Textile Technology :: "Open End Spinning"

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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.

• •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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