MIXING (COTTON)

Cotton is a hygroscopic material , hence it easily adopts to the atmospheric airconditions. Air temperature inside the mixing 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 :

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.

It 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.

why?

• 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 production 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%.