Preparatory process - key points

Cotton Mixing & Blowroom technical points

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Sriyadithatextile - Cotton Mixing & Blowroom technical points

Mixing and Blowroom
TFA

COTTON MIXING

Cotton is a hygroscopic material, hence it easily adapts to the atmospheric

airconditions. Air temperature inside the mxing and blowroom area should be more than

25 degree centigrade and the relative humidity (RH %) should be around 45 to 60 %,

because high moisture in the fibre leads to poor cleaning and dryness in the fibre leads

to fibre damages which ultimately reduces the spinnability of cotton.

Cotton is a natural fibre. The following properties vary very much between bales

(between fibres) fibre micronaire fibre length fibre strength fibre color fibre maturity. Out

of these, fibre micronaire, color, maturity and the origin of growth results in dye

absorption variation. There fore it is a good practice to check the maturity, color and

micronaire of all the bales and to maintain the following to avoid dye pick up variation

and barre in the finished fabric.

 

BALE MANAGEMENT:

 

In a particular lot

  • Micronaire range of the cotton bales used should be same for all the mixings of a

lot

  • Micronaire average of the cotton bales used should be same for all the mixings of

a lot

  • Range of color of cotton bales used should be same for all the mixings of a lot
  • Average of color of cotton bales used should be same for all the mixings of a lot
  • Range of matutrity coefficient of cotton bales used should be same for all mixings

of a lot

  • Average of maturity coefficient of cotton bales used should be same for all

mixings of a lot

Please note, In practice people do not consider maturity coefficient since

Micronaire variation and maturity variation are related to each other for a

particular cotton.

 

If the cotton received is from different ginners, it is better to maintain the percentage of

cotton from different ginners throught the lot, even though the type of cotton is same.

It is not advisable to mix the yarn made of out of two different shipments of same cotton.

For example, the first shipment of west-african cotton is in january and the second

shipment is in march, it is not advisable to mix the yarn made out of these two different

shipments. If there is no shadevariation after dyeing, then it can be mixed.

According to me, stack mixing is the best way of doing the mixing compared to using

automatic bale openers which picks up the material from 40 to 70 bales depending on

the length of the machine and bale size, provided stack mixing is done perfectly.

Improper stack mixing will lead to BARRE or SHADE VARIATION problem. Stack

mixing with Bale opener takes care of short term blending and two mixers in series

takes care of long term blending.

 

  • Tuft sizes can be as low as 10 grams and it is the best way of opening the

material(nep creation will be less, care has to be taken to reduce recyling in the

inclined lattice)

  • contaminations can be removed before mixing is made
  • The raw material gets acclamatised to the required temp and R.H.%, since it is

allowed to stay in the room for more than 24 hours and the fibre is opened , the

fibre gets conditioned well.

Disadvantages:

  • more labour is required
  • more space is required
  • mixing may not be 100% homogeneous( can be overcome by installing double

mixers)

 

If automatic bale opening machine is used the bales should be arranged as

follows

let us assume that there are five different micronaires and five different colors in

the mixing, 50 bales are used in the mxing. 5 to 10 groups should be made by

grouping the bales in a mixing so that each group will have average micronaire

and average color as that of the overall mixing. The position of a bale for

micronaire and color should be fixed for the group and it should repeat in the

same order for all the groups

It is always advisable to use a mixing with very low Micronaire range.Preferably

.6 to 1.0. Because

  • It is easy to optimise the process parameters in blow room and cards
  • drafting faults will be less
  • dyed cloth appearance will be better because of uniform dye pickup etc

It is advisable to use single cotton in a mixing, provided the length, strength

micronaire, maturity coefficient and trash content of the cotton will be suitable for

producing the required counts. Automatic bale opener is a must if more than two

cottons are used in the mixing, to avoid BARRE or SHADE VARIATION problem.

It is better to avoid using the following cottons

  • cottons with inseparable trash (very small size), even though the trash % is less
  • sticky cotton (with honey dew or sugar)
  • cotton with low maturity co-efficient

Stickiness of cotton consists of two major causes. Honeydew from Whiteflies and

aphids and high level of natural plant sugars. The problems with the randomly

distributed honey dew contamination often results in costly proudction

interruptions and requires immediate action often as severe as discontinuing the

use of contaminated cottons. An effective way to control cotton stickiness in

processing is to blend sticky and non-sticky cotton. Sticky cotton percentage

should be less than 25%.

 

BLOWROOM

 

BLOWROOM

Basic operations in the blowroom:

  1. opening
  2. cleaning
  3. mixing or blending
  4. microdust removal
  5. uniform feed to the carding machine
  6. 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
  1. two feed rollers( clamped)
  2. feed roller and a feed table
  3. 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

recommeded due to various reasons.

  • It is better to control the climate inside the department when sticky cotton is used.

Low temperature (around 22 degree celcius) 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 heavier particles by buoyanccy differences.

  • General factors which affect the degree of opening , cleaning and fibre loss are,
  1. thickness of the feed web
  2. density of the feed web
  3. fibre coherence
  4. fibre alignment
  5. size of the flocks in the feed (flock size may be same but density is

different)

  1. the type of opening device
  2. speed of the opening device
  3. degree of penetration
  4. type of feed (loose or clamped)
  5. distance between feed and opening device
  6. type of opening device
  7. type of clothing
  8. point density of clothing
  9. arrangement of pins, needles, teeth
  10. speeds of the opening devices
  11. throughput speed of material
  12. type of grid bars
  13. area of the grid surface
  14. grid settings
  15. airflow through the grid
  16. condition of pre-opening
  17. quantity of material processed,
  18. position of the machine in the machine sequence
  19. feeding quantity variation to the beater
  20. ambient R.H.%
  21. ambient temperature

 

  • 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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