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Twisting

The two yarn ends comprising the splice are twisted around the body of the yarn, each yarn strand twists on the body of the yarn on either side of the middle of the splice. The cross-section of this region distinctly shows the fibres of the two yarn strands separately without any intermingling of the fibres.

Tucking / Intermingling

The middle portion of the splice is a region (2-5 mm) with no distinct order. The fibres from each yarn end intermingle in this splice zone just by tucking. The studies on quantitative contribution of splice elements showed that intermingling/tucking contributes the most to the strength of splice (52%), followed by twisting (33%) and wrapping (about 15%). The lower strength of the splice is attributed to the lower packing coefficient of the splice zone. Spliced yarn has a lower breaking elongation than normal yarn. Breaking elongation is mainly affected by intermingling. Wrapping and twisting provides mainly transverse forces. The absence of fibre migration gives lower breaking elongation to splice.

Effect of Variables on the Properties of the Spliced yarn

Several studies have been conducted on the effect of various variables on the properties of the spliced yarn.

Effect of Fibre Properties and Blend

Fibre properties such as torsional rigidity, breaking twist angle and coefficient of friction affect splice strength and appearance. The lower torsional rigidity and higher breaking twist angle permit better fibre intermingling. Higher coefficient of friction of fibres generates more inter-fibre friction to give a more cohesive yarn. Thus, these properties of fibre contribute to better retention of splice strength. In blended yarn, usually the addition of polyester to other fibre blend like P/W, P/C both for ring and rotor spun yarn increases splice strength.

 

Effect of Yarn Fineness

Several studies on cotton, polyester and wool report that coarser yarns have higher breaking strength but a moderate extension. The coarse yarn cross section contains more fibres and provides better fibre intermingling during pre-opening, hence the splice is stronger than  that of finer yarns.

Effect of Yarn Twist

An increase in the twist significantly increases the breaking load and elongation, even at higher pneumatic pressure. This could be due to better opening of the strands at higher pneumatic pressure. Splicing of twisted ply yarn is more complicated than single yarn due to the yarn structure having opposing twists in the single and doubled yarns. Twisted yarns also require a relatively longer time for complete opening of the yarn ends.

Effect of Different Spinning Methods

Yarn produced with different spinning methods exhibit different structure and properties. Therefore, these yarns show significant differences in splice quality. The ring spun yarn lent best splicing but the potential of splicing is affected by the spinning conditions. The breaking strength percentage of ring spliced yarns to a parent yarn is 70% to 85% for cotton yarn. However, the breaking strength and extension of splice vary with fibre and yarn properties. Rotor spun yarns, due to the presence of wrapper fibres, make it difficult to untwist and the disordered structure is less ideal for splicing. The breaking strength retention varies from 54% to 71% and is much lower compared to the splice of ring spun yarns. In case of friction spun yarns, the highest relative tensile strength obtained at the spliced joints can be above 80%, but a number of splicing failures occurs due to unfavourable yarn structure. The air-jet-spun (MJS) yarn and the cover spun yarn are virtually impossible to splice. Only very low tensile strengths and elongation values can be attained due to the inadequate opening of the yarn ends during preparation of the splicing. The coefficient of variation of these properties is also generally high.

 

Effect of Opening Pressure

A study on 50/50 polyester cotton, 25 tex ring spun yarn shows a rise in tensile strength up to a certain opening pressure. However, long opening time deteriorates the strength. An increase in pressure up to 5 bar caused release of fibre tufts and fibre loss from the yarn ends in P/C blend which is due to  intensive opening, but beyond this pressure, drafting and twisting in the opposite direction may also occur.

Effect of Splicing Duration

With a given splicing length, when the splicing is extended for a long period of time, the breaking strength of the spliced yarn and also their strength retention over the normal value of the basic yarn increases because of increased cohesive force resulting from an increased number of wrapping coils in a given length. The effects are more pronounced at higher splicing lengths. It is desirable however, that splicing duration be as short as possible. The splicing duration alone has no conclusive effect on elongation properties of splice yarn. It has also been observed that, for maximum splice strength, different materials require different durations of blast. These are between 0.5 to 1.8 seconds.

Effect of Splicing Length

Studies on splicing of flyer and wrap spun yarns spun with different materials, showed that regardless of the splicing material, the breaking strength and strength retention of both yarn types increase with the splicing length because of the increased binding length of the two yarn ends. Elongation at break and retention of elongation of both flyer and wrap spun spliced yarns increase with the splice length. Compared to the splicing duration, the splicing length has more pronounced effect on the load-elongation properties of the spliced yarn. It can be therefore be stated that the splices made on longer lengths and for longer period of time have more uniform strength.

Comparison of Dry and Wet Splicing

The comparative studies on dry and wet splicing with water showed that the breaking load retention for wet spliced yarns are significantly greater than dry spliced yarns. In fact, wet splicing is more effective for yarn made from long staple fibres and for coarse yarn. This may be due to higher packing coefficient resulting from wet splicing.

Effect of Splicing Chamber

The factors like method and mode of air supply and pressure along with type of prism affect the splicing quality. It was observed that irregular air pressure has advantages over constant pressure for better intermingling in the splicing chamber, which varies with different staple fibres, filament yarns, and yarns with S and Z twists. It is not possible to make a general comment regarding potential of the splicing chamber due to the multiplicity of factors influencing splicing.

Assessment of Yarn Splice Quality

The two important characteristics of a splice are appearance and strength. Although quality of splice can be assessed by methods like load-elongation, work of rupture, % increase in diameter and evaluation of its performance in down stream process etc., the appearance can be assessed either by simple visual assessment or by comparing with photograph of standard splice.

CHARACTERISTICS OF BOBBIN FORMATION:

  • Strectch length: It is the length of the yarn deposited on the bobbin tube during each chase (one  up and down movement of ringrail ) of ring rail. The length should be around 3.5 to 5 meters.  It should be shorter for coarser yarns and longer for fine yarns.
  • Winding ratio:It is the ratio of the length of yarn wound  during the upward movement of the ring rail and the length wound during  the downward movement of the ringrail.
  • Bobbin taper: The ratio of the length of the upper taper of the cop (bobbin with yarn) to the diameter of the bobbin must be 1:2 or greater.

WINDING SPEED: It depends upon the following factors

  • count
  • type of yarn, (type of fibre, average strength and minimum strength)
  • type and charactersitics of bobbin
  • package taper
  • final use of package

The best winding speed is the speed which allows the highest level of production possible for a given type of yarn and type of package, and with no damage whatsoever to the yarn.(abrasion and breaks due to excessive tension)

WINDING PRODUCTION: It depends upon the following factors

  • winding speed
  • time required by the machine to carry out one splicing operation
  • bobbin length  per bobbin( both bobbin weight and tpi to be considered, because TPI will affect the bobbin length). This decides the number of bobbin changes
  • the number of faults in the yarn and the clearer settings, this decides the clearer cuts
  • count
  • the number of doffs. It depends upon the doff weight. Higher the doff weight, lower the number of doffs
  • the time taken for each doff either by the doffer or by an operator
  • Down time due to red light.  It depends upon, number of red lights, number of repeaters  setting for red lights, clearer settings like off count channel, cluster setting which will result in red lights and others
  • bobbin rejections, it depends on weak yarn, wrong gaiting, double gaiting, bobbin characteritics etc.

WINDING PACKAGE DEFECTS: Following are some of the package defects which will result in complaints

  • Yarn waste in the cones. This is due to loose yarn ends that are wound on to the cone
  • Stitch, drop over, web:  Yarn is visible on the small or on the big side of the cone either across the side , around the tube, or going back in the cone
  • Damaged edges or broken ends on the cone: The yarn is broken on the edges or in the middle of the cone.
  • Ring formation:  The yarn runs in belt formation on to the  package, because it is misguided
  • Without transfer tail: The desired transfer tail is missing or too short
  • Ribbon formation: Pattern or ring formation are made by the drum when rpm are stying the same
  • Displaced yarn layers: yarn layers are disturbed and are sliding towards the small diameter of the cone
  • Misguided yarn : The yarn is not equally guided over the hole package
  • Cauliflower: On the smaller side of the package,  the yarn shows a wrinkle effect
  • Soft and Hard yarn layer:  Some layer of yarn are pushed out on the small side of the cone
  • Soft and Hard cones: Great difference in package density from one winder head to another

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