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- •When
a new spinning process is implemented, the downstream
processes are nearly always affected. Accordingly, the
implications of rotor spinning have had to be examined not
only by the spinners but also by weavers , knitters &
finishers, because the yarn spun by the process differs in its
structure & properties from the familiar ring spun
yarn .
- •Studies
have been shown that , for a range of fabric types , rotor
spun yarns woven on sulzer machines give effectively as good a
performance as a ring-spun yarns.
- •Table
1 shows the results of comparative ends down tests. The woven
cloths from rotor spun yarns were easily results of
comparative ends down tests. The woven cloths from the rotor
spun yarns were easily distinguished by their more regular
appearance & better cover compared with the ring-spun yarn
fabrics. The rotor spun yarn fabrics were found to take up
about 10% more finishing liquor, which resulted in sharper
prints & colours that were somewhat fuller. Table 2 shows
the result of tests for fabric handle , cover , uniformity
& tensile strength on fabrics woven from rotor spun
& ring spun yarns.
- •Investigations
into the use of rotor spun yarns on air jet looms have
resulted in the following conclusions
-
- –There
is a 40% reduction in the warp-breakage rate per 10000
picks, with the weft-breakage rate remaining at a similar
level that for ring spun yarns;
- –There
is an improved quality in the grey & finished fabric
appearance; &.
- –Machine
speeds above 300rpm, with weft insertion rates from 900 to
1000 m/min., Can be attained with rotor-spun yarns,
without the need for accepting too high a stoppage rate.
- •The
improved running properties obtained with rotor spun yarns can
only be secured , however , through optimization in Warping
& Sizing.
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Warping
of OE Yarns
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- •In
carrying out comparisons between rotor-&-ring spun yarns, it
is important to take into account the value of a well prepared
package for the warping process .
- • The
yarn breaks during warping are often claimed to be as commonly
caused by spinning faults as by winding faults.
- • Spinning
faults are usually thick & thin places & slipped
Piecings, whereas the
winding faults are the result of undersized packages running
empty, loose ends & transfer tails tangling with running
yarn, & pattern zones causing tension breaks.
- • Tests
carried out on cotton rotor-spun yarns of a commonly spun count
of 56 tex, without rewinding or clearing, showed that a creeling
set of 590 packages.
- • i.e..,
A warp length of 37000 , gave breakage rate of 21.18 per 10000
km. Spinning faults accounted for 4.95 breaks per 10000 km, the
remainder being attributed to a poor build & to packages
running empty prematurely because of having insufficient length
to be warped is given in order to overcome premature emptying of
packages , the calculated length to be warped is given a
generous reserve, significant amount of yarn can be left on the
packages
- •Observations
have shown that in such situation
15-20 % of a full package can be left as a remnants.
Rewinding of the remnants to form new packages can be done, but,
because the yarn will experience extra work, its properties ,
eg. , Hairiness , can change sufficiently , albeit only slightly
, to cause fabric faults.
- •Thus
the remnant yarns should not be reused.
- •The
cost-effectiveness of the rotor spun yarn can therefore be
unfavorably altered.
- • It
is recommended that , as a measure for strict quality control,
rotor-spun yarns, should be rewound & cleared before
warping.
- •This,
however, may not be necessary if automatic piecing & doffing
procedures are incorporated in the rotor spinning line, provided
that the machines can also demonstrate good & consistent
package-building, i.e., In both package density &
anti-patterning.
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- •It
is well known that open-end-spun yarns have a lower tensile
strength than ring-spun yarns.
- • But,
depending on the yarn fineness , the strength of rotor-spun
yarns can be increased through sizing by 30-40 % , i.e., An
increase higher than that observed for conventional yarns.
- • This
effect is due to the different structure & the greater
bulkiness of rotor spun yarns.
- •The
sizing liquor penetrates even into the yarn core , & very
good results are obtained with modified starch sizes.
- • In
the sizing of open end spun yarns, the following factors must be
taken into account:-.
- –The
higher twist level of the yarn size;
- –Increased
bulk;
- –The
lower breaking strength;
- The difference in hairiness;
- –The
increased elongation.
- •These
factors will determine:
- –The
required concentration of sizing agents;
- –The
optimum tension during sizing; &.
- –The
optimum nip pressure.
- •The
concentration should be lower for rotor spun yarns than for ring
spun yarns because of the compact arrangement of the fibre in
the yarn cross-section & the difference in hairiness.
- • If
the same size concentrations were used, the add-on for the yarns
would be 20-25% higher, resulting from the larger number of
short & looped fibres projecting from the yarn.
- • Moreover,
because of the compactness of the yarn ,size penetration would
be different at this level of add-on , & an uneven coating
of the yarn surface would result.
- • End-breaks
would therefore occur because the size could not penetrate the
yarn to give the good flexibility required.
- • In
order to improve the sizing of rotor spun yarns, the nip
pressure should be increased & the size viscosity reduced.
- •The
recommended tensions, given as a percentage of the
rotor-spun-yarn breaking strength are: -.
- •In
zone 1 [from the bobbin to the nip roller in the size bath]
3-5% ;
- •In
zone 2 [from the second nip rollers to the first drying drum]
5 - 7 % ;
- •In
zone 3 [from the drying drum to the chain area] 8
– 10 %;
- •In
zone 4 [the warp beam]
18 – 20 % .
- •Rotor
spun yarns are sensitive to over drying, which happens when the
machine is switched to low speeds & can result in an
increase in breaks by 35-40%.
- •The
moisture content of the yarn should therefore be kept at 8.5-9%.
- •The
quality of sizing is best determined by comparing the strength
& extension of the sized & the unsized yarn.
- •In
one report, it is recommended that for the unsized yarn &
that the elongation should suffer no more than a 15% reduction;
Others have claimed up to a 20% reduction in elongation.
- •The
extension of the unsized yarn is important factor ; if this is
too low, then the sized yarn will be unsuitable for being woven.
- •In
a study involving the use of an shkv 140 sizing machine for
processing 25-tex cotton rotor-spun yarns, it was concluded that
the optimum running conditions were :
- –Sizing
speed : 80 m/min.;
- –Nip-roller
pressure: 1.5 atm.;
- –Tension
during warp beaming : 5-6 gf/yarn [49-59 mn/yarn];
- –Temperature
in size bath : 86 deg. Celsius.
- •The
above mentioned resulted in a drop in the number of loom breaks
from 0.26 to 0.12 break/metre.
- •Until
recently, the structures of all rotor spun yarns were regarded
as being more or less the same , & it was generally assumed
that these yarns absorbed 10% more size than ring spun yarns.
- • Experience
has shown that the structure of rotor spun yarns now produced
varies a great deal, depending on the type of machine &
spinning parameters used.
- • For
this reason, it can hardly be assumed that all currently
commercially available rotor-spun yarns, with their varying
structure, will take up size in the same manner & that, when
sized, these yarns will show a similar behaviour.
- • Difference
in the voluminosity of these sized yarns sufficiently noticeable
to have an influence on the appearance of the woven cloth.
- • It
is therefore inappropriate simply to regard rotor-spun yarn as a
standard product, as is the case with conventional ring-spun
yarns.
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