Advance Spinning

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5. New Spinning Systems

5.5 Friction Spinning



Friction spinning was first developed when Fehrer produced the DREF friction spinning system in 1973.

In this machine, the pre-opened fibres were made to fall onto a perforated cylindrical drum, the

rotation of which imparted twist to the fibre assembly. Due to problems in controlling the flow, slippage

occured between the fibre assembly and the perforated roller, which reduced the twist efficiency.

DREF-II friction spinning

Later the DREF-II friction spinning machine was developed to overcome this problem. This machine

incorporates a specially designed inlet system which provides the required draft. These drafted slivers

are opened into individual fibres by a rotating carding drum (opening roller) covered with saw-tooth

wires. The individual fibres are stripped from the carding drum by centrifugal force supported by an air

stream from a blower. The fibres are then transported by additional rollers to two perforated friction

drums. The mechanical friction on the surface of the drums twists the fibres. Suction through the

perforation of the drum assists the twisting process and helps in the removal of dust and dirt.

Friction spinning technology works on the principle of friction twisting. Figure 1 shows the working

principle of friction spinning. In this system, the pre-opened fibres are fed onto a moving, perforated

collecting drum underneath which there is suction device. The fibres are fed between this and a second

rotating drum. Twisting occurs due to the frictional forces between the drums and the fibre assembly.

The process is also known as mechanical-aerodynamic spinning due to the fact that the spinning effect

is produced by the movement of two spinning bodies (friction drums) assisted by air suction. Due to its

versatility and high output speed of up to 300 m/min, the friction spinning system is considered

suitable for producing yarns in the coarse count range, i.e. greater than 20sNe.



Figure 1. Principle of Friction Spinning

The main operations in friction spinning are:

sliver feed

fibre opening

fibre transportation

fibre accumulation

twisting and winding

DREF-III friction spinning

The DREF-III friction spinning machine was introduced into the market in 1981. This machine was

developed to improve yarn quality, extend the yarn count up to 18s Ne and produce multi-componentyarns. The DREF-III uses a core-sheath type friction arrangement as shown in Figure 2. In this

machine an attempt is made to improve the quality of yarn by aligning the majority of fibres in the

direction of yarn axis. The remaining fibres are wrapped round the core fibres to form a sheath. The

sheath fibres are wrapped round the core fibres by the false twist generated by the rotating action of

drums. Two drafting units are used in this system, one for the core fibres and other for the sheath

fibres. This system produces a variety of core-sheath type structures and multi-component yarns using

different core and sheath fibres in the count range of 1-18sNe with delivery speeds as high as 300

m/min.



Figure 2 : DREF-III friction spinning system

DREF-2000

DREF-2000 employs a rotating carding drum which opens the slivers into single fibres. The fibres are

stripped from the carding drum by centrifugal force and carried to two perforated spinning drums. As

with previous designs, the fibres are subsequently twisted by mechanical friction on the surface of the

drums which rotate in the same direction. The process is assisted by air suction through the drum

perforations. The machine can produce „S‟ and „Z‟ twisting yarn without having to reconfigure the

machine.

Platt Saco Lowell’s (PSL) Master spinner

Platt Saco Lowell‟s (PSL) Master spinner is also a true open-end (OE) friction spinning system. It differs

from the DREF-II in respect of fibre feed and the construction of the friction drums. The principle of

operation of this machine is shown in Figure 3. A drawframe sliver (1) runs from a can into an opening

assembly. This consists of a feed roller and an opening roller (2), and opens the fiber strand in the

same way as the opening device in rotor spinning.



Figure 3 : Working Principle of PSL Masterspinner.

The separated fibers pass through a specially shaped fiber channel (3), carried by an air flow from a

vacuum inside the suction roller (4) into the converging region between the two friction rollers. One of

these rollers is perforated to act as a suction roller, whereas the second roller is solid(5). A yarn (6) is

formed in the convergent zone.

A secondary suction duct at the end of transfer duct helps to give fibre orientation, and therefore to

keep the fibres parallel to the yarn axis, resulting in improved fibre orientation and fibre extent in the

final yarn. In the twisting assembly, one friction drum is perforated and includes a suction slot while the

other is a solid roller which provides effective friction transfer. Unlike the DREF system, the spinning

assembly is enclosed and so makes more efficient use of the air flow generated. However, these



machines have not been successful in the longer run, mainly for two reasons:

inadequate yarn strength, i.e. low utilization of the fiber properties, and

inconsistency of the spinning results

Features of Friction Spinning

The main advantage of the friction spinning system lies in its ability to generate a number of turns per

unit length of yarn with one revolution of the twisting element. It is possible to spin yarn at very high

production rate up to 300 m/min due to the low spinning tension required. This system can process a

wide range of fibres. It is possible to produce large package, therefore no rewinding is required. It is

also possible to spin core-spun yarns and multi-component yarns on DREF-III machine.

Friction spinning systems have number of limitations which restrict its acceptance as a viable system

for producing general-purpose yarns.

The main drawback is lower yarn strength. Poor fibre orientation renders the friction spun yarns

relatively weak.

The extent of disorientation and buckling is greater with longer and finer fibres.

The twist variation from surface to core is quite high. This is another reason for the low

strength of friction-spun yarns.

The count range is limited and it is not possible to produce fine yarn.

Friction spun yarns have a higher tendency to snarl.

Yarns unevenness and imperfections also increase as production speed increases.

Fibre processing in friction spinning

The opening roller assembly plays an important role in creating a stream of individualized fibres and is

similar to that used in rotor spinning. It is recommended to use garnet wire or needle pin-clothed

opening rollers to cope up with the high throughput. The feeding of slivers varies with the type of

friction spinning machine. In case of PSL Masterspinner and DREF-5 friction spinning machine, a single

sliver enters the unit through a fibre duct. In case of other DREF friction spinning machines a group of

slivers arranged parallel to each other are fed through together. In comparing the two types of feeding

system, it is found that the multiple sliver feed system produces a higher rate and reliability of feed.

In the case of DREF-II friction spinning machine, for example, slivers with a feed weight of 10-15 ktex

can be fed. The drafting unit for the DREF-II spinning system consists of a specially designed drafting

unit. The drafting unit of two pairs of inlet rollers retains the slivers (normally five) and provides the

required drafting. The drafted slivers are opened and separated into individual fibres by a rotating

carding drum. The fibres are subsequently stripped off by air currents and deposited in the nip of the

spinning drums.

As has been noted, the DREF-III spinning system uses two sliver feed units. A drafted single sliver of

2.5-3.5 ktex is fed into the drafting unit, forming the yarn core. A second drafting unit feeds five slivers

which form the yarn sheath. The first drafting unit consists of three drafting zones (with four pairs of

rollers) which drafts the core sliver. The inlet speed varies from 0.85-8.5 m/min. There is also scope to

feed a filament or a wire as the core component in a multi-component yarn. The core constitutes up to



80% of the yarn density. The second drafting unit consists of two pairs of inlets rollers which draft the

sheath slivers. The inlet speed ranges between 0.12-1.2 m/min. The opening rollers rotate at 12,000

rpm and have saw tooth wire covering. The angle of the teeth can be varied e.g. 10º for synthetic and

20º for cotton fibres.

The individualized fibres are transported by air currents through the feed duct and deposited in the nip

of the spinning drums. These fibres are in free flight under the influence of the air current through theduct. It is essential to maintain a homogeneous fibre flow with proper alignment and orientation of

fibres. Figure 4 shows the fibre opening and feeding device of the DREF- III friction spinner.



Figure 4 : Fibre opening and feeding device of DREF- III friction spin

There is a practical problem of assembling fibres in the yarn with good orientation because of varying

amount of turbulence in the transport duct. The fibres move at very high speed through the duct but

slow down on leaving the duct and arriving at the nip of the friction drum. This not only disrupts the





Sources :

W. Klein, “Technology of Short Staple Spinning”, The Textile Institute, Manual of Textile Technology, A

Carl A. Lawrence , “ Fundamentals of Spun Yarn Technology”, CRC Publications, 2003.

P.R. Lord, Hand Book of Yarn Production : Science, Technology and Economics, Tailor and Francis, 200 Eric Oxtoby, “Spun Yarn Technology”, Butterworths, 1987.

NCUTE publications on Yarn Manufacturing, Indian Institute of Technology, Delhi.

http://www.google.de/search?hl=de&tbo=p&tbm=bks&q=inauthor:%22Carl+A.+Lawrence%22




5. New Spinning Systems5.6 Air Jet Spinning

Yarn manufacture using the air jet primarily produces fascinated yarns using the false twist principle.

Hence, we discuss about the principle of false twisting before going into actual air jet spinning.

False Twisting

Figure 1 demonstrates the principle of operation of false twisting. If a fiber strand A is held firmly at

two spaced points by clamps K1 and K2 and is twisted somewhere between them, this strand always

takes up the same number of turns of twist before and after the twist element (T). However, these

turns have opposing directions of twist, which are represented in the example in Figure 1A as Z-twist

on the right and S-twist on the left. If the clamps are replaced by rotating cylinders (Z1 and

Z2 in Figure 1B) and the yarn is allowed to pass through the cylinders while twist is being imparted,

the result is governed by the false-twist law and is different from the case of the stationary yarns, as

previously assumed. A moving yarn entering the section (b) already has turns of twist imparted

in section (a). In the example illustrated (B), there are turns of Z twist.

As the twist element is generating turns of S twist in the left hand section, this simply means that

each turn of the Z twist imparted in the first section (a) is canceled by a turn of S twist imparted in the

second section (b). The fiber strand thus never has any twist between the twisting element and the

delivery cylinder. In a false-twist assembly, turns of twist are present only between the feed cylinders

and the twisting element. This principle is exploited, for instance, in false-twist texturing.

Figure 1 : Principle of False Twisting



Fasciated Yarn through False Twisting:

The idealized structure of the fascinated yarn, as shown in Figure 2 consists of parallel fibres held

together by wrapper fibres. The wrapper and core fibres are composed of same staple fibre material.

Since there is no real twist in the core, this type of yarn structures facilitate high production rates.

Figure 2 : Idealized Structure of Fasciated Yarn

Figure 3 demonstrates the principle involved in the production of fascinated yarn using the false

twisting method.

Figure 3 : Principle of Production of Fasciated Yarn throughFalse Twisting.



As already explained, the fibres upstream of the false twister have twist which gets cancelled with

opposite twist once it passes the false twister leading to no twist downstream of the false twister. If

there are enough edge fibres in the feed fibrous assembly, then these edge fibres do not get twisted

with the core fibres upstream of the false twister. Hence, as the core fibres get untwisted after the

false twister, these wrappers which had no twist earlier, get wrapped around the core fibres. This

produces fascinated yarn structure. These types of yarn structures were first promoted byDuPont. Figure 4 shows the schematic of the DuPont system which did not get commercial success.

Figure 4 : DuPont System of Air Jet Spinning

Murata MJS System:

Figure 5 shows a schematic of a Murata MJS double nozzle air jet spinning system. The feed material

is a draw frame sliver fed from a can (1) which is passed to a drafting arrangement (2), where it is

attenuated by a draft in the range of 100 - 200. The fiber strand delivered then proceeds to two air

ets (3 and 4) arranged directly after the drafting arrangement. The second jet (4) is the actual false-

twist element. The air vortex generated in this jet, with an angular velocity of more than 2 million

rpm, twists the strand as it passes through so that the strand rotates along a screw-thread path in the

et, achieving rotation speeds of about 250 000 rpm. The compressed air reaches the speed of sound

when entering the central canal of the false-twist element. Since the axial forces are very low during

this rotation, only low tensions arise in the yarn.



Figure 5 : Two nozzle air-jet spinning principle (Murata MJS)

The ability of the vortex to impart torque is so high that the turns of twist in the yarn run back to the

drafting arrangement. The fiber strand is therefore accelerated practically to full rotation speed as

soon as it leaves the front roller. The edge fibers which ultimately bind the yarn together by becoming

wrapping fibers are in a minority. For process reasons, they do not exceed about 5% of the total yarn

mass. These edge fibers exhibit relatively few turns of twist in the same direction as the false-twisted

core fibers or can even be slightly twisted in the opposite direction. This is partly ensured by causing

the strand to emerge from the nip line in a broadly spread form, but mainly by generating in the first

et (3) a vortex with an opposite direction of rotation to the vortex in the second jet (4).



This first vortex is in fact weaker in intensity than the second and cannot really affect the core fibers,

but can grasp the edge fibers projecting from the strand at one end. Since the first vortex acts against

the twist direction generated by the second jet, it prevents the edge fibers from being twisted into the

core or even twists them in the opposite direction around the core fibers. As the strand runs through

the second jet, the following occurs.

The turns of twist generated by the jet (4) are canceled in accordance with the false-twist law. Thecore fibers, i.e. the vast majority, no longer exhibit any twist; these fibers are arranged in parallel. On

the other hand, the edge fibers (which previously exhibited no twist, relatively little twist, or even

twist in the opposite direction) receive twist in the direction imparted by the jet (4), as determined by

the law of false twist; they are therefore wound around the parallel fiber strand. They bind the body of

fibers together and ensure coherence.

A twist diagram prepared by Dr. H. Stalder demonstrates this twisting procedure (see Figure 6).

Figure 6 : The distribution of twist in the running fiberstrand



The resulting bundled staple-fiber yarn passes from the take-off rollers (6 in Figure 5) through a

yarn-suction device (7) and an electronic yarn clearer (8) before being wound onto a cross-wound

package (9). The two nozzle air-jet spinning system represents a very interesting process, which has

already been introduced into practical operation with some success.

Yarn strength

Figure 7 : Disposition of Edge fibres in Fasciated Yarn.

The tenacity of the fascinated yarns spun with air jet depend on the yarn count. The coarser yarns are

weaker than the finer yarns for the same fibre type. Contrary to the expectation, yarns produced with

finer fibres show lower tenacity compared to the yarns produced with coarser fibres.

The reason for the above observations is that the strength of the fascinated yarns is derived from the

amount of wrapper fibres and the intensity of wrapping. The edge fibres are the ones which ultimatelyget converted into wrapper fibres. The number of edge fibres are limited to the surface of the yarn and

are independent of the number of fibres in the core as shown in Figure 7.



Figure 8 : Extend of Wrapping in Fine and Coarse Yarns

In case of finer fibres, the number of core fibres increase but the edge fibres remain constant. Thisleads to reduction in the proportion of edge fibres, which in turn reduces the lateral stress brought in

by the wrapper fibres. This results in decrease in yarn strength. Again in case of coarser yarns, in

addition to having lesser proportion of wrapper fibres, the intensity of wrapping also less as shown in

Figure 8 as compared to finer yarns.

. 5. New Spinning Systems

5.7 Vortex SpinningVortex spinning technology was introduced by Murata Machinery Ltd. Japan in 1997. This technology is

best explained as a development of air-jet spinning, making use of air jets for yarn twisting. The main

features of Murata vortex spinning (MVS) are

Ability to produce yarn at 400 m/min. which is almost 20 times greater than ring spinning

frame production .

Low maintenance costs, a fully automated piecing system and elimination of roving frame.

The yarn and the fabric properties of MVS yarn are claimed by the manufacturer to be



comparable to those of ring spun yarn.

Principle of operation

The basic principle of operation is shown in Figurs 1 and 2. The sliver is fed to 4-over-4 (or a four-

pair) drafting unit. As t he fibers come out of the front rollers, they are sucked into the spiral-shaped

opening of the air jet nozzle. The nozzle provides a swirling air current which twists the fibres . A guide

needle within the nozzle controls the movement of the fibres towards a hollow spindle. After the fibers

have passed through the nozzle, they twine over the hollow spindle. The leading ends of the fiber

bundle are drawn into the hollow spindle by the fibers of the preceding portion of the fiber bundle

being twisted into a spun yarn. The finished yarn is then wound onto a package.

Figure 1 : Feed material Passage



Figure 2: Expansion of fibre edges due to whirling force of the jet air stream

The structure of vortex yarn compared to other yarns

Vortex yarn has a two-part structure: a core surrounded by wrapper fibres. The number of wrapper

fibres compared to the fibre core is higher compared to the air jet spinning. During yarn formation, theleading ends of the fibres are directed towards the yarn core and the trailing ends wrap around the

core fibres. Such a structure provides the necessary fibre orientation and, at the same time, the

required yarn strength.

One problem with the vortex system is significant fibre loss during the yarn formation. This is related

to the problem of variations in yarn quality which are not detectable by conventional evenness testers

and sometimes only identified by weak points in the finished fabric. The path followed by the fibre in

the currents created by the air jets play a crucial role in yarn quality. Most structural defects are

caused by the deflection of fibres in the air jet from their ideal path.

Both delivery speed and yarn count are significant factors for yarn evenness and imperfections. An

increase in delivery speed results in deterioration of yarn evenness. This is the result of decreasing

efficiency of the air jet stream at higher delivery speeds because there is less time for the wrapperfibres to wrap around the parallel core properly. This particularly affects finer yarns and means that

vortex spinning is best suited for coarser grades of yarn. Nozzle pressure also has a significant effect

on yarn properties. A higher pressure can improve strength because wrapper fibres wrap more tightly

around the core. However, it can also lead to more lost fibres. This creates potential weak points and

increases unevenness in the yarn. A low pressure leads to improved evenness though strength is

reduced. The distance between the front roller nip point and the tip of the spindle (indicated by L in

figure 2) also affects yarn structure. The greater the distance, the higher the level of fibre wastage



and yarn unevenness.

In Vortex yarns, the centre of the yarn is not twisted. Twisting occurs at the outer sides of the yarn, as

shown in Figures 3 and 4. Fibres at the centre of the yarn remain loose while those at the outer side

are fully twisted. I n ring spun yarn, twist is given to the entire yarn from the centre to the surface of

the yarn (Figures 5 and 6). The yarn thickness in vortex yarns is uneven. Twisting is concentrated at

the thinner sections, while twisting is loose at the thicker section, leading to greater yarn hairiness. Inthe case of rotor yarn all the fibre s are twisted from the centre to the outer side (Figures 7 and 8).

Twisting is more uneven for fibre s near the surface of the yarn. Table 1 provides a comparison

between the three types of yarns.

Figure 3 : Vortex yarn cross- section

Figure 4 : Micrograph of vortex yarn structure



Figure 5 : Cross-section of the ring yarn

Figure 6 : Micrograph of ring yarn structure

Figure .7 : Cross section of the rotor yarn

Figure 8 : Micrograph of rotor yarn structure

Property Ring Yarn Rotor Yarn Vortex Yarn

Parallelization and Fibre orientation Max Min

Hairiness Max Min

Pilling Max Min

Strength Max Min

Unevenness Max Min

Surface smoothness Max Min

Core fibres Max Min

Neps and Thick places Min Max

Bulkiness Min Max

Table 1: Comparison in yarn characteristics

Figure 9 compares twist in vortex, rotor and ring-spun yarn. The figure shows that at centre of vortex

yarn there is zero twist in the fibres i.e. they form a parallel alignment at the very centre. Twist



increases towards the outer part of the yarn and is greatest in the outer wrapper fibres. Rotor-spun

yarns have a high twist at the centre of the yarn which decreases towards the surface of the yarn.

Ring yarns have a relatively consistent twisted structure from the centre to the surface of the yarn

body.

Figure 9 : Difference in twist distribution in vortex, rotor and ring yarns

The overall advantages of vortex yarn over the ring and rotor yarns are :

- Better resistance to pilling and abrasion: this gives longer-lasting fabric performance through a

greater number of washing cycles.

- Less hairiness: this reduces potential problems in fabric production and gives a smooth appearance

to the fabric.

- Less shrinkage: unlike ring spun yarn, the structure of vortex yarns means they are less prone to

shrink

- Moisture absorption and drying: the looser structure of fibres at the cenre of vortex yarns means

that they absorb moisture and dry quickly



5. New Spinning Systems5.8 Other Spinning Systems

Electrostatic Spinning

The principle of electrostatic spinning is shown in Figure 1. In this process, a roving (2) taken from

the roving frame is passed to a conventional double-apron drafting arrangement (3) and is subjectedto a draft of up to 80-fold. The fibers exit freely from the front cylinder. They must then be collected

to form a fiber strand and twisted to form a yarn. The first of these operations is performed by the

electrostatic field, and twisting is carried out in a twist-imparting unit (6). Twisting presents no

problems. The complexity of this method lies wholly in the electrostatic field generated between the

front roller and the twist element (6) by earthing the front roller and applying a high voltage (about

30 000 - 35 000 V) to the twist element. This field has to accelerate the fibers and guide them toward

yarn end (5) while maintaining the elongated configuration of the fibers. When the fibers enter this

field, they take up charge and form dipoles, i.e. one end becomes positively charged and the other

negatively charged. An open yarn end (5) projects from the twist element into the field. This yarn is

negatively charged and is therefore always attracted to the front roller.

Figure 1 : The principle of electrostatic spinning

Due to the dipole pattern, there is thus a relatively high degree of fiber straightening between the

front roller and the twist element. Fibers leaving the roller are accelerated and attracted to the yarn as

a result of the charges carried by the two parts. They join continuously to the yarn. Since the yarn



rotates, the fibers are bound in. A yarn is formed continuously and is withdrawn by withdrawal rollers

(8), to be passed to a take-up device (9) for winding onto a crosswound package.

The problem associated with this process is the formation of a yarn in an electrostatic field, as follows:

Charging of the fibers, and hence their behavior in the spinning zone, is dependent upon air

humidity. Accordingly, for each fiber type, a specific and highly uniform environment must be

created. The machine may need to be air-conditioned.

The charge on each fiber, and hence its movement, is dependent upon its mass. Short fibers

with low mass will therefore behave differently from long fibers.

A limit must be placed upon the number of fibers in the electrostatic field, because otherwise

they will cause mutual disturbance when charging and dipole formation takes place. Only fine

yarns can therefore be produced.

The same effect is observed with high throughput speeds; there is a corresponding limit on

the production rate.

Due to these problems, electrostatic spinning has little chance of being used in spinning mills.

Air-Vortex Spinning

In this spinning method (Figure 2), yarn is formed by an air vortex in a tube (1). For this purpose, air

is sucked by a vacuum source (6) into the tube through tangential slots (2). This incoming air moves

upward along the tube wall in a spiral and finally arrives at the upper tube seal (3). Since the top of

the tube is closed by the seal (3), the air then flows to the center of the tube and moves down again

to the vacuum source. Thus an air vortex (5), rotating continuously in the same direction, is

generated at the seal (3).

Figure 2 : The air-vortex spinning principle



Opened fiber material is allowed to enter the system through a tangential opening (4). The rising air

stream grasps this material and transports it upward into the vortex (5). To form a yarn, an open yarn

end is passed into the tube through a passage in the upper seal (3). The vortex grasps this yarn end

and whirls it around in circles in the same way as the fibers. Since the upper yarn length is held by

the withdrawal rollers and the lower end is rotating, each revolution of the yarn end in the vortex

inserts a turn of twist into the yarn.

Formation of the fiber strand itself arises because the rotating open yarn end in the vortex is

presented with a multiplicity of floating, rotating fibers, which are caught by the bound-in fibers of the

yarn end and are thus continuously twisted in.

One associated problem is maintaining good fiber configuration and achieving correct, ordered

binding-in of the fibers, i.e. achieving adequate strength in the yarn. For this reason, synthetic fibers

of the highest attainable uniformity were mainly used. A second deficiency is variability in the degree

of twist in the spun yarn. In fact, the rotation speed of the fiber ring in the vortex (5) is not constant,

due to mass variations in this fiber ring. Hence, the imparted yarn twist also varies as a function of

time. On the other hand, a major advantage of the process is the absence of any kind of rapidly

rotating machine parts.

University of Manchester Disc Spinner:

Figure 3 : The disc-spinning principle

Figure 3 shows that, as in the case of most open-end spinning processes, a single drawframe sliver

(1) is passed via a feed device (2) to the opening roller (3), which opens the strand into individual

fibers. A fan generates a partial vacuum (airstream 8) in the disc (4), and this draws the separated

fibers onto the collection surface of the perforated disc (spinning disc 4). The open end of the yarn (5)

is drawn by the suction into this spinning zone, which lies directly opposite the opening roller. The

yarn continuously receives twist imparted to it by an external twist element (6), so that the open yarn



end is continuously rolling on the perforated surface of the spinning disc.

This in turn causes rolling-in of fibers engaging the yarn end and hence leads to continuous yarn

formation in accordance with the open-end spinning principle (Section 2.1.1). The yarn formed in this

way simply has to be withdrawn by the withdrawal rollers (7) and wound up onto a cross-wound

package.

It is an interesting feature of this process that collection and twisting of the fibers are separated. Each

is performed by a different element. This makes it possible to use various types of twisting element.

The process thus becomes very flexible. However, it has never advanced beyond the development

stage.

Twist Spinning

This method of spinning is used mainly in worsted spinning mills. Two systems are available:

Duospun, from Ems SA and Huber and Suhner AG; and

Sirospun, from Zinser Textilmaschinen GmbH.

The difference, and the only patentable aspect of the process, lies in the procedure adopted when one

of the two ends leaving the drafting arrangement breaks. In the Duospin process, the two yarns arerecombined almost instantly, whereas the Sirospun system interrupts spinning at this single spinning

position.

The mode of operation is shown in Figure 4 . Figure 4(a) shows the manner in which the yarn is

formed and Figure 4(b) shows the components needed for the spinning process. Two rovings are

passed individually through a slightly modified, but generally conventional drafting arrangement of a

normal ring spinning machine. The fiber strands, attenuated by a draft in the normal range, leave the

delivery roller separately. At this point, they are each subjected to twist generated by a common

spindle (cop); thus, within the spinning triangle, they are twisted into two single yarns, and these are

simultaneously bound together to form a composite yarn. Each of the two single strands and the

resulting composite yarn contains twist, and the direction of twist is the same for both the single ends

and the composite product. This twist-on-twist (ZZ or SS) produces a yarn that is somewhat morecompact, with a firmer core, than the usual ply yarn with opposing twist (ZS or SZ). To produce twist-

spun yarn, it is only necessary to add several auxiliary components to the ring frame and to provide

an enlarged creel to accommodate twice the usual number of packages.

This spinning process, which is already in use in worsted spinning, primarily offers economic

advantages, because the production of the ring spinning and winding machines is roughly doubled

(two ends instead of one at approximately the same speed). In addition, plying and twisting are

eliminated.

In worsted spinning, twist spinning has therefore secured a certain share of the market. However, due

to the different twist structure, it cannot completely replace the conventional 2-fold yarn process.



(a) (b)

Figure 4 : The twist-spinning process

REPCO Spinning (Self-twist spinning)



Platt Saco Lowell has obtained a license from CSIRO for the self-twist spinning process. The

corresponding machine has been called the Repco Spinner.

Eight roving strands (2) run from a creel (1) into a double apron drafting arrangement (3), where they

are drafted in a normal drafting range (Figure 5). A friction assembly (4) adjoins the drafting

arrangement and consists of two reciprocating friction rollers. In passing through this device, the fiber

strands leaving the drafting arrangement are subjected to alternating twist. Before the turns of twist

can cancel each other out, the strands are brought together in pairs with a phase shift between the

components of the two strands (Fig. 5). This produces the previously described self-twist (ST) twofold

yarn. The four yarns proceed to a winding device (5), where they are wound onto cross-wound

packages. This process is suited only to the spinning of long staple fibers and is therefore used solely

in worsted spinning mills.



Figure 5 : REPCO Spinning Machine

WRAP SPINNING

This system is shown in Figure 6 and Figure 7.A roving or sliver feedstock (1) is drafted in a three-,

four- or five-roller drafting arrangement. The fiber strand delivered runs through a hollow spindle (3)

without receiving true twist. In order to impart strength to the strand before it falls apart, a

continuous-filament thread (4) is wound around the strand as it emerges from the drafting

arrangement. The continuous-filament thread comes from a small, rapidly rotating bobbin (5)

mounted on the hollow spindle. Take-off rollers lead the resulting wrap yarn to a winding device. The

wrap yarn thus always consists of two components, one twist-free staple-fiber component in the yarn

core (a), and a filament (b) wound around the core. This process has been offered by several

manufacturers, e.g., Leesona, Mackie, etc. The most common wrap spinning system is ParafiL by the

Suessen company, and this process will be briefly described.



Figure 6 : The wrap-spinning principle





Figure 8 : The false-twisting device in the ParafiL process by Suessen

The yarns are used primarily for:

machine-knitting yarn;

velours (home and automobile upholstery materials);

woven goods (men„s and ladies„ wear);

carpet yarns (mainly for tufted carpets).

At present, the process is more suited to the long-staple than the short-staple field, i.e. for fiber

lengths above 60 mm. In ParafiL yarns, the filament makes up 2 - 5% of the yarn.



Core Spinning:

Core spun yarns have continuous filament yarn in the core and staple fibres form the sheeth. Existing

ring spinning technique can be used to manufacture core spun yarns with modifications at the process

level. In its conventional form, this technique comprises of pair of rollers for drafting, twisting and

winding mechanism, being able to handle only one type of fiber that too in the staple form to

manufacture spun yarns. With slight modifications and little investment, this technique can be suitably

used to produce core yarns.

In addition to the conventional creel of ring frame, another creel to support the filament yarn is

required along with tensioning and guide arrangements to position the filament correctly. The filament

is pulled over from creel and fed to the nip of the front drafting rollers. Thus front drafting roller

receives a continuous filament as well as drafted strand of roving. These are twisted together upon

delivery from the front drafting roller and wound onto the package. The filament guide and the roving

guide are held on the same bar thereby giving same to and fro motion to the filament to that of

roving.

Optimization of filament pre-tension is one of the most important aspects of core spinning because

adequate tension helps the core component to adapt the axial position and to be well covered . A

common problem with core spun yarns made on a ring spinning frame is the slippage of the staple

fibers relative to the filament, which gives a length of bare filament with a clump of fibers at one end.

This effect is known as “strip-back or Barberpole”. This fault may lead to incomplete core coverage

and results in end break in the subsequent processing. Thus, a rather high level of twist is normally

needed to build up the necessary cohesion between the sheath and the core components. The high

twist reduces the production speed and thereby increases the production costs. The high levels of

twist is also not desirable for composite applications, as this would lead to more breakage of high

performance filaments in the core and also more drop in the axial properties of the composites.



Figure 9. Improved core spinning system

Figure 9 describes an improved core spun system, which they claim, produces a yarn of superior

quality with no barber pole effect. The spinning frame as shown in the Figure 9 is retrofitted with a

core stabilizer bar, which has a special groove for the filament core and a polished surface for the

wrap.

Twistless Yarns:In most of the yarn manufacturing processes using staple fibres, twist is imparted to attain strength in

the yarn. The imparted twist helps to develop lateral pressure in the yarn, which in turn helps in

developing frictional resistance when the strand of fibres is subjected to tensile forces. In this process,

the fibres are placed at an angle to the axis of the yarn, leading to decreased translation of the fibre

strength in the axial direction of the yarn. Since yarns are commonly subjected to axial tensile forces,

the fibre strength is not fully utilized in the twisted yarns. In twistless yarns with cotton and synthetic

fibres, the staple fibres are held together by means of adhesives.



Pioneer achievements using the adhesive have been made by:

the Vezelinstitut TNO (Holland), with the Twilo process,

Rieter (Switzerland), with the Pavena process, and

Bobtex Corporation (Canada), with the Bobtex process.

The line of thought is very attractive, but the realization has proved just as difficult. These processes

have so far been unable to achieve acceptance, and Rieter has abandoned this line of development.

A strand of parallel fibres can be made to adhere by means of:

a binding agent (pavena, Twilo new),

adhesive fibres (Twilo), or

polymer (Bobtex).

Glue and adhesive fibres only have to hold the fibres together during processing. When the woven or

knitted fabric is produced, coherence is provided by the yam-binding points of the cloth structure. The

binder is then superfluous and is therefore washed out during making-up. In the Bobtex process,

however, the polymer remains as an integral part of the thread.The end-products of the Twilo and Pavena processes have good characteristics because the fibre

strand consists of fibres arranged with a high degree of parallelism. These fibres are not subject to

any degradation of their properties (handle, stiffness, suppleness, etc.) caused by twist. Furthermore,

their covering power is high. An additional advantage of a practical process would be a high

production speed. On the other hand, one disadvantage is the somewhat poorer washing performance

because of the lack of firm anchoring of the fibres in the yarn.

The Twilo Process

In this method, which is used on machinery made by Signaalapparaten, of Holland, third passage

draw frame sliver is used as feedstock.. The first passage is usually carried out on a blending draw

frame at which a small percentage (5-11%) of adhesive fibres is blended with a sliver of cotton,

synthetic fibre, or viscose. The adhesive fibres can be poly(vinyl alcohol) (PVA) fibres, which become

tacky and activated at a water temperature of about 7O° C. The addition of water is therefore a

precondition for bonding.



Figure 10. The Twilo spinning principle

The draw frame sliver (1) passes into a first drafting zone (2) of a four-line drafting arrangement and

is here pre-drafted in a still-dry condition with a draft of 5-10 (Figure 10). The pre-drafting zone (2)

is followed by the wetting position (3), which also contains a false-twist assembly. Here, the use of a

water-jet leads to twisting of the strand (false twist). Thereafter, the final attenuation is performed in



a twist-free condition in a second two-line drafting zone (4), with a draft of up to 40. To ensure that

the strand leaves the drafting arrangement (4) as narrow and compact as possible, the drafting

arrangement is followed by a second false-twist device (5). This device also serves to assist warming

of the yarn to about 7O°C (7). A steam-jet is therefore used here for twisting. Finally, cylindrical

cross-wound packages above the machine take up the yarn. Instead of adhesive fibres,

Signaalapparaten now also uses a bonding agent as an alternative means of imparting strength.

In this process, c otton and pure synthetic fibres can be processed, and so can blends. The range of

fibre linear density lies between 1.4 and 6 dtex, with staple lengths in the range 30-80 mm. The finer

the fibres, the more adhesive fibres must be used. The latter usually have a linear density of 1.7 dtex

and length of 40 mm.

The yam is not round but flat and therefore gives an end product with high covering power. Because

of the binder, the yam is stiff with low elongation. The evenness corresponds to that of ring-spun

yam. The strength is partly dependent upon delivery speed.

Characteristics of the process are:

relatively high energy consumption;

the use of water in a spinning mill;

the adhesive fibres or binder must be washed out, and are therefore lost; if they were not

washed out, the endproduct would be unusable;

a great deal of specific know-how is needed.

Bobtex process :

The Bobtex spinning machine (the name "Bobtex" is derived from the name of the inventor,

Bobkowicz) has two spinning positions and produces a multiple-component yam, which is composed

of:

a core of mono- or multi-filaments making up 10-60% and forming the yam carrier (a);

a polymer intermediate layer (20-50%) (b); and

staple fibres embedded in the intermediate layer to provide a covering layer and making up30--60% (c).



Figure 11a : The Bobtex spinning principle



Figure 11b : A Bobtex yarn

In the course of production of this yarn, as shown in Figure 11, the filament (2) runs through an

extruder (3), after which a coating of molten polymer (1) remains stuck to it. Before this polymer can

solidify, opened staple fibres forming a covering layer are pressed into the molten material in the unit

(4).

This unit represents an opening assembly for the attenuation of two draw frame or card slivers (5) fed

in from the side. A false-twist device (7) ensures good binding-in of the staple fibres. The resulting

yarns are wound onto large packages on the base of the machine.

Sources :

W. Klein, “Technology of Short Staple Spinning”, The Textile Institute, Manual of Textile Technology, A

Carl A. Lawrence , “ Fundamentals of Spun Yarn Technology”, CRC Publications, 2003.

P.R. Lord, Hand Book of Yarn Production : Science, Technology and Economics, Tailor and Francis, 200

Eric Oxtoby, “Spun Yarn Technology”, Butterworths, 1987.

NCUTE publications on Yarn Manufacturing, Indian Institute of Technology, Delhi.







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