Sem 3 size reduction

SIZE REDUCTION
By
Yogeshwary Bhongade
Assistant Professor
Gondia College of Pharmacy, Gondia.

CONTENTS
 Introduction
 Objectives
 Methods of size reduction
 Advantages of size reduction
 Disadvantages of size reduction
 Mechanism of size reduction
 Laws governing to the size reduction
 Principle of Size Reduction, Construction, working and
uses of following-
Hammer mill
Ball mill
Fluid Energy Mill
Edge Runner Mill
End Runner Mill

SIZE REDUCTION
 Definition:
Size reduction is the process of reducing large solid units
or substances into the smaller unit mass, course particles
or fine particles.
 The process also termed as comminution or diminution
or pulverisation
 Reduction of particle size above 40 mm- machine known
as Crushers and below it machine known as Mill

CONT.
 Degree of size reduction depends upon the
machinery, methods, duration to which size of
particle is reduced.
Eg. To reduce particle in very small size then longer
duration will be required and vice versa.

CONT.
Usually size reduction in material processing industry carry
out in order to-
 To increase the surface area
 Break material into very small particles in order to
separate the desired particle from the mixture of two
constituent
 To achieve the intimate mixing

OBJECTIVES OF SIZE REDUCTION
 Size reduction leads to increase of surface area.
Pharmaceutical capsules, insufflations (i.e. powders
inhaled directly into the lungs), suppositories and ointments
require particles size to be below 60 mm size.
 To increase the therapeutic effectiveness of certain drugs
by reducing the particle size.
Eg. Griseofulvin (half of the dose of drug required after
size reduction)
 Size reduction produces particles in narrow size range.
 Mixing of powders with narrow size range is easier.
 The mixing of several solid ingredients is easier and more
uniform if the ingredients are reduced to same particle size.

CONT.
 Pharmaceutical suspensions require finer particle size. It
reduces rate of sedimentation.
 The stability of emulsions is increased by decreasing the
size of the oil globules.
 All the ophthalmic preparations and preparations meant for
external application to the skin must be free from gritty
particles to avoid irritation of the area to which they are
applied.
 The rate of absorption of a drug depends on the dosage
form, route of administration and particle size. The smaller
the particle size, quicker and greater will be rate of
absorption.
 The physical appearance of ointments, pastes and creams
can be improved by reducing its particle size

METHOD OF SIZE REDUCTION
 Grinding and cutting
This method employed for the solid substances
 Emulsification or Atomization
This method employed for the for liquid phase

ADVANTAGES
 Effective particle size mixing
 Increase surface area
 Increase flow of powder material
 Effective Extraction
 Effective drying
 Enhance the viscosity
 Improve bioavailability of drug

DISADVANTAGES
 Decomposition of thermo labile substances
 Chances of contamination
 Poor mixing
 Noisy environment

MECHANISM OF SIZE REDUCTION
Impact - A sudden force occurring when one object collides with
another
Attrition - Frictional force applied to the material due to the
opposing motion of two hard surfaces
Shear - A force applied when the material is compressed
between the edges of two hard surfaces moving tangentially
Compression - Force applied by the faces of hard surfaces
moving towards each other.

LAWS GOVERNING SIZE REDUCTION
 Various theories are there to establish a relationship
between energy input and the degree of size reduction.
Theories of size
reduction
Kick’s Law
Rittinger’s
Law
Bond’s Law

KICK’S LAW
According to Kick’s Law-
Energy require to reduce size of particle is proportional to
ratio of initial size of a typical dimension to the final size of
dimension.
Where
E : Energy require per mass of feed
Kk : Kick’s Constant
di : Diameter of initial particles
dn : Diameter of new particles
di/dn : Ratio of size reduction

APPLICATION
 For compression of large particle Kick’s theory is
useful

RITTINGER’S LAW
According to this law-
The energy (E) required for reduction in particle size of a
solid is directly proportional to the increase in surface
area.
E= KR (Sn- Si)
Where,
E - Amount of energy
KR - Rittinger’ constant
Sn - New specific surface area
Si - Initial surface area

APPLICATION
 Applicable to brittle material under going fine milling
 This theory ignore deformation before fracture

BOND’S LAW
According to the bonds law-
Size reduction of particles is proportional to the new crack
length.
Where
E - Amount of energy
KB - Bond’s work index
Di - Initial diameter
Dn - New diameter

APPLICATIONS
 The theory is useful for rough mill
 The work index is useful for comparing efficient milling
operations

CLASSIFIATION OF SIZE REDUCTION EQUIPMENTS
Machines
Crusher Grinder
Ultrafine
Grinders
Cutting
Machine

A. Crusher
ex. Edge runner mill.
End runner mill.
B. Grinder
1)Impact mill.
ex-Hammer mill.
2)Rolling-compression.
ex-Roller mill.
3)Attrition mills
ex-Attrition mill.
4)Tumbling mills.
ex-Ball mill.
C. Ultrafine grinder
ex-Fluid energy mill.
D.Cutting machine
ex- Cutter mill.

HAMMER MILL
Principle:
It work on principle of impact (material is more or less
stationary and is hit by objeect moving in high speed)
Construction

CONT.
It consist of stout metal casing enclosed a centre
shaft to which more than four swinging hammers are
attached
lower part of the casing consist of screen, through
which material can pass in receiver.
Working:
Material is put into hopper. Due to rotation rotation of
hammer,he material is powdered into desired size.
https://youtu.be/Y93rf2cNloI

PHARMACEUTICAL USES OF HAMMER MILL
1. It is used in pharmaceutical industries to process wet or
dry granulations and disperse powder mixtures.
2. It is used in milling pharmaceutical raw materials, herbal
medicine, and sugar.
3. It is used in powdering of barks, leaves, and roots of
medicinal plants.
4. It is applied in the milling of Active Pharmaceutical
Ingredient (API), excipients, etc.

ADVANTAGES OF HAMMER MILL
1. It produces specified top size without the need for a closed-
circuit crushing system.
2. It produces relatively numerous size distributions with a
minimum of fines due to self-classification.
3. It has a high reduction ratio and high capacity whether used
for primary, secondary or tertiary grinding.
4. Relatively reasonable energy requirements.
5. Brittle materials are best fractured by impact from blunt
hammers.
6. It is capable of grinding many different types of materials
7. The machine is easy to install and operate and its operation
is continuous.

CONT.
8. It occupies small space.
9. It is easy to maintain and clean.
10. It is inexpensive.
11. Its ease of manufacture allows easier local construction.

DISADVANTAGES OF HAMMER MILL
1. Not recommended for the fine grinding of very hard and
abrasive material due to excessive wear.
2. Not suitable for low-melting sticky or plastic-like
material due to heat generation in the mill head as a result
of mill fouling.
3. The mill may be choked if the feed rate is not controlled,
leading to damage.
4. Presence of foreign materials like stone or metals which
finds its way into the material due to inadequate garbling
process
5. There is a possibility of clogging of the screen.

BALL MILL
Principle: it work on principle of impact and attrition
A ball mill also known as pebble mill or tumbling mill is a
milling machine that consists of a hallow cylinder containing
balls
mounted on a metallic frame such that it can be rotated
along its longitudinal axis. The balls which could be of
different diameter occupy 30 – 50 % of the mill volume and
its size depends on the feed and mill size. The large balls
tend to break down the coarse feed materials and the
smaller balls help to form fine product by reducing void
spaces between the balls. Ball mills grind material by impact
and atrrition.

BALL MILL
Construction:
consist of two hollow cylinder which is mounted on metallic
frame in such a way that it can be rotated on its longitudinal
axis.

BALL MILL
Working
drug to be ground put into the cylinder of mill and rotated.
speed of rotation is very important
low speed-mass od ball is side or role over each other only
negligible ammount of size reduction occures.(a)
high speed- balls will be thrown out to the wall by
centrifugation(b)
2/3rd speed- centrifugal force occures, ball are carried almost
to the top of the mill and then fall in.(c)
https://www.youtube.com/watch?v=zUtQZtfVJN8

CONT.
The degree of milling in a ball mill is influenced by;
a. Residence time of the material in the mill chamber.
b. The size, density, and number of the balls.
c. The nature of the balls (hardness of the grinding
material)
d. Feed rate and feed level in the vessel.
e. Rotation speed of the cylinder.

PHARMACEUTICAL USES OF BALL MILL
1. The small and average capacity ball mills are used for
the final grinding of drugs or for grinding suspensions.
2. The maximum capacity ball mills are used for milling
ores prior to manufacture of pharmaceutical chemicals.

ADVANTAGES OF BALL MILLS
1. It produces very fine powder (particle size less than or
equal to 10 microns).
2. It is suitable for milling toxic materials since it can be
used in a completely enclosed form.
3. Has a wide application.
4. It can be used for continuous operation.

DISADVANTAGES OF BALL MILLS
1. Contamination of product may occur as a result of wear
and tear which occurs principally from the balls and
partially from the casing.
2. High machine noise level especially if the hollow
cylinder is made of metal, but much less if rubber is used.
3. Relatively long milling time.
4. It is difficult to clean the machine after use.

FLUID ENERGY MILL
Principle:
Works on the principle of Impact and Attrition
Construction:
consist of loop of pipe (20- 200 mm diameter depending on
height of loop which may be upto 2 m)
There are an inlet for
food and series of nozel
for inlet of air or an
ineret gas
also have outlet with
classifier which allow the
aie to escap but prevent
the particles to pass until
they become sufficiently
fine

FLUID ENERGY MILL
Working
through nozzles air or intert gas introduce at very high
pressure. solids are introduce through the inlet. Due to
high degree of turbulence, impact and attritional forces
occurse between the particles. The fine particles are
collected through a classifier. Fluid energy mill reduces the
partile to 1 to 20 micron.
https://www.youtube.com/watch?v=iWgRm5LSJek

PHARMACEUTICAL USES OF FLUIDIZED ENERGY
MILL
a. Fluidized energy is used in milling thermolabile
materials
b. It is the choice of mill when a higher degree of drug
purity is required
c. Fluidized energy mill is used for the fine grinding of
frits, Kaolin, Zircon, titanium, and calcium, alumina.

ADVANTAGES OF FLUIDIZED ENERGY MILL
1. The machine has no moving parts and thus the
tendency of contamination due to wear of parts is
minimized.
2. The equipment is easily sterilized.
3. Small particle size (between 2 and 10) is usually
obtained at the end of milling.
4. Thermolabile materials can be milled with little
degradation since the heat produced by the process is
nullified by the cooling effect of the expansion of the
compressed gas

DISADVANTAGES OF FLUIDIZED ENERGY MILL
1. Tendency of forming aggregates or agglomerates
after milling.
2. Generation of amorphous content due to high
energy impact.
3. Formation of ultra-fine particles

EDGE RUNNER MILL
Principle:
Crushing is the principle for edge runner mill.
Edge runner mill, also known as Chilean mill or Roller stone
mill.
Construction
Consists of one or two heavy steel or granite rollers
mounted on a horizontal shaft and turned round a central
vertical shaft on a bed of steel or granite and they revolved
on axis of central shaft.
The stones may vary from 0.5 to 2.5 m in diameter, the
larger size weighing up to about 6 tonnes.

EDGE RUNNER MILL
Working
The material to be ground is kept in the path of the runner
by scrapers. The reduction is partly due to crushing: by the
weight of the stones, but more to friction between the
surfaces of contact between the runners and the bed
stone.https://www.youtube.com/watch?v=DPggUMaktjk

EDGE RUNNER MILL
Uses
 Although the edge runner mills are gradually being
replaced by more sophisticated machines they are still
used, particularly for reducing extremely tough and fibrous
materials – roots and barks to the form of powder.
 used to grind most of drugs to fine poweder but require
more floor space

END RUNNER MILL
Principle: Impact and shear is the principle of end runner
mill
Construction:
The end-runner mill consists of a weighted pestle mounted
eccentrically in a ceramic, granite or metal mortar, which is
rotated by a motor.

END RUNNER MILL
Working
End runer mill provides moderately
fine powder and operates
successfully with fibrous materials,
bark, woods fruits, leaves, etc.
The pestle rotates by friction and is
free to rise and fall in the mortar so
that its grinding action involves both
impact and shear, the material being
crushed and rubbed between it and
the rotating mortar.
Spring-loaded scrapers ensure that
material is constantly returned to the
grinding area and at the end of the
operation the pestle can be swung
clear of the mortar to facilitate
emptying and cleaning.

END-RUNNER MILL AND EDGE-RUNNER MILL
Advantages of End-runner mill and Edge-runner mill
 1. It produces fine particles
 2. Requires less attention during the milling operation
Disadvantages of End-runner mill and Edge-runner mill
 1. It is not suitable for milling sticky materials
 2. Machine noise leading to noise pollution

FACTOR AFFECTING SIZE REDUCTION
 Hardness
It is easier to break soft material than hard materials.
 Toughness
Fibrous materials are tough. These are tough in nature. A soft,
tough material has more difficulty than a hard, brittle
substance.
Ex: Rauwlfia, Ginger. Here cutters can be used.
 Stickiness
Stickiness causes lots of difficulties during size reduction.
This is due to adhesion of material to grinding surface or sieve
surface of mill.

 Material Structure
Material having special structure shows problem during
size reduction eg. Vegetable produce circular structure
produce large fibrous particle on size reduction
 Softening Temperature
Waxy substances such as steric acids or drugs containing
oil or fat, become softened during the size reduction.
So if heat generated this can be avoided by cooling mill.

 Friable material.
These tend to fracture along well defined planes.
 Purity Required
Various mills used for size reduction often cause the
grinding surfaces to wear off and thus impurities come in
the powder.

 Melting point
Waxy substances, fats and oils are softened during size
reduction due to heat generated.
This is avoided by cooling the mill and the substance.
 Moisture Content
Hygroscopic - Certain substances absorb moisture content
rapidly. This wet mass hampers the milling process.
Ex: Potassium carbonate. Closed system such as
porcelain ball mill is used.

 Physiological effect
Some drugs are very potent. During their particle size
reduction in mill dust may have produce which may have
effect on operator.
To avoid dust closed mill can be used
 Ratio of feed size to product size
Small feed size required to get fine particle.
 Bulk density
Output of size reduction of material in a machine, depends
on bulk density of substances.

GENETRAL CHARACTERISTICS OF MILLS
Sr.
No.
Name of mill Action/
Principle
Product
size
Uses Not used for
1 Cutter Mill Cutting 20- 80
Mesh
Fribrous,
Crude(Animal and
Vegetavle Drug)
Friable
Material
2 Roller Mill Compression 20- 200
Mesh
Soft Matrial Abrasive
material
3 Hammer Mill Impact 4-325
Mesh
Almost all ddrug Abrasive
material
4 Ball Mill Attrition &
Impact
20- 200
Mesh
Brittle Drug Soft material
5 Fluid Energy Mill Attrition &
Impact
1-30 Mesh Moderately hard and
friabl material
Soft & sticky
material
6 Edge Runner Mill Crushing &
Sharing
20-80
Mesh
Almost all drug Sticky
Material

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