Spinning Jenny Easy Drawing Creel With Roving

Overview of developments in yarn spinning technology

C.A. Lawrence , in Advances in Yarn Spinning Technology, 2010

1.7.1 Surface fibre wrapping

Two techniques are used: friction spinning and air-jet spinning.

Friction spinning

With this technique a ribbon of fibres is fed from a roller drafting system along the V-shaped groove formed by the rotating friction drums. Fibres travelling from an opening roller unit are deposited onto the fibre ribbon. The friction drums insert a false twist into the fibre ribbon while wrapping the deposited individual fibres around it.

Air-jet spinning

This technique is also known as fasciated yarn spinning [23, 24]. There are many variants of the technique, and Chapter 10 gives detailed descriptions of these. Here, for the purpose of illustration, only the basic technique will be considered.

Figure 1.22 portrays a typical air-jet spinning system which consists of a 3-over-3 high-speed roller drafting unit, two compressed-air twisting jets arranged in tandem, a pair of take-up rollers and a yarn package build unit. The basic jet design is also shown. This has a central cylindrical channel (the spinning channel) through which the fibre ribbon from the drafting unit passes. Inclined to the channel axis but tangential to its circumference are four nozzles through which compressed air is injected into the channel, creating a vortex airflow. Each jet of compressed air entering and expanding into the channel has two velocity components of airflow: V ₁, a circular motion of the air around the channel circumference, and V ₂, the movement of the air to the channel outlet. The suction at the jet inlet created by V ₂ gives automatic threading-up of the spinning process. Provided the drafted ribbon is not tautly held between the front drafting rollers and take-up rollers, the V₁ component of flow rotates it, inducing a false-twisting action via a rotating standing waveform (a spinning balloon) while V ₂ assists movement of the twisted ribbon through the channel.

1.22. Principles of air-jet spinning.

The nozzles of the first jet are set to give a counter-clockwise vortex producing a Z–S false-twist action; the second jet gives an S–Z false-twist action. The pressures applied to the jets are such that jet 2 has the higher twisting vortex. Although the jets impart a false twist, while doing so they do not have a positive hold on the ribbon being twisted. Because of this the S-twist from jet 2 propagates along the twisted ribbon and nullifies the Z-twist from jet 1, leaving some S-twist to travel towards the nip line of the front rollers. The balloon of the thread line near the front rollers tends to move edge fibres, leaving the nip line, away from the core of fibres being twisted together. Consequently, the leading ends of the edge fibres are not controlled by the S-twist propagating from jet 2; they are free to move with the vortex of jet 1, in the opposite direction (the Z-direction) to the twist in the core. The vortex of jet 1 therefore wraps the edge fibre around the twisted core, forming the wrap-spun or fasciated yarn.

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Fundamental principles of ring spinning of yarns

R.S. Rengasamy , in Advances in Yarn Spinning Technology, 2010

2.2.1 Fibre assembly in ring spinning

Assembling the required number of fibres prior to twisting is done by means of drafting of the fibre strand by roller drafting. In a roller drafting system, the rollers run at higher speeds from the back- to the front-rollers and in the process the fibres are redistributed over a longer length of the fibre strand and the fibre strand becomes thinner, i.e. with fewer fibres in the cross-section of the final fibre strand. The draft between any pair of rollers is defined as the ratio of the surface speed of succeeding rollers to that of the preceding rollers. The cotton sliver having 20,000–40,000 fibres is thinned down to the form of roving having 1500–3500 fibres by the previous process, ' roving'. A 3-over-3 roller drafting system with double apron is used to draft the roving at the ring spinning machine. For cotton spinning, the drafts from the back-to the front-zones usually vary from 1.1 to 1.5 (break draft) and from 6 to 30 (main draft) respectively. Selection of a break draft depends on the fibre properties and is crucial in controlling the irregularity of the yarn. Break draft other than optimum exhibits stick-slip phenomena of fibre movement that gives rise to uneven yarn. For cotton, the number of fibres at the nip of the front rollers of the ring spinning machine is around 100 to 400 for the finest to the coarsest yarn respectively. These fibres on leaving the front roller nip are subjected to twisting in the downstream operation.

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Common principles

Peter R. Lord , in Handbook of Yarn Production, 2003

3.7 Drawing

3.7.1 Terminology

Historically, the term 'drawing' was used in connection with the drawframe in staple spinning. 'Drafting' was used regarding roller drafting systems in roving and ring spinning. Upon the appearance of man-made fibers, the term 'drawing' was also used to describe the elongational process to improve the molecular orientation of the filaments. Custom still insists on the use of the historically founded words but in essence there is little fundamental difference between drafting and drawing.

Linear density is defined as mass per unit length of a strand or along the flow path of a stream of fibers.

3.7.2 Purposes of drafting or drawing

Drafting occurs when a stream of fibers passes through an acceleration zone ⁵ . The place where the acceleration occurs is called a 'draft zone' and it is necessary to control the fiber flowing through it. The solutions to the problem of fiber control are diverse and only a few examples can be given to illustrate the importance of mass flow control by passive devices.

There are two major reasons for drafting or drawing, which are (a) to better orient the molecules or fibers in the strand, and (b) to change the cross-sectional area of the strand ⁶ . In the drawing of polymers, one very important objective is to orient the long-chain molecules to give the filament better properties. In staple processing, an important objective is to orient the fibers within the strand by causing them to slide over one another to give the strand better properties. It should be noted that improved orientation can only be achieved by drafting the strand to give a smaller output cross-section.

There are cases that are not always regarded as drawing but which really are. For example, in extrusion, the linear density of the molten polymer approaching the spinneret is higher than the sum of the linear densities of the output filaments even before conventional drawing. The speed of the output material is faster than that of the input. While an extruder is not regarded as a drawing machine, it always is.

3.7.3 Control of flowing material

Both polymer and staple drawing and drafting have instabilities in flow. Control is exercised by imposing restraints on the systems. With polymer in the solid state, control is exercised by hot pins or the like. Heat flow from the control surface permits control of the local visco-elastic constants of the polymer in such a way as to promote stability. In the case of staple processing, the variable frictional forces between the flowing fibers are a strong factor in producing the instability, which reduces their value in both yarn and fabric forms. These instabilities produce quasi-random errors in the product. The addition of an external retarding force to the flowing fiber reduces the instability.

3.7.4 Principle of drafting or drawing

Consider a sample of the input material before and after discontinuous drafting or drawing. If there were no losses in the process, the mass of the input sample would be the same as it is after drawing. Let ρ be the packing density (not to be confused with linear density), a the cross-sectional area, l the sample length, ρ_i a _i l _i be the mass in the input sample, and ρ_o a _o l _o be the mass after drafting. It follows that:

${\mathrm{\rho }}_{\mathrm{i}}{a}_{\mathrm{i}}{l}_{\mathrm{i}}\approx {\mathrm{\rho }}_{\mathrm{o}}{a}_{\mathrm{o}}{l}_{\mathrm{o}}$

and if the packing density is constant,

[3.1] $a_{\mathrm{i}}{l}_{\mathrm{i}}\approx a_{\mathrm{o}}{l}_{\mathrm{o}}$

For the purely theoretical case, the change in cross-sectional area is inversely proportional to the change in length. This is discontinuous drafting. However, in production, the process of elongation takes place continuously with the input and output mass flows nominally constant. Thus, the formula of Equation [3.1] can be restated to say that the cross-sectional area is inversely proportional to the speed ratio. In practice, this is modified by changes in the packing density and small losses have to be taken into account, but it forms the basis of all drafting and drawing.

3.7.5 Drawing in staple fiber processing

In staple spinning, the material flows through the drafting or drawing zones of the equipment. (The term 'drawing' is often used to describe the particular overall process but it is common to refer to the components that carry it out with the adjective 'drafting'. Thus we speak of drafting rolls and draft in a drawframe which seems odd, but that is the common usage.)

Fibers are accelerated as they pass through each zone. Also fibers can, and do, migrate with respect to one another along the direction of flow. Conventional theory has been mainly restricted to roller drafting, in which there are fiber acceleration zones within the spaces between two consecutive sets of rollers. (A similar idea applies to filament drawing but godets are used rather than rollers. Godets are cylinders about which a yarn is wrapped to grip the yarn for the purpose of elongating it.) However, fundamentals merely require that the exit material moves at a greater velocity than the entry material. The theory in Appendix 8 seeks to include the case where fibers are drafted by toothed rolls.

3.7.6 Cumulative draft

It is not possible to achieve sufficient drafting or drawing in one step; consequently most systems use multiple, consecutive draft or draw zones (Fig. 3.13). As shown in Appendix 1:

Fig. 3.13. Draft distribution

[3.2] $\Delta ={\Delta }_1\times {\Delta }_2$

where	Δ = total draft ratio
	Δ1 = draft ratio in stage 1
	Δ2 = draft ratio in stage 2.

NB The term draft ratio is technically correct but it is frequently shortened to 'draft'.

In staple spinning, there are usually two zones. The first (or break-draft zone) has the function of breaking frictional bonds which form in roving (or other strands) due to (a) setting, (b) fiber migration, (c) fiber crimp, or any combination thereof. Newly drafted material is easier to draft immediately after such an operation even if the break draft is small because the crimp gets set over time, and the fibers no longer slide over one another as smoothly as freshly drafted material. The break draft varies according to the type of fiber and the linear density of the strand; it usually varies between 1.1 and 1.4. Overall draft is the product of the break and main drafts and it varies from about 6 to 30 according to the machine concerned. In polymer drawing, there is often more than one stage of drawing (perhaps using different machines) to complete the total process and the mathematical treatment is the same as for drafting in a staple process. However, one would use the term drawing rather than drafting. Nevertheless, for simplicity the explanation will be expressed in terms of draft.

Normally, it is arranged that there is little change in fiber characteristics, to prevent the need to change the draft program and hence unnecessarily escalate costs.

For more than one stage, all the drafts are multiplied together to give the overall draft. In staple spinning, the process starts with a bale laydown that might be regarded as an extremely thick strand (a linear density of perhaps a billion (10⁹) tex). The yarn leaving the mill may have a linear density of less than 10² tex. (1 tex = 1 g/km or 1 mg/m as discussed in Appendix 1.) The mill can be regarded as a gigantic complex drafting system and it is clear that a drastic amount of drafting is needed over all the various machines in the production line. Although the foregoing has been explained for staple spinning with roller drafting, much of it is equally applicable to toothed drafting (as in an opening line). Some machines, like cards, have draft ratios of roughly 100, whereas machines such as drawframes, roving frames, and ring frames usually have overall drafts of the order of 10. A large number of stages of drafting are required including those that precede the card.

3.7.7 Effects of roller errors

It is essential that the operating surfaces of all rolls, gears, and other cylindrical elements should be perfectly round and concentric if periodic errors are to be avoided. It might be noted that the operating surface of a gear is at its pitch-circle diameter.

An eccentric element produces a sinusoidal error. If a drafting system is left standing with the pressure acting on the soft cushion rolls, deformations might be developed in the rubber. Such deformations cause periodic errors in the textile product, which contains fundamental and harmonic components. Even though an elliptical roll is a rarity, it is useful to demonstrate the effects. Therefore consider an elliptical roll in a simple four-roll staple system such as is shown in Fig. 3.14. (Other deformed rolls will produce somewhat similar effects, irrespective of the type of system.) The bottom front (delivery) roll has been drawn as excessively elliptical for the purposes of illustration. All the other rolls are perfectly round and concentric; the back rolls deliver material at V inches/s. The elliptical bottom front roll rotates at ω radians/s and the surface velocity is V ₁ = ω r ₁ inches/s, where r ₁ is radius of the roll at the point of contact. The middle diagram refers to the bottom front roll after it has turned through 90°. The active radius is now r ₂ and the velocity is V ₂ = ω r ₂ inches/s. Meanwhile, the back roll speed, V, remains unchanged. Consequently, the draft changes from V ₁/V to V ₂/V as the front roll moves through 90°. As the elliptical roll rotates, there is a periodic change in draft, which in turn causes a periodic change in linear density of the output strand. In this case, the periodic wavelength is half the circumference of the deformed roll. A similar effect would have occurred if the roll had been round but off-center (i.e. eccentric). In this case, however, the error wavelength would have been the whole circumference of the deformed roll. Any deformity of the roll produces an error and, as mentioned earlier, a common cause of such errors is deformation of the top rolls (which are normally rubber covered). The rubber is used to improve the grip on the fibers but it is visco-elastic and will deform if the load is left on while the machine is stationary. It might be added that the rubber coverings harden unevenly with time and use. The result is that the deformation of the rubber also becomes uneven. Even if no geometric error is present, an uneven strand is produced because the rubber deforms in a cyclic fashion. These problems are controlled by using special tools to measure roundness, concentricity, and rubber hardness on a regular basis.

Fig. 3.14. Deformed rolls

There is a further complication. The nip-to-nip distance changes, as shown in Fig. 3.14(c), when an elliptical or any other non-round roll meshes with another. At the given angle of the bottom front roll, the setting has changed by δL. In effect, there is a cyclic variation in setting that not only produces a cyclic error of its own but actually magnifies it. Consequently a great deal of trouble is taken to keep the rolls, and other elements, round and concentric. The spectrogram is useful in this regard because out-of-true rolls generate a spike at a wavelength λ_o, which can be used to diagnose the source of the error. Further, any error produced upstream is elongated by the drafting to be ∆ times as long, where ∆ is the overall draft. Consequently, the spectrograph can show multiple sources of error. (An actual example is given later, in Fig. 3.18.)

In symbols:

[3.3] ${\mathrm{\lambda }}_{\mathrm{o}}={\mathrm{\lambda }}_1\times \left(\Delta /\mathrm{k}\right)$

Where	λo = error wavelength in strand measured
	λ1 = circumference of bad roll
	Δ = draft between bad roll and point of offtake of the material measured
	k = a factor which is an integer that takes into account how many lobes are on the bad roll.

λ_o and λ₁ must have the same units of measurement.

3.7.8 Drawing a filament

Filaments are made to grip the surface of the drawing elements (godets) by the simple expedient of wrapping the filaments several times round the godet as shown in Fig. 3.15. The pins, P, lie at an angle; this merely serves to separate the turns on the godet. The wrap friction effect is the same as is used in a capstan winch; indeed it is sometimes referred to as capstan friction. Yarn is wrapped round two godets rotating at different surface velocities, and the draw ratio is calculated from the velocity ratio. It is important that the surfaces of the godets are concentric with the axis of rotation, and round, otherwise errors similar to those described earlier will occur. A common reason for problems arises from irregular deposits of finish and debris on the operating surfaces.

Fig. 3.15. Filament drawing

3.7.9 Drawing a sliver (staple processing)

In the drawing or drafting of staple fibers, pairs of rollers are caused to grip the strand as shown in Fig. 3.16. Weighting by deadweights, springs, or pneumatic systems is used to press the rollers together and prevent slippage between the fiber and the rolls. Normally, one roll is made of metal and is fluted; the covering of the other is usually made of synthetic, elastic material (i.e. it is a cushion roll or 'cot'). As previously indicated, the cushion rolls should not be left under pressure, otherwise the rubber becomes deformed and produces mechanical errors in drafting. Fiber condensers are necessary to gather the fibers and introduce enough fiber migration to give the sliver cohesion. Drawframes are made to facilitate easy access to the elements, for example, easy removal of parts liable to fairly rapid wear (such as the cots). They are also designed to give a direct fiber flow path to minimize chokes.

Fig. 3.16. Staple fiber drafting

A sliver is an untwisted rope-like strand of loosely aggregated fibers that are held together solely by interfiber entanglement. To make good yarn, it is desirable that the fibers be aligned as well as possible, and this is one of the purposes of drawing. However, alignment or orientation of the fibers lowers the strength of the sliver. Sliver becomes weak if it is drawn too much or has too low a linear density. Thus, there is a limit to how much a sliver can be drawn and there is a limit to how fine it can be drawn before it is too weak to handle. The minimum linear density is affected by the degree of fiber orientation and crimp. Therefore, it is normal to set the mechanical draft to be about the same as the number of slivers fed. This limits the draft for one 'passage of drawing'. The term 'passage' refers to a sliver passing through a drawframe a single time.

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Spin finishes for textiles

I.A. Elhawary , in Advances in Yarn Spinning Technology, 2010

16.5 Quality issues in the use of spin finishes

The quantity of spin finish applied to the artificial staple fibres of continuous filaments during their processing is also critical and must be optimized so that neither too much nor too little is used. Too little spin finish can also generate technical problems such as increased static electricity charges on the frictional surfaces of the fibres or filaments during processing, and dry surfaces on fibres which lead to surface flakes.

The addition of too much spin finish can lead to a greater amount of smearing, e.g. in the rotor groove (collecting surface) of the rotor spinning machine. In addition to this, it can cause choking in the metallic card cloth and the pins (teeth) of the opening cylinder of the rotor spinning machine. The smearing effect is associated with fibre debris that can generate what is known as hard cake which can cause significant damage to machinery as well as affecting fibre appearance.

It is important that the type and application of spin finish achieves the right balance in the degree of friction achieved during processing. A high fibre-to-fibre friction can lead to efficient binding and cohesion between the fibres in the carding web and in the carded or drawn slivers, lack of excessive bulkiness of the fibrous tufts and the achievement of a reasonable yarn strength. It can also increase the false-twist effect during rotor spinning that helps yarn formation inside the rotor.

A low friction between fibres and machine parts prevents choking of the metallic card cloth, allows easy separation of the fibre wedge from the collecting surface of the rotor's spinning machines, and produces less fibre breakage during carding or opening, and less fibre accumulation in the yarn guides. A low friction between fibres can also result in less fibre disturbance during operations in such operations as roller drafting, the opening line, carding and rotor spinning.

Potential spin finish problems in short-staple plants include:

•

Swelling of the rubber aprons and cots of the top rollers of the roller drafting system

•

Flaking of fibres and an increase in static charge accumulation, caused by an uneven distribution of spin finish spraying

•

The formation of hard coatings on different machine parts such as the teeth of the licker-in, opening roller pins (teeth) of the rotor spinning machines, trumpets on the card, or on the drawframe and the speed frames (flyers) and the pressing arm eyelet; this can lead to an increase in production costs due to the need for more cleaning and more downtime

•

A decrease in wear in machine parts such as the sliding wall of the rotor spinning machine's rotors, the traveller of the ring spinning machines, and the toothed cylinders of the feeding section of the rotor spinning machines, due to the fact that the spin finish recipes contain corrosion inhibitors. Whilst, overall, this is beneficial, it is well known that a degree of wear in machine parts enhances the quality of yarn spinning.

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Self-twist spinning

M.R. Mahmoudi , in Advances in Yarn Spinning Technology, 2010

14.3 Self-twist spinning technology

A typical self-twist spinning machine contains a number of production channels. Each channel comprises:

•

A roving supply package delivering the two rovings to the rollers

•

A roller drafting section with an oscillating (shuffling) and rotating (twisting) rollers

•

A strand combination system which ensures the strands are combined to avoid zero-twist zones coinciding

•

A take-up system.

The first self-twist spinning system was devised at the CSIRO laboratories at Geelong, Australia, by Henshaw (1971). To date, the only method of alternate (S and Z) twist insertion into a staple fibre is the Repco self-twist machine (GB Patent 1962, US Patent 1977a) and the WinSpin machine from the Saurer Group. In the Repco system, introduced in the 1970s, the top and bottom twisting rollers are typically 22.9   cm long and 4.1   cm in diameter. Both are hollow cylinders mounted horizontally and coated with rubber. The drafted fibre strands pass through the rollers which reciprocate axially in opposition to insert intermittent 'S' and 'Z' twist. The rollers also rotate to advance the finished strands of fibre. The twisting rollers are mounted on two externally pressurised air bearings, which obtain their motion by means of a pair of rods connected to a pair of epicyclic gearboxes, operating at 180° out of phase. The epicyclic drive unit conveys the reciprocating as well as the rotating motion of the self-twist rollers. The twisting rollers reciprocate at a fixed stroke of 7.6   cm, and rotational delivery speed is synchronised with the front drafting rollers' delivery speed. The epicyclic driving unit can reciprocate 7.6   cm, up to 1000 oscillations per minute, and gives a nominal cycle length of 22   cm. In contrast to the bottom twisting roller, the upper twisting roller is mounted so that it can pivot freely in order to regulate the nip pressure using a deadweight system. The level of twist in the fibre strands is controlled by the pressure exerted on the bottom roller by the top roller. The level of twist is adjusted by changing the weight. Phasing is introduced to the self-twist yarn by increasing the pass length of one of the strands prior to the convergence point in order to prevent two adjacent no-twist zones at twist changeover coinciding with each other. A diagram of the Repco self-twist machine is shown in Fig. 14.6.

14.6. Principle of self-twist machine.

The standard Repco system consists of a creel for four pairs of rovings or strands, i.e. two rovings per self-twist yarn. S and Z twist is inserted alternately into each of the pair of strands. These are then brought together out of phase by the strand combination system so that they wrap around each other to form an alternating twist two-ply structure (22   cm total cycle length). The drafting zone is a modified double-apron system with three sets of rollers (back rollers, aprons and front rollers), the optimum draft being around 25 for wool (Simpson and Crawshaw 2002). Figure 14.7 shows twist distribution of a full cycle length plus no twist zones.

14.7. Typical twist distribution in self-twist yarn.

When two strands converge with coincidental zero-twist and twist regions, the resultant yarn is called in-phase self-twist yarn. Figure 14.7 shows an in-phase or zero-phase ST yarn profile. If, using the strand combination system, one of the strands travels a longer path before coming together with the second strand, so that the zero-twist zones are displaced, the resultant self-twist yarn is called a phased self-twist yarn. Phasing can be defined as the ratio of the path length difference to the cycle length, as shown in equation14.1 expressed as a fraction of 360° which corresponds to a full cycle length:

14.1 $\mathrm{Phasing}\mathrm{degree}=\frac{\mathrm{Path}\mathrm{length}\mathrm{difference}\mathrm{in}\mathrm{cm}}{\mathrm{ful}}$

A modified Repco spinning machine was introduced at ITMA 2003 as the Macart spinning system S300 ST. The S300 ST spinning machine is equipped with a pre-drafting system in order to process sliver of up to 12   g   m⁻¹ rather than roving, and on-line steaming technology after self-twisting to relax the yarn and allow for bulkier yarn packages (Oxenham 2003). The S300 ST spinning machine also incorporates an intermediate traction roller to control tension between the twisting section and the yarn coiling head prior to the bulking chamber.

The WinSpin self-twisting spinning machine from Oerlikon Saurer also uses two rollers which simultaneously oscillate and rotate to insert twist. In the WinSpin machine the direction of twist changes every 11   cm, producing a no-twist zone every 11   cm. As can be seen from Fig. 14.8(a), after the twisted strands leave the twisting roller, one strand in each pair passes over an idler (Fig. 14.8(b)) in order to make a longer pass prior to joining together to make an out-of-phase self-twist yarn. The two sets of yarn are then combined and wound on the package to make four-ply knitting yarn. The production speed can reach up to 250   m   min⁻¹.

14.8. Principle of WinSpin self-twist machine.

(courtesy of Saurer)

14.3.1 Self-twist spinning using air-jet technology

The distance between no-twist zones is the result of the time taken for the self-twist rollers to change their direction in proportion to the production speed. The existing technology available with the ST rollers in the Repco spinning machine means that, with the minimum time required for the roller to reverse after stopping, there is a minimum distance between no-twist zones of around 20   mm. Air-jet technology provides switching more rapidly in the direction of twist from 'S' to 'Z' or vice versa than is possible with a self-twist roller system. US Patent (1989), 1993a, 1995, 1996a, 1996b, 1997 and 1998) and GB patent 1341918 describe an alternative method of twist insertion which uses torque and booster jets. After the twist is imparted into each individual strand by the torque and booster jets, the twisted strands are allowed to self-twist and bond together. The method produces a cycle length (S and Z) of up to 140 inches. Other US patents (1977b, 1993b) also describe the application of air-jet technology for production of selftwist yarn. Most of the devices are designed for insertion of alternate twist into filament yarns. A method of using tandem air jets was introduced by Mahmoudi et al. (2003). Their method used four jets, two for each twist direction as shown in Fig. 14.9.

14.9. Tandem air-jet self-twist device.

Comparing the results of two self-twist yarns produced using ST roller and air-jet technology showed that the ST roller's yarn appearance was less hairy compared to the air-jet ST yarn, especially at high pressure (Henshaw 1971). The rate of twist loss with production speed was less with ST rollers than with air-jet technology. In air-jet spinning the rate of twist insertion is not known directly because the twist is inserted by means of energy created by the vortex at the twister nozzle. If one assumes that the fibres in the twisting channel at the twist nozzle are situated in the middle of the twisting chamber and the vortex is uniform and tangential, then one rotation of the vortex gives one turn of twist. In air-jet spinning, each channel generates a fixed amount of energy per unit of time at a given pressure. If yarn is fed through the channel more quickly, the energy per unit time is divided along a greater length of yarn. Thus the number of turns of twist inserted per unit length of yarn decreases. Although the twist drop was greater for the air-jet self-twist yarn than the ST roller yarn as the production speed increased from 120 to 220   m   min⁻¹, the no-twist zones were much shorter for the air-jet ST yarn. This could be explained by the speed of changing from one set of jets to another.

The NV air system from Gilbos produces self-twist yarn by using detorque jets to insert the alternating twist with no twisting zones reinforced by the use of intermingling jets (Elkhamy 2007). Figures 14.10 and 14.11 show this system. The NV air twister self-plying machine produces yarn at a rate between 400 to 800   m   min⁻¹, with 50 to 250 tpm with a twisted length of 25 to 150   cm. The air twister applies alternating twist onto filaments to resemble a multi-fold twisted yarn for the carpet industry. It also produces high tenacity yarn for hoses, ropes, and other industrial applications. All machine parameters are fully computer controlled, and each zone can operate independently. The NV air twister machine contains four spindle sections with a total of 12 spindles, i.e. three spindles per section.

14.10. NV-Gilbos self-twisting device.

(courtesy of NV-Gilbos)

14.11. NV-Gilbos self-twist yarn.

Belmont textile machinery (US Patent 2002) uses a maximum of four filament yarns. These travel through yarn separators to rotary air jet twisters in order to prevent the yarns twisting together while they are receiving twist. The twisted single filaments yarns are bonded in a group by air tack before they are allowed to ply together to make self-twist yarn. Air tack is inserted using a moving air bonder that allows the Roto-twist machine to be a continuous process that can run at a very high speed of 550   m   min⁻¹. The twisting elements of the Roto-twist or Fluid-jet twist insertion are shown in Fig. 14.12. The system produces a long twisted zone of about 90   cm with yarn mainly used in the carpet industry.

14.12. Belmont Roto-twist twist elements.

(courtesy of Belmont textile machinery)

14.3.2 Other variations in self-twist spinning technology

Air vortex technology is a highly promising method of intermittent twist insertion for filament yarn (Australian Patent 1957). The alternating twist is achieved by means of an air vortex from which the yarn is fed to a long convergence tube in which filaments self-twist (Fig. 14.13). Henshaw (1971) noted that a major problem with this system is air escaping from the end of the jet at high speed causing the strand to blow apart at zerotwist regions. Commercial machines using this technology were exhibited at ITMA 2004.

14.13. Self-twist spinning machine for continuous filaments.

(courtesy of CSIRO)

The centrifugal-jaw twister is a well-established false-twisting device generally associated with ring spinning machines for wool. The centrifugal-jaw twister comprises a stationery tube through which the strand passes through the rotating central tube. On rotation centrifugal force causes the jaws to grip. The twisting tube is capable of limited axial movement and is connected to an arm, as shown in Fig. 14.14, which in turn carries a cam follower. When it has reached the lobed part of the arm, the twisting tube is forced forward. This also forces the jaws to open and thereby interrupts the twisting action. The alternative twist is achieved by intermittent reversing of the twisting tube. The number of twists is dependent mainly on two parameters: the extent of centrifugal-jaw strength and the speed of passing fibre strand through the twisting tube. The cam speed controls the yarn cycle length. The degree of phasing is also determined by the rotational disposition of the cam.

14.14. Centrifugal-jaw twister.

(courtesy of CSIRO)

The tube twister is a method of intermittent twist insertion reported by Rohatgi (1974). This method of alternating twist insertion basically consists of a pair of tubes which are oscillated between two moving belts (Fig. 14.15). As the tubes touch the top belt they insert 'Z' twist, while contact with the bottom belt produces 'S' twist. Ozmen (1976) noted that, due to low twisting efficiency and slippage, the tube twisting method could only be used for producing woollen self-twist yarn.

14.15. Tube twister.

(courtesy of J. S. Rohatgi)

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Developments in hybrid yarns

H.R. Mankodi , in Specialist Yarn and Fabric Structures, 2011

2.4.4 Wrap spinning

The concept of wrapping a filament over a staple fiber core began with wrap spinning. A roving or sliver feedstock is drafted in a three-, four- or five-roller drafting arrangement, and the fiber strand that is delivered runs through a hollow spindle without receiving a true twist. In order to impart strength to the strand before it falls apart, continuous filaments are wound around the strand from the drafting arrangement. This thread comes from a small and rapidly rotating bobbin mounted on the hollow spindle as shown in Fig. 2.12. Withdrawal rollers lead the resulting wrap yarn to a winding device. The wrap yarn consists of two components: one twist-free staple fiber component in the yarn core and a filament wound around the core. These yarns are used mainly for making home textiles, automotive textiles, outerwear, carpet yarns, etc.

2.12. Wrap-spinning process (Mankodi, 2007).

Filament–filament wrapping can be similarly achieved through the use of the hollow spindle technique as shown in Fig. 2.13. The hollow spindle unit was developed in order to produce conductive thermoplastic hybrid yarns consisting of a glass core and a copper wire, which is passed through the center of the hollow spindle and then moves upward through the device. The principle behind the hollow spindle wrapping technique is that the core yarn passes through the bottom of the hollow spindle and the double flange bobbin with wrap yarn is mounted on the spindle as shown in Fig. 2.14. As the spindle rotates, the filament is unwound from the double flange bobbin and binds the core yarn by spiral wraps. The required number of wraps in the yarn can be obtained by controlling the spindle speed and yarn take-up speed. The hollow spindle wrapping technique is mainly used to produce zari yarns, elastomeric yarns and other cover yarns in which the core component determines the technical properties of the yarn and the sheath component covering the core gives the yarn its aesthetic value. This process is also known as the covering process.

2.13. Wrap yarn by the hollow spindle process (Mankodi, 2007).

2.14. Hollow spindle unit attachment (Mankodi, 2007).

Hybrid yarns can be produced by combining the matrix and reinforcing material using the hollow spindle wrapping technique. Hybrid yarns for industrial applications are produced mainly by combining thermoplastic yarn with a reinforcing material such as glass and carbon. Conductive materials can be incorporated into hybrid yarns for protective or shielding applications. This type of hybrid yarn improves weavability as well as knitting performance as compared to the direct use of glass or carbon yarns for preform. The machine consists of a feeding unit, a hollow spindle unit and a winding unit, and can be adjusted for the required number of wraps per meter in the yarn. Fig. 2.15 shows a cross-sectional view of a hybrid yarn.

2.15. Core (glass filament)/wrap (polypropylene filament) hollow spindle yarn cross-section (Mankodi, 2007).

The covering of a core yarn by twisting and retwisting is achieved through a new technique called 'direct twist covering'. This method produces two types of hybrid yarns: one is single (S) twist (similar to the hollow spindle wrapping method) and the other is double (SZ) twist. In the fiber twist technique, it is possible to adjust the thermoplastic fiber and glass fiber composition by controlling fiber and twist number. In the single twist method, twisting thermoplastic fiber around the reinforcement fiber in an 'S' twist produces a hybrid yarn. On the other hand, in the double twist method a hybrid yarn is produced by twisting thermoplastic fiber around the reinforcement fiber in both 'S' and 'Z' twists (Agteks, 2005).

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Speciality fabrics and machines

David J. Spencer , in Knitting Technology (Third Edition), 2001

14.10 Sliver or high-pile knitting

Sliver or high-pile knitting is single-jersey made on a circular machine having sliver feeds where the stock- or dope-dyed slivers are drawn from cans at ground level. They are then prepared by mini three-roller drafting card units followed by two wire-covered rollers that draw and transfer the thin film of fibres to the needles ( Fig. 14.6). At each sliver feed, the needles are lifted to an extra high level where they rise through the wires of the doffer roller to collect a tuft of staple fibres in their hooks.

Fig. 14.6. Sliver high pile machine.

Air-jet nozzles over the knitting points ensure that the tufts are retained in the needle hooks and that the free fibre ends are orientated through to the inside of the fabric tube (the technical back), which is the pile side.

As the needles start to descend, the ground yarn is fed to them, so that each has a ground loop and a tuft of fibres that are drawn through the previous loop. A range of facilities are available from different machines including up to 16 roller speed settings, the use of two different fibre lengths, and mechanical or electronic needle selection and sliver selection. Electronic selection can select needles to take fibres from one of four different coloured slivers.

Borg Textiles pioneered specialised sliver knitting in the 1950s in co-operation with Wildman Jacquard although J. C. Tauber obtained US patents as early as 1914. A typical machine now has a diameter of 24 inches in a gauge of 10npi and runs at 45 rpm with 12–18 sliver feeds.

The fabric finishes 54–58 inches wide (137–147 cm) in a weight of about 450 g/m when knitting 360 denier fibrillated polypropylene ground yarn and a modacrylic sliver having a 3 denier 1½ inch staple.

Fibre staple lengths can range from 20 to 120 mm, in sliver weights from 8 to 25 g/m², giving greige (unfinished) weights of 200–2000 g/m², for end-uses such as fun furs, linings, gloves, cushions, industrial polishers and paint rollers.

A typical high-pile finishing route is: rough shearing, heat setting and back- coating, pile cropping, electrifying or polishing (to develop the lustre and remove crimp from the fibre ends), tiger framing (to distribute the pile effect), and controlled torque winding (to further develop the pile uniformity).

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Yarns: Production, processability and properties

R. Alagirusamy , A. Das , in Fibrous and Composite Materials for Civil Engineering Applications, 2011

2.5.4 Spinning

This is the final process of yarn manufacturing. The spinning process basically consists of three important stages. (a) Reduction of strand thickness from the supply roving (or sliver) to the required yarn count. This is usually done by roller drafting with some means of fibre control such as double apron, but a different arrangement is used in open-end spinning and in mule spinning. It is important that the correct yarn count is produced, because there is no subsequent opportunity for correcting any mistakes in this respect. (b) The prevention of further fibre slippage – usually by twist insertion, although there are other methods. (c) Winding on to a package which is convenient for handling and which protects the yarn. There are different types of spinning machines for jute/flax fibres, e.g. flyer spinning, ring spinning and cap spinning. ^{25 , 26} Of the conventional frame-spinning machines, ring spinning has proved to be the most amenable to improvements in speed and package size. The flyer-spinning method uses the yarn to pull the bobbin round; it is only suitable for thick counts and, because of relatively lower spindle speed, flyer spinning has been replaced by ring spinning where possible. It is also used for spinning flax, hemp, and jute yarns thicker than about 240 tex at spindle speeds up to about 5000 rev/min with a bobbin capacity of about 500–600   g. This method is used where twist insertion is required as well as package formation; the type of package used is a double-flanged bobbin (Fig. 2.15). The method is only suitable for relatively long and strong fibrous materials such as jute and flax, because the slubbing produced must be strong enough to pull the bobbin round during winding on. There is no drive to the bobbin and it rotates by flyer with the help of yarn pull. The twisting take place by flyer rotation, whereas the winding is carried out due to a difference in motion of the flyer and the bobbin.

2.15. Flyer lead delivery double-flanged bobbin. ²⁵

The spindle arrangement in the flyer-spinning method is shown in Fig. 2.16. (a) hollow spindle top; (b) flyer leg; (c) bobbin; (d) spindle (driven from bottom); (e) felt drag washer; (f) lifter rail (vertical traverse); (g) slubbing (pulling bobbin round); (h) drafting zone bottom front roller; (j) drafting zone top front roller; (k) drafted fibres.

2.16. Flyer lead delivery side elevation. ²⁵

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Yarn and thread manufacturing methods for high-performance apparel

M. Tausif , ... I. Butcher , in High-Performance Apparel, 2018

3.2.4.3 Drawing

The fibers in carded sliver are not well aligned and the alignment is important for maximum contribution of fiber strength to yarn strength. Hence, drawing aims to produce straightened and aligned drawn slivers, with a high degree of parallelism. Drawing involves the doubling and roller drafting of sliver. Doubling refers to combining of two or more, usually six to eight, carded slivers as input to the first drawing frame. The combined slivers are drafted equal to the number of input slivers. This doubling helps to decreases irregularities and enables blending of the fibers. A sliver contains about 20,000–40,000 fibers in cross section and this number needs to be reduced to about 100 fibers in the final yarn's cross section. The drafting involves the even distribution of fibers over a longer length and roller drafting is an essential part of drawing, roving, and spinning operations. In roller drafting, a front set of rollers runs at a higher surface speed than the back set of rollers, the ratio of the surface speeds determines the degree of drafting. Fig. 3.9 shows a two-zone drafting system, aka three over three systems. The surface speed of rollers increases in the direction of material flow and two drafting zones, A and B, exist. The draft in Zone B is the break draft (usually in range of 1.1–1.4), which reduces the interfiber cohesion and friction, and prepares the material for the main draft Zone A. The actual draft is the increase in delivered length (compared to fed length) or decrease in linear density ² of the sliver (Klein, 2016a; Gordon & Hsieh, 2006; Lawrence, 2003).

Fig. 3.9. Roller drafting arrangement in draw frame (Klein, 2016b).

The number of drawing passages can vary from one to three. More commonly two drawing passages (breaker and finisher) are used to produce single-fiber yarns whereas three passages (breaker, intermediate, and finisher) are used for blending fibers at the drawing frame level. The blending of natural and man-made fibers such as cotton and polyester is predominantly performed at the drawing stage. Drawing operations are known as draw frame and gill box in cotton (short-staple) and wool (long-staple and variables staple) spinning, respectively. In gilling, a single-zone drafting system along with pins is used, to comb through and orientate the longer worsted fibers, which can stand this more robust mechanical action.

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Adaptive neuro-fuzzy systems in yarn modelling

A. Majumdar , in Soft Computing in Textile Engineering, 2011

Effect of input parameters on yarn unevenness

Figure 7.5 depicts the effect of mean fibre length and short fibre content on yarn unevenness in accordance with the ANFIS rules, keeping the third input variable (yarn count) constant at the mid-level (23.4 Ne). It is observed that as the fibre length increases there is consistent reduction in yarn unevenness, although the effect is not very pronounced. It is also noted that the increase in short fibre content in cotton leads to a drastic increase in yarn unevenness. During roller drafting, short fibres float in between the front and back roller nip and their velocity is totally uncertain. Thus, the short fibres generate drafting waves and increase the unevenness of the fibre strand. Figure 7.6 shows the impact of yarn count and short fibre content on yarn unevenness, keeping fibre length constant at mid-level (0.93 inch). In general, finer yarns exhibit higher unevenness, as expected. The effect of short fibre content on unevenness is very gradual for coarser yarns and radical for finer yarns. In the case of finer yarns, there are fewer fibres in the yarn cross-section and thus the generation of drafting wave causes increase of irregularity by a greater extent as compared to coarser yarns. Therefore, short fibre content should be given more importance when selecting the cotton fibres for finer counts.

7.5. Effect of fibre length and short fibre content on ring yarn unevenness.

(source: Majumdar et al., 2008)

7.6. Effect of yarn count and short fibre content on ring yarn unevenness.

(source: Majumdar et al., 2008)

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