Barre in Fabrics - Page 3
- Preparation of samples from cotton with different colour levels:
For studying the influence of colour, the parameter 'Degree of yellowness(+b)' provided by the high volume fibre testers was taken as the reference. Five spinnings were carried out with cottons of different +b values. The values are shown below.
Serial No. Sample Degree of Yellowness (+b) 1 A1 9.2 2 B1 10.5 3 C1 11.6 4 D1 13.5 5 E1 14.7
- Table : Degree of Yellowness (+b) for Basic Samples
- The spinnings for these samples were also carried out using
the miniature spinning system.
FFor all the trials to study the influence of count, fibre micronaire and colour, to detect the presence or otherwise of the barre effect, different combination of two levels were selected. The yarn samples were knit into single jersey fabrics on a circular knitting machine with 2.5mm stitch length such that the two different levels of the combination formed alternate portions of the fabric as shown below :
Fabric knitted with a combination of yarn samples.
The fabrics were knitted with 48 cones of each of the two levels feeding the machine.
The fabrics for all the combinations were dyed using Procion Blue MR dye of 2.5% concentration. The same batch of dye bath was used to dye all the fabrics pertaining to a particular property in order to eliminate the introduction of any possible errors in the process of dyeing.
- RESULTS AND DISCUSSIONS
Influence of Yarn Count
The intensity of the barre effect noticed for the various count combinations in terms of the visual grading are represented in the following table.
combination count difference in count average grade 1 2 AB 28 30 2 4.25 BC 30 32 2 4.5 AC 28 32 4 4.75
- Table : Influence of Count on Barre Intensity
The table clearly shows that the intensity of barre is more severe as the difference in count levels increases. It can also be noted that even if a count deviation of +2 Nec from the average is present, a grade of more than 4.0 is recorded which indicates a reasonably high amount of barre.
- Influence of Fibre Micronaire:
The four basic yarn samples obtained from cotton with different micronaire values were used to knit fabrics in a total of 6 combinations with the difference in micronaire values ranging from 0.15 to 0.52. The intensity of barre for these combinations are tabulated below in terms of the average visual grade.
Combination Micronaire value Difference in Micronaire Average grade PQ 3.8 3.95 0.15 3 RS 4.14 4.32 0.18 2 OR 3.95 4.14 0.19 3 PR 3.8 4.14 0.34 2 QS 3.95 4.32 0.37 3 PS 3.8 4.32 0.52 2
Table : Influence of Micronaire on Barre Intensity
The table shows that, within the range of micronaire taken-up in the present study, the intensity of Barre remains fairly constant. An important observation is that the intensity of Barre is serious even with a micronaire difference of 0.15. Hence when preparing mixings of single cotton variety, it should be ensured that the difference in average
micronaire between successive mixings is less than 0.15.
Influence of Fibre Colour:
From the basic 5 samples of yarn differing in terms of the 'Degree of Yellowness (+b)', a total of 10 combination of fabrics could be obtained, with the colour difference ranging from 1.1 to 5.2. The details of the samples and the intensity of barre noticed in these samples are tabulated below.
Micronaire Value Combination
Serial No Combination Degree of Yellowness difference in +b values visual grade 1 B1C1 10.5 11.6 1.1 1 2 D1E1 13.5 14.7 1.2 2 3 A1B1 9.2 10.5 1.3 3 4 C1D1 11.6 13.5 1.9 4 5 A1C1 9.2 11.6 2.4 3 6 B1D1 10.5 13.5 3.0 5 7 C1E1 11.6 14.7 3.1 4 8 B1E1 10.5 14.7 4.2 5 9 A1D1 9.2 13.5 4.3 5 10 A1E1 9.2 14.7 5.5 4
Table : Influence of Degree of Yellowness on Barre Intensity
The influence of colour on the barre intensity is clearly seen from the last two columns of the table where the visual barre grade shows a direct relationship with the difference in +b values of the cottons used. An exclusive consideration of the +b value gave the following best-fit equation for the Visual Grade (VG).
VG = 5.101 - 0.078(+b) - ((4.393 )/square(+b))
A good correlation of 0.90 was obtained between actual and predicted grades.
The influence of three important parameters - yarn count, fibre micronaire and fibre colour - on the intensity of the barre defect iin cotton knitted fabrics are discussed. Of the fibre parameters, the degree of yellowness of cotton seems to have a relatively more significant effect on the Barre intensity in fabrics than the micronaire. However even deviation of micronaire value to the extent of +0.15 results in a visible barre defect. Deviations in yarn
count also shows up significantly as Barre defects. Avoidance of the Barre effect, therefore, requires proper control on all these parameters.
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