Types of Woven Fabrics

Types of Woven Fabrics

Woven fabrics are classified as to weave or structure according to the manner in which warp and weft cross each other. The three fundamental weaves, of which others are variations, are the plain, twill, and satin. In plain weave, also known as calico, tabby, taffeta, or homespun weaves, the weft passes over alternate warp threads, requiring two harnesses only. The relatively simple construction suits it to cheap fabrics, heavy yarns, and printed designs. Variations are produced by the use of groups of yarns, as in basket weave and monk's cloth, or by alternating fine and coarse yarns to make ribbed and corded fabrics, as the warp-ribbed Bedford cord, piqué, and dimity and the weft-ribbed poplin, rep, and grosgrain. The second primary weave, twill, shows a diagonal design made by causing weft threads to interlace two to four warp threads, moving a step to right or left on each pick and capable of variations, such as herringbone and corkscrew designs. Noted for their firm, close weave, twill fabrics include gabardine, serge, drill, and denim. Satin weave has floating or overshot warp threads on the surface which reflect light, giving a characteristic luster. When the uncrossed threads are in the weft, the weave is called sateen.

Pile fabrics have an additional set of yarns drawn over wires to form loops, and may be cut or uncut. Warp-pile fabrics include terry and plush; weft-pile, velveteen and corduroy. In double-cloth weave two cloths are woven at once, each with its warp and filling threads, and combined by interlacing some yarns or by adding a fifth set. The cloth may be made for extra warmth or strength, to permit use of a cheaper back, or to produce a different pattern or weave on each surface, e.g., steamer rugs, heavy overcoating, and machine belting. Velvet is commonly woven as a double cloth. In swivel weaving, extra shuttles with a circular motion insert filling yarns to form simple decorations, such as the dots on swiss muslin. Figure weaves are made by causing warp and weft to intersect in varied groups. Simple geometric designs may be woven on machine looms by using a cam or a dobby attachment to operate the harnesses. For curves and large figures each heddle must be separately governed. The Jacquard loom attachment permits machine weaving of the most complicated designs.

Warp and weft in plain weaving

Weaving is a textile craft in which two distinct sets of yarns or threads are interlaced to form a fabric or cloth. The threads which run lengthways are called the warp and the threads which run across from side to side are the weft or filling.

Cloth is usually woven on a loom, a device that holds the warp threads in place while filling threads are woven through them. Weft is an old English word meaning "that which is woven".^[1] A fabric band which meets this definition of cloth (warp threads with a weft thread winding between) can also be made using other methods, inclluding tablet weaving, backstrap, or other techniques without looms.

The way the warp and filling threads interlace with each other is called the weave. The majority of woven products are created with one of three basic weaves: plain weave, satin weave, or twill. Woven cloth can be plain (in one colour or a simple pattern), or can be woven in decorative or artistic designs, including tapestries. Fabric in which the warp and/or weft is tie-dyed before weaving is called ikat.

Though traditional handweaving and spinning remain popular crafts, nowadays the majority of commercial fabrics in the West are woven on computer-controlled Jacquard looms. In the past, simpler fabrics were woven on dobby looms, while the Jacquard harness adaptation was reserved for more complex patterns. Some believe the efficiency of the Jacquard loom, with its Jacquard weaving process, makes it more economical for mills to use them to weave all of their fabrics, regardless of the complexity of the design.

Process and terminology

An Indian weaver preparing his warp

A woman weaving with a manual loom

In general, weaving involves the interlacing of two sets of threads at right angles to each other: the warp and the weft (older woof). The warp threads are held taut and in parallel order, typically by means of a loom, though some forms of weaving may use other methods. The loom is warped (or dressed) with the warp threads passing through heddles on two or more harnesses. The warp threads are moved up or down by the harnesses creating a space called the shed. The weft thread is wound onto spools called bobbins. The bobbins are placed in a shuttle that carries the weft thread through the shed.

The raising and lowering sequence of warp threads in various sequences gives rise to many possible weave structures:

• plain weave,
• twill weave,
• satin weave, and
• complex computer-generated interlacings.

Both warp and weft can be visible in the final product. By spacing the warp more closely, it can completely cover the weft that binds it, giving a warp faced textile such as rep weave. Conversely, if the warp is spread out, the weft can slide down and completely cover the warp, giving a weft faced textile, such as a tapestry or a Kilim rug. There are a variety of loom styles for hand weaving and tapestry. In tapestry, the image is created by placing various colors of weft only in certain warp areas, rather than across the entire warp width.

Ancient and traditional cultures

Prehistoric woven objects and weaving tools

Weaving in ancient Egypt

Women weaving. Detail from an Ancient Greek Attic black-figure epinetron, ca. 500 BC, from Athens. Louvre Museum, Paris.

There are some indications that weaving was already known in the Palaeolithic era. An indistinct textile impression has been found at Pavlov, Moravia. Neolithic textiles are well known from finds in pile dwellings in Switzerland. One extant fragment from the Neolithic was found in Fayum, at a site dated to about 5000 BCE. This fragment is woven at about 12 threads by 9 threads per cm in a plain weave. Flax was the predominant fibre in Egypt at this time and continued popularity in the Nile Valley, even after wool became the primary fibre used in other cultures around 2000 BCE. Another Ancient Egyptian item, known as the Badari dish, depicts a textile workshop. This item, catalogue number UC9547, is now housed at the Petrie Museum and dates to about 3600 BCE. Enslaved women worked as weavers during the Sumerian Era. They washed wool fibers in hot water and wood-ash soap and then dried them. Next, they beat out the dirt and carded the wool. The wool was then graded, bleached, and spun into a thread. The spinners pulled out fibers and twisted them together. This was done either by rolling fibers between palms or using a hooked stick. The thread was then placed on a wooden or bone spindle and rotated on a clay whorl, which operated like a flywheel.

The slaves then worked in three-woman teams on looms, where they stretched the threads, after which they passed threads over and under each other at perpendicular angles. The finished cloth was then taken to a fuller.

Easton's Bible Dictionary (1897) refers to numerous Biblical references to weaving in ancient times:

Weaving was an art practised in very early times (Ex 35:35). The Egyptians were specially skilled in it (Isa 19:9; Ezek 27:7), and some have regarded them as its inventors.

In the wilderness, the Hebrews practised weaving (Ex 26:1, 26:8; 28:4, 28:39; Lev 13:47). It is referred to subsequently as specially the women's work (2 Kings 23:7; Prov 31:13, 24). No mention of the loom is found in Scripture, but we read of the "shuttle" (Job 7:6), "the pin" of the beam (Judg 16:14), "the web" (13, 14), and "the beam" (1 Sam 17:7; 2 Sam 21:19). The rendering, "with pining sickness," in Isa. 38:12 (A.V.) should be, as in the Revised Version, "from the loom," or, as in the margin, "from the thrum." We read also of the "warp" and "woof" (Lev. 13:48, 49, 51–53, 58, 59), but the Revised Version margin has, instead of "warp," "woven or knitted stuff."

American Southwest

Weaving a traditional Navajo rug

Textile weaving, using cotton dyed with pigments, was a dominant craft among pre-contact tribes of the American southwest, including various Pueblo peoples, the Zuni, and the Ute tribes. The first Spaniards to visit the region wrote about seeing Navajo blankets. With the introduction of Navajo-Churro sheep, the resulting woolen products have become very well known. By the 18th century the Navajo had begun to import yarn with their favorite color, Bayeta red. Using an upright loom, the Navajos wove blankets worn as garments and then rugs after the 1880s for trade. Navajo traded for commercial wool, such as Germantown, imported from Pennsylvania. Under the influence of European-American settlers at trading posts, Navajos created new and distinct styles, including "Two Gray Hills" (predominantly black and white, with traditional patterns), "Teec Nos Pos" (colorful, with very extensive patterns), "Ganado" (founded by Don Lorenzo Hubbell), red dominated patterns with black and white, "Crystal" (founded by J. B. Moore), Oriental and Persian styles (almost always with natural dyes), "Wide Ruins," "Chinlee," banded geometric patterns, "Klagetoh," diamond type patterns, "Red Mesa" and bold diamond patterns. Many of these patterns exhibit a fourfold symmetry, which is thought to embody traditional ideas about harmony, or hózhó.

Amazonia

In Native Amazonia, densely woven palm-bast mosquito netting, or tents, were utilized by the Panoans, Tupí, Western Tucano, Yameo, Záparoans, and perhaps by the indigenous peoples of the central Huallaga River basin (Steward 1963:520). Aguaje palm-bast (Mauritia flexuosa, Mauritia minor, or swamp palm) and the frond spears of the Chambira palm (Astrocaryum chambira, A.munbaca, A.tucuma, also known as Cumare or Tucum) have been used for centuries by the Urarina of the Peruvian Amazon to make cordage, net-bags hammocks, and to weave fabric. Among the Urarina, the production of woven palm-fiber goods is imbued with varying degrees of an aesthetic attitude, which draws its authentication from referencing the Urarina’s primordial past. Urarina mythology attests to the centrality of weaving and its role in engendering Urarina society. The post-diluvial creation myth accords women’s weaving knowledge a pivotal role in Urarina social reproduction.^[2] Even though palm-fiber cloth is regularly removed from circulation through mortuary rites, Urarina palm-fiber wealth is neither completely inalienable, nor fungible since it is a fundamental medium for the expression of labor and exchange. The circulation of palm-fiber wealth stabilizes a host of social relationships, ranging from marriage and fictive kinship (compadrazco, spiritual compeership) to perpetuating relationships with the deceased.^[3]

Islamic world

Girls weaving a Persian rug, Hamadan, circa 1922. Note the design templates (called 'cartoons') at top of loom.

Hand weaving of Persian carpets and kilims has been an important element of the tribal crafts of many of the subregions of modern day Iran. Examples of carpet types are the Lavar Kerman carpet from Kerman and the Seraband rug from Arak.

An important innovation in weaving that was developed in the Muslim world during the Islamic Golden Age was the introduction of foot pedals to operate a loom. The first such devices appeared in Syria, Iran and Islamic parts of East Africa, where "the operator sat with his feet in a pit below a fairly low-slung loom." By 1177, it was further developed in Al-Andalus, where having the mechanism was "raised higher above the ground on a more substantial frame." This type of loom spread to the Christian parts of Spain and soon became popular all over medieval Europe.^{[4][not in citation given]}

Europe

Dark Age and Medieval Europe

Weighted-warp looms were commonplace in Europe until the development of more advanced looms around the 10th–11th centuries. Especially in colder climates, where a large floor loom would take up too much valuable floor space, the more primitive looms remained in use until the 20th Century to produce "homespun" cloth for individual family needs. The primary material woven in most of Europe was wool, though linen was also common, and imported silk thread was occasionally made into cloth. Both men and women were weavers, though the task often fell to the wife of a farming household. Fabric width was limited to the reach of the weaver, but was sufficient for the tunic-style garments worn in much of Europe at the time. A plain weave or twill was common, since professional weavers with skills to produce better fabrics were rare.

Weaving was a strictly local enterprise until later in the period, when larger weaving operations sprung up in places like Brugges, in Flanders. Within this setting, master weavers could improve their craft and pass skills along to apprentices. As the Middle Ages progressed, significant trade in fine cloth developed, and loom technology improved to allow very thin threads to be woven. Weaver's guilds (and associated craft guilds, like fullers) gained significant political and economic power in some of the bigger weaving cities.

In the medieval period, weaving was considered part of the set of seven mechanical arts.

Colonial America

Colonial America was heavily reliant on Great Britain for manufactured goods of all kinds. British policy was to encourage the production of raw materials in colonies. Weaving was not prohibited, but the export of British wool was. As a result many people wove cloth from locally produced fibers in Colonial America.

In Colonial times the colonists mostly used wool, cotton and flax (linen) for weaving, though hemp fiber could be made into serviceable canvas and heavy cloth also. They could get one cotton crop each fall, but until the invention of the cotton gin it was a labor-intensive process to separate the seeds from the cotton fiber. It generally took an entire year to produce cloth from raw materials, including processing, spinning, an weaving. Flax and hemp were harvested in the summer, and the stalks rendered for the long fibers within. Wool could be sheared up to twice yearly, depending on the breed of sheep. The relative ease of processing wool, and its durability, meant that a great proportion of weaving was wool cloth.

A plain weave was preferred in Colonial times, and the added skill and time required to make more complex weaves kept them from common use in the average household. Sometimes designs were woven into the fabric but most were added after weaving using wood block prints or embroidery. Leter, the use of multi-harness looms enabled color or texture patterns to be directly woven into the fabric.

Industrial Revolution

Main article: Textile manufacture during the Industrial Revolution

Before the Industrial Revolution, weaving was a manual craft, usually undertaken part-time by family craftspeople. Looms might be broad or narrow; broad looms were those too wide for the weaver to pass the shuttle through the shed, so that the weaver needed an assistant (often an apprentice). This ceased to be necessary after John Kay invented the flying shuttle in 1733, which also sped up the process of weaving.

Great Britain

Edmund Cartwright was the first to attempt to mechanise weaving from 1785. He built a factory at Doncaster and obtained a series of patents between 1785 and 1792. In 1788, his brother Major John Cartwight built Revolution Mill at Retford (named for the centenary of the Glorious Revolution. In 1791, he licensed his loom to the Grimshaw brothers of Manchester, but their Knott Mill burnt down the following year (possibly a case of arson). Edmund Cartwight was granted a reward of £10,000 by Parliament for his efforts in 1809.^[5] However, success in power-weaving also required improvements by others, including H. Horrocks of Stockport. Only during the two decades after about 1805, did power-weaving take hold. Textile manufacture was one of the leading sectors in the British Industrial Revolution, but weaving was a comparatively late sector to be mechanised. The loom became semi-automatic in 1842 with Kenworthy and Bulloughs Lancashire Loom. The various innovations took weaving from a home-based artisan activity (labour intensive and man-powered) to steam driven factories process. A large metal manufacturing industry grew to produce the looms, firms such as Howard & Bullough of Accrington, and Tweedales and Smalley and Platt Brothers. Most cotton weaving took place in weaving sheds, in small towns circling Greater Manchester and worsted weaving in West Yorkshire – men and women with weaving skills emigrated, and took the knowledge to their new homes in New England, in places like Pawtucket and Lowell.

The invention in France of the Jacquard loom in about 1803, enabled complicated patterned cloths to be woven, by using punched cards to determine which threads of coloured yarn should appear on the upper side of the cloth.

America, 1800–1900

Jacquard loom

The Jacquard loom attachment was perfected in 1801, and was becoming common in Europe by 1806. It came to the US in the early 1820s, some immigrant weavers bringing jacquard equipment with them, and spread west from New England. At first it was used with traditional human-powered looms. As a practical matter, previous looms were mostly limited to the production of simple geometric patterns. The jacquard allowed individual control of each warp thread, row by row without repeating, so very complex patterns were suddenly feasible. woven coverlets (bedspreads) became popular by mid-century, in some cases being custom-woven with the name of the customer embedded in the programmed pattern. Undyed cotton warp was usually combined with dyed wool weft.

Natural dyes were used until just before the American Civil War, when synthetic dyes began to come into use.

Weaving can also refer to a person such as weave hair styles. Weaving or the term "weaver" can also refer to ones last name.

INTRODUCTION TO YARN

Basic Textile Technology

YARN MANUFACTURING TECHNOLOGY

INTRODUCTION TO YARN

1.    what is yarn?

All fabrics- except plastics and non-woven’s- depend upon the use of yarns. A yarn is an assemblage of fibres that are laid or twisted together to form a continuous strand. Yarns may be made from either staple fibres or filament fibres. Staple fibres are twisted into yarns; filament fibres need little or no twist to hold them together in yarns. The type and length of fiber, the type, ply, and size of yarns, and the amount of twist given to yarns determine many of the characteristics of fabrics made from the yarns. For example, fabrics constructed of spun yarns are less smooth than fabrics constructed of filament yarns. They also have a lower luster. Cord or rib fabrics contain ply or larger yarns in the rib direction.

2.    single, ply and cord yarn

Single Yarns are made from single filaments or from group of staple or filament fibres twisted together to form the desired yarn. Monofilament, multifilament and spun yarns are all single yarns.

Ply Yarns are made by twisting together two or more single yarns. Each part of the yarn is called a ply. Most ply  yarns are twisted in the opposite direction to the twist of their component singles. Ply yarns are stronger than their equivalent single yarns of the same diameter and fibre.

 Cord Yarns are ply yarns twisted together. They are seldom used in conventional fabrics.

3.    carded yarn and combed yarn

Carded yarn: A yarn produced from fibres that have been carded but not combed.

Carding is a process, which eliminates fibers too short for inclusion in the spun yarn. The process also removes dirt and foreign matter still remaining in the fiber mass, and arranges the fibers into a very thin layer.

Combed yarn: Yarn produced from fibres that have been carded (or prepared) and combed.

The combing process is an additional step beyond carding. In this process the fibers are arranged in a highly parallel form, and additional short fibers are removed, producing high quality yarns with excellent strength, fineness, and uniformity.

4.    classification of yarn by fibre content

Yarns may be made entirely of one fibre (homogeneous) and be classified as such by the name of the fibre used. Or yarns may be a blend of two or more fibres the names of which are included in the description of the yarn. Yarns are blended to capitalize on the good qualities of a fibre and to minimize its weaker qualities by the combining of fibres that complement each other in the desirable characteristics they provide.

Blended yarns may be combined or blended in any of these ways:

•by mixing staples fibres before they are spun

•by combining filament fibres before adding twist

•by combining simple yarns of different fibre content into a ply yarn

A combination can also be achieved by blending two generically different polymers before they are spun.

Elastomeric fibre yarns are made from rubber or spandex fibres. They differ from stretch yarns that are made by texturising. Elastomeric yarns may be Covered, Core-spun or bare elastic yarns.

In addition, Metallic yarns, Fibrillated or Tape yarns are used in the textile industry.

5.    100% cotton, pc/tc, cvc & core yarn

100% Cotton: The yarn has 100% cotton fiber.

P/C or T/C :  (polyester/cotton or Terelyne/cotton): Yarn produced by blending cotton and polyester fibres

CVC: (Chief value cotton): A blended yarn having more percentage of cotton as compared to that of polyester. For example, Cotton : Polyester 70 : 30 or 60 : 40.

Core yarn: Yarn consisting of a central thread surrounded by staple fibres. The yarn has the strength and elongation of the central thread whilst exhibiting most of the other characteristics of the surface staple fibres.

Example 1: A sewing thread consisting of a central synthetic continuous-filament yarn surrounded by cotton fibres.

Example 2: Worsted yarn with bulked-nylon core, e.g., typically 1/24s worsted count (37 tex) with approximately 33% of nylon. These yarns are normally produced to give strength and elasticity to the fabric.

Example 3: A spun yarn from either natural or man-made fibres incorporating an elastomeric core, These yarns are normally used in stretch fabrics.

6.    yarn count and lot number

Yarn count: The 'count' of yarn is a numerical expression, which defines its fineness. Definition given by The Textile Institute says "Count: A number indicating the mass per unit length or the length per unit mass of yarn."

 There are two types of counting systems-

1.      Direct system: In a direct yarn counting system the yarn number or count is the weight of a unit length of yarn. Example: Tex, Denier.

2.      Indirect system: In an indirect system the yarn number or count is the number of 'units of length' per 'unit of weight'. Example: English count (N_e), Metric count (N_m).

Normally according to mill practice count stands for English count and can be defined as the number of hanks (1 hank = 840 yards) of yarn weighting 1 lb. The higher the count number the finer is the yarn. For example, 40 N_e means, 840 X 40 yards of this yarn will weigh 1 lb.

Tex is equal to the weight in grams of 1000 meters of yarn where as Denier is equal to the weight in grams of 9000 meters of yarn.

Yarn counts commonly used in BTL

YARN

Ratio

Available Count

100 % Cotton (carded & combed)

10/1

16/1

20/1

30/1

40/1

50/1

80/1

100/1

30/2

40/2

80/2

100/2

PC (Poly :Cotton)

70:30 60:40 65:35 80:20

12.5

20/1

30/1

16/1

45/1

Chief value  cotton (CVC)

70:30 65:35 80:20

30/1

38/1

45/1

26/2

Polyester/cotton core spun

32/2

16/1

Lycra core spun

16+ 70d

20+ 70d

30+ 70d

40+ 70d

Yarn Lot Number: This number is the Grey yarn lot number from Padma Textiles Limited. Yarn with different lot numbers is made from raw material of different sources. Yarn of same count but different lot numbers can have different inherent properties that can affect weaving and dyeing.

7.    yarn Twist & related terms

Yarn twist can be defined as the spiral turns given to a yarn to hold its constituent fibres or threads togather.

Twist in yarns brings the fibres closer together and makes them more compact. Twist is necessary in order to make yarns from staple fibres. In contrast, fabrics can be made from filament yarns, which have little or no twist.

 The amount or degree of twist is expressed by the intended end-use of the yarns or in a more technical way as the number of turns per inch, expressed as the tpi. As the degree of twist is increased, the yarns become harder, its lustre decreases, its strength increases up to a certain point of twist, and it becomes shorter in length. Yarns of very high twist are used to produce the crinkle in true crepe fabrics. Yarns of very low twist are used in fabrics to be napped.

There are only two directions of yarn twist - clockwise and counter clockwise. Either direction can be used. Counter-clockwise twist is known as "S" twist while clockwise is known as "Z" twist. The direction of twist also affects fabric characteristics and 'Z' twist is the standard twist used for yarns. 'S' twist is used for special purposes and also for ply yarns.

Twist factor; twist multiplier: In a yarn, the product of twist level and the square root of the linear density.

YARN MANUFACTURING

8.    basic principle of spun yarn spinning

The figure given below describes the essential stages in converting loose fibres into yarns.

The loose fibre A is brought by carding and combing into the form of a sliver B in which the fibres are fairly parallel and without twist. The sliver is then drawn and simultaneously lightly twisted to give it the necessary strength to give the finer roving C, and this is then finally spun into fine yarn D.

9.    different spinning systems

Spinning:

The present participle of the verb 'to spin' used verbally, adjectivally, or as a noun, meaning process or the processes used in the production of yarns or filaments.

The term may apply to:

(i)    The drafting and, where appropriate, the insertion of twist in natural or staple man-made fibres to form a yarn;

(ii)    The extrusion of filaments by spiders or silkworms; or

(iii)     The production of filaments from glass, metals, fibre-forming polymers or ceramics.

 In the spinning of man-made filaments, fibre-forming substances in the plastic or molten state, or in solution, are forced through the holes of a spinneret or die at a controlled rate. There are five general methods of spinning man-made filaments i.e. dispersion spinning, dry spinning, melt spinning, reaction spinning, and wet spinning, but combinations of these methods may be used.

In the bast and leaf-fibre industries, the terms 'wet spinning' and 'dry spinning' refer to the spinning of fibres into yarns in the wet state and in the dry state respectively.

Open-end spinning; break spinning:

A spinning system in which sliver feedstock is highly drafted, ideally to individual fibre state, and thus creates an open end or break in the fibre flow. The fibres are subsequently assembled on the end of a rotating yarn and twisted in. Various techniques are available for collecting and twisting the fibres into a yarn, the most noteworthy being rotor spinning and friction spinning.

Rotor spinning:

A method of open-end spinning which uses a rotor (a high-speed centrifuge) to collect  individual fibres into a yarn. The fibres on entering a rapidly rotating rotor are distributed around its circumference and temporarily held there by centrifugal force. The yarn is withdrawn from the rotor wall and, because of the rotation, twist is generated.

Friction spinning:

A method of open-end spinning which uses the external surface of two rotating rollers to collect and twist individual fibres into a yarn. At least one of the rollers is perforated so that air can be drawn through its surface to facilitate fibre collection. The twisting occurs near the nip of the rollers and, because of the relatively large difference between the yam and roller diameters, high yarn rotational speeds are achieved by the friction between the roller surface and the yarns.

Air-jet Spinning:

A system of staple-fibre spinning which utilizes air to apply the twisting couple to the yarn during its formation. The air is blown through small holes arranged tangentially to the yarn surface and this causes the yarn to rotate. The majority of systems using this technique produce fasciated yarns, but by using two air jets operating in opposing twist directions it is possible to produce yarns with more controlled properties but of more complex structure.

Centrifugal spinning:

A method of man-made fibre production in which the molten or dissolved polymer is thrown centrifugally in fibre form from the edge of a surface rotating at high speed.

The term is also used to describe a method of yarn formation involving a rotating cylindrical container, in which, the yarn passes down a central guide tube and is then carried by centrifugal force to the inside of a rotating cylindrical container.

Dispersion spinning:

A process in which the polymers that tend to an infusible, insoluble, and generally intractable character (e.g., polytetrafluoroethylene) are dispersed as fine particles in a carrier such as sodium alginate or sodium xanthate solutions. These permit extrusion into fibres, after which the dispersed polymer is caused to coalesce by a heating process, the carrier being removed either by heating or by a dissolving process.

Draw-spinning:

A process for spinning partially or highly oriented filaments in which the orientation is introduced prior to the first forwarding or collecting device.

Dry spinning (man-made fibre production):

The spinning process involving conversion of a dissolved polymer into filaments by extrusion and evaporation of the solvent from the extrudate.

Flash spinning:

A modification of the accepted dry-spinning method in which a solution of a polymer is extruded at a temperature well above the boiling point of the solvent such that on emerging from the spinneret evaporation occurs so rapidly that the individual filaments are disrupted into a highly fibrillar form.

Flyer spinning:

A spinning system in which yarn passes through a revolving flyer leg guide on to the package. The yarn is wound-on by making the flyer and spinning package rotate at slightly different speeds.

Melt spinning (man-made fibre production):

The spinning process involving conversion of a molten polymer into filaments by extrusion and subsequent cooling of the extrudate.

Reaction spinning (man-made-fibre production):

A process in which polymerization is achieved during the extrusion of reactants through a spinneret system.

Ring spinning:

A spinning system in which twist is inserted in a yarn by using a revolving traveller. The yarn is wound on since the rotational speed of the package is greater than that of the traveller.

Wet spinning (man-made-fibre production):

The spinning process involving conversion of a dissolved polymer into filaments by extrusion into a coagulating liquid.

The extrusion may be directly into the coagulating liquid or through a small air-gap. In the latter case it may be known as dry-jet wet spinning or air-gap wet spinning.

10. essential stages of conventional cotton spinning system

The conventional cotton spinning system essentially includes the following processing stages:

Blowroom (opning/cleaning): The bales of raw fibres are opened, cleaned and blended, then formed into laps.

Carding (and Combing): The laps of fibre are formed into fleece and then card slivers (rope-like strands). For higher grade and finer yarns, the combing process is continued with the removal of short fibres and neps.

Drawing: Several slivers are combined and drawn out into a longer, thinner strand, i.e. sliver.

Roving (for ring spinning): This process is to draw out the sliver into an even finer strand (roving) and twist it slightly.

Spinning: The roving is drawn out (drafted) into yarn with twist for strength and onto bobbins or tubes.

Twisting/ Winding: For plying two or more yarns together, and rewinding the yarn-bobbins onto cheese or cones.

11.  blending process and purpose

Blending:

A process or processes concerned primarily with efficient mixing of various lots of fibres. Blending is normally carried out to mix fibres, which may be of different physical properties, market values, or colours.

Process overview:

The long continuous filament fibers can't be used for blending because they're too long and too difficult to handle. Also, natural fibers, such as wool and cotton, with which many manufactured fibers are blended, are very short. Therefore, before blending, manufactured fibers are first cut into short fibers, called staple fibers. The staple fibers can more easily be twisted with the shorter natural fibers, or with staple fibers of another manufactured fiber.

Staple fibers are created by extruding many conitinuous filaments of specific denier from the spinneret and collecting them in a large bundle called a "tow". A tow may contain over a million continuous filaments. The tow bundle is then crimped, in much the same way a curling iron is used to crimp a woman's hair, and is then mechanically cut into staple fibers, usually ranging in length from 1 to 6-1/2 inches, depending how they are to be used.

Purposes of Blending:

Blending of different fibers is done to enhance the performance and improve the aesthetic qualities of the fabric. Fibers are selected and blended in certain proportions so the fabric will retain the best characteristics of each fiber. Blending can be done with either natural or manufactured fibers, in a variety of combinations and percentages.

For example, polyester is the most blended manufactured fiber. Polyester fiber is strong, resists shrinkage, stretching and wrinkles, is abrasion resistant and is easily washable. Blends of 50 to 65% polyester with cotton provides a minimum care fabric used in a variety of shirts, slacks, dresses, blouses, sportswear and many home fashion items A 50/50 polyester/acrylic blend is used for slacks, sportswear and dresses. And, blends of polyester (45 to 55%) and worsted wool creates a fabric which retains the beautiful drape and feel of 100% wool, while the polyester adds durability and resistance to wrinkles.

12. yarn texturing methods

Yarns used to create other than comparatively smooth textures in fabrics may be achieved by the following methods:

Modification in the spinning process of single yarns:

Various textures that results from modifications in the spinning process of simple yarns are identified by such terms as:

•Boucle yarn is one of the most widely used fancy yarns. It is characterized by an effect yarn forming tight loops that project from the body of the yarn at regular intervals.

•Slub yarns are made by varying the tension of yarn twist at regular intervals to produce soft, thick elongated low twist areas (slub).

•Snarl yarn is made by twisting at one time two or more yarns held at different tension. The effect yarn forms alternating unclosed loops along both sides of the core yarn.

•Spiral or Corkscrew yarn is made by twisting together two yarns of different thickness and twist, one soft and heavy and the other fine. The heavy yarn is fed faster than the fine yarn and winds around it in a spiral formation.

Modification of Thermoplastic filament yarns:

Variations in texture can be done by application of heat to the thermoplastic yarns by texturization or crimping. Texturization  is the process by which filaments are distorted to impart crimp, curl, coil and loop structures along their length to achieve bulk, stretch and absorbency.

In texturization process, untextured yarns are heated to plastic condition after it was distorted by texturing element (spindle, gear, knife etc.). Then they are cooled to retain the required shape. Textured yarns are basically three types:

•Bulk yarn - Mainly Gear crimping, Stuffer box and Air Jet methods are used to produce these yarns of increased bulk but minimum stretch. These processes can increase bulk from 100 to 300 percent. They are used as carpet yarns and in sweater fabrics. The resultant fabrics are usually soft with some degree of bulk and warmth but are light in weight.

•Stretch yarn - False twist and Edge crimping method is used to produce this type of yarns having 300 to 500 percent elongation. In the first method, the yarn is twisted, heat-set, and untwisted to get a coiled yarn. In the second method, the hot filaments are drawn over a knifelike edge, which flattens one side and causes the yarn to curl. They are used in swimsuits, lingerie, stockings, one-sized garments where a form-fitting resilience without pressure is required.

•Modified Stretch yarns - They are between the above two in stretch properties (about 10 to 15 percent). They are made in basically the same manner as stretch yarns except for a final step of heat-setting the yarn after the untwisting step.

Yarns made from Bicomponent Fibres:

Bicomponent fibres are composed of two different polymers joined physically in a single filament. The components can be joined side by side or in a sheath-core structure. Due to chemical differences of the components each shrinks to a different degree when exposed to certain conditions such as heat or moisture. The difference in shrinkage causes a pulling of the yarn into a crimped conformation creating bulk and texture.

YARN QUALITY CONTROL

13. yarn defects

Defects present in yarn can be classified in to five categories:

1)      Count variation: Variation in diameter along the length of yarn beyond acceptable range.

2)      Unevenness or irregularity: it is mass variation per unit length (cm). This fault is expressed as U% or CV% and evenness tester is used to measure it.

3)      Frequently occurring faults: These are the faults that occur in range of the 10 to 5000 times per 1000 m of yarn. Yarns spun from staple fibres contain imperfections, which can be subdivided into three groups:

Thin places: Cross sectional size -30% to -60% of normal yarn with fault length of 4 to 25 mm.

Thick places: Cross sectional size +30% to +100% of normal yarn with fault length of 4 to 25 mm.

Neps: Cross sectional size +140% to +400% of normal yarn with fault length of 1 mm. Neps are defined as small tight balls of entangled fibres on linear textile strands.

4)      Seldom occurring faults: These are the thick and thin places in yarn which occur so seldom that for their determination at least 100,000 m of yarn must be tested. This faults may be classified into the following classes:

A.     Short thick places: 1 to 8 cm and above +100%

B.     Long thick places: Above 8 cm and above +45%

C.     Long thin places: Above 8 cm and less than -30%

5)      Periodic faults: If any fault repeats after a certain length/time then the fault is called periodic or systematic fault.

6)      Hairiness: This is the measure for the protruding fibres from the yarn body.

7)      Lot mixing: Some times yarn lot can be mixed at the stages of spinning process as well as in the preparatory section of weaving/knitting mill. This type of mixing causes severe problem in subsequent processes.

14. important yarn tests for quality control

The important yarn tests are given below:

1)      Determination of Yarn Count

2)      Determination of Yarn Evenness

3)      Tensile Strength Testing

4)      Twist Testing

5)      Abrasion resistance

Determination of Yarn Count:

To determine the yarn count of a sample, it is needed to measure the length and weight of the sample. The equipment used for this purpose are Wrap reel and Analytical balance or Knowles balance or Quadrant balance etc. Beesley's balance can be used to get the yarn count directly from the balance. When yarn specimen supplied is not sufficient to perform the tests on the above methods, Beesley's balance can be used to examine the yarn count with reliability.

Determination of Yarn Evenness:

The surface irregularity of yarn is of particular importance in relation to processing properties, as even with a well maintained mean count, the appearance of the fabric can sometimes be affected considerably. Yarn evenness is assessed basically by deriving either the variation along the length of a yarn in the mass per unit length (or number of fibres per cross-section) or the variation in diameter. Visual evaluation and electronic methods are used for this purpose.

Tensile Strength Testing:

Particular importance is often attached to the tensile strength attained in a single or folded yarn of particular type and composition. Yarn extension also plays a considerable role in the processing of the yarn and in the end-use properties of the fabric produced.

The range of instruments which are available for testing the strength of yarns is quite wide e.g. Single -thread testers operating on the principles of pendulum lever, inclined plane, Strained gauge, and Constant-tension hank testers of the pendulum lever or Ballistic type. Some of these instruments are relatively simple, some complicated, some have recording devices, and some are automatic. The choice of the best type to use is often difficult. Strength testing deals with the finding of load-elongation curve or stress-strain curve and breaking point or stress etc.

Twist Testing:

Generally, the Twist tester is used to determine the number of twist per unit length or tpi manually.

Abrasion resistance:

Abrasion resistance is the ability of a fibre to withstand the rubbing or abrasion it gets in everyday use. This property of yarn plays an important part in its processing e.g. it determines the friction occurring on thread guides. A measurement of abrasion resistance is the number of cycles required to break the test specimen at a given initial tension.

15. classimat system & EYC

Classimat is a system, which can detect seldom-occurring faults of yarn. Yarn clearer that are used with automatic winders will detect only the large defects that may adversely effect the quality of finished products. In contrast, classimat system can evaluate all defects i.e. small defects as well as large ones in the yarn produced on spinning frames. Measurement should be made for more than 100 Km, 200 Km to 300 Km if possible, and their results must be calculated for every 100 Km.

Classimat defect classification:

Length classes: A: shorter than 1 cm B: 1 to 2 cm C: 2 to 4 cm D: 4 to 8 cm E: longer than 8 cm F and H: 8 to 32 cm G and I: longer than 32 cm Cross-section classes: 1.    +100% to +150% 2.    +150% to +250% 3.    +250% to 400% 4.    Over +400% E: Over +100% F and G: +45% to +100% H1 and I1: -30% to -45% H2 and I2: -45% to -75%

Fault Cross-sectional size

A4

B4

C4

D4

+400%

A3

B3

C3

D3

+250%

A2

B2

C2

D2

E

+150%

A1

B1

C1

D1

+100%

F

G

+45%

-30%

H1

I1

-45%

H2

I2

-75%

0.1

1

2

4

8

32

cm

Fault length

The Uster Classimat system thus evaluates 23 classes of various cross sectional size and length. Within each length class a cumulative counting is undertaken i.e. an indication of, for instance-

B1 = Sum of the counting in the classes B1 + B2 + B3 + B4

B2 = Sum of the counting in the classes B2 + B3 + B4

B3 = Sum of the counting in the classes B3 + B4

B4 = Sum of the counting in the class B4

The same is valid for the length classes A, C and D.

Furthermore, H1 = Sum of the counting in the classes H1 + H2

                  I1 = Sum of the counting in the classes I1 + I2

In this way, only with A4, B4, C4, D4, E, F, G, H2 and I2 will the faults be indicated which are actually counted in the respective classes. With other classes, the indicated fault figures refer to cumulative values.

With Classimat, the mean value is determined over a length approx. 150 m of yarn and this mean value serves as the reference point for the fault cross-sectional size. A fault is therefore classified in the cross-sectional class 3 if its cross-section oversteps the yarn mean value by 250% but has not reached the limit of +400%. (Refer to Annex 1)

The Electronic yarn clearer (EYC) can detect the fault length and cross-section of yarn passed through its channels and according to set ranges its clearer clears the yarn. Different channels and their set range are given below:

1.      Nep channel: Set for short very thick defect and set range is +100% to +500%

2.      S channel: Set for short thick defect and set range is +50% to +300%, 1 to 10 cm

3.      L channel: Set for long thick defect and set range is +10% to +200%, 10 to 200 cm

4.      T channel: Set for long thin defect and set range is -10% to -80%, 10 to 200 cm

5.      C channel: Set for delivery yarn count and set range is ±5% to ±80%, 12.8 m

6.      Splice channel: Set for splice quality