Vinita

Bilaspur University
Bilaspur (C.G)
Session: 2017-18
A presentation on: size reduction process

Subject: skill development
Submitted by:
Guided by:
Vinita vinayak
Roll no. no- 17110015022
Er. Yashwant kumar patel
B.Sc fpt 5th sem
Definition:
Size reduction is the unit operation in which the average size of solid pieces of food is reduced by the
application of grinding, compression or impact forces. Size reduction have little or no preservative effect.
They are used to improve the eating quality or suitability of foods for further processing and to increase the
range of products available. In some foods they may promote degradation by the release of naturally
occurring enzymes from damaged tissues, or by microbial activity and oxidation at the increased area of
exposed surfaces, unless other preservative treatments are employed.
Benefits of size reduction:
• There is an increase in the surface-area-to-volume ratio of the food which

increases the rate of drying, heating or cooling.
• When combined with screening, a predetermined range of particle sizes is
produced which is important for the correct functional or processing properties of
some products (for example icing sugar, spices and cornstarch).
• A similar range of particle sizes allows more complete mixing of ingredients (for
example dried soup and cake mixes).
Size reduction procedures :
The size of agricultural products may be reduced several ways, but mainly the following four
methods are used in size reduction machines:
 Compression
 Crushing
 impact
 Shearing
 cutting
Crushing:
 When an external force applied on a material excess of its strength, the

material fails because of its rupture in many directions.
 The particles produced after crushing are irregular in shape and size.
 Food grain flour, grits and meal, grits and meal, ground feed for live stock are
made by crushing process.
 Crushing is also used to extract oil from oilseeds and juice from sugarcane.
Impact:
 When a material is subjected to sudden blow of force in
excess of its strength, it fails, like cracking of nut with the
help of a hammer.
 Operation of an hammer mill is an example of impact
method.
Shearing:
 It is a process of size reduction which combines cutting and crushing, the

shearing unit consist of a knife and a bar.
 If the edge of knife or shearing edge is thin enough and sharp, the size
reduction process nears to that of cutting, whereas a thick and dull shearing
edge performs like a crusher.
 In a good shearing unit the knife is usually thick enough to overcome the
shock resulting from material hitting.
Cutting:
 In this method, size reduction is accomplished by forcing a sharp and thin

knife through the material.
 In this process minimum deformation and rupture of the material results and
the new surface created is more or less undamaged.
 An ideal cutting device is a knife of excellent sharpness and it should be as
thin as practicable, the size of vegetables and fruits are reduced by cutting.
Size reduction machinery:
 Size reducing devices are grouped as follows:

 Crushers
 Grinders
 Fine grinders
 Cutting machines
Crushers:
These type of reducing machines squeeze or press the material until it breaks.
Crushers are mostly used to break large pieces of solid materials into small
lamps. Crushers are used in industrial operations, like mines etc.
The crushers in use are :
 Jaw crushers
 Gyratory crushers
 Crushing rolls
Jaw crushers:
 In a jaw crusher feed is admitted between two jaws, which are open at the top like ‘v’. One of the jaw
is fixed and somewhat vertical while the other is the swinging jaw. It makes an angle of 20-30 degree
with the fixed jaw. The solid which has to be broken is caught between the two jaws.
 large lumps of solid materials are caught between the upper parts of the jaws and subsequently
broken and dropped into the narrower space below. The broken pieces are further reduced next time
when jaws come closer.
Gyratory crusher:
 In a gyratory crusher the jaws between which the solid materials fed, are circular. In such crushers the
material is being crushed at all times at some points. Solid are caught between ‘V’ shaped space
between the head and casing. The material is repeatedly broken in sufficiently small pieces to pass out
from the bottom.
 the crushing head is rotate by an eccentric unit. The speed of crushing head ranges between 125 to
425 gyrations per minute. The discharge from the gyratory crusher is continuous. Its power
requirement is low.
Crushing rolls:
In agricultural operations crushing rolls are mainly used for extraction of juice from sugar cane. The
crushing rolls are of two broad types :
1. Smooth roll crusher – Two heavy smooth faced metal rolls rotating towards each other at same speed
on parallel horizontal axes are the working elements of the smooth – roll crusher. Smooth-roll crushers
are used to make grits or meal from food grains.
Serrated or toothed rolls :
 In such crusher the rolls are toothed as per need. Toothed roll crusher are
much more versatile than smooth roll crushers.
 The best example of such type are the break and reduction rolls of a
wheat flour milling plant.
 These machine tear the feed apart. The size reduction in serrated roll
crushers is by compression, impact and shear, and not by compression
alone, as in the case of smooth roll crushers.
Grinders :
 The grinders are used to mill the grains into

powder. The grinder comprises a variety of size
reduction machines like attrition mills, hammer
mills, impactors and rolling compression mills.
Attrition mills :
 In an attrition mill the grains are rubbed between the grooved flat faces of rotating circular disks. These mills
are also known as plate mills.
 The axis of the roughened disks may be horizontal or vertical. In attrition mill one plate is stationary and
fixed with the body of the mill, while other one is rotating disk.
 The material is fed between the plates and is reduced by crushing and shear. In attrition mill the materials
are slowly fed, over feeding lowers the grinders performance, also heat generation during milling increases.
 The disk of plate mill are usually 20 to 137cm in diameter and are operated at 350 to 700 rpm.
Hammer mill:
 Hammer mills are used for various types of size reduction job. These mill contain high speed rotor,
rotating inside a cylindrical casing.
 Materials are fed into the mill from the top of the casing and Is broken by the rotating hammers and
fall out through a screen at the bottom.
 The material or feed is broken by fixed or swinging hammers which are pinned to a rotor. The
hammers are rotated between 1500 to 4000 rpm, strike and grind the material until it become small
enough to pass through the broken screen.
Ball mills:
 The ball mill is a cylindrical or conical shell slowly rotating about a horizontal axis. Half of its
volume is filled with solid grinding balls.
 The shell is usually made of steel lined with high carbon steel plate, porcelain or silica rock. For
medium and fine reduction of abrasive materials ball mills are used.
 In ball mill size reduction is achieved by impact of the balls when they drop from near the top of
the shell. The balls are carried up the side of the hell nearby to the top. By gravity the balls drop on
the feed underneath.
CONCLUSION
Thank you.

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Bilaspur University

A presentation on: size reduction process

• There is an increase in the surface-area-to-volume ratio of the food which

 When an external force applied on a material excess of its strength, the

 It is a process of size reduction which combines cutting and crushing, the

 In this method, size reduction is accomplished by forcing a sharp and thin

 Size reducing devices are grouped as follows:

 The grinders are used to mill the grains into

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