Yarn pacxking density

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PackingDensityofCompactYarns

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1

PACKING DENSITY OF COMPACT YARNS

Demet Yilmaz, Fatma Göktepe, Dana Kremenakova* and Özer Göktepe

Suleyman Demirel University, Textile Engineering Department, Isparta-Turkey * Technical University of Liberec, Textile Faculty, Dept. of Textile Technology, 46117

Liberec, Czech Republic E-mail: [email protected]

Fax: +90 246 211 1180

Abstract

In this work, fibre distribution through the cross-sections of compact yarns and their packing

density values were investigated to provide a better understanding of the internal structures of

compact yarns produced by different compact spinning systems since there is no information

available so far regarding their internal structure. The results of packing density analysis

indicate that compact yarns have nearly 15-30% higher packing density values compare to

that of the conventional ring spun yarns. Also, the packing density values of compact yarns

produced by three different compact yarn spinning systems, namely Rieter K44, Suessen Elite

and Zinser Air-Com-Tex700, reveal that there are no significant differences among these

systems, in terms of yarn packing density values.

Keywords: Yarn Packing Density, Compact Yarn, Fibre Distribution.

1. INTRODUCTION

The mechanical properties of staple yarns depend not only on the physical properties of the

constituent fibres, but also the yarn structure characterized by the arrangement of the

individual fibres in yarn cross-section. Therefore, the arrangement of the individual fibres has

attracted much attention to understand yarn structure and explain resulting yarn properties in a

better way. Many properties, such as yarn strength, extensibility, appearance, compactness as

2

well as uniformity of the structure are related to fibre distribution along yarn cross-section,

and packing density analysis reveals quite valuable information regarding these properties.

In this work, we investigated internal structure of compact yarns obtained from three different

systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700 as these are the

dominant systems in compact spinning field today and a better understanding of internal

structure is still needed for compact yarns.

In most of the researches related to the compact yarns, mainly the properties of compact and

conventional ring spun yarns are compared. These studies reveal that compact yarns have

better properties in many ways as the fibres in compact yarns are almost completely

integrated into yarn body [1, 3, 19]. On the other hand, Başal [2] indicated that migration

occurs at higher levels for a compact yarn in contrary of the expectations and this leads to

better yarn structure and quality. The main advantages of compact yarns are lower yarn

hairiness, higher strength and elongation values depending on their compactness as well

known today, but we have no information about a value indicating their compactness in

comparison to the conventional ring spun yarns. The packing density values would give us

such information and therefore that is the main focus of this work.

In packing density evaluation, there are various approaches used by different researchers. One

of the early approaches was proposed by Schwarz [18] based on mainly open and hexagonal

close packing while an improved approach is based on dividing the yarn cross-section into

zones of equal radius by which fibre distribution is defined by yarn packing fraction [8]. On

the other hand, Doğu [4] indicated fibre packing density is a function of the radial distance

and defined it as the number of fibres per unit area perpendicular to fibre axis. However, it is

3

suggested that fibre packing density measurements should be based on the ratio of the cross-

sectional area of fibres in a given zone to the area of that zone since fibre-number density per

unit cross-sectional area is inapplicable [9]. Driscoll and Postle [5], later on, defined fibre

distribution as the ratio of fibre volume to yarn volume at radius (r) generalizing the definition

of yarn packing fraction suggested by Hearle and also taking into account of the obliquity of

the fibres to improve the earlier approaches further. Neckar also followed the similar

approaches above dividing yarn cross-section into several annular zones having equal widths

or equal areas [13] as similarly Punj et. al. [17] divided the yarn cross-section into five

concentric zones having equal widths to determine packing density of MJS yarns. On the

other hand, more recently Grishanov et al. proposed a different approach called as virtual

locations as fibres are virtually distributed neither in the form of a ring nor a hexagonal

configuration but a combination of these two [7]. This approach enables the simulation of air

gaps between fibres and gives a good representation of fibre location. Morris et. al. [12],

developed a geometric model to predict the possible arrangements of fibres within a

continuous filament yam as the model includes some of the randomness found in real yarns.

Different from above, Petrulis and Petrulyte [16] proposed new approaches for calculating the

packing indices of close-packed yarn. In spite of all these various approaches and different

methods, the one based on dividing yarn cross-section into zones of equal radius or areas is

still used commonly since it can be applied easily and more precise results can be obtained.

2. MATERIAL AND METHOD

2.1. Yarn Production

We produced 100% cotton, combed compact yarns of 29.5 tex, 20 tex and 14.4 tex by using

three different compact yarn spinning systems.

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The yarns of 29.5 tex and 20 tex were produced from Agean cotton of 695 tex rovings while

the yarns of 14.4 tex were produced from Greek cotton of 590.6 tex roving. The fibre

properties are given in Table 1.

Table 1. The fibre properties

Mean values Properties Agean Cotton Greek Cotton Staple Length (mm) 30.1 28.2 Micronaire 4.6 4.2 U.I. 85.6 82.6 Strength (g/tex) 30.6 27.9 Breaking Elongation (%) 7.3 6.9 SFI 6.7 11.6 +b 8.0 7.6 Rd 76.5 74.85 CG 31-2 41-1 SCI 153 128.6

During yarn spinning, the same rovings were fed in the same order to the spindles of each

different compact yarn spinning machine to eliminate the any variation between roving

bobbins. In addition, all yarn samples were produced with the same spinning parameters, e.g.

the same twist multiplier, draft and spindle speed etc.

2.2. Compact Yarn Spinning Systems Used

We used three different systems: Rieter K44, Suessen Elite and Zinser Air-Com-Tex700 as

these systems are the most commonly used compact spinning systems today in short staple

spinning mills. The basic principles of these systems are mainly the same that fibres are first

drafted by 3 over 3 classical drafting systems and then condensed at the end of the drafting

region pneumatically while the design details differ significantly.

2.3. The Evaluation of Yarn Packing Density and Yarn Diameter Values

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The yarn packing density analysis method which we used here is based on the Internal

Standard No. 22-103-01/01 mainly characterised by Neckar’s theory [11]. The packing

density is calculated by the ratio between total areas of the fibres in a given zone to the area of

this zone in a yarn cross section which is shown as:

µ =V/Vc ~ S/Sc (1)

Where µ is yarn packing density, V is fibre volume, Vc is whole volume, S is fibre area and Sc

is whole yarn cross sectional area, respectively.

For packing density analysis, the main requirement is to acquire yarn cross sectional images

to provide input data for calculations. As a result, sample preparation is required. Samples are

prepared according to the IS 46-108-01/01 standard. This standard includes two different

methods to prepare the samples: we used soft section method. By this method, a sample block

is formed and placed in a freezer under 18 °C temperature for 24 hours for hardening and then

clamped onto a microtome. The thickness of a section or a slice is set about 15 µm. A xylene

drop is put on the slices for a better illumination. The cross-sectional images were observed

under a microscope and captured by a camera. During the examinations of the cross sections

under microscope, it is essential to find precise and proper images. Therefore we prepared and

analysed 40 sample blocks for each type. LUCIA software is used for the packing density

analysis.

During the analysis, the gravity centre of the each fibre cross-section is determined and this

step is called as ‘yarn axis definition’. Gravity centres of the fibres are defined by co-

ordinates (Xj,Yj). The centre of yarn (X0,Y0) is estimated by the median of the fibre co-

6

ordinates in the yarn cross section. Also each gravity centre co-ordinates (Xj,Yj) define the

number of the fibres in yarn cross section.

In the following step, the area of fibre cross sections is reconstructed around the gravity centre

of the section. At first we consider that fibres are ideal fibres, so they have circular cross

section (de) and cross section is parallel to yarn axis. The fibre diameter de is calculated from

fibre fineness and mass density as following and then one fibre area is calculated using the

fibre diameter value which is presented by Equations 2 and 3:

πρ/4Tde = (2)

S=4

2edπ

(3)

Where de is fibre diameter (mm), T is fibre fineness (tex) and ρ is fibre mass density (kg/m3),

S is fibre area (mm2).

In the next step, the radial rings are placed with constant width h from the yarn axis centre

(X0,Y0) towards the yarn radius (rk).

According to the helical yarn model, as well known fibres follow a helical path because of the

yarn twist; therefore, fibre cross-sections perpendicular to the yarn axis would have elliptical

shapes. At the beginning, we considered that fibres are ideal fibres and so they have circular

cross section. Therefore, the ideal circular area should be corrected according to yarn twist as

well as the distance between fibre gravity centre and yarn axis. As it is shown in Equation 4,

the radial packing density (µk) in k-th radial ring and i-th yarn cross section is calculated by

the ratio of the total fibre area in related radial rings (Sk) to the area of individual radial rings

(Sck).

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µk=Sk/Sck k=1,2,3…. (4)

Where k is the number of a radial ring, each k number includes the fibre areas of related radial

ring as well as that of the previous one. Therefore, the radial packing density (µk) changes

from yarn centre to yarn radius surface and this change is represented by a histogram (Figure

1). Histogram gives information about the variation in yarn packing density along the yarn

radius and identifies the distribution of fibres in yarn cross-section.

On the last radial ring, a few fibre areas can be located at a considerably higher distance than

that of the most fibres. To get real yarn diameter as much as possible, the term of effective

yarn diameter (Def) is therefore identified as it is obtained from the radial packing density

curves (Figure 1). In those curves, Def values are obtained according to radial packing density

value of 0.15. Yarn diameter found this way was confirmed as the best value representing the

real yarn diameter and found empirically [11].

The effective packing density is calculated by the ratio between the total fibre areas in a circle

of diameter Def and the area of the circle of the effective diameter Def, this calculation is

shown in Equation 5. Therefore, effective packing density represents the overall packing

density of the yarn.

µef = Sef /Scef (5)

Where Sef is the total fibre areas in a circle of diameter Def, Scef is the area of the circle of the

effective diameter Def and µef is the effective packing density.

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3. RESULTS and DISCUSSIONS

3.1. Yarn Appearance

The yarn appearances were analysed by Scanning Electron Microscopy and typical views

were shown in Figure 2 as indicating that more compact yarn structure would be obtained as

the yarns get finer.

3.2. Yarn Packing Density Values

The evaluation of yarn packing density gives information about the radial distribution of the

fibres. Typical views for compact yarn cross-sections are shown in Figures 3-5. As can be

seen by these figures, compact yarns have more compact yarn structure and fibres are not

scattered as much as conventional ring spun yarns leading to more circular cross-sections as

might be well expected.

On the other hand, the packing density values of compact yarns are depicted in Figure 1. It

shows that packing density of all compact yarns is not uniform along the yarn cross section as

the packing density decreases from yarn centre towards the yarn surface for all compact yarns

which we analysed, therefore it changes parabolicaly. This trend is very similar to the

conventional ring and rotor yarns studied earlier [9-10].

The packing densities are very high near yarn centre and reach to its maximum level which is

located around one fifth of the yarn radius. After such a peak value, packing densities start to

decrease towards the yarn surface as such a trend shows that fibre arrangement is very dense

in the yarn centre. The Figure 1 shows that packing density values at the centre is between

0.55 and 0.7. Moreover, the yarn produced by Zinser Air-Com-Tex700 system has even a

value higher than 0.7. As well known, the packing density value is about 0.5-0.6 for

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conventional ring spun (combed) yarn while it is around 0.38-0.55 for carded ring spun yarns

[14]. Similarly, OE-rotor spun yarns have much lower packing density compared to the

conventional ring spun yarns [6, 15]. These packing density values indicate that compact

yarns have higher packing density values as might be well expected and this is almost 15-30%

higher compare to the conventional ring spun yarns. On the other hand, yarns produced on

Zinser Air-Com-Tex700 have the highest packing value of all at the centre. For all packing

density values however, there is no statistically significant differences between the yarns

produced on three different systems.

From Figure 1, also we can see the effect of twist and yarn count on packing density and this

is similar to that of conventional yarns: i.e. as the twist increases, higher packing density

values are obtained.

On the other hand, when we analysed the effective packing density values, we can easily see

that yarns produced by Zinser Air-Com-Tex700 and Suessen Elite have the same trends

(Figure 6): As the yarns get coarser, effective packing density values decrease. This can be

easily explained by increasing fibre numbers in yarn cross section as it is shown by Figure 7.

The differences between the effective packing density values are considerably high for 29.5

and 20 tex yarn counts.

For Rieter K44, on the other hand, the effective packing density shows different trend for 29.5

tex yarn count. This may result from the high variation in yarn properties observed with the

yarns produced by this system. Finally, Zinser Air-Com-Tex700 has the highest effective

packing density values for all yarn counts we examined.

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The change in yarn diameter was shown by Figure 8 indicating that all yarns which we

analysed have similar yarn diameter values for the three different yarn counts produced.

4. CONCLUSIONS

In this work, we aimed to provide a better understanding of compact yarn internal structure.

For this purpose, we investigated fibre distribution in yarn cross-section as well as yarn

packing density values of compact yarns produced on three different compact spinning

systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700, which are

commonly used systems in spinning industry today.

Packing density analysis results show that packing densities of all compact yarns are not

uniform in yarn cross section, but decrease from yarn centre towards the yarn surface as it was

the case for conventional ring spun yarns, too.

The packing density values of compact yarns we investigated are between 0.55 and 0.7 while

this value is known to be between 0.5-0.6 and 0.38-0.55 for combed and carded cotton ring

spun yarns, respectively. This result confirms that compact yarns have much higher packing

density values, therefore they have more compact yarn structure compared to the conventional

ring spun yarns as expected.

On the other hand, there is no significant difference between the packing density values of the

yarns produced on three different systems mentioned above.

We were also able to determine the number of fibres in yarn cross-section. As in the

conventional ring spun yarns, the number of fibres in yarn cross-section and yarn diameter

11

increase as the yarns get coarser. However, significant differences were not observed

regarding fibre numbers in yarn cross-sections of the yarns produced by three compact yarn

spinning systems.

In conclusion, compact yarns have almost 30% higher packing density compare to that of

conventional ring spun yarns as such a compact structure would of course affect yarn

properties significantly.

LITERATURE CITED

1. Artzt, P., The Special Structure of Compact Yarns-Advantages In Downstream

Processing, ITB Yarn And Fabric Forming, No 2, 41-48, (1997).

2. Başal, G.D., The Structure And Properties Of Vortex And Compact Spun Yarns, North

Caroline State University, PhD Thesis, Raleigh, U.S.A. (2003).

3. Cheng, K.P.S., Yu, C., A Study Of Compact Spun Yarns, Textile Research Journal, 73

(4), 345-349 (2003).

4. Doğu, I., The Distribution Of Transverse Pressure In A Twisted Yarn Allowing For The

Fiber Migration And Variation Of Fiber Packing Density, Textile Research Journal, 42

(12), 726-733 (1972).

5. Driscoll, R.H., Postle, R., Modelling The Distribution Of Fibres In A Yarn, Journal of The

Textile Institute, 79 (1), 141-143 (1986).

6. Göktepe, F., The Effect of Yarn Structure of the Deformation of the Yarn Cross-Section,

University of Leeds, PhD Thesis, Leeds, England (1997).

7. Grishanov, S.A., Lomov, S.V., Harwood, R.J., et al., The Mechanical Simulation of the

Geometry of a Two-Component Yarn, Part II: Fibre Distribution in the Yarn Cross-

Section, Journal Of The Textile Institute, Vol. 88, 352-372 (1997).

12

8. Hearle, J.W.S., Grosberg, P., Backer, S., Structural Mechanics of Fibers, Yarns and

Fabrics, Volume I, Wiley Interscience, United States of America, 113, (1969).

9. Hickie, T.S., Chaikin, M., Some Aspects of Worsted-Yarn Structure, Part III: The Fibre-

Packing Density in the Cross-Section of Some Worsted Yarns, 432-437 (1973).

10. Jiang, X.Y., Hu, J.L., Cheng, K.P.S., Postle, R., Determining the Cross-Sectional Packing

Density of Rotor Spun Yarns, Textile Research Journal, Vol. 75, No. 3, 233-239 (2004).

11. Kremenakova, D., Internal Standards: Textile Materials and Design of Textile Products,

Technical University of Liberec, Liberec, Czech Republic, 2004.

12. Morris, P.J., Merkin, J.H., Rennell, R.W., Modelling of Yarn Geometry: Continuous

Filament Yarns, Mathematical Engineering In Industry, 6 (1): 63-78 (1997).

13. Neckar, B., Ishtiaque, S.M. and Svehlova, L., Rotor Yarn Structure by Cross-Sectional

Microtomy, Textile Research Journal, Vol. 79, 625-632 (1988).

14. Neckar, B., Sayed, I., Structural Theory of Fibrous Assemblies and Yarns: Structure of

Fibrous Assemblies, Technical University of Liberec, Liberec, Czech Republic (2003).

15. Novackova, J., Kremenakova, D., Structural Analysis Of Fine Cotton Yarns, Technical

University of Liberec, Liberec, Czech Republic (2003).

16. Petrulis, D., Petrulyte, S., Properties Of Close Packing Of Filaments In Yarn, Fibres &

Textiles In Eastern Europe, 11 (1): 16-20 (2003).

17. Punj, S.K., Debnath, S., Ishtiaque, S.M., Radial Packing Density Of MJS Yarns, Indian

Journal Of Fibre & Textile Research, 23 (4): 229-232 (1998).

18. Schwarz, E., Certain Aspects of Yarn Structure, Textile Research Journal, Volume 21,

No. 3, 125-136 (1951).

19. Stalder, H., Ring Spinning Advance, Textile Asia, 43-46, March (2000).

FIGURES LIST

13

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

0 0,05 0,1 0,15 0,2 0,25Yarn Radius [mm]

Yarn

Pac

king

Den

sity

µk [

-]Air-Com-Tex700-29.5 tex

K44-29.5 tex

Elite-29.5 tex

Air-Com-Tex700-20 tex

K44-20 tex

Elite-20 tex

Air-Com-Tex700-14.4 tex

K44-14.4 tex

Elite-14.4 tex

Figure 1. The change in packing density values along yarn radius

14.4 tex 20 tex 29.5 tex

Figure 2. Typical views of compact yarns (40x)

(A, B, C denote the yarns produced on Suessen Elite, Rieter K44 and

Zinser Air-Com-Tex700, respectively)

14

Suessen Elite Rieter K44 Zinser Air-Com-Tex700

Figure 3. Typical cross-sectional views of compact yarns (29.5 tex) (100x)

Suessen Elite Rieter K44 Zinser Air-Com-Tex700

Figure 4. Typical cross-sectional views of compact yarns (20 tex) (100x)

Suessen Elite Rieter K44 Zinser Air-Com-Tex700

Figure 5. Typical cross-sectional views of compact yarns (14.4 tex) (100x)

15

0,45

0,47

0,49

0,51

0,53

0,55

0,57

0,59

0,61

14.4 tex 20 tex 29.5 tex

Effe

ctiv

e Pa

ckin

g D

ensi

ty µ

ef [-

] Air-Com-Tex700K44Elite

Figure 6. The effective packing density values of compact yarns

100

120

140

160

180

200

220

240

14.4 tex 20 tex 29.5 tex

Num

ber o

f Fib

ers

Air-Com-Tex700K44Elite

Figure 7. The variation of fibre numbers in compact yarn cross sections

16

0,12

0,14

0,16

0,18

0,2

0,22

0,24

14.4 tex 20 tex 29.5 tex

Effe

ctiv

e Ya

rn D

iam

eter

Def

[mm

]

Air-Com-Tex700K44Elite

Figure 8. The variation in effective yarn diameter

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