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REPORT Twist-less & self twist yarns Group Members Weerasingha W.H.A . : 061058U Wickramarathne T. I : 061060T Wijerathna E.A.C.N. : 061061X Wijesena.R.N. : 061062C Gunawardana C.A. : 061063F Subject : TT 4140 – Advanced Yarn Formation Date of Sub.: 23/12/2009

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REPORT

Twist-less & self twist yarns Group Members Weerasingha W.H.A . : 061058U Wickramarathne T. I : 061060T Wijerathna E.A.C.N. : 061061X Wijesena.R.N. : 061062C Gunawardana C.A. : 061063F

Subject : TT 4140 – Advanced Yarn Formation

Date of Sub.: 23/12/2009

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1. Twist-less yarns

Twist-less yarns are belong to a special yarn category which yarn formation involve certain inter fiber

cohesion enhancing methods than twisting. Most common methods of improving inter fiber cohesion

without using a twist to form a twist-less yarn are temporary or permanent adhesive bonding and

continuous felting. These methods provide certain level of cohesion to the fibers so that the fibers are

bonding together with enough attractive force form to spin a yarn.

1.1 Methods

As previously introduced there are two major well established methods of manufacturing twist-less

yarns. They are,

• Adhesive bonding

• Continuous felting

1.1.1 Adhesive bonding

In adhesive bonding inter fiber cohesion between fibers are improved in to a level which is sufficient

enough to spin a yarn is given by using an adhesive. The adhesive is applied to the yarn during the

yarn manufacturing process and then let the adhesive forces to build up in the yarn. The adhesive is

applied as an adhesive solution in the process. The yarn impregnated with the adhesive solution is

processed through a dryer unit so that the water part of the solution is vaporized leaving the adhesive

in the yarn, giving the required cohesion forces between fibers.

1.1.1.1 Adhesive bonding process

Adhesive bonding process can be classified in to two main areas. They are namely as staple adhesive

bonding method and filament bonding process. The staple bonding process is again divided in to two

levels based on the drying system. These two methods can be identified as methods where the

combined dryer with the spinning system and separated dryer and spinning system. The purposes of

having combined and separated dryer is discussed in later in the report.

Adhesive bonding

Staple bonding process Filament bonding process

Combined dryer Separated dryer

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Process of adhesive bonding with combined dryer

Process of adhesive bonding with separate dryer

Drawing

Introduction of adhesive Mixture

Introduction of false twist

Drying

Winding

Fig.1.1: Process flow of adhesive bonding with combined dryer

Fig.1.2: Process flow of adhesive bonding with separate dryer

Drawing

Applying inactive inactive Adhesive mixture

Introduction of false twist Cone winding

Steaming

Unwinding

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Process of filament bonding

1.1.1.2 Control parameters in adhesive bonding

In spinning a twist-less yarn in adhesive bonding methods following five control parameters are very

critical. They are described in following.

• Fiber control in roller drafting

Fiber control in the roller drafting system is very important parameter that should be controlled in

twist-less yarn manufacturing. It’s evident in most of the cases the machines are occupied with very

basic types of drafting system to allow high speed production. Especially in the speeds such which are

three to five times faster than the normal ring spinning systems it’s the performance of the roller

drafting is very critically yielded than most of other parameters. But the problems are raised whether

the simple roller drafting would be capable of providing the yarn evenness and other spinning

performances especially in very high speeds as noted above. In twist-less spinning machines with

adhesive bonding the drawbacks of the roller drafting system in high speeds is somewhat avoided by

using two methods.

Ø Wet spinning

Ø Using additional fiber control devices in drafting section.

Fig.1.3: Process flow of adhesive bonding for filament

Filament unwinding

Appling of the thermoplastic resin

Covering with staple fibers

Condensing

Introduction of False twist

winding

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From above wet spinning has given the twist-less yarn spinner the capability of drafting fibers with

sufficient evenness and with required level of spinning properties in high speeds. Wet spinning is the

process where the fiber roving is applied with the suitable amount of moisture to before process

through the drafting rollers. Due to the moisture present in the roving the inter fiber cohesion between

fibers is significantly improved allowing fibers much controllable in the roller drafting region.

Especially in wet spinning the drawing evenness is not highly affected with the increasing production

speeds. Due to this reason spinners are given the opportunity to go with high speeds in twist-less

spinning than using dry spinning. Apart from this it’s found that the drafting settings are not

significantly affect to the drafting evenness as well. Following two graphs describes the scenario much

better.

• Adhesive percentage

Adhesive percentage determines the final strength of the yarn. The reason behind that is that adhesive

is the agent actually giving the cohesion between the fibers to form the yarn. So as the twist level of a

yarn determines the strength of the ring spun yarn adhesive percentage plays a major role in

determining the strength of the yarn in twist-less spinning. However the adhesive percentage can not

be increased as the way the spinner requires as well. More the adhesive percentage in the yarn more

will be the stiffness of the yarn as well. Hence finding the correct adhesive percentage is a quest of

determining the maximum level of stiffness and minimum level of strength required in the yarn for

certain end use.

• Condensation

Condensation of the fibers is another control parameter that needs to be given consideration in twist-

less spinning yarn manufacturing processes. Condensation governs how much the fibers are packed

together. We can safely assume that the fibers are drawn from the front roller nip of the drafting unit of

twist-less spinning machine is having a flat cross section. Additional device should be used to

condense the fibers more so the final yarn will be having a near circular cross section.

Fig.1.4: Yarn evenness Vs production speed Fig.1.5: Yarn evenness Vs Draft settings

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• Fiber support in the material path

It’s important to note that the adhesive doesn’t play much role during the spinning process in

strengthening the fiber strand before drying. Understanding that yarn has to be passed through certain

distance and will be applied some tension specially in winding some methods should be used to

support the fiber strand on its material path. The supporting would help to minimize the irregularities

of the process yarn as well as avoid yarn breakages due to high tension in the material path

• Drying

In the drying process the water part of the adhesive solution will be vaporized leaving only the

adhesive component in the yarn. But achieving the right drying quality in a machine which is operating

three or five times greater than the normal ring spinning conditions the drying unit needs to be long

and of complex design. Due to this reason drying has made the major limitations in twist-less yarn

manufacturing speeds. It’s found that the combined drying with the spinning system is not feasible in

the production rates over 100m/mins.

To overcome the drawbacks of the online drying, a new drying method call inactive adhesive system is

introduced. In inactive adhesive system the yarns are applied with inactive starch and wound in to

cones. And later to this process the cones are taken to a steaming chamber and steamed to activate the

adhesive. After sufficiently activating the adhesive cones are then again unwound and wound in to

separate packages.

1.1.1.3 Adhesive bonding machinery

Tek-Ja machine

Fig. 1.6: Tek-ja machine

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• Fiber control in roller drafting : Wet spinning, Aprons

• Adhesive percentage : Adjusting the rotation and pressure in press roll

• Condensation : Rub cylinder

• Fiber support in the material path : Yarn is supported by presser cylinders along the surface of

the carrier cylinder.

• Drying : Online dryer unit

Bobtex staple process

• Fiber control in roller drafting : Wet spinning

• Adhesive percentage : Adjusting the rotation and pressure in feed roller

• Condensation : False twisting device

• Fiber support in the material path : By applying a false twist

• Drying : Inactive starch application with intermitted dryer unit.

R : Creel P1, P2 : Press rollers T : False twist device G : Yarn guide P : Cross wound package F : Feed roller S : Stirrer

Fig. 1.7: Bobtex staple machine

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Bobtex filament process

1.1.2 Continuous felting

In continuous felting, wool and wool blends are used as the fibers. The reason behind this is that,

continuous felting is using the inherent characteristic of wool fibers named as felting as the method of

improving the inter fiber cohesion between the fibers to spin a yarn. Felting is a effect when two wool

fibers trying to make a relative motion abrading their surfaces, the scales of the fibers are giving a

locking effect, increasing the inter fiber strength significantly. This characteristic is encouraged by

applying a felting medium. The purpose of felting medium is that, it acts as a lubricate encouraging the

relative fiber movement thereby providing more opportunities to felting.

In continuous felting machine, the fibers are forced to move unidirectional under a mechanical force

providing opportunities to relative motion between fibers. The resistive force caused by fiber scales

finally result in fiber entanglement increasing frictional forces. Felting of yarn readily occurs in suitable liquid medium offered in felting machine when the fibers are mechanically agitated. Liquid

acts as a lubricant improving fiber relative movement, thereby increasing felting effect.

The machine which was commercially successful in continuous felting is known as periloc machine.

Following is the machine details.

Fig. 1.8: Bobtex filament machine

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Wool sliver is fed to the felting medium under a zero tension conditions to enhance the felting

lubricate absorption. The naval like device fixed to the end of the felting medium outlet is giving

certain false twist to support the yarn by applying additional strength to the yarn. The felting device is

a rotating main cylinder with rotating rollers. When the yarn is fed over the rotating rollers and main

cylinder which is rotating in opposite directions the fibers are forced to perform a relative motion

between each other. The lubricate applied to the sliver is encouraging this effect and after going over

several rotating rollers fiber is given sufficient strength to spin a yarn. At the output the sliver is

squeezed to drain out any remaining felting liquid and then sent for winding.

1.2 Twist-less yarn structure, properties & end use

1.2.1 Twist-less yarn structure

Since there is no twists in the yarn, twist less-less yarn structure is different to the normal twisted yarn

structure. Twist-less yarn has flat and ribbon like in appearance.

The twist-less yarn is formed by binding the individual fibres to each other by using starch. After the

yarn is used to manufacture the fabric the starch is washed and removed. Then it is difficult to clearly

separate individual yarns in the fabric.

Fig. 1.9: Periloc machine

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1.2.2 Twist-less yarn fabric properties

• Strength

In textile materials strength is a major property which is considered in use. The strength of a fabric

which is made out of twist-less yarns is depend on the amount of inter fibre friction. As the friction

increase with increasing fibre crossing points the strength of the fabric also increases. After the twist-

less yarns are washed to remove starch, virtually there are no strength in the yarn. Due to this the

structure of the fabric is more important in the aspect of strength since the structure determines the

number of yarn crossing points.

As the strength of the fabric that is made from twist-less yarns is depend on the inter fibre friction, the

tensile and tearing strength of such fabric is higher than a normal fabric made out of twisted yarns.

• Cover factor

Twist-less yarn fabric have higher cover factor than normal twisted yarn fabrics. That is due to the flat

& ribbon like structure of the twist-less yarns and the loose fibre arrangement within the fabric. And

also the twist-less yarn flatten within the fabric structure after washing to remove starch. A much

lighter twist-less yarn fabric is able to match a comparatively heavy normal fabric with same cover

factor. This is achieved by decreasing the number of yarns per centimeter in the fabric. However the

decrease in number of yarns per centimeter tends to decrease the fabric strength.

• Luster

The fabrics made from twist-less yarns show a different characteristic luster than normal fabrics. Since

there is no twist in the yarn, light is reflected without scattering ultimately giving an attractive luster

effect.

• Bulkiness

When considering the twist-less yarn structure, the yarn is very bulky than a normal twisted yarn. This

is because of the loose arrangement of the fibres and less stressing forces such as twist, in the twist-

less yarn fabrics.

• Water and air permeability

Twist-less yarn fabrics has a more open structure than normal fabrics. This has a greater effect when

considering the permeability of fabrics which is made from twist-less yarns. Air and water

permeability is high in twist-less yarn fabric, comparatively to normal fabric.

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• Effect of laundering

As mentioned above the strength is an important parameter in textile materials. When a fabric is

subjected to a laundering process fabric strength will decrease. Lose of fabric strength has a direct

influence in the fabric durability. Usually fabrics loose the strength in two ways in washing.

1. by chemical degradation of fibres

2. by loss of fibres from the yarn

Chemical degradation of fibres happen with the chemical reactions which will occur at specific

conditions (such as temperature, time and method etc.) used in the laundering process. Due to this

chemical reactions the fibre tends to diminish resulting lose of strength.

It is clear that with the loss of fibres from the yarn, the yarn loose strength and ultimately it results in

loss of fabric strength.

In the washing processes chemical degradation of fibres can be considered very small. Hence, lose of

strength can be attributed to the loss of fibres from the yarn. In twist-less yarns, the loss of fibres is

higher than a normal twisted yarn. When considering only that phenomenon, the fabrics made from

twist-less yarn should decrease the strength, but actually it is not the case. In twist-less yarn fabrics the

fall in strength due to fibre loss is counter-balanced by increase in friction between fibres as a result of

fabric shrinkage. Therefore the loose of strength of the twist-less fabrics during the washing operation

is negligible.

• Wet-ability

Normal twisted yarns are tightly constructed with the twist inserted to the yarns in order to bind the

fibres together. And the fabrics constructed with those yarns also comparably tighter. But the fibres in

the twist-less yarn fabrics are not twisted and loosely packed. Therefore the twist-less yarn fabrics can

easily absorb water than the normal fabrics. So the wet-ability of twist-less yarn fabrics are

comparatively high than normal fabrics. That means twist-less yarn fabrics take a less time to absorb a

standard amount of water into the fabric.

• Wicking property

As described above, since the twist-less yarn fabrics have loose structure than normal twisted yarns it

allows easy and quick abortion of water in to the yarn. At the same time due to the open structure of

the twist-less yarn fabrics the capillary action that will be generated within the fabric will be high

causing higher wicking property.

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• Shrinkage under tension

Both knitted and woven fabrics of twist-less yarns suffer much less shrinkage in the fabric forming

process. This is due to the less stresses that will be stored within the twist-less structure during the

knitting and weaving operations. And to this lower storage of tension, the release of tension after the

fabric forming process also will be lower in the twist-less yarn fabrics resulting lower shrinkage.

• Crease Resistance

When considering about the crease resistance property, the twist-less yarn fabrics give similar results

as with the normal fabrics.

1.2.3 End uses

• Towels

When considering the bulkiness and the softer handle of twist-less yarn fabrics, they are more suitable

to be use in towels such as bath towels, hand towels & face towels etc. And also the good absorbency

properties of twist-less yarn fabrics enhance the usability as towels.

• Pyjamas and cotton bath wear

Usually in a pyjama or a bath cloth, the user expects properties like light weight and comfortability.

All those requirements can be easily matched with twist-less yarn fabrics without much difficulty. In

addition to that twist-less yarn fabrics are able to give a luxury look in the fabric due to the good luster

properties.

• Shirts

The light weight, softness, comfortability and luxury look (luster) of the twist-less yarn fabrics enable

them to be used as shirt fabrics.

• Tent clothes

Light weight twist-less yarn fabric is almost equal to normal heavy tent cloth in respect of air & water

permeability. And the tearing strength of twist-less yarn fabric is high than normal fabrics. These

properties allow twist-less yarns to be used as tent fabrics.

• Composites

Twist-less yarn with long, aligned fibres are now using to manufacture composites. One such

composite is as load bearing applications. This is because twist-less yarns has an added advantage of

having a lower weight than conventional reinforcements. Some other composite applications are to

reinforce naturally derived plastics and interior parts for automotive industry.

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2. Self twist yarns

2.1 Basic Concepts

2.1.1 Introduction

Since textiles were first produced, yarn composed of staple fibres has been given strength by the use of

continuous, unidirectional twist. No alternative technique has been developed on a commercial scale,

although attempts have been made to use adhesive bonding.

The insertion of unidirectional twist is a comparatively slow process. Where it is done on conventional

ring or cap frames, production rate is limited by factors such as traveler speed, balloon tension, and

power to rotate the bobbins. Thus, spinning is expensive, and it also represents a production

bottleneck.

Open end spinning is a development which can lower the cost of the spinning process. However, there

are doubts about its ability to produce a worsted type yarn and to spin wool fibres.

The concept of self twist arose from a consideration of the use of alternating twist. In conventional

spinning, it is necessary to rotate the yarn take-up package in order to insert unidirectional twist. This

is a short-coming of the process. If it were possible to accept twist alternating in S and Z directions, it

would be necessary only to rotate the strand of fibres rather than the associated take-up package. A

strand of fibres has a small mass and diameter. Therefore it should be possible to rotate it at high speed

with the expenditure of very little energy.

Fig. 2.1: The layout of a hypothetical spinner for spinning a single yarn with alternating twist.

A hypothetical spinning system based on this concept is shown in fig.2.1. The resultant alternating

twist yarn is depicted in fig.2.2. No twisting mechanism is shown in fig.2.1 but it is possible to

imagine the strand being pulled through a pair of transversely reciprocating surfaces which would

impart alternating twist.

Fig. 2.2: The alternating twist form of the hypothetical yarn

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Unfortunately, the insertion of alternating untwisting twist into the strand of fibres also inserts an

alternating torque, So that as soon as the yarn is removed from the restraint of the take-up package it

untwists. This can be overcome by setting the yarn on the package. However, the application of

tension causes the strand to untwist so that it has a low strength.

If, however, two such strands are brought together before the untwisting torque has been released, the

untwisting torque, together with the frictional engagement between the two strands, causes them to ply

about one another. The untwisting torque of the two strands decreases during this operation until it is

balanced by the plying torque. Also, twist has been conserved; if the structure is “un-plied”, the strand

twists are restored to their original values.

Fig. 2.3: Four steps in the demonstration of the principal of self-twist yarn

Two simple demonstrations illustrate the mechanism of self-twisting. If a twist-lively yarn is laid back

on itself it snarls or plies; the untwisting torque of the yarn in the snarl is decreased until it is in

equilibrium with the plying torque of the snarl.

The second demonstration is more complete. If a hank of yarn is setup as in fig.2.3 (a), each side of the

loop twisted as in fig.2.3 (b), then brought together as in fig.2.3 (c), the assembly will self-twist upon

being released (fig.2.3 (d)).

The most general concept of self-twisting involves bringing together at least two strands, at least one

of which has alternating twist along its length, in practice, a staple self twist yarn is made most

conveniently from two identical strands having identical levels of alternating twist. DuPont show some

preference for three identical strands in their filament carpet yarns.

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Fig. 2.4: The basic foam of a simple self-twist spinner

The self-twist spinner in its simplest form is shown in fig.2.4. A drafting system presents two strands

of fibres to a pair of rubbers-covered reciprocating and rotating rollers which insert alternating regions

of S and Z twist into each of the two strands. The two strands are then immediately converged and

allowed to self-twist, after which the self-twist yarn is wound on a take-up package.

Fig.2.6: Block diagram of the twisting regions of a self-twister spinner

Fig.2.6 shows a block diagram of a self-twisting arrangement. Strand 1 travels between nip 1a and

nip2, and strand 2 travels between nip 1b and 2. Usually, nip 1 is provided by a common roller nip, the

front drafting roller, and nip2 is often replaced by a convergence guide. Twister devices, 1 and 2 act on

the strands.

Fig.2.7: Each strand in the twisting zone is divided into two zones of length u, and v

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In theory, any false twisting device can be used providing its action is made intermittent. Suppose a

cycle of twisting to be divided into two equal intervals, the twister twisting during the first, and the

strand passing through it without hindrance during the second. If the twister rotates so as to insert, say,

s-twist in the strand over u (fig.2.7), it will, while inserting s-twist , also insert z-twist in the strand

leaving the twister over v. during this half of the twisting cycle the z-twist in v passes beyond nip 2

and proceeds to generate self-twist.

If this first interval of twisting were prolonged, the steady state condition of false-twisting would be

attained where u would be s-twisted and there would be no twist in v. However, before this state is

approached, the twisting action is halted and the s-twist in u runs into v. reverses the previous z-twist

there, and commences to pass beyond nip 2. As this half-cycle continues, the level of s-twist in u + v

diminishes until the next cycle commences.

Thus, with an intermittent twister the twist in u is always in the same direction but varies cyclically in

intensity, while the twist in v, which enters the self-twist yarn, varies cyclically in direction.

Obviously, the smaller is v, the greater is the twisting efficiency,

Fig. 2.8: Representation of the foam of self-twist yarn

This simplest form of yarn is depicted in fig.2.8 (a). Both strands have been converged with their twist

structures exactly in phase, and such a yarn is called a “zero-phase” or “in-phase” yarn. The points in

the yarn where there is no twist are termed “twist changeovers”; they are obviously points of weakness

in the yarn.

It is possible to bring the two identically twisted strands together out of phase, as shown in fig.2.8 (b).

Such a yarn is termed a “phased” yarn. Its phasing is specified with reference to a complete cycle

(3600) of twist distribution, i.e., the length of a zone of S-twist plus a zone of Z-twist. Such phased

structures can be stronger than zero-phase structures, since there is no point in the yarn where there is

no twist. Where one strand has zero twist the other is twisted and there is ply twist; where there is zero

ply twist both strands have twisted.

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2.1.2 In-phase yarn under stress

When an in-phase self-twist yarn is subjected to stress, several things happen. Firstly, the ply twist

starts to decrease, and it is a reversible process. Secondly provided the twist changeover is sufficiently

sharp or short enough, a slippage or loss of twist can be seen to occur in the region of the changeover.

This is a non-reversible process. If the increase of stress is halted, this new twist distribution is stable

until such time as the stress is again exceeded.

The strength of the yarn, as in the case of conventional yarn, is dependent on the binding effect of the

twist, so that the weak portion in the region of twist must be bridged by fibres having both ends

extending into regions of appreciable twist. As the region of low twist extends under increasing yarn

load, the number of fibres bridging it decreases until the yarn consequently breaks.

Fig.2.9: (a) upper diagram: the expected twist distribution of S1 and S2 along a 60-tex 1200

- Phase yarn of 20cm cycle length.

(b) Lower diagram: The values of S1, S2 and D observed in the yarn

2.1.3 Phased yarn under stress

A phased self-twist yarn, twisted and phased for maximum strength, behaves differently from an in-

phase yarn in that rotational slippage and twist redistribution of the strands occur simultaneously with

self-twisting and is independent of yarn tension. Subsequently, the twist distribution is completely

stable.

Fig. 2.9(a) shows the expected twist distribution in the two strands of a 60-tex self twist yarn spun on a

disc on a disc spinner. A feature of this spinner is that it should give very sharp twist changeovers.

Examination of the actual twist distribution in fig. 2.9(b) shows that changeovers have decayed.

With in-phased yarn, the regions of zero twist in the strands and the zero ply twist are all concurrent.

As can be seen in fig. 2.9 (b), phasing serves to displace these regions of zero twist so that they are not

concurrent. Where there is zero ply twist, both strands are twisted, and, where one strand has zero

twist, its fibres are still contributing to yarn strength by virtue of the ply twist. In general, a strong

phased yarn has no particular zone of weakness and breaks at any random point along its length.

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2.2 Methods of inserting alternative twist

2.2.1 Centrifugal-jaw twister

Centrifugal-jaw false twist tubes are a well known feature of woolen ring frames. An obvious way of

making their action intermittent is illustrated in following figure, which represents a cross section of a

twister used in a self-twist spinner.

Fig.2.10.The centrifugal- jaw and twisting head, the rotating cam cyclically opens the rotating

jaws

The strand passes through the body of the tube and is gripped by the centrifugally loaded jaws. These

are pivoted in the rotor which is driven by a belt or tape. Passing coaxially through the rotor and its

mounting tube is a cam-driven actuator carrying a freely rotating nose piece which bears against the

twister jaws. The rotating cam then serves cyclically to force the jaw apart.

Fig.2.11: Configuration of the centrifugal jaw twister

Above depicts a layout for a self-twist spinner in-corpora ting these twisters. To avoid duplication of

the drafting system, and to minimize the distance v, the two strands are converged around a six-roller

assembly. To ensure that strands come together, four of the rollers have circumferential grooves to

guide the twisted strands.

The twist intensity is governed to some extent by the magnitude of the centrifugal-jaw loading and by

the relative speed of the strands through the twisters. The cycle length is governed by the relative

Pulley & belt

Nose piece

Centrifugal jaws

Centrifugal cam

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rotational speed of the cams, and the yarn phasing is determined by the rotational disposition of the

cams with respect to each other.

The production rate is rather limited since it has not been possible to design such a complex twisting

tube to run at the high speed common with false twist tube to run at the high speeds common with false

twist tubes for texturizing. A more practical figure is 10,000r.p.m. Additionally, there is a frictional

force generated in pulling the strand through the jaws and, certainly with wool, this sets a limit on the

centrifugal load and therefore on the twisting efficiency. Typically, one turn of the twister tube

generated only about 0.6turns in the issuing strand.

2.2.2 Intermittent Nip Twister

Fig.2.11: The intermittent- nip twister. Te moving belt creates an intermittent – nip immediately

behind the twister

A variation on the previous twister may be obtained by divorcing the intermittency of action from the

twister tube having, instead an intermittent nip immediately behind the twister. The particular nip

shown is obtained when a raised section of the belt contacts the lower roller. When this nip is open the

twister tube inserts s-twist over u back to the preceding nip, and inserts z-twist into the issuing strand.

When the adjacent nip closes, the tube rapidly reverts to a false twist tube which will have no effect on

the strand twist, so that s-twist begins to pass through it to the output strand. The nip belt should, of

course, have a length of one or an integral number of cycle lengths.

The system can hardly be described as viable for the spinning of staple fibers. There is still the need to

pull the strand through the twist tube and there are difficulties in threading. However, it could

conceivable be of use in the twisting of heavy continuous-filament self-twist yarns and the twisting

tube is amenable to design for high speed.

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2.2.3 Disc Twister

Fig.2.12: Disk twister assembly

In this type of spinner each strand is twisted by passing it between two transversely contra-moving,

elastomeric surfaces. These surface are provided by mounting rubber annuli on the disc, as shown in

hear

Fig.2.13: Disk twister device

A comparatively slow rotational speed of the discs gives rise to high twisting rates of the strands.

Intermittency twisting is obtained most conveniently by cutting away suitable portions of the rubber

annuli on the large disc. The phase relationship between the strands is likewise determined by the

angular relationship of the portions cut away.

A critical factor in the successful operation of the disc twister is the stability of the strand position in

the twisting region while it is being twisted. It has been found that this position is stable if the

transverse motion of the twisting surface has a small component in the direction from which the strand

is delivered. This accounts for the off setting of the discs and their direction of rotation as indicated in

above figure. Some limitations have this method there are slippage between the twisting surface and

the strand and this increase the possibility of wear of the twisting surface. In fact, during operation, the

gap between the twisting surfaces must be adjusted occasionally to compensate for wear.

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2.2.4 Fluid-Vortex Twister

Fig.2.14: Fluid vortex twister assembly

This is another technique of twisting a moving strand of fibers by passing it through a small chamber

having a tangential air jet. Air enters the chamber, preferably at over half sonic velocity, and spiral

around the chamber before escaping at the ends. The spiraling action of the air causes twisting of the

strand. This twisting method has been used to spin staple self-twist yarns and self-twist continuous-

filament yarns.

The air twister is mechanically simple and easy to set up. Limited experience suggests that its twisting

efficiency is influenced significantly by variables such as strand tension, with the consequence that the

twist in the resultant yarn is very variable. For staple fibers the size of the twisting chamber must be

large enough to allow the passage of any slubs which may occur, it’s possible that more constant

twisting could be obtained if a smaller twisting chamber could be used. There appear to be the same

limits on production rate as with the disc twister.

2.2.5 Oscillating Roller Twister

Fig.2.15: Oscillating roller twister assembly

Oscillating rollers

Drafting system Convergence guide

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In the case of staple fibers, the most suitable method of inserting alternating twist is to pass the strand

of fibers through the nip of a pair of rubber-covered rollers which rotate to transport the strand and also

reciprocate or oscillate axially in opposition to twist the strand. The virtue of this arrangement is that it

is easy to spin phased yarn. One strand of the pair is twisted by one roller pair and the second strand by

the other roller pair. The reciprocation of the two roller pairs is coupled together in the desired phase

relationship.

Compares with others some problems has identified in this method, these simple roller systems is

maintenances of constant and predictable twister nip or gap conditions.

2.3 Alternative spinning Systems utilizing self twist

2.3.1 ST yarn

ST is the abbreviation used for in phase yarn or low phase angle yarn from basic self twist machine. It

is a two or more strand structure wherein each strand has same count. It has below disadvantages in

using in fabrics.

Unable to withstand as warp yarn in weaving is another problem .Inter yarn abrasion in a warp sheet

cause fibres trapping between yarns and entangled fibres tend to unpeel or untwist the self twist

structure at twist change overs.

Another problem is the cyclic nature of self twist structure manifested as patterning in a fabric. Due to

the difference of reflectance in different twist sections shows a patterning effect. Hide the patterning

can be done through Use of dyed yarns and by Raising or Brushing.

2.3.2 STm yarn

One strand of self twist yarn is reduced in weight, the untwisting torque of the other strand tends to

predominate at the self twisting and the heavy strand tends to wrap the lighter about it self in an

alternative manner. STm refers to the situation where heavier strand is staple and other is a

monofilament.

The resultant STm structure is a strand of sThe staple fibres having a very low alternating twist bound

together by a monofilament spiraling helically in reversing direction about the outside. Advantages are

mainly that spinning limit is extended and increase productivity and also Patterning would be less.

2.3.3 Duplex self twist yarn

• 2ST yarn

Two ST yarns are assembly wound on the one package at the self twist spinner and the final 2ST yarn

is a 4 ply structure. In 3ST, there are three ST yarns would be assembly wound successively phased

and twisted. It has certain superior properties but count range is restricted and Production is impaired.

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• 2STm yarn

Two STm yarns are assembly wound on to the spinning package .No of strands twisted from twisting

rollers are reduced because of monofilaments at the expense of inconvenience of handling

monofilaments.

2.3.4 Double twister Systems

The concept involves self twisting together of two self twist structures.

• ST2 Yarn

Fig.2.16: ST2 yarn preparation Fig.2.17: ST2 yarn structure

This is where self twisting together of two self twist structures (ST) yarns take place The resultant yarn

Weaves exceptionally well. But Patterning still prevails on such fabric and count range is limited.

• (ST)m yarn

Fig.2.18: (ST)m yarn preparation

Add a monofilament to ST yarn in its second twisting stage. The resultant yarn is stable enough to

withstand weaving. By adding a monofilament to the ST yarn at second twisting stage it is possible to

bind the twist changeovers with the monofilament.

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• (STm)2 yarn

Fig.2.19: (STm)2 yarn preparation

Two STm yarns are self twisted together to give (STm)2 yarn.

The substitution of fine monofilaments for two of the strands extends the available count ranges.

Weave exceptionally well and less patterning due to the presence of monofilament. This will reduce

the number of fibre strands passing through the twisting rollers which improves productivity.

• STmm yarn

Fig.2.20: STmm yarn preparation

The second monofilament serves to bind the first monofilament and the stability and robustness of

resultant yarn structure are enhanced compared to STm yarn. In this method the linear productivity is

doubled in comparison to ST yarns due to monofilaments which do not pass through the twisting

rollers.

2.3.5 STT yarns

Alternative way of the ST system where spinning two singles on to an assembly wound and transfers

to the twisting process. The output of ST spinner should have sufficient tenacity to ensure the

satisfactory level in the next process of twisting. The operation of ST spinning within the STT system

is similar to conventional spinning.

The commercial development of spinning system was undertaken by Repco Research Incorporation, Australia. Yarn characteristics depend on ply twist and added twist. If the level of twist is suitably

chosen the STT yarn is competitive with conventional yarns in processing performance. The major

problems of yarn robustness are solved and the fabric patterning is eliminated by the addition of

unidirectional twist. STT provide the capability of providing a wide range of properties especially for

woven fabric and selection of added twist factor is a key for this. There by for STT has been developed

to the stage of commercial use.