Yarn Conditioning Process : An Overview
High
speed spinning machines generate more friction thus giving additional heat to
the yarn and as a result of such heat transfer the yarn moisture content is
vaporized. Rising speeds in spinning result in decreased yarn quality for other
processes and it is well known that dry yarns have worse properties. For
quality reasons it is absolutely important to have even distribution of this
recuperated moisture throughout the entire yarn package. Only the vacuum
technology provides the conditions for the required moisture regain. This paper
attempts to comprehensively review the yarn conditioning mechanism, process
parameters of conditioning and applications of yarn conditioning.
Moisture
in atmosphere has a great impact on the physical properties of textile fibres
and yarns. A high degree of moisture improves the physical properties of yarn
and it helps the yarn to attain the standard moisture regain value of the
fibre. Yarns sold with lower moisture content than the standard value will
result in monetary loss. Therefore the aim of yarn conditioning is to provide
an economical device for supplying the necessary moisture in a short time, in
order to achieve a lasting improvement in quality.
In
these days there is a dramatic change in the production level of weaving and
knitting machines, because of the sophisticated manufacturing techniques. Yarn
quality required to run on these machines is extremely high. In order to
satisfy these demands without altering the raw material, it is possible to make
use of the physical properties inherent in the cotton fibres. Cotton fiber is
hygroscopic material and has the ability to absorb water in the form of steam.
It is quite evident that the hygroscopic property of cotton fibers depends on
the relative humidity. The higher the humidity is, more the moisture
absorption. The increase in the relative atmospheric humidity causes a rise in
the moisture content of the cotton fiber.
The
fibre strength and elasticity increase proportionately with the increase in
humidity. If the water content of the cotton fibre is increased, the fibre is
able to swell, resulting in increased fibre to fibre friction in the twisted
yarn structure. This positive alteration in the properties of the fibre will
again have a positive effect on the strength and elasticity of the yarn.
Problems
in conventional yarn conditioning method
The
standard conventional steaming treatment for yarn is chiefly used for twist
setting to avoid snarling in further processing. It does not result in lasting
improvement in yarn quality. The steaming process may fail to ensure even
distribution of the moisture, especially on cross-wound bobbins (cheeses) with
medium to high compactness (Fig. 1).
The absence of vacuum in
conventional conditioning chambers prevents Conventional homogeneous
penetration. The outer layers of the package are also too moist and the
transition from moist to dry yarn gives rise to substantial
variations in downstream processing of the package, both with regard to
friction data and strength.
Since
the moisture is applied superficially in the wet steam zone or by misting with
water jets, it has a tendency to become re-adjusted immediately to the ambient
humidity level owing to the large surface area. Equipment of this kind also
prevents the optimum flow of goods and takes up too much space.
CONTEXXOR
conditioning process by Xorella
The
thermal conditioning process of the yarn according to the CONTEXXOR process
developed by Xorella, is a new type of system for conditioning the yarn package
(Fig. 2). Thermal conditioning uses low-temperature saturated steam in vacuum.
With the vacuum principle and indirect steam, the yarn is treated very gently
in an absolutely saturated steam atmosphere. The vacuum first removes the air
pockets from the yarn package to ensure accelerated steam penetration and also
removes the atmospheric oxygen in order to prevent oxidation. The conditioning
process makes use of the physical properties of saturated steam or wet steam
(100% moisture in gas-state). The yarn is uniformly moistened by the gas. The
great advantage of this process is that the moisture in the form of gas is very
finely distributed throughout the yarn package and does not cling to the yarn
in the form of drops. This is achieved in any cross-wound bobbins, whether the
yarn packages are packed on open pallets or in cardboard boxes.
Effect
of conditioning process parameters on yarn properties
Although
yarn conditioning machine can add the moisture of yarn, one must consider
different raw material and yarn counts to make different yarn conditioning
programs. In spite of higher moisture, if there is high vacuum condition, the
low quality of raw cotton, coarse count and higher ratio of short fibre would
make yarn over relaxed and thus will have less strength. Thus cotton yarn less
than Ne 21s, needs less vacuum, low steam temperature, longer heating up time
and constant temperature. For PC or pure polyester fibre as well as combed
yarn. It requires high vacuum degree and high steam temperature. The time for
heating up and constant temperature is related to the actual twist but maximum
should not exceed 70 minutes.
Steam
temperature is set according to the types of fibers. If cotton fiber is
conditioned under 100 for 20 days, it would have only 92% strength left, but
polyester fibre under the same conditions would retain 100% strength. For
different fibers, there is a big difference in the flow temperature, fusion,
resolution and other index of thermo logy. Maximum temperature for cotton fiber
in yarn conditioning machine should not exceed 85 but pure polyester could
reach 140. Otherwise it will have negative effects on breakage strength and
colors.
P.
V. Kadole et al found that, the cycle with first cycle temperature 58C - 05
min. and second cycle temperature 62C - 25 min. (with total time for the cycle
55 min.) gives optimized yarn properties for 20KW (4.26 TM), 20KH (3.78) waxed,
20 CH waxed. (3.6 TM) yarns. They also stated that in case of conditioning
waxed and unwaxed yarn simultaneously with same programme, care should be taken
while selecting maximum temperature in second cycle. Always it should be less
than melting point of the wax. They showed that the combined programme helps in
achieving best yarn results at low power cost and higher production rate.
Sibel
Sardag et al studied the effects of vacuum steaming process parameters
(temperature and duration) on tenacity properties of 1 00 % cotton and 100 %
viscose yarns. For this purpose, the yarns with different twist coefficients
and numbers were twisted and exposed to vacuum steaming at different
temperatures and for durations appropriate to their raw material properties.
Tenacity properties of the yarns were measured before and after vacuum
steaming. They found that vacuum steaming temperature has significant effect on
tenacity properties of 100% cotton and 100 % viscose yarns but vacuum steaming
duration has been found to be statistically insignificant on tenacity
properties of cotton yarns, and viscose yarns.
In
another study, these authors showed that tenacity, elongation at break (in per
cent), and work of rupture of 30 tex and 20 tex PES/viscose yarns were to be
enhanced due to heat-setting. They also showed that the tenacity and elongation
at break values of the yarns decreased after dyeing; however, these values are
still high when compared with those of the pre-heat setting. The increase of
temperature from 90C to 110C caused a decrease in the strength values of the
yarns. For this reason, they considered the heat- setting at 90C to be sufficient
to enhance the strength properties of PES/viscose yarns - consisting of 67% PES
and 33% viscose.
Yarn
conditioning machine does improve the CV of yarn and also it does not make it
worse. It is the fact that CV and neps of yarn detected by yarn evenness tester
is raised rapidly for yarn, just taken from the yarn conditioning machine.
However, leaving it for 24 hours, later the data will remain as before. The
reason is after processing, a part of water gets into the inner core of yarn
and becomes relatively steady crystal water, and water attached to the surface
of yarn becomes unsteady. The difference in each part of the surface water
would result in different dielectric coefficient, which makes the yarn evenness
tester give inaccurate results.
In
case of cotton fiber, absorption of moisture is delayed after processing in the
yarn conditioning machine. It is therefore, better to pack or use the yarn
after 30 minutes rest in the yarn stock room. This would allow enough time for
the surface water to evaporate and also to retain the same moisture level both
inside and outside of the yarn. The yarn that has been processed in the yarn
conditioning machine should not be mixed with the one which has not been
processed; otherwise, there will appear long and narrow shadow on the final
product after dyeing, especially for knitted fabric.
Major
applications of the yarn conditioning
In
spinning process yarn conditioning machine is used to adjust the moisture of
yarn and to improve efficiency in the next process. After processing, when the
moisture level of yarn would reach about 8.5 %, strength and elongation can be
increased greatly, which help the performance at processing line. The dealing
of cone yarn would improve the efficiency on winding, doubling and twisting and
also reduce the yarn hairiness. It will be also helpful to improve warping
efficiency and to reduce the defects from rewinding and warping. Owing to the
conformity of moisture of the yarn, the efficiency of sizing and weaving will
also improved ensuring the quality of the final fabric.
The
yarns after processing by yarn conditioning machine would improve the working
process as well as the quality of final fabric. Because of fixed twisting and
shaping of the yarn, it will give equal height of rising and looping, reduce
the unwinding tension, stable the structure and size of the end fabric and give
better appearance. Especially it is the key process for setting the seamless
underclothes. The process of conditioning will not only stabilize the twist,
but also fully relax the yarn to reduce the shrinkage of final product.
In
dyeing industry, processing after yarn conditioning machine can remove the
stress on grey fabric, which will be helpful for uniform absorption of dyes to
obtain bright color as well as uniform shade of the fabric. In garment
industry, yarn conditioning machine can make fabric with stable size, reducing
the shrinkage and improving the quality. Processing yarn, especially the
chemical fiber, in the conditioning machine can greatly improve the quality and
appreciation of product.
Conclusion
Textile
market is becoming sensitive buyer's market. Weaver is demanding dimensioned
quality with consistency from spinners. Therefore in order to satisfy these
demands without altering the raw material; the hygroscopic nature of cotton
fibers can be used. Therefore most of the spinning mills are now going for YCP.
These modern YCP gives us even penetration of steam into all the layers of
yarns on cone & ensures even conditioning effect throughout the package.
The yarn conditioning plant supply the yarn with increased strength &
elongations, that have reduced snarling of yarn, improved working at post
spinning processes like warping, weaving, knitting, etc. Yarn conditioning
reduces invisible loss to the spinners. Though its initial cost of investment
is high, but its payback period is very less.
This article was
originally published in the Textile Review magazine, January, 2013, published
by Saket Projects Limited, Ahmedabad.
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