Cleaning, Sorting and Grading Devices.pdf

LECTURE 3 & 4
CLEANING, SORTING AND
GRADING DEVICES

Cleaning, Sorting & Grading
Cleaning
• After threshing, grains are contaminated by impurities (earth, small
pebbles, plant and insect waste, seed cases, etc.).
• These impurities hinder drying operations and make them longer
and more costly.
• After drying, especially by traditional methods such as open-air
drying, the grain may still be contaminated by impurities.
• These impurities lower the quality of the product and also cause
potential infestation during storage.
• "Cleaning" means the phase or phases of the post-harvest system
during which the impurities mixed with the grain mass are
eliminated.
• The cleaning may be done by washing, screening, hand picking etc.

Cleaning, Sorting & Grading (contd.)
Sorting
• Sorting is done mostly by hand to remove the fruits and
vegetables which are unsuitable to market or storage due to
damage by mechanical injuries, insects, diseases, immature,
over-mature, misshapen etc.
• This is usually carried out manually and done before
washing.
• By removing damaged produce from the healthy ones, it
reduces losses by preventing secondary contamination.
• Sorting is done either at farm level or in the pack-houses. In
sorting, only sensory quality parameters are taken into
consideration.

Cleaning, Sorting & Grading (contd.)
Grading
• The produce is separated into two or more grades on the basis of
the surface color, shape, size, weight, soundness, firmness,
cleanliness, maturity & free from foreign matter /diseases insect
damage /mechanical injury.
• A classification of the material on the basis of commercial value
and usage.
• e.g. Apple I. Extra Fancy II. Fancy III. Standard IV. Cull (for
processing).
• Grading may be done manually or mechanically. It consists of
sorting product in grades or categories based on weight/size.

Grade Factors
Grade factors are characterized by following
characteristics:
1. Physical
2. Biological
3. Chemical etc.
1. Physical Characteristics
i. Moisture Content
ii. Unit size
iii. Texture
iv. Color
v. Foreign matter
vi. Shape

Grade Factors (Contd.)
2. Chemical Characteristics
i. Analysis (Composition)
ii. Rancidity (refers to the spoilage), free fatty acid index
iii. Odor and flavor
3. Biological Characteristics
i. Germinations
ii. Type and amount of insect damage
iii. Type and amount of mold damage
iv. Bacteria count

Washing of Agricultural Produce
The primary operation of cleaning is washing. It
has following types
1) Soaking in still or in moving water of other fluids
2) Water sprayers
3) Rotary drums
4) Rotating brushes
5) Shuffle or shaker washers

(Contd.)
1. Soaking
Adopted for loosely attached dirt particles and are in
small quantities.
2. Water Sprays
a) It consists of low pressure to very high pressure
water jets directed at wide angles.
b) It removes firmly attached particles due to
agitation when placed in water bath.
c) The intensity of spray or pressure should be
carefully adopted.

(Contd.)
Soaking and Water Sprays

(Contd.)
3. Rotary Drum
a) Commercial washing device.
b) Minimum damage, simple, high capacity washes.
c) The performance depend on speed of rotation, the roughness and
length of time the product is retained in water.
d) Auxiliary aids such as spray nozzles may facilitate the job.
e) The washing time is controlled by the pitch of the drum or
helical retaining fences which screw the product through the
drum.

(Contd.)
Rotary Drum Washer

(Contd.)
4. Brush Washers
a) Effective for sandy or loamy soil spray
residues.
b)Washing time controlled by rotating motion of
brushes which moves the product through a
definite path.
c) Brushes made of fiber, rubber, sponge, other
material which may be replaced frequently.

(Contd.)
Brush Washers

(Contd.)
5. Shaker Washers
a) Used for difficult washing jobs.
b)A vigorous reciprocating motion is involved so
it is made robust.
c) More expensive but effective and sometime
unsuitable for product that are easily managed.

Sorting of Agricultural Produce
They can be sort out by the following procedures
i. Screening
ii. Diverging belts
iii.Roller sorter
iv. Weight sorter

(Contd.)
1. Screening
a) Vibrating screens are used for fruits and vegetables
which are made of coper, stainless steel or other
materials which are not chemically active.
b) The un-sized material passes on a vibrating screen or
rotating, which perforates to pass.
c) The largest material which goes over the end of screen.
d) The material that passes the screen is rescreened and
into new fractions are moved to the other operations.

(Contd.)
Screen Sorter

(Contd.)
2. Diverging Belts
a) Widely used sorter, consists of two or more
belts which diverge as they travel.
b)The fruit is carried on and between the belts.
c) Since the distance between the belts increases
symmetrically, the smaller pieces will drop
between the belts at the beginning of travel
whereas the larger pieces will drop farther.

(Contd.)
Belt Sorters

(Contd.)
3. Roller Sorters
a) Roller sorters are fast, accurate and cause little damage to
product.
b) Each roll rotates in a counter-clock wise direction.
c) The fruit is contentiously rotated so that individual piece
has an opportunity to resister its minimum dimension with
the space in the sorter.
d) The roller sorter is divided into multiple roll units, which
are hinged so that the gauging space increases progressively
through the sorter.
e) When the roller unit closes the space at the end of its travel
the turning roller ejects any fruit trying to pass through the
space without damage.

(Contd.)
3. Roller Sorters (Contd.)
f) Roller conveyers with fixed space are used for removing
the leaves and twigs and small fruits.
g) The roller sizer which gangs on minimum diameter only
works well on objects of uniform geometric proportions.
h) If proportion in a lot vary, a given size grade will contain a
greater range of volumes than is defined by the minimum
diameters.
i) A set of rolls with a profile defined by spools has been
designed for grades which give an impression of relatively
uniform size within a grade, even with fruits of different
proportions.

(Contd.)
Roller Sorters

(Contd.)
4. WEIGHT SORTERS
a) They operate on the basis of unit weight and are accurate,
moderately fast and damage to product is minimum.
b) They can be used on large size products as apples, oranges, and
are also adopted for eggs handling.
c) The material is placed into individual cups by an automatic
indexing fees.
d) As the cup travel through the sorter, they are indexed with spring
loaded trips. The spring tension is progressively weaker from the
beginning to the end of movement.
e) The heavier units overcome the spring reaction and are
discharged at the beginning of travel. The lighter units moving
the greater distance before being discharged.

(Contd.)
Weight Sorters

Cleaning and Sorting of grains, nuts
and seeds
It depends upon the following characteristics of
materials
i. Size
ii. Shape
iii.Specific gravity
iv. Surface characteristics
It can be done by
i. Winnowing
ii. Screening

and seeds (Contd.)
1. Winnowing
a) Winnowing is a traditional agricultural method developed
by ancient cultures for separating grain from chaff.
b) It can also be used to remove pests from stored grain.
Winnowing usually follows threshing in grain preparation.
c) In its simplest form it involves throwing the mixture into
the air so that the wind blows away the lighter chaff, while
the heavier grains fall back down for recovery.
d) Techniques included using a winnowing fan (a shaped
basket shaken to raise the chaff) or using a tool (a
winnowing fork or shovel) on a pile of harvested grain.

and seeds (Contd.)
Winnowing

and seeds (Contd.)
2. Screening
a) Most widely used device for grains/seeds etc. is screen or
sieve.
b) Sieves used in conjunction of air blast will satisfactory
clean and sort most granular materials.
c) The screen unit is composed of two or more screens
d) These screens are suspended by hangers in such a way that
they have a horizontal oscillating motion and a smaller
vertical motion
e) The combination of these two motions move the grain
down the screen and at the same time tosses it sufficiently
so that the sheet of grain is thoroughly stirred.

and seeds (Contd.)
Basic screen arrangement for sorting of grain

and seeds (Contd.)
Dual Screen Grain Cleaner/Sorter

and seeds (Contd.)
This Slide
Contain
video of
Drum
Washer
-
Click and
PLAY

and seeds (Contd.)
2. Screening (Contd.)
f) The screen pitch is adjustable this controls the
downward travel of the grain.
g) Screens are available with round, triangular or
slatted holes. The slots may be oriented in the
direction of travel perpendicular to it or both.
h) Performance depends on screen selection and
pitch as a steep pitch works better.
i) The material should not more so fast that these is
insufficient time for each individual grain to
register with a hole.

and seeds (Contd.)
j) The sieve A is called the scalper and is for scalping off
material large than that to be retained.
k) Generally, screen A should have round holes that
should be just large enough to pass the material to be
retained. But if the material is flat than oblong hole
screen is recommended.
l) The screen B should have holes just small enough to
retain the best material. If the screen A has round holes
then lower screen should have slotted holes or Vice
Versa.
m)Frequently screen C is omitted the light seeds and weed
seeds being permitted to fall onto the solid Pan D.

and seeds (Contd.)
n) On the other hand if it is mixture of material and is to be
sorted then are more additional screens are required.
o) In this arrangement the material is not contaminated with
the small fractions rejected by D.
p) The pitch of the lower bank of screen can be carried relative
to the upper bank and also the vibrating characteristics can
be varied between the two sets to accommodate the job at
hand.
q) When a fine degree of soring is being made grains will
frequently lodge in the holes. So screens are fitted with
moving brushes beneath and pushes the lodged seeds back
through the screen.

Aerodynamics of Small Particles
• Undesirable materials such as light grains, weed seeds,
chaff, plant leaves and stalks can be removed with air flow,
when grains, fruits and vegetables are mechanically
harvested.
• In addition, agricultural materials are routinely conveyed
using air stream in pneumatic conveyers. If these systems
are not used properly, they could cause problems.
• For example, in a combine harvester, if the air speed is low,
the materials would not be separated from each other and
there will be extra foreign material with the product.
• If air speed is high, the product will be exhausted along with
extra material and product loss will increase.

(Contd.)
• For conveying agricultural material, the range of
proper air streams should be used.
• With low air speed, there is stagnation in the
system, or with high air speed, there is not only
energy lost, but also grains may be broken.
• The proper air speed can be determined from
aerodynamic properties of agricultural materials.
• These properties are terminal velocity and drag
coefficient.

(Contd.)
• If an object is dropped from a sufficient height, the force of gravity will accelerate
it until the drag force exerted by the air, balances the gravitational force. It will then
fall at a constant velocity called the terminal velocity.
𝑚 × 𝑔 =
1
2
× 𝜌 × 𝑉𝑡
2
× 𝐶𝑑 × 𝐴
• The drag coefficient of an object can be found from its terminal velocity:
𝐶𝑑 =
2𝑚𝑔
𝜌𝑉𝑡
2
𝐴
Where:
m = is mass of the object (kg),
g = is gravitational acceleration (m/s2),
Cd = is drag coefficient,
ρ = is air density (kg/m3),
A = is projected area (m2), and
Vt = is terminal velocity (m/s).

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