Production of Metallic Powder Machinery's Handbook, 31st Edition
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Molten Metal
Water
Water
Chamber
Water Jet
Water
Metal Powders
Fig. 5. Water Atomization Method for Producing Metal Powder Gas Atomization: In the area of metal powder production by atomization of molten metal, twin-fluid atomization by means of inert gases is typically used. The main reasons for using this specific atomization technique are: • the possibility of high throughputs and disintegration of high mass flow rates • the greater amount of heat transfer between gas and particles for rapid partial cooling of the particles • the direct delivery of kinetic energy to accelerate the particles towards the substrate/ deposit for compaction • the minimization of oxidation risks of the atomized materials within the spray process by use of inert gases. In this process, atomization is accomplished by forcing a molten metal stream through an orifice at moderate pressures ( Fig. 6). An inert gas at pressures from 29 to 290 psi (0.2 to 2.0 MPa) is introduced into the metal stream just before it leaves the nozzle, serving to create turbulence as the entrained gas expands (due to heating) and exits into a large col- lection volume exterior to the orifice. The collection volume is filled with gas to promote further turbulence of the molten metal jet.
Molten Metal
Gas
Gas
Chamber
Metal Powders Fig. 6. Gas Atomization Method for Producing Metal Powder
This process as compared to water atomization makes a similarly broad distribution and produce very fine powders. However, the process must be operated more slowly than water atomization and the energy needed to compress the gas is far higher than that needed to pump water. Because this cools the metal at a slower rate, it creates a more cir- cular particle. The advantage of the inert gas process is better control of oxygen levels in oxygen-sensitive materials.
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