BARRE IN FABRICS
INTRODUCTION
In textile industry, one of the most common and perplexing quality control problems is barre(repetitive yarn direction streaks). The factors which can cause or contribute to barre are varied and diverse.
Barre is defined as
"unintentional, repetitive visual pattern of continuous bars or stripes
usually parallel to the filling of woven fabric or to the courses of circular
knit fabric." Barre is sometimes used as a synonym for WARP STREAKS.
Barre
can be caused by physical, optical or dye differences in the yarns, geometric
differences in the fabric structure or by any combination of these differences.
Barre
is basically a visual phenomenon and any property of yarn which makes it 'look'
different from the adjacent yarn in a fabric would result in this defect.
Barre can be due to the following
- fibre properties
- yarn characterisitics
- knitting parameters
In
weft knit fabrics Barre is taken to include only those fabric defects
charecterised by coursewise (widthwise) repearing bars or stripes. In warp
knits, the warp (or length) direction. This is symptomatic of the way in which
the fabrics are produced.
CAUSES
OF BARRE
All barre is the consequence of subtle differences in yarn reflectance between individual yarn in the knit structure. Any mechanism that can change the reflectance of a yarn in a knit structure is a potential barre source. Barre can be caused by physical, optical, or dye differences in the yarns, geometric differences in the fabric structure, or by any combination of these differences. A barre streak can be one course or end wide or it can be several - a "shadow band"
It
is not the inadequacy of the raw material property which results in Barre, It
is the inconsistency or the variability of the particular property which
results in Barre.
The
properties which are the causes of Barre are given below.
- Fibre Micronaire variation
- Fibre color variation
- Yarn linear density variation
- Yarn twist variation
- yarn hairiness variation
- knitting tension variation
- improper mixing of cotton from different origin
- improper mixing of cotton from different varieties
- improper mixing of cotton grown in different seasons
- Zellweger Uster has published the following details regarding Barre
|
causes
|
%
ge of defect
|
|
fibre
|
70
|
|
yarn
count variation
|
10
|
|
twist
variation
|
10
|
|
hairiness
|
10
|
Micronaire:
- The difference in Micronaire average of the mixings of the entire lot should not be more than 0.2
- The range of the Micronaire of the individual bales used in the mixings should be same
- the C.V.% of Micronaire of individual bales within the mixing should be less than 12 %
- Same micronaire bales should not be placed side by side and a group should be formed with the different micronaire bales and it should be repeated in the bale laydown
- David M. Clapp 5 , of Cotton Incorporated demonstrated that as the difference in micronaire value increases, the intensity of the barre effect becomes more serious. In the process, he observed that the cause of barre is not the difference in dye uptake between the thin cell walls of the low micronaire fibres and the thicker cell walls of the high micronaire fibres.He showed that per unit weight, dye exhaustion / fixation is essentially the same for the low micronaire and high micronaire fibres and also illustrated that at high micronairevalues, both the maturity and fineness registered an increase. More importantly, he extended his study and showed that by proper blending of the cottons, the occurrence of barre due to differences of even upto 1.6 micronaire can be eliminated.
Fluorescence:
- The difference in UV reading average of the mixings of the entire lot should be same
- Variation in UV readings within the bale should be less
- out side storage of cotton should be avoided
- UV readings increase over time if it is stored for a long time
- should not mix high and low UV bales
- Colour has been one of the primary factors of cotton quality for quite a long time. Colour is particularly important as a measure of how well a yarn or fabric will dye or bleach. Colour in general is expressed in trichromatic terms, such as L, a and b (Reflectance, Redness/greenness and Yellowness / blueness). The significance of these components with regard to cotton has been extensively studied and is generally agreed upon that only reflectance and degree of yellowness are important in assessing cotton colour
- The influence of cotton colour on the dyeability characteristics of fabrics have been studied and reported by the U.S. Department of Agriculture , which revealed that a significant correlation exists between the colour characteristics of raw cotton and the colour of washed and wash-dyed cotton fabrics. Since much of the barre effects are due to the variations in dyeability characteristics within a fabric, difference in colour properties could be expected to influence the seriousness of any barre incidences in the fabric.
Yarn
properties:
- It has been widely accepted that it is the inconsistency or the variation aspect of the yarn properties which is a prime cause for 'Barre"
- Of the various quality characteristics tested, variation in hairiness count and twist are considered to be three important properties which need proper control to avoid barre.
- Slippage of spindle tape is the main reason for the TPI variations. If the TPI is more in yarn then the yarn diameter will reduce adn number of helical angle will increase. If the diameter of the yarn is low then more light will pass through that region of cloth because the gap between the two yarn is more.When more ridges are present, then more light reflects from the surface of the yarn. Hence regions with high TPI yarn appear light coloured after dying.
Knitting:
- A bar or stripe may be caused by several variables shown below
- Tight loops: This may take the form of a shaddow ( several courses involved) or a discreet line ( one course involved). It will normally show up as a dark or dense line or shaddow
- Slack loop: Similar to above, but it shows up as a sheer or light line.
- improper stich length at a feed
- improper tension at a feed
- variation in fabric take-up from loose to tight
- Worn needles, which generaly produce length direction streaks
- Uneven cylinder height needles(wavy barre)
- Uneven loops: In this the "average" stitch length is the same in all cases but the distribution of the length of yarn between the dial and the cylinder of knitting machine is not balanced on a particular course. Thus it will appear as a tight or slack course on one side but analysis will not show up the fault.
Weaving:
- Uneven warping tension
- Uneven take-up tension
- Uneven let-off motion
- Uneven tension on filling
- Scuffing or filling yarn on the beam
- Bent beam gudgeons
BARRE IN FABRICS - Page 2
VISUAL
BARRE ANALYSIS:
- The first step in Barre investigation is to observe and define the problem. Barre can be the cause of physical causes which can usually be detected, or it can be casued by dyeability differences which may be nearly impossible to isolate in fabric. Barre analysis methods that help to discriminate between physical barre and barre caused by dyeability differences incluede Flat Table Examination, Light source Observation, and the Atlas Streak analyser.
FLAT
TABLE EXAMINATION:
- For a visual barre analysis, the first step is to lay a full width fabric sample out on a table and view both sides from various angles. Generally, if the streaky lines run in the yarn direction, color differences can be seen by looking down at the fabric in a direct visual line with the yarn direction, and the defect can be positively identified as a barre defect. Viewing the fabric with a light source in the back ground will show if the barre is physical.
LIGHT
SOURCE OBSERVATION:
- After completing an initial Flat Table Examination, a Light Source Examination may provide further useful information. Full width fabric samples should be examined under two light conditions, fluorescent and ultraviolet (UV) light. Observations that should be made while viewing under lights are: frequency and direction of the barre whether streaks are dark or light and total length of pattern repeat.
- Ultraviolet light, commonly referred to as a "black light", allows the presence of mineral iols to be more easily detected, due to their radiant energy (glow). When observed under UV light, fabrics with streaks that exhibit glow suggest improper preparation. A change in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in scouring can create this problem.
PHYSICAL
BARRE ANALYSIS:
- When the cause of barre is determined or presumed to be physical in nature, physical fabric analysis should be done. Physical barre causes are generally considered to be those which can be linked to yarn or machine differences. Methods of physical barre analysis include fabric dissection, microscopy, and the Roselon Knit Extension Tester.
FABRIC
DISSECTION:
- To perform accurate fabric dissection analysis, a fabric sample which contains several barre repetitions is required. First, the barre streak boundaries are marked by the placement of straight pins and/or felt markers. Individual yarns are removed from light and dark streak sections, and twist levels, twist direction, and cut length weight determinations are made and recorded. For reliable mean values to be established, data should be collected from at least two light/dark repeats. After compilation of yarn information, the numbers can be compared individually to adjacent yarns as well as by groupings of light and dark shades.
MICROSCOPY:
- Microscopic examination is useful for verifying yarn spinning systems. Yarns from different spinning systems can have different light reflectance and dye absorption properties. Ring spinnning produces yarn that is smooth. Open end spinning produces yarn with wrapper fibres at irregular intervals. Air jet spinning produces yarn with more wrapper fibres than open end and inner fibres are more paralle. Microscopy can also reveal a shift in loop formation in knitted fabrics when twist direction (S and Z) differences are present.
- Barre is noticed in a fabric when the visual perception of colour of a particular portion of a fabric is different from that of an adjacent portion. Numerous attempts have been made by research workers to arrive at a mathematical number which gives an equal change when a change in perceptible colour difference exists.
- Reflectance differences have been considered by many researches to be indication of barre in fabrics. E.R.Cairns, H.A.Davis and J.W.Coryell 5 hypothesised that double knit barre is caused by textured yarn reflectance differences in the knit structure. Depending on the detailed arrangement of these differences, barre is seen as continuous or random and either as single end streaks or bands. Based on studies made with a research grade spectrophotometer, they also found that yarn reflectance differences are caused by differences in key textured yarn properties like bulk, cross section, loop size etc.
PREVENTION
OF BARRE:
- As outlined, Barre is caused by INCONSISTENCIES in materials, equipment, or processing. To prevent Barre form occuring, consistency must be maintained through all phases of textile production. Stock yarns should be properly and carefully labelled to avoid mixups. Fugitive tints can be useful for accurate yarn segregation. Inventory should be controlled on a First In/ First Out basis. All equipement should be properly maintained and periodically checked. Before beginning full scale production, sample dyeings can be done to check for Barre.
- Salvaging a fabric lot with a Barre problem may be possible through careful dye selection. Color differences can be masked by using shades with very low light reflectance (navy blue, black) or high light reflectance (light yellow, orange, or finished white). Dye suppliers should be able to offer assistance in this area. Also, if the cause of the barre is an uneven distribution of oil or wax, a more thorough preparation of the fabric prior to dyeing may result in more uniform dye coverage.
- With close cooperation between production and quality control personnel, barre problems can be successfully analysed and solved.
EXPERIMENT:
- The experiments done by Mr.ANBARASAN of PREMIER POLYTRONICS is given below.
FIBRE
PROPERTY INFLUENCE ON FABRIC BARRE:
- EXPERIMENTAL
PROCEDURE
It was identified that the incidences of fabric barre was more common in knitted fabrics. So one of the most commonly used hosiery counts - 30s Nec Combed Hosiery was chosen for the study. - Preparation of
basic yarn samples:
Preparation of samples with different yarn count:
The extent of influence of yarn count was studied by taking into consideration three levels of count. To avoid any abnormal conditions of spinning, one of the levels was maintained at the normal level used by mill for regular production. The other two samples were obtained by spinning counts differing by 2 Nec(6.7%) from the normal. The three count samples of 28, 30 and 32 Nec are designated as A, B and C respectively. - The raw
material and the process parameters maintained in all departments upto
ring spinning were maintained the same for all the three samples. In ring
frames, the count change pinion was changed to obtain the required count.
All the other process parameters were maintained the same in ring frames
as well.
Preparation of samples from different micronaire cottons: - The samples for studying the influence of fibre micronaire were prepared by spinning yarn from cottons of micronaire values ranging from 3.8 to 4.32. The micronaire values of the samples are given in Table 1 along with their designations. The cottons were obtained by segregating samples of the same cotton variety to avoid influences of other varietal factors.
|
Serial
No.
|
Sample
designation
|
Micronaire
|
|
1
|
P
|
3.8
|
|
2
|
Q
|
3.95
|
|
3
|
R
|
4.14
|
|
4
|
S
|
4.32
|
Table
: Micronaire Values of Basic Samples
- Cottons with difference in micronaire readings of less than 0.15 were not taken up since 0.15 represented the measurement accuracy of the micronaire instrument. The spinnings were carried out using a miniature spinning system having the following sequential processing stages :
- Carding
- Drawing
- Sliver to Yarn Spinning
About 50gms of cotton was processed from each sample to obtain yarns sufficient for the subsequent knitting process.
Barre in Fabrics
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.
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
|
1
|
- Table : Degree of Yellowness (+b) for Basic Samples
- The spinnings
for these samples were also carried out using the miniature spinning
system.
Fabric Preparation
For 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.
Dyeing
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.
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.
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.
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
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.
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.
VG = 5.101 - 0.078(+b) - ((4.393 )/square(+b))
A good correlation of 0.90 was obtained between actual and predicted grades.
CONCLUSIONS
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.
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.
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.
|
FABRIC
BARRE
|
|
|
CAUSE
|
%
OF DEFECTS
|
|
Fibre
|
70
|
|
Yarn
count variation
|
10
|
|
Twist
variation
|
10
|
|
Hairiness
|
10
|
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.
STUDY ON BARRE CAUSED
BY RAWMATERIAL
The
AFIS Maturity module is a single fiber measurement of individual fiber
maturity. The individual fiber maturity information gives a distribution of
fiber maturity as well as the average fiber maturity. The distribution enables
us to identify the very immature fibers and it is described by the Immature
Fiber Content (IFC%). Figure 2 clearly shows a considerable difference of the
three bales in the IFC%. Maturity differences in cotton can also cause defects
in fabric such as white speck neps. Fabric in figure 3 was knitted from yarn
produced from three different cottons having similar micronaire values. There
was a significant difference in the amount of white specks in the three fabric
samples. The three cottons were tested on the AFIS Maturity module and the results
are given in figure 4. The differences in the AFIS IFC% correlates visually to
the amount of white specks in the three fabrics. Interesting is that the
overall average maturity ratio from the three cottons was very similar,
giving no indication of a potential problem of white specks.
Variation of Maturity in Sliver
There
is a possibility to optimize the carding process to make sure all cards remove
as much of the immature fiber as possible. Figure 5 shows the results from
testing a line of cards all fed from the same bale laydown. It is interesting
that while the card mats all show very similar results the card slivers show
quite some variation. The possibility of the influence of carding on the
maturity of the sliver was investigated further using the AFIS Maturity module.
Several individual cards were analyzed and it was apparent that there was a
large variation in the amount of immature fibers removed by the cards. This
initial trial indicated that it is possible to change the mechanical setup of a
card to influence the removal of immature cotton fibers. These results are
shown in figure 6.
Fluorescence
Another
major cause of fabric barre’ is a change in the cotton fiber fluorescence.
Fluorescence can be measured by the Uster Fiberglow, which measures the
ultraviolet light that is reflected from the cotton sample. Fluorescence (UV)
is not cotton color, but the effect of sunlight on the structure of the fibers.
Fluorescence can cause BARRE if
- the variation in average UV readings between mixings is high
- C.V.% in UV readings within a mix is high
- End of season cotton crop changes
- Outside storage of cotton bales is practiced
- mixing high and low UV bales is done
- UV readings increase over time in the warehose
Bale
laydowns should be controlled using similar techniques that are used for Micronaire.
These solutions for controlling fluorescence are given below
- UV test every bale before making mix
- don’t allow more than 10 points difference of UV readings within mix
- UV average should be less than 1 point between mixes
- category groups should be set up for UV
The
variation within a single mix should be a maximum of +/- 5 points. The average
UV reading of the mix should not change more than +/- 1 point from mix to mix.
There is normal change in the UV readings from crop year to crop year. This is
due to seasonal changes as well as the difference in UV from cotton stored in a
warehouse from 9-12 months. Blending old crop and new crop must be done
carefully to reduce the chance of creating fabric barre’. Typically each new
year the cotton crop will have a different UV average and range depending on
the weather at the time of the harvest.
Conclusions
At
least 70% of the causes of fabric barre’ are due to variations in fiber
properties. There are specific solutions available for spinning mills to
control the key fiber properties that affect the dyeing and finishing of cotton
fabrics. Individual bale measurements of Micronaire, maturity and fluorescence
will help the spinning mill to control all aspects of fiber barre’ problems.
The exact solution will depend greatly on the specifics of end product,
spinning system and raw materials used by individual mills. Application
guidelines are available for use in selecting bales for mixes and storing bales
in the warehouse. Instruments and software programs are available to help the
spinning mill monitor and control these specific fiber properties.
REFERENCE:USTER
APPLIACTION HANDBOOK FOR AFIS PRO
