Size reduction is the process of reducing the particle size of a substance through mechanical means like grinding or milling. It has several objectives like increasing surface area, improving mixability and compressibility. Factors like hardness, toughness, abrasiveness affect size reduction. Common mechanisms are cutting, compression, impact and attrition. Equipment used include colloid mill, hammer mill, ball mill and jet mill which work on different principles to produce fine particles.

1. SIZE REDUCTION
Phr.Nirmal Raj Marasine
(B. Pharm.TU, M. Pharm clinical
pharmacy PU)
WHSA

2. SIZE REDUCTION
Definition
Size reduction is the process of reducing the particle size of a
substance to a finer state of subdivision to smaller pieces, to
coarse particles or to powder.
 Synonyms: Comminution, Grinding.
 When the particle size of solids is reduced by mechanical means
it is called milling .
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3. OBJECTIVES OF SIZE REDUCTION
a) Size reduction increases the surface area of drugs
which helps in rapid solution formation in the case
of chemical substances
b) With increase in surface area,the extraction from
animal glands such as liver and pancreas from
crude vegetables drug is facilitated.
c) The therapeutic effectiveness of certain drugs is
increased by reducing the particle size
d) The mixing of several solid ingredients is easier
and more uniform if the ingredients are reduced to
same particle size

4. e)Particle size is important in tablet manufacturing
during compression
f) The stability of emulsion is increased by decreasing
the size of the oil globules
g) The suspended particle size in suspension is
important for the stability of suspension
h)Appropriate size of particle is important for
inhalation product such as aerosol .
i)The elegance of creams, ointments and pastes can
be improved by reducing the particle size
j)The smaller the particle size ,quicker and greater will
be rate of absorption.

5. FACTORS AFFECTING SIZE REDUCTION
a. Hardness
 Harder the materials; more difficult to reduce the size.
b. Toughness
 Toughness is the ability of a material to absorb energy and
resist impact.
 Soft but tough material is more difficult to reduce size than
hard but brittle.
 Increase toughness, decrease in reduction of sizes
 For example it is difficult to break rubber than a stick of
blackboard chalk

6. c. Abrasiveness
 Abrasiveness is a property of hard materials (particularly
those of mineral origin) and may limit the type of
machinery that can be used.
 Increase abrasiveness, Increase particle size reduction
rate but increase contamination (worn out).
d. Softening temperature
 During size reduction process sometimes heat is
generated which may cause some substances to soften,
and the temperature at which this occurs can be important.
 Waxy substances, such as stearic acid, or drugs
containing oils or fats are examples that may be affected
and choke or block the machine.

7. e. Stickiness & Slipperiness
 pharmaceutical substances that are gummy or
resinous may be troublesome to the size
reduction process If the method used for size
reduction produces heat.
f.Moisture content
 Moisture content of a material can affect its
hardness, toughness or stickiness. Generally
materials should be dry and contain less than 5%
moisture

8. g. Physiological effect
 Some substances are very potent and small amounts of dust
have an effect on the operators.
 To avoid this dust, enclose mills must be used, systems that
can extract air are also desirable, and wet grinding also, if
possible, as it eliminates the problem entirely.
h. Purity required
 Certain types of size reduction apparatus cause the grinding
surfaces to wear, and such methods must be avoided if a
high degree of purity of product is needed.
 Similarly, some machines will be unsuitable if cleaning
between batches of different materials is difficult.

9. j. Ratio of feed size to product size
 Machines that produce a fine product require a small feed
size.
k. Bulk density
 The capacity of most batch mills depend on volume,
whereas processes usually demand solid materials by
weight.
 Hence, all other factors being equal, the output of the
machine is related to the bulk density of the substance.

10. MECHANISM OF SIZE REDUCTION
a. Cutting b. Compression/Shearing
c. Impact d. Attrition
Cutting
Compression
Impact
Attrition
Approx.
increase
in
fineness
of product

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Mechanism of size reduction
1.Cutting:
During this process the material is cut into small pieces by means of a
sharp blade or any other sharp instruments.
2.Compression:
During this process the material is crushed by application of pressure
with a suitable device.
3.Impact:
During impact the material which is more or less stationary, is hit by an
object moving at a high speed or the moving particles strike a stationary
surface and the material is broken into smaller particles.
4.Attrition:
During attrition the pressure is applied to the material as in the case of
compression but the surfaces are in motion in relation to each-other,
resulting in shear force which breaks the particles into still smaller
particles.

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Size reduction equipment
1.Cutting:
I. Rotary cutter mill
2.Compression:
I. Roller mill
II. Colloid mill
III. Mortar & Pestle : a. End runner mill , b. Edge runner mill
3.Impact:
I. Hammer mill
II. Vibration mill
4.Attrition:
I. Roller mill
5. Combined Impact & Attrition
I. Ball/Tube/Rod/Hardinge mill
II. Fluid energy/jet mill
III. Cage mill
IV. Pin mill

13. COLLOID MILL
 It works on the principle of shearing.
 Colloid mill consists of a conical rotor and stator.
 The distance between rotor and stator is adjusted
between 0.005 to 0.075 cm. The rotor is connected to a
high speed motor which can revolve at a speed of 3000
to 20000 rpm.
 The material is feed to hopper and size of material is
reduced as it passes through moving rotor and stator.

16. Uses
 Used for the preparing colloidal dispersions, suspension, emulsion
ointments.
Advantages
 Extremely fine particle distribution through optimal shear force.
 High capacity with minimal space requirements.
 Rapid handling and easy cleaning.
 Virtually unlimited application due to highly flexible homogenization
system.
Disadvantages
 Air might be incorporated within the product. Thus the product should be
allowed to deaeration.
 Heat generation occur during milling so that water should be circulated
around the milling chamber.
 Not suitable for the dry milling

17. HAMMER MILL
 It works on the principle of impact.
 Hammer mill consists of central shaft attached with
number of hammers in a steel case.
 When shaft is rotated hammers swing in radial position.
Screen of desired size is fitted on the lower portion.
 The material is feed to hopper and size of material is
reduced by the impact of hammers.

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19. Advantage
 They are simple to install and operate, the operation is
continuous.
 They are rapid in action and many different types of
materials can be ground with them.
 There is no chance of contamination due to abrasion of
metal from the mill because no surfaces of the mill move
against each other.
 The particle size of the material to be reduced can be
easily controlled by changing the speed of the rotor,
hammer type, shape & size of the screen.
 They are easy to clean and may be operated as a closed
system to reduce dust and explosion hazards.

20. Disadvantage
 A hammer mill must be operated with internal or
external classification to produce ultra fine
particles.
 Cannot be used for abrasive material.
Use
 In pharmaceutical industry they are used for
grinding dry materials, wet filter cakes, ointments
and slurries.
 Can be used for granulation and close control of
the particle size of powders.

21. BALL MILL
 This mill works on the principle of impact and attrition.
 It consists of cylindrical container filled with number of
balls made up of steels. The balls acts as grinder. The
size of the balls determines the particle size. The
cylindrical container is rotated at slow speed.
 The material is feed to the hopper and the moving balls
reduces the size of the material.

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Use
 Used for time grinding of hard, abrasive materials.
 They can be easily sterilized therefore can be used for grinding the
materials to be used in parenteral and ophthalmic preparation.
 Used for batch or continuous operation.
Advantage
 They are economical and simple to operate.
 They can be used for wet and dry grinding.
 They afford a large grinding surface within a compact space
 A wide variety of materials can be ground with it.
 They are easy to clean as compared to other mills.
Disadvantage
 Not applicable for soft and sticky materials.

26. FLUID ENERGY/JET MILL
 It is also known as jet mill, ultrafine grinding mill or
micronizer.
 It works on principle of impact and attrition.
 A fluid (usually air) is passed through the nozzle at
high pressure which will move the materials at high
velocity with turbulence.
 Coarse particle are feed into the mill and turbulence
causes impact and attrition to produce fine
particles.

29. Advantages
 The particle size of the product is smaller than that
produced by any other method of size reduction.
 Expansion of gases at the nozzles leads to cooling,
counteracting the usual frictional heat which can affect
heat-sensitive materials.
 Since the size reduction is by inter-particulate attrition there
is little or no abrasion of the mill and so virtually no
contamination of the product.
 For special cases with very sensitive materials it is possible
to use inert gases.
 Having a classifier as an integral part of the system
permits close control of particle size and of particle size
distribution.