Introduction to Open End Spinning

Introduction to Open End Spinning

1.In conventional spinning ,the fibre supply is reduced to the required mass per unit length by drafting & then consolidated into a yarn by the application of twist.

2.There is no opportunity for the internal stresses created in the fibres during drafting to relax.

3.In open end spinning, the fibre supply is reduced, as far as possible , to individual fibres, which are then carried forward on an air-stream as free fibres.

4.This permits internal stresses to be relaxed & gives rise to the term free fibre spinning.

5.These fibres are then progressively attached to the tail or open end of already formed rotating yarn.

6.This enables twist to be imparted by rotation of the yarn end.

7.Thus the continuously formed yarn has only to be withdrawn & taken up on a cross-wound package.

There are various types of open end spinning viz. Rotor spinning , electrostatic spinning , friction spinning , air-vortex spinning & disc spinning.

2.But rotor spinning is the most successful method among the above mentioned methods. It is called as the spinning of 21st century.

3.In the rotor system , airborne fibres are deposited continuosly upon the external or, more usually , the internal peripheral surface of a rapidly rotating drum so as to form a ring of fibres ,which is then peeled off & withdrawn along the axis of rotation of the drum.Thus twist is imparted & a yarn is formed.

4.One of the great advantages of rotor open-end spinning is that twist insertion & yarn take-up are completely separated from each other, which permits the twisting mechanism to operate at very high speeds , while the package need rotate at the slow speed necessary to wind on the yarn produced.

Sliver is slowly drawn into the m/c by a feed roller ,operating in conjunction with a spring-loaded feed pedal.

The rapidly rotating opening roller , which may be pinned or covered with metallic card clothing ,combs out the leading ends of fibres untill they are released ,

When it carries them forward virtually as individual fibres.

Provision may be made for trash to escape through an aperture in the beater casing while the fibres are sucked through the transit tube & onto the inner ,grooved, periferal surface of the rotor.

The transit tube may tapered so as to create an accelerating air-stream, which it is hoped will tend to straighten the fibres in flight.

In order to achive ideal fibre flux i.E. Unity {fibre flux =number of fibres in cross section},in the transport tube , the air speed in the tube would have to be as high as 75m/s for fine yarns & 600 m/s for coarse yarns. {Generally flux = 7-8}.

Some straightening of fibres occur as they enter the rotor , since the surface speed of the rotor is greater than the air-speed.

Centrifugal force flings the fibres outwards & presses them onto the collecting surface of the rotor ,where a ring consisting of many layers of fibres forms.

To start spinning ,an existing seed yarn is introduced through the exit tube . since the rotor & the air contained in it are rotating , the yarn tail is also caused to rotate.

Centrifugal force throws it against the inner peripheral surface of the rotor ,where it makes contact with the ring of fibres.As soon as this occurs , the seed yarn is withdrawn , and yarn production begins.

Each revolution of the yarn arm puts a turn of twist into the yarn in the exit tube, &, since there is little to stop it , some of this twist leaks back along the yarn arm to the rotor surface,which thus causes the tip of the seed yarn to become entangled with the ring of fibres , which can then be progressively peeled off the surface of the rotor to form a yarn.

The yarn produced is simply wound onto a large package, usually a cheese.

Feed ZoneFigure shows that the sliver runs from the can via a trumpet into the feed shoe {m}.

A fluted feed roller {s} is designed to clamp the sliver evenly over its whole width & to move it forward slowly into the operating region of the opening roller{a}.

The feed roller generally has diagonal fluting in order to increase the clamping effect.

In some brands of machine, it is necessary to adopt the feed shoe to the material because it is important that the fibre beard is presented to the opening roller in an optimal manner.

In this case, the form of the feed shoe & the opening roller must be changed. The distance between the feed shoe & the opening roller must be changed.

The distance must be decreased for finer feed sliver or smoother fibres or both.

If the yarn breaks , feed of material into the machine ceases immediately.

This is done by stopping rotation of the feed roller or by pivoting the feed trumpet so that the sliver can not run through the shoe.

Opening Roller

The teeth of the opening roller [a] pass at high speed [ 35 m/s] through the fibre beard being slowly pushed forward by the feed roller .

By means of this continuous intensive combing action, the opening roller carries along by friction all fibres emerging from the clamping nip between the feed shoe & feed roller.

The projecting fibre beard takes on a wedge shaped form.

Combing out will be more intensive & even if:

The thinner the fibre strand {sliver fineness},

The more parallel the fibres arrangement

The more highly straightened the fibres,

The smoother the fibres [lustrous or delustred] ,

The shorter the clamping distance

The optimum rotational speed of the roller high roller speed will damage the fibres while lower roller speed would deteriorates yarn quality].

The clothing on the opening roller naturally exerts a great influence on the opening of the fibre strand with drafts of up to 2000.

This influence depends mainly upon the type of clothing, the shape of the teeth & the point density.

The opening roller rotates between 5000 & 10000 rpm, usually between 6500 & 8000rpm.

Higher speeds of rotation are chosen where material throughout is high of rotation are chosen where material throughput is high [coarse yarns] & lower speeds where material throughput is low.

The diameter of the opening roller lies between 60 & 80mm, depending upon the manufacturers.

The opening roller is the part subject to wear & must be periodically reclothed or replaced , depending upon the respective wear rate. If this is too long delayed , then yarn quality & spinning conditions decline

In processing synthetic fibres, a low tooth angle of rake is chosen so that the fibres are treated gently.

In some cases, it is necessary to operate with low roller rates of rotation to avoid heat damage to the fibres.

The required high degree of opening can nevertheless be obtained by locating the clothing close together at the feet to give a higher point density.

Very sensitive fine fibres can be processed with an os25 clothing having an angle of rake of only 9 degrees.

The clothing of opening roller depends upon type of fibre, fibre characteristics & the material throughput {coarse or fine yarns}.

Basically a distinction is drawn between two clothing types : metallic clothing & needle clothing.

Metallic clothing are generally used today in short-staple spinning because they are robust & have a very good opening capability.

The use of needle rollers is generally limited to the processing of raw materials that do not separate easily from the clothing.

Two clothing types have found wide acceptance

OS20 ,with an angle of attack of 25degrees for cotton , viscose & blends of those materials &

OS21, with an angle of attack of 12degrees for synthetic fibres & all blends containing synthetic fibres.

Trash Removal Zone

Basically, all trash-removal devices in the rotor-spinning machines are the same, namely, nothing more than a larger or smaller opening roller housing.

The high peripheral speed of the opening roller causes the coarser trash particles to be hurled outwards at this position [a] while the fibres continue with the roller & pass into the feed tube [b].

Unfortunately, on account of its lighter weight, a large part of the fine dust goes with them.

The eliminated trash is carried away either :

Pneumatically , by suction extraction, or

Mechanically, by a small transport belt on the floor of the collection chamber [c].

The removal density depends upon :

The design of the assembly.

The air-flow conditions.

The degree of opening of the feedstock.

The speed of rotation of the opening roller.

Rotor

The rotor is the main spinning element of the rotor spinning machine.

Yarn quality, yarn chracter ,working performance, productivity, costs, etc. All depend chiefly upon the rotor.

The most important parameters of the rotor that exert influence are:

The rotor form & material.

The rotor groove

The rotor bearing.

The rotor revolutions.

The Direction Of Withdrawl

Basically, yarn can be withdrawn opposite the rotor shaft or through it.

In some circumstances , the latter arrangement gives a better self-cleaning effect because the yarn is dragged over the floor of the rotor .

however, this method can not always be used owing to the associated larger shaft diameter { and for other reasons} & is in any event more expensive .

accordingly , the withdrawl direction shown in figure is now the only one used.

The yarn runs through the withdrawl tube in passing from the rotor to the withdrawl rolls.

The tube has to guide the yarn so that it changes from the horizontal doffing disposition in the rotor to the vertical disposition in the rotor to the vertical disposition for winding.

Friction arises at the bend in the tube & exerts some influence on the twist distribution .

The angle of the bend has therefore been optimized most manufacturers.

For some time, several manufacturers have been incorporating twist -blocking elements in the withdrawl tube , especially for the production of knitting yarns.

These raise the twist level between the navel & the rotor groove

the fibres can then be better bound in ,which thus increases spinning stability & reduces the ends-down rate.

However , these elements can also cause slight increases in imperfections & hairiness

The Requirements For The Package

The yarn must be unwound at high speed on further processing machines , particularly the warping machine.

The package build is therefore of some importance .

Currently, the following package types can be wound :

Cylindrical cross wound packages { weaving} &.

Conical cross-wound packages {knitting} ,with taper angles of 2, 3.30{3.51usa} , 4.20{5.57} degrees as either normal packages or Those suitable for package-dying.

Advantages of cross-wound packages of the rotor spinning m/cs as compared with those of the winder :

The rotor spinning package contains only 2-3% of the number of Piecings in the winder package is made up of yarn from small Cops, of 60-120 grams, joined together by corresponding spices.

Winding is carried out at speeds of up to 200 m/min. As compared with 1400m/min. In the winder; This gives a better package build & the yarn lengths on the individual packages can be kept more uniform; Admittedly, however ,a large balloon is generated in unwinding yarns from rotor spinning packages

The following requirements must be fulfilled by packages of yarn from modern rotor spinning m/cs. :-.

High net mass ; this can now reach a maximum of 5kg ,but usually lies in the region of 2-3.5 kg.

Package density as uniform as possible from one package to another ;

The same yarn length on all packages ; this can be achieved exactly only with the help of individual length measuring devices , which are now offered by manufacturers.

Adaptable winding density attainable by adjustable yarn tension & above all, by a variable crossing angle of the windings in the Package;

Packages free of zones of patterning;

Yarn-waxing were necessary;

Formation of an accessible yarn reserve on the tube so that , before the package runs out in unwinding , the thread end can be knotted to the start of the yarn on the next package to be unwound ;This enables stoppages to be avoided at the time of package change in further processing.

The Winding Process Continual withdrawl of the yarn from the rotor is ensured by the withdrawl rolls {a}. Winding up is effected under light tension by rotation of the package {s}, driven by friction from the winding roll, the yarn will in any case run through a thread guide {f} &may additionally pass : a bow{b} ,a yarn storage device {r} &a waxing device [p]. Waxing devices are used mainly in the spinning of knitting yarns.

The thread guide {f} is arranged to effect crosswise laying of the yarn in the package by means of its to & fro movement.

The bow{b} or the store device{r} is needed to even out path length variations, which arise because the length of yarn between the withdrawl rolls & the right or left hand edge of the package is greater than the length between those rolls & the middle of the package is also constant {in the winding of cylindrical packages} , corresponding curvature of the bow { steep in centre , flatter towards the ends} ensures a constant path length for the yarn.

Path-length compensation by means of a bow is , however , adequate only for the winding of cylindrical packages {cheeses} and cones of up to 2 degrees taper.

The bow is no longer enough with larger taper angles.

The circumferential velocity at the right hand end is therefore noticeably different from that at the left -hand end. In this case , a yarn store can be used .

The rotation rate of the package is the same at all points of the package, but the package diameter varies significantly from one end to the other .

During winding on the smaller package diameter { lower circumferential velocity} ,the lever arm {r} is moved to the right & thereby forms a loop in excess yarn length {thread reserve}.

As one yarn moves from the smaller to the larger end of the package ( high circumferential velocity}, a greater yarn length is needed.

As the lever moves to the left , the loop decreases, i.e. The excess yarn length is released.

The yarn store can be eliminated if the speed of rotation of the winding roll can be continually varied to adopt it to the winding diameter of the package.

Package Density And Winding Angle The yarn winding angle [b] mainly affects the package density [r] & the unwinding performance of the package .

It therefore has to be matched to the requirements with the utmost precision by adjusting the traverse per unit time of the thread guide.

The angle can usually be varied between 30-50 {33-46}degrees. The larger the angle , the lower the density & hence the greater the softness of the package.

In very general terms , the following operating ranges can be assumed:

33-36 degrees for cylindrical packages;

About 40 degrees for cones;

40-45 degrees for packages intended for package dyeing.

Where the latest generation of high-pressure dyeing equipment is available , dyeing can also be carried out with harder packages.

However , the density r of the package depends not only upon the winding angle but also on :

The winding tension

The contact pressure of the package on the winding roll &

The yarn fineness . {finer yarn always give higher density}

Schlofhorst cites the following package densities {cotton yarns & yarns of fibres comparable with cotton

Packages for package dyeing : r = 0.38 - 0. 42 g / cubic cm

Hard packages : r=0.33 - 0.37 g/cubic cm

The Auxillary Winding Devices

Traverse varying devices :-.

At the reversal points of the traverse i.E. At the edges of the package , a short dwell arises in the movement of the thread guide owing to the deceleration & subsequent reverse acceleration required here.

More yarn is wound up at these points than at other points along the package length. This leads to considerable accumulations of material with the following results:-.

Too high a density;

A high yarn stress ;

Thrown ends {loops of yarn projecting from the package ends}; &.

Variability of dye uptake in packages for package - dyeing.

Traverse-varying devices are designed to shift the reversal points of the yarn through a very short distance so as to prevent improper package

Pattern-breaking devices :-.

When the ratio of traverse frequency to the rate of revolution of the package , becomes 1:1 ,1:2, 1:3,etc. , The turns of a new layer are deposited exactly on the top of the turns of the preceding layer, & this process repeats itself for several successive layers .

This generates uniformly crossing rhomboidal ridges ,

The so-called pattern windings or or pattern zones.

They reduce the take up capacity of the package & make unwinding difficult & are therefore to be avoided at all costs.

The pattern breaking devices ensure that the traverse speed is not uniform but is subjected to variations.

Yarn waxing devices : -.

In the production of knitted goods in particular , where the yarn is strongly bent around the needles , rough yarns can cause disturbances , broken threads & a high degree of wear .

In order to improve the running performance ,knitting yarns have always been waxed , & the rotor spinning m/c now enables this to be done directly at the spinning stage.

The waxing device is arranged in between the withdrawl rolls & the package so that small particles of lubricant can settle on the yarn as it passes over a body of wax.

These particles are rubbed off as the yarn is strongly bent at the needles of the knitting machine ,& they then ensure good running properties.

The Fibre Flow Into The Rotor

Depending upon the arrangement of the feed tube , the fibres can move into the rotor in one of the two ways , viz . axial & tangential.

In axial feed , centrifugal force distributes the fibres within the collection groove in a purely random fashion & in accordance with an umbrella principle .

This type of feed has three major defects:

Fibre orientation in the groove is bad & the yarn quality is correspondingly poor.

A large rotor diameter is needed , & this limits rotor revolutions.

The spun yarn has to be withdrawn through the rotor axis.

These problems led to the adoption of the currently almost universal tangential-feed technique. Here , the rotation of the rotor , & a corresponding air circulation within the rotor, ensure ordered deposition of the fibres in the groove.

Formation Of Coherent Fibre Strand

At the start of the development of the rotor spinning, the fibres were mistakenly guided directly into the fibre-collection groove.

The disadvantage was that , during the acceleration that had to be carried out, the fibres inevitably collided with the radial yarn end .

This led to a deterioration in the fibre orientation.

In currently available rotor spinning m/cs , the fibres flowing into the rotor strike directly against the rotor wall above the groove.

The yarn so produced had the typical sauerkrut structure, with very low strength.

Higher rotor peripheral speed than colliding fibres gives the drafting effect which ensures straightening & lining-up of fibre.

Since at this juncture drafting is essential , it imposes lower & upper limits to the rotor speed.

The air flows are very important in this region .

There should not be any air turbulence between the feed tube & the rotor wall.

The aim is to generate a uniform , rotating air stream that assists in forwarding the fibres onto the rotor wall in straight condition.

This depends , among other things , on the distance of the feed tube from the wall & the formation of the rotor cover that contains the feed tube.

Accordingly, several manufacturers use replaceable covers matched to the diameter of the rotor, which is also replaceable.

An incoming fibre strikes an inclined wall & is pressed outwards by an enormous centrifugal force -over 100000 times the weight of the fibre.

This causes the fibre to slide downwards on the rotor wall while being accelerated in the peripheral direction & to be deposited on the other fibres in the collection groove.

Back Doubling In rotor spinning, doubling takes place when fibres are fed & deposited one on the other in rotor.

Since a fibre strand is first totally opened up & then reconstituted in the course of this operation , the term back-doubling is used.

The evenness obtained inthis way is of a high degree & is always better than that of ring spun yarn, for which feedstock with a high short-fibre content is used.

The only disadvantage is that all unevenness in sliver which are greater than internal periphery of the rotor {geneally=3.14*35=110 mm. Where 35mm. Is rotor diameter.} Pass straight into the yarn.

Schlafhorst formula of backdoubling:-.

Since the yarn is pulled out of the rotor , the yarn separation point shifts continually forward within the rotor.

It therefore has a higher peripheral speed than the rotor itself.

This lead {x} is equal to the witdrawl speed of yarn / rotor circumference { c} .

The withdrawl speed in turn identical to the delivery speed {l} which is equal to the rotor rpm {n} / twist per metre {t}.

Now according to the schafhorst ,

Back doubling = n / x.

= Nc / l.

= Nct / n.

= Ct.

= 3.14 * DT metres.

{Since c=3.14 * d. Where d is diameter of the rotor}.

= 3.14*DT /1000 mm

Formation OF The Yarn

The yarn end is pressed against the rotor wall by the high centrifugal force, & the separation point therefore rotates within the rotor .

Each revolution of the yarn at this point inserts one turn of twist.

The yarn twist penetrates into the fibre ring in the collecting groove, where the fibres are to be bound together to form a yarn.

The length of this binding in zone is of some significance for the spinning conditions & the the yarn characteristics.

If this length is too short , the ends-down rate will be high ;

If it is too long , twisting-in will be very tight , & there will be many wrapping fibres

Twist In Yarn Accordingly , in rotor spinning , it is not possible under given conditions to lower the yarn twist coefficient below a certain value {=a min.} Because otherwise the length of the binding-in zone will be reduced to zero.

The yarn twist momentum will then be negligible & transmission of twist to the fibres in the ring will not be assured. Therefore minimum value of twist coefficient {A min.} Is independent of yarn strength.

Twist / metre=rpm of yarn separation point / withdrawl speed {l}.

Now since the lead of yarn sparation point over rotor rpm is very small we can safely write.

Twist / metre = rotor rpm /l where l is expressed in terms of m/min

The spun yarn is withdrawn through a passage in the navel t;

The yarn therefore rolls continually on the trumpet shaped mouthpiece of this nozzle.

The partial rolling of the yarn gives rise to false twist between the twisting-in point {g} for the fibres & the navel {t}.

The yarn in the spinning section {b} therefore exhibits more turns of twist than the spun yarn.

Moreover , the twist level increases continuously from the navel towards the rotor wall.

Twist level at separation point is about 20-40% higher than those at navel.

This difference arises from variations in tension along the yarn.

Yarn tension is generated by the withdrawl rolls during withdrawl in opposition to the centrifugal force in the rotor.

Tension is highest at the withdrawl rolls themselves & declines towards rotor wall.

However , the yarn tension & twist level are inversely proportional , that is, if there are sections of low tension in the yarn {b}, these will exhibit more twist whereas sections of high tensions {a} take up less twist.

It is only these additional turns at the separation point, caused by false twist & yarn tension variations, that enable spinning to be done under stable conditions.

The false twist effect is dependent upon roughness of the contact surface of the navel & rotor rpm.

Wrapping Fibres The rotor , & hence the fibre ring , revolve continuously under the stationary feed tube - as also does the spun yarn in the binding-in zone.

A stream of individual fibres flows from the feed tube & is deposited in the groove.

Normally , incoming fibres that have not yet been twisted in, but, in the binding -in zone , they strike an already-twisted yarn section rotating around its own axis.

Fibres arriving here can not be bound into the strand:

They wrap themselves around the yarn core in the form of of a band , called wrapping fibres.

This is a typical characteristic , & simultaneously an identification feature, of rotor spun yarns.

The number of wrapping fibres is dependent , among other things, upon :-

The position at which the fibres land on the rotor wall.

The length of binding-in zone.

The ratio of the fibre length to the rotor circumference.

The false twist level.

The rotor rpm . &

Fibre fineness

Various Types OF Binding Fibres Class 1 fibre :- the yarn tail picks up the trailing end of a fibre which lies wholly on the surface of the rotor. The fibre is integrated into the yarn & tends to take a helical form, which will be distorted by migration. The original fibre direction is reversed. This fibre is called as class1 fibre.

Class 2 fibre :- the fibre is just emerging from the transport tube as the yarn tail sweeps past. The leading end of the fibre is picked up & moves towards the centre ; the trailing end is flung onto the surface of the rotor ;The fibre becomes a bridging fibres. I.E., Fibres that bridge the gap that should theoretically occur behind the pick-up point, p. The fibre is integrated in the yarn & tends to take a helical form as in class 1, but there is no change in fibre direction. This fibre is called as class 2 fibre.

Class 3 fibre : a fibre that has partly emerged when the yarn tail arrives : the leading part is on the surface of the rotor ; the trailing part is tube. The fibre is picked up at some point along its length. The leading end is integrated in the reverse direction . the trailing end is integrated in the forward direction. A leading hook is created. This fibre is called as class 3 fibre.

Fibre Integration

For a class1 fibre, any leading hook present in the fibre as it lies on the rotor goes forward into the yarn as a trailing hook & vice versa.

For class2 fibres , leading hooks pass into the fibre as leading hooks, but any original trailing hooks will almost certainly be straighten out, either as the fibres are snatched from the tube or by frictional contact with the fibre ring.

For class3 fibres, the end result depends upon the pick up point relative to any hooks. There is strong tendency to create new leading hooks in fibres, whether they be originally straight or hooked, whereas there is no corresponding tendency to create new trailing hooks.

Structure Of Rotor Spun Yarn Open end spun yarns are basically three part construction. There is the core of substantially straight fibres , there is next the body of more loosely wound fibres , & then there are the tightly wound belts .

some fibres may fall into more than one type.

A class 1 fibre

It should become firmly embedded in the groove of the rotor before being picked up by the yarn tail & integrated into the yarn under considerable tension .

class 1 fibres should therefore go into the yarn under tension. Class 1 fibres therefore go into the core of the yarn.

A class 2 fibre

It starts to be integrated while it still lies mainly inside the transport tube , i.e. , Before it comes under the influence of the rotor & before it has any centrifugal force applied to it , so that the tension within the fibre is very low.

This type of fibre therefore starts as a rather loosely wound surface fibre .

however , as its trailing end is withdrawn progressively from the tube, it makes increasing contact with the rotor surface, & the tension in the fibre builds up so that the tail end of the fibre tends to work its way into the core of the yarn.

A class 3 fibre

It is picked up at some point along its length , the leading part being pressed onto the rotor surface by centrifugal force while the trailing part is still in the tube.

This results in the formation of a leading hook. Furthermore , the original leading end , being under tension ,enters the core of the yarn , whereas the original trailing end starts on the surface but works its way into the core as in the case of class 2 fibres .

Class 3 fibres should therefore form leading hook such that both ends are in the core while the fold appears on the surface & may form a belt. As the tail of bridging fibres ploughs round the groove , it disturbs or ruffles some of the fibres that are already in the groove & thus forms loops or folds in them. These loops tend to be held in place by frictional contract with neighboring fibres , so that many of them persist into the yarn. Small loops may appear in the yarn as such, but longer ones become folded over & either become trapped in the yarn as central deformation or wrapped around the outside in the form of belts.

Belts can contribute little to the strength of the yarn , but their presence may explain why open - end spun yarns have greater resistance to abrasion . furthermore , in the absence of a comprehensive pattern of fibre migration , it may be only the belts that hold the yarn together.

Forces Acting On The Yarn Inside The Rotor There are various forces acting on the yarn inside the rotor viz. :-

Centrifugal forces on the length of yarn in the rotor

Frictional forces between yarn & rotor surface , & also particularly in the draw-off tube.

Air-drag forces between yarn & air.

Coriolis forces.

It should be mentioned that centrifugal forces , of course ,increase in proportion to the yarn count & as the square of both the rotor diameter & the speed of rotation .

The frictional forces depend upon the design of the system & on the fibres being spun.

The combined effects of these variables can be described by a system constant which the the theoretical draw-off forces , i.e. essentially the centrifugal forces , must be multiplied.

This system constant is the quotient of the actual draw-off tension divided by the theoretical draw-off tension.

Coriolis forces arise when a rotating mass changes its radius of rotation .

the dimensions of rotor spinning systems are such that the coriolis forces are negligible, relative to the centrifugal forces, & they can in practice be ignored.

Draw - off forces are negligible till rotor rpm of 30000, but varies almost directly with further increase in rotor rpm. It also varies directly with rotor diameter. Which also increases power consumption in the same proportion.

Classification of Rotor Spinning Machines

Coaxial spinning units. Biaxial spinning units.

INCLUDEPICTURE "http://textiletechnology.bravehost.com/open-end-spinning/images/classi3.gif" \* MERGEFORMATINET The opening roller is arranged co-axially with rotor. The opening roller is arranged bi-axially with rotor

Proves better for long staple Fibres spinning.Proves better for short staple Fibres spinning.

There is air frictional losses only on one side of rotor & opening rollerhere is air frictional losses on both sides of rotor & opening roller.

35% less energy consumption.35% more energy consumption.

Comparatively less draw - off tension.High draw off tension which limits performance.

Fibres are always under control while passage from opening roller to rotor .Passage of fibres in long conduction channel from opening roller to rotor.

Fibres are fed in the form of webIndividual fibres are fed

Modifications In The Design Of The Spinning Unit

The design of the rotor unit may be divided according to its operation, into four sections :-

Sliver Delivery

To accommodate changes in the mean fibre length , certain designs require the operative to reset the distance of the delivery-roller nip from the striking point of the opening roller.

This involves either dismantling the housing to exchange certain parts or alternatively obtaining acess to adjusting screws; Both techniques are too time consuming.

Figure 1 show patented design proposed for controlling a range of fibre lengths without major readjustments .

The figure show the device to consist , in principle, of two gripper elements , replacing the commonly used feed plate.

With these , a feed funnel is associated with several delivery rollers or feed ducts, through which the sliver can selectively fed according to the mean fibre length.

In some other approaches , the aim is to keep a good control on the fibres in the sliver, & there is a change from idea of nip point for the feed roller to a nip area over which the feed roller will accommodate a length distribution as well as changes in fibre length.

With the ease of change from one gripper to another {see fig. 1 [29]} changes in mean fibre length are catered for.

Although in principle , the adjustments appear to be simple, engineering these devices would more than likely be complicated & would further increase the price of an already expensive machine.

Fibre Separation And Transportation

To separate fibres from the sliver feed, the sliver is fed over a supporting surface towards the opening roller, the arrangement being similar to the taker-in region of a conventional card.

Thus to prevent damage to fibres , the supporting surface is machined to provide a curved but wedge shaped space in which the sliver fringe is held during separation of the fibres.

The optimum dimensions & position of the supporting surface relative to the sliver feed roller & to opening roller clothing will depend on the sliver count ,fibre fineness & the fibre length.

Optimization of the support surface dimensions has shown that the distances designated g & h in fig.1 have the main effect on the yarn evenness & strength. For h = {1.5 to 2.2}t, where t is the linear density ktex of the sliver, & g={[2.3 to 4.2]^3}l, where l is the staple length [mm] of the fibre being processed, the resultant yarns were found to have well-above-average properties even at low opening-roller speeds.

In order to effect a high degree of fibre separation , pressing roller can be mounted on a pivot able bracket, which, through pressure from spring , makes the roller press lightly on the land of the clothing of the rotating opening roller.

When in operation , this arrangement enables the fibres in the extreme end of the sliver fringe to be separated by the opening roller. After separation , not all the separated fibres remain attached to the opening roller.

Some enter the thin layer of air {the boundary air-layer} that revolves with the opening roller .Only when all the fibres reach the separating edge of the transport tube .

Those fibres that travel in the boundary air-layer to the transport tube can readily become caught on irregular projections on the inside wall of the opening roller housing.

Accumulations of fibre can result, which are eventually removed & follow the fibre flow to the rotor to form defects in the yarn, such as slubs or neps , or cause an end break.

To overcome this problem , an air-stream is directed downward through an additional inlet to remove any caught fibres from the wall of the opening roller housing.

Other designs have been reported, which prevent fibres from accumulating on the roller itself. Many of the irregular projections on the inside rotor wall of the opening roller housing result from the abrasive action of the fibres.

Some designs shows the use of a replaceable hard wearing metal band fitting the area where the fibres makes contact with opening roller housing.

Some designs illustrates how the action of fibre contact with the housing can be manipulated to give better fibre alignment. By using a similar notion to the stationary- top cards , two saw tooth-wire clothed inserts are positioned in the wall of the housing close to the opening roller. The carding action that results is presumed to give a more definite control of the fibres as they approach the transport tube. The claim is for better fibre alignment & parallelisation. One important major drawback with the design is the possible flats-stripping effect". The fibres are likely to become caught in the additional clothing and build up to the point where they either bring about a deterioration in the yarn properties or cause excessive end breaks. No provisions have been made to prevent this situation from occurring. In obtaining good fibre separation, the design of the opening roller clothing predictably plays a major part.

There are at present two kinds of clothing that are commonly used : saw tooth-wire & pinned-type clothing.

The saw tooth-wire clothing is usually wound in a helical manner around the surface of the roller drum, the drum having grooves cut into the circumferential surface to facilitate the fixing of the wire clothing.

The manufacture of the wire clothing is similar to that for cards in that the tooth shape, angle & size are cold-formed by press dies by using an already-rolled-mild steel bar.

After forming, the working surfaces of the clothing are usually hardened to increase their wear resistance.

For pinned rollers, the pins are made from polished hardened steel.

The roller drum is made hallow i.e. Tubular , which enables the unpointed inner ends of the pins to project & almost meet in the interior of the drum.

The pins are held in place by a cured synthetic resin.

Both types of roller have to be dynamically balanced; With the wire type, opening portions are removed from the solid drum; With the pinned type ,inert fillers may be added to the resin to give a density more comparable to that of the metal sections.

These fillers can be colour-coded to indicate for which fibres the opening roller is best suited.

It has been reported that the pinned type of wire gives the better all-round effect, that is to say, better fibre separation & longer working life.

With some saw tooth -wire clothing it has proved impossible to spin certain blends , particularly synthetic fibres blends.

In other cases ,it has been found that, although a yarn can be made, the distribution of the different fibres throughout the fibres is inhomogeneous.

The flat land of tooth is unable to penetrate between individual fibres or small fibre bundles of the same fibre type, which are often in the sliver after drawframe blending, & intimate mixing of the fibre types is therefore prevented.

The different working angles for both wire &pinned type rollers have been reported.

However, the results have now shown that 60 degrees angles, which are usually recommended for cotton, although effective in separation, give poor trash ejection & often cause trash build up in the rotor.

The sawtooth wire clothing is usually given a hardening treatment, but because this can only be done after cold forming of the tooth profile, & also because a degree of ductility is required for helical winding onto the drum, the effectiveness of the treatment is poorer than for the pinned clothing.

It has , however, been found that a ceramic coating can be applied to the surface of both wire & pins to improve the resistance to wear.

In order to change the opening-roller drum rapidly without changing the bearing drive , several roller designs are available that allow the clothing section of the roller drum to be replaced by merely removing the 4 screws.

This reduces not only the operatives time time taken up in changing rollers but also the cost in carrying spares , since the former practice of replacing a worn damaged roller with a spare already fitted with new bearing drive - shafts was expensive.

Further development in this area has lead to the refitting of a base roll component made from a plastics material.

This approach offers various advantages, in that the component can be injection moulded, which cuts the costs & with good quality control, the reduced weight could enable the rebalancing of the opening roller to be dispensed with.

Latest Developments in Rotor Spinning MachinesMain features of these machine are :-.

1. Rotor speeds up to 130000 rpm with aero air bearings.

2. Delivery speeds up to 200 m/min.

3. Up to 280 spinning positions.

4. Gauge of 245mm for large round cans & rectangular cans.

5. Count range from 125 tex to 10 tex [ne 5 to 60].

6. Spinning unit for drafts up to 400.

7. Complete range of spinning elements for all types of rotor yarns.

8. Rotor diameter from 30 to 56 mm.

9. Efficient trash removal.

10. Syncro top technology for yarn-like Piecings.

11. Modern compressed air technology for rotor cleaning.

12. Redipac package quality for cylindrical & conical cross-wound packages [ 2 degrees , 3 degrees 51 minutes , 4 degrees 20 minutes].

13. Package weight up to 5 kg.

14. Package diameter up to 340 mm.

15. Infinitely variable drives for draft & twist.

16. Integrated automation for rotor cleaning, piecing, package change , batch change, empty tube feeding.

17. Package & batch change without starter bobbins.

18. Package removal systems :- a] package lift. B] servopac. C] Servocone.

19. Comprehensive function & quality monitoring systems.

20. Cubican system for fully automatic can handling.

21. Extremely low noise emission.

Yarn and Fabric Properties Structural differences between rotor-& ring-spun yarns

It will be recalled that ring-spun yarn contains envelope twist [twisting in the fibres from outside inwards], whereas rotor-spun yarn has core twist [twisting in the fibres from the inside outwards].

Rotor spun yarn is therefore more voluminous, more open & rougher than ring spun yarn.

The fibres in the envelope layer of a rotor-spun yarn can partly escape the twisting action during spinning & therefore take up turns of twist.

They thus contribute relatively little to yarn strength & can more easily be rubbed together axially to form slubs, etc.

Rotor spun yarn generally needs rather more turns of twist than ring spun yarn.

Furthermore, the fibres in a rotor-spun yarn are less parallel than those in a ring-spun yarn.

The core twist structure & the lower degree of parallelism are the causes of lower strength of rotor-spun yarn, & also of most other character differences.

The role of the wrapping fibres should also not be overlooked, but it is less important than those roles mentioned above.

The positive characteristics of rotor-spun yarns become more marked the shorter the fibres in the strand.

The following sections will set out the most important differences in the characteristics of rotor-& ring-spun yarn [ of carded cotton].

Rotor-spun yarn compared with ring spun yarn

PropertiesRotor Spun Yarns Compared With The Ring Spun Yarns

Breaking strength. Lower

Coefficient of variation of strength Better

Elongation at break. Often Higher

Mass irregularity [over short lengths] Better

Imperfections Lower

VolumeGreater

Resistance To AbrasionBetter

StiffnessHigher

HandleHarder

Aesthetic Properties

SurfaceRougher

HairinessLower

LusterDuller

Important Differences In Further Processing

Tendency to form slubs under axial force. Greater

Coefficient Of FrictionHigher

Knot (Loop) StrengthLower

Resistance To AbrasionBetter

HairinessLower

Tendency To SnarlLower

Work Capacity Under Cyclic LoadingHigher

Capacity To Take Up DyeHigher

End Breaks In WarpingLesser By 50%

Knots After WindingLesser By 15-17 /Kg.

Warp Breaks In WeavingLesser By 70%

Weft Breaks In WeavingLesser By 25%

Fabric Properties

Tensile StrengthLesser

Tearing StrengthLesser

Bursting StrengthLesser

AppearanceMore Uniform

BarringVery Much Better

Cover10% Better

CleanlinessBetter

NeppinessFewer Neps

Resistance To Abrasion5-7% Better

HandleHarsher Or Crisper

Thermal Insulation10-15% Better

Air Permeability15-25% Better

Absorption Of WaterMuch Better

Take Up Of DyesBetter

ShrinkageSame

RaisingsEasier & Uniformer

Quality And Economic AspectsQuality Aspects

Regularity tests shows open-end spun yarns to be more uniform than conventional yarns, but they still fall far short of perfection.

Detailed examination of open end spun yarns reveals various defects, which may be attributed to flaws in the fibres themselves, inclusions such as neps & trash, irregularities in preparation, or the operation of the rotor.

Fibre defects stem from inherent fibre properties.

For example, highly elastic fibres tend to contain poorly cut or over-length fibres, which may interfere with drafting or cause lapping of the carding roller, whereas brittle fibres, such as acrylic fibres, are susceptible to fibre damage, which results in an increase in short fibre & in accumulation of dust & fibre debris within rotor.

Fused fibre bundles cause disturbances inside the rotor & lead to end-breakages.

Dyes & fibre finishes can form powdery or tacky deposits, which necessitate frequent cleaning of the rotors if end-breaks are to be avoided. The amount of crimp in man-made fibres can be important.

In the early days, successful open-end spinning was only feasible if very high quality standards were maintained in the sliver fed

Partly owing to improvements in the machine & partly owing to a better understanding of the process, it has now been found possible to relax these requirements to some extent.

Investa recommend that the sliver fed to the open-end spinner should conform to the following criteria :

It should contain no particles of trash individually weighing over 0.15mg;

The average weight of the particles of trash that may be extracted by hand should not exceed 0.10mg;

The average weight of the particles of trash that may be extracted by Shirley analyzer should not exceed 0.025mg; &.

The total weight of trash present should not exceed 0.4%, i.e., 4mg/g of sliver.

Unfortunately, few existing mills can meet such requirements with existing blowroom machinery & cards, so that it is often necessary in practice to accept rather lower standards of sliver excellence.

In such an event, the main thing is to avoid hard impurities weighing more than 0.15mg each. Neps can not be broken down in the spinning unit & are normally extracted with the trash, but fortunately some neps do become buried in yarn during the formation of the ring by layering & are therefore not seen in the yarn.

In order to achieve satisfactory yarn regularity, it is recommended that second-passage drawframe sliver should be used & that the sliver should be regular according to uster standards, e.g., not more than 3 u% for a 3 ktex sliver.

Defects that can be attributed directly to the rotor system & to general disorientation of the fibres.

All the points mentioned above affect the end breakage rate & thus the cost of yarn manufacture.

Economic Aspects

Whereas ring spinning dominates in the range of ne 18-48 [13-33 tex] & for finer yarns, rotor spinning covers in the range ne 6-20 [30-100tex].

Developments In Rotor Drives As increasingly higher rotor spinning speeds become commercially realistic , m/c manufacturers have realized that new bearings have to be designed to meet the required low-noise , low vibration & acceptable working life specifications.

Present rotor spinning m/cs have the design concept of central control drive , that is , all the rotor s are driven by a common belt running the length of the m/c , the driving motor & transmission mechanisms being housed at one end of m/c.

However , with increasing speeds , individually driven rotors are becoming an attractive alternative.

Individual Drives

Advantages :-.

Noise reduction .

Reduced energy consumption.

Simplified construction .

Improved economy.

Improved regulations during transitions.

Higher efficiency of spinning machines.

Possibilities for simplified & inexpensive operation & yarn quality control.

With an individual drive , most of the energy at the rotor & stator surface is converted into frictional heat.

The spinning conditions are therefore thermally influenced by energy losses, since air- flow through the unit is not sufficient to cool the driving mechanisms .

To overcome this problem , some modified designs have an additional cooling system provided.

The additional air-flow {the cooling air } is separated from the fibre transporting air-flow & is conveyed into space between the spinning rotor & the stator of an electrical motor, which thus reduces the temperature of the rotating components.

With the additional cooling system , a constant temperature of 20 c can be kept within the rotor system , which is suitable for spinning most fibre types.

Above a rotor speed of 30000 rpm , the rotation of the rotor must be free of resonance , & the upper limiting speed is then not dictated by the drive .

The maximum spinning speed is instead limited by the yarn breaking tenacity or the maximum allowable rotor temperature or both.

To achieve accuracy of rotational speed , the design of the drive system must ensure a stable nominal frequency input & continuous frequency regulation

Central Drives

Most central drive systems utilise a common tangential belt-drive arrangement.

This drive is cheaper & more simple than individual-drive system.

However in order to operate at high speeds , the problems of vibration, high temperature , noise,& wear have also be resolved. The solution lies primarily in the improvement of the rotor bearings.

The ball bearing system :

Reported improvements in the ball-bearing system were obtained by using elastically mounted arrangements similar to that shown in fig. 1.

Resiliently yieldable rings are sandwitched by bearing casing & a holder so that any vibrations can be absorbed.

The modulus , the number , the size ,& the sucuring positions can be arbitrarily changed.

At least two such rings , spaced apart along the axis of the spindle , should be disposed between the bearing casing {19} & the holder {5} & at least one{8b} or {13}detachably secured to the bearing casing.

The elasticity mounted bearings gives high reliability in operation,reduces the noisiness of the machine , & eliminates the negative effect of oscillation on the other parts of soinning unit.

The high temperature generated in the rotor area will shorten the life of the anti-friction bearings & also that of the resilient support members of the bearing arrangement.

In order to cool a bearing arrangement of the type shown in fig. 1 with maximum efficiency & the lowest possible cost , a heat condusive body of high thermal conductivity , made in the form of a sleeve, was positioned between the bearing casing & the rotor housing [see fig. 2] .

As the fig. Shows [a-e] , a number of thermally efficient profiles can be used to effect good heat transfer from the bearing casing to the rotor housing.

Fig. 3 shows that a finned design to the outer bottom surface of the rotor base [15] can be used to give extra cooling of the bearing casing.

Further cooling is also obtained with the oil-feed device[18].

The device includes a reservoir, which is responsive to reduced pressure caused by rotation of the spinning shaft.

Thus no oil is supplied when the shaft is stopped.

However , during operation , the bearings are kept reasonably cool while being lubricated.

Air Bearings

With current rotor speeds up to 60000 rpm ,rotors fitted with ball bearing drives are operating at the practical limit for central drive system.

Thus , with constant developed aimed at achieving faster & faster rotor spinning speeds , air bearings have become an attractive alternative , particularly because of their low power consumption.

At present air-bearings are not in wide usage , although the constraints in using them are not so much economic as technical.

This is because of the difficulties in ensuring the high m/c tolerances, the fear of breakdown during long running times, & the high rates of air consumption.

Several reported modifications have been made to reduce the air consumption to acceptable levels.

Indirect Bearings Drive

A second alternative to using direct bearing drives is the use of indirect bearing drives & because the technology is simpler than that of air bearings & facilitates certain operational advantages like replacement of spinning components such as rotor, some machinery manufacturers have already opted for this system.

The majority of commercial open end spinning machines capable of spinning at a rotor speed of 100000rpm utlize indirect-bearing drives.

In this system the shaft of the rotor is driven by a tangential belt & rests in a cradle formed by four supporting discs .

The discs acts as the bearings for the rotor shaft &themselves fitted with direct ball bearing drives.

The outer circumference of each disc is fitted with a synthetic fibre ring, which acts as a damper to give vibration-free running of the rotor.

The complete system is then supported on the elastic base as one block to prevent any problems due to rocking motions at right angles to the rotor shaft.

It would appear, from the number of patented design modifications , that the elastic support block en masse had not totally solved the problem.

The rotor shaft itself is subjected to a twisting-rocking motion, resulting from the relationship between the tangential belt drive & pivot points on the disc, the result being constant defluxions of the rotor shaft from the true axis of rotation.

A completely new approach to the problems of indirect-bearing drives is illustrated in figure.

Here three tapered rollers , 4 ,5,6 are positioned in a housing {9} with their axes forming a tetrahedron to support a shortened tapered rotor shaft.

The shaft is driven by the tapered roller[4],which is that the full length of the rotor shaft is in contact with the rotating discs & this will ensure a constant axial location.

Twist Insertion

Factors affecting twist insertion :- the insertion of twist in rotor spinning is influenced by design of two machine components, namely , the doffing tube or withdrawl tube & the rotor.

Effect of doffing tube on twist insertion :-.

Under dynamic equilibrium, the twist propagates from the navel of the doffing tube into the first 8-10mm. Of fibres collected in the rotor groove.

This length of 8-10mm. Of the fibres as the peripheral twist extent & is important for obtaining both a good spinning performance & acceptable yarn properties.

It has been reported that the degree of peripheral twist present during spinning is controlled by the much reported false twist effect of doffing tube.

The sudden drop in twist after the navel is an indication of the false twist effect.

If the false twist is suppressed, as in spinning with rotating doffing tube, the peripheral twist extent is small, & a considerably higher twist factor is needed to spin without a high end breakage rate.

In controlling the insertion of twist in the yarn , the doffing tube also influences the yarn structure. Results show that , as more false twist is inserted , then the more the wrapper fibre are present on the yarn surface.

At the navel of the doffing tube, the yarn twist back to the true twist value, which causes part of the wrapper fibres to become untwisted in producing the final surface structure.

It is ,however, the degree of twist in the core of the yarn that gives the yarn strength.

Since the core fibres are those in the rotor groove the yarn strength shows good correlation with the peripheral twist extent.

There are two possible reasons for this.

Firstly , results are given which shows that the twist in the core is not always the same as that calculated from the rotor speed & the yarn delivery rate; It varies directly with the peripheral twist.

Secondly, the core of the yarn does not consider entirely of helically wound fibres , but it shows a twist difference across its diameter that is inversely proportional to the peripheral twist. Because of the relatively high tensions present within the rotor & high rotational & draw-off speeds of the yarn, wear readily occurs on the doffing tube navel. This of course will influence the false twist & ultimately the yarn properties. In designing the doffing tube, two factors therefore to be considered : control of the false twist effect & the reduction of wear.

Control of false twist effect :-.

The false twist depends on the frictional behaviour between the yarn tail & the navel of the doffing tube & is influenced by various factors, which include the type & count of the yarn, the draw off speed & the texture of the contact surface, as well as the atmospheric conditions.

A very important factor, however , is the ratio of the yarn draw off tension f2, measured downstream of the doffing tube & to the calculated tension f1 in the yarn tail between the navel & the rotor wall.

The tension f2 must be greater than f1 if spinning is to take place. However, for stable conditions , the ratio should be within the range of 1.2-2 .

For given yarn count , f1 is dependent upon the rotor speed & the rotor diameter & is not significantly changed by changes in the doffing tube design. The tension f2, however, will be affected by the doffing tube profile & frictional properties.

Any such changes in the doffing tube design, in combination with f1, will control the false twist effect.

A compromise must therefore be reached in trying to improve the false twist effect in order not to exceed a value of 2 for the ratio f2/f1.

Taking these things into consideration various navel designs are made. Click here to watch them.

Reduction in wear :-.

The draw off speed through the doffing tube is usually between 60 & 150 m/min. While the rotational speed of the yarn tail in contact with the navel is up to 80000 rpm.

On average, depending upon the diameter of the navel, the rubbing speed of the yarn across the navel up to 1500 m/min.

This can lead to severe wear, quickly destroying the texture & making slight but significant modification to the profile of the navel.

The rate of wear depends upon the fibre being spun,& is reported that synthetic fibres that are strongly pigmented, e.g., spun dyed polyester fibre , give the fastest wear rate.

Doffing tubes are usually made from mild steel, which is easily machined but has not a sufficiently high resistance to this rapid wear action.

By coating the surface of the mild steel doffing tube with a sintered aluminum oxide, the life of component is more than doubled.

The high friction & rubbing of the yarn on the navel can also produce high temperature spots resulting in localized melting of fibres on the yarn surface.

Increasing the wear resistance of the component will not prevent localized melting.

Effect of the rotor parameters on twist insertion :-.

It is the compactness of the fibres in the rotor groove that both aids twist insertion, to give a good peripheral twist extent & produces an improved yarn strength.

Results have shown that the degree of fibre compactness in the rotor groove will depend on the rotor speed , the rotor diameter & the tightness of the groove angle.

It is now well known that stronger yarns are obtained with large diameter rotors & a 30 degrees v-grooved rotor, provided that the rotor speed does not produce a spinning tension greater than the yarn strength.

In order to increase the degree of fibre compactness in the rotor groove , several patented device have fitted mechanical means, which exert a controlled force on the fibre in the groove

Yarn Monitoring A precise analysis of the moir effect { a fabric defect} has shown that the associated periodically occurring defects in the yarn lie in the area where measured thick places , which usually occur in conjunction with thin place , are a disturbing factor only in their periodicity & not in their size .

The size of a thick place is about 8-10% of the average yarn count, with lengths ranging from 5 to 10 mm. In order to prevent individual spinning units from producing such defective yarn on rotor bobbin, it is recommended that the yarn be continuously monitored .

When such a periodic disturbance occurs ,it can be detected & removed , either manually or with a programmed autocleaner or doffer.

There are to types of monitoring systems being marketed , namely:

An individual monitoring system.

A mobile monitoring system.

An Individual Monitoring System

In this system every spinning unit has a detector, which is designed to measure continuously either the yarn diameter or the spinning tension.

In order to detect periodic faults in the yarn, it is necessary to convey the signal generated by the detector through electric filters , which are adjusted to the expected frequency of these faults, termed the moir frequency, f0.

The moir frequency can be calculated according to the equation :

f0 = v0 / ( 3.14 * d ).

Where, v0 is withdrawl speed & d is rotor diameter.

One reported method subjects the yarn signal to pulse-shaping, after which the shaped pulse train is is integrated & compared with predetermined threshold value.

The range of yarn counts that can be monitored is extended as a result of the fact that the processing of the thread signal is kept independent of the thread delivery speed.

One well reported commercially available unit based on the continuous measurement of the yarn diameter is the peyer-turocon monitor.

The signal evolution system used in this method carries out a continuous frequency analysis of the yarn signal.

This is performed over a frequency band of from -5% to 5% of the moir -defect frequency to achieve a good separation of the periodic moir signal from simultaneously existing normal yarn irregularity.

Fmk mfg. Ltd. Manufactures an electronic multipoint tension monitoring system based on the principle of measuring the difference between the centrifugal force acting in the rotor on a defective length of yarn & that acting on a perfect length & comparing with a predetermined threshold value.

It has the trade name tenscan which contains a solid state transducer unit , which can be fitted to any yarn processing machine.

The tenscan system is entirely electronic & is now claimed to perform three primary functions :

It sequentially measures in groups of four positions the tension value of each yarn emerging from the spinning unit by an individual solid-state transducer, which reads the tension continuously over a pre-set measuring period;

It compares the tension measured on each position with the pre-set limit; &.

It indicates on a data-logger display the location of each position found to be outside the permitted-deviation limits.

If individual motor drives are fitted to the rotor machine, the current consumption of each motor can be used to monitor the yarn irregularity.

To recognize the incidence of slubs & flaws or structured changes {or both } in the yarn, a sensor device located to respond to changes in the current flow to the motor is provided.

As with the previously mentioned system , if the changes in the value of the measured factor ( in this case , the current) exceeds a pre selected value , an electric signal is generated, which flashes a warning light or shuts off the rotor drive. A Mobile Monitoring System

The proposed use of a mobile monitoring system is to offset the relatively high capital outlay associated with individual monitoring arrangements .

With the mobile - monitoring approach , a carriage is fitted to the spinning machine with a sensing device {or devices} of the type used for individual monitoring.

The carriage can be programmed to monitor each position consecutively for a given time interval or to monitor units giving a sample of the production selectively.

The carriage can be made to stop the rotor unit or mark individual rotor units where the running quality of yarn is below that required.

Automation Of Rotor Spinning MachinesThe Need For Automation

One of the objectives of open end spinning research & development has been to develop fully automated systems for rotor spinning machines in order to increase production.

Automation of the rotor spinning machine must include automatic piecing-up after an end-break during the spinning, automatic cleaning of rotors when cleaning of the rotors when cleaning is required,& automatic doffing of the full yarn packages.

The necessity for automation stems from technical, economical & social factors.

The technical factors can be summarized as follows :

A productivity increase ;

Quality improvement & quality assurance ;

The future oriented machine concept,

The economic arguments are :

Comparable with the ring spinning frame & manually operated rotor spinning frame, the automatic machine , under present day conditions, produces yarn more economically up to a count of 20 tex{ 30 ne} ; {refer fig.}.

If account is taken of the future increases in labour costs & further developments in the productivity of the automatic rotor spinning frame , then the economic viability of automation should increase year by year;

Automation offers the possibility to activate capacity reserves currently under-utilized {e.g. , Operation over the week end}.

These are the unique arguments in favour of the automatic rotor spinning machine, even if, in certain countries , the spinning costs are at present at the same level as those of competing systems.

As a machine, the rotor spinning frame is best suited, owing to the application of the latest construction experience, to fulfill the demands for the reduction of noise & dust levels .

If successful operation of an automatic rotor-spinning frame can be achieved with a greatly reduced work force during night shift, a further contribution to amenable working conditions can be realized.

The advantages for the social & human aspect therefore become self-evident.

Developments In Automatic Piecing-Up

In order to increase the productivity of the rotor spinning machine substantially, the rotor must run more quickly , i.E. In excess of 60000rpm .

This , of course, does not just mean that only the rotor speed has to be increased.

Associated with higher rotor speeds are:

A higher take-up rate, which can be up to 200 m/min.;

A higher fibre throughput via the opening roller;&.

A shorter dwell time for the yarn in the rotor.

An important condition for running at high rotor speeds is that it is still possible to make Piecings while meeting the requirements relating to the quality of Piecings , which are :

An adequate extension ;

An adequate strength (an at least 80% of the yarn strength);

A low variation in mass ( i.e., In thick places a mass no higher than + 100% compared with the over-all yarn mass).

In one study, it was concluded that the optimum strength of of pieced -up section is very strongly influenced by the accuracy with which the requisite number of fibres in the yarn cross section is initially fed into the rotor , both too many & too few resulting in a weak resulting in a weak piecing .

Too many fibres will produce a thick piecing with a twist level lower than the set twist level, & too few will give a thin piecing with a high twist level.

By measuring the fraction of a second for which the feed roller supplies fibres to the rotor before piecing commences for a number of currently used commercial rotor speeds , it was found that the optimum piecing strengths were obtained after the following times :-.

For 45000/min. : After 0.55sec;

For 55000 /min. : After 0.45sec.;

For 67000/min. : After 0.33 sec.

This means that the feed time has to be reduced at higher speeds ,& thus a situation is reached at which piecing-up can no longer be managed manually.

Practical experience has also shown that the limit at which manual piecing is possible depends on the yarn count and material, as well as on the rotor speed.

Piecing-up with this system can be done on each unit separately, or on all units in one assembly.

Because of the rapid reactions of the servo-mechanism, it is possible to piece up at almost full rotor speed.

Each unit is activated by central electronic-control circuitry.

For a fault in the system, it is possible to replace the faulty part immediately; Even the central control l unit can be exchanged.

This reduces production losses during a breakdown. Fig.2 shows diagrammatically the traveling type of device.

The mechanism used for piecing up is positioned outside the delivery rollers & the normal package winding units & travels around one or more machines.

This means that, when an end breaks , an individual spinning unit has to wait until its position in the patrol route is reached before being pieced-up, which, of course , loses production time .

Any fault in the mechanism itself has to be removed from the machine.

A reserve device has therefore to be used, since it is impossible to replace any of the mechanisms in the traveling system quickly because of lack of accessibility & the handling of its considerable weight.

The use of a reserve device, however, increases the cost.

A comparative study of both systems showed that individual piecing-up was more advantageous than the traveling system.

With the individual system, the production losses did not exceed 0.25% , whereas, with the traveling system, losses can be from 0.15 to 20.7%.

However, the capital costs for fitting individual units to each spinning position are likely to far exceed those of traveling system.

Further Development Work

When a yarn breaks, the sliver feed has to be stopped & the rotating package braked.

With increasingly higher production rates, the stoppage of the fibre supply to the spinning rotor needs to be carried out as quickly as possible.

If the interruption in feed is too slow, then an overflow of fibres into the rotor will occur & will clog the rotor.

With rotor speeds in excess of 45000rpm , clogging of the rotor presents a fire hazard, owing to the frictional heat generated by the fibres being rubbed against the rotor casing.

To alleviate this problem , several new sensing devices have been developed to replace spring loaded trip wire switches commonly used on present commercial machines to detect yarn breaks & switch off the the feed roller drive.

Improved braking arrangements have also been designed for stopping the drives to the feed rollers, the delivery rollers & the wind up drum.

The fibre feed required for producing the ring of fibres for the piecing operation depends not only on the manner of restarting the feed but also , to considerable extent , on the condition of the sliver fringe offered to the opening roller.

In open end spinning, the fibre length has less significance with respect to the strength of the yarn than it has in ring spinning .

Thus , shortened fibres present relatively little problem.

On the other hand, short fibres permit the ring to be broken with less trouble, which improves the appearance & quality of the yarn piecing.

During piecing , irregularities can can result from bridging fibres , i.e. Wrapper fibres .

These are more pronounced when longer fibres are present.

The sliver feed therefore needs to be performed in two stages.

I.E. With shortened fibres fed first & followed by longer fibres.

To accomplish this, the opening roller, in combination with compressed air supply, serves as means for parting the two lengths, the compressed air acting on the sliver fringe before opening roller & removing the short fibres before the opening roller removes the larger lengths.

In the rejoining of a broken yarn , several operations are required, namely, cleaning the rotor, locating the end of the broken yarn on spool, returning the yarn to the doffing-tube outle, reinseting the yarn into the rotor, starting the feed & reinserting the yarn between the delivery rollers.

These operations are carried out as the rotor is accelerated up to its spinning speed.

Among the operations, two are particularly delicate, namely conveying the yarn to the doffing tube outlet & reinserting it into the rotor so that the end of the yarn attaches itself to the fibres in the rotor groove.

The success & quality of joint depend on this latter operation. Basically there exist three methods of conveying the yarn to the doffing tube outlet.

For one method, the piecing up device has a yarn locating head ( e.g.. A hook) which locates the broken end of the yarn on the package while a friction roller drives the package.

The device also has guides for determining its trajectory between the position of the package on the wind up drum & the position at which the retrieved yarn end is inserted into the doffing tube outlet.

In a second method, the piecing up device includes a two arm suction tube with a suction nozzle.

The suction tube is mounted on a pivot which enables it to scan the package for the yarn end.

The yarn end appears to be transferred from one arm to the other when being inserted into the doffing tube outlet.

A third method consists in the yarn end is being returned from the package via the wind up drum & delivery rollers, which are switched to a reversed motion.

The yarn end enters the spinning rotor through a withdrawl chamber .

When piecing up occurs, the delivery rollers are switched to their forward motion, & spinning recommences.

As mentioned earlier, timing has a crucial effect on the quality of piecing up.

This means that automatic piecing up does not always produce good pieced up sections with the requisite quality criteria.

It has to be programmed to obtain maximum success rate.

In order to control the process & particularly the operation of feeding in the fibre & drawing off the yarn , the rotor spinning machine should be provided with a pulse generator, to generate pulses proportional to the rotor speed, the generator being connected to a control circuit box.

The preliminary feed to rotor of the number of fibres required for the piecing operation, the return to the rotor of the yarn end to be pieced ,& the removal of the yarn from the rotor during its acceleration up to speed can all then be automatically timed .

The advantages of the generated pulse system reside in the facts that the nature & quality of piecing position are adapted as accurately as possible to the nature & quality of the spun yarn & neither piecing apparatus nor the control unit will generally have to be readapted or reset if the operating speed of the rotor is altered or if the fibre being processed or count being spun is changed.

The pulse can be produced by means of a photo electric cell operated by suitable reflective marking applied to the surface of at least one spinning rotor, a high pulse frequency being obtained from a large number of markings.

The pulses are processed into control signals with counters or multipliers or both.

To further ensure an acceptable yarn-piecing, control of the rotor acceleration up to spinning speed should be provided so as to lengthen the time in which the piecing steps can be performed.

A non-contact electromagnet or electric-eddy- current braking can be provided for countering the driving torque to the rotors.

The result is a flattening of the acceleration curve & a lengthening of the time period for piecing.

In order to prevent or reduce the formation of the loops & kinking in the yarn during the acceleration phase after the initial piecing , due to the difference in the inertia of the spool & the thread & feed rollers, the piecing device should control the course of the yarn between the feed rollers & the the spool.

The driving mechanism for the wind-up drum should also be adjusted to ensure a correspondingly rapid acceleration because of the greater inertia of the drum compared with the delivery rollers.

A yarn-tensioning means for maintaining constant yarn tension can also be included.

When the yarn package is driven at a greater speed in the normal winding direction, the pieced end is returned under tension to the yarn guide.

The winding speed of the package is then restored to its normal value.

For conical packages , the tension is maintained only when a special length store is provided.

The traversing of the yarn by the traverse guide should therefore not begin before the pieced joint is wound on the cheese, since otherwise a yarn break could occur & would be considered a failure of the automatic piecing operation.

In order to maintain a standard quality of piecing, a device for monitoring the yarn can be used. A data logger is provided for storing the information concerning the number of successful piecing operations at respective spinning units or machines.

Automatic Cleaning Of Rotors

It is now well known that , as the running time of the spinning unit of an open end spinning machine increases , the rotor becomes fouled , & the quality of the spun yarn deteriorates.

Cleaning of the rotor is therefore of importance not only in relation to the properties of the yarns but also for obtaining a good piecing after an end break, since otherwise the piecing-up operation will fail.

If the cleaning of the rotor is carried out manually, the degree of cleaning & the ultimate success in piecing will depend largely on the thoroughness & skill of the operating personnel.

However, for consistently well-cleaned rotors, automatic cleaning is needed, which can be effected independently of the skill of the operating personnel.

If an interruption in the spinning process occurs, such as a yarn break or the doffing of full yarn packages , it is necessary to remove from the spinning rotor the fibrous ribbon & the yarn end that have been sucked into the rotor after the yarn has been severed.

Besides this, in order to confine the rotor-soiling within certain limits, it is recommended that the spinning rotor should from time to time be stopped & cleaned .

Cleaning of the rotor can be carried out by two methods : mechanically & pneumatically.

In the mechanical method, the cleaning elements are usually rotary brushes.

A mobile service device includes the brushes , having a diameter smaller than the open side of the rotor to be cleaned, a drive motor for rotably driving the cleaning brush around its support shaft, & a selectively movable lever mechanism for moving the brush into & out of the rotor.

The cleaning brush & its support shaft are carried by a crank mechanism for moving the the shaft & brush in a circular motion so as to ensure engagement of the brush with the yarn-collecting groove in the spinning rotor being cleaned.

Another arrangement is for the cleaning brushes to be connected to the drive by spring loaded lever, which gives the brushes a radial movement during the cleaning operation in response to centrifugal forces.

With this arrangement, there is advantage that the cleaning elements can be pressed with sufficient force against the inner walls of the rotor, & especially against the yarn collecting groove, without danger of damage to the rotor.

The adjustability of the cleaning elements radially with reference to the rotor axis further allows cleaning independently of the rotor diameter & shape.

With the pneumatic method , compressed air is used for cleaning the spinning rotor. In one arrangement , the spinning rotor is moved from its normal operating position to one in which a nozzle can direct a pressurized air-stream towards the sliding surface & collecting groove of the rotor.

In an alternative arrangement, the rotor is rotated at a speed less than the spinning speed.

A first flow of cleaning air is directed to collecting groove of the rotor, & second flow of cleaning air is simultaneously directed to the periphery of the rotor at an angle different from first.

At least one of the flows of air is directed in pulsating manner. The air flows can be supplied through ducts machined into the cover plate of the rotor housing.

It is claimed that in this way not only satisfactory loosening of the trash from the rotor wall is achieved , but, even with the rotor not stationary , positive removal of the trash also occurs.

In order to produce a deliberate interruption in the spinning to enable the rotor to be cleaned, a yarn monitor should be positioned so that , on measuring a fall-off in the yarn properties, it switches off the sliver feed roller.

Alternatively, to ensure that the length of yarn leaving the rotor after the break does not contain the fault , the yarn itself can be broken .

In this case, a mechanical device slackens off the yarn tension in the vicinity of the monitoring sensor sufficiently for a cut to be made in the yarn & ultimately interrupt the supply of fibres to the rotor.

Automatic Yarn Of Full Yarn Packages

One of the most difficult tasks of the operative is undoubtedly the doffing of full open end spun yarn packages, which are situated above the rotor in nearly all makes of machine.

It requires a degree of skill & physical strength , especially if the mass of the full yarn package exceeds 1 kg. , & this applies to all bobbins whose width exceeds 85 mm. Moreover, it is important to replace full bobbins by empty tubes safely while the machine is running, without interrupting the spinning process.

In order to reduce the physical & mental exertion of the operative , automatic doffing of full open end spun yarn packages has been developed. There are two systems:

Semi-automatic &.

Fully automatic.

For the semi-automatic system, a supply station is fixed at each spinning unit for storing a supply of empty spool tubes already wound with starter yarns.

A traveling servicing carriage is guided on tracks adjacent to the spinning units & has lever mechanisms for effecting the removal of a full bobbin & its replacement with an empty spool tube at each supply station.

Package -changing with this system means repiecing the yarn.

Each supply station is filled manually while the traveling servicing carriage is automatically driven to effect the tube transfer operation.

In the fully automatic system, doffing is performed without interrupting the spinning process.

While the full package is being removed & replaced with an empty one, the running end of yarn passes through a suction tube into the machine's waste collection system.

After empty spool tube is in place, the running yarn is returned to the tube, where a transfer-tail is wound before releasing the yarn to regular winding traverse.

Doffing without interruption of spinning has the advantage that there is no loss in production; The spinning position does not stand idle while it waits for the subsequent piece up operation.

On removal by the automatic doffer, the package are placed on a conveyor extending the length of spinning machine.

A second conveyor is positioned between the first conveyor & a container, which ultimately receives the packages.

This second conveyor is driven at a higher speed than the first to allow the packages to be automatically stacked in columns in the container.

On the whole fully automatic system greatly reduces the effort of the operative's job & in saving labour increases the number of machines per operative.

The net result is an improvement in the working conditions & a possible reduction in production costs

Effect Of Trash On Rotor Spinning

In ring spinning , the trash particles are ejected harmlessly from the spinning balloon , but in rotor spinning these particles accumulate in the yarn -forming groove of the rotor in the following way :-.

Firstly the ring tapers from a maximum cross -section at the peeling point to virtically zero behind it.

Secondly , the surface of the slide wall is continually exposed to a varying degree as the yarn arm revolves relative to the rotor. & This permits the deposition of particles on the slide wall. Rotation of yarn arm in the peripheral - twist zone works such deposits down the slide wall & into the the bottom of the rotor groove.

These trash particles displace the fibres to wider part of groove [as shown in figure] so that the process of yarn formation becomes less precisely controlled.

Yarn strength declines ; yarn uniformity deteriorates ; yarn hairyness & appearance are preceptibly altered .

Ultimately ,the trash builds up to a point at which the process of yarn formation is interuped , & an end break occurs.

Time taken to end break from start is called maximum spinning time.

It also results in