Process Flow Chart of Yarn Spinning Technology | Working Process Flow Chart of Yarn Spinning Technology

SPINNING

The cotton fiber grows in the seedpod or boll, of the cotton plant. Each fiber is a single elongated cell that is flat, twisted, and ribbon like with a wide inner hollow (lumen).It is composed of about 90 percent cellulose and about 6 percent moisture; the remainder consists of natural impurities. The outer surface of the fiber is covered with a protective wax like coating which gives the fiber a somewhat adhesive quality. After this hydraulic pressing is done and cotton is been tested for the quality control. And then it has been sent for even moisture distribution. After all these processes this bale cotton gone to traders and textile mills receives these bale cotton from traders. As soon as the cotton arrives at the mill after ginning process in large bales weighing about 500 pounds (225 kg) each it is been kept for 24 hours.

1. BLENDING STEPS: Cotton is passed from bales and then to apron. Apron moves cotton to blending apron. Blending apron has sharp spikes the raise cotton until part of it is knocked off by the roll. Some of the cotton stays on apron. The cotton knocked back by roll and continues to chum and blend until picked up again by apron. Another roll strips off cotton that was not knocked back by previous roll. Cotton falls on conveyor belt and is carried to next process. WHY ITвАЩS BEEN DONE?It is necessary so as to obtain uniformity of fiber quality.

2. OPENING STEPS: Lint cotton falls on apron and passes between feeder rolls to beater cylinder. The rapidly whirling beater blades take off small tufts of cotton, knock out trash, and loosen up the mass. The two screen rolls are made of screen material and air is sucked out of them by fan. This draws the cotton from beater and condenses it on the surface of the screen rolls from which it is taken and passed on by the small rolls. Air suction through cotton takes out dirt and trash. Conveyor belt passes cotton to another type of beater. From beater the cotton passes to a conveyor and is carried to (Cotton going through the picker. WHY ITвАЩS BEEN DONE?It 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. Mechanical bale pickers pluck thin, even layers of the matted fibers from each of a predetermined number of bales in turn and deposit them into a opening machine where the fibers are loosened) 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 limp and free 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 from the opener, it still contains small tufts with about two-thirds of the trash. It may be conveyed as lap. GBR- Here the cottons are fed for homogenous mixtures and for removing dirts.MPM-8 вАУ it has got 8 chambers. Generally used for homogenous mixture of fibers like while harvesting some cotton are from matured plants and some are not. So that it will affect the fabric. So, after homogeneous mixing all will be the same.

3. CARDING PROCESS: Before the raw stock can be made into yarn, the remaining impurities must be removed, the fibers must be disentangles, and they must be straightened. The straightening process puts the fibers into somewhat parallel CARDING. The work is done by carding machine. The lap is passed through a beater section and drawn o rapidly revolving cylinder covered with very fine hooks or 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 trashes, disentangles the fibers , and arranges them in a relatively parallel manner in form of a thin web. This web is drawn through a funnel shaped device that molds it into a round rope like mass called card sliver. Card sliver produces carded yarns or carded cottons serviceable for inexpensive cotton fabrics.

STEPS: The lap from pucker unrolls and feed roll passes cotton licker in roll (covered with saw toothed wire).The licker in roll passes fiber against cleaner bars and gives it up to large cylinder which passes between the thousands of fine wires on surface of cylinder and on flats. The cotton follows large cylinder to doffer cylinder, which remove lint from large cylinder. The doffer comb vibrates against doffer cylinder and takes lint off in a filmy web that passes through condenser rolls, coiler head, and then into can. The sliver may be passed from one can to combing for further removal of foreign matter and parallelization of fiber or directly to drawing. 

4. DOUBLING PROCESS: 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 attenuated, or drawn out, to a sliver of smaller diameter without falling apart.

5. COMBING PROCESS: 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 out 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 as much as 25% of the original card sliver; thus almost one fourth of the raw cotton becomes waste. The combing process, therefore, is identified with consumer 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 yarns or combed yarns.

6. DRAWING PROCESS: The combining of several fibers for the drawing, or drafting, process eliminates irregularities that would cause too much variation if the slivers were pulling 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. STEPS: Her six cans that were filled at cards feed each drawing from delivery. The spoons are connected so that if any one of the six slivers from can should break, the machine automatically stops. This prevents making uneven yarn later. Each of four set of rolls runs successively faster than preceding set. The last set runs approximately six times as the first set; consequently, sliver coming out is the same size as each one of six going in. but is attenuated to six times the length per minute. The sliver is neatly coiled again in roving can by coiler head. The sliver is now much more uniform and fibers much more nearly parallel. The sliver is now ready for roving frames.

8. SPINNING PROCESS: 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 types; ring frame and mule frame. The ring frame is faster process, but produces a relatively coarse yarn. for very fine yarns, such as worsted, the mule frame is required because of its slow, intermittent operation. The ring frame, which is general in use, is more suitable for the manufacture of cotton yarns in mass production. Its hundreds of spindles, whirling thousands of revolutions per minute, and its constant spinning action provide a fast operation. The ring spinning frame completes the manufacture of yarn (1) by drawing out the roving (2) by inserting twist, and (3) by winding the yarn on bobbins-all in one operation. 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. STEPS: The principle of spinning is same as that used in roving except that the operation is more refined and a ring and traveler are used instead of the flyer. From bobbin roving is fed between set of drafting rolls to draw strand down to its final desired size. The spindle turns bobbin at a constant speed. The front set of rolls is adjusted to deliver yarn at a speed sufficient to insert desired mount of twist as strand moves along. The traveler glides freely around ring. The tension caused by drag of traveler causes yarn to wind on bobbin at same rate of speed as it delivered by rolls.

Modern Blow Room Line | The Installation as a Sequence of Blowroom Machines | Modern Blow Room Line for American

In processing the material, different types of machines are necessary, namely those suitable for  opening, those for cleaning and those for blending. Different intensities of processing are also required, because the tufts continually become smaller as they pass from stage to stage.Accordingly, while a coarsely clothed cleaning assembly is ideal after the bale opener, for example, it is inappropriate at the end of the line.

 Therefore, there are no universal machines, and a blowroom line is a sequence of different machines arranged in series and connected by transport ducts. In its own position in the line, each machine gives optimum performance – at any other position it gives less than its optimum. Also there may be advantages in different modes of transport, feeding, processing, cleaning and so on from one machine to another along the line. Finally, the assembly of a blowroom line depends among other things on:

Modern Blow Room Line

• the type of raw material;
• the characteristics of the raw material;
• waste content;
• dirt content;
• material throughput;
• the number of different origins of the material in a given blend. 

In most cases a modern blowroom line consists of the following machines, as shown in Fig. 8 (Rieter) and Fig. 9 (Trützschler), illustrating two typical blowroom lines.

Modern blow room line for American:

Pima Cotton:

Blendomat

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Heavy material separator

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Multiple mixture

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CVT1 (fine) / CVT3 (coarse)

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Dustex

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Feeding unit (chute feed) for card

? Modern blow room for American upland cotton containing more than 3% trash:

Blendomat

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Heavy material separator

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Multiple mixture

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Dustex

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Feeding unit for card

Draw frame | Actions involved in Draw Frame | Tasks of Draw frame | Working Process of Draw Frame

Draw frame is a machine for combining and drawing slivers of a textile fiber (as of hemp for rope manufacture or cotton for spinning) . Drawing is the operation by which slivers are blended, doubled and leveled. In short staple spinning the term is only applied to the process at a draw frame.

In drawing slivers are elongated when passing through a group of pair rollers, each pair is moving faster than previous one.

Actions involved in Draw Frame

Drafting: It is the process of increasing length per unit weight of sliver. It is mainly due to peripheral speed of the rollers.

Doubling: The process of combing two or more carded sliver into a single form is called doubling. In draw frame m/c generally six slivers are fed to convert into one i.e. six doubling.

Drawing: In the cotton industry the term is applied exclusively to processing on the draw frame, where the operation is one of doubling and drafting. Drawing= Drafting + Doubling.

Tasks of Draw frame

• Equalizing

• Parallelizing

• Blending

• Dust removal

Equalizing: One of the main tasks of draw frame is improving evenness over short, medium and especially long terms. Carded slivers are fed to the draw frame have degree on unevenness that cannot be tolerated in practice and slivers from the comber contain the “infamous” piecing. It is obscured by draw frame.

Equalizing is always performed by a first process, namely doubling and can optionally also be performed by a second process, namely auto leveling. The draft and the doubling have the same value and lie in the range of 6 to 8.

Parallelizing: To obtain an optional value for strength in the yarn characteristics, the fibers must be arranged parallel in the fiber strand. The draw frame has the tasks of creating this parallel arrangement. It fulfills the task by way of the draft, since every drafting step leads to straightening the fibers.

Blending: In addition to the equalizing effect, doubling also provides a degree of compensation of raw material variation by blending. Their results are exploited in particular way in the production of blended yarns comprising cotton or synthetic blends. At the draw frame metering of the individual components can be carried out very simply be selection of the number of slivers entering the machines.

Dust Removal: Dust is steadily becoming a greater problem both in processing and for the personnel involved. It is therefore important to remove dust to the greatest practical extent at every possible point within the overall process.

Dust removal can only be carried out to a significant when there are high levels of fiber. Since a large function the smallest particles adhere relatively strong to the fibers. High performance draw frame is equipped with appropriate suction removal systems; more than 80% of the incoming dust is extracted.

Drawing or Draw Frame | Objects of drawing | Importance or Necessity of Draw frame

Drawing is the operation by which slivers are blended, doubled and leveled. In short staple spinning the term is only applied to the process at a draw frame. In drawing slivers are elongated when passing through a group of pair rollers, each pair is moving faster than previous one. This permits combing, drawing and elongating of several slivers to make them strong and uniform.In most modern worsted drawing sets there are 3 passages of pin drafting and roving process.

Objects of drawing

1. To straighten the crimped, curled and hooked fibers.
2. To make the fiber parallel to their neighbors.
3. To improve uniformity of fibers by drafting and doubling.
4. To reduce weight per length unit of sliver.
5. To remove dust from slivers.
6. To blend raw material of same hank perfectly.

Importance or Necessity of Draw frame

To parallelization of fiber and blending the carded sliver, draw frame is needed.

In carded sliver, fibers are present in hook form i.e. trailing hooks and leading hooks. To parallel these hooks raw frame is used.

Majority of the fiber hooks in a carded sliver are trailing hooks while leading hooks are comparatively less. Trailing hooks are also known as major hooks, while leading hooks are known as minor hooks.

Process Flow Chart of Carded Yarn Manufacturing Process

If you want to make a yarn you will have two method to follow. One is Carded yarn manufacturing method and another is Combed yarn manufacturing method.

Combed yarn is most precious, finer and thiner than the carded yarn. Because the Carded Yarn is produced by following some less manufacturing steps than the Combed Yarn.

So let us know about the carded yarn manufacturing.

 Flow Chart of Carded Yarn Manufacturing:

Input Material ———Processing Machines ——–Output Materials

Raw Cotton »»> Blow Room»»»Lap

Lap»»»»»>Carding»»»»>Carded Sliver

Carded Sliver»»Drawing 1»»»»Drawn Sliver

Breaker Sliver»>Drawing 2»»»»Finisher Drawn Sliver

Finisher Drawn Sliver»Simplex/ Speed Frame»»Roving

Roving»»»»Ring Frame»»»>Yarn

Yarn»»»»>Winding»»»»>Yarn In Large Package.

The process flowchart of Yarn Manufacturing mentioning above is currently followed by the Textile Spinning Mills.

Feature of Yarn Ring Spinning frame | Drafting Zone | Ring & Traveller | Rubber Cots and Apron | Yarn Twist

Yarn Ring Spinning frame Technology is a simple and old technology, but the production and quality requirements at the present scenario puts in a lot of pressure on the Technologist to select the optimum process parameters and machine parameters, so that a good quality yarn can be produced at a lower manufacturing cost.

Following are the Points to be Considered in a Ring Frame

• Draft distribution and settings
• Ring and travellers
• spindle speed
• Twist
• Lift of the machine
• Creel type
• Feed material
• Length of the machine
• Type of drive

Raw material chracteristic plays a major role in selecting the above said process parameters in Ring Frame.
Technical information and guidelines are given below based on the learnings from personal experience and discussions with Technologists. This could be used as a guideline and can be implemented based on the trials taken at site. Some of this information can be disproved in some other applications, because many of the parameters are affected by so many variables. A same machine or rawmaterial cannot perform in the same way in two different factories. This is because of the fact that no two factories can be identical.

DraftingThe break draft should depend upon the following,

• Fibre type
• Fibre length
• Roving T.M
• Main draft

Main Draft Zone

Mostly for cotton fibres, short cradles are used in the top arm. Front zone setting is around 42.5 mm to 44 mm depending upon the type of drafting system. The distance between the front top roller and top apron should be around 0.5to 0.7mm when correct size top roller is used. This is normally taken care of by the machinery manufcturer. If a technician changes this setting, this will surely result in more imperfections, especially with karded count the impact will be more. Therefore when processing cotton fibres, care should be taken that the front zone setting should be according to the machinery.

Ring & Traveller

Ring diameter, flange width and ring profile depends upon the fibre, twist per inch, lift of the machine,maximum spindle speed, winding capacity etc.

• Operating speed of the traveller has a maximum limit, because the heat generated between ring and traveller should be dissipated by the low mass of the traveller with in a short time available.
• If the cotton combed yarn is for knitting, traveller speed will not be a limiting factor. Since yarn TPI is less, the yarn strand is not strong enough. Therefore the limiting factor will be yarn tension. Following points to be considered

1) For 12s to 24s , 42mm ring with 180 mm lift can be used 

2) For 24s to 36s, 40 mm ring with 180 lift can be used

3) For 36s to 60s , 38 mm ring with 170 mm lift can be used4) For 70s to 120s, 36 mmring with 160 mm lift can be used.
5) If winding is a problem, it is better to go for reduced production with bigger ring dia.
6) Anti-wedge ring profile is better, because of better heat dissipation
7) Elliptical traveller should be used, to avoid start-up breaks in hosiery counts
8) Special type of travller clearer can be used to avoid accumulation of fibre on the traveller as traveller with waste does not perform well during start-up.

• For polyester/cotton blends and cotton weaving counts yarn strength is not a problem. The limiting factor will be a traveller speed. For a ring diameter of 40 mm, spindle speed upto 19500 should not be a problem. Rings like Titan(from Braecker), NCN(bergosesia) etc, will be able to meet the requirements.
• For spindle speeds more than 20000 rpm, ORBIT rings or SU-RINGS should be used. As the area of contact is more with this rings, with higher speeds and pressure, the heat produced can be dissipated without any problem. Normal ring and traveller profile will not be able to run at speeds higher than 20000 to produce a good quality yarn.
• ORBIT rings will be of great help, to work 100% polyester at higher spindle speeds. Because, of the tension, the heat produced between ring and traveller is extremely high. But one should understand, that ,the yarn strength of polyester is very high. Here the limiting factor is only the heat dissipation. Therefore ORBIT RINGS with high area of contact will be able to run well at higher spindle speeds when processing 100% polyester.
• While running 100% cotton, the fibre dust in cotton, acts like a lubricant. All the cottons do not form same amount of lubricating film. If there is no fibre lubrication, traveller wears out very fast. Because of this worn out or burn out travellers, microwelding occurs on the ring surface,
• Lubrication is good with west african cottons. It may not be true with all the cottons from West africa. In general there is a feeling, cottons from Russia, or from very dry places, lubrication is very bad. If the fibre lubrication is very bad, it is better to use lighter travellers and change the travellers as early as possible.
• Traveller life depends upon the type of raw material, humidity conditions, ringframe speeds, the yarn count, etc. If the climate is dry , fibre lubrication will be less while processing cotton.
• Traveller life is very less when Viscose rayon is processed especially semi dull fibre, because of low lubrication. Traveller life is better for optical bright fibres.
• Traveller life is better for Poly/cotton blends, because of better lubricatiion between ring and traveller.
• Because of the centrifugal force excerted by the traveller on the yarn, the particles from the fibre fall on the ring where the traveller is in contact. These particles act like a lubricating film between ring and traveller. 

Rubber Cots and Apron

• For processing combed cotton, soft cots (60 to 65 degree shorehardness) will result in lower U%, thin and thick places
• There are different types of cores (inner fixing part of a rubber cot)available from different manaufacturers. Aluminimum core,PVC core,etc. It is always better to use softer cots with aluminium core.
• When softer cots are used, buffing frequency should be reduced to 45 to 90 days depending upon the quality of the rubber cots, if the mill is aiming at very high consistent quality in cotton counts.
• If the lapping tendency is very high when processing synthetic fibres for non critical end uses, It is better to use 90 degree shore harness cots, to avoid cots damages. This will improve the working and the yarn quality compared to working with 83 degree shore hardness.
• If rubber cots damages are more due to lapping, frequent buffings as high as once in 30 days will be of great help to improve the working and quality. Of course,one should try to work the ringframe without lapping. 

The basic reasons for lapping in the case of processing synthetic fibre is

• End breaks
• Pneumafil suction
• Rubber cots type
• Fibre fineness
• Oil content(electrostatic charges)
• Department temprature and humidity 

Almost all the lappings orginate after an end break. If a mill has an abnormally high lapping problem the first thing to do is to control the end breaks,

• After doffing
• During speed change
• During the maximum speed by optimising the process paramters.
• It is obvious that fine fibres will have a stronger tendency to follow the profile of the roller. Therefore lapping tendency will be more.
• If the fibre is fine, the number of fibres in the cross section will be more, therefore lapping frequency will be more.
• If the pressure applied on the roller is more, then lapping tendancy will be more. Hence fine and longer fibres will have more tendency for lapping because of high top roller pressure required to overcome the drafting resistance.
• If the pneumafil suction is less, the lapping tendency will be more both on top and bottom roller. But the pneumafil suction depends on the fan diamater, fan type, fan speed, duct design, length of the machine, profile of the suction tube etc. If any one of the above can be modified and the suction can be improved, it is better to do that to reduce the lapping.
• The closer the setting between the suction nozzle and the bottom roller, the higher the suction efficiency and lower the lapping propensity
• Higher roving twist will reduce the lapping tendency to some extent. Therefore it is better to have a slightly higher roving twist, provided there is no problem in ringframe drafting, when the lapping tendency is more
• With Softer rubber cots lapping tendency will be more due to more surface contact.
• The most minute pores, pinholes in the rubber cots or impurities in the cots can cause lapping. Therefore the quality of buffing and the cots treatment after buffing is very important. Acid treatment is good for synthetic fibres and Berkolising is good for cotton.
• Electrostatic charges are troublesome especially where relatively large amount of fibre are being processed in a loose state e.g drawframe, card etc.Lapping tendency on the top roll increases with increasing relative humidity. The frequently held opinion is that processing performace remains stable at a steady absolute relative humidity, i.e. at a constant moisture content per Kg of dry air. 

TWIST:
The strength of a thread twisted from staple fibres increases with increasing twist, upto certain level. Once it reaches the maximum strength, further increase in twist results in reduction in yarn strength

• Coarser and shorter fibres require more Twist per unit length than finer and longer fibres
• Twist multiplier is a unit which helps to decide the twist per unit length for different counts from the same raw material.This is nothing but the angle of inclination of the helical disposition of the fibre in the yarn. This is normally expressed as TWIST PER INCH = TWIST MULTIPLIER * SQRT(Ne)
• If the two yarns are to have the same strength, then the inclination angles must be the same
• For 40s combed knitting application, if the average micronaire of cotton is 3.8 and the 2.5% span length is around 29 mm, Twist multiplier of 3.4 to 3.5 is enough . If the average micronaire is around 4.3, it should be around 3.6 to have better working in Ring frame.
• cotton combed knitting T.M. = 3.4 to 3.6 
• cotton combed weaving T.M. = 3.7 to 3.8 
• cotton carded knitting T.M. = 3.8 to 4.0 
• cotton carded weaving T.M. = 3.9 to 4.2

The above details are for cottons of 2.5% span length of 27 to 30 mm and the average Micronaire of 3.7 to 4.4. For finer and longer staple, the T.M. will be lower than the above.

• In general for processing poly/viscose , the T.M. is as follows
• 51 mm, 1.4 denier fibre : T.M. = 2.7 to 2.9 for knitting application
• 51 mm, 1.4 denier fibre : T.M. = 2.9 to 3.1 for weaving application
• 44 mm, 1.2 denier fibre : T.M. = 2.9 to 3.0 for knitting application
• 44 mm, 1.4 denier fibre : T.M. = 3.0 to 3.1 for knitting application
• 38 mm, 1.2 denier fibre : T.M. = 3.1 to 3.3 for knitting application

Others

The following ROVING parameters will affect the ring frame process parameters
1) Roving T.M.
2) Bobbin weight
3) Bobbin height

• Higher the roving T.M., wider the back bottom roller setting or higher the break draft in ring frame
• For combed material the creel height should be as low as possible in ringframe
• Very long creel heights in ringframe, lower roving T.M. and heavier roving package will result in many long thin places in the yarn.(especially in combed hosiery counts)
• In general 16 x 6 ” bobbins are used. This helps to increase the spare rovings per machine with higher creel running time. Therefore one should aim at increasing the bobbin weight as well as increasing the number of spare rovings in the ring frame.
• Normally 6 row creels are used in modern ring frames. Six row creels will accomodate more spare rovings compared to 5 row creels.(around 150 rovings for 1000 spindle machine.) Creel height should be as low as possible for cotton combed counts.Spare rovings will improve the operators efficiency.
• Shorter machines are always better compared to longer machines. But the cost per spindle will go up. For cotton , polyester/cotton blends, poly/viscose(upto 44mm length), number of spindles upto 1200, should not be a problem. But maintenance is more critical compared to shorter machines.
• For synthetic fibres with very high drafting resistance, it is better to use shorter machines, because the load on break draft gears and on second bottom rollers will be extremely high. If long machines are used and the maintenance is not good for such application, the bearing damages, gear damages, bottom roller damages etc. will increase. This will result in coarse counts, higher count C.V., long thin and thick places.
• Four spindle drive is always better compared to Tangential belt drive. Because small variation in machining accuracy of bolster , spindle beam etc will affect the spindle speeds, thereby the twist per inch. Waste accumulation between contact rollers, bent contact rollers, damaged contact rollers, oil spilling from any one spindle etc. will affect the spindle speeds and thereby TPI. The spindle speed variation between spindles in a 5 year old ringframe will be verh high incase of tangential belt ? drive compared to 4 spindle drive.
• Noise level and energy consumption will be low in 4 spindle drive compared to Tangential belt drive
• Compared to Contact rollers, Jockey pully damages are nil. I have worked with 20 year old ring frames with Jocky pulleys,but the variations in spindle speed between spindles is very less compared to a 5 year old ringframe with Tangential belt drive. I have made this comment based on my personal experience.
• When processing coarse counts at higher speeds, the air current below the machine is a big problem with 4 spindle drive . This is due to the more running parts like tinrollers and jockey pullys. This will lead to more fluff in the yarn, if humidification system is not good enough to suck the floating ,fluff.
• If spindle speeds is high for cotton counts, every end breaks will result in more fluff in the department due to the free end of the yarn getting cut by the traveller when the distance between traveller and the bobbin with the yarn is less. Higher the delay in attending the end break , higher the fly liberation.If the number of openings of return air system for a ringframe is less and the exhaust air volume is not sufficient enough, then fly liberation from an end break will increase the endbreaks and thereby will lead to multiple breaks. End break due to a fly entering the traveller will get struck with the traveller and will result in heavier traveller weight and that particular spindle will continue to work bad.
• Multiple breaks are very dangerous, as it will result in big variation in yarn hairiness and the ringframe working will be very badly affected due to heavier travellers because of the fluff in the traveller.
• Dry atmosphere in ringframe department will result in more yarn hairiness, more fly liberation and more end breaks
• It is a good practice to change spindle tapes once in 24 months.Worn out spindle tapes will result in tpi variations which is determinetal to yarn quality.

Yarn Twist | Twisting Process of Yarn | Mechanism of twist insertion to the strand

Twisting is a very essential process in the production of staple yarn, twine, cord and ropes. Twist is inserted to the staple yarn to hold the constituent fibres together, thus giving enough strength to the yarn, and also producing a continuous length of yarn. The twist in the yarn has a two-fold effect; firstly the twist increases cohesion between the fibres by increasing the lateral pressure in the yarn, thus giving enough strength to the yarn. Secondly, twist increases the helical angle of fibres and prevents the ability to aooly the maximum fibre strength to the yarn. Due to the above effects, as the twist increases, the yarn strength increases up to a certain level, beyond which the increase in twist actually decreases the strength of staple yarn. The continuous filament yarn also requires a small amount of twist in order to avoid the fraying of filaments and to increase abrasion resistance. 

However, twisting the continuous filament yarn reduces the strength of the yarn . Yarn is often ply-twisted in a direction opposite to a single yarn twist to improve evenness, strength, elongation, bulkiness, lustre and abrasion resistance, and to reduce twist liveliness, hairiness and variation in strength .

The twisting of fibres strands are carried out on a roving frame, ring frame, rotor spinning and DREF spinning machines etc. This twisted strand has to be wound on the delivery package in a certain form for easy withdrawal of these strands in the next process. Since the open end of the yarn is rotated in the rotor and DREF spinning systems, the delivery package has to be rotated axially to wind the yarn. The twisting and winding operations are separated in the open-end spinning . However, this is not possible on a roving frame or a ring frame.

There should be two rotating elements (the spindle and traveller or flyer and bobbin) in order to twist and wind the strand on the package. The winding rate should be equal to the delivery rate from the drafting device. As the winding on the diameter of the package varies continuously throughout the process, the difference in speed between the two elements also has to be varied continuously. Since the delivery rate is constant, the product of winding on diameter and the speed difference between the two rotating elements should be kept constant. On a roving frame, this is achieved by adjusting the bobbin speed continuously and keeping the flyer speed constant, whereas in ring spinning, only the spindle is rotated at a constant rate and the traveller is dragged around the ring by the yarn. Due to the frictional force between the ring and traveller, the required speed difference between the spindle and traveller is automatically adjusted. In both the ring and roving frame of the short-staple spinning system, the bobbin lead is used. For calculating twist in the roving, the flyer speed is taken into account, whereas in ring spinning, the spindle speed is considered .

Twist/cm in the roving = flyer speed in rpm)/ delivery rate in cm/min 

Twist/cm in the yarn = spindle speed in rpm/ delivery rate in cm/min

The reasons for the above, and the mechanism of twisting strands on a roving frame and ring frame are not explained in textbooks or literature. In the present paper, the mechanism of twisting strands on a roving frame and ring frame is explained. 

Mechanism of twist insertion to the strand

Twist insertion to the yarn when the spindle is stationary. We assume that the spindle is stationary and the traveller rotates in the ring frame. Each revolution of the traveller winds one coil of yarn onto the cop. This is similar to gripping and winding the yarn on a cop by hand. The yarn will rotate 3600 per coil wind while winding the yarn onto a stationary cop by hand; hence the winding causes yarn twisting.

Length of yarn wound per revolution of traveller = πd

Turns/cm due to winding = 1/πd 

where d – Winding on diameter of cop or bobbin in cm.

If the yarn is unwound in parallel from the cop, the yarn will retain all the twists present in the yarn, whereas if the yarn is over-end unwound, unwinding a coil removes one turn of twist. The unwinding causes twisting. So, the twists inserted into the yarn during winding are removed during over-end unwinding. The over-end withdrawal may be from any side of the cop. If the traveller rotates in a clockwise direction to wind the yarn onto the cop, each coil of wind inserts one turn of ‘Z’ twist to the yarn. When the same is over-end unwound, every unwinding coil inserts one turn of twist in an ‘S’ direction, and so the resultant yarn will not have any twist.

Twist insertion into the yarn when the traveller is stationary. We assume that the traveller is fixed on a stationary ring and that the spindle is rotating at a constant speed. Every revolution of spindle winds one coil of yarn onto the cop. Here winding does not cause twisting, and hence the yarn in the cop will not have any twist. But if the yarn is over-end unwound, every unwinding of a coil of yarn inserts one turn of twist into the yarn.

Turns/cm due to over-end unwinding = 1/πd

The direction of twist insertion during over end unwinding depends on direction of yarn winding. If the spindle rotates in an anticlockwise direction to wind the yarn onto the cop, during over-end unwinding a ‘Z’ twist will be inserted into the yarn. But if the same yarn is unwound in parallel, the yarn will not receive any twist.

Twist insertion onto the yarn when both spindle and traveller rotate in opposite direction. It may be wondered why it should be necessary to rotate the traveller and spindle in the opposite direction, and also how to rotate the traveller in the opposite direction. This is only to enable the reader to clearly understand the mechanism of twisting. When both the spindle and traveller rotate in the opposite direction, each revolution of the spindle and traveller winds one coil each. The length of yarn wound per min and twist/cm can be calculated.

Length of yarn wound per min = π d (NS+NT)

Twist/cm due to winding = - NT/ π d (NS+NT) where

NS – spindle speed in rpm,

NT – traveller speed in rpm.

If the spindle and traveller rotate in clockwise and anticlockwise directions respectively, the direction of twist insertion due to winding would be ‘S’. But during over-end unwinding, the direction of twist insertion would be ‘Z’. + and - signs are used to represent the Z and S twist directions respectively.

Twist/cm due to over-end unwinding = (NT/ π d (NS+NT)) + (NS/ π d (NS+NT))

Twist/cm in the yarn after over-end withdrawal = (NS/ π d (NS+NT) 

Twist insertion onto the yarn when the spindle leads the traveller. In ring spinning, both the spindle and traveller rotate in the same direction. However, the spindle rotates at a higher speed than the traveller. If both rotate at the same speed, only the twisting of yarn takes place without winding. Due to the difference in their rotational speeds, the winding of the yarn takes place on the cop.

Length of yarn wound on the cop per min = πd (NS –NT)

Due to rotation, both spindle and traveller insert twists onto the yarn. If both the spindle and traveller rotate in a clockwise direction, a ‘Z’ twist is inserted to the yarn.

Turns/cm in the yarn = NT/πd (NS –NT)

The winding rate should be equal to the delivery rate.

Length of yarn delivered (cm/min) = πd (NS –NT)

Here winding takes place in similar conditions to when the traveller is stationary and the spindle is rotating; hence winding does not insert any twist onto the yarn. On the other hand, during over-end unwinding one turn of twist is inserted for every unwound of coil.

Turns/cm for unwinding = 1/πd

Total twist present in the yarn after over-end unwound = NT/πd(NS –NT) + 1/πd = NS/πd(NS-NT)

Since yarn from the ring cop is normally over-end withdrawn during the winding process, the spindle speed is taken for calculating the turns/cm in the yarn instead of using traveller speed. However, turns/cm in the roving is calculated by taking the flyer speed into account. This is due to the parallel withdrawal of roving during spinning.

Twist insertion onto the strand when flyer leads bobbin. Due to the difference in the speeds of the flyer and the bobbin, the winding of roving takes place on the bobbin.

Twist/cm due to twisting = NB / πd(NF-NB)

Twist/cm due to winding = (NF-NB)/ πd(NF-NB)

Twist/cm in the roving = NF / πd(NF-NB) where

NF - flyer speed in rpm,

NB - bobbin speed in rpm.

If the roving is unwound in parallel, the roving will have the same amount of twist as in the bobbin, but if it is over-end withdrawn, it will lose a certain amount of twist during unwinding.

Turns/cm due to over-end withdrawal = - (NF-NB)/ πd(NF-NB)

Turns/cm in the roving after over-end withdrawal = NB/πd (NF-NB) 

Summary and conclusion

• Yarn will rotate 3600 per coil wound while winding yarn onto a stationary cop by hand. When it is over-end unwound from the cop, all twists present in the yarn are removed. Hence both winding and over-end unwinding cause twisting, but in opposite directions.
• If the yarn is wound onto the cop by feeding the yarn perpendicular to the cop and rotating it, winding the yarn will not cause any twisting. But if the yarn is over-end withdrawn, the yarn will receive one turn of twist per coil unwound.
• If the flyer leads the bobbin in the roving frame, twisting of the roving takes place due to both twisting and winding.
• Since the yarn from the cop is over-end withdrawn during winding, the spindle speed is taken for calculating the twist in the yarn, whereas the flyer speed is taken for calculating the twist in the roving, due to parallel unwinding of the roving during spinning.
• The over-end unwinding of yarn helps in getting extra twist to the yarn, and the parallel unwinding of roving will not introduce any extra twist to the roving. If the roving is over-end withdrawn during spinning, every coil unwound will insert one turn of twist onto the roving. Hence the break draft and the setting of the back roller have to be increased to facilitate the breakage of the twist present in the roving. Otherwise, undrafting of the strand will occur during drafting. Hence the roving is normally unwound in parallel from the bobbin during ring spinning.