11 March 2013
Introduction of Blowroom Section | Objects of Blow-room | Basic Operations in the Blowroom
Blowroom consists a number of
machines used on succession to open and clean the cotton fibre. Since
the tuft size of cotton becomes smaller and smaller, the required
intensities of processing necessitates different machine
configuration.
Objects of Blowroom:
1. Opening:
a) To open the compressed bales of fibres.
b) To make the cotton tuft as small as far as possible.
2. Cleaning:
To remove dirt, dust, broken seeds, broken leaves, and other foreign materials from the fibre.
3. Mixing & Blending:
To make good value of yarn and to decrease production cost mixing and blending is done.
4. Lap or flocks formation:
To
transfer opened and cleaned fibre into sheet form of definite width
and length which is called lap or in modern system directly feed to the
carding machine into flocks form.
Basic Operations in the Blowroom:
- opening
- cleaning
- mixing or blending
- microdust removal
- uniform feed to the carding machine
- Recycling the waste
Blow room installations consists
of a sequence of different machines to carry out the above said
operations.Moreover Since the tuft size of cotton becomes smaller and
smaller, the required intensities of processing necessitates different
machine configuration.
Technological Points in Blowroom
Opening in blowroom
means opening into small flocks.Technological operation of opening means
the volume of the flock is increased while the number of fibres remains
constant. i.e. the specific density of the material is reduced
The larger the dirt particle ,
the better they can be removed . Since almost every blowroom machine can
shatter particles, as far as possible a lot of impurities should be
eliminated at the start of the process.Opening should be followed
immediately by cleaning, if possible in the same machine.
The higher the degree of
opening, the higher the degree of cleaning. A very high cleaning effect
is almost always purchased at the cost of a high fibre loss. Higher
roller speeds give a better cleaning effect but also more stress on the
fibre.
Cleaning is made more difficult
if the impurities of dirty cotton are distributed through a larger
quantity of material by mxing with clean cotton.The cleaning efficiency
is strongly dependent on the TRASH %. It is also affected by the size of
the particle and stickyness of cotton. Therefore cleaning efficiency
can be different for different cottons with the same trash %. There is a
new concept called CLEANING RESISTANCE. Different cottons have
different cleaning resistance.
If cotton is opened well in the
opening process, cleaning becomes easier because opened cotton has more
surface area, therefore cleaning is more efficient . If automatic bale
opener is used, the tuft size should be as small as possible and the
machine stop time should be reduced to the minimum level possible .
If Manual Bale openers are used,
the tuft size fed to the feed lattice should be as small as possible
.Due to machine harvesting , cotton contains more and more impurities,
which furthermore are shattered by hard ginning. Therefore cleaning is
always an important basic operation.
In cleaning, it is necessary to
release the adhesion of the impurities to the fibres and to give hte
particles an opportunity to separate from the stock. The former is
achieved mostly by picking of flocks, the latter is achieved by leading
the flocks over a grid.
Using Inclined spiked lattice
for opening cotton in the intial stages is always a better way of
opening the cotton with minimum damages. Ofcourse the production is less
with such type of machines.
But one should bear in mind that
if material is recyled more in the lattice, neps may increase.
Traditional methods use more number of machines to open and clean
natural fibres. Mechanical action on fibres causes some deterioration on
yarn quality, particularly in terms of neps . Moreover it is true that
the staple length of cotton can be significantly shortened . Intensive
opening in the initial machines like Bale breaker and blending machines
means that shorter overall cleaning lines are adequate.
In a beating operation, the
flocks are subjected to a sudden strong blow. The inertia of the
impurities accelerated to a high speed, is substantially greater than
that of the opened flocks due to the low air resistance of the
impurities. The latter are hurled against the grid and because of their
small size, pass between the grid bars into the waste box, while the
flocks continue around the periphery of the rotating beater. By using a
much shorter machine sequence, fibres with better elastic properties and improved spinnability can be produced.
Air streams are often used in
the latest machine sequence, to separate fibres from trash particles by
buoyancy differences rather than beating the material against a series
of grid bars. There are three types of feeding apparatus in the blowroom
opening machines two feed rollers( clamped) feed roller and a feed
table a feed roller and pedals
Two feed roller arrangements
gives the best forwarding motion, but unfortunately results in greatest
clamping distance between the cylinders and the beating element feed
roller and pedal arrangement gives secure clamping throughout the width
and a small clamping distance, which is very critical for an opening
machine In a feed roller and table arrangement, the clamping distance
can be made very small. This gives intensive opening, but clamping over
the whole width is poor, because the roller presses only on the highest
points of the web.
Thin places in the web can be
dragged out of hte web as a clump by the beaters Honeydew(sugar) or
stickiness in cotton affect the process very badly. Beacause of that
production and quality is affected. Particles stick to metal surfaces,
and it gets aggreavated with heat and pressure. These deposits change
the surface characteristics which directly affects the quality and
running behavior.
There are chemicals which can be
sprayed to split up the sugar drops to achieve better distribution.But
this system should use water solutions which is not recommended due to
various reasons. It is better to control the climate inside the
department when sticky cotton is used. Low temperature ( around 22
degree Celsius) and low humidity (45% RH). This requires an expensive
air conditioning set up.
The easiest way to process sticky cotton is to mix with good cotton and to process through two blending machines with 6 and 8 doublings and to install machines which will seggregate a heavier particles by buoyancy differences.
General factors which affect the degree of opening , cleaning and fibre loss are,
- thickness of the feed web
- density of the feed web
- fibre coherence
- fibre alignment
- size of the flocks in the feed (flock size may be same but density is different)
- the type of opening device
- speed of the opening device
- degree of penetration
- type of feed (loose or clamped)
- distance between feed and opening device
- type of opening device
- type of clothing
- point density of clothing
- arrangement of pins, needles, teeth
- speeds of the opening devices
- throughput speed of material
- type of grid bars
- area of the grid surface
- grid settings
- airflow through the grid
- condition of pre-opening
- quantity of material processed,
- position of the machine in the machine sequence
- feeding quantity variation to the beater
- ambient R.H.%
- ambient teperature
Cotton contains very little dust
before ginning. Dust is therefore caused by working of the material on
the machine. New dust is being created through shattering of impurities
and smashing and rubbing of fibres. However removal of dust is not
simple. Dust particles are very light and therefore float with the
cotton in the transport stream.Furthermore the particles adhere quite
strongly to the fibres. If they are to be eliminated they are to be
rubbed off.The main elimination points for adhering dust therefore, are
those points in the process at which high fibre/metal friction or high
fibre/fibre friction is produced.
Removal of finest particles of
contaminants and fibre fragments can be accomplished by releasing the
dust into the air, like by turning the material over, and then removing
the dust-contaminated air. Release of dust into the air occurs whereever
the raw material is rolled, beaten or thrown about. Accordingly the air
at such positions is sucked away. Perforated drums, stationary
perforated drums, stationary combs etc. are some instruments used to
remove dust.
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