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6 Rieter . LINK 52 . 1 /2008
TECHNOLOGY
Maximum work load vs. twist factor and raw material
viscose 1.3 dtex, 38 mm, C 60 80 kg, R 40 rotor 33 mm XT-5B, 115 000 rpm, Ne 30.
Maximum work load [cN*cm]
900
850
800
750
700
96 98 100 102 104 106 108 110 112
Mima 1 Mima 2 nano 4 nano 4
Fig. 3 Maximum work
load vs. twist factor
and raw material,
viscose 1.3 dtex, 38
mm, C 60 80 kg, R 40
rotor 33 mm XT-5B,
115 000 rpm, Ne 30.
Twist factor
SPV
Asian
viscose
The main technology elements and setting levels in
this case are the draw-off nozzle, the twist factor and
the type of rotor. There is a wide diversity of draw-off
nozzles on the market, but in the absence of systematic
studies, i.e. due to the effort involved, only few
precise recommendations for processing viscose fibers
exist. The draw-off nozzles customarily used for
viscose, plus those in the process of development,
were therefore compared in this study.
The latest version of draw-off nozzles Mima1 and
Mima2 produces the cleanest yarn and thus also the
highest yarn regularity with optimal drawframe sliver
feeding. These results were confirmed irrespective
of viscose type, rotor speed, rotor diameter and twist
factor. Yarn cleanliness when processing viscose can
be improved by up to 50% through the influence of
the draw-off nozzle, depending on rotor speed. The
twist factor has virtually no impact on yarn cleanliness
in the αm 100-110 range. Yarn cleanliness is
primarily influenced by the type of draw-off nozzle
and viscose.
Given raw material
However, with a given raw material it must be borne
in mind that compromises will also have to be made
in the choice of draw-off nozzle due to other important
criteria. The best yarn values achievable with
a given draw-off nozzle are of little use if disadvantages
in running properties and thus economics result
for customers.
Due to the fiber properties, higher yarn tenacity
cannot be achieved by increasing yarn twist with
both types of viscose and rotor spinning technology.
A twist factor of αm 105 can therefore be recommended
with regard to the strength and hand of
the textile fabric. The draw-off nozzles can influence
yarn tenacity up to an absolute figure of 0.7 cN/tex.
As was to be expected, yarn elongation is also higher
in SPV viscose due to the higher fiber elongation
at break.
Maximum work load
Maximum work load in the yarn differs between the
two types of viscose. SPV viscose displays approx.
10% higher Maximum work load under otherwise
equal conditions, such as:
• number of fibers in the cross-section
• yarn count
• final spinning process
• spinning elements
• settings
Higher maximum work load in the yarn will also be of
advantage at high spinning tensions caused by high
rotor speeds (Fig. 3).
Twist factor, draw-off nozzle and raw material have
a significant influence on hairiness levels. SPV viscose
displayed better fiber integration compared
with the Asian viscose, taking the draw-off nozzles
into account. Lower hairiness, i.e. greater fiber integration
in the yarn bundle, can have a positive impact
on yarn tenacity, yarn elongation or Maximum
work load. Depending on the sphere of application
in downstream yarn processing, lower hairiness has
a positive impact on pilling behavior and fiber abrasion.