04-01-2013, 11:38 AM
Powder Metallurgy
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POWDER METALLURGY
Definition :- Powder metallurgy is the art and science of producing fine metal powders and then making objects from individual, mixed or alloyed metal powders with or without the inclusion of non metallic constituents.
Or
Powder metallurgy is a branch of metallurgy which deals with the production of metal and non metal powders and subsequently manufacture of components by using these powders.
POWDER METALLURGY PROCESS
A. Producing metal powders
B. Mixing
C. Pressing
D. Reinterring
E. Sintering
F. Finishing and sizing the final product
Producing metal powders
Various methods for manufacturing powders are -
1. Atomization
2. Reduction
3. Crushing
4. Milling
5. Shutting
6. Electrolysis.
Atomization
The process of metal spraying against a stream of compressed air or inert gas is Atomization.
It is an excellent means of producing metal powders from many of the low temperature metals such as lead, aluminium, zinc and tin.
Reduction
Reduction process is carried out in an atmosphere controlled furnace.
In reduction process, the compounds of metals usually oxides like iron oxides are reduced with CO/H2 at temperature below melting point of metal.
Tungsten, molybdenum, iron, cobalt, nickel powders are commercially produced by this process.
Milling.
Milling is carried out by using equipment’s such as ball mill, rod mill, impact mill, disk mill etc.
In ball milling, material to be powdered is collected in a container with a large number of hard steel balls. These balls hit the material and break it in powder form.
Electrolysis.
In this method, an electrolytic cell is set up as shown in figure.
The desired metal is made to act as anode.
Anode slowly dissolves and gets deposited on the cathode from where the deposit is removed, washed and dried.
PRESINTERING The Powder
Powder metallurgy is used to make parts from materials that are very difficult to machine.
When some machining is required on such parts, Reinterring is done before actual sintering operation.
Compact is heated for a short time at a temperature below sintering temperature.
Reinterring removes lubricants and binders added to powders during blending operation.
After Reinterring, the part acquires sufficient strength to be handled and machined without difficulty.