Size reduction is the process of reducing larger particles into smaller particles using external forces. It has several objectives like increasing surface area, separating constituents, improving handling, and facilitating mixing. The key mechanisms of size reduction are cutting, impact, compression, attrition, and combined impact and attrition. Several types of mills are used for size reduction including cutter mills, roller mills, hammer mills, ball mills, fluid energy mills, and edge runner mills. Factors like hardness, moisture content, and ratio of feed size influence size reduction effectiveness.

1. SIZE REDUCTION
PRESENTED BY:
Harshada R. Bafna.
M.Pharmacy (QA)

2. Definition of size reduction
• Size reduction is the operation carried out for reducing the size of
bigger particles into smaller one of desired size and shape with the
help of external forces.
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3.  Objectives of size reduction
• In the materials processing industry, size reduction is usually
carried out in order to:
• Increase the surface area because, in most reactions involving
solid particles, the rate of reactions is directly proportional to the
area of contact with a second phase.
• Break a material into very small particles in order to separate the
valuable amongst the two constituents.
• Achieve intimate mixing.
• To dispose solid wastes easily .
• To improve the handling characteristics.
• To mix solid particle more intimately.
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4. Advantages of size reduction
• Content uniformity
• Uniform flow
• Effective drying
• Increases surface area or viscosity
• Uniform mixing and drying
• Improve rate of absorption . Smaller the particles greater is
absorption.
• Improve dissolution rate.
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5. Disadvantages of size reduction
• Drug degradation
• Contamination
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6. Factors affecting size reduction
• Hardness.
• Toughness.
• Stickiness.
• Material structure.
• Moisture content.
• Softening temperature.
• Purity required.
• Physiological effect.
• Ratio of feed size to product size.
• Bulk density.
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7. Mechanism of size reduction
1. Cutting .
2. Impact - Particle concussion by a single rigid force .
3. Compression- Particle disintegration by two rigid forces .
4. Attrition - Arising from particles scraping against one another
or against a rigid surface .
5. Combined impact and attrition .
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8. CUTTER MILL
Principle:
In the cutter mill, size reduction involves successive cutting or shearing
the feed materials with the help of sharp knives.
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Feed
Milling
chamber
Stationary
knives
Rotating
knives
Fig: cutter mill

9. Uses:
 Size reduction of tough and fibrous material.
 Ex. Medicinal plant, plant parts and animal tissue.
 It also used in manufacture of rubber, plastics, recycling of paper
waste and plastic material.
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Working:
 Rotor disc rotate at 200-900 revolution per min.
 Feed material loaded through hopper.
 Material is cut between rotating & stationary knives in small
pieces, therefore particle pass through the screen product is collected
into receiver.

10. ROLLER MILL
Principle:
The material is crushed (compressed) by the application of
stress. The stress is applied by rotator wheels, rollers.
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Fig: Roller mill.
Feed
Hopper
Rollers
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11. Working:
The rollers are allowed to rotate. The material is feed into
hopper through gap between two rollers by applying high
pressure material is cursed.
Uses:
1. Roller mill is used for crushing and cracking of seed before
extraction of fixed oils
2. Used to crush soft tissue to help in the penetration of
solvent during extraction process.
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12. HAMMER MILL
Principle:
The hammer mill operates on the principle of impact between
rapidly moving hammer mounted on a rotor and the powder
material.
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Fig: Hammer mill 12
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13. Working: The hammers are allowed to be in continuous motion(8000-
15000 rpm) the feed material is placed into the hopper, whiles hammers
are in continuous motion.
Uses:
 Particle size obtained from 10-400mm.
 Also used to mill dry, wet and filter press cakes materials.
Advantage:
 Easy to setup and clean up.
 Occupies small space.
Disadvantage:
 Heat buildup during milling is more , therefore, product
degradation is possible.
 Not suitable for milling of soft, tacky and fibrous materials.
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14. BALLMILL
Principle:
The ball mill works on the impact between the rapidly moving ball and
the powder material, both enclosed in a hollow cylinder. Thus, in the
ball mill, impact or attrition or both are responsible for the size
reduction.
Fig: Ball mill
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15. Working:
The drug is filled into cylinder 60% of the volume.
A fixed number of ball introduced and cylinder is close.
Uses:
Fine grinding with a particle size of 100-5 mm or less
can be obtained.
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16.  Very fine powder produce.
 Suitable for both wet and dry grinding processes.
 Close system, sterility can be achieved.
Disadvantage:
 Very noisy machine.
 Not suitable for milling of soft, tacky and fibrous materials.
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Advantage:
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17. Fluid Energy Mill
Principle:
Fluid energy mill operates on the principle of impact and attrition the
feed stock is suspended with in a high velocity air stream.
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Fig: Fluid energy mill 17
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18. Working:
Powder is introduced through the inlet of venture. Air introduce through
the grinding nozzles transport the powder in the circular track of the
mill. The turbulent air stream break the particles colloids with each
other and break. Particles are carried out to outlet and the coarse
particle undergo recirculation.
Uses:
 Fluid energy mill is used to reduce the particle size(10-325mesh) of
most of the drugs such as antibiotics and vitamins.
 Ultrafine grinding can be achieved moderately hard material can be
processed for size reduction.
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19. Advantages:
Contamination is not possible.
Disadvantage:
Not suitable for milling of soft, tacky and fibrous materials.
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20. EDGE RUNNER MILL
Principle
The size reduction is done by crushing due to heavy
weight of stone.
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Fig : Edge runner mill
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21. Working:
Material to be ground is placed on the bed at the same time travel
around the shallow stone bed so the size reduction is achieved by sharing as
well as crushing.
Uses:
Grinding tough material to fine powder.
Advantages:
Does not require attention during operation.
Disadvantages:
More space than other mill, Contamination, Time consuming, Not use
for sticky materials.
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22. References -
• R. M. Mehta, Pharmaceutics-I 6Th edition,Vallabh Prakashan,
2002, 104-115.
• www.google.com.
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