STUDY ON BARRE CAUSED BY RAWMATERIAL

The current expansion of the worldwide market for cotton has opened up many possibilities for the spinning mill. Spinning mills now have many options in the raw materials they purchase for producing yarn. This expansion in the availability of raw material has helped in reducing costs and improving yarn quality and spinning efficiency. Unfortunately this situation has also presented some new challenges for the spinning managers and cotton buyers. Traditionally purchased cottons had well established seed varieties and growing regions. This meant that with an average control of micronaire they had few problems with the dying and finishing of cotton fabrics.

Over the past two years we have seen a rapid increase of the problems with dying and fabric finishing. This is especially evident in the claims and rejects 100% cotton knitted fabrics for fabric barre’. Claims and rejects can easily wipe out any savings in raw material costs obtained by purchasing cotton from several international sources.  Many spinning mills are under the impression that all upland seed varieties mature the same as related to the micronaire. Unfortunately what they discover is that cottons with similar micronaire that have different growing regions and seed varieties dye differently.

Controlling some of the basic fiber properties can give the spinning mill the information necessary to reduce and or eliminate the recurring problems of barre’. Mill experience and trials have given us the necessary information to set up guidelines for controlling the fiber properties that influence the dyability of cotton yarns in knitted fabrics. There are several mechanical causes of fabric barre’ that are associated with the spinning and sliver preparation processes in the spinning mill.  The following table shows that the major cause of BARRE is due fiber.

While mechanical differences and variations in yarn count, twist and hairiness can also be a cause of the barre’ effect the single largest cause lies in the variation in fiber properties. Figure 3 shows the fiber properties that have a major influence in the causes of barre’. Micronaire, maturity/fineness and fluorescence all play a major role in the consistent dying and finishing of knitted fabric.

Micronaire

Most mills have learned over the years that they need to control the average of the micronaire in the bale laydown. Most mills have some type of system to categorize cotton bales into groups in an effort to control the average micronaire. While controlling the average micronaire is a good first step many times this is not enough control to eliminate the barre’ effect, especially in knitted fabric. The  causes and controls necessary for eliminating dying problems as they relate to micronaire are given below

• difference in micronaire should be less than 0.2

• change in average micronaire from mix to mix should be less than 0.1

• C.V% of micronaire within mix should be within 10%

• Bales with same micronaire should not be placed side by side

The additional control of the variation or CV% of the micronaire must be added to the overall control of the average in each laydown. It is also necessary to change the average of the laydown over time so that all bales in the warehouse can be processed. The change in average micronaire in the laydown must be changed slowly over time.The maximum bale-to-bale variation ( c.v%)within the mix should be 10%. A variation(c.v%) of micronaire higher than 10% will very likely cause a barre’ effect in the fabric.

Maturity & Fineness

Micronaire is an indication of the maturity in cotton fiber, although it is not a direct measurement of the fiber maturity. Micronaire can be used successfully to control barre’ if the cotton being processed is from the same seed variety. If cottons from several varieties or growing areas are being blended together, then additional testing and maturity information may be necessary.

Causes of Barre due to Maturity

• Blending cottons from different growth areas

• Blending cottons from different seed varieties

• seasonal changes in cotton growth cycle 1. weather 2. insects

• Immature fibre cotent % (IFC%)   1.White speck neps 2. carding speeds

An example of fabrics made of yarn produced from three (3) different bales of cotton is shown in figure .

The cottons all had the same micronaire (4.2) but, as can be seen, the dye uptake on the individual yarns were very different. The above Figure  is a good example of how cotton fiber maturity (not micronaire) can cause a barre’ effect in fabric. These bales of cotton were tested on the HVI instrument and the yarn was tested on the Uster Evenness tester. These results are shown in figures 1  , it is not possible to determine any significant differences between these three cottons that would cause a problem in dying and finishing. The cottons are also tested on the new AFIS Length and Maturity to determine if any difference could be found. The results from the AFIS Maturity module are shown in figure 2.

FIG:1

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