powder metallurgy

1. SUBJECT: POWDER METALLURGY
Presented By : Sammed Kamire
Swarup Nagonkar
Saurabh Nikam
Shubham Parit
Chinmay Patil

2. POWDER PRODUCTION METHODS
This classification is based on the nature of energy
used for the powder production
POWDER
PRODUCTION
MECHANIC
AL
METHODS
CHEMICAL
METHODS
PHYSICAL
METHODS

3. Mechanical methods
 These methods are among the cheapest methods
employed for powder production
 These methods involve use of mechanical forces such
as compressive , shear or impact to reduce size of bulk
materials.

4. MECHANICAL METHODS
Mechanical
methods
Machining
Shotting
Grinding
Milling

5. Machining
 Magnesium , beryllium , silver powders etc. are
specifically made by machining.
 Turning and chips obtained during machining are
subsequently crushed or ground into powders.

6. SHOTTING
 In this method, a fine stream of molten metal is
poured through a vibratory screen into air or other
protective gas medium.
 When molten metal fall through the screen it
disintegrates and solidifies into spherical particles.
 Size of particles depends on various factor lkike
temperature, gas used , aperture size of screen,
frequency of vibrations etc.

7. GRINDING
 This process is exactly like shotting but material falling
through the sieve is collected in water.
 Powders produced using this methods including
cadmium, bismuth, antimony.

8. MILLING
Main objective of milling
 Particle size reduction.
 Particle size growth.
 Shape change.
 Agglomeration.
 Solid state alloying.
 Solid state mixing/blending.
 Modification of material properties such as density.

9. MECHANISUM OF MILLING
 This method is most widely used in powder metallurgy
industry.
 Hammer and rod mills are used to mill spongy cakes of
oxides reduced atomised electrolytic powders.
 Impact is due to striking of one powder particle against
another. Attrition refers to the production of wear
debris due to rubbing action between two particles.
 Shear is due to cleaving or cutting of particles resulting
in fracturing while compression is the application of
compressive forces by crushing or squeezing the
particle usually associated with jaw crushers.

10. PHYSICAL METHODS
Electrolytic Deposition
 Metal powders can be produced by electro-deposition from
aqueous solution and fused salt.
 Here,the processing condition are so chosen that metals of high
purity are precipitated from aqueous solution on the cathode of
the electrolytic cell.
 This method is generally used to make powders of iron, copper,
zinc etc.
 Rections involved in method,
 At anode
Cu Cu2+ +2e-
 At cathode
Cu2+ +2e- Cu
PHYSICAL METHODS
Electrolytic Deposition

11. Atomization
 Atomization is accomplished by forcing a molten metal stream through an
orifice at moderate pressures. A gas 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 collection volume exterior to the
orifice. The collection volume is filled with gas to promote further turbulence
of the molten metal jet. Air and powder streams are segregated using gravity
or cyclonic separation. Most atomized powders are annealed, which helps
reduce the oxide and carbon content. The water atomized particles are smaller,
cleaner, and nonporous and have a greater breadth of size, which allows better
compacting. The particles produced through this method are normally of
spherical or pear shape. Usually, they also carry a layer of oxide over them.
 There are three types of atomization:
• Liquid atomization
• Gas atomization
• Centrifugal atomization

12. Water atomization
 High-pressure water jets are used to bring about the
disintegration of molten metal stream.
 Water jets are used in atomization of metals due to
their higher viscosity and superior quenching ability.
 The process is inexpensive and can be used both for
small and large-scale production.
 The technique is limited to metals or alloys that do not
chemically react with water.
Liquid metal
Water or
oil jets
FIG. Water or oil atomization

13. Gas atomization
 The molten metal stream is disintegrated using high
velocity argon, nitrogen or helium gas jets.
 The atomized powders are collected in water bath.
 Fluidized bed cooling is used when certain
characteristics of powders are desirable, for example
spherical shape or particles with little or no oxide
content.
 This process is costlier than water atomization.
Liquid metal
Gas jets
FIG. Gas atomization

14. Soluble gas atomization or vacuum
atomization
 When a molten metal supersaturated
with a gas under pressure is suddenly
exposed to vaccum the gas coming out
the metal solution expands rapidly,
causing atomization of metal stream.
 This process gives very high purity
powders.
 The metal is usually saturated with a
soluble and non-reactive gas like
Hydrogen.
Vacuum
Powder
port
Liquid
metal
Transfer
tube
FIG.Vacuum (soluble gas) atomization