Size separation, also known as screening or sieving, involves separating particles into two or more portions based on differences in particle size, shape, and density. This is done using screening surfaces with meshes of different sizes. Common methods of size separation include sieving using oscillation, vibration, gyration, brushing, or centrifugal force to separate particles. Size separation is useful for obtaining specific particle size ranges for applications like tablet and capsule production.

1. Size serration is a unit operation that involve the serration of mixture of various size of particle into two or more
portion by melas of screening surface.
Size separation is also known as sieve, sitting or screening. This technique is based on difference b/w the particle
sizes shape & density.
The material that remain on the screening surface is known as oversize particle whereas surface is known as
unclear size particle.
 OBJECTIVE &
APPLICATION OF SIZE
SERATION
Size reduction of solid materiel never gives particles of same size, if gives particles of different size. This materiel
must be subjected to size separation technique to obtain narrow size range.
The advantage of size separation is-
01]. It is a method to determine particle size which are useful in production of tablet & capsules.
02]. A quality control tool for the analysis of row materiel such as Aspirin & Griseofulvin.
03]. To recover valuable product.
04]. To test the efficiency size reduction equipment.
The Indian pharmacopeia has given the standard
for powder for pharmaceutical purpose. The IP
specified 5 grads of powder, which are-
[01]. Coarse powder: A powder of which all the particles passed through a sieve with nominal mesh aperture of
1.70mm (number 10 sieve) & not more than 40% through a sieve with nominal aperture of 355m (number
44shiev) is known as ‘coarse powder”.
[02]. Moderately coarse powder: A powder of which all the particle passes through a sieve with nominal mesh
aperture of 710nm (number 22 sieve) & not more than 40% passes through sieve with nominal aperture of 250nm
(sieve number 60) is called “moderately coarse powder”
[03]. Moderately fine particle: If all the particles of through a sieve with nominal mesh aperture of 355m
(number 85 sieve) is called as “Moderately fine particle”
[04]. Fine particle: In the case all the particle of powder through sieve with nominal mesh aperture of 180m
(number 85 sieve), called as “fine particle”.
SIZE
SEPARATION
❑ OFFICIEL STANDARD FOR POWDER

2. [05]. Very fine particle: If all the particles of powder through sieve with nominal mesh aperture of 125m (number
120 sieve), are called “very fine particle”.
Sieve for pharmaceutical testing are constructed form wire cloth with square mashes, woven form wire of braas,
bronze, stainless steel or any stable material.
There should not be any reaction between the materiel of sieves & the substance to be sieved
Standard for sieve used for pharmacopoeial testing must specify the following =
A). Number of sieves:
Sieve number indicate the number of mashes per linear length of 25.4mm.
B). Nominal size of aperture: Nominal size of aperture indicates the distance between the two adjacent wire. It
represents the side of square aperture.
C). Nominal diameter of wire: Wire mesh sieve is made from wire having the specified diameter in order to give a
suitable aperture size & sufficient strength to avoid distortion of the sieve.
D). Approximate percentage sieving area: This standard expresses the area of the meshes a percentage of the
total area of the sieve.
E). Tolerance average aperture size- This variation is expressed as a % & known as “aperture tolerance average”.
Screening is the method of separating particles according
to size alone. This basic technique involves passing the
particles through a series of sieves of unichrome size. Coarse particles can drop easily to large opening, but it is
difficult to screen the fine powder.
Size separation can be done by three method=
01.Agitation.
02.Brushing.
03.Centrifugal.
 SIEVE
 MECHANISM OF SIZE
SEPARATION

3. AGITATION
METHOD
A]. Oscillation: The sieves is mounted in a frame that oscillates back & forth.it is a simple method but the material
may roll on the surface of the sieve.
The motion is parallel to the frame of sieve.
B]. 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 the sieve.
C]. Gyration: In this method, a system is made so that sieve is on rubber mounting & connected to an eccentric fly
wheel. This gives a rotatory movement of the particles on the sieve, that help than to pass through the sieve.
In this case a brush is used to move the particles on the surface of the sieve & to keep the meshes clear. The brush
is rotated in the middle in case of circular sieve, but spiral brush is rotated on
the longitudinal axis in case of a horizontal cylindrical sieve.
CENTRIFUGAL
METHOD
In this method a high-speed rotor is fixed inside a vertical cylinder sieve so that on rotation the particles are
thrown outwards by centrifugal force. The current of air can be generated due to high speed of rotor which helps
in separating the particles.
BRUSHING
METHOD

4. SIEVE SHAKER MACHINE
PRINCIPLE
The powdered drug is separated according to its particle size using a number of sieves in a nest. These are
subjected to different types of agitation so that size separation is rapid.
CONSTRUCTION
Standard sieve of different meshes number are available commercially as per specification of IP & USP. These
sieves are fixed in a mechanical shaker apparatus.
WORKING
Sieve are arranged in a nest with the coursed particle at the top. A sample of powder is
placed on the top of sieves. This sieves set is fixed to a mechanical shaker & shaker for a certain period of time
(20minutes). The powder retained on each sieve is weighed.
ADVANTAGES
It is inexpensive simple & rapid.
DISADVANTAGES
❑ If the powder is not dry the sieve may clog with the particle which results in improper sieving.

5. CYCLONE SEPARATOR
Principle
The centrifugal force is used to separating solids from fluids. The separation depends not only on the particle size
but also on density of particle. Hence depending on the fluid velocity, the cyclone separator can be used to
separate all types of particles or to remove only coarse particles & allow fine particles to be carried through with
the fluid.
: It consists of a cylindrical vessel with a conical base. In the upper part of the vessel is fitted
with a tangential inlet & a fluid outlet & at the base it is fitted with solid outlet.
:
The suspension of a solid in gas 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
Construction
Working

6. within the cyclone separator causes the particles to be acted on by centrifugal force. The solids are thrown out to
discharge out through solids outlet.
Cyclone separators are used to separate the suspension of a solid in a gas.
It can be used with liquid suspension of solids & used in oil refineries to separate oils &
gases.
Advantages
 Low capital cost.
 Low pressure drops.
 Dry collection & disposal.
 No moving parts.
 Can be used under extreme processing conditions.
Disadvantages
Inability to handle sticky materials.Offer low particulate efficiencies especially for particulate sizes below 5m.
Uses

7. AIR SEPARATOR
Principle
It works on the same principle as that of cyclone separator, but in this case the air movement is obtained by means
of rotating disc & blade. To improve the separation, the blade is used. By controlling these blades & the speed of
rotation, it is possible to vary the size at which separation occurs.
Construction
It consists of a cylindrical vessel with a conical base. In the upper part of the separator the vessel is fitted with feed
inlet, & at the base there are two outlets, one for line particles & other for heavy particles. The rotating disc &
rotating blades are attached to the central shaft, to produce air movement.
Working
The sample powder is passed through the feed inlet, which falls on the rotating disc. The rotating blades are
attached to the same shaft. These produce a current of air as shown by the arrows.

8. USES
The fine particles are picked up & are carried into space, where air velocity is sufficiently reduced. The fine
particles are dropped & ultimately collected at an outlet meant for fine particles. The heavy particles which fall
downward are removed at an outlet meant for heavy particles.
Air separator is often attached to the ball mill or hammer mill to separate & return oversized particles for further
size reduction.
Advantages
 It gives efficient separation in smaller apparatus.
 Low maintenance.
 Low pressure drops.
 High reliability.
Disadvantages
Low separation yield.Unsuitable for separating smaller particle.

9. ELUTRIATION TANK
Elutriation is a method of separation of particles on the basis of their density. The smaller size particles have low
density whereas the particles of larger size have more density. These particles are separated using a fluid flow.
The separation of powder is based on the low density of fine particles & high density of the coarse particle.
Elutriating tank is used to separate the coarse & fine particles of after levigation. After the levigation process
material is kept in elutriating tank & mixed with a large quantity of water. The solid particles are uniformly
distributed in the liquid by stirring & then it is allowed to settle down. Depending on the density of solid particles,
it will be suspended in water.
The apparatus consists of a vertical column with an inlet near the bottom for
suspension, an outlet at the base for coarse particles & an overflow near the top for fluid & fine particles. One
column will give single separation into two fractions. If more than one fraction is required a number of tubes of
increasing area of cross section can be connected in series.
Principle
Construction

10. Working
The material which is to be separated is first legated. Then this powder is kept in elutriating tank & the quantity of
water is poured into the tank. The content of the tank is mixed with the water by stirring. The particles are
uniformly distributed in the water. They are allowed to settle for some time. The particle which are having large
size will get settle down & the particles with smaller size will remain suspended in the liquid. If the tank contains
outlet at different heights then the multiple fraction can be separated containing the particles of different size
range. Then these fractions are dried to collect the powder.
USES
This technique is useful for separation of insoluble solids. These solids are first subjected to grinding & then
elutriation.
The process is continuous process.
 Depending on the fractions required, the same number of tubes of different areas of cross section can be
connected.
 The separation is quick as compare to other methods of separation.
 The apparatus is more compact than as that as used in sedimentation methods.
Disadvantage’s
 The main disadvantages of this method are that the suspension of solid particles has to be diluted which
may not be desired in certain cases.
 Dilution of suspension may be undesirable in some cases.
Advantages

11. BAG FILTER
PRINCIPLE
The separation of fine powder from coarse powder is carried out by applying suction. Firstly,
the mixture of powder which is to be separated is passed through a bag which is made up of cloth by applying
suction at opposite side of the feeding. This causes the separation of fine & coarse powder.
After this separation the bags are shaken by giving pressure to remove the powder which is adhered on the bags.
After that powder is collected from conical base.
CONSTRUCTION
It consists of number of bags made of cotton or wool fabrics. These are suspended in a metal container. A hopper
is arranged at the bottom of the filter to receive the feed. At the top of the metal container, a provision is made for
vacuum fan.
At the top of the vessel a bell-crank liver arrangement is made to change the action form filtering to shaking.

12. WORKING
01). Filtering period:
During this period the vacuum fan produces a pressure lower than the atmospheric pressure with in the
vessel. Gas to be filtered enters the hopper, passes through the bags, & out of the top of the apparatus.
The particles are retained with in the bags.
02). Shaking period =
During this period the bell-crank liver first close the discharge many fold & airs enters through
the top so the vacuum is broken.
At the same time, it gives a violent jerking action to the bags so that they are freed for the dust.
The fine particles are collected at the conical base.
USES
o They are used on the top of fluidized brayer for drying to separate the dust.
o They are used to clean the air of a room.
o Household vacuum cleaner is simple version of bag filter.
ADVANTAGES
❑ These can be used to remove dust.
❑ Reduced sensitivity to particle size distribution.
❑ No high voltage requirements.
DISADVANTAGES
• It has a high resistance which is about 600-1200p.
• Loss of cleaning efficiency.
• Large pressure losses.