Post Spinning Processes
- •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
- –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.
Warping of OE Yarns
- •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.
Sizing of OE Yarns
- •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
- –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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