Close-coupled Gas Atomization Research Articles

Advantages of innovative large-scale metal powder production

Powder metallurgy (PM) refers to a range of engineering techniques whereby net shape or near-net shape bodies are produced through the aggregation of a powder substrate. Specifically, the emergence of Additive Layer Manufacturing (ALM) is an exciting development in this field. However, the quality of any product produced by ALM is highly dependent upon the quality of the powder used. Gas atomisation is a specialised processing route in the PM field for the production of fine, spherical powders directly from a molten metal melt. The close-coupled gas atomisation process involves a melt stream being impacted by high velocity, under-expanded gas jets which initiate its break-up in two distinct phases; the second critical in determining the final particle size distribution (PSD) of the powder produced. However, fully understanding the mechanisms at work and exerting a high level of control over any produced powder is a challenge faced by the powder manufacturing industry; highlighted by the stringent requirements of the new ALM manufacturing technique.Utilising Ansys Fluent v14.5 computational fluid dynamics (CFD) software, a 3D axi-symmetric simulation has been developed of a close-coupled atomising gas jet nozzle configuration utilised by a powder manufacturer. Through the two-way coupling of the CFD with a Discrete Particle Model (DPM) using the Euler–Lagrange approach, an assessment has been made of the effect of process parameters on the final PSD of the metal powders produced. The most appropriate model for the simulation of the secondary break-up phase has been identified from the Kelvin–Helmholtz (KH), Kelvin–Helmholtz Rayleigh-Transport (KHRT) and Taylor Analogy Break-up (TAB) models. Subsequently, the validated simulation approach has been used for the qualitative assessment of the effect of altering the atomising nozzle geometry and process conditions on the average size of powders produced i.e. finer or coarser. It was also established that there is potential for the model to be used as a quantitative predictive tool of powder size; useful for quality control especially when manufacturing powder for use in ALM. However, further development and validation is required for confirmation of this function.

Close coupled gas atomization

Close coupled gas atomization

Close-coupled gas atomization using gas at elevated temperature: J.T.Strauss. (HJE Company Inc, USA.)

Close-coupled gas atomization using gas at elevated temperature: J.T.Strauss. (HJE Company Inc, USA.)

Experimental investigation of close coupled high pressure gas atomizer nozzles: I.E.Anderson et al. (Ames Laboratory, USA.)

Experimental investigation of close coupled high pressure gas atomizer nozzles: I.E.Anderson et al. (Ames Laboratory, USA.)

Numerical investigation of close coupled high pressure gas atomizer nozzles: I.E.Anderson et al. (Ames Laboratory, USA.)

Numerical investigation of close coupled high pressure gas atomizer nozzles: I.E.Anderson et al. (Ames Laboratory, USA.)

Low pressure close coupled gas atomization: J.T.Strauss. (HJE Co Inc, USA.)

Low pressure close coupled gas atomization: J.T.Strauss. (HJE Co Inc, USA.)

Production of fine metal powders by close coupled gas atomization: M.J.H. Ruscoe, N. Tuffrey (Sherrit Inc., Canada)

Production of fine metal powders by close coupled gas atomization: M.J.H. Ruscoe, N. Tuffrey (Sherrit Inc., Canada)

Chamber pressure effects during close coupled gas atomization: M.W. Perretti (Crucible Research, Pittsburg, USA)

Chamber pressure effects during close coupled gas atomization: M.W. Perretti (Crucible Research, Pittsburg, USA)

An integrated approach to optimization of close coupled gas atomization: S.A. Miller et al (General Electric Inc, Schenectady, USA)

An integrated approach to optimization of close coupled gas atomization: S.A. Miller et al (General Electric Inc, Schenectady, USA)

Real time visualization of close coupled gas atomization: S.A. Miller, R.S. Miller (General Electric Corporate Research, USA)

Real time visualization of close coupled gas atomization: S.A. Miller, R.S. Miller (General Electric Corporate Research, USA)

Modeling of spray deposition: Measurements of particle size, gas velocity, particle velocity, and spray temperature in Gas-Atomized sprays

Spray deposition is a novel manufacturing process which is currently being developed for producing near-net-shape preforms. Spray deposition involves the creation of a spray of droplets by a gas atomizer and the consolidation of these droplets on a substrate to create a preform. In order to maximize the metallurgical benefits of spray deposition, a thorough characterization of momentum and heat transfer in the gas-atomized spray is required. The present paper describes measurements of particle size, gas velocity, particle velocity, and spray temperature in gasatomized Sn-Pb sprays. Measurements were performed on steady-state axisymmetric sprays which were generated using a close-coupled gas atomizer with Sn-5 wt p t Pb and Sn-38 wt p t Pb alloys, atomizer gas flow rates of 2.5 g/s (0.56 MPa) and 3.4 g/s (1.04 MPa), melt flow rates of 35 and 61 g/s, and atomizer-substrate distances of 180 and 360 mm. Gas velocities in the range to 4 m/s were measured using Pitot tube and laser Doppler anemometry (LDA). Droplet velocities in the range 3 to 32 m/s were determined from photographic streak-length measurements and LDA. Oil calorimetry of the spray enthalpy indicated that the spray temperature decreased with increasing axial distance from the gas atomizer, increasing gas flow rate, and decreasing melt flow rate.

Fine powder! Close-coupled or open-die atomization?

As the requirements for finer, cleaner metal powders grow within the PM industry, equipment to produce these materials is under constant development. Close-coupled gas atomisation provides one answer and the following article compares this technique with conventional open-die atomisation.