•Regularity tests shows open-end
spun yarns to be more uniform than conventional yarns,
but they still fall far short of perfection.
•Detailed examination of open end spun yarns
reveals various defects, which may be attributed to
flaws in the fibres themselves, inclusions such as neps
& trash, irregularities in preparation, or the operation
of the rotor.
•Fibre defects stem from
inherent fibre properties.
•For example, highly
elastic fibres tend to contain poorly cut or over-length
fibres, which may interfere with drafting or cause
lapping of the carding roller, whereas brittle fibres,
such as acrylic fibres, are susceptible to fibre damage,
which results in an increase in short fibre & in
accumulation of dust & fibre debris within rotor.
•Fused fibre bundles cause disturbances inside
the rotor & lead to end-breakages.
•Dyes & fibre finishes can
form powdery or tacky deposits, which necessitate
frequent cleaning of the rotors if end-breaks are to be
avoided. The amount of crimp in man-made fibres can be
important.
•In the early days,
successful open-end spinning was only feasible if very
high quality standards were maintained in the sliver fed
•Partly owing to improvements in the
machine & partly owing to a better understanding
of the process, it has now been found possible
to relax these requirements to some extent.
•Investa recommend that
the sliver fed to the open-end spinner should conform to
the following criteria :
–It should contain no particles of trash
individually weighing over 0.15mg;
–The average weight of the particles of
trash that may be extracted by hand should not
exceed 0.10mg;
–The average weight of the particles of
trash that may be extracted by Shirley analyzer
should not exceed 0.025mg; &.
–The total weight of trash present should
not exceed 0.4%, i.e., 4mg/g of sliver.
•Unfortunately, few existing mills can meet such
requirements with existing blowroom machinery & cards,
so that it is often necessary in practice to accept
rather lower standards of sliver excellence.
•In such an event, the
main thing is to avoid hard impurities weighing more
than 0.15mg each. Neps can not be broken down in the
spinning unit & are normally extracted with the trash,
but fortunately some neps do become buried in yarn
during the formation of the ring by layering & are
therefore not seen in the yarn.
•In order to achieve satisfactory yarn
regularity, it is recommended that second-passage
drawframe sliver should be used & that the sliver should
be regular according to uster standards, e.g., not more
than 3 u% for a 3 ktex sliver.
•Defects that can be
attributed directly to the rotor system & to general
disorientation of the fibres.
•All the points mentioned
above affect the end breakage rate & thus the cost of
yarn manufacture.
Economic Aspects
•Whereas ring spinning
dominates in the range of ne 18-48 [13-33 tex] & for
finer yarns, rotor spinning covers in the range ne
6-20 [30-100tex].
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