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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Rotor spinning; Open-End Spinning

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Self twist spinning or Open-End Spinning 

Open-end spinning omits the step of forming the roving. Instead, a sliver of textile fibers is fed into the spinning machine spinner by a stream of air. The sliver is delivered to a rotary beater that separates the fibers into a thin stream. It is carried into the rotor by a current of air through a duct and is deposited in a V-shaped groove along the outer edge of the rotor. Twist is provided by the turning of the rotor. 

Fibers fed to the rotor are incorporated into the rapidly rotating “open end” of a previously formed yarn that extends out of the delivery tube; hence, the name open- end spinning. As the fibers join the yarn, which is constantly being pulled out of the delivery rube, twist from the movement of the rotor is conveyed to the fibers. A constant stream of new fibers enters the rotor, is distributed in the groove, and is removed at the end of the formed yarn, becoming part of the yarn itself. 

The fineness of the yarn is determined by the rate at which it is drawn out of the rotor relative to the rate at which fibers are being fed into the rotor. In other words, if fewer fibers are being fed in while fibers are being withdrawn rapidly, a thinner yarn will result, and vice versa. The twist is determined by the ratio of the rotor turning speed to the linear or withdrawal speed of the yarn (that is, the higher the speed of the rotor, the greater the twist). 

Theoretically, a variety of different means may be used to form the yarn and insert twist. These have been divided into the following categories: mechanical spinning (of which rotor spinning is an example), electrostatic spinning, fluid spinning, air spinning, and friction spinning. Of these, only rotor and friction open-end spinning machines have been commercialized and most of the open-end spinning machines now in use are of the mechanical rotor spinning type Friction open-end spinning machines are also available. 

Friction spinning systems use friction to insert twist. A mixture of air and fibers is fed to the surface of a moving, perforated drum. Suction holds the fibers against the surface while a second drum rotates in the opposite direction. Twist is inserted and the yarn begins forming as the fibers pass between the two drums. The newly forming yarn is added to the open end of an already formed yarn, and the completed yarn is continuously drawn away. 

The advantages of open-end spinning are that it increases the speed of production, eliminates the step of drawing out the roving before spinning, and permits finished yarns to be wound on any sized bobbin or spool. As a result, it is less expensive. It produces yarns of more even diameter than does ring spinning. Yarns are more uniform in diameter, bulkier, rougher, more absorbent, and less variable in strength than are ring-spun yarns. 

Fabrics made from open-end spun yarns compared with ring spun yarns are more uniform and more opaque in appearance, lower in strength, less likely to pill, and inferior in crease recovery. A number of sources indicated that they are more subject to abrasion. 

Neither friction nor rotor spinning will produce yarns as fine and strong as ring- spun yarns, although recent advances have extended the range of yarn sizes possible. Open-end spun yarns have a handle that has been characterized as “harsh.” Some of the kinds of products that seem to be especially well suited to the use of open-end spun yarns are in filling yarns for fabrics where yarn strength is not a factor, toweling pile yarns, denim, and heavier weights of bed sheeting. The yarns even surface makes them desirable as base fabrics for plastic-coated materials. On the other hand, the more acceptable feel of ring-spun yarns has led knitwear manufacturers to prefer them, and they are better for fine blends of polyester and cotton.

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