Atomization Of Molten Metal Research Articles

Experimental and numerical investigations on molten metal atomization techniques – A critical review

• All major types of atomizing techniques for molten metal are reviewed and compared. • Recent studies are tabulated including major results and operating conditions. • TAB and KHRT are common models for the numerical modeling of atomizers. • Hybrid geometries or combination of different techniques produce finer powders. • Centrifugal atomization is the most economical technique in industrial scale. Metal powders are highly practical in many applications such as solders, 3D printing, dental activities, etc. Atomization of molten metals and alloys is one of the common mechanisms for the production of powders. In this review, different techniques for the atomizing of molten metals including gas atomization, centrifugal atomization, water/oil atomization, and special atomization are compared and the advantages and disadvantages of each technique are discussed in detail. Furthermore, recent experimental and numerical investigations regarding different atomization techniques are reviewed in different operating conditions and materials for better understanding of the effects of different parameters on powder size. Hybrid atomization, which is the combination of different atomization techniques, is also represented. Finally, some special designs of atomizers for improving the size and quality of powders are introduced.

Коррозионностойкие стали в аддитивном производстве

This review discusses the main methods for producing spherical powder particles of corrosion-resistant steels as a material widely used in all industries. Also the examples of products made by modern additive methods are described. Currently, spherical powder particles of corrosion-resistant steels are used in the following additive methods: selective laser melting, selective laser sintering, direct laser sintering, and electron beam melting. Each of these methods has its own requirements for the characteristics of spherical powder particles of corrosion-resistant steels. The review provides a brief description of the principles of operation of each method and the requirements for spherical powder particles of corrosion-resistant steels. It also considers a detailed description of each method of additive manufacturing with a description of the principle of operation and specific examples of obtaining spherical particles of corrosion-resistant steel powders with indication of their properties (morphology, structural features, chemical composition, fluidity, bulk density). A comparative analysis was carried out with a description of disadvantages and advantages of each method. Examples of the use of spherical particles of corrosion-resistant steel powders for the manufacture of products by various additive methods (including post-processing) are given with description of the final products characteristics. Based on the data presented, a conclusion was made about the preferred methods for obtaining spherical particles of corrosion-resistant steel powders for specific additive methods used in modern industry. The review considers the following methods for producing spherical powder particles: water atomization (atomization of liquid metal with a jet of water under pressure); gas atomization (atomization of the melt with a jet of inert gas (argon or nitrogen) under pressure); centrifugal atomization (atomization of molten metal with a high-speed rotating disc); ultrasonic atomization (atomization of liquid metal by ultrasound); non-contact atomization (atomization of liquid metal with a powerful pulse of electric current); plasma wire spraying; plasma spraying of a rotating electrode; plasma spheroidization.

Numerical modeling of secondary breakup in molten metals gas-atomization using dimensionless analysis

Numerical modeling of secondary breakup in gas atomization of molten metals has been successfully performed by others to optimize the powder particle size distribution for various additive manufacturing techniques and metal alloys. The application of breakup analytical models has been tested and validated through experimental campaigns by several researchers. They have demonstrated the suitability of the models in predicting particle size distribution as a function of process parameters.The limit of these models is a lack of information about the particle shape. Assessing the particle morphology could be of great relevance for optimizing the gas atomization parameters of already produced or new alloys.To overcome this limitation, the method described in this paper resorts to the Volume Of Fluid (VOF) modeling approach. This method does not apply to gas atomization breakup because supersonic velocities bring to unaffordable computation times and lack of metal mass conservation. The new approach is conceived to scale down the high velocity flow towards much lower intensities. It makes use of a reference frame moving with the primary droplet and of the similarity theory. At present, the model has been validated through the comparison with DPM results. It demonstrated to be a reliable alternative model allowing to gain deeper insights. Heat transfer among gas and droplets is not simulated yet, thus the droplet deformation does not stop at the solidification time. Further developments are forecast to allow to freeze the particle shape at the time it is completely solidified.

The Production of AZ31 Alloys by Gas Atomization Method and Its Characteristics

The aim of this study is to investigate the AZ31 alloy powder production and characterization processes experimentally using the gas atomization method. For this purpose, firstly, the design and production of gas atomization units were done at Karabuk University Faculty of Technology Department of Manufacturing Engineering. In this gas atomization unit, the manufacturability of AZ31 powder from magnesium alloys was investigated by the gas atomization method which is one of the production methods by powder metallurgy. The parameters and the literature used in the production of materials similar to the AZ31 alloy are taken into account as producibility parameters. In the gas atomization method, parameters such as nozzle diameter, gas pressure, and temperature must be controlled in order to produce the desired properties in metal powder production. The diameter of the nozzle is crucial because it affects the gas pressure and temperature, the size of the powder, and the shape of the powders. Experimental studies were carried out using 3 different temperatures (790, 820, and 850°C), 4 different nozzle diameters (2, 3, 4, and 5 mm) and 4 different gas pressures (5, 15, 25, and 35 bar). In the molten metal atomization process and in the process of forming a protective gas atmosphere, argon gas was preferred. Scanning electron microscopy (SEM) was used to determine the shape of the AZ31 powders produced, XRD, XRF, and SEM-EDX analyses were used to determine the phases in the internals of the produced powders and percentages of these phases. Laser measurement devices were used for powder size analysis and hardness tests were performed to determine the mechanical properties of the produced powders. The powders produced were pressed into masses at 4 different pressing pressures (300, 400, 500, and 600 MPa). The best sinterability values of the bulked powders and sintering process were performed at 3 different temperatures (500, 550, and 600°C). Density measurements were made after pressing and sintering the powders. As a result of the experimental studies, it was found that the powder size decreased with the increase of the gas pressure but the nozzle diameter, and the powder shape changed to the dripping and the spherical in the ligament and complex form. It has been observed that the temperature has no significant effect on the powder size and shape.

Computational fluid dynamic investigation of the primary and secondary atomization of the free-fall atomizer in electrode induction melting gas atomization process

Nickel-based superalloy is mainly used for fabricating the important high temperature parts including the turbine disk, turbine baffle, compressor disk, and other critical components. Ceramic inclusions in powder metallurgy (PM) superalloy could promote fatigue crack initiation, and thus accelerating the crack propagation under certain conditions. In this case, the ultra-clean nickel-based superalloy powder is critical for PM superalloy components. Generally, there are two well-known methods of fabricating superalloy powders, i.e., argon gas atomization (AA) and plasma rotating electrode process (PREP). Electrode induction melting gas atomization (EIGA) process is a newly developed method of preparing ultra-clean metal powders. The EIGA process is a completely crucible-free melting and atomization process developed by ALD vacuum technologies. In this process, a slowly rotating prealloyed bar is fed into a conical induction coil. The end of the bar is inductively heated and molten alloys falls into an atomizer where the liquid alloy is atomized with a high-pressure inert gas. The EIGA prepared powders possess the advantages of AA (more fine powders) and PREP (ultra-clean powders) processes. Generally, there are two key issues in EIGA process, and the free-fall gas atomizer design is one of the critical issues for the powder yield and quality. Free-fall gas atomizers are some of the first two fluid atomizer designs to be used for molten metal atomization. In a simple open (unconfined stream) design a melt stream falls from a tundish exit via gravity into the convergence of focused atomization gas jets where it is disintegrated. The gas-melt interaction is complex, and it is difficult to characterize the interaction process directly. To have a good understanding of the atomisation technology, the physical break-up process instead of correlating the gas dynamics with droplet fragmentation indirectly must be able to be examined. And it will be desirable, if we input the atomization parameters, we can obtain the particles' distributions directly. In this work, a computational fluid dynamic approach to simulating the primary and secondary atomization processes is developed by using the volume of fluid method and discrete phase model. By integrating the metal stream break-up (in primary atomization) with the flow field and particles distribution simulation (in second atomization), this numerical simulation method is able to provide the direct assessment for the atomisation process. To verify the method performance, the melt stream is initialized into a 4 mm-diameter stream, which is then injected into the gas flow field for further fragmentation. The experimental results show that the simulated particles' diameter distribution is consistent with the experimental results in the same conditions.

Design and evaluation of a Laval-type supersonic atomizer for low-pressure gas atomization of molten metals

A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design objectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and optimizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atomizer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m·s−1; this value is independent of the atomization gas pressure P0 when P0 > 0.7 MPa. When P0 = 1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a minimum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0 = 1.0 MPa and with 7055Al alloy at P0 = 0.8 and 0.4 MPa were conducted to evaluate the atomization capability of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5 μm, respectively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.

Atomization Using a Pressure-Gas-Atomizer

An update and the latest results on molten metal atomization using a Pressure-Gas- Atomizer will be given. This atomizer combines a swirl-pressure atomizer, to generate a liquid hollow cone film and a gas atomizer to atomize the film and/or the fragments of the film. The paper is focused on powder production, but this atomization system is also applicable for deposition purposes. Different alloys (Sn, SnCu) were atomized to study the characteristics of the Pressure- Gas-Atomizer. The powders produced were analyzed by laser diffraction and image processing. Among other parameters, the molten metal mass flow (~140 – 200 kg/h), the gas mass flow and the atomizer design were varied. The results include the effects of these variances on particle size and particle shape.

Particle Size Distribution in a Wire-Arc Spraying System

The size and velocity of particles produced by a ValuArc 200 (Sulzer-Metco, Westbury, NY) twin-wire-arc spraying system were measured in-flight using a DPV-2000 system (Tecnar Ltd., St-Bruno, QC, Canada) for a range of operating parameters. A technique was developed to identify and separate the size distributions of particles produced by atomization of molten metal at either the anode or the cathode by assuming that both follow a log-normal distribution. It was shown that particles produced by the anode are almost two times larger in diameter than those originating from the cathode. Experiments showed that increasing the pressure of atomizing gas decreased the size of both anodic and cathodic particles, but changing wire feed rate and operating voltage did not change particle size significantly.

Use of extended phase-doppler anemometry for investigation of atomization of molten metal: K.Bauckhage et al. (University of Bremen, Bremen, Germany.)

Use of extended phase-doppler anemometry for investigation of atomization of molten metal: K.Bauckhage et al. (University of Bremen, Bremen, Germany.)

Control of molten metal atomization by measurements of gas and liquid atomization: J.Raimann et al. (University of Erlangen-Nürnberg, Erlangen, Germany.)

Control of molten metal atomization by measurements of gas and liquid atomization: J.Raimann et al. (University of Erlangen-Nürnberg, Erlangen, Germany.)

Thermodynamics of dissolution and liberation of gases in the atomization of molten metals by plasma-induced expansion

Theoretical and experimental investigations of the solubility of gases dissolved in their plasma state in molten metals have shown that these solubilities are higher than the equilibrium solubilities attainable when the same gases are dissolved in their molecular state. Thermodynamic input-output balances for the dissolution and liberation of gases in molten metals, and calculation of the activation energies needed for these processes, yield guidelines for the design of equipment in which plasma torches will be able to supersaturate molten metals with gases at much lower pressures than are currently necessary.

Ensemble and Single Particle Laser probe sizing results for gas atomized zinc powders

AbstractOn‐line characterization of powder and droplets during gas atomization of molten metals and alloys offers extensive opportunities for real‐time process monitoring and control. The capability to make on‐line measurements can significantly reduce tedious and costly powder classification, which, currently, is always carried out subsequent to the atomization process. Two laser‐based particle sizing instruments, the EPCS (ensemble instrument) and PCSV (single particle instrument), were used during gas atomization of zinc with a double Coanda nozzle configuration. The laser instruments were positioned in the duct leading from the bottom of the atomization tower to the powder collection cyclone. The effect of gas to metal ratio on particle size was studied by varying the atomization gas pressure from 0.69 MPa to 1.03 MPa. Air was used as the atomizing gas for some of the 0.69 MPa runs, while nitrogen was used for all of the higher‐pressure runs. Experimental apparatus and procedures for atomization and on‐line powder sizing with the EPCS and PCSV are described. EPCS and PCSV measurements, which were compared with standard sieve analyses, indicate that the ensemble instrument is a good candidate for on‐line process monitoring and control.

Modelling of rod growth during spray forming: H.C. Lee et al (Seoul National University, Seoul, Korea), J Korean Inst of Metals, Vol 30, No 9, 1992, 107–1077. (In Korean).

Developments in molten metal atomization have followed the requirements of clearly identifiable markets for advanced alloy compositions. Consequently, new requirements are leading to detailed differences in the atomization processes. The following article outlines some of the developments which have taken place over recent years in the atomization processes for the molten metals, and which can replace water/gas and rotary atomization.

Production of powder by atomization of molten metal with low temperature liquid gas : J.Backer. (Krupp Pulvermetall GmbH, Essen, Germany). Metall, Vol 25, No 8, 1991, 764–771, (In German)

Production of powder by atomization of molten metal with low temperature liquid gas : J.Backer. (Krupp Pulvermetall GmbH, Essen, Germany). Metall, Vol 25, No 8, 1991, 764–771, (In German)

Mechanical atomization of molten metals

Developments in molten metal atomization have followed the requirements of clearly identifiable markets for advanced alloy compositions. Consequently, new requirements are leading to detailed differences in the atomization processes. The following article outlines some of the developments which have taken place over recent years in the atomization processes for the molten metals, and which can replace water/gas and rotary atomization.

Technological properties of R6M5 steel powder produced by atomization of molten metal with high-pressure water

Technological properties of R6M5 steel powder produced by atomization of molten metal with high-pressure water

Production of metal powders with an amorphous structure by centrifugal hydraulic atomization of molten metal

Production of metal powders with an amorphous structure by centrifugal hydraulic atomization of molten metal

電磁気力による溶融金属の微粒化

電磁気力による溶融金属の微粒化

Atomization of Molten Metals Using the Coanda Effect

Abstract This paper presents the results of an investigation into the fundamentals of the atomization of molten metals using the Coanda effect. Various visualization techniques were used to study the flow of the gas jet out of a Coanda nozzle, the aspiration of surrounding gas to the Coanda jet, and the atomization of molten metal. It has been shown that the Coanda gas jet is very sensitive to both nozzle surface and nozzle geometry. These design parameters control jet expansion and the efficiency of the conversion of nozzle velocity into jet momentum. The gas flowrate from a Coanda nozzle was found to be at least equivalent to that from a converging nozzle operating under frictionless and adiabatic conditions. The atomizing mechanism using the Coanda nozzle determined using high speed photography was found to follow the same sequence of events as in conventional gas atomization. However, owing to the large pressure gradient normal to the Coanda surface, the molten metal forms a semiconical sheet in the p...

Method of calculating the rate of gas consumption in the process of gas stream atomization of molten metal

Method of calculating the rate of gas consumption in the process of gas stream atomization of molten metal