Size separation, or sieving, is a technique to segregate particles by size, vital in pharmaceuticals, food processing, and mining. Methods include sieving (particles pass through mesh sieves), sedimentation (based on settling velocities in fluid), cyclone separation (using centrifugal forces), and filtration (using barriers with specific pore sizes). Applications range from ensuring uniform drug formulations to grading grains and extracting minerals. Size separation offers efficiency, precision, and versatility, making it essential for quality control and consistency across various industries.

2. content
 Introduction
 Objectives
 Mechanism
 Official Standards For Powders
 Sieves
 Material of construction of Sieves
 Official Standards For Sieves
 Cyclone Separator
Pragati K. Mahajan

3. Introduction
• The process of size reduction is
followed by size separation of the
powdered material.
• During the process of size reduction, it
is not possible to obtain the particles of
uniform size.
• Hence a special technique is used to
separate particles of specified size
which is known as the "process of size
separation".
• Size separation is the process that
involves the separation of particles of
desired size from the mixture of
various size particles.
• Size separation is also known as
sieving, sifting, or screening.
Pragati K. Mahajan

4. I. To determine particle size for the
production of tablets and capsules.
II. To improve mixing of powders.
III. To improve the solubility and
stability of particles during
production.
IV. To optimize feed rate, agitation,
screening during production.
V. Quality control of raw materials.
VI. Useful in production of tablets,
capsules, suspension, emulsion,
ophthalmic preparations,
ointments, creams, etc.
Pragati K. Mahajan

5. Mechanism of Size
Separation
Agitation
Oscillation
Vibration
Gyration
Brushing Centrifugal
Pragati K. Mahajan

6.  The working of mechanical sieving devices are based on following
methods.
1. Agitation
2.Brushing
3. Centrifugal
 Agitation methods Sieves may be agitated in a number of different
ways, such as:
1.Oscillation: The sieve is mounted in a frame that oscillates back and
forth. Movement of sieve is upward and downward.
2. Vibration: The sieve is vibrated at high speed by means of an electric
device. The rapid vibration is imparted to the particles on the sieve
which helps to pass the powdered material through it. Movement of
sieve is sideways.
3. Gyration: In this method, Movement of sieve is clockwise and
anticlockwise
Pragati K. Mahajan

7. Oscillation Vibration Gyration
Pragati K. Mahajan

8.  Brushing methods
• In this case, a brush is used
to move the particles on the
surface of the sieve and to
keep the meshes clear.
• The brush is rotated in the
middle in the case of a
circular sieve but spiral brush
is rotated on the longitudinal
axis in case of a horizontal
cylindrical sieve.
Pragati K. Mahajan

9.  Centrifugal methods
• It is technique used for separation
on basis of their shapes, size,
density and weight of particles.
• A high speed rotor is fixed inside
the vertical cylindrical sieve, so
that on rotation of rotor the
particles are thrown outwards by
centrifugal force.
• The current of air which is
produced due to high speed of
rotor helps in sieving the powder.
• When we revolve substance with
high speed heavy particles fall
near and light particles fall to far.
Pragati K. Mahajan

10. The Indian Pharmacopoeia has laid down the standards for powders for
pharmaceutical purposes. According to that, the degree of coarseness or
fineness of a powder is expressed by reference to the nominal mesh
aperture size of the sieve through which powder is able to pass. The I.P.
specifies five grades of powder which are as under:
1.Coarse powder: A powder of which all the particles pass through a
sieve with nominal mesh aperture of 1.70 mm (No. 10 sieve) and not
more than 40.0 per cent through a sieve with nominal mesh aperture
of 355 µm (No. 44 sieve) is called coarse powder.
2. Moderately coarse powder: A powder of which all the particles pass
through a sieve with nominal mesh aperture of 710 µm (No. 22
sieve) and not more than 40.0 per cent through a sieve with nominal
mesh aperture of 250 µm (No. 60 sieve) is called moderately coarse
powder.
Pragati K. Mahajan

11. 3.Moderately fine powder: If all the particles of a powder
pass through a sieve with nominal mesh aperture of
355 µm (No. 44 sieve) and not more than 40.0 per
cent through a sieve with nominal mesh aperture of
180 µm (No. 85 sieve), it falls in this group.
4.Fine powder: In case all the particles pass through a
sieve with a nominal mesh aperture of 180 µm (No.
85 sieve), it is called fine powder.
5.Very fine powder If all the particles of the powder pass
through a sieve with a nominal mesh aperture of 125
µm (No. 120 sieve), it is said to be very fine powder.
Pragati K. Mahajan

12. Sr.
no
Grade of powder Sieve
through
which all
particles
must pass
Sieve through
which not more
than 40 per cent of
particles pass
1. coarse 10 44
2. Moderately coarse 22 60
3. Moderately Fine 44 85
4. Fine 85 Not specified
5. Very fine 120 Not specified
Pragati K. Mahajan

13.  Sieves are constructed from wire cloth with square
meshes, woven from wires of brass, bronze, stainless
steel or any other suitable material.
 The wires should be of uniform circular cross-section
and should not be coated or plated.
 Mesh: These are the holes in the screen.
 Mesh number: This indicate number of holes included
in a length of 1 inch.
 Aperture of screen: It is the clear space between wires
of screen opening and it is given in term of mm.
 Screen Number: It is number of meshes in a linear
length of 25.4mm
Pragati K. Mahajan

14.  Sieves are woven from wire of brass, bronze, stainless steels.
Sieves should not be coated with any material. It should be
non reactive with material used. The material used for
construction should be resistance to corrosion
 Generally iron wire is used as screen material because it is
cheap but their disadvantage are corrosive nature and
chances of contamination by iron. These disadvantages can
be overcome by coating iron with galvanizing agent which
increase the strength and also make it corrosion resistant.
 Brass, phosphor-bronze and stainless steel are the metals
used due to their corrosive resistance good strength and non
contamination qualities.
 Non metal such as nylon and terylene are also suitable
because they avoid risk of metallic contamination
Pragati K. Mahajan

15.  Standards for sieves used to testing must specify the
following
 1. Number of sieve: Sieve number indicates the
number of meshes in a length of 2.54 cm in each
transverse direction parallel to the wires.
 2. Nominal size of aperture: Nominal size of aperture
indicates the distance between the wires. It represents
the length of the side of the square aperture. The I.P.
has given the nominal mesh aperture size for majority
of sieves in mm or in cm.
Pragati K. Mahajan

16.  3. Nominal diameter of the wire: Wire mesh sieves are made
from the wire having the specified diameter in order to give a
suitable aperture size and sufficient strength to avoid distortion of
the sieve.
 4. Approximate percentage sieving area: This standard
expresses the area of the meshes as a percentage of the total area of
the sieve. It depends on the size of the wire used for any particular
sieve number. Generally the sieving area is kept within the range of
35 to 40 per cent in order to give suitable strength to the sieve
 5. Tolerance average aperture size: Some variation in the
aperture size is unavoidable and when this variation is expressed as
a percentage, it is known as the 'aperture tolerance average'.
Pragati K. Mahajan

17. Size
Separation
SIEVING
CYCLONE
SEPARATOR
AIR
SEPARATOR
ELUTRIATION
Pragati K. Mahajan

18. Principle :
• In cyclone separator, the centrifugal force is used to
separate solids from fluids.
• The separation depends not only on the particle size but
also on density of particles.
• Hence depending on the fluid velocity, the cyclone
separator can be used to separate all types of particles or
to remove only coarse particles and allow fine particles
to be carried through with the fluid.
Construction:
 It consists of a cylindrical vessel with a conical base.
 In the upper part of the vessel is fitted with a tangential
inlet and a fluid outlet and at the base it is fitted with
solid outlet.
Pragati K. Mahajan

19. Pragati K. Mahajan

20. Working :
• The suspension of a solid in gas (usually air) is introduced
tangentially at a very high velocity, so that rotary
movement takes place within the vessel.
• The fluid is removed from a central outlet at the top.
• The rotatory flow within the cyclone separator causes the
particles to be acted on by centrifugal force.
• The solids are thrown out to the walls, thereafter it falls to
the conical base and discharged out through solids outlet.
Uses:
1.Cyclone separators are used to separate the suspension of
a solid in a gas (air).
2. It can be used with liquid suspensions of solids.
Pragati K. Mahajan

21. Advantages:
1. It has no moving parts.
2. Continuous disposal of solid particles.
3. They are not expensive to install or maintain.
Disadvantages:
1. Low collection efficiency for the particles below 5µm in
diameter i.e. below their 'cut-off diameter when operated
under low solids- loading conditions.
2. 2. Equipment is subjected to severe abrasive deterioration
usually higher pressure loss than other separator types,
including bag filters and low pressure drop scrubbers.
Pragati K. Mahajan

22. Thank you
PRAGATI K. MAHAJAN