Yarn manufacturing

1.1 Yarn

It is an assembly of substantial length and relatively small cross-section of fibres and or / filaments with or without twist. Yarn occurs in the following forms [1]:

1. A number of fibres twisted together;

2. A number of filaments laid together without twist (a zero-twist yarn);

3. A number of filaments laid together with a degree of twist;

4. A single filament with or without twist (a monofilament); or

5. A narrow strip of material, such as paper, plastic film, or metal foil, with or without twist, intended for use in a textile construction.

1.2 Spun Yarn

The yarn which consists of staple fibres held together by twist is known as spun yarn. The yarns produced on ring spinning, open end rotor spinning and air jet spinning systems, all are the spun yarns.

1.3 Yarn Number

The number which shows the fineness or coarseness of yarn is called yarn number. There are two systems of yarn numbering.

1. Direct system

2. Indirect system

In direct system, yarn number is called the linear density of yarn with units of tex, denier and dtex, etc. Similarly, in the indirect system yarn number is called the yarn count with units of N_EC, Nm and N woollen, etc.

Following is the detailed explanation of these two systems:

1. Indirect system

It is used for the measurement of length per unit weight of the yarn. In this system, weight is kept constant while length is variable.

In the indirect system, yarn thickness and yarn number are inversely proportional. This means that as the yarn count increases the yarn weight decreases and hence yarn becomes finer.

The indirect system is also known as English system of counting. The most commonly used indirect numbering systems are

1. English Cotton Nec=No.ofhankslbs

2. Metric system Nm=KmKg

3. Worsted N=No.ofhankslbs

Different hank lengths for different fibres are given in Table 1

1. Direct system

It is used for the measurement of linear density that is the weight per unit length of yarn. In this system yarn length is kept constant and weight is variable.

In the direct system, yarn thickness and yarn number are directly proportional. The most widely used direct numbering systems are:

1. Tex (Tex = No. of grams/1000 m)

2. Grex (Grex = No. of grams/10,000 m)

3. Denier (Denier = No. of grams/9000 m)

2.1 Lap

A sheet of fibres wrapped around a rod / or roller to facilitate transfer from one process to the other is called lap [2]. Output of Scutcher and Lap former are the examples of lap. Width of lap produced by lap former is about one third of the scutcher lap so it is called mini lap.

2.2 Sliver

The assemblage of loose, roughly parallel fibres in continuous form without twist is called sliver [2]. Outputs of card and drawing are the examples of sliver.

2.3 Roving

A name given, individually or collectively, to the relatively fine fibrous strands used in the later or final processes of preparation for spinning is roving [2]. Output of roving frame which is used as input for Ring frame is the example of roving.

3.1 Preparation of Cotton to Feed the Blow Room

After opening the strips of selected bale / bales and cleaning the sides, small tufts from the bales are taken and spread on the floor selected area for making the layers of heap, as shown in Figure 1. A number of horizontal layer upon layers are made till the end of bales. This heap of cotton is left for 24 hours to release the packing pressure and condition the material so that moisture in the material becomes homogeneous.

Fig. 1

Heap of opened cotton.

3.2 Blow Room

Blow room line consists of different machines and each manufacturer provides its own line of machines. The sequence of machines in a typical blow room line is shown in the Fig. 2.

Fig. 2

Ohara blow room line.

Objectives of a blow room line are as follows:

1. Opening: To open the compressed fibres up to very small tufts

2. Cleaning: To remove the impurities like seed fragments, stem pieces, leaf particles, neps, short fibres, dust and sand

3. Mixing and blending: To make homogenous mixture of the material

4. De-dusting: To extract the dust if present

5. Uniform feed for card: To convert the mass of fibres into thick sheet called lap which should be uniform length and width wise or to provide output in the form of tufts of optimum size

Following is the blow room operation summary:

Cotton is fed manually on the feed belt of the blending feeder. The opening, cleaning and blending is carried out by the inclined lattice and evener roller. The stripper roller transports this material to the feed lattice of fine opener-I. Fig. 3 shows the material flow through the blending feeder machine. The beater of fine opener-I beats it against the grid bars for cleaning. This material is sucked by a condenser transport fan through two rollers cleaner, which performs the opening, cleaning and dust extraction of cotton.

Fig. 3

Material flow through blending feeder (1) Feed Table, (2) Internal Feed Lattice, (3) Light Barriers, (4) Baffle Plate, (5) Brush Rolls, (6) Spiked Lattice, (7) Cleaner Roller, (8) Evener Roller, (9) Stripper Roller.

The cage of the condenser separates the dusty air from the material and delivers it on the control tower feed rollers. A beater in the control tower beats the material against the grid bars and transfers to the spiked rollers of super cleaner. The six spiked rollers of super cleaner perform the opening and cleaning of material and deliver it to the feed lattice of fine opener-II. Where a Krishnor beater with steel pins further reduce the tuft size and help in cleaning.

The opened and cleaned material from the fine opener-II is sucked by cage condenser fan and then it is delivered to the control tower. At the bottom of the control tower the material is fed to a beater with the help of a pair of feed rollers. The beater treats the material against the grid bars for cleaning and transfers to the feed lattice of the Hopper feeder. A spiked lattice and an evener roller in the Hopper feeder perform the operation of blending, opening and cleaning. A stripper roller delivers the material to the feed lattice of the scutcher through a condensing box.

The Scutcher consists of a regulating feed unit, pin beater, lap forming cage, calendering unit and lap winding unit. The incoming feeding material in the form of a bulky sheet is checked length-wise and width-wise by a regulating feeding system. Thus a uniform amount of material is fed to the beater. The beater further opens and cleans the material and delivers it to the cage, which makes a lap sheet. The calender rollers compact this lap sheet while shell rollers wind it on a lap rod. Thus a compact roll of lap sheet is delivered by the scutcher, which is transferred manually on a trolley to the next machine called the card.

In the latest blow room lines, the material from fine opners / cleaners is transferred to the card directly by a fan through a chute feed system which is attached at the back of the card. Fig. 4 shows the latest blow room line in which the scutcher is excluded and fine cleaner delivery pipes are directly connected to the cards.

Fig. 4

Latest blow room line.

3.3 Card

The objectives of carding process are:

1. Opening up to individual fibres

2. Elimination of impurities

3. Disentanglement of neps

4. Elimination of dust

5. Elimination of short fibres

6. Fibre blending

7. Fibre orientation or alignment

8. Sliver formation

Following is the operation summary to achieve the tasks of card:

Lap prepared from the blow room is placed on the lap roller. Flow of material through the lap feed card is shown in Fig. 5 while chute feed card in Fig. 6. Feed roller with the help of feed plate delivers it to the taker-in. The taker-in opens and cleans the cotton by dragging it on the mote knives and carding elements. Then this cleaned material in the form of tiny tufts and single fibres is transferred to the cylinder. Cylinder further cleans the cotton and converts it into individual fibre state with the help of stationary and movable flats. At this stage, neps are disentangled and short fibres are separated from cotton. A fan sucks all the waste as well as dirt and dust from the whole machine and collects them in a box.

Fig. 5

Material flow through revolving flat card.

Fig. 6

Material flow through chute feed card (1) Conveying duct, (2) Feed chute, (3) Feed Roller, (4) Card Feed, (5) Taker-In, (6) Knife Grid, (7) Suction duct, (8) Cylinder, (9) Front Carding Segment, (10) Flats, (11) Cleaning Unit, (12) Post carding segment, (13) Cylinder Grid, (14) Doffer, (15) Stripping Device, (16) Calender Roller, (17) Can, (18) Coiler.

The doffer takes the fibres from the cylinder in fleece form. From the doffer, the fleece runs through the doffing roller, crush rollers and tongue-groove rollers. These rollers scanned the cross-section / thickness of the carding sliver. The recorded results are compared with the set target value of sliver linear density. Deviations from the set value are corrected by altering the speed of the feed roller. From there, sliver in its final form is coiled into the cans with the help of coiler.

3.4 Difference Between Blow Room and Card Cleaning

In the blow room the tightly packed bales are converted into small tufts. These tufts are then transported step by step through a series of machines installed in a sequence. The coarse and gentle opening at the start of blow room line is converted to the intensive and fine opening and cleaning at the end of line. As the larger tufts are further converted into smaller tufts, the degree of cleaning increases gradually due to the generation of new surfaces and decreasing the density of material. In the blow room the opening and cleaning are performed at the same time by a combined action of air currents, opening spikes and cleaning devices. The composition of trash, dust, fibre fragments and fibres removed is called waste. In case of card machine the material is opened to the individual fibre state. So, there are more chances of elimination of impurities, dust and short fibres. In the taker-in zone the coarse trash along with dust is separated from the material. While in carding zone the improved elimination of dirt and dust along with the removal of short fibres is carried out with the help of carding elements, mote knives, guiding elements and suction tubes. The waste of card is categorised into licker-in waste and fly waste.

3.5 Drawing

Following are objectives of drawing:

1. Equalizing: To improve evenness of the sliver by doubling

2. Parallelizing: To create parallel arrangement of fibres in the sliver by drafting

3. Blending: To compensate the raw material variations by doubling

4. Dust removal: To remove dust within the overall process by suction

5. Sliver formation: To make sliver and coil in a can by condensing and calendering

Following is the operation summary to achieve the objectives of drawing:

Four or eight sliver cans prepared on the card are arranged under the creel rollers of the drawing as shown in Figure 7. Flow of material through the draw frame is shown in Fig. 8. Creel rollers withdraw the slivers from the cans and feed to the drafting system. The slivers running into the drafting arrangement are attenuated by a draft of 4 to 8 and a web having less cohesion is delivered. In order to avoid disintegration of the web, it is condensed into a sliver immediately after the drafting arrangement. This sliver is then guided through a pair of calender roller and a tube which coiled it into a can.

Fig. 7

Draw frame.

Fig. 8

Material flow through draw frame (1) Can, (2) Feed roller pair, (3) Drafting arrangement, (4) Tube (Funnel), (5) Calendering roller, (6) Passage (Coiler tube), (7) Can.

For cotton, normally two passages of draw frame are given while for blends of cotton with synthetic fibres three passages are used. Drawing frames may be of single delivery or double delivery. Now a days, single delivery draw frames are used for final passage of material which is shown in Fig. 9.

Fig. 9

Material flow through Unilap.

3.6 Lap Former

The objectives of lap former are as follow.

1. Equalizing: To improve evenness of the lap by doubling of slivers

2. Parallelizing: To create parallel arrangement of fibres in the lap by drafting of slivers

3. Blending: To compensate the raw material variations by the doubling of slivers

4. Dust removal: To remove dust within the overall process by suction

5. Lap formation: To make lap by calendering

Following is the operation summary to achieve the objectives of lap former:

Twenty eight cans of drawn sliver from the first draw frame are placed under the two creel rails of the lap former. Flow of material through the lap former is shown in the Fig. 9. Creel rollers withdraw the slivers from the cans and feed to the drafting system. The slivers running into the drafting arrangement are attenuated by a draft of 1.3 to 2.5.

The two webs created by the drafting system pass over two deflecting plates onto the web table. These webs are superimposed or placed one above the other. The calender rollers draw these superimposed webs from the table and compact them to make lap and deliver it to the lap winding assembly. Winding assembly winds the lap on an empty tube. Empty tubes are automatically exchanged when length of the lap is completed.

3.7 Comber

The objectives of comber are:

1. Noil removal: To remove short fibres, neps and impurities by combing

2. Equalizing: To improve evenness of the sliver by doubling

3. Parallelizing: To create parallel arrangement of fibres in the sliver by drafting

4. Blending: To compensate the raw material variations by doubling

5. Dust removal: To remove dust within the overall process by suction

6. Sliver formation: To make sliver and coil in a can by condensing and calendering

Following is the operation summary to achieve the objectives of comber:

Eight laps made on lap former are placed on the support rolls of the comber which unwind the laps very slowly and deliver to the feed roller as shown in Figure 10. Flow of material through the comber is shown in the Fig. 11 and 13. Assembly of nippers takes the lap from feed roller. Circular combs comb the lap fringe hanging from the nippers and thus remove the short fibres, neps and impurities. Nippers transfer the combed fibres to the detaching rollers which deliver it in the web pan.

Fig. 10

Comber machine.

Fig. 11

Guiding the sliver from the web table to the drafting arrangement.

Fig. 12

Standard parts of combing head.

Fig. 13

Material flow through comber.

This web is condensed in to a sliver with the help of draw-off rollers, trumpet and table calender rollers. Eight slivers coming from each lap are arranged parallel on the table and fed to the drafting system as shown in the Fig. 12. The slivers running into the drafting arrangement are attenuated by a draft of 9 to 16. At the delivery end of the drafting arrangement, discharged web is condensed into a sliver. This sliver is then guided through a pair of calender roller and a tube which coiled it into a can. Fig. 13 shows a latest comber machine which is being used now a day in the industry.

3.8 Roving Machine

Following are the objectives of a roving frame:

1. Drafting to attenuate the sliver up to required fineness

2. Twisting to impart strength

3. Winding to make a roving package

Following is the operation summary to achieve the objectives of roving frame:

Sliver cans from the 2^nd drawframe or finisher draw frame are placed under the creel of roving frame. Flow of material through roving frame is shown in Fig. 14. Creel rollers withdraw the slivers from the cans and forward them to drafting arrangement. The drafting arrangement attenuates the slivers with a draft of about 5 to 20. The material exiting from the drafting system is too thin and it cannot withstand itself. Twist inserting step is necessary immediately at the exit of the drafting arrangement in order to impart strength.

Fig. 14

Material flow through roving machine (1) Can, (2) Transport roller, (3) Drafting arrangement, (4) Roving, (5) Flyer, (6) Spindle, (7) Bobbin, (8) Bobbin Rail, (9) Lever.

Twist insertion is done by rotating flyer, usually in the range of 25–70 turns per meter. Roving from the flyer top runs through the hollow flyer leg and reaches to the wind-up point with the help of presser arm. Winding of roving is carried out due to higher speed of bobbin than the flyer. The roving coils are arranged on the bobbin very closely and parallel to one another by bobbin rail which moves up and down continuously. Speed of bobbin is reduced as the bobbin diameter is increased in order to keep its surface speed constant.

Similarly, bobbin rail speed is decreased with the increase in bobbin diameter in order to maintain the coils per inch constant throughout the package building. During package building, length of each next layer of roving is reduced continuously both from bottom and top in order to insert the taper on both ends. Fig. 15 shows the latest roving frame which is in use in the industry today.

Fig. 15

Roving machine.

4.1 Ring Spinning

Following are the tasks which are required to achieve from ring spinning:

1. Drafting to attenuate the roving up to the required fineness

2. Twisting to impart strength

3. Yarn winding to make a suitable package

Following is the operation summary to achieve the tasks of ring frame:

Roving packages made on roving frame are positioned on the hangers of the ring frame creel. Flow of material through ring frame is shown in Fig. 16. Roving is fed to drafting system through guiding rods and roving guide. The drafting arrangement attenuates the roving with a draft required to make the final yarn count.

Fig. 16

Material flow through ring frame (1) Creel, (2) Guide roller, (3) Roving guide, (4) Drafting rollers, (5) Yarn guide, (6) Lappet, (7) Balloon control ring, (8) Traveller, (9) Ring, (10) Spindle.

The ribbon exiting from the drafting system is too thin and it cannot withstand itself. So twist inserting step is necessary to impart strength immediately. This step is performed by the ring and traveller with the help of spindle. In this process, each rotation of the traveller on the spinning ring produces a twist in the yarn.

The ring traveller has no drive of its own; it is dragged with spindle via the yarn attached to it. Winding of yarn on the bobbin is carried out due to the higher speed of spindle than the traveller. The yarn is wound up into a cop form by raising and lowering of ring rail. Fig. 17 shows a latest ring frame which is being used nowadays in the industry.

Fig. 17

Ring frame.

4.2 Winding

Winding is the creation of large yarn packages that can be easily unwound. This makes easier and economical use of yarn on subsequent machines. Thus all yarns made on ring frame are wound in the form of large cones on Autocone winding machine. Yarn faults are also removed on this machine with the help of yarn clearer. Fig. 18 shows the latest autowinding machine used in the industry today.

Fig. 18

Winding machine.

4.3 Open End Rotor Spinning

In open end rotor spinning process the preparatory processes include the operation of the blow room, card and draw frame passage. For the spinning of coarser yarn counts with shorter fibre length, card sliver can directly be fed to the rotor machine. However the need of right quality of sliver determines the requirement of one or two draw frame passage after carding process. Instead of classical roller drafting technique, the dispersion drafting is used in rotor machine. Twist is also inserted due to rotation of rotor.

Usually, the sliver cans from the first draw frame are placed under the Open end rotor machine. The flow of material through open end rotor machine is shown in Fig. 19. The sliver from can is fed to the feed roller with the help of sliver guide. Combing roller takes the sliver from feed roller and opens it up to individual fibre and delivers these fibres to the rotor through a fibre transfer tube. The fibres are deposited onto the rotating rotor and slide down into the rotor groove and form a ribbon of fibres. The rotor rotates at very high speed creating a centrifugal force due to which rotor is under a partial vacuum.

Fig. 19

Material flow through open end rotor machine.

To start spinning, a length of yarn already wound onto the package of the take-up mechanism is threaded through the nip line of the delivery rollers and into the draw-off tube. Because of the partial vacuum, the tail end of this yarn is sucked into the rotor due to vacuum. The rotation of the rotor pulls the yarn end onto collected ribbon of fibres and simultaneously inserts twist into the yarn tail. A little of this twist propagates into that part of the ribbon in contact with the yarn tail, binding it to the yarn end. Once the yarn tail enters the rotor, the delivery roller is set in motion to pull the tail out of the rotor. The pulling action on the tail results in a peeling of the fibre ribbon from the rotor groove. The newly formed yarn is wound up on the package by a winding drum.

The production rate of rotor spinning is 6–8 times higher than that of ring spinning. Open end rotor machines are fed directly by sliver and yarn is wound onto packages ready for use in fabric formation so in open end rotor spinning, only one machine is used instead of three machines (Roving frame, Ring frame and Autowinding) in ring spinning. Rotor spun yarns are more even but somewhat weaker and have a harsher feel than ring spun yarns.

Rotor spun yarns are mainly produced in the medium count (40 Ne, 20 tex) to coarse count (05 Ne, 60 tex) range. End uses include denim, towels, blankets socks, t-shirts, shirts and pants. Fig. 20 shows a latest open end rotor machine used in the industry today.

Fig. 20

Rotor spinning machine.

4.4 Air Jet Spinning

Flow of material through Air jet spinning machine is shown in Fig. 21. In order to have adequate parallelization of fibres required for air jet spinning, the sliver which has passed through three passages of draw frame is preferred as infeed material. The slivers coming from the creel portion are passed over the stationary creel rods being directed to the drafting arrangement. The drafting arrangement permits draft of 100 to 200 depending upon the required yarn fineness. The highly attenuated fibre strand then passed through the spinning nozzles. The false twist is imparted by the power air vortex generated by the nozzles. The direction of air vortex in these two nozzles is opposite to each other. A typical nozzle arrangement is shown in Fig. 22.

Fig. 21

Material flow through air jet spinning machine.

Fig. 22

Two-nozzle arrangement.

Due to low intensity of first jet, it only affects the small number of edge fibres. Thus it wraps the edge fibres around the core fibres. The angular velocity of the air vortex inside the second jet is more than 1 million rpm which inserts the twist to all the edge fibres and wound around the parallel fibre strand. They bind the body of fibres together and ensure coherence. The resultant yarn is cleared of any defects and wound onto packages.

The production rate of air jet / vortex spinning is 3–5 times higher than rotor spinning and 10–20 times that of ring spinning machine. Just like rotor spinning; the air-jet spun yarn is very cheaper to produce since it also uses a fewer production stages. As is the case with rotor spun yarns, the air jet spun yarns are more even, but weaker and have a harsher feel than that of ring spun yarns. The air jet spun yarns are mostly produced in the medium count (30 Ne, 20 Tex) range and are mainly polyester / cotton blended yarns. End users of vortex spun yarn include woven sheets and knitted lightweight shirting. Fig. 23 shows a latest air jet machine.

Fig. 23

Air jet spinning machine.

5.1 Staple Spun Yarn

1. Is made from staple fibres – cotton or wool or manufactured fibres cut into short lengths

2. Is an uneven, weak yarn with poor lustre and durability?

3. Staple spun yarns have good elasticity, resiliency and absorbency

4. Are used mainly for apparel and furnishings

5.2 Monofilament Yarn

1. Monofilaments are simply single filaments of synthetic fibres that are strong enough to be useful without being twisted with other filaments into a yarn.

2. They are fine and strong with good lustre and durability, but are inelastic in nature with poor resiliency and absorbency.

3. Monofilament yarns are used primarily for hosiery and invisible sewing thread.

5.3 Multifilament Yarn

1. Is made from two or more filaments of a manufactured fibre

2. Is an even, strong yarn with good lustre and durability; has medium elasticity and resiliency and is slightly absorbent

3. Is used primarily for evening wear and lingerie