Atomizing Gas Pressure Research Articles

Criterion of gas and solid dual-phase flow atomization crash in molten metal

A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepared by common gas atomization and dual-phase flow atomization under similar conditions were compared. The experimental results show that the dual-phase flow-atomized powders have average particle sizes that are one-half that of the common gas-atomized particles; additionally, they possess a finer microstructure and higher cooling rate under the same atomization gas pressure and the same gas flow. The Weber number in the crash criteria of liquid atomization is adopted to measure the crash ability of the atomization media. The Weber number of the dual-phase flow atomization medium is the sum of that of the gas and the solid particles. Furthermore, the critical equation of the crash model in dual-phase flow atomization is established, and the main regularities associated with this process were analyzed.

Numerical and experimental modelling of back stream flow during close-coupled gas atomization

This paper reports the numerical and experimental investigation into the effects of different gas jet mis-match angles (for an external melt nozzle wall) on the back-stream flow in close coupled gas atomization. The Pulse Laser Imaging (PLI) technique was applied for visualising the back-stream melt flow phenomena with an analogue water atomizer and the associated PLI images compared with numerical results. In the investigation a Convergent–Divergent (C–D) discrete gas jet die at five different atomization gas pressures of 1–5MPa, with different gas exit jet distances of 1.65, 1.6, 1.55, 1.5, 1.45 and 1.40mm from the melt nozzle external wall, was combined with four melt nozzles of varying gas jet mis-match angles of 0°, 3°, 5°, and 7° relative to the melt nozzle external wall (referred to as nozzle types 1–4). The results show that nozzle type 1 with the smallest mis-match angle of zero degrees has highest back-stream flow at an atomization gas pressure of 1MPa and a gas die exit jet located between 1.65mm and 1.5mm from the external melt nozzle wall. This phenomenon decreased with increasing mis-match angle and at higher atomization gas pressure. For nozzle type 2, with a mis-match angle of 3 degrees, a weak back-stream flow occurred with a gas exit jet distance of 1.65mm from the melt nozzle external wall. For a gas pressure of 1MPa with a decrease in the gas jet exit distance from the external wall of the melt nozzle this phenomenon was eliminated. This phenomenon was not seen for nozzle types 3 and 4 at any gas pressure and C–D gas exit jet distances.

O50 Implication de SRB1, CD36 et NPC1l1 dans le transport intestinal de la vitamine K

This paper reports the numerical and experimental investigation into the effects of different gas jet mis-match angles (for an external melt nozzle wall) on the back-stream flow in close coupled gas atomization. The Pulse Laser Imaging (PLI) technique was applied for visualising the back-stream melt flow phenomena with an analogue water atomizer and the associated PLI images compared with numerical results. In the investigation a Convergent–Divergent (C–D) discrete gas jet die at five different atomization gas pressures of 1–5 MPa, with different gas exit jet distances of 1.65, 1.6, 1.55, 1.5, 1.45 and 1.40 mm from the melt nozzle external wall, was combined with four melt nozzles of varying gas jet mis-match angles of 0°, 3°, 5°, and 7° relative to the melt nozzle external wall (referred to as nozzle types 1–4). The results show that nozzle type 1 with the smallest mis-match angle of zero degrees has highest back-stream flow at an atomization gas pressure of 1 MPa and a gas die exit jet located between 1.65 mm and 1.5 mm from the external melt nozzle wall. This phenomenon decreased with increasing mis-match angle and at higher atomization gas pressure. For nozzle type 2, with a mis-match angle of 3 degrees, a weak back-stream flow occurred with a gas exit jet distance of 1.65 mm from the melt nozzle external wall. For a gas pressure of 1 MPa with a decrease in the gas jet exit distance from the external wall of the melt nozzle this phenomenon was eliminated. This phenomenon was not seen for nozzle types 3 and 4 at any gas pressure and C–D gas exit jet distances.

Spray-Formed Stainless Steel Matrix Composites with Co-Injected Carbide Particles

In order to develop new types of wear-resistant and corrosion-resistant materials, TiC and VC particles were injected into martensitic stainless steel X46Cr13 during spray forming, respectively. The microstructures of the spray-formed steel matrix composites under different processing conditions were investigated. The mechanisms of interactions between the injected particles and the matrix materials during spray forming and their effects on the microstructures of the composites were discussed and clarified based on experimental and theoretical investigations. The current results show that the injected particles may penetrate into the metallic droplets or adhere to the surface of the droplets and, therefore, are incorporated into the deposits to form metal matrix composites. Substantial heat transfer from superheated metallic melts to the room temperature carbide particles takes place as they are incorporated into the matrix material. The matrix steel solidifies in the vicinity of the carbides due to their chilling effect, and thus, the carbides may be engulfed in the matrix or pushed to the grain boundaries by the solidification fronts. TiC particles essentially retain their shape and size in the steel composites, while VC particles dissolve at least partially in the matrix and reprecipitate or form new phases in the final solidification and cooling stage. The porosity in the deposits increases with the gas to melt ratio (GMR) and the powder to melt ratio (PMR) by increasing atomizing gas pressure and powder feeding rate. Carbide type also affects the porosity of the deposits, because different thermodynamic properties of carbides change the heat dissipation and local solidification behavior of the mixture of matrix material and dissolved carbides. Moreover, the microstructure of the matrix material X46Cr13 is refined considerably with increasing GMR and PMR.

Variation Mechanism of Aspiration Pressure at the Tip of Metal Delivery Tube in Supersonic Atomization

The aspiration pressure variation at the tip of metal delivery tube in the supersonic atomization nozzle during gas-only atomization performance had been investigated in this work. The results reveal that the aspiration pressure is subambient at all operating pressures. A general trend is that with increasing atomization gas pressure, the value of aspiration pressure decreases at P0 between 0.5 and 1.5MPa, then increases as P0 ranges from 1.5~3.5MPa, finally decreases again at higher gas pressure (P0>~3.5MPa). When P0>2.0MPa, as the included angle α augments, the aspiration pressure ΔP increases. Meanwhile, the change range of aspiration pressure ΔP significantly enlarges when the jet included angle α raises from16 to 28º. The lager is the apex angle β of metal delivery tube, the greater is the aspiration pressure ΔP. And as the protrusion length of melt delivery tube h increases, the aspiration pressure ΔP decreases gradually.

Influences of Atomizing Pressure on Preparation Processing of Lead-Free Solder Powder

An investigation on the melt delivery tube tip pressure and the effective atomizing efficiency of atomizing powder was carried out. The results show that all of melt delivery tube tip pressures are negative value in the atomization gas pressure range of 0.4~0.9 MPa, and they monotonously increase with increasing the atomizing pressure; when the atomizing pressure is higher than 0.7 MPa, the negative pressure of the melt delivery tube tip is slowly increasing with continuously increasing the atomizing pressure; the atomized powder possesses higher effective atomizing efficiency, more uniform size distribution, better sphericity and smoother surface at the atomizing pressure of 0.7 MPa and the pressure of the melt delivery tube tip of -39.44 kPa.

Experimental and numerical modeling of the gas atomization nozzle for gas flow behavior

Gas atomization is a widely used process for manufacturing of fine metal- and alloy-powder. To ensure a stable process with high yields of metal powder, the negative pressure at the melt delivery tube tip base and no flow separation conditions are necessary for a good atomization process. An important feature of these jets is that flow separation may occur over the outer surface of the liquid delivery tube for some conditions. Flow separation cause solidification and accumulation of metal, leading to a shape alteration of the liquid delivery tube in gas atomization process. Using computational fluid dynamics (CFD) software, a parametric study was conducted to determine the effects of atomizing gas pressure on the melt delivery tube tip base pressure and flow separation. Atomization gas pressures of 1.0, 1.3, 1.7, 2.2, and 2.7 MPa were used in the CFD model to initialize the pressure in gas inlet. CFD simulations were performed and the modeling results were compared with experimental data. These results showed that the CFD modeling can be used for the estimation of the melt tip base pressure of the nozzle. It is found that the flow separation formation is strongly dependent on the atomizing gas pressure.

Highly tuned gas atomization for controlled preparation of coarse powder

AbstractWhile close‐coupled gas atomization has been demonstrated for highly controlled production of fine powders in many alloy systems, defense applications for Mg powder demand that such an atomization system also be capable of producing a narrow standard deviation for coarse Mg powders. To develop this capability, a series of 5 gas atomization experiments were conducted with Al, as a less hazardous surrogate for Mg, over a range of a very low atomization gas pressures. The optimum result produced an average particle diameter of about 460 μm with a standard deviation of 1.53 using Ar atomization gas, sufficiently close to the 500 μm target size. These experiments achieved the process uniformity needed for this narrow standard deviation by stabilizing melt filming with an expanded discrete jet, close‐coupled atomization nozzle and a slotted trumpet bell pour tube. Initial analysis of the size results indicated that decreased atomization gas velocity, acting within the acceleration wave model, was the key controlling variable in this low‐pressure regime. No consistent influence of gas/melt mass flow ratio was detected in the data. Experimental observation of the atomization spray images also indicated that a practical lower limit to atomization gas pressure is about 69 kPa for achieving atomization process uniformity with the method of this study.

VOF Method for Impinging-Jet Atomizers

Impinging jet atomization is an effective method to produce fine sprays for extremely high viscosity fuels such as coal water slurry (CWS). This technique has been used successfully in a number of CWS applications since its inception. The purpose of this study is to analyze the effect of liquid viscosity and jet velocity in an impinging jet atomizer with a combined volume of fluid (VOF) model. It is observed that the film thickness increases with increased liquid viscosity, and the (a) relative velocity between the liquid and gas phase, (b) the gas liquid ratio (GLR), and (c) the atomizing gas pressure all play important roles. Mean droplet size predicted with the VOF model agrees well with experiments.

Effect of atomization gas pressure variation on gas flow field in supersonic gas atomization

In this paper, a computational fluid flow model was adopted to investigate the effect of varying atomization gas pressure ( P 0) on the gas flow field in supersonic gas atomization. The influence of P 0 on static pressure and velocity magnitude of the central axis of the flow field was also examined. The numerical results indicate that the maximum gas velocity within the gas field increases with increasing P 0. The aspiration pressure (Δ P ) is found to decrease as P 0 increases at a lower atomization gas pressure. However, at a higher atomization gas pressure increasing P 0 causes the opposite: the higher atomization gas pressure, the higher aspiration pressure. The alternation of Δ P is caused by the variations of stagnation point pressure and location of Mach disk, while hardly by the location of stagnation point. A radical pressure gradient is formed along the tip of the delivery tube and increases as P 0 increases.

Arc Sprayed Steel: Microstructure in Severe Substrate Features

The effect of severe substrate topography on the microstructure of thermally sprayed coatings has been relatively neglected, but is critical in controlling the performance of thick electric arc sprayed steel shells for rapid tooling applications. This paper shows how the spray angle and the atomizing gas pressure control the distribution of porosity and oxide in steel sprayed in and around cylindrical holes of different diameter and depth. Droplet splashing and the secondary deposition of splash droplets caused systematic variations in microstructure. In particular, the origin of the phenomenon of “bridging,” the premature closure of features, has been revealed by microstructural analysis and explained in terms of the trajectories of droplets. The filling of features with higher-quality material can be aided by using a low atomizing gas pressure, reducing the oxygen partial pressure of the surrounding atmosphere and careful selection of the spray angle.

Spray deposition of polymer nanocomposite films for dielectric applications

A scalable processing route for fabrication of polymer-based dielectric nanocomposite films has been developed by spray deposition and in situ polymerization of monomer–nanoparticle dispersions. Polydiacrylate–BaTiO 3 films with filler loadings of 10 vol% to 30 vol% and controlled thickness of 5–30 μ m were achieved by optimizing spray conditions of spray liquid flow rate, atomizing gas pressure and substrate traverse speed and temperature. Microstructural investigations showed well-dispersed BaTiO 3 nanoparticles embedded in the polydiacrylate matrix. Dielectric constants of ∼ 39 at 10 kHz, high breakdown strengths of > 100 kV/mm and low leakage currents of 1 0 − 9 to 1 0 − 8 A/cm 2 above 1000 V, and thermal stability up to 150 °C were attained for PTPGDA–30 vol%BaTiO 3 films. The low-cost, atmospheric spray deposition technique developed in this work has potential for larger-scale manufacture of dielectric nanocomposite films for power capacitor and other applications.

Investigation about the Chrome Steel Wire Arc Spray Process and the Resulting Coating Properties

Nowadays, wire-arc spraying of chromium steel has gained an important market share for corrosion and wear protection applications. However, detailed studies are the basis for further process optimization. In order to optimize the process parameters and to evaluate the effects of the spray parameters DoE-based experiments had been carried out with high-speed camera shoots. In this article, the effects of spray current, voltage, and atomizing gas pressure on the particle jet properties, mean particle velocity and mean particle temperature and plume width on X46Cr13 wire are presented using an online process monitoring device. Moreover, the properties of the coatings concerning the morphology, composition and phase formation were subject of the investigations using SEM, EDX, and XRD-analysis. These deep investigations allow a defined verification of the influence of process parameters on spray plume and coating properties and are the basis for further process optimization.

Improvements to close coupled gas atomisation nozzle for fine powder production

In the present study, a new close coupled annular slit type nozzle was designed and constructed to produce metal powders in order to investigate the improvement of efficiency of fine powder production. The atomisation runs for the present study were performed with a small scale close coupled gas atomisation system designed and constructed at the Mechanical Engineering Department of Dumlupinar University. Pure tin powders were produced using nitrogen gas. The effects of the atomisation gas pressure on the backpressure and powder size have been discussed. The present atomisation runs showed that particle size decreased as atomising gas pressure increased. The particle size was reduced from 55·4 to 12·9 μm with increasing pressure from 0·9 to 3·1 MPa. The mass median particle sizes decreased continuously from 55 μm at a G/M of 0·22 to 12·9 μm at a G/M of 1·36 with increasing G/M ratio. Above a certain G/M, the resultant particle sizes cannot be considerably reduced by further increasing atomising pressure.

Effect of System Parameters on Metal Breakup and Particle Formation in the Wire Arc Spray Process

The significance of metal atomization in the wire arc spray process is directly related to the final coating quality produced. Since the early observations of the melting behavior of the wire tips by Steffens, relatively little has been done to further the understanding of the mechanisms involved. The primary atomization of the molten wire tips show existence of sheets and extrusions on both electrodes, which are strongly dependent on the system operating parameters. High-speed imaging has been used in this study, for classification of sheet, membrane and extrusion formations as a function of atomizing gas pressure, voltage and current settings. The breakup of metal structures formed on the electrodes is further classified in a manner consistent with established classifications for the break-up of other liquids, e.g., water or fuel. Quantitative descriptions of metal sheet lengths and breakup times are presented. The improved understanding of the metal breakup mechanisms in the wire arc spray process may provide a basis for (a) modification of existing computational codes for prediction of particle sizes and trajectories, and (b) for modifications to torch designs for providing more uniform particle fluxes.

The influence of the pressure formation at the tip of the melt delivery tube on tin powder size and gas/melt ratio in gas atomization method

The production of metal powder using gas atomization technique is a wide spread process for manufacturing a wide range of spherical metal powder alloys. Metal powder properties generally improve with smaller powder particle size. Close-coupled atomizers are of great interest and controlling their performance parameters is critical for metal powder producing industries. In this study a new designed close-coupled nozzle system was used to produce tin powder to investigate the effect of the protrusion length of the melt delivery tube on the pressure formation at the melt tip. Observed improvement in particle refinement cannot be directly attributed to an increase in atomizing pressures and gas kinetics. Results from this study indicated that the observed metal flow rate was not behaving as what was earlier assumed, namely that, deeper aspiration enhanced metal flow rate. The melt flow rate was reduced with increasing the atomizing gas pressure. So that gas to melt mass flow ratio was increased for the same protrusion length and this ratio increase caused the finer powder particle size.

가스분무 공정에 의한 고강도 과공정 Al-Si 합금 분말의 제조 및 특성 연구 I. 분말 제조 및 성형성

In order to improve mechanical properties, the hypereutectic Al-20 wt%Si based prealloy powder was prepared by gas atomization process. Microstructure and compressibility of the atomized Al-Si powder were investigated. The average powder size was decreased with increasing the atomization gas pressure. Size of primary Si particles of the as-atomized powder was about <TEX>$5-8\;\mu{m}$</TEX>. The as-atomized Al-Si powder such as AMB 2712 and AMB 7775 to increase compressibility and sinterability. Relative density of the mixed powder samples sintered at <TEX>$600^{\circ}C$</TEX> was reached about 96% of a theoretical density.

Size distribution of particles from individual wires and the effects of nozzle geometry in twin wire arc spraying

By separating particles from the anode and the cathode wires, particle properties of individual electrodes of the arc spray process were investigated. Bimodal size distribution was observed for particles from each single wire. In addition, after atomisation and acceleration, average diameter difference between particles from the anode and cathode becomes quite small and the difference can be reduced by increasing atomising gas pressure and/or by using a closed nozzle system with a converging–diverging orifice (CD/CL). Microstructure analysis indicates that the CD/CL nozzle tends to produce coatings with finer microstructure, lower porosity and higher oxide content, while the open nozzle system leads to very coarse coating microstructure with higher porosity but less oxide content. CFD analysis of the gas dynamics was performed for different nozzles and led to numerical prediction of splat diameter distribution. Results show a smaller average splat diameter and a narrower splat diameter distribution for the CD/CL nozzle that is in close agreements with the microstructure analysis. It was found that a major disadvantage of the open nozzle system is its relatively longer distance between the wires interception point and the nozzle exit where the gas velocity attains its maximum value.

The velocity and temperature of steel droplets during electric arc spraying

The average dynamic and thermal behaviour of electric arc sprayed Fe–0.8wt.%C droplets has been investigated using a laser based time of flight velocimeter system (Laser2Focus—L2F) and a two-colour pyrometry system (In-flight Particle Pyrometer—IPP) respectively. Radial and axial variations of the spray velocity and temperature have been investigated, together with their dependence on atomising gas type, arc voltage, atomising gas pressure, and wire feed rate. Under all conditions, the average spray temperature was significantly above the steel liquidus temperature indicating most droplets were fully molten. Once projected away from the region of atomisation, the droplet spray typically cooled at ∼1 °C mm −1 and ∼10 5 °C s −1 and typical axial velocities were 100 m s −1. Because of asymmetry in the arc itself and the resulting differences in the melting behaviour of the wires, the spray exhibited asymmetric radial variations of both velocity and temperature about the spray cone axis. The presence of oxygen in the atomising gas had a significant effect in increasing spray temperature via exothermic oxidation of the steel droplets. Processing maps have been constructed in which the variation of average spray velocity and temperature with arc voltage, gas pressure and wire feed rate have been fitted to a series of simple polynomial expressions. These maps have been explained in terms of the heat and momentum transfer processes occurring during atomisation and subsequent droplet flight.

Oxide formation in the Sprayform Tool Process

The Sprayform Tool Process is a novel alternative to CNC machining for the rapid manufacture of hard tooling. The process is based on the robot controlled sprayforming of molten steel droplets onto a ceramic master pattern to form a thick, dimensionally accurate steel shell. This paper describes the Sprayform Tool Process, and investigates the evolution of microstructure in thick steel shells in terms of the oxide fraction as a function of process parameters: (i) spray height; (ii) atomising gas pressure; (iii) wire feed rate; and (iv) manipulating robot velocity. Spray height had the strongest influence on oxide content; by reducing spray height from 160 to 120 mm the oxide fraction in the microstructure was halved. The role of droplet splashing on the subsequent oxidation of splash droplets has been revealed as an important phenomenon controlling sprayed microstructure and oxide fraction. On the basis of the presented experimental results, the implications for the manufacture of large steel shells by the Sprayform Tool Process are discussed.