CHAPTER - 3
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OUTLINE OF PRESENT WORK
3.1 INTRODUCTION ;
The present need of textile industry is to
produce quality yarn and fabric without increasing the
cost of manufacture. A major or minor defect occurs
*
every 4.5 metres of our fabric and of the total defects,
about 52% of the defects can be attributed to spinning
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faults. The general appearance and sale value of the
yarn and fabric is influenced by the level of
imperfections and yarn faults. A critical study of
imperfections and faults in the yarn is therefore
carried out in the present work. A brief outline of the
various studies conducted are given below :
3.2 STUDIES OF IMPERFECTIONS IN YARN :
3.2.1. Study of U% and Imperfection Level of Mill yarns
Samples of yarns were spun from regular mixing
used in the mills. Yarn tests were carried out and U%
values and imperfections of these yarns were compared
with Uster 50% experience values (1989 statistics)
3.2.2. Effect of overspinning on Imperfections :
Mixing from the mills were used to spin two or
three different counts and the effect of overspinning on
U% and imperfections in yarn was studied.
3.2.3. Within spindle and between spindle variation in
yarn imperfections :
From the same inter bobbins in the creel of the
ringframe successive doffs of ringframe bobbins from the
same ten spindles were collected. U% and imperfections
of the samples were recorded. Within spindle variation
over successive doffs and between spindle variation in
U% and imperfection readings were studied.
3.2.4. Correlation between imperfections and
irregularity given by linear and quadratic
integrators
Uster irregularity testers having linear
integrator give U% (or PMD) value and those having
quadratic integrator give CV% value of yarn. It is of
interest to know which of them is more sensitive to
imperfections in yarn. In the present study, linear and
quadratic integrators were connected in parallel and
simultaneous measurement of U%, CV% and number of
imperfections in the yarn were made. From the results,
relationship between U% and imperfections and between
CV% and imperfections were evaluated. The association
between U% and CV% was also worked out.
3.3 STUDY OF THE CHARACTERISTICS OF IMPERFECTIONS IN
YARNS :
Cotton and polyester/cotton blend yarns from
mills were taken for this study. With Uster
Imperfection Selector, thin places (-50% level), and
thick places (3 i.e. +50% level) were collected and
compared with normal yarn portions for their following
properties
1. Yarn diameter
2. Weight per unit length
3. Turns per cm
4. Hairiness
5. Fibre length
6 . Breaking strength and elongation %
7. Blend composition of polyester/cotton yarns.
Comparison of yarn properties at thin and thick
places with normal yarn was carried out to get better
understanding of the contribution of imperfections to
yarn quality.
3*3.1. Double counting of thick places :
It is reported in the literature that while Uster
IPI measures thick places and neps seperately with their
respective counters, some of these are counted double
i.e. by both the counters. Uster IPI is therefore said
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to be overestimating the imperfections in yarn. A
study was carried out with cotton and polyester/cotton
blended yarns to measure the frequency of double
counting and critically inspect the double counted thick
places/neps to observe the nature of the fault.
3.4 EFFECT OF DRAFTING PARAMETERS AT RING FRAT-IE ON
YARN QUALITY ;
The review of literature shows that ring frame
parameters like roller settings, break draft, top roller
pressure, apron spacing etc. affect yarn quality and
there is a high degree of interaction between these
parameters. It is also seen that for every mixing there
exists an optimum apron spacing at which irregularity
and imperfection level reach a minimum and the optimum
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is at a lower level with increase of top-roller load.
In the present study therefore a higher top
roller load of 15-12-15kg (Front-Second-Back) was used
on UT 620 drafting system to study the effect of
following parameters at ringframe on yarn properties
i) Back zone setting of bottom rollers AND
ii) Apron spacer settings.
3.4.1. Effect of apron spacing on imperfections and yarn
tenacity :
From the results of studies carried out in 3.4 it
was observed that changes in apron spacer setting affect
yarn irregularity and imperfection level in yarn. But
there is no effect on yarn strength or tenacity. The
yarn samples were therefore tested at different levels
of sensitivity to get an explanation for this
phenomenon.
3.5 CORRELATION BETWEEN YARN IRREGULARITY (CV%) AND
IMPERFECTIONS :
Yarn irregularity is closely related to the
presence of thin and thick places in yarn.^^^ In the
present study, the theoratical number of thin/thick
places were calculated from the actual count and yarn
irregularity (CV%) and their correlation with actual
number of thin/thick places was worked out.
3.6 SELDOM OCCURRING YARN FAULTS ;
Seldom occurring yarn faults are those which are
>1 0 0 % of the mean weight per unit length of material.
They have a more damaging effect on fabric appearance
and cause breakages in further processing. Out of
these, the objectionable faults are removed on winding
machines by using electronic yarn clearers for good
quality or export yarns/fabrics. But presence of
excessive objectionable faults affects adversely the
winding machine efficiency and introduce excessive
number of knots in the yarn (when splicer is not used)
which is again a source of end break in weaving.
Studies of yarn faults were carried out in actual mill
working. The following studies were carried out on
Murata winding machine No.7-II MACH CONER having Uster
electronic yarn clearer Model C3.
3.6.1 Types of faults :
On Murata winding machine, a sufficiently large
number of faults were collected while processing
polyester/cotton Ne 14 (42 tex) yarn. The faults were
classified into their different types to find out the
frequency distribution of spinners' doubles, slubs, fly,
piecings etc.
Then weight per unit length of each fault was
recorded and the frequency distribution according to
weight per unit length of faults was prepared. The
characteristic of the curve of the frequency
distribution of fault weights was also seen.
Yarn faults of polyester/cotton blended yarn were
analysed for their blend composition and compared with
the blend composition in normal portion of yarn to get
an insight into the formation of faults in blend yarns.
3.6.2. Effect of electronic yarn clearer settings :
The measurement of yarn fault by Uster electronic
yarn clearer depends on the dielectric constant of fibre
tested and the moisture content of the material. To
take care of these changes, a Material Number setting
(M) is provided on Uster yarn clearer. A detailed study
was carried out on Murata winding machine with
polyester/cotton blended yarn to see the effect of
change in material number setting on the sensitivity of
electronic yarn clearer. The changes in number of
breaks on winding machine and weight per unit length of
the smallest faults eliminated were studied in this
experiment.
Other important setting on Uster electronic yarn
clearer is sensitivity (SE%) setting. According to the
thickness (or diameter) of the fault which is decided as
objectionable in relation to the diameter of the knot,
the sensitivity setting is kept on the clearer. For Ne
40 (15 tex) combed yarn, the effect of changing
sensitivity level (SE%) from 150%to 250% was studied by
observing the winding breaks and diameter of the
smallest faults eliminated at the respective sensitivity
levels in relation to the diameter of yarn knots.
3.6.3. Effectiveness of routine maintenance :
With continuous working of the machines the fluff
accumulates on machine parts and there is also wear out
of parts. Under extreme conditions this could affect
quality of the product. To maintain the quality of the
product, regular cleaning and maintenance operations are
therefore carried out on machines. The schedules of
cleaning and maintenance of ringframe followed in the
mills were assessed for their effectiveness in
maintaining the quality of yarn over the period of
maintenance. The yarn quality before the scheduled
maintenance and after carrying out the maintenance
operation was compared by observing the winding breaks
and objectionable yarn faults present and if the values
show a significant difference.
The following schedules of maintenance operations
were checked
i) Oiling and cleaning of ringframe
ii) Buffing of top roller cots
iii) Routine traveller change
iv) Resetting of top arms
3.6.4. Effect of changes in process parameters on yarn
faults
Thylnfluence of process parameters in ringframe,
speedframe and comber on yarn quality with special
reference to objectional faults was studied. The
objectionable yarn faults before changing the parameters
and after changing were compared by observing yarn
breaks at Murata winding machine for sufficient length
of yarn cleared. The effect of changing the following
parameters on yarn faults was studied.
i) Wider back zone setting at inter and
ringframe affecting yarn faults,
ii) Wider back zone setting at ring frame
affecting fabric faults,
iii) Change in U% value of Inter bobbins,
iv) Change in U% value of comber sliver.
v) Pressure on top rollers of ringframe.
vi) Comparison of drawing blend and blowroom
blend on yarn quality.
The next chapter gives methods of tests adopted
in these experiments.
