Yarn Requirements For Knitting PDF

Knitting Technology  Introduction ►The yarn characteristics have a major influence on the performance of knitting as well as on the appearance of finished fabric. ► Improvements in the performance of knitting industry demand improvements in the knitting machines as well a...

Knitting Technology  Introduction ►The yarn characteristics have a major influence on the performance of knitting as well as on the appearance of finished fabric. ► Improvements in the performance of knitting industry demand improvements in the knitting machines as well as optimisation of yarn properties.  Introduction ►Various hosiery yarns are manufactured using the range of fibres available to suit different end uses. ►Majority of the knitted products are made from cotton yarn.  Yarn Count & Machine Gauge ►The yarn count to be used on the circular knitting machine depends mainly upon pitch or machine gauge. ►For any given machine gauge it can lie within a larger range, because on the same machine different yarn count can be used, depending on the knitted structure, the desired fabric appearance and the fabric properties.  Yarn Count & Machine Gauge Machine Gauge Relanit Single Fleecy Fine Rib Interlock Jacquard Needles/inch Ne Jersey Ne Ne Ne Ne 08 ** 7/2-14/2 ** 19.0/2-12 ** ** 10 ** 9.5/2-8.5 ** 12.0-18.0 16.5/2-12 14/2-18/2 12 ** 10.5/2-10 2.5-9.5 14.0-20.0 21.5/2-14 20/2-23/2 14 ** 14.0/2-12 3.5-12.0 16.5-23.5 12.0-16.5 13.0-18.0 16 ** 12.0-19.0 6.0-16.5 23.5-35.5 16.5-21.5 16.5-21.5 18 10.5-23.5 14.0-23.5 7.0-18.0 29.5-47.5 21.5-23.5 18.0-23.5 20 14.0-.0 18.0-.0 8.5-20.0 41.5-53.0 23.5-29.5 21.5-.0 22 16.5-29.5 21.5-29.5 10.5-23.5 47.5-59.0 28.5-35.5 23.5-28.5 24 19.0-35.5 23.5-35.5 14.0-.0 53.0-71.0 33.0-41.5.0-33.0 21.5-41.5.0-41.5 16.5-29.5 ** 35.5-47.5 ** 28 23.5-47.5 29.5-47.5 19.0-35.5 ** 41.5-53.0 ** 30 29.5-59.0 35.5-59.0 21.5-41.5 ** 47.5-59.0 **  Yarn Count & Machine Gauge Fiber Machine Gauge (Needles /Inch) 10 12 14 15 16 18 20 22-24 28-32 40-42 Wool 640 500 420 300 250 250 200 Yarn count in dTex Cotton 300 280 235 220 194 150 125 63 Polyester 280 235 190 140 140 140 122 95 50 Polyamide 400 350 250 150 150 125 125 100 76 33 Acrylic 300 235 200 200 200 167 150 Yarn count in dTex  Knitting Demands of Yarn ►The following are the important yarn quality requirements (given in the order of importance) for efficient running on knitting: High work of rupture value Substantial elongation at break Low flexural, torsional and initial stretch resistance Good resiliency Knitting Demands of Yarn Reasonable tenacity and loop strength Resistance to fatigue due to cyclic stress and strain Regularity of physical characteristics such as twist, evenness, moisture content Smooth and low frictional yarn properties.  Knitting Yarn ►The practice in the industry in assessment of hosiery yarn quality is on the lines with the established norms for weaving or for general understanding of yarn grade rather than anything specific to knitting, except waxing.  Knitting Yarn ►The purchase of yarn is based on the general parameters like count, U%, imperfections, strength and elongation and TPM. ►Most of the knitters in SMEs test only the count for setting the GSM of the fabric.  Twist ►Twist in hosiery yarn should be less. ►Still in few cases, yarn of higher twist being preferred on the ground that it performs well in knitting in terms of lesser yarn breakages. ►That is true but the benefit is at the cost of fabric quality.  Twist ►Unlike woven fabrics, knit structures are formed by bending the yarn into a loop and then interlacing them to create a fabric. ►The curvature of loop would be smooth and well defined if the bulkiness of the yarn is higher.  Twist ►The bulkiness eliminates sharp bending and improves resiliency of the structure, these fabrics are expected to stretch easily and recover during use. ►The very purpose of using low twist yarn is to achieve this smooth curvature to loops and high resiliency to fabric.  Uniformity ►For obtaining smooth curvature to loop and its uniformity the yarn should be uniform in thickness and imperfections should be minimum.  Uniformity ►The thin place in yarn receives more twist resulting in compact structure i.e. high torsional rigidity or sharp bends in loop while thick place receives less twist and forms a large curvature at loop.  Uniformity ►This variation in bending, twisting and surface friction can vary tension in yarn during loop formation. This would result in shift of loop forming point in knitting zone leading to variation in loop dimension. ►The shape of loop, obviously, has changed.  Coefficient of Friction ► Waxing to cotton hosiery yarns is common. ►A great improvement in quality of wax and there by the reduction in coefficient of yarn friction.  Flexural Rigidity ►Flexural rigidity is the resistance of the yarn to bending. ►Formation of loop involves torsional, flexural and tensile deformations.  Tenacity & Breaking Extension ►Tenacity is specific stress at rupture and expressed as cN/Tex. ►Breaking Extension is the extension registered at the highest strength  Tenacity ►The strength of the yarn must be sufficient to resist tensile strain occurring while knitting on the machine. ►It must also contribute to the required stability of the fabric.  Tenacity ►In staple fiber yarns the strength is mainly proportional to the level of twist inserted. ► Higher twist lead to harder or firmer yarns. ►This is not desired in knitwear, which one requires a soft twisted yarn. ►A constant compromise is therefore always required.  Breaking Extension ►Extension in yarn is necessary, so that it can resist bending strains or neutralise them by getting extended in such a way that it does not break. ►The extension of staple yarn is inversely proportional to their twist level. ►Compared to filament yarns, the extension of staple fiber yarns considerably lower.  Yarn Hairiness ►Excessive yarn hairiness causes excessive yarn friction between yarn and metal, which hinders proper loop formation and particularly with cotton yarn, generates lots of fly. ►It spoils the fabric appearance and causes excessive pilling ► It also gives the improper dyeing.  Elasticity ►Elasticity is often confused with extension or extensibility of a yarn or a fabric. ►In order to prevent, or keep a permanent yarn deformation within acceptable tolerance while producing a circular knit fabric, the yarn should not be strained beyond its elastic limits.  Summary ► In contrast to weaving the yarn strength of knitting yarn is secondary, as the loading placed on the yarn during knitting is lower than weaving. ►However, the yarn must exhibits enough elongation and elasticity. ►There must be no weak places or thick places that can result in stop holes in knitted material, or even break needles.  Summary ►Particularly important is the low friction value because of which yarn will pass easily through the various guide elements of the machine.  Summary ►The moisture content of the yarn should be evenly distributed. ►In most cases, a constant and high hairiness value with a low twist is required in order to achieve a soft handle fabric handle. Knitting Demands of Yarn  Warp Knitting Yarns ►The two main types of yarn are supplied to the Warp Kitting machine in warp sheet form are Continuous filament yarn Staple fiber yarns Includes the fancy yarns or Yarn made from blends of fibers.  Filament Yarns ►Continuous filaments yarns are very popular in Warp knitting for various reasons.. Filament yarns being regular and uniform, can easily pass through the knitting elements which are precision set closely.  Filament Yarns As the speed of knitting is high, the rate of lint formation will also be high because of yarn to metal friction. Lint is the big problem in knitting as it will obstruct the free running of the yarn through knitting elements. Filament yarns do not form lints which are common in staple fiber yarns.  Filament Yarns Mechanical properties such as tenacity, elasticity, flexural rigidity, bending modulus are more uniform in continuous filament yarn than staple fiber yarns. Uniform continuity, knot free yarn and pliability of continuous filament yarn affords easy lapping and loop formation actions.  Filament Yarns ► The filament yarn properties are depends on Yarn denier Number of filament & denier of individual filament twist surface characteristics like friction & Mechanical properties like tenacity, elongation at break, work of rupture, bending, flexural & torsional rigidity  Filament Yarns ►Flexural and torsional rigidity of yarns is proportional to the fourth power of the yarn diameter and the yarn diameter is depends on the yarn denier. ►Thus the mechanical properties of the filament yarns is depends on the denier.  Filament Yarns ►The yarn diameter is also depends on the specific gravity and the shape factor of the material which change with the type of synthetic material used.  Filament Yarns ►The number of filaments and the denier of each filament also affects the warp knitting performance. ►The diameter of 30 denier monofilament is much larger than that of the multifilament yarn having 10 filaments each of three denier.  Filament Yarns ►At the same time, a multifilament strand up to certain deniers, is much more flexible and pliable than the monofilament of equivalent denier. ►In order to reduce the rigidities to low value, the yarn strand is assembled from a large number of low denier filament.  Filament Yarns ►Nylon yarns consisting of 7 and 8 filaments are suitable for outerwear fabrics, 10 to 13 filaments being suitable for underwear fabrics while 34 filaments yarns give suppleness to the fabric along with good moisture absorbing capacity with excellent opacity and subdued lusture.  Filament Yarns ►Twist is an important variable in yarn which affects the quality and working of knitting. ►In warp knitting, the twist of continuous filament yarns ranges between 0 – 7 tpi. ►For special crepe yarns it may be reach a high value of 50 – 60.  Filament Yarns ►Twist also effects the tenacity and the elastic properties of yarn. ► Tenacity increases with increase in twist. ►The finer the yarn, the greater is the twist required to bring tenacity to its peak level. ►Higher the twist, greater the elongation for a given load.  Filament Yarns ►Twist also affects the denier and diameter of filament due to the shrinkage taking place as the angle of helix increases.  Filament Yarns ► Some of the other effects of twists are: Twist reduces the frictional drag of yarn, the greater the twist the lower the coefficient of friction and hence less drag on yarn. twist affects the diameter of yarn which decreases to a level when compact and cylindrical yarn is obtained.  Filament Yarns twist reduces absorption and dye uptake of yarn and fabric. twist changes the air permeability of the fabric. it has dulling effect on yarn the greater the twist, greater is the diffusing effect and less lusture.  Filament Yarns ►It is better to have twistless filament in knitting for certain end properties, like feel, hand and drape. ►It is also common practice to use some kind of lubricant like wax or oil during warp preparation. ►Excessive amount of Waxing or oiling may increases the coefficient of friction. ► Normally 0.5 – 2% waxing is recommended.  Filament Yarns ► Lubrication is mainly done to Achieve better cohesion among the strand of filaments. Reduce the drag or friction of the yarn Enhance the yarn pliability Dissipate static charges.  Staple Fiber Yarns ►Staple yarns are used to a very limited extent in tricot knitting. ►However, it is used to a greater extent in raschel trade. ►Only good cottons with proper twist and gassed and lubricated can be used for tricot knitting.  Important Yarn Properties For Warp Knitting ► Work of rupture Should be high ► Elongation Should be good ► Tenacity Minimum value should be determined by requirements of the wrapping process.  Important Yarn Properties For Warp Knitting ► Bending and Flexural Rigidity Should be low ► Torsional Rigidity Should be low ►Resiliency Greater the resiliency the more resistance to rupture.  Wrapping ►Wrapping is a method of producing vertically- orientated patterning with warp threads on a single jersey weft knitted base structure. ►Specially controlled warp thread guides are used which make unidirectional warp knitted overlaps into selected needle hooks.  Wrapping ► If selected empty needle hooks rise to receive the warp yarn (as is the case on a few single jersey machines), pure wrapping or warp insertion is produced. ►If, however, wrapping takes place on needles, all of which already hold a ground yarn at that knitting cycle, embroidery plating or wrap striping is produced.