Natural fibres have been used since
thousands of years but there are not enough of them to meet the demands of
today’s world population . Therefore the
invention of synthetic fibres was undoubtedly one of the most important
discoveries of the twentieth century.
point is the competition in the textile sector. In order to satisfy new
demands of the customer, various improvements in the production technology
of filament yarns and their characteristics have been made and the filament
yarn industry has become more and more important.
article deals with the measurement of mass variations of filament yarns and
with the interpretation of test results. In spun yarns, yarn evenness is
inevitable because it arises from the fundamental nature of the fibres,
their manufacturing methods and the arrangement of fibres in the yarn. In
case of filament yarns, granulate heterogeneity, spinning process
irregularity, faults in subsequent yarn cooling and winding operations,
together with machine defects and drafting faults quickly lead to mass
variations which can affect the mass of the yarn over thousands of meters of
material, because the production speed is very high. Such variations often
cause difficulties in the subsequent processes like draw-twisting, texturing
or dyeing. These mass variations reduce the quality of the yarn, and a
comprehensive evenness testing is a must for a quality control system .
Technologies has been manufacturing textile testing systems for measuring
filament yarns since 1955. The USTER® TESTER 5-C800 for filament yarns was
introduced in the market as the 5th generation in 2005. The quality
characteristics of filament yarns can be quickly assessed by means of this
testing system. The test results can also be used to judge the consequences
on subsequent processes.
sources of faults in the melt spinning process
yarns can be manufactured according to different spinning methods. In Table
1 these methods are mentioned below.
1. Different spinning methods of filament yarns 
In this article we will concentrate on the melt
spinning process. Melt-spinning is described as the simplest method of
filament yarn manufacturing because it does not involve problems associated
with the use of solvents .
Many scientists have worked on the analyses of
melt spinning, both theoretically and experimentally[2,4,5,6,7] .The
spinning of synthetic fibres is sensitive to any variation of process
parameters, as for example, the temperature of the polymer melt or the
temperature of the quench air of the spinning unit. Particularly, the
conditions in the quenching zone influence the formation of a suitable
As we can see in Figure 1, in melt spinning there are
mainly three stages; hopper, spinning and wind-up.
In the hopper stage,
the raw material is stored, melted and then processed. The starting material
for melt-spinning is polymer granules or chips and they are first dried and
then melted in the extruder. Today in modern plants, polyester and polyamide
are produced in continuous polymerisation units in which the melt is
directly transported from the final polymeriser to the melt-spinning unit.
Polypropylene is different because polymerisation leads to a solid product.
For this reason it is separated from the spinning process.
spinning stage, every time the same amount of homogenised and filtered melt,
which is transferred from extruder to the spinning pumps, is pressed through
the orifices in the same amount of time. After the spinning heads, at a
distance of 5 to 20 cm below the orifices, in the quench air duct, the
filaments spun from the melt are cooled by a jet of air and freeze. When
using a multiple of orifices in the form of a spinneret, the bundle of
filaments can be drawn off as an undrawn or partially drawn filament
In the wind-up stage, after leaving the quench air duct, the
filament material is drawn over preparation rollers through an
oil-fat-emulsion (spin finish). The filament bundle, which has passed the
spin finish application, is wound on spinning packages and can be
transported in this state to other processing machines.
of faults during this spinning process will be illustrated by taking the
example of polyamide yarn manufacturing.
In Figure 1, the faults resulting
from certain machine groups as indicated with a “Circle” and a “Triangle”
can be determined with the help of the diagram, spectrogram, evenness value,
variance-length curve and relative count. The faults at machine groups which
are indicated with a “triangle” can also be determined with measurements
undertaken throughout one full package with the help of the diagram,
spectrogram, evenness value, variance-length curve and relative count.
The maximum mass deviations from the nominal value within the test length
can also be measured.
Evenness testing of filament yarns and USTER®
STATISTICS for filament yarns
As we have mentioned before, the quality
characteristics of filament yarns can be quickly determined by using USTER®
TESTER 5-C800 for filament yarns. The test results which are obtained from
this measuring system, can be evaluated both in graphical and numerical
The diagram is an important part of evenness test and provides an
enormous amount of details on the spinning process for a filament yarn
2 shows diagrams of two different filament yarns. The
lower filament yarn has a very high mass variation compared to the upper
The evenness of the yarn of the upper diagram in Figure 2 was CVm =
1,15%, the evenness of the lower diagram was CVm = 2,60%. The source of the
high mass variation of the lower diagram was a significant problem with the
air intensity and air guiding in the quench air duct which causes intensive
vibration during the solidification of the filament yarn.
of filament yarns
Table 2 shows a selection of the result columns of a
filament yarn test. Yarn: Polyester, dtex 76f100. The test was carried out
at 10 POY packages; test length was 1000 m per package. The value U% is the
evenness; the value CVm is the coefficient of variation of the yarn mass
while the measuring system was set to "Normal test". The values
CVm 1 m, 3 m, 10 m and 50 m represent the coefficient of variation of the
yarn mass of various “cut lengths”.
Table 2. Numeric results of a
filament yarn test
The column "Rel. Count" describes the relative
fineness of the yarn. The testing system calculates the mean of the yarn
fineness for the entire measuring series and always prints out zero as a
mean value. Afterwards, the system calculates the deviation of each
individual package relative to the mean. The basis for this calculation is
the capacitive measurement of the mass over the entire test length. The
columns mMin and mMax describe the maximum deviation from the mean value
during the tests.
The spectrogram as shown in Figure 3 is a
representation of mass variation in the frequency domain, ie, the measuring
system detects periodic mass variations. Figure 3 shows the spectrogram of
the polyester filament yarn, dtex 76f100, described in Table 2.
spectrogram taken from the USTER® TESTER 5-C800 shows a significant
periodic fault with a wavelength of 1.2 m, which was caused by an eccentric
spinning package during wind-up. The second severe quality problem is shown
in Figure 3 as an increase of the spectrogram between 10 and 80 m. Such mass
variations sometimes lead to misinterpretations if one only checks the
diagram because the variations look like strictly periodic faults in the
diagram. Only the spectrogram shows precisely what is happening. The origin
is a non-optimised air stream in the quench air duct (Figure 4) as already
The quenching zone of the spinning machine is very
important. A non-optimised air system in the quench air duct is one of the
most frequent sources of considerable mass variations of filament yarns.
Since the take-off of filament yarns takes place at very high speed, the
cooling process in the quench air duct has to be efficient. If the air
stream is not conducted properly the individual filaments start to vibrate.
Because the filaments are not solidified at this point of the manufacturing
process, the vibrations cause mass variations.
Figure 5 is the recording
of 10 spectrograms of the described filament yarn of 10 packages from the
same spinning machine. All the spectrograms show that the faults are common
to all packages.
Spectrograms of filament yarns frequently have many peaks,
which have to be interpreted correctly. Several peaks in the spectrogram do
not necessarily mean that there are several manufacturing problems. The
correct interpretation of the peaks, however, can provide detailed
information where manufacturing problems exist. In order to find the correct
origin of the manufacturing problem, the USTER® TESTER 5-C800 also has a
Knowledge Based System which simplifies the interpretation of the
Benchmarking for polyester and polyamide filament yarns
USTER® TESTER 5-C800 also supports the user with experience values which
can be used for benchmarking and evaluation. Figure 6 shows the USTER®
STATISTICS of polyester and polyamide filament yarn tests. It represents the
evaluation of mass variations of various packages. The coefficient of
variation depends on the fineness (dtex) of the individual filaments in the
filament bundle and on the amount of periodic and non-periodic mass
variations. Figure 6 can be used for partially oriented yarn as well as for
fully oriented yarn.
As a result of continuous improvements in
the filament yarn industry, the demand of reliable and reproducible test
methods for the filament yarn industry has also increased. Especially the
yarn evenness is still a very important quality parameter in the area of
filament yarns since small mass variations can already have a considerable
effect on the appearance of fabrics, particularly after dyeing. As it is
well-known, the evenness values of filament yarns can drop below CVm = 1%.
This means that even the smallest deviations can have an adverse effect on
the product quality in the subsequent processing. Uster Technologies began
to test the evenness of filament yarns at a very early stage. With the USTER®
TESTER 5-C800 for filament yarns, the quality characteristics of yarns can
be assessed quickly and worldwide compatibility of the same types of yarn
can be guaranteed. This is especially important because, in the
high-performance production of filament yarn spinning mills even a small
reduction in quality can result in disastrous financial losses.
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Manufactured Fibre Technology, Chapman & Hall, 2-6 Boundary Row, London,
First Edition, 1997.
3. Uster Technologies AG, Application Manual, Testing
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Synthetische Fasern: Herstellung, Maschinen und Apparate, Eigenschaften;
Handbuch für Anlagenplanung, Maschinenkonstruktion und Betrieb, Carl Hanser
Verlag, München, Wien, 1995.
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Relationship Between Spinning Temperature and Melt Viscosity of Precursor
Polymers, Journal of Materials Science, 36, 5565 – 5569, 2001.
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OH, et al: Numerical Simulation of the Melt Spinning of Hollow Fibres,
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Dr Serap Dönmez
Uster Technologies AG,