Atomization of metals is a method in which molten metal is forced through a nozzle into a stream of compressed air or water. The metal on cooling solidifies into tiny particles of various sizes and irregular shapes. The size of these particles depends on the size of the nozzle, rate of flow of metal and temperature and pressure of air and water stream. This process is widely used in the production of powders of metals having low melting points such as zinc, tin, and aluminum. The air is usually supplied at a pressure of about 0.2 to 2.3N/mm2.
A stream of inert gas may also be used in atomization of metal powders. The powders produced by this method are usually spherical or pear-shaped coated with a thin oxide layer. The formation of oxide on individual particles during stirring is known as granulation.
Understanding powder metallurgy
Powder metallurgy refers to an art of manufacturing commercial products from the powdered metals and alloys. This process consists of compressing the irregularly shaped powdered metal particles in a die of the desired shape of the part to be produced. The part is then heated in a temperature controlled furnace at a temperature below the melting point of one or more of the constituents of the powdered metals. This is known as sintering. The particles are subsequently heat treated to a required hardness.
The powder metallurgy techniques are used:
For producing parts from certain hard materials or refractory materials which are difficult to work with machines.
In the fabrication of non-ferrous products like alloys of tungsten, carbide etc.
In lamination of intricate parts such as magnets and self-lubricating bearing.
In the production of special electrical contacts and turbine blades having high thermal strength.
In producing friction materials clutch facings, brake linings, etc.