Method of preparing metal powders can be roughly divided into two categories: physical chemical and mechanical method. Mechanical method is about mechanical crushing method and metal melt atomization. The former one uses the mechanical grinding, vortex grinding, crushing and centrifugal air flow crushed and other technologies.
The second one is divided into general atomization and rapid solidification atomization method. The one using rapid solidification directly from the metal melt atomized metal powder in the powder metallurgy and materials science has attracted much attention. Double atomization is the main method of the present industrial production of metal powder.
The high-pressure water atomization and high-pressure gas atomization method using high pressure water and high pressure gas as the atomizing media to break the continuous thin stream of molten metal, they are the most important method for the production of metal powder. The atomization mechanism including the formation of fluid thin layer, the thin layer of broken metal flow of silk and metal flow thread contraction of the three stages of the micro-droplets. High-pressure gas atomization of 50-100¼m diameter metal powder, high-pressure water atomized powder particle size between 75-200¼m; gas atomized powder for smooth spherical cooling rate of about 102-103 ° C / s, water atomization powder often has an irregular shape and surface, the cooling rate of 102-104 / s. High-pressure gas atomization and water atomization is widely used in large-tonnage production of aluminum, tool steel, super alloys, bronze powder(FCu 663), iron, tin and low-alloy powder.
The rapidly rotating cup method also known as the rotating water law. Squeeze into the rotating cup quenching medium (which may be aqueous solutions, hydrocarbons, cryogenic fluids, etc.), metal flow is broken under the pressure of the argon, liquid metal, quench, under the centrifugal force through rapid quenching media to reach the rotation and finally get the powder. Analysis showed that increasing the speed of the rotating cup, reduce the liquid metal nozzle size, and improve the superheat of the liquid metal can be refined powder size; increase the gas injection pressure can reduce the splashing of the liquid metal on the surface of quenching medium, and then improve powder recovery rate. The molten metal first gas atomization, centrifugal atomization and shock atomization, and then into the rotating cup quenching medium, which can be avoided crucible nozzle clogging and corrosion, but also improve the atomization efficiency. Rotating cup method can produce all kinds of steel, high temperature alloys, aluminum, copper, nickel and other alloy systems of metal powder, powder of spherical or irregular shape. For iron-based alloys, with a diameter less than 50¼m powder particle cooling rate of at least 106 / s. Rapid solidification and general atomized powder, with a rapidly rotating cup method of production of powder size distribution is narrow, fine nickel powder yield rate, but the fast rotating cup is still in the laboratory research stage.
Mechanical atomization method is using the purely mechanical fragmentation to make the liquid metal into small droplets, and then quickly solidified into a metal powder. Hammer anvil method is a metal material is placed in the horizontal plane of the anvil, with the arc, ion beam or electron beam melting, the hammer will hit the anvil seat, resulting in a round flaky powder, powder size of 25mm diameter to a thickness of 5-300¼m. The cooling rate depends on the thickness of the flaky powder in the range of 104-106 / s. Principle of hammer and anvil method is similar to the piston anvil technology and dual-piston technology, they are in the movement of the piston and the anvil, between the two opposite movement of the piston, squeeze the metal droplets, resulting in sheet powder. Hammer anvil method is widely used in the laboratory system to take flake powder sample. It also applies to a variety of metal and alloy powder.Source:http://www.mhcmp.com
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