This document discusses size reduction, which is the process of reducing drugs into smaller pieces or fine powder. It defines size reduction and lists its purposes. Factors that affect size reduction include hardness, fiber content, elasticity, melting point, and hygroscopicity. Common size reduction methods are cutting, compression, impact, attrition, and shear. Equipment used for size reduction includes cutter mills, roller mills, hammer mills, and ball mills. Cutter mills use knives to cut materials while roller mills use compression between rollers. Hammer mills rely on impact from hammers and ball mills use impact and attrition from balls within a rotating cylinder.

1. Sandip M. Sonwane
Lecturer (D.Pharm)
Bajiraoji Karanjekar College of Pharmacy,
Sakoli
Contact-9673949199
Email id-sonwanesandip09@gmail.com
SIZE REDUCTION

2. DEFINITION OF SIZE REDUCTION
 Size reduction is the process of reducing drugs (vegetable &
chemical substances) into smaller pieces, coarse particles or
fine powder.
 It also known as comminution or pulverization.

3.  To increase the rate of solution
To allow the rapid penetration of solvent during extraction
To get a uniform powder
To increase the rate of absorption of a drug
To improve the stability of certain Dosage forms
To help in the process of separation of solids from liquids

4. FACTORS AFFECTING SIZE REDUCTION
 Hardness :- It is easier to break soft material than hard materials. Ex. For iodine
hammer mill is used
Fibrous :- These are tough in nature. A soft, tough material has more difficulty
than a hard, brittle substance. Ex. Rauwolfia, Ginger
 Elastic / Sticky :- Become soft during milling. Ex. Synthetic gums, waxes, resins
 Melting point :- Waxy substances, fats or oils become softened during size
reduction due to heat generation.

5. FACTORS AFFECTING SIZE REDUCTION
Hygroscopic :- Certain substances absorbed moisture content rapidly. This
wet mass hampers the milling process. Ex. Potassium carbonate
 Purity required :- Mills used for SR often cause the grinding surfaces to
wear off & thus impurities come in powder. For high purity such mills are
avoided.

6.  Cutting –The material is cut on a small scale by means of a sharp blade,
knife, root cutter or any other sharp instrument.
 Compression - The material is crushed by means of application of
pressure.
 Impact – Impact occurs when material is stationary & hit by an object
moving at high speed or moving particle strikes to stationary surface.
 Attrition – arising from particles scraping against one another or against
a rigid surface
 Shear – Shear is produced when the particle is compressed between the
edges of two hard surfaces moving tangentially.

7. EQUIPMENTS USED FOR SIZE REDUCTION
1 . CUTTER MILL
Principle :
The size reduction is
done by cutting with the help of
sharp knives.
Construction:
Mainly consist of following
• Hopper
• Knives (Stationary &
Rotating)
• Rotor
• Screen
Fig . 1 Cutter Mill

8. Working :
The material to be cut put into hopper of the mill. Rotor rotates at high speed.
The stationary & rotating knives cuts the material into small pieces during rotation.
Screen retains the material.
Uses:
The mill used to obtain a coarse degree of size reduction of soft materials such
as roots, peels or wood before extraction.

9. Principle :
It works on the principle of
compression of material by applying
pressure on it.
Construction:
 Two cylindrical rollers mounted
horizontally
 Rollers capable of rotation on their
longitudinal axis
 One roller driven directly while
another one runs freely
Fig . 2 Roller Mill
EQUIPMENTS USED FOR SIZE REDUCTION
2. ROLLER MILL

10. Working :
• The material is fed from the hopper into the gap between wo rollers.
• Due to rotation of these rollars, the material is crushed.
• The gap between rollars can be adjusted to control the degree of size
reduction.
Uses:
It is used for crushing & cracking of seeds before extraction of fixed oil from
the same. It also used to crush soft tissues, to help in the penetration of solvent
during extraction process.

11. Principle :
It works on the principle of
Impact
Construction:
It consists of a stout metal casing,
enclosing a central shaft, to which four
or more swinging hammers are
attached. The lower part consists of a
screen thourgh which material can pass
and collected in receiver.
EQUIPMENTS USED FOR SIZE REDUCTION
3. HAMMER MILL
Fig . 3 Hammer Mill

12. Working :
• The material put into the hopper.
• Due to fast rotation of hammers material is powdered to the desired size &
colleted under the screen.
• The mill can produce coarse to moderately fine powder.
Uses:
The hammer mill is used for producing immediate grades of powder from
almost all types of substances except sticky materials that choke the screen.

13. Principle :
It works on the principle of impact & attrition.
Construction:
It consists of hollow cylinder which is mounted on a
metallic frame in such way that it can be rotated on its
longitudinal axis.
Cylinder contains metallic ball usually lined with chrome. In
Pharmaceutical industry sometimes the cylinder of the ball
mill is lined with rubber or porcelain. The ball used in these
mills are also made of rubber or porcelain.
EQUIPMENTS USED FOR SIZE REDUCTION
4. BALL MILL
Fig . 4 Ball Mill

14. Working :
Ball Mill grinds material by rotating a cylinder with steel grinding balls, causing the
balls to fall back into the cylinder and onto the material to be ground. The rotation is
usually between 4 to 20 revolutions per minute, depending upon the diameter of the
mill. The larger the diameter, the slower the rotation. If the peripheral speed of the mill
is too great, it begins to act like a centrifuge and the balls do not fall back, but stay on
the perimeter of the mill.
Uses:
The mill is used to grind brittle drugs to fine powder.

15. References:
1) R.M. Mehta Pharmaceutics I , 94-101
2) http://www.mine-engineer.com/mining/ballmill.htm
3) Images from online sources