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1. Mechanical Method
Ball Milling / Mechanical Milling

3. Overview of mechanical-physical nanoparticle production
processes

4. • Ball mill is a grinder for reducing hard materials
to powder.
• Ball milling is a process where particles
placed in the ball mill is subjected to high-
energy collision from the balls
• Material is forced to the walls and pressed
against the wall by the balls
• The reduction of particle size by high energy
ball milling is termed as mechanical milling
which is a top down approach.
• John Benjamin developed mechanical milling in
1960
Ball mill

5. Ball milling process
Motions of the balls and the powder during ball milling process

6. Ball milling process
 In ball milling the rotation directions of the bowl and
balls are opposite, the centrifugal forces are
alternately synchronized.
 Thus, friction resulted from the hardened milling balls
and the powder mixture being ground alternately
rolling on the inner wall of the bowl and striking the
opposite wall.
 The impact energy of the milling balls in the normal
direction attains a value of up to 40 times higher than
that due to gravitational acceleration. Hence, the
planetary ball mill can be used for high-speed milling


7. High-energy ball milling
High energy milling produces
nanostructured materials by the structural
disintegration of coarse-grained structure
as a result of severe plastic deformation.
High energy milling consists of repeated
deformation (welding, fracturing and
rewelding) of powder particles under a
protective atmosphere in equipment
capable of high-energy compressive
impact forces
Welding -joining two or more pieces of metal to make them act as a single piece

8. • Induce structural changes and chemical reactions at
room temperature.
• A complex mixture of fracturing, grinding, high-speed
plastic deformation, cold welding, thermal shock,
intimate mixing, etc.
• The structural changes and chemical reactions are
realized by mechanical energy rather than thermal
energy
• Reactions are possible at low temperatures
High-energy ball milling

9. Mechanical Milling (MM) - Milling of uniform composition
powders, such as pure metals, intermetallics, or pre-
alloyed powders, where material transfer is not required for
homogenization
Mechanical Alloying (MA) - the process when mixtures of
powders (of different metals or alloys/compounds) are
milled together. Material transfer is involved in this process
to obtain a homogeneous alloy.
MM requires half the time required for MA to achieve the same
effect
Processing of powder particles in high-
energy ball mills

10. Mechanical Milling: Mechanics and Physics
 The central occurrence in mechanical
milling is the ball-powder-ball
collision.
 Powder particles are trapped between
the balls during milling and undergo
deformation and/or fracture processes
which define the ultimate structure of
the powder.


11. Mechanical Alloying
 Means of fabricating composite
metal powders with extremely
fine microstructure.
 This process (the production of
metal powders with controlled
microstructures ) involves
repeated welding, fracturing and
re-welding of a mixture of
powder particles in a dry, highly
energetic ball charge.
Magnesium diboride
Al-Mg alloys

12. Different milling machines
Planetary miller
 Medium-high energy research
miller (<250g)
Tumbler mill
 Energy depends on diameter and speed of drum
 Primarily used for large-scale industrial applications
SPEX miller:
 High energy, research-scale
 ~10cm3
Attrition mill
 High energy small-industry
scale (<100kg)

13. Ball Milling - Parameters
• Type of mill (planetary, attrition, vibratory, rod, tumbler,
etc.)
• Speed of mill: relative speeds of pot rotation to disk
revolution in a planetary mill
• Composition, size, shape and surface of pot
• Degree of filling pot
• Number, size(s), material (density, elasticity), and surface
of milling balls
• Weight, shape, size and composition of starting material
• Macroscopic temperatures of pot, ball and powder
• Microscopic Temperature at collision point
• Milling atmosphere
• Milling time

14. Advantages of Ball Mills
 Produces very fine powder (particle size less than
or equal to 100 nm).
 It is suitable for milling toxic materials since it can
be used in a completely enclosed form.
 Has a wide application.
 It can be used for continuous operation.
 It is used in milling highly abrasive materials.
 .

15. Disadvantages of Ball Mills
 Contamination of product may occur as a result
of wear and tear which occurs principally from
the balls and partially from the casing.
 High machine noise level
 It is difficult to clean the machine after use.