COTTON GINNING - BASICS

8/22/2019 COTTON GINNING - BASICS

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UNIT-1

Ginning

1B.TECH TEXTILE TECHNOLOGY 2nd YEAR 1st SEM


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The primary object of the ginning consists in

separating the fibres from the seed

A Perfect ginning operation would bePerformed if the separation of fibres

from seed was effected without the slightest

injury to either seeds or to the fiber.

2nd YEAR 1st SEM 2B.TECH TEXTILE TECHNOLOGY


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The cotton first goes through

dryers to reduce moisture

content and then through

cleaning equipment to removeforeign matter.

These operations facilitate

processing and improve fiberquality.



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A typical gin will process about 12 bales per

hour, while some of todays more modern gins

may process as many as 60 bales an hour.



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Previous to the introduction of Modern

Machinery, ginning was performed by hand or

by machines of a primitive character such as

the "Foot Roller" and its improvement the"Churka".

As the cotton industry developed, greater

production than these were capable of was

necessary, and machines driven by powerwere introduced.



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Numerous forms of gins have been tried, but

at the present time only three are used to

any large extent. They are

1. KNIFE ROLLER GIN 2. SAW GIN

3. THREE TYPES OF MACARTHY GIN

I. Single acting macarthy gin.

ii. Double acting macarthy gin

iii. Double roller macarthy gin.



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The ginning roller is the most important and

expensive component in the gin stand.

Roller-covering material is made from 13 layers

of plain-woven cotton fabric cemented together

with a white rubber compound.

The fabric lays on the bias so that neither the

warp or fill yarn are parallel to the direction of

cutting; this prevents the material from

unraveling from the roller surface.

The roller material mounts on to the roller core

with the cut edges of the fabric layers serving as

the ginning surface.



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Rotary-knife roller gin stands separate fiber

from seed by using the frictional forces

between a moving roller and fixed

stationary-knife surface.

During normal ginning, the roller-to-fiber

force is greater than the stationary knife-to

fiber force; therefore, the fiber sticks to the

roller surface and slips on the stationaryknife surface.



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Cotton is ginned as fibers adhered to the

roller surface slip under the stationary knife

which holds the seed.

Each stroke of the rotary knife clears thestationary knife edge of accumulated seed

cotton and ginned and partially-ginned seed.

Partially ginned seed are either pulled back

to the stationary knife and completelyginned or swept along with the seed and

carryover and later reclaimed.



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The seed cotton is placed in bulk on the

table.

By means of the reciprocating motion of the

table by the crank arrangement, the seedcotton comes into contact with knife roller

(formed of a number of knife discs).

Auxiliary roller breaks the large cluster of

seed cotton and maintains a constant supplyof cotton to knife roller.



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Knife portion being arranged in such amanner that anything coming into contactwith it is given a reciprocal or to and fromotion as well as being subject to a striking

action due to its revolution. The seed cotton is carried forward in the

direction of knife roller's motion until it isbrought into touch with leather roller.

This roller, which has a much roughenedsurface, due spirally-formed saw cuts Haspressing against, it by means of springand steel doctor Knife.



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The cotton fibres brought into contact with

the leather adhere to it, and are carried

round past the knife.

It is impossible for the seeds to follow. So,seeds will remain at the point of contact of

the doctor knife and leather roller, with the

fibres still connected with it.

The essential feature of this gin now comesinto play.



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The knife roller is so set as to act upon,

these adhering seeds, and it gives to them a

gentle to and fro motion, repeated very

quickly 'and at the same time a slight striking

action or pressure also repeated quickly.

The combined action soon causes the seeds

to separate from the fibres and to fall down

through the grid to floor.



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The freed fiber passing forward is stripped

from the roller by some arrangement of the

stripping board.

The seed cotton not taken up by one leatherroller (on the right of the figure) is brought

round into contact with another Leather

roller where same process as described

above is gone through and to which the sameparts equally apply.



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The seed cotton is placed on the table. By

means of the reciprocating motion of the

table by the crank arrangement, the seed

cotton comes into contact with the revolving

leather covered roller.

Some cotton fibres are carried in the

direction of leather roller, but seed cottons

are arrested by the doctor knife.



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A steel beater blade is connected by means of a

connecting rod, with a crank on the driving

shaft.

Due to the seeds being acted upon by the rapid

reciprocating motion given to the beater blade

by the crank, the seeds are separated from

fibres.

Ginned cotton fibres are carried onward in the

direction of leather roller, stripping board stripthe fibres from the leather roller and empty

seeds are thrown into grid, through which they

pass into suitable receptacle.



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The vertical movement of the beater bladeshould be 3/8 inch above the doctor knife.

Sharp edge of the doctor knife should not cutthe fibres.

The degree of pressure of the doctor knife

upon the leather roller can be varied accordingto the tenacity with which the fibres adhere tothe seeds. This is done by adjusting the springand thumb screws.

The pressure of the doctor knife

and distance between leather roller anddoctor knife should be in such a way that noseed will be allowed to pass in the direct ion ofleather roller.



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There are two leather roller and a doctor

knives is pressed against each leather roller.

The beater knives act from above, and are

given a reciprocating motion from a crank.Crank pin slide in a slot of arm carried by a

vibrating shaft.

Beater blades are fixed on arms projecting

from vibrating shaft Also grid and fingers arefixed on vibrating shaft.



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Seed cotton is fed into hopper -spaces.

The crank movement lowers this cotton intocontact with leather roller in one side and raises itaway from the roller on other side.

When the cotton comes into contact with leather

roller, some cotton fibres are carried in the directionof leather roller but seed cottons are arrested by thedoctor knife due to the seeds being acted upon by-the rapid reciprocating motion given to the beaterblade by crank, the seeds are separated from fibres.Ginned cotton fibres are carried forward in the

direction of leather roller. Empty seeds are thrown into grid.

As the grid lowers, the space in it permit the fixedfinger to pass between them, and so shake the seedto cause them to fall out readily.



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The seed cotton is fed upon the lattice and

carried forward to the spiked roller, which

loosens the cotton and throw;

it into the hopper.

In hopper, the seed cotton comes into

contact with rapidly revolving saw

roller. Approximately 70 saws are threaded

on a shaft.



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As the saws revolve, the teeth carry the

fibres forward, but it is impossible for the

seeds to follow and also, due to the heavier

beating of the rapidly revolving saws on the

seed cotton, the fibres are separated from

seed and taken round until the brush strips

the fibre from the teeth.

Empty seeds husks and other broken seedsare thrown into grid, through which they

pass into suitable receptacle.



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An air current from the cage draw the fibres

along the trunk passage, and on reaching therevolving cage are brought under the

pressure roller and delivered as a sheet,

from which it is taken to the baling press.



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SETTINGS:

An air current from cage should be optimum

to 'suck only fibres.

If air current is high - it will "suck seed also withfibres.

If air current is low - fibre accumulation under

brush roller causes to block the machine.



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Saw gin is suitable to process American

cotton and wherever American cotton is

grown, such as west Africa- India, Ceylon

etc.

These cottons are oily type in which the

fibres are not too easily separated from the

seeds, so heavier beating on seed is required

to separate the fibres. This is achieved in this gin by giving heavier

beating of the rapidly revolving saws on the

seed cotton.



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CAUSES FOR BROKEN SEEDS:

1. Improper setting between knife roller and dish

rail.

2. Improper setting between knife roller and

leather roller.

3. Improper setting between beater blade and

doctor knife in McCarthy gin

4. Improper setting of the adjustable plate, Bars

in saw gin.



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CAUSES FOR FIBRE DAMAGES:

1. Too much pressure of doctor knife on leather

roller.

2. Knives of the knife rollers are too sharp.

3. Sharp edges of the saw discs.

4. Improper setting between doctor knife and

leather roller.

5. Too close setting .between knife roller and dish

rail.



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CAUSES FOR NEPS FORMATION:

1. High speed of knife roller and saw roller.

2. Blunt edges of knife and saw disc.

To avoid defective ginning,

(I) various settings in the gin should be proper

(ii) speeds of the rollers should be in correct

range (iii) condition of the knife disc and saw disc

should not too sharp or too blunt and it should be

optimum.



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COTTON GINNING - BASICS