Production of filament yarn with man-made fibre by Emulsion spinning and Wet spinning

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In melt spinning the fiber polymer is melted and the molten solution is forced through the spinneret. As the soft filaments emerge from the spinneret into the cooler environment, they harden into a standard filament form. Melt spinning requires no chemical change & any kind in the polymeric material from which the fiber is formed. It does require that the fiber polymer can be melted without altering the chemical state of the material. Fibers formed by this process are Nylon, Polyester, and glass. 

Emulsion Spinning 

Emulsion spinning is not used to a great extent but it is important for selected types of specialty fibers. Some raw polymeric materials cannot be processed by wet/dry/melt methods, because they either breaks drown when heated to a melting temperature or are not soluble in solution that can be used. For these substances the emulsion process is necessary. 

The polymer dispersed or emulsified into a solution, the dispersion or emulsion is then forced through a spinneret, and as the emulsion leaves the spinneret, the polymer form into a fibrous shape. Depending on the type & fiber, the fibrous form produced by this method may be staple / filament length. Teflon is an example of a fiber spun by the emulsion process. First, polymers, whether natural or synthetic, must be converted into liquid form to be spun. This is done either by dissolving the polymer in a suitable solvent or by melting it. This polymer solution or polymer melt is sometimes referred to as the spinning dope. Cellulose, the raw material for most naturally derived manufactured fibers, is not easily dissolved. Accordingly, the cellulose polymer is usually modified before it is dissolved. Synthetic polymers are put together in the plant before the dissolution or melting step. 

Before actually forming the fiber, certain characteristics can be added to the polymer material. Many manufactured fibers are naturally bright, with a high luster. If dull or semi-dull fibers are wanted, delustering agents can be added to the molten polymer to break up light rays and decrease shine. Colored pigments, flame retardants, and compounds to absorb ultraviolet light can also be added. Occasionally substances are added during polymer synthesis so that they are incorporated into the polymer molecules themselves. 

Wet Spinning 

Wet-spun polymers are, like dry-spun polymers, converted into liquid form by dissolving them in a suitable solvent. The polymer solution is extruded through a jet into a liquid bath. The bath causes coagulation and precipitation of the fiber. Solvents are usually recovered from the liquid bath and are recycled. Viscose rayon and some acrylics are wet spun. 

It is possible to add special chemical reagents to the liquid bath that produce selected changes in the fiber. This is done in the manufacture of some high-strength rayons, for example; into a liquid bath. The bath causes coagulation and precipitation of the fiber. Solvents are usually recovered from the liquid bath and are recycled. Viscose rayon and some acrylics are wet spun. The polymer or substance to be used is making the fiber is dissolved into some type & solution, then is forced through the spinning jet into another liquid, which react with fiber solution the process involves one & the following reaction: 

(a) The fiber polymer may have been chemically changed in order to make it soluble in the solvent used when this occurs the fiber solution reacts with the receiving solution & reverses the chemical reaction so that the material is reformed into a fiber shape. The difference is that in reforming, a filament fiber shape has been made rather than a polymer in some other form, such as fibrous mass, chip or pellet. This process refers to the fiber solution as a derivation & the fiber form, the solution into which this passes is the coagulating bath & the actual process is typically called regeneration. 

(b) Wet-spinning may also be used when the fiber solution does not change the chemical form of the fiber. The solution is forced into a coagulating bath, which reduce the concentration of the fiber solution sufficiently to reform the fiber, this time in a filament form Fibers formed by wet spinning are rayon, acrylicA variant of wet spinning, called dry-jet wet spinning, has been developed to produce some of the newer fibers such as the aramid. Instead of the spinneret being immersed in the spinning bath, it is placed slightly above the bath so that there is a small air gap, usually less than an inch. The fibers exiting the spinneret can be stretched to orient the molecules before they enter the bath to be solidified. 

This process develops high orientation and crystallinity in one step, rather than drawing in a separate step Although melt-, dry-, and wet-spinning techniques are used to form the vast major-ity of manufactured fibers, several other spinning techniques also exist and may be applied in a limited number of specialized situations. High-molecular-weight poly-mers, such as those in Spectra@ polyethylene, are formed by solution spinning or gel spinning. As in wet and dry spinning, the polymer is dissolved in a solvent. The polymer and solvent together form a viscous gel that can be processed on conventional melt-spinning equipment to form a gel-like fiber strand. Later in the processing, the solvent is extracted and the fibers stretched. Fibers made from polymers that have extremely high melting points and are in-soluble present obvious difficulties in spinning. Such materials may be spun by a complex process called emulsion spinning in which small, fibrous polymers are formed into an emulsion, aligned by passing the emulsion through a capillary, then fused or sintered (combined by treating with heat without melting), passed through the spin-neret into a coagulating bath, and subsequently stretched

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Production of filament yarn with man-made fibre by Melt spinning and dry spinning

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Man Made Fiber Formation 

Man-made fibers are polymeric forms that are produced by some type of chemical which or by the regeneration & natural polymers in a new physical form. The polymer is connected into some type & liquid / fluid state and forced through a spinnerette. Although most spinnerette are made with round openings, some may use orifices & other shape is order to produce fiber with special characteristics. 

The basic steps in producing manufactured fibers are as; 

The liquid polymer is then extruded through a spinneret. Each spinneret has a number of holes, and each hole produces one filament. As they exit the spinneret the filament fibers are solidified by cooling of melted polymers, by evaporating the solvent, or by precipitating the polymer from solution. These methods of solidification are the bases of the three primary fiber manufacturing processes. Other spinning methods that have been developed are described later in this chapter. 

Filament yarns are described by denier (that is, size) and number of filaments; for example, filaments described as 70/34 represent 70 denier/34 filaments. When fibers being extruded are intended for conversion into staple lengths, spinnerets with larger numbers of holes are used to produce more filaments that are later cut into staple lengths. Spinneret holes are spaced to allow the filaments to be extruded without touching each other. The holes must be exactly the same size to produce uniform fibers. The metal used in the plate must be capable of withstanding high pressures or corrosive spinning solutions. 

Most fiber spinning processes include a final step of drawing in which the filaments are stretched around rollers. 

Melt Spinning 

Melt spinning take advantage of the thermoplastic characteristics of polymers. Chips of solid polymer about the size of rice grains are dropped from a hopper into a melter where heat converts the solid polymer into a viscous liquid. The liquid forms a “melt pool” that is pumped through filters to remove any impurities that, would clog the spinneret and is delivered to the spinneret at a carefully controlled rate of Row. Melt spinning is simpler and cheaper than other spinning methods; therefore, it is used except when polymers cannot be melt spun. 

The spinneret holes are usually round, but noncircular holes are also used to make filaments of various cross-sectional shapes. Melt-spun fibers may be made through Y-shaped holes that yield a three-lobed fiber or C-shaped holes to produce a hollow filament, for example; The diameter of the fiber is determined by the rate’ at which the polymer is supplied to the hole in the spinneret and the windup speed, not by the diameter of the hole. When the molten polymer emerges from the spinneret hole, a cool air current is passed over the fiber, causing it to harden. Failure to maintain constant feeding speed of molten polymer or changes in the temperature of cooling will cause irregularities in the diameter of the fiber. Nylon and polyester are the most common melt-spun fibers. One of the latest developments in melt spinning has been the significant increase in spinning speeds. Processing speed has increased from less than 1,000 meters per minute in the 1960s to over 7,000 meters per minute today. This is the equivalent of a car traveling over 250 miles per hour. Higher-speed spinning is cost-effective and up to a certain point increases the orientation of the polymers in the fibers. Beyond a speed of about 6500 meters per minute, however, this advantage disappears as there is not enough time for the polymers to crystallize and the fibers may break. 

Dry Spinning 

In dry spinning the fiber solution is forced through the spinneret into a warm air chamber. The warm air causes the solvent used to make the fiber solution evaporate & the filament fibers are formed & hardened. This process, too may involve converting the fiber polymer into a different chemical form that is soluble in a suitable liquid As the solvent evaporate, the fiber polymer is reconstituted & return to its original chemical form, but now it is in a filament shape. 

Many polymers are adversely affected by heat at or close to their melting temperatures. Polymers that cannot be melt spun undergo other methods of spinning, such as dry spinning, to produce filaments. Dry spinning requires the dissolving of the polymer in a solvent to convert it into liquid form. Substances used as solvents are chosen not only because they will dissolve the polymer but also because they are safe and can be reclaimed and reused. 

The polymer and solvent are extruded through a spinneret into a circulating current of hot gas that evaporates the solvent from the polymer and causes the filament to harden. The solvent is removed and recycled to be used again. Dry-spun filaments generally have an irregular cross section. Because the solvent evaporates first from the outside of the fiber, a hard surface skin of solid polymer forms. As the solvent evaporates from the inner part of the fiber, this skin “collapses” or folds to produce an irregular shape. If the rate of evaporation is slowed, the cross section of the filament will be more nearly round. Acetate fibers and some acrylic fibers are dry spun. 

 

Fibers formed are: acetate, triacetate, acrylic, modacrylic, aramid fibers. 

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Modern spinning method; Ultra Modern method of manufacturing yarn.

OTHER METHODS OF MANUFACTURING YARNS 

In addition to ring and open-end spinning, techniques that insert true twist into yarn, there are other types of yarn construction. Three of those that have some current commercial application are described in the following sections: false-twist, or self-twist, spinning; yarn wrapping; and splitting or slitting films made from synthetic polymers. The viability of these processes for commercial purposes varies. 

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Air-Jet Spinning 

Air Jet spinning is a ultra modern spinning or yarn manufacturing method The Murata Company, a Japanese firm, has commercialized an air-jet spinning machine that functions as follows. A largely untwisted sliver is fed into the machine. Two nozzles, each forcing an air jet against the sliver from opposite directions, cause fibers from the outer layer of the sliver to wrap around the interior fibers, thereby forming the yarn. 

Hollow Spindle Spinning 

Hollow spindle spinning is another modern yarn manufacturing process. In hollow spindle spinning, a sliver of core fibers is fed through a hollow spindle where it is wrapped by a filament yarn unwinding from the spindle. An interesting application of the technique has been in the manufacture of towels and other fabrics, in which the wrapped yarns are used in the pile. In this instance, the wrapping yarn is made from soluble polyvinyl alcohol (PVA) fibers. After the fabric has been put through the finishing processes, these yarns dissolve, leaving a soft, all-cotton twist less and absorbent yarn in the pile 

Core Spinning 

Core spinning is also a special spinning for yarn manufacturing. Core-spun yarns are usually made with a continuous filament core surrounded by twisted fibers or other yarns. Recently, core spun yarns with a staple core of one fiber and an outer sheath of another fiber have been produced by an adaptation of ring spinning. Two rovings, one of polyester and one of cotton, are fed through drafting rollers and then pass through separate channels before being wound on the spindle. The channel for the cotton sheath is longer, ensuring that it will wrap around the polyester core as the twist is inserted. Fabrics from staple core yarns are more durable and have more easy-care features than those of 100 percent cotton yarns. 

Making Yarns from Films 

Recently, various new techniques have emerged that allow yarns to be formed directly from synthetic polymers without the formation of fibers or the twisting of fibers into yarns. These processes include the formation of yarns by the split-film and slit-film processes. Slit-film yarns could be classified as monofilaments. Yarns made by the split-film process do not fit neatly into the categories of staple or filament yarns. 

Split Films 

In the creation of yarns by the split-film technique, a sheet of polymer is formed. The formed sheet is drawn in the lengthwise direction. Through drawing, the molecules in the polymer are oriented in the direction of the draw, causing the film to be strengthened in the lengthwise direction and weakened in the crosswise direction. This causes a breakdown of the film into a mass of interconnected fibers, most of which are aligned in the direction of the drawing, but some of which also connect in the crosswise direction. The process is known as fibrillation. 

The fibrillated materials can be twisted into strings or twines or other coarse, yarn like materials. The usefulness of split-film yarns is limited because the yarns created are coarse. Olefins are made into split-film yarns for use in making bags, sacks, ropes, and other industrial products. 

Slit Films 

Slit films are made by cutting film into narrow, ribbon like sections. Depending upon the process used for cutting and drawing the film, the tapes may display some degree of fibrillation, like that described for split films. When tapes are made that do not fibrillate, they are flatter and are more suitable for certain uses. Flat tapes are used as warp yarns in weaving and can be made into carpet backings that will be very stable, remaining flat and even. All types of tape yarns are used in making wall coverings, packaging materials, carpet backing, and as a replacement for jute in bags and sacks. 

Lurex@, a flat, ribbon like yarn with a metallic appearance, is a slit film yarn that is often used to add decorative touches to apparel or-household textiles. Lurex@ is made from single or multiple layers of polyester film. Multi-layered types are made by placing a layer of aluminum foil between two layers of polyester film. 

Monoply types are cut from metallized polyester film, protected by a clear or colored resin coating. The natural color of Lurex@ is silver. Other colors are produced by adding pigments to the lacquer coating or to the bonding adhesive. The width of these yarns ranges from 0.069 to 0.010 inch. 

Ply Yarns 

Ply yarns are made from two or more single yarns that are twisted together. Ply yarns are much more expensive than single yarns but are nevertheless often produced to achieve certain benefits. Ply yarns made from identical single yarns are more regular in diameter and are stronger. Ply yarns are often made to achieve particular decorative effects. 

In general, the steps involved in creating ply yarns include: 

1. Winding single yarns and clearing any flaws. 

2. Placing the required number of component yarns alongside each other, in place, ready for supplying to the machine 

3. Insertion of twist to form the ply yarn by any of a number of different machines 

4. Winding the finished yarn on a cone or package for delivery to the customer 

A number of different machines are used in making ply yarns, which may also be referred to as folded yarns. Ring-folding machines, for example, operate on the same principle as ringspinning machines except that instead of a roving being fed to the traveler, the single yarns to be combined are both fed together for twisting.

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Yarn construction; Basic yarn manufacturing process

YARN CONSTRUCTION 

Basic Yarn Manufacturing Processes:
Carding –– Combing –– drafting –– twisting –– winding. 

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As the fibers pass through these processes, they are successively formed into: lap, sliver, roving and finally yarn.
The manufacturing operation in which these stages occurred
(1)Lap to card sliver by the lading process
(2)Card Sliver to Cone sliver by combing process.
(3)Shiver to roving by the drafting, or drawing out process
(4)Roving to yarn by further drafting and twisting process.
(5)Yarn reeled on bobbins, spools or cones by the winding process. 

(1) Bending, Ending, Opening and Cleaning: 
(i) The cotton arrives at the mill in large bales weighing about 500 pounds / 225 kg. The compressed mass of raw fibers must be removed from the bales, blended, opened & cleaned.
(ii) Opening is necessary in order to loosen hard lumps of fibers & disentangle them.
(iii) Cleaning is required to remove trash – such as dirt, leaves, burrs, seeds, etc.
(iv) Blending is necessary to obtain uniformity of fiber quality.
(v) Blending: Mechanical bale pickers pluck thin, even layers of the matted fiber from each of a predetermined number of bales in turn and deposit them on Hooper. The fiber is mixed & passed to an opener.
(vi) Opening: As the mass of fiber passes through the openers, cylinders with protruding fingers open up the lumps & free the trash. The number & kind of cylinder, or beaters, employed depend upon the type of cotton that is being processed.
(vii) Cleaning: As the cotton is opened, trash falls through a series of grid bars. When the cotton emerges from the opener, it still contains small tuffs with about 2/3rd of trash.
(vii) This may be conveyed as a lap, which is loosely entangled mass about 1" thick and about 40" wide. Or it may be fed by chute directly to the card for further cleaning and fiber separation.

Blending

Opening and Cleaning

(2) Carding: 

(i) This is the process of arranging the fibers in a parallel fashion. This is necessary for all staple fibers; otherwise, it would be impossible to produce fine yarns from what is originally a tangled mass.
(ii) Before the raw stock can be made into yarn, the remaining impurities must be removed, the fibers must be disentangled, and they must be straightened.
(iii) The lap is passed through a beater section and drawn on a rapidly revolving cylinder covered with very fine hooks or wire brushes.
(iv) A moving belt of wire brushes slowly moves concentrically above this cylinder. As the cylinder rotate, the cotton is pulled by the cylinder through the small gap under the brushes, the teasing action remove the remaining trash, disentangles the fibers and arranges them in a relatively parallel manner in the form of a thin web.
(v) This web is drawn through a funnel – Shaped device that molds it into a round ropelike mass called the card sliver (about thickness of a broom stick).

Carding

(3) Combing: 
(i) In this operation, fine-toothed combs continue straightening the fibers until they are arranged with such high degree of parallelism that the short fibers called ‘noils’ are combed out and completely separated.
(ii) This procedure is not done when processing man-made staple fibers because they are cut into predetermined uniform length.
(iii) This operation eliminate, as much as 25% of the original card sliver, thus almost one-fourth of the raw cotton becomes waste.
(iv) The combing process forms a comb sliver made of the longest fibers, which, in then, produces a smoother & more even yarn. 

Combing

(4) Drafting / Drawing 

(i) The draw frame has several pairs of rollers, each advance set of which revolves at a progressively faster speed.
(ii) This action pulls the staple lengthwise over each other, thereby producing longer & thinner slivers.
(iii) After several stages of drawing out, the condensed sliver is taken to the slubber, where rollers similar to those in the drawing frame draw out the cotton further.
(iv) The slubbing is passed to the spindles, where it is given its first twist & is then wound on bobbins.

Drawing

(5) Roving: 
(i) Roving is the final product of several drawing out-operation.
(ii) These bobbins are placed on the roving frame, where further drawing out and twisting take place until the cotton stock is about the diameter of a pencil lead
(iii) To this point, only enough twist has been given the stock to hold the fibers together.
(iv) Roving has no tensile strength, it will break apart easily with any slight pull. 

Roving

(6) Spinning: 
(i) The ring spinning frame complete the manufacture of yarn
• By drawing out the roving
• By inserting twist
• By winding the yarn on bobbins.
(ii) Ring Spinning draws; twist s& winds in one continuous process. The traveler carries the yarn as it slides around the ring, thus inserting the twist.

Ring Spinning

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Ring Spinning 

The ring spinning could be defined, the process of manufacturing yarn with flying ring.

The ring spinner is made up of the following parts: 

Ring spinning 

1. Spools on which the roving is wound 

2. A series of drafting rollers through which the roving passes 

3. A guiding ring or eyelet 

4. A stationary ring around the spindle 

5. A traveler-a small, V-shaped clip on the ring 

6. A spindle 

7. A bobbin 

The roving is fed from the spool through the drafting rollers. The rollers elongate the roving, which passes through the eyelet, moving down and through the traveler. The traveler moves freely around the stationary ring. The spindle turns the bobbin at a constant speed. This turning of the bobbin and the movement of the traveler impart the twist to the yarn. The yarn is twisted and wound onto a bobbin in one operation. 

Bobbins must be removed from the machine when full. From here, bobbins are transported to a winding machine where yarn is wound onto packages. Automated systems for doffing and winding have been developed and are widely used. Winding is considered an important step. It provides an opportunity to condition yarn that is, to bring the yarn into equilibrium with the moisture in the atmosphere, and to add wax or other coatings that will facilitate weaving. Winding also allows the identification of flaws in the yarn and formation of larger yarn packages than the spindles on the ring spinning frame. 

1. The value and character of a yarn are determined by 

• Kind and quality of fibers 

• Amount of processing necessary to produce fineness. 

• Amount of twist, which increases tensile strength in the finished yarn. 

2. The purpose of the yarn must be anticipated, as this determines the number and kind & many manufacturing operations. 

3. The formation of yarn from staple fibers by shinning becomes possible when they have surfaces capable of cohesiveness. This quality is exemplified by the natural twist of the cotton fibers, which enables them to entwine around each other, the roughness of the linen fibers, which cause them to cling together, and the scale on the surface of the wool fibers, which cause them to graph each other. 

4. Flexibility permits the fibers to be twisted around one another. 

5. Uniformity & staple give yarn a required evenness & improve the quality. 

Yarn Twist due to ring spinning:

The amount of twist is an important factor in finished consumers’ goods. It determines the appearance as well as the durability and serviceability of a fabric. Fine yarns require more twist than coarse yarns. Warp yarns, which are used for the lengthwise threads in woven fabrics, are given more twist than are filling yarns, which are used for the crosswise threads. To retain the twist in the yarns and prevent any tendency to untwist or kink, the yarns are given a twist-setting finish with heat or moisture, depending upon the kind of fiber used. The direction of twist may be observed by holding the yarn in a vertical position. If the spirals conform to the direction of the slope of the central part of the letter S, the yarn has an S twist; if they conform to the slope of the letter Z, the yarn has a Z twist. 

Yarn Count maintain with ring spinning:

In the spinning process, there is always a fixed relation between the weight of the original quantity of fiber and the length of the yarn produced from that amount of raw material. 

This relation indicates the thickness of the yarn. It is determined by the extent of the drawing process and is designated by numbers, which are called the yarn count. 

The International Organization for Standardization (ISO) fixed relationship between the weight and length of all yarns: one tex equals 1 gram (g) per kilometer. The greater the weight, the thicker the yarn, and consequently the higher the tex number Because of the speed limitations in ring spinning, researchers concentrated on developing techniques for inserting twist into yarns that would permit more rapid production. A result of this search was the introduction, in the 1960s, of the open-end spinning machine, which operated at higher speeds but produced a yarn with slightly different characteristics than conventional ring-spun yarns with ring spinning.

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