pressing and sintering. Hence not all necessary requirements for the powders in use are fully known yet. This makes an increase in control of the powder properties a crucial task to achieve. To reach this goal one must understand the different influences on the powder production process from the beginning of the whole production route. In this work, the influence of the spray chamber flow on the particle morphology is examined. The nozzle system used to produce the metal powders is a close-coupled atomization system with a convergent-divergent gas nozzle configuration. The particle morphology as well as the particle size distribution have been analyzed to examine the influence of the atomization gas flow compared to an additional use of a coaxial gas flow. To review the changes of the flow patterns, computational fluid dynamic simulations have been performed. The particle trajectories were calculated to assess the change in particle behavior as well. Atomization experiments have been conducted with an AISI 52100 (1.3505) steel in a small batch atomization plant to evaluate the influence of the change in flow on the particle size distribution and circularity. The experimental results show that a use of additional coaxial gas leads to an increase in particle circularity up to 10% for relevant particle sizes. An approach for the quantification of satellite occurrence is given by examination of the shift of the particle size distribution to smaller diameters.     

Effects of geometry and position of the metal delivery tube on ultrasonic gas atomization

The effects of the geometry and the position of the metal delivery tube on the pressure condition in the gas-metal interaction zone were studied. The measurements were performed under conditions which simulated ultrasonic gas atomization experiments, but at low gas atomization pressures (50–200 psig, 345–1380 kPa). Low gas atomization pressures are used in spray atomization and deposition processes such as liquid dynamic compaction (LDC), and Osprey. Depending on the experimental conditions, either underpressure or overpressure in the metal delivery tube was detected. The magnitude of the underpressures and overpressures was found to increase with the gas atomization pressure; the maximum pressure differences with respect to the atomization tank pressure were about 3 psi (21 kPa) when argon was used as an atomization gas with a pressure of 200 psig (1380 kPa). Underpressure or overpressure effects of such magnitude have a large effect on the metal flow rate during gas atomization. The large pressure differences measured in the present work result from using an atomizer with gas jet diameters larger than those used in previous investigations. Using a large ultrasonic atomizer, argon gas flow rates of about 5 kg/min can be obtained for atomization pressures of 200 psig (1380 kPa).     

高频感应熔化金属丝气雾化制备球形钛粉

提出了新型低成本球形钛粉气雾化制备技术——高频感应熔化金属丝气体雾化技术(Wire induction heating-gas atomization,WIGA),研究了雾化气体压力、熔体温度、送料速度对粉末性能的影响。结果表明:所制钛粉末的形貌为球形,球形度较高,粉末表面存在少量"卫星球"颗粒,占比约为1%;提高雾化压力、熔体温度和降低送丝速度均使粉末平均粒径D50减小。实验所得最佳雾化参数为:雾化气体压力4.0 MPa,熔体温度2 000℃,送料速度0.8m/min,在此条件下得到的钛粉末平均粒径为41.8μm。     

Effect of gas Mach number on the flow field of close-coupled gas atomization,particle size and cooling rate of as-atomized powder: Simulation and experiment

Gas velocity is a key parameter regulating the particle size and the cooling rate of the gas atomized powder applied in additive manufacturing, metal injection molding, thermal spraying, and soft magnetic composites. In this paper, on basis of the well-designed close-coupled nozzles with different gas Mach numbers at the outlet, the gas field structure was simulated by Computational Fluid Dynamics (CFD) software, and the process of cooling and solidification of Fe-6.5 wt% Si metal droplets was calculated by finite difference method. The results show that with the increase of Mach number, both the gas velocity downstream and the pressure at the base of melt delivery tube tip rise, whereas the mass flow rate of the melt decreases. The nozzles with high Mach number can produce finer powder with higher cooling rate. The median diameter of the powder prepared by the nozzle with Mach numbers of 1.0, 1.5, 2.0, and 2.5 is 44.9, 39.0, 32.5, and 29.1 μm, respectively, and the corresponding cooling rate of the metal droplet with a diameter of 80 μm is 2.85 × 10⁴, 2.98 × 10⁴, 3.32 × 10⁴, and 3.50 × 10⁴ K/s, respectively. This work provides new ideas and suggestions for the preparation of metal powder with small particle size at high cooling rate.     

Microstructures and Mechanical Properties of Rapidly Solidified Mg-Al-Zn-MM Alloys

Mg-Al-Zn-M M （misch metal） alloy powders were manufactured by inert gas atomization and the characteristics of alloy powders were investigated.In spite of the low fluidity and easy oxidation of the magnesium melt,the spherical powder was made successfully with the improved three piece nozzle systems of gas atomization unit. It was found that most of the solidified powders with particles size of less than 50μm in diameter were single crystal and the solidification structure of rapidly solidified powders showed a typical dendritic morphology because of supercooling prior to nucleation.The spacing of secondary denrite arms was deceasing as the size of powders was decreasing.The rapidly solidified powders were consolidated by vacuum hot extrusion and the effects of misch metal addition to AZ91 on mechanical properties of extruded bars were also examined.During extrusion of the rapidly solidified powders,their dendritic structure was broken into fragments and remained as grains of about 3μm in size.The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were finely broken,too.The tensile strength and ductility obtained in as-extruded Mg-9 wt pct Al-1 wt pct Zn-3 wt pct MM alloy wereσ-（T.S.） =383 MPa andε=10.6%,respectively.All of these improvements on mechanical properties were resulted from the refined microstructure and second-phase dispersions.     

雾化法制备锌粉技术研究

用自行设计的限制式雾化喷嘴为核心的雾化装置,研究了在喷嘴关键结构参数（输液管的直径、喷嘴狭缝尺寸、喷射角等）一定的条件下,雾化压力及熔融温度对液锌的雾化效果的影响。结果表明,当雾化介质为Ｎ２,压力为０．４０～０．５０ＭＰａ,液锌温度为６５０℃时,液锌可以获得较好的雾化效果,通过显微镜观察和电镜扫描,发现制备的锌粉大部分为不规则形状。     

功率对EIGA制备3D打印用TC4合金粉末特性的影响

与传统的雾化制粉技术不同,电极感应熔炼气体雾化(EIGA)技术是采用预合金棒料为电极,无坩埚感应加热,熔化后直接滴落雾化区被惰性气体雾化的技术.该技术由于在熔炼过程中液态金属与坩埚不接触,有效地减少了钛合金粉末中的夹杂物,改善了合金粉末的质量.本文利用自主设计制造的EIGA制粉设备,采用激光粒度分析仪、扫描电镜(SEM)、X射线衍射仪(XRD)等分析手段,研究了不同功率参数对雾化制备TC4合金粉末的粒度分布、组织形貌、空心球等的影响.研究表明:EIGA法制备的TC4合金粉末整体球形度均较好,空心球缺陷较少,空心球率低于3%.熔炼功率较低时,粗颗粒粉末较多,且存在一定比例不规则的棒形和哑铃状粉末颗粒;当功率提高到62 k W时,细粉比例明显提高,不规则形状的粉末颗粒基本消失.随着功率的升高,粉末中的氧含量呈增加趋势,但仍基本保持在0.08%~0.10%较低范围内.功率为56 k W时,粉末松装密度最好,为2.686 g/cm3,松装密度比为60.63%,符合激光3D打印用TC4钛合金粉末松装密度比要求.     

Increasing the amorphous yield of {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders by hot gas atomization

The synthesis of metallic glasses requires high cooling rates leading to product size limitations of a few millimeters when using conventional casting techniques. One way to overcome these size limitations is powder metallurgy. Melt atomization and the subsequent powder processing can result in larger, amorphous components as long as no crystallization takes place during powder consolidation.An iron-based glass-forming alloy {(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05}₉₆Nb₄ was formed through both ambient room and high temperature inert gas atomization at various melt flow rates (close-coupled atomization). The use of hot gas generally decreases the droplet size and hence leads to an increased cooling rate and amorphous fraction of the atomized powders.Hot gas atomization results in a lower gas consumption, a smaller gas-to-melt mass flow ratio (GMR), smaller particles and a smaller geometric standard deviation.Particles atomized in ambient temperature were fully amorphous up to a particle size fraction of 90?µm. Larger particle size fractions resulted in a higher crystalline fraction. According to the XRD and DSC analyses, hot gas atomization has only a very small influence on the cooling rate and the amorphous fraction. However, the amorphous yield is significantly increased using hot gas atomization.     

Studies on process optimisation of multistage atomisation

Abstract

In order to understand more about the multistage atomisation process, process experiments and orthogonal optimisation of multistage atomisation were carried out for pure tin to make clear the effect of every main process parameter and the optimum conditions. The orthogonal experiments showed that the disk rotating speed and superheat temperature have the largest effects on the mean particle size and that spraying height affects the powder shape coefficient remarkably. The delivery tube position has a pronounced effect on the result and rate of atomisation through changing the pressure characteristics of the nozzle tip and is also an important process factor, while the effect of gas pressure on atomisation result is relatively small. The optimum process conditions for multistage atomisation of pure tin are as follows: superheat 350 K; spraying height 85 mm; gas pressure 0·8 MPa; disk rotating speed 4000 rev min^-1; and protrusion height of delivery tube 2–3 mm.     

双介质喷嘴雾化特性数值模拟研究

目的 双介质喷嘴雾化效果直接影响烟卷加料工艺的进一步提升，通过对雾化过程进行数值模拟，方便对雾化特性进行透彻的分析，提升雾化效果。方法 采用数值模拟方法构建两相流连续相流场与DPM离散态双向耦合的数值模型，研究蒸汽压力、液体流量以及双介质喷嘴结构对喷嘴雾化特性的影响。结果 适当增加蒸汽压力，可以在不影响最大流速、颗粒粒径均匀度及颗粒中值粒径的情况下，减小雾化扩散角，小幅度地增加喷射距离，雾化细度变好，进而提高雾化效果。随着有机液流量的增加，雾化扩散角增大，喷射距离增加，雾化粒径均匀度变好，从而使雾化效果变好。液体路通流面积越大喷雾的贯穿距离越小，气路通流面积越大喷雾的雾化扩散角度越大。若需要得到较好的雾化效果，需要保证较小的蒸汽路通流面积，与此同时液路侧保持正常开度。结论 适当地提高有机液流量或者蒸汽压力，以及采用较小蒸汽路通流面积，同时液路侧保持正常开度的结构，有利于提高料液喷洒的均匀性，减少了料液的浪费，提高了烟丝制备的工艺水平。     

真空气雾化法制备AlSi10Mg粉末参数优化及打印态组织性能研究

目的 探究利用真空气雾化法制备AlSi10Mg球形粉末过程中各参数对粉末质量的影响,以得到最佳的制粉工艺参数。以制备的粉末进行增材制造,研究块体组织及其力学性能。方法 针对制备的球形粉末,采用扫描电镜（SEM）观察粉末的球形度及其内部组织。通过分析球形粉末的平均粒径与粒度分布区间总结最优制粉参数。针对以球形粉末增材制造出的沉积态样品,采用X射线衍射仪（XRD）、扫描电镜（SEM）研究其微观组织形貌并通过拉伸试验研究其力学性能。结果 真空气雾化法制备出的粉末表面光洁且球形度良好,同时粉末平均粒径随雾化压力的增大呈现先减小后增大的趋势并在4.0 MPa时粒径最小,且与环孔喷嘴相比,环缝喷嘴制备出的粉末粒径更小。粉末内部组织由胞状晶与树枝晶构成。通过SLM制备的沉积态样品组织以沿沉积方向的枝晶为主,该样品的力学性能较优异,断裂方式主要为沿晶断裂。结论 在使用真空气雾化法制备增材制造用球形粉末时,应选择4.0 MPa的气雾化压力并选择环缝喷嘴,方能得到质量最佳的球形粉末。     

Evaluation of the splats properties and relation with droplets diameters in atomization process using a De Laval Nozzle

Properties of the powders developed during atomization process are essentially determined by process parameters. Experiments based on splat collection have been performed at different stages of the process evolution. Formation of splat formed as a result of impingement of the melted metallic droplets onto a substrate was studied. Splat characteristics have been determined from image analysis in function of process parameters and time progress. Droplet diameters were measured using laser Coulter analyzer. Direct relationships between splat diameter and droplet diameter were established. The atomization experiments point out the strong influence of two processing parameters (atomizing gas and melt nozzle diameter) on splat characteristics and particle size. It has been observed that increasing atomizing pressure leads to a decrease of mean splat diameter and width of the size distribution. Similar evolution was found for droplet diameter. Moreover, it is clearly shown that increasing melt nozzle diameter induces an increase of both splat diameters and droplet diameters. The results provide a better understanding of the influence of atomization parameters on the size distribution.     

SnAgCu系无铅焊锡粉末特性的实验研究

实验研究了导液管内径对SnAgCu系无铅焊锡雾化粉末有效雾化率及粒度分布的影响。结果表明：在一定雾化条件下，导液管内径为3mm，雾化粉末具有较高的有效雾化率、粒度分布及最佳离散度；随着导液管内径的减小，粉末明显细化，有效雾化率略有增加，但粒度分布变差；随着导液管内径的增大，粉末有效雾化率急剧降低，粒度分布变差。     

Visualization and modeling for water atomization of low melting point alloy

Liquid metal fragmentation by impinging fast water spray, so called water atomization, is widely used to produce metal powders efficiently. In the present paper, we conduct the high-speed visualization experiments and theoretical modeling for elucidating the mechanism of fragmentation and solidification processes, which are essentially important to control the metal powder characters. We successfully visualize the detailed sequential events from the water spray ejection, freely dropped molten metal of 42Sn-58Bi, followed by their collision, metal fragmentation in liquid phase, and solidification, leading to revealing the fragmentation processes as the impact of water spray and the vapor explosion. Quantified metal particle size convinces that the water atomization simultaneously proceeds fragmentation of metal in liquid phase with solidification. The experimental results of size distribution and mean diameter well validate the proposed physically-consistent theoretical modeling for the prediction of particle size.     

雾化方法对弥散强化铜材料性能与冷加工性能影响的研究

氧化铝弥散强化铜材料具有高温强度、高导电的特性和不可替代的作用.研究了气雾化、气雾化 离心雾化及高压水雾化方法制取铜铝合金粉对弥散强化铜材料性能及冷加工性能的影响.结果表明:不同雾化方法制取的粉末,其颗粒形貌不同;-150目粉末收取率不同;材料的技术性能和冷加工性能不同.     

The effect of MHD interactions on the input shock waves in a supersonic diffuser

The interaction with an external magnetic field modifies the variation of the shock wave configuration in a pure inert gas plasma at the entrance of a supersonic diffuser. The phenomenon was studied using an experimental setup based on a shock tube with a flat nozzle and the model supersonic diffuser. The experiments were conducted in krypton, for the shock wave Mach number in the shock tube M=7.8 and the Mach number at the nozzle exit M=4.2. The gasodynamic discontinuities and their structural variations induced by the magnetic induction changes were by visualized by the schlieren method and by photography of the intrinsic emission accompanying the process. Three regions of the MHD interaction affecting the shock wave configuration in the gas flow were revealed.     

大豆蛋白喷涂液雾化粒子场实验

目的研究大豆蛋白喷涂液雾化场的粒度分布,及喷涂过程中喷涂参数对大豆蛋白液雾化液滴粒径的影响,从而在蔬菜复合纸覆膜成型过程中选择最优喷涂参数。方法利用激光粒度仪测量不同喷涂参数下大豆蛋白液喷涂雾化场的粒度分布,并通过数据分析软件Origin研究喷涂参数对大豆蛋白液喷涂雾化粒度的影响。结果喷涂参数相同时,喷涂雾化场中随着轴向距离的增加,大豆蛋白液液滴粒径先显著减小后趋于稳定;喷涂雾化场中同一轴向位置随着径向距离的增加,大豆蛋白液液滴粒径呈减小趋势。在喷涂雾化场同一测量点,随着喷涂气压的增大,大豆蛋白液液滴粒径逐渐减小;喷涂液压对大豆蛋白液液滴粒径没有显著影响。结论喷涂气压为0.2 MPa,喷涂液压为0.16 MPa,喷涂雾化场轴向30 cm平面内,大豆蛋白液雾化液滴粒径较小且均匀。