Yarn Formation Techniques
Major yarn manufacturing techniques and yarn defects
The Fibre formation process includes a change in shape, structure, and properties of the thermoplastic polymer. The polymer pellets or granules are fed into an extruder where, through heating, their melting temperature is exceeded. The polymeric melt is then transported, under pressure, to the spinneret. Yarn formation methods were originally developed for spinning of natural fibers including cotton, linen, wool and silk.
The thickness of yarn is measured as Counts. Yarns are made in different counts like 2’s, 4’s, 10’s, 16’s, 20’s, 24’s, 25’s, 30’s, 34’s, 36’s, 38’s, 40’s, 60’s, 80’s, 100’s, etc. We can consider like this. 0’s counts are cotton fiber. 20’s counts yarn is thicker than 24’s yarn. Likewise, 30’s yarn is thicker than 34’s. So when the yarn counts are increasing, the thickness becomes lesser. We can see, the higher the counts, the lesser the thickness.
Yarn prices based on the thickness. Price of 20’s yarn is lesser than 24’s. Price of 30’s yarn is lesser than 34’s yarn. We must know, higher the counts, higher the prices. There are 2 qualities of yarn. Combed and Carded.
Combed is superior quality. The cotton fibers are in different lengths from 0.25 inches to 2.5 inches. According to the technical parameters, the fibers with more length are considered to be better. These long fibers give more evenness and more strength for yarns.
Also, the short fibers are increasing hairiness whereas the long fibers are decreasing hairiness in yarns. Hence in order to get uniformity in fiber lengths, the short length fibers are to be eliminated from the long length fibers. For this purpose, a special process is being done. This process is called ‘Combing’. Because of the same longer length of fibers, the yarn will be very even with lesser hairiness. Hence after knitting or weaving, the fabric will have very even look.
The carded yarn is inferior in quality. As the above said ‘combing’ process is not being done, the carded yarn will be made of the fibers in different lengths. Hence the yarn strength will be lesser than combed yarn. Also, the carded yarn will have more hairiness and due to this, the fabric made with carded yarns will have more unevenness. Because of this extra process, the Combed yarn price is higher than Carded yarn. Also Combed yarn quality is superior to Carded yarn.
Mixing and Blending
Mixing: It is generally meant as the intermingling of different classes of fibers of the same grade e.g. USA Pima grade2, CIS
Blending: IT is meant as the intermingling of different kinds of fibers or different grade of same fibers e.g. polyester & cotton, Viscose &
Objectives of missing or blending
- Processing performance
- Functional properties
The yarn is a continuous strand which is made up of filaments or fibers. It is used to make fabric/textiles of different kinds.
Yarn formation methods were originally developed for spinning of natural fibers including cotton, linen, wool, and silk. Since the overall physical characteristics of the fibers and processing factors needed to differ from fiber to fiber, separate processing systems were developed. As synthetic fibers were introduced, synthetic spinning systems for texturized and untexturized cut staple were developed as modifications of existing staple systems, whereas spinning systems for texturized and untexturized filament were developed separately.
Grams per Square Metre (GSM)
GSM is the short form of Grams per Square Metre. GSM is the very most important thing which defines the weight of the fabrics of knit garments.
Garment price and quality based on many things like GSM, fabric quality, colors, finishing, prints, embroidery, style, etc. But GSM is the most important thing to be decided when confirming the prices between the sellers and buyers.
GSM is the weight of 1mtr x 1mtr fabric. It means 100cm x 100cm = 10,000 sq.cms. It can be found out by any one of the below ways.
By the weight of 100cm x 100cm fabric bit.
By the weight of 50cm x 50cm fabric bit multiplied by 4.
By the weight of 25cm x 25cm fabric bit multiplied by 16.
By the weight of 10cm x 10cm fabric bit multiplied by 100.
We must be aware that if we use the smaller size bit, accurate GSM cannot be achieved. The bigger size of fabric bit is better used to get exact or closer GSM.
If we have fabrics, then we don’t have any problem in finding GSM, as we can cut any dimension to find GSM. But most of the times, we will have only the garments to find GSM. And we will have to keep the garment style, making and other references.
So we will be allowed to cut a small bit from the garments. Hence nowadays, round cutters are used. This system is used worldwide. With the help of this round cutter, the fabric will be cut into small bits.
Then the GSM of the fabric can be found out by multiplying the weight of this round bit by 100. This round bit is to be weighed on an electronic scale with milligram accuracy. As this bit is very small and as the weight has to be multiplied by 100, the fabric has to be cut very sharply to get the exact GSM. Hence the blades of this round cutter are to be sharp and new to get the exact GSM.
- Primitive people discovered that a succession of short fibers could be twisted into a continuous yarn. This was probably accomplished slowly and laboriously at first.
- It was necessary to invent simple methods of disentangling, separating, and arranging the fibers according to their length, other than by just using the fingers.
- Thus, crude methods of carding were invented to separate the fibers according to their length of staple.
- Eventually, techniques were refined and long filament strands unwound from silk cocoons, and filaments formed by chemical synthesis were made into yarns.
- Now yarns are also made by integrating the staple and filament fibers.
Yarns are classified into two main categories
- Spun yarns are composed of relatively short lengths of fiber twisted or spun so that they hold together. The short lengths of fiber (measured in inches) are called staple fibers. Staple fibers are made into yarn by mechanical processes that first make the fibers more or less parallel, and then alternately pull and twist them. High twist is necessary to press the fibers together to give strength to the resulting yarn. It is important that staple fibers possess sufficient surface friction to adhere to each other.
- Filament yarns are composed of continuous strands of fiber that may be miles long. These yarns are produced directly from a spinnerette or from a silk cocoon. Because filament yarns, unlike spun yarns, contain fibers of infinite length, they do not need to be highly twisted. Most filament yarns are of low twist (enough to hold the fibers together) to provide a smooth, lustrous surface. Filament yarns may be tightly twisted, thus producing special effects such as crepe.
Conventional Ring Spinning
The value and character of yarn are determined by:
- Kind and quality of fiber
- Amount of processing necessary to produce fineness
- Amount of twist, which increases tensile strength in the finished yarn
- The purpose of the yarn must be anticipated, as this determines the number and kind of manufacturing operations.
- The formation of yarn from staple fibers by spinning 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 scales on the surfaces of the wool fibers which cause them to grasp each other.
The manufacturing operations in which these stages occur:
- Lap to card sliver by the carding process
- Card sliver to comb sliver by the combing process (if the fiber is to be combed)
- Sliver to roving by the drafting, or drawing-out, process
- Roving to the yarn by further drafting and twisting process
- Yarn reeled on bobbins, spools, or cones by the winding process
Stages in Conventional Ring Spinning
Chute Feed System
Chute feed is a system of feeding small tufts of cotton fibers directly from the blow room to a series of cards, arranged in a circuit through the pneumatic pipe.
A condenser in the pneumatic pipe sucks the material from the blow room and delivers it to the flock feeder through the pneumatic pipe by way of the filling trunk.
Blending, Opening, and Cleaning.
- The cotton arrives at the mill in large bales weighing about 500 pounds (225 kgs) each. The compressed mass of raw fiber must be removed from the bales, blended, opened, and cleaned.
- Blending is necessary so as to obtain uniformity of fiber quality; opening is necessary in order to loosen hard lumps of fiber and disentangle them; cleaning is required to remove trash – such as dirt, leaves, burrs, and any remaining seeds – in order to prepare the fiber for spinning into yarn.
- Mechanical bale pickers pluck thin, even layers of the matted fiber from each of a predetermined number of bales in turn and deposit them into the hopper.
- The fiber is mixed and passed to an opener. As the mass of fiber passes through the opener, cylinders with protruding fingers open up the lumps and tree the trash.
- The kind and number of cylinders, or beaters, employed depend upon the type of cotton that is being processed; the commonly used porcupine beater revolves about 1000 revolutions per minute. As the cotton is opened, trash falls through a series of grid bars.
- When the cotton emerges in front of the opener, it still contains small tufts with about two-thirds of the trash.
- It may be conveyed as a lap, which is a loosely entangled mass about 1 inch (2.5 cm) thick and about 40 inches (1m) wide, or it may be fed by chute directly to the card For further cleaning and fiber separation.
- 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.
- The straightening process puts the fibers into a somewhat parallel lengthwise alignment.
- This is necessary for all staple fibers otherwise, it would be impossible to produce fine yarns from what is originally a tangled mass.
- This initial process of arranging the fibers in a parallel fashion is known as carding. The work is done on a carding machine.
- The lap is passed through a beater section and drawn on a rapidly revolving cylinder covered with very fine hooks or wire brushes.
- A moving belt of wire brushes slowly moves concentrically above this cylinder. As the cylinder rotates, the cotton is pulled by the cylinder through the small gap under the brushes; the teasing action removes the remaining trash, disentangles the fibers, and arranges them in a relatively parallel manner in the form of a thin web.
- This web is drawn through a funnel-shaped device that molds it into a round ropelike mass called card sliver about the thickness of a broomstick.
- Card sliver produces carded yarns or carded cotton; serviceable for inexpensive cotton fabrics.
- After carding, several slivers are combined.
- This results in a relatively narrow lap of compactly placed staple fibers.
- The compactness of these fibers permits this cotton stock to be drawn out, to a sliver of the smaller diameter without falling apart.
- When the fiber is intended for fine yarns, the sliver is put through an additional straightening called combing.
- In this operation, fine-toothed combs continue straightening the fibers until they are arranged with such a high degree of parallelism that the short fibers, called noils, are combed out and completely separated from the longer fibers.
- The combing process forms a comb sliver made of the longest fibers, which, in turn, produces a smoother and more even yarn.
- This operation eliminates as much as 25 percent of the original card sliver; thus almost one-fourth of the raw cotton becomes waste.
- The combing process, therefore, is identified with consumers’ goods of better quality.
- Since long-staple yarns produce stronger, smoother, and more serviceable fabrics, quality cotton goods carry labels indicating that they are made from combed yams or combed cotton.
- The combining of several slivers for the drawing, or drafting, the process eliminates irregularities that would cause too much variation if the slivers were put through singly.
- The draw frame has several pairs of rollers, each advanced set of which revolves at a progressively faster speed. This action pulls the staple lengthwise over each other, thereby producing longer and thinner slivers.
- 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.
- Here the slubbing is passed to the spindles, where it is given its first twist and is then wound on bobbins.
- 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.
- There are two stages of roving: intermediate and fine.
- The operations are identical, but each machine yields a finer product than the stock it received. Roving is the final product of the several drawing-out operations.
- It is a preparatory stage for the final insertion of the twist. To this point, only enough twist has been given the stock to hold the fibers together.
- Roving has no tensile strength; it will break apart easily with any slight pull.
- The roving, on bobbins, is placed in the spinning frame, where it passes through several sets of rollers running at successively higher rates of speed and is finally drawn out to yarn of the size desired.
- Spinning machines are of two kinds – Ring Frame and Mule Frame.
- The ring frame is a faster process but produces a relatively coarse yarn. For very fine yarns, such as worsted, the mule frame is required because of its slow operation.
- The ring frame, which is in general use, is more suitable for the manufacture of cotton yarns for mass production.
- Its hundreds of spindles, whirling thousands of revolutions a minute, and its constant spinning action provide a fast operation.
The ring spinning frame completes the manufacture of yarn
- By drawing out the roving
- By inserting twist
- By winding the yarn on bobbins
The bobbins of yarn are removed for such processing as may be desired; for example, the yarn may be reeled into skeins for bleaching or may be wound on cheeses, or spools, for ultimate weaving.
Following are the few more spinning methods:
- Open End Spinning or Rotor Spinning
- Friction Spinning
- Self Twist Spinning
- Electrostatic Spinning
- Vortex Spinning
- Air-Jet Spinning
- Twistless Spinning
Open End Spinning
- A relatively recent development in the production of spun yarn is the open-end, or break, spinning process.
- This technique was developed in Czechoslovakia at the Cotton Research Institute in Usti nad Orlici during the 1960s.
- The technique has reached wide acceptance as a satisfactory process for spinning coarser yarns of counts of up to about 40 (14.8 tex).
- The open-end (O-E) spinning process begins with the carded sliver (combed sliver is not used), which is fed past a single-spiked roller or a succession of rollers, each advanced set of which revolves at a progressively faster speed, thereby completely opening up the sliver so that the fibers can be fed virtually individually into the spinning operation (this, in effect, breaks apart the sliver; hence, the terms “open-end” and “break”).
Open End Spinning Process
- As the fibers are separated, they are transported forward by an air stream and are collected as a thin layer in a groove on the inner surface of a funnel-shaped rotor, which rotates at a very high speed.
- The centrifugal force of the rotor builds up a multilayer of fibers which is peeled away from the collecting groove as it is simultaneously twisted by the rotation of the rotor and withdrawn continuously, thus being formed into yarn.
- The primary difference between conventional ring spinning and open-end spinning is that in the latter the spool does not need to be rotated in order to put a twist into the yarn.
- Also, much larger spools can be wound, thereby providing very long lengths of knot-free yarn and consequent reduction in handling the spools.
- The system also allows for greater automation in yarn production and therefore provides a greater production economy.
- Open-end spinning can produce yarn spun at a rate of 3 to 5 times that of the conventional ring spinning.
- While the open-end spinning process provides better fiber elongation, the resultant yarn is only as even as a good ringspun yarn, but not better.
- The yarn produced has excellent dyeability, particularly with bright shades. The system homogenizes blends very well, even better than ring spinning utilizing the same preparatory blending techniques.
- On the other hand, open-end spinning has its limitations. Problems arise in spinning yarns of 100 percent manmade staple (with the exception of rayon staple) on account of the fiber finish, which gets deposited in the rotor and causes clogging; and it is not possible to spin combed yarn.
- The yarn has a carded character and it has a rougher, sandier hand.
- The yarn counts are generally lower than 40 (14.8 tex), which limits their use to heavier, coarser fabrics, such as denim, towels, some poplins, and interlinings.
- Although open-end yarns are spun with 20 percent more twists, they are 15 to 20 percent weaker due to their coarseness.
- Also, the character of these yarns due to the twist formation is sufficiently different from that of ringspun yarns so that they cannot be mixed in manufacture.
- From the point of view of the manufacturer’s further concern, it is essential that the slivers be free of foreign matter in order to operate the open-end system effectively.
- The power requirements increase geometrically with the increase in spun yarn count. Also, the longer the staple, the larger the rotor must be, which in turn reduces the maximum turbine speed and thus the productivity.
- In the early 1970’s, Dr. Ernst Fehrer received an Austrian patent for a friction spinning process which was subsequently commercialized under the trademark DREF
- The system has since been modified and is identified as DREF II, a variation of the open-end Spinning process.
- The principle of the technique is that of passing along the longitudinal drum axis a stream of carded fibers in the roll nip of the perforated drums, both of which are moving in the same direction. This action forces the fibers to be wedged along with the nip, thereby becoming compressed; the friction of the rollers causes the fibers to twist around each other.
- The process utilizes a current of air to transport the carded fibers to the longitudinal nip region of the two drums. To improve parallelization, parallel orienting disks with fingers are used to align the fibers in the take-off direction of the yarn.
- The airstream gives the sliver end the initial twist as it presses the disentangled fibers against the continuously forming yarn compound wedged into the roll nip.
- Air suction through the perforated drums produces a uniform twist effect as the yarn is drawn off the end of the drums. The amount of twists may be controlled by regulating the suction. The yarn count is determined by the thickness of the wedge in the yarn-forming nip and the width (diameter) of the nip itself.
- There are certain advantages to the DREF II system. The fiber preparation costs are lower because the direct feed of card slivers to the spinning zone is possible.
- The high-speed elements required for ring and rotor spinning are eliminated. Yarn breakage during spinning is avoided because there is no tension in the spinning area. The process allows the use of a wide variety and quality of fibers that can be used independently or blended into the slivers.
- However, the yarns produced may lack uniform distribution of twists through the cross-section.
- The resultant yarns are bulky and have surface and mechanical properties similar to those of woolen yarns. They have low tensile strength. Improvements in the technique continue to be developed and there are a number of variations of this system.
- Also, by feeding a filament core yarn axially into the Center of the spinning zone, core-spun yarns can be produced.
Air Jet Spinning
- A further variation of spinning yarn with the aid of an airstream was developed in Japan and commercially introduced in 1981. It is a patented pneumatic process that produces yarn directly from high-quality drawing sliver of wool, manmade staple, or manmade and cotton staple blends.
- This air-jet spinning technique drafts the sliver to a predetermined size and passes it through rollers over a friction plate (to prevent back twists) into a cylindrical pneumatic twisting chamber.
- As compressed air is released from jets set in the walls of the chamber at predetermined angles to the central axis of the tube, the fibers are whirled around each other.
- Special rings and specific grooves within the tube are used to loosen the fibers from the sides and to control the twist and strength parameters of the forming yarn.
- As the fibers are whirled through the first chamber, they are given either an S or Z twist. With the aid of air suction, the strand is passed into a second chamber where it is first stabilized and then given an equal amount of twist in the opposite direction.
- The strand is again stabilized to prevent back twist as delivery rolls draw off the yarn which is wound onto a take-up package.
- The air-jet spinning produces yarn of uniform diameter without thick or thin areas. However, it has a somewhat harsh hand. Yarn can be produced in counts equal to or somewhat finer than those made by open-end spinning.
- Although the tensile strength of air-jet spun yarn has been reported to be less than that of ring-spun yarn, it may be greater than that of open-end yarn.
- It weaves and knits well, but performance and durability in the fabric remain to be fully determined.
Woollen & Worsted Spinning System
Mainly used for wool and similar fibers.
Basically designed for long-staple fibers.
Three main stages
- Sliver or slubbing formation – involves disentanglement and individualization of the fibers, mixing and blending, removal of vegetable matter, and formation of a sliver; all occurring at the card
- Preparation for spinning – involves fiber alignment, evening by doubling, drafting, and removal of short fibers, neps, and other impurities; carried out at gilling, combing, and drawing.
- Yarn spinning – final attenuation/drafting and twisting to impart strength
Three routes or systems:
- Woollen System
- Worsted System
- Semi-worsted System
With the advent of manmade fibers, it became possible to produce endless, fine strands of fiber.
These filaments are produced by different methods, and they can be formed directly into yarn without the use of techniques to connect fibers together to form the required lengths.
- The first commercially successful method for the manufacture of manmade fiber was the wet spinning of the cellulosic fiber, rayon.
- The process involves the use of an appropriate liquid solution which is pumped through a small nozzle, which is called a spinnerette, into a chemical bath that coagulates the extruded solution of endless strands of filaments.
- These coagulated continuous fibers are drawn out of the bath, purified by washing, dried, and then wound onto spools.
- The construction of the spinnerette may be varied according to the desired results. lf the spinnerette has one extrusion hole, then the monoﬁlament yarn will be produced. If the spinnerette has many holes, then a multifilament yarn will be produced. The size and number of the holes of the spinnerette may be varied.
- The process involves the use of an appropriate liquid solution which is pumped through a spinnerette into an air chamber.
- The air reacts with the extruded streams causing them to solidify.
- These coagulated continuous fibers are then drawn out of the chamber, twisted and/or processed further, and then wound onto spools.
- As in the case of wet spinning, monofilament or multifilament can be produced, and the diameter of the yarn will depend upon the number and size of the spinnerette holes.
- Polymer chips obtained from previously reacted chemical combinations are melted and then pumped through a spinnerette into an air chamber.
- The extruded streams cool and solidify into continuous filaments and are then drawn out of the chamber, twisted and/or processed further, and subsequently wound onto spools.
- Monofilament and multifilament yarns of various diameters can be produced as is done with the other extruded filaments.