Drafting and Twisting Processes in Open-end Spinning

Drafting and Twisting Processes in

Open-end Spinning Machine MS-400

By Teiryo Kojima, Kozo Susami and Masaaki Tabata, Members, TMSJ

Based on the Journal of the Textile Machinery Society of Japan, Proceedings, Vol. 21, No. 11, p. 737 (1968); Vol. 25, No. 9, p. 623 (1972)

Abstract

1. Introduction

Principal processes of spinning machines consist of drafting, twisting and winding. If fiber properties are being fixed, yarn qualities are mostly governed by fiber motion in drafting and twisting processes, although these processes are quite different in open-end spinning from those in ring spinning; this characterizes the yarn property produced by open-end spinning. In this report, discussion will be made on drafting and twisting processes in the open-end spinning machine MS-400 and their relation to the yarn properties. Also the characteristics of the open-end spun yarn will be considered.

Toray Industries Inc. carried on the study of open-end spinning in cooperation with 1-iowa Machinery Ltd. for several years, and developed MS-400; it belongs to a drumtype spinning machine, as schematically shown in Fig. 1, A sliver is fed to 4-line double apron drafting system (1), and passes through an ejector (2) into which compressed air (6) is fed through a valve (10). A fiber bundle is separated to single fibers, and they are sent to a drum (3) rotating in Fig. 1 Main constitution of MS-400

Journal of The Textile Machinery Society of Japar

The most characteristic features of the open-end spinning compared to the ring spinning are in the drafting and twisting mechanism. In the present paper, some discussion will be

made on the analysis of the drafting and twisting processes in MS-400 open-end spinning and their relation to the properties of its spun yarn.

The mechanical characteristics of MS-400 are;

(1) Roller drafting device

(2) Ejector for fiber separation(3) Special eyelet, a yarn guide attached to the axis of the drum.These mechanisms make MS-400 a suitable spinning machine for man-made fibers.

In the first part of this paper, the behaviour of fibers in the ejector separated into individuals from a fiber bundle by the air stream will be considered. The discussion will be extended on the degree of fiber separation and the state of fibers, such as straightness at the outlet of the

ejector.The second part deals with some mathematical analysis of the process of fiber collection in

the drum and its self-doubling effect on the yarn irregularity. It is shown that the self-doubling

effect is extremely useful for decreasing the yarn irregularity of short wave length and for improving the blend uniformity of fibers in the yarn.

In the third part, the effect of the eyelet equipped in the drum is considered. The eyelet is shown to have a great influence on the yarn strength and on the end down in spinning.

In the last part, a brief mention will be made on the spinning features obtained by the

practical production in MS-400.

KEY WORDS: DRAFTING, TWISTING, OPEN END SPINNING

8

high speed, and then twisted by the rotation of the drum (3) relative to delivery rollers (4), forming a yarn which is wound in a cheese (14) on a winding drum (5).

The most characteristic processes of yarn formation in MS-400 are the separation of a fiber bundle in the ejector and the fiber motion in the drum; these characteristics will be discussed in the following chapters.

2. Separation of Fiber Bundle by Ejector-Air Draft

Fig. 2 Constitiuton of the ejector

Fig. 2 shows a schematic diagram of an ejector, which consists of two parts; nozzle and diffuser. Fibers sent from front rollers of the drafting device are fed into the ejector through the nozzle. Compressed air is fed into an air chamber and is gushed out through the alley between the nozzle and the diffuser, causing a sucking air stream in the nozzle. The fiber bundle is separated by the air-friction between fibers and air stream in the nozzle.

We shall consider the variation of the flying speed of a single fiber supplied in the ejector from front rollers of the drafting device, in order to guess the process of the fiber bundle separation. The following symbols are adopted[1]:

x= Distance from the nip point of front rollers to the trailing end of a fiber at time t.

m= Mass of a fiber.V= Flying speed of a fiber at time t.Va=Air speed in the ejector.

When a fiber was placed in air stream and its one end was connected to a strain meter, the air resistance of the fiber was proportional to (air speed)2. This suggests that the air resistance acting on a moving fiber should be proportional to (relative speed between the fiber and air)2. So, the fiber motion after the release from the nip point of front rollers is:

where C=const.When the initial speed of the fiber is Vo (equal to the surface speed of front rollers of the drafting device), the fiber speed Vat an arbitrary position x is given by:

where

F0=C(Va-V0)2

F=C(Va-V)2

Vd=V0/Va

Fig. 3 Relation between distance and flying speed V of a fiber

Fig. 3 shows the variation of the fiber speed calculated by the above equation, indicating that a fiber in the ejector

gets nearly the same velocity as air at few centi-meters distant from the nip point of front rollers. This distance is extremely shorter than that anticipated. However, the friction between neighboring fibers in the bundle acts on the fiber in the ejector, adding to air force, causing a slightly longer distance until the fiber gets the same velocity as air. Nevertheless, an ejector 1.5 times longer than the fiber length would be enough to separate a fiber bundle.

Now, considering the state of fibers separated with the ejector, the performance of fiber esparation is very important not only in MS-400 but also in any other open-end machines: it directly influences upon both the evenness of and the breakage of yarns. It is desirable to get uniform separation of fibers in the ejector. But the degree of fiber separation is dependent on the properties of raw materials, quality of fiber bundles, ability of the ejector and air pressure supplied to it, etc. The relation among them is too complicated to make a theoretical analysis, and experimental observation would be reasonable.

Figs. 4 and 5 show photographs of fibers flowing from the ejector to the drum in spinning condition. They are taken with a camera equipped with 75mm telescope lens, 20mm ring, film of ASA 400 (Kodak), and flash time of 12 micro-second. In Fig. 4, four fibers are shown supplied simultaneously to the drum. In Fig. 5, a single fiber is

presented. By this way, the behavior of fibers moving from the ejector to the drum was observed to estimate the uniformity of fiber separation from 1,000 frames of photographs.

Fig. 6 shows an example of the relation between the number of fibers in a frame of the photographs (horizontalaxis) and its frequency (vertical-axis). No fibers in a frame means the occurrence of "open-end" there. The distri

Vol. 20 No. 1 (1974) 9

Fig. 6 Relation between number of fibers per frame

of photos and its frequency

Fig. 4, Fig. 5 Photograph of hbers flowing trom the ejector to the drum in spinning

celerated in the air stream and supplied to the drum at the

velocity equal to air velocity. So the degree of fiber sepa

ration can be estimated by the average number of fibers

supplied to the drum, which could be calculated from

bution in Fig. 6 almost follows Poisson distribution. Assuming the number of fibers be n and its frequency be f, an average number of fibers n can be expressed by

which n can be considered the average fiber density in the air flow blowing from the ejector to the drum. When the

yarn take-up speed is Vy and the number of fibers in the yarn cross-section is ny which is determined by both the yarn count and the fiber denier, the average fiber speed V supplied from the ejector to the drum is calculated by

Table 1 shows the average fiber speed V and the average

number n•Œ of fibers with different kinds of fibers having the

staple length of 51 mm. It can be seen that the higher the

air pressure, the better the fiber separation. But the air

Table 1. Degree of Fiber Separation

The calculated speed is almost equal to the air speed blowing from the ejector to the drum which can be experimentally measured. This shows that fibers are fully ac

Table 2. Content of Hook Fibers after Separation (%)

10 Journal of The Textile Machinery Society of Japan

pressure supplied to the ejector should not be raised excessively, because if the fiber speed exceeds the surface speed of the drum, the fiber arrangement and its straightness are disturbed. Comparing the materials of fibers used, the degrees of fiber separation of polyester or polyesterrayon blended are worse than those of polypropylene or

polyacrylonitrile.Table 2 shows the fiber-hook observed on photographs

mentioned above. Fibers used are polyester, polyacrylonitrile, nylon and polyester-rayon blended of 51mm staple length. In any case, the amount of total hook-fibers is only two to three percent. This fact suggests that the ejector can straighten the fibers supplied from the drafting device.

3. Fiber Motion on Drum-Collecting Process and Selfdoubling Effect

Fibers laid on the inside of the drum by air flow are subjected to a doubling operation. The web on the drum is

jointed to a twisted yarn, which is then removed by take-up rollers. The surface speed of the inside wall of the drum is

perhaps 100 to 300 times higher than that of take-up rollers. Thus the draft ratio at this stage is fractional i.e. 1/100 to 1/300. A self-doubling effect is caused by the fractional draft ratio, resulting in an extremely uniform yarn.

The effect of self doubling, which was already reported

qualitatively by Rohlona et al[2], will be considered mathematically as follows. The number of fibers supplied to the drum by air flow is so small that the flow continuity of fibers is practically interrupted. However, assuming a continuous flow of fibers, we call it a sub-yarn for convenience sake. The sub-yarn is wound on the inside of the drum, more exactly on the collecting surface.

Fig. 7 shows layers of the sub-yarns on the drum. When the surface speed of the take-up roller is w, the peeling speed of the bundle from the collecting surface is equal to w. When the surface speed of the collecting surface of the drum is v, it is equal to the supplying speed of the sub-yarn to the drum. In fact, the fiber supplying inlet to the drum is fixed and the drum is rotating, but it would be convenient for simplicity to consider reversely: the drum is fixed and the fiber supplying inlet is rotating. In this case as shown in

Fig. 8 Relative motion of the peeling point A and

the supplying point B

Fig. 8, the supplying point of the sub-yarn B is rotating at

the velocity v clockwise and the peeling point of the layers

of the sub-yarn A is rotating at the velocity w anti-clock

wise (it is rarely rotating clockwise). When the circumfer

ence of the collecting surface is I and the peeling point A

meets with the supplying point B at time t=0 on the point

P (it is decided as the original point), the time r for A to

meet with B next, is given by,

wƒÑ+ƒËƒÑ=l .........(1)

then

ƒÑ=l/(w+ƒË) .........(2)

And the distance d from the meeting point to the original

point is

?? =wƒÑ=wl/(w+ƒË)=1/(ƒË/w+l) .........(3)

=1/(Q+1), .........(4)

where

ƒË/ w=Q

Fig. 9 shows the layers of the sub-yarns on the collecting

surface of the drum at time ƒÑ.

When the supplying point B goes over the peeling point

A, the newly supplied sub-yarn is divided at that point;

one part of the sub-yarn supplied before is peeled by the

advance of the peeling point but the other of the sub-yarn

which will be supplied after, will make new layers on the

collecting surface. And thus the sub-yarn is repeatedly

divided and deposited on the collecting surface. The di

vided length of the sub-yarn is given by,

ƒËƒÑ=ƒËl/(w+ƒË)=1Q/(Q+1) .........(5)

or

ƒËƒÑ =1-wƒÑ=1- ?? ......(6)

The time for the peeling point to come back to the origi

nal point P is 1/w. As the drum speed is ƒË/l, the revolution

Fig. 7 Layers of sub-yarns deposited on the drum

Fig. 9 Layers of sub-yarns on the collecting surface

at time t=ƒÑ

Vol. 20 No. 1 (1974) 11

Fig. 10 Positions of deviding points of sub-yarns

number of the drum during that time is

ƒË/l•E1/w=ƒË/w=Q

That is equal to the revolution number of the supplying

point. As mentioned above, Q (=ƒË/w) layers of the sub

yarn are deposited on the point P, when the peeling point A

comes back again to the original point P. This process does

not change, even if the original point may be taken any

place on the collecting surface. Therefore, on the peeling

point, Q layers of the sub-yarns are always deposited and

then those are collected, peeled, twisted and spun out as a

yarn. We call this a self-doubling effect. The number Q of

the self-doubling in the open-end spinning system of drum

type is decided by the ratio of the surface speed of the drum

to the take-up speed, ƒË/w.

As shown in Fig. 10, the sub-yarn is divided in the length

IQ/(Q+1) and the divided sub-yarns are deposited in the

distance of 4=l/(Q+1) on the collecting surface. Then the

sub-yarn is placed in the spun yarn as shown in Fig. 11, in

which, i and i•Œ show the divided points of the sub-yarn. i

shows the leading end of the divided piece number (i+1)

of the sub-yarn and i•Œ is the trailing end of the divided piece

number i. It should be noticed that, in Fig. 10 the leading

end of the sub-yarn is in the left hand and in Fig. 11 the

leading end of the spun yarn is in the right hand.

We put y-axis on the length wise axis of the yarn and

assume the thickness of the yarn at y as S(y). It is clear that

S(y) is the sum of the thickness of the sub-yarns at y, as

shown in Fig. 11. Next, we may calculate S(y). Now, the

original point of y-axis is the leading end 0 of the first

divided piece of the sub-yarn (Fig. 11).

To clear the variance of the thickness within short

ranges, we consider it within (i-1) ?? •ƒy•… ?? . In Fig. 12,

when we put points Mi, Mi+i,...for each sub-yarns at y,

the position xi on the sub-yarn corresponding with the po

sition Mi is

xi=i(l- ?? )+(i ?? -y)=-y+il .........(7)

Fig. 11 Positions of deviding points of sub-yarns

on the spun yarn

Fig. 12 Positions of devided sub-yarns on the spun yarn

And the position xi+k corresponding with Milk is

xi+k=-y+i¥1+k¥1 .........(8)

where x-axis is put on the lengthwise axis of the sub-yarn

and the original point of x-axis is the leading end of the

sub-yarn. As the doubling number of the sub-yarns is Q,

k in eq.(8) has values from 0 to (Q-1). Then, when the

thickness of the sub-yarn is S(x), the thickness of yarn

S(y) within the region (i-1)4•…y•ƒi ?? is

For simplicity, the sub-yarn delivered to the drum may be

assumed to have the sinusoidal thickness irregularity of

wave-length 2 and relative amplitude a, as follows:

From eqs. (9) and (10), the thickness of yarn S(y) is:

while

Then, eq.(11) is re-arranged:

If ƒÎl•áƒÉ, then sin So, eq.(13) can be ex.

pressed as

where

As the draft ratio in the fiber opening device of open-end

spinning machines is very large, the wave-length of sinu

soidal thickness irregularity of the sub-yarns is long . Then,

we may consider ƒÎl•á2. So, eq.(14) shows that the spun

yarn has also the sinusoidal thickness irregularity of wave

length ), and relative amplitude aA within the region of

(i-l) ?? •ƒy•…i ?? .

In order to know the thickness of yarn S(y) in wide


Fig. 14 Evenness of spun yarns

Fig. 13 Relation between A and 1Q/ƒÉ

range, we may calculate S(y) when y= ?? , 2 ?? , 3 ?? , Putting y=i ?? ,

then-Y+il=-y+(Q+1)y=Q¥u .........(17)

Thus eq.(14) is changed to

where y= ?? , 2 ?? , 3 ?? ...........,i ?? ..........

As mentioned above, we can see that the spun yarn as a

whole has the sinusoidal thickness irregularity of wave

length ƒÉ/Q and relative amplitude aA. If Q is very large and

1/Q is very small, eq.(18) may be considered to show the

true variation of yarn thickness S(y) in whole yarn length.

Using eqs.(14) or (18), the sinusoidal thickness irregu

larity of wave-length ƒÉ and relative amplitude a, existing in

sub-yarns is changed to the sinusoidal thickness irregulari

ty of relative amplitude aA due to the self-doubling effect

in the drum. As shown in eq.(l 5), A is always smaller than

1. Then, the relative amplitude of sinusoidal thickness ir

regularity in spun yarns is always smaller than that in sub

yarns.

Fig. 13 shows the relation between A and lQ/ƒÉ. It can be

seen that A (decreasing ratio of irregularity amplitude)

decreases with increase of lQ/ƒÉ, and that it becomes very

small when lQ/2 is greater than 1. This means that the

periodic irregularity or irregularity factor of short wave

length existing in sub-yarns or fiber bundles supplied to the

drum, is almost diminished to zero. This self-doubling

effect is the most characteristic feature in open-end spinn

ing.

In order to illustrate the effect of self-doubling as described above, a yarn of 24's (English cotton count) was spun in an open-end spinning machine MS-400 especially

equipped with an eccentric roller drafting device. The same

count yarn was also spun in a ring spinning machine

equipped with the same drafting device, using the same

roving. The fiber used was polypropylene staples of 1.5

denier and 38mm length. The front top roller was 29.1mm

in diameter and 0.52mm in eccentricity. The draft ratio

between the front and second rollers was 20.0. In this case,

l Q/ƒÉ was 1.75, A being 0.14. Fig. 14 shows the evenness

curves of spun yarns. As can be seen from it, periodic

amplitude irregularity of about 18% was observed in the

ring spun yarn, whilst there was scarcely any in the yarn

produced with the open-end spinning machine. Successive

ly, experiments were made using some front top rollers

with different eccentricity, but periodic irregularity was

scarcely observed.

Self-doubling is very effective for not only making a uniform yarn in lengthwise but making a uniform blend of fibers in the yarn. Because Q layers of sub-yarns are de

posited on the inside wall of the drum, this has the same effect as the doubling of Q slivers in roller drafting. When different fibers are blended, the greater the number of doubling, the more uniform the blend of fibers in the yarn. The theoretical number of total doubling is said to be more than the average number of fibers in the yarn cross section. So, in conventional spinning, several separate doubling

processes are necessary. But in open-end spinning this is not so, because doubling effect corresponding with doubling number Q (=v/w) is given by self-doubling. For example, the number of self-doubling is nearly equal to 140 when the drum diameter is 6 cm, the drum speed being 30,000 rpm, the take-up speed being 40m/min; this is equivalent to the doubling of 140 times. For this reason, in open-end spinning, usually the blending in preparing process is not necessary. To demonstrate this effect, yarns of 26's cotton count were produced by feeding two rovings to both a ring and an open-end spinning machine. The two rovings were of polyester staple fibers, 1.5 denier and 38mm length, one roving being white and the other dyed black. Fig. 15 shows photographs of the cross sections of

yarns produced by both methods; it is clear that the yarn produced by open-end spinning has an extremely uniform fiber blend. The value of Q in this experiment was about 140. Self-doubling effect of an open-end spinning machine

Vol. 20 No. 1 (1974) 13

(a) ring spun yarn (b) open-end spun yarn

Fig. 15 Photographs of cross sections of yarns

MS-400 was discussed above. This effect is generally characteristic in a drum-type open-end spinning machine. So, the yarn produced on MS-400 has extremely uniform thickness nearly equal to a random sliver because of selfdoubling.

As shown in the experiment mentioned in the previous chapter, a sliver is not always separated into individual fibers in the opening device, and a part of fibers is supplied to the drum in groups. Then, strictly speaking, it can be said that the spun yarn is composed of collection of fiber

groups (a single fiber being considered a group having one fiber). Using Tabata's theory[3,4], the relative variance C2(S) of the spun yarn of thickness S is expressed by

c2(S)=k{l+c2(k)}/Swhere S is the average thickness of the spun yarn, k the number of fibers in groups, k the average of k, c2(k) the relative variance of k. And.

relative variance=(variance)/(mean)t.As the relative variance given in the above equation is, in strict meaning, the relative variance of the number of fibers in a yarn cross section, the relative variance of yarn thickness must be obtained by adding it the effect of single fiber thickness irregularity.

The above equation shows that the smaller k or ct(k), the better the evenness of spun yarn thickness. Therefore, it is desirable that the fiber opening device separates the fiber bundle as fully as possible into individual fibers, and also that the fiber opening device does not hurt or cual fibers. As seen in Table 2, the value k is slightly samller than 2 in case of MS-400 in good condition. This value is near to that measured before by Tabata about group behavior of fibers in ring spinning machines[5]. This shows that the superior uniformity of spun yarns produced by MS-400 depends mainly on the fact that it has extremely few

periodic irregularity of short wave length, compared with conventional machine.

4. Fiber and Yarn Behavior in Twisting

4-1. Behavior of Fibers

The drum of MS-400 has two actions; one is "recollection" of separated fibers to predetermined thickness, and the other is "twisting" of the re-collected fiber bundle to form a yarn. As the re-collection was discussed in the

previous chapter, we may now consider the fiber behavior in twisting.

In the conventional ring spinning machine, the fleece fed from front rollers is nipped tightly between rollers on its trailing end, and twisted under rather high tension caused by ballooning of the yarn. On the other hand, in the open-end spinning machine, the web deposited on the collecting surface of the drum is peeled and twisted. Therefore, the end of the yarn now being twisted is maintained only by the frictional force between the web and the collecting surface (caused by centrifugal force acting on the web) and by the friction acting between fibers. This force is very small, but the tension acting on the yarn being twisted is also small. It can be said that a ring spun yarn is twisted under high tension with its trailing end nipped tightly, while an open-end spun yarn is twisted under lower tension with its trailing end nipped loosely. For this reason, a ring spun yarn has tight construction, but an open-end spun yarn is soft and bulky. In open-end spinning, fiber slip occurs more easily in twisting. So in extreme case of open-end spinning, fibers in outer layers of the yarn remain in outer layers extending lengthwise and fibers in inner layers remain in inner layers. Also twist numbers of fibers in outer layers differ from those in inner layers.

There are unusual groups of fibers distinguishing the appearance of open-end spun yarns from that of ring spun

yarns. As shown in Fig. 16, some fibers G may be taken off from the thin end of the web lying on the collecting surface, and some fibers may be blown to the portion H of the yarn already formed. These fibers form a coil of fine helical

pitch around the parent yarn and they are called bridging fibers. The number of these fibers is affected by the design of the drum and can be decreased in some degree by adopting an adequate position of the ejector outlet against the drum or using a separator insulating the yarn from the supplied fibers. The longer the circumference of the collecting surface or the shorter the staple length, the less the number of the bridging fibers.

Fig. 16 Unusual groups of fibers


(upper) good yarn (below) bad yarn

Fig. 17 Yarn appearance

Fibers G and H except those normally taken off and

twisted, can scarcely contribute to yarn strength, but spoil

yam appearance. Fig. 17 shows good and bad open-end

yarns. The good yarn looks like a ring spun yarn; the bad

yarn is quite different in appearance, having many fibers

coiled around the outer layer of the yarn.

4-2. False Twisting Action of Eyelet

In this chapter, the eyelet may be considered which

touches the yarn taken from the drum (Fig. 18, B). Its

shape, material, surface finish and contact angle ƒÆ with the

yarn are important and exert much influence upon the yarn

quality and the yarn breakage during spinning.

In Fig. 18, the yarn end A moves on the circle which the

collecting surface describes due to the rotation of the drum,

and the yarn between A and C is given a true twist (its

direction being z twist in Fig. 18). Twist density of the yarn

between B and C is equal to that of the yarn spun out,

whilst that between A and B is not so. This is because,

false twist occurs due to the rolling of the yarn on the inner

Fig. 18 False twisting

action of eyelet

Fig. 19 False twisting action of

the false twisting machine in

friction type

surface of the eyelet B, when the yarn end A moves. Be

havior of the yarn in this stage is similar to that of the

friction type false twisting machine.

For example, in the friction type false twisting machine

shown in Fig. 19, the rotation of a friction ring B•Œ corre

sponding with B in Fig. 18 rotates the yarn which touchs

B•Œ. When there is no slip between the yarn and the friction

ring, the yarn at B•Œ rotates with ƒÁB•Œ/ƒÁy turns during 1

revolution of the friction ring, where rB' is the radius of

the friction ring and ƒÁY is that of the yarn. Therefore, when

the rotating speed of the friction ring is V•Œ, the false twisting

speed is V•Œ-ƒÁB•Œ /ƒÁy. In the stable state of false twisting, a

yarn is twisted only in the region A•ŒB•Œ (before the friction

ring), and untwisted in the region B•ŒC•Œ (after the friction

ring). The twist density of the yarn fed with velocity W•Œ,

in the region A•ŒB•Œ, is (V•Œ/ W•Œ) x(ƒÁB•Œ/ry)

Actually, there is some slip between the friction ring and

the yarn. Assuming k (0•ƒk•ƒ1) be a constant expressing

the degree of slip, the false twisting speed U•Œ is equal to

kV•ŒƒÁB•Œ/r, and the twist density of the yarn in the region

A•ŒB•Œ is equal to k(V•Œ/W•Œ) (ƒÁB•Œ/ƒÁY). In Fig. 18, the eyelet B

is fixed and the yarn is moving on the inner surface of the

eyelet B. It is dissimilar to Fig. 19, but false twisting of the

yarn is similar to Fig. 19. Then in open-end spinning, the

yarn in the region AB is given a false twist caused by

friction atainst the eyelet B, in addition to true twist given

by the drum rotation; the twist density of the yasn in this

region is given by

(V/W)+k(V/W)(ƒÁB/ƒÁY)=(V/W)(1+k. ƒÁB/ƒÁY),

where V is the drum speed and W is the take up speed of

the yarn.

A constant k is affected by friction between the yarn and

the eyelet B, contact angle between both, yarn tension and

yarn rigidity; the greater the k, the higher the twist density.

Therefore in this case, the web deposited on the collecting

surface of the drum is taken off more easily and yarn

breaks during spinning decrease, but contrarily the yarn

quality is spoiled. The eyelet should be chosen carefully in

its material, shape and contact angle of the yarn. Though

the eyelet of MS-400 machine is fixed, a rotatable eyelet

can be considered. For example, the eyelet fixed to the

drum will have scarcely false twisting effect, but that rotat

ing to reverse direction against the drum will have a greater

false twisting effect.

Fig. 20 shows the measuring device of false twist density,

U/W. As shown in Fig. 18, actually the yarn is rotating on

the fixed eyelet and taken off downward, but in this device,

a yarn (1) is only running downward by rollers (7), and the

eyelet rotates to reverse direction aginst the drum with the

same velocity as the drum. In Fig. 20, a yarn (1) is unwound

from a cone cheese, running through the snail guide (2),

a disk tensioner (3) and the eyelet (4), and taken-off with

delivery rollers (7). The eyelet (4) is fixed on the upper end

Vol. 20 No. 1 (1974) 15

Table 3. Yarn qualities produced with MS-400

Fig. 21 False twist number U/W (turn/25 mm)

Fig. 20 Measuring device of false twist number U/W

of the tube (5), which is driven by a driving belt (6). The yarn (1) touches a twist-measuring device (8), which has a rotor (9) supported with pivot, which has little resistance against rotation, and whose rotation is proportional to that of the yarn (1). The rotor (9) has eight holes, through which a ray from a light source (10) is cast to a photo-electric element (11) at the time when a hole comes on the line connecting the light source (10) and the photo-electric element (11), which is connected to a degital-counter (12). Then, the rotation of the yarn (2) driven by the friction force between the yarn and the eyelet (4), is delivered to the rotor (9) of the twist-measuring device (8), and the number proportional to the rotation of the yarn is expressed on the degital-counter (12).

Fig. 21 shows the relation between the false twist number U/W (vertical axis) and the frictional coefficient of yarn against the eyelet (horizontal axis), measured with several

different eyelets. The yarn used was polyester rayon blended of 30's (English cotton count). Its blending ratio was 65/35 and the twist number was 19.2 turns/25mm. Same yarn was used in the measurement of frictional coefficient. The

greater the frictional coefficient, the greater the false twist number U/W. Therefore, it is suggested that the twist density of the yarn in the drum can be raised by using the eyelet with high frictional coefficient, and that yarn-breaks decrease even if the true twist number determined by the ratio of the drum speed to the take-up speed is lowered.

Fig. 22 shows an example of spinning condition when several eyelets with different frictional coefficients are used. End-down index is the number such as the least end-down is taken as a unit, yarn strength index being such as the highest yarn strength is taken as a unit. The yarn used was the same as that in Fig. 21. The greater the frictional coefficient, the less the end-down during spinning and the lower the yarn strength. The reason of the former phenomenon was discussed already, and the latter is caused by the yarn damage during yarn-passing through the eyelet having high frictional coefficient. In fact, when the eyelet having high frictional coefficient is used, a lot of powder is


After time dt, the variance of twist number ?? N1 between

A and B may be written as

......(19)

Then

When U is constant, by integrating the above equation

we have:

Assuming N1=0 at t=0, then

Therefore

........(20)

Fig. 22 End-down and yarn strength when different

eyelets are used

deposited in the drum, which is recognized to be fine pieces of fibers by observating through a microscope.

As mentioned above, the role of the eyelet is not only to lead out a yarn formed in the drum, but to raise the twist density of the yarn in the drum by false twist given by friction between the eyelet and the yarn. The higher the frictional coefficient of the eyelet, the more the twist density of the yarn, and the more stable spinning condition with a low true twist number. But the eyelet with high frictional coefficient sometimes hurts the yarn passing on it. Therefore, in selecting the eyelet, these contradictory effects should be considered to suit for the spinning condition and raw material used.4-3. Variance of Twist Density of Spun Yarns

False twisting discussed before acts not only in MS-400 but in all the drum-type open-end spinning machines, such as BD-200. This effect is useful for decreasing yarn-breaks and for stabilizing spinning. But in case that false twisting speed varies, the twist density of the yarn varies too. This problem may be considered mathematically as follows. The following symbols are adopted (see Fig. 18).

V, W: defined before,l1=Yarn length between A and B.l2=Yarn length between B and C.Nl=Twist number of yarn existing between A and

B at time t.N2=Twist number of yarn existing between B and C

at time t.- U=False twist number per unit time given by the

friction between eyelet B and yarn.(the rotating direction of yarn in false twist is reverse to that given by rotation of the drum)C1, C2 =integral constants.

Eq.(20) shows that the twist density of the yarn in the region AB is (V+U)/Win stable state (t being infinite).

Next, the twist density of the yarn in the region BC may be considered. Similary as above mentioned, the variance of twist number 4N2 of the yarn in the region BC after the time ?? t, is:

Substituting eq.(20) into eq.(21)

When U is constant,

Assuming N2=O at t=0, eq.(22) is changed to

where

The twist density of the yarn in the region BC is V/Win stable state (t being infinite). Namely, if the false twisting speed U is constant, twist densities of yarns in the region AB and BC have respectively constant number, (V+U)/W and V/U in stable state, giving the spun yarn a constant twist.

But in case when the false twisting speed U varies by, for example, unstable yarn touch with the eyelet, twist densities of yarns in the region AB and BC vary too, and the spun yarn becomes uneven. For simplicity, the false twisting speed U may be assumed to have sinusoidal irregularity such as:

U=a+b sinwt .........(24)

Putting eq.(24) into eq.(19), we have:

Vol. 20 No. 1 (1974) 17

where

As the second term in the right hand side of the above

equation diminishes in stable state,

Also, from eqs.(21) and (24):

where

Fig. 23 Full spinning process including MS-400

As the third and forth terms reduce to zero in stable state,

Eq.(28) shows the twist density of the yarn in the region

BC and it is equal to that of yarn spun out. Therefore, the

ratio of the amplitude of the periodic irregularity of spun

yarn's twist density to that of false twisting speed b is expressed as:

This value is always less than one. But in case of using the

eyelet with extremely high frictional coefficient and of spin

ning with low twist, the variance of twist density of yarn

shown in eq.(28) may be extremely large. In that case, the

yarn structure becomes uneven, and the yarn strength is extremely weak. To prevent this trouble, the eyelet used

should be selected to suit for raw material and spinning

condition, and it is effective to shorten the distance l1, from

the collecting surface of the drum to the eyelet, and to ex

tend the distance 12 from the eyelet to the take-up rollers,

as shown by eq.(29).

5. Production of Yarn with MS-400

In preceding chapters, drafting and twisting processes

have been considered basically. In this chapter, practical

production using MS-400 will be mentioned briefly.

We, Toray Ind. Inc., started yarn production with MS

400 in our Seta plant in 1968, and have acquired considera

ble experience during these five years.

Fig. 23 shows full spinning process including MS-400;

drawing is two passages and roving process is excluded.

Sliver cans supplied to MS-400 can contain 20 pounds.

Fig. 24 MS-400 during spinning

Fig. 25 Automatic yarn piecing machine


Fig. 26 Auto-Doffer

Fig. 27 Sideview of a spinning room

The drum of MS-400 rotates at 30,000 to 37,000 r.p.m. during spinning. Yarn count being spun is Nm 24 to 68

(see Figs. 24 and 25). To reduce labor, auto-doffers and automatic yarn piecing machines are running (Figs. 26 and 27). The yarn piecing machine pieces a broken yarn by using an already prepared yarn, takes off the slub made on

the piecing part and knotts the end of the yarn being spun out from the drum with the end of the yarn unwound from the cheese by using a knotter. As the result, the spun yarn has no slub made at piecing. Rewinding is scarcely needed, but only partial cheeses produced at machine-breaks or

yarns used for special fabrics are rewound.At the present time, pure acrylic yarns and polyester

yarns and polyester-rayon blended yarns are being spun. Fibers used have 1.5 to 2 denier and these staple lengths are 38,44 and 51mm. The qualities of these spun yarns are shown in Table 3; these yarns are uniform, bulky and soft with little hairiness and knots. Utilizing these properties,

greater parts of these spun yarns are used in knitting.

6. Conclusion

The most characterystic processes of open-end spinning,

particularly in MS-400, compared with ring spinning are fiber separating, recollecting and twisting. These characterize the open-end spun yarn. In this paper, these matters were considered. Specialized points of MS-400 from other open-end spinning machines are to use air stream for fiber separating and to use the special eyelet for stabilizing the

yarn formation in the drum. Therefore, MS-400 can make the yarn with longer staple fibers, and the produced yarn has good parallelism, low twists and high tenacity as ring spun yarns. These results reported in this paper may give some suggestions to the research which will be widely done in future.

Literature cited

[1] M. Tabata, et al.; J. Text. Mach. Soc. Japan, 25, 623 (1972)

[2] M. Tabata, K. Susami; ibid, 21, 737 (1968)[3] M. Tabata, S. Ishikawa; J. Text. Mach. Soc. Japan,

13, 454 (1957)[4] M. Tabata, S. Ishikawa; J. Text. Mach. Soc. Japan,

11, 447 (1958)[5] M. Tabata; ibid, 11, 678 (1958)

Vol. 20 No. 1 (1974) 19

Documents

Drafting and Twisting Processes in Open-end Spinning