Indian Journal of Fibre & Textile Research Vol. 27, March 2002, pp. 52-58

Structure of air-jet spun yams produced with various twisting nozzles on PLYfiL 1 000 system

B U Nergis" & B Ozipek

Textile Engineering Department, Istanbul Technical University, Gumussuyu, Istanbul, Turkey

Received 16 August 2000; accepted 4 January 2001

The effects of various twisting nozzle constructions on the structures of Iyocell , cotton and polyester/cotton two-fold yams produced with PL YfiL l Ooo system have been studied. It is observed that the yams basically consist of wrapped and unwrapped lengths, and can be classified into 4 categories on the basis of their structure. The effect of proportion and length of each class on tenacity and extension of both untwisted and twisted yams has also been studied. The construction of the twisting nozzle affects the physical properties of the yams produced and the yam structure that has tight and regular wraps around the core fibres influences the tenacity of the yams positively.

Keywords: Air-jet spinning, Cotton, Lyocell, PL YfiL l Ooo system, Polyester/cotton yam, Twisting nozzle

1 Introduction Air-jet fasciated yarn has a structure varying along

its length. The structure of air-jet spun yarns has been classified by various researchers in a similar way but with minor differences. In a broad sense, the structure of an air-jet yarn is described as a bundle of parallel fibres in the core of the yarn with outside wrap of fibres (Fig. 1 ) .

Yarn characteristics and spinning stability are dependent on a number of factors. Jet design is one of those factors which affects the properties of air-jet spun yarns. The helical angle of the jet orifices, the diameter of twisting chamber, the surface friction of twisting chamber, the outlet shape and the length of jet are the parameters of the jet believed to play an important role in changing the yarn structure and hence influence the yarn properties ' .

As the jet's orifice angle increases the axial suction force increases but the radial component which is responsible for twisting declines. It is apparent that the jet angle is a compromise that results in adequate combination of suction and twisting forces.

The surface inside the twisting chamber could be critical not only because of the possible friction with the rotating yarn but also because of its interaction with the rapidly rotating air. Surface friction appears to have a systematic influence on the yarn strength

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and the gain in yarn strength is also possible by modifying the surface frictional characteristics of the twisting chamber.

Artz et al.2 reported that the critical jet design parameters in imparting twist are the number of jet holes at the periphery, the angle of the holes and the diameter of jet holes. The spinning stability improves with greater number of holes. The twist is imparted more homogenously over the entire periphery . A further option for better utilization of twist energy is the variation in the angle at which air stream impinges upon the yarn core. At the equal yarn strength, a higher delivery rate was obtained with increasing hole angle. This is due to the increase in the twist level. Steeper hole angle also decreases yarn hairiness in relative terms. The high thread tensions, caused by the higher efficiency in imparting twist, also produce controlled tying-in of fibres, including at high delivery speeds. The jet hole diameter was selected between 0.25 mm and 0.40 mm. The twist jet with 0.25 mm hole, because of the thread tensions produced, permits stable spinning performance at 260 mfmin. However, the twist jet with 0.40 mm hole

Fig. 1 - Schemati<." diagram of structure of air-jet spun yarn

NERGIS & OZIPEK : STRUCTURE OF AIR-JET SPUN YARNS 53

shows the production rate of about 80 m1min at the same air consumption.

In the present work, the structure of air-jet spun yarns produced by using various twisting nozzle designs on PL YfiL 1000 system has been studied. The influence of air-jet spun yarn structure on the physical properties of the yams has also been evaluated.

2 Materials and Methods To study the structure of air-jet spun yams, 60 Ne

2-ply (Ne 60/2) yams were produced on PL YfiL 1000 system. In this system, there are two successive nozzles. The first nozzle is �n assembly nozzle which assembles the fibres false twisted by the twisting nozzle, and then aligns and consolidates free edge fibres with the body of the yam. The second one is a twisting nozzle which gives false twist to the bundle. The system produces 2-ply air-jet spun yams. The plied air-jet yams were later twisted in a two-for-one twister and referred to as untwisted before they were given twist in the twister where they were referred to as twisted. The ply twist was applied to the yams in the opposite direction of the wrapper fibres.

The air-jet spun yarns were spun from a 2nd passage draw frame sliver of lyocell (fineness, 1 .3 dtex and length, 39 mm), from a combed 2nd passage drawframe sliver of cotton (micronaire value, 4.4 and 2.5% span length, 29 mm) and, from a 50/50 polyester/cotton blend (polyester: fineness, 0,85 dtex and length, 38 mm; and combed cotton: fineness, 4.0 micronaire and 2.5% span length, 29 mm).

During the production of yams, a delivery speed of 250 m1min, assembly nozzle pressure of 2 .0 bar and twisting nozzle pressure of 2.5 bar were used. The four twisting nozzles used were coded as I, II, m and IV and ranked in the order of I<II<III<IV according to the 'dimension of the twisting chamber into which the air is blown from air-carrying channels and through which rile yarn passes. The air consumption values of twisting nozzles I, II, III and IV at 2.5 bar pressure are 1 1 1 3 , 1 075, 1 0 1 2 and 10 10 NUh respectively. Air consumption of Nozzle I is slightly higher than that of Nozzle II. The air consumption of Nozzles III and IV are almost the same and lower than those of the other nozzles. The variation in air consumption of the nozzles might be due to the differences in the nozzle constructions. The varying dimension of the twisting chamber inside the twisting nozzles may be the cause of the difference in the air consumption of the twisting nozzles.

The yarn properties, such as tenacity, extension, irregularity and hairiness, were evaluated for both untwisted and twisted yams. The yams were tested for their tenacity and extension on Textechno Statimat strength tester using the CRE (constant rate of specimen extension) principle. The tests were performed in accordance with BS 1 932 standard. The irregularity and hairiness were measured on Uster Tester 3 . Although it is not appropriate to test the irregularity and hairiness properties of plied yarns, they were tested for the assembled and ply-twisted air-jet spun yarns. The yarns produced from the PL YfiL machines should not be used for further processing into fabric directly from the spinning machine without twisting and it is almost impossible to test the properties of the single yarns produced by this system due to the lack of sufficient strength before inserting ply twist to them.

The structural studies were carried out on a Zeiss Stereo Microscope connected to a Sony monitor with a Mitsubishi Video copy processor. For the analysis of structural classes, the testing procedure used by Rajamanickam et a/.3 was adapted and a total of eight yarn samples each of the size of one meter were selected at random from each variety and viewed on the monitor in a continuous series of 1 .6 mm sections, the length of the sections being l imited oy the field of the microscope' s length. As the yarns are produced in assembled form in this system, two yams are produced by two nozzles of the same construction in one spinning position. Four samples ( l m each) were selected from each ply produced in the same position so that the variation from different nozzles with identical constructions could also be taken into account. The small portions of the slivers were dyed randomly by pulverizing blue blend dye to take photographs of different fibre types.

The yams were classified into 4 categories on the basis of variations in their structure along the length. The statistical studies on the classification of air-jet yarns were carried out. The photographs of the dyed fibres in the yams were taken using Photomakroskop M 400 (Fa. Wild) which has a top Illumination type of testing method. The photographs of the fibres that formed each structural class were also taken.

The air consumption measurement of the nozzles was carried out with a ROTA rotameter. The measurement of the frequency at which the yams hit the walls of the nozzles was carried out with an HP 3561A Dynamic Signal Analyzer and B&K Charge Amplifier Type 2635.

54 INDIAN J. FIBRE TEXT. RES., MARCH 2002

3 Results and Discussion The microscopic study shows variations in the struc­

ture of all the samples along the length of the yam. These findings were generally in agreement with those reported earlier4-8. The yams basically consist of wrapped and unwrapped lengths. The yams are classi­fied into 4 categories on the basis of their structure: (i) Class A - Parallel fibres, lying in the core of the yam, are wrapped tightly and uniformly with almost regular intervals by the wrapper fibres. The fibres in the core have no twist, (ii) Class B - Parallel fibres in the core are wrapped randomly and loosely by wrapper fibres which are either in singular state or in group. The ap­pearance of the yam is not uniform, (iii) Class C - In this type of yam, the fibres are so entangled that they look like knots, and (iv) Class D - This class is formed by parallel fibres that have no wraps.

The wrapper fibres are neither constantly nor uniformly present at all points of the yam and this

(a)

results in the formation of several structural classes. This indicates that the air vortex produced by the twisting nozzle, which gives false twist to the fibre bundle and forms wrapper fibres, is not constant throughout the yam formation process .

Figs 2 and 3 show the main features of each class and the types of the fibres that form structure of all the classes. .

Table 1 shows that the nozzles with narrower twisting chamber and high air consumption have generally the best tenacity and hairiness values. Whereas no considerable change in irregularity of the yams is observed. In air-jet spinning, the twisting chamber diameter is important as it not only influences the twisting efficiency, but also plays a significant role in the ballooning of the yam I . The contact between the nozzle and the yam is critical because of the possible friction between the yam and the walls of the twisting chamber, and this contact

(b)

(d) Fig. 2 - Appearance of structure of different classes [(a) class A, (b) Class B, (c) Class C, and (d) Class DJ

NERGIS & OZIPEK : STRUCTURE OF AIR-JET SPUN YARNS 55

b , '.

Fig. 3 - Appearance of fibres forming structure of different classes [(a) Class A, (b) Class B, (c) Class C, (d) Class DJ

controls the rotating yam. The frequencies at which the yams contact the walls of the twisting chambers of the twisting nozzles were Ipeasured and are shown in Table 2. These measurements were also done at a known pressure combination (assembly nozzle pressure, 2.0 bar and twisting nozzle pressure, 2.5 bar).

Table 2 shows that the frequency values for Nozzle I are the highest among all nozzle types for all the samples. The more the yam contacts the walls of the twisting chamber, the better is the control of it and so the results obtained. Nozzle I also has the highest air consumption and this might have influenced the frequency of the yams. On the other hand, the lyocell yams, whose tenacity is higher than those of the other yams, give the lowest frequency readings whereas cotton yams give the highest. This shows that the interaction between the yam and the nozzle is important for better yam properties, and nozzle type is

not the only factor which influences the quality of the yam. The properties of the materials used also play a decisive role on the quality.

Table 1 shows that the average length and proportion of the classes vary between 1 2 samples that represent a range of nozzle and blend types. The microscopic study reveals that the structural classes distribute randomly along the length of the yam and there is no preferred occurrence of these classes.

The average lengths for Classes A, B and 0 increase with their respective class proportions, showing the correlation coefficients of 0.8, 0.5 and 0.7 respectively. There is no correlation between the proportion and average length of Class C. Table 1 also reveals that the percentage of Class A structure in lyocell yams is higher than those in polyester/cotton and cotton yams, whereas percentage of Class 0 structure is the lowest in lyocell yams. The percentage of Class B structure is similar in all the samples. The proportion and length of Class C structure are lower than those of other structural classes. The percentage of Class B is always higher than that of Class A. This indicates that the edge fibres wrap the core fibres at various angles and in an irregular manner more frequently due to the irregular air vortex in the twisting nozzle.

It is also observed that the average length of Class A structure is the highest and that of Class 0 structure is the lowest for lyocell yams. There seems to be only minor variation in the lengths of Class B and Class C structures of different yams. According to these results, it can be inferred that the quantity and length

. of various structural classes also change according to the fibre types used for the production of the yams.

The proportion and length of each structural class are related to tenacity, extension and hairiness properties of untwisted and twisted yams. The correlation coefficients for different relationships are given in Tables 3 and 4. The proportion and length of each structural class are not related to irregularity as this property shows no considerable variation.

Tables 3 and 4 show that there is a positive correlation between the tenacity and both proportion and average length of Class A structure for untwisted and twisted yams. It is also evident that the correlation for twisted yams is stronger than that for untwisted yams. In air-jet yams, it is the wrapper fibres that give strength to yam. When air-jet spun yams are ply twisted in the direction opposite to their wrapping twist, the wrapper fibres tend to untwist or loosen to some extent and even some may start to

Yam

Class A

Lyoce\l

Nozzle I 38 Nozzle II 36 Nozzle ll 39 Nozzle IV 30

Polyester:Cotton (50:50) Nozzle I 26 Nozzle II 29 Nozzle m 3 1 Nozzle IV 33

Cotton

Nozzle I 25

Nozzle II 26 Nozzle m 24 Nozzle IV 28

Table 1 - Proportion and length of the structural Classes and the properties of Ne (:/)/2 yams before and after twisting [Pressure, 2.0-2.5 bar]

Yam properties

Proportion, % Average length, nun Before twisting After twisting

Class Class Class Class Class Class Class Tenacity Extension Hairiness Irregularity Tenacity Extension Hairiness B C D A B C D cN/tex % (H) index cN/tex % (H)

43 4 15 4.4 3.9 1 .9 3.3 12.3 5.5 8.0 1 .7 23.6 8.6 7.2 37 5 22 3.4 3.4 1 .7 2.8 12.9 5.6 8.5 1 .9 21 .8 8.2 7.7 40 5 17 3.5 3 . 1 2.2 3.0 12.3 5.3 8.8 1 .7 22.5 8.4 7.7 36 4 30 3. 1 3.5 1 .7 3.5 12.6 5.6 9.0 1 .8 22.3 8.2 8.1

40 2 32 3.2 3.2 2.0 3.8 6.9 4.3 7.3 1 .7 20.2 8.1 6.3 35 2 34 3.3 3.3 2.6 4.3 5.3 3.3 7.9 1 .7 19.5 8.0 6.7 42 4 23 3.3 3.5 1 .6 3.5 5.4 3.3 8.0 1 .7 19.2 8.1 .7.7 . 35 3 1 3.4 3 . 1 1 .6 4.6 4.8 2.9 8. 1 1 .7 19.5 8 . 1 7.5

35 8 33 2.9 3.1 1 .9 3.6 7.8 4.9 7.0 1 .4 14.8 5.3 7.2 40 2 32 3.3 2.8 2.3 3.7 6.6 4. 1 7.4 1 .4 1 3.9 5.2 7.4 42 5 29 2.6 3.7 1 .7 3.7 6.6 3.9 7.6 1 .4 14.4 5.4 7.7 42 29 2.9 3.6 1 .6 3.4 6.2 3.9 7.8 1 .3 1 3.6 5.4 7.4

Irregularity index

1 .7 1.7 1 .7 1 .8

1.4 1 .3 1 .3 1 .3

1 .4 1 .3 1 .3 1 .3

VI 0'1

Z 0 ;; Z !-' :!l tl:l :;Q tTl o-l tTl :><: :-l :;Q tTl � � :> :;Q () ::c N 8 N

NERGIS & OZIPEK : STRUCTURE OF AIR-JET SPUN YARNS 57

Table 2 - Frequency at which the yarns contact the walls of the twisting chamber

Yarn Frequency. Hz

Nozzle I Nozzle II Nozzle III Nozzle IV

Lyocell

Polyester/Cotton

Cotton

7550

841 0

8850

7400

8 100

8650

7350

7850

8400

7300

7700

8200

Table 3 - Relationship between untwisted and twisted yarn properties (Y)and proportions (X) of the classes

Y

Tenacity

Tenacity

Tenacity

Tenacity

Extension

Extension

Extension

Extension

Hairiness

Hairiness

Hairiness

Hairiness

Tenacity

Tenacity

Tenacity

Tenacity

Extension

Extension

Extension

Extension

Hairiness

Hairiness

Hairiness

Hairiness

x

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Equation

Untwisted

Y=-3.8+0.4X

Y=5.7+0.7X

Y=1 7-O.3X

Y=1 .9+0.08X

Y=3.4+0.3X

Y=6.5-O.07 X

Y=5.4+0. IX

Y=8.8-O.02X

Class D Y=9.2-O.05X

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Twisted

Y=0.5+0.6X

Y=28-O.4X

Y=I +0.2X

Y=9.6-0. IX

Y=7.5-O. IX

Y=IO.2-O . IX

Y=6.5+0.02X

Y=7. 1 +0. IX

Y=8. I-O.3X

Correlation coefficient (R)

0.6

o 0.5

-0.6

0.6

o 0.6

-0.5

0.7

-0. 1

o -0.5

0.8

o o

-0.6

0.7

-0. 1

-0. 1

-0.5

0.3

o 0.3

-0.3

have twist in the opposite direction. The two strands are also wrapped around each other to provide mutual support. thus giving strength to the yarns. After being ply twisted, the presence of any wrapper fibre in the structure of the yarn may contribute towards reinforcing the structure, and this might be the reason for the better correlation obtained for twisted yarns.

Although Iyocell yarns show a different behaviour, it can be said for the other yarns that an increase in the proportion of Class A structure Increases the

Table 4 - Relationship between untwisted and twisted yarn properties ( Y) and average length (2) of the classes

Y

Tenacity

Tenacity

Tenacity

Tenacity

Extension

Extension

Extension

Extension

Hairiness

Hairiness

Hairiness

Hairiness

Tenacity

Tenacity

Tenacity

Tenacity

Extension

Extension

Extension

Extension

Hairiness

Hairiness

Hairiness

Hairiness

Z

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Class A Class B

Class C

Class D

Class A

Class B

Class C

Class D

Class A

Class B

Class C

Class D

Equation

Untwisted

Y=-2.2+3.2Z

Y=-O.7+2.7Z

Y=25.9-4.9Z

Y=2. 1+0.7Z

Y=2.3+0.6Z

Y=9.8-1 .5Z

Y=-O.8+6Z

Y=6.5+0.4Z

Y=8.5-O.3Z

Y=9.5-O.4Z

Twisted

Y=-O.8+6Z

Y=9.6+2.74Z

Y=25.3-1 .8Z

Y=O.4+2 . 1Z

Y=4.4+0 9Z

Y=7.8-O. 1Z

Y=6.4+0.3Z

Y=8.9-O.8Z

Y=8.8-O.4Z

Correlation Coefficient (R)

0.4

0.3

o -0.8

0.3

0.2

o -0.8

0.3

0.2

-0.2

-0.4

0.7

0.2

o -0.2

0.6

0.2

o o

-0. 1

0.2

-0.2

-0.4

hairiness of untwisted yarns. A wrapper fibre might be wrapping the yarn core across its entire length but its ends might not be embedded in the core. These ends might protrude from the body of the yarn and cause hairiness. The number of such ends may increase with the increase in proportion of Class A structure.

Tables 3 and 4 show that the Class B and Class C structures hardly correlate with the tenacity and hairiness values of both untwisted and twisted yarns, except that the proportion of Class C structure seems to be augmenting the tenacity of untwisted yarns. This may be due to the presence of non-uniformly wrapping or entangled fibres in these classes that may not always be capable of exerting uniform pressure on the core fibres. Some of these fibres may be held together tightly, thus increasing the tenacity . While others may be loosely wrapped, playing no significant or a negative role on the tenacity. These two effects

58 INDIAN J. FIBRE TEXT. RES., MARCH 2002

might have cancelled each other, resulting in no correlation between Class B and Class C structures and tenacity of untwisted and twisted yams. There .is also very weak or no correlation between these classes' structures and hairiness of the yams. This is somewhat surprising as Class C structure is expected to increase the hairiness of yams. This may be due to the smaller percentage and shorter length of this class.

The length and proportion of Class 0 relate inversely to the untwisted yarn tenacity and extension. This is an expected result as there are no wrapper fibres in Class 0 structures that hold the core fibres together and prevent the slippage. However, the proportion of this class also correlates negatively with the tenacity values of twisted yams, where there is no relationship between length of Class 0 and tenacity of twisted yams. This behaviour of Class 0 is far from the expected behaviour of parallel fibres in a ring­spun yarn. This may be due to the shorter lengths of Class D structures in comparison to the fibre lengths. An increase in both proportion and length of Class D decreases the hairiness of untwisted and twisted yams.

4 Conclusions It is inferred that the dimension of the twisting

chamber in the twisting nozzle is important in producing air-jet spun yams with better physical

properties. The narrower the dimension of the twisting chamber, the better the results obtained. Air­jet spun yarn structure produced by PL YfiL WOO system is classified into 4 categories (Classes A,B,C and D) . . The Class A structure, which has parallel fibres in the core of the yarn wrapped tightly and uniformly with almost regular intervals by the wrapper fibres, influences the tenacity of both untwisted and twisted yams positively.

Acknowledgement The authors are thankful to the MIs Spindelfabrik

SUESSEN for providing us the opportunity to work with PL YfiL 1000 system and various twisting nozzle designs.

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