Objective measurement of structural parameters of rotor-spun ... - NOPR

Indian Journal of Fibre & Textile Research Vol. 26, December 200 1 , pp. 358-365

Obj ective measurement of structural parameters of rotor-spun yarns Arindam Basua The South India Textile Research Association, Coimbatore 64 1 014, India

Received 4 July 2000; accepted 1 November 2000 An intensive study has been carried out to define the structure of rotor-spun yarns objectively and to find out the con­ tribution of structural parameters to yarn properties. It is observed that the measured twist of rotor-spun yarn is correlated poorly with yarn tenacity, count strength product (CSP) and elongation-at-break. The structural parameters of the yarn are highly correlated with yarn tenacity, extension, CSP and hairiness. The addition of twist enhances the correlation in some cases. Keywords:

Cotton, Count strength product, Elongation-at-break, Hairiness, Ring-spun yarn, Rotor-spun yarn, Wrapper fibre, Yarn tenacity

1 Introduction

Today, rotor yarns account for 30% of the total spun yarn production and about 23% of the equivalent ring spindle installation in the world is on rotor spin­ ning l . Though the Indian textile industry has not re­ sponded adequately to it, the total number of rotors installed in India is around 3 lakh2 . Similarly, despite being a new technology, there is a considerable num­ ber of air-jet spinning positions in India and it is fur­ ther increasing. Presently, there are around 4500 spin­ ning positions in India, which are equivalent to around 90000 ring spindles. The difference between the developments from hand to ring spinning and the post ring spinning de­ velopments is that in the former case the yarns pro­ duced have real uni-directional twist and do not cause any significant change in the yarn structure. The un­ conventional spinning system developments, i.e. post ring spinning, produce yarn whose structure is differ­ ent from that of ring-spun yarn. Rotor-spun yarns are known to have two-part structure, consisting of a central core and an outer sheath containing a random disarray of fibres and wrappers. Researchers have observed that the wrapper fibres influence the yarn tensile properties 3.9 . Gener­ ally, for ring-spun yarn the twist is measured by un­ twist or untwist-retwist method. As ring-spun yarn has uni-directional twist, these methods give a good estimate and the twist values given by the two meth"Phone: 574367-9; Fax: 09 1 -0422-57 1 896; E-mail : silra@ vsnl .com

ods are well related with yarn properties. Holdawa/ o presented a theoretical model for predicting the strength of single yarn. According to this theory, the mean strength of a yarn can be expressed by the fol­ lowing relationship: F = (J/i

-

0.05 1 8d lll ) 2 P, ( Till )

where F is the mean breaking tension (g wt); M, the linear density of the pretensioned yarn (tex); dill, the mean diameter of the single fibre (microns); Till, the effective twist factor [ Till = t ( J/i - 0.05 1 8 d m ) ] ; t, the turns per inch; and p" the function of T,I/' In a later publication, Holdaway and Robinson I I reported that the theoretical model, in spite of the complexity of spun yarn structure, is in good agree­ ment with experimentally obtained values of yarn strength. Being a complicated structure, it is very dif­ ficult to assess the twist of unconventional yarns by conventional method 12. 13 . Also, the structural pa­ rameters, other than twist, contribute towards the physical properties of rotor and air-jet spun yams. In the present work, a study has been carried out to find the relationship between the structural parameters and physical properties of rotor-spun yarns. The in­ tluence of various process parameters and fibre prop­ erties has also been studied. A part of the study has 4 been reported elsewhere l . 2 Materials and Methods

Two cotton mixings were used to produce two sets of yarns. The properties of these cotton mixings are

359

BASU: OBJECTIVE MEASUREMENT OF STRUCTURAL PARAMETERS OF ROTOR-SPUN YARNS

shown in Table 1 . The process parameters used to spin yarns are shown in Table 2. The yarns were con­ ditioned for 24 h at 65 ± 2% RH and 27 ± 2°C and then tested for yarn twist, count strength product (CSP), single yarn strength, elongation-at-break, un­ evenness, imperfections and hairiness. For the testing of yarn twist, the untwist-retwist principle was followed and SITRA microprocessor twist tester was used. Forty (40) readings were taken for each sample. Uster Tensorapid was used to meas­ ure the tensile strength and elongation of the yarns with a gauge length of 50 cm and traverse speed of 5000mlmin. For each sample, 200 readings were taken. From the count and breaking load, the tenacity was calculated. The yarn unevenness, imperfections and hairiness were measured by using Uster UT3. The test speed was maintained at 400 m1min and for each sample, a minimum of 5 km yarn was tested. The sen­ sitivity selected for imperfections was -50%, +50% and +200% for thin places, thick places and neps re­ spectively. For structural analysis of the yarns, a microscope linked to computer with x20 magnification was used. For each category, more than 200 readings per sample were taken. The yarn structures were defined by three parameters: incidence of wrappers per 1 0 cm of yarn (I), average number of wraps per cm of wrapped por­ tion (AN), and average length of wrapped portion (AL). These parameters are schematically shown in Fig. 1 . 3 Results and Discussion 3.1 Twist Deviation

In rotor spinning, the process involved in imparting twist is far from simple. The spun yarn is withdrawn through a passage in the navel and the yarn, therefore, rolls continually on the trumpet shaped mouthpiece of the nozzle. The mouthpiece generates a false twist. The partial rolling of yarn gives rise to false twist between the twisting in point for the fibres and the navel. The yarn in the spinning section, therefore, ex­ hibits more turns of twist than the spun yarn. This false twist effect is dependent upon various factors, such as roughness of the contact surface, rotational speed of the rotor, etc. Moreover, the measurement of twist is carried out by the conventional twist tester (untwist-retwist prin­ ciple) which was basically produced for ring-spun yarn. The rotor-spun yarn contains wrappers on the

Table I -Properties of cotton fibres used Property

Cotton I

Cotton 2

24.0 1 1 .7 4.8 20.8

23. 1 9.96 4. 1 19.8

2.5% span length, mm 50% span length, mm Micronaire Strength, gltex (3 mm gauge length)

Table 2-Process parameters used to produce rotor-spun yarns Cotton

Parameter

Cotton 2

I

Rotor diam., mm

43

43

Rotor speed, rpm Opening roller speed, rpm Twist (TM) Yarn count, Ne

45000/50000/55000 6000/650017000

65000170000175000 6000/650017000

4.0/4.9/5 .5 6s/IOsl l 2s

5.0 I Osl l 2s

AN

=

3

AN

=

2

AL Fig. I-Structural parameters of yarn (AN -Average no. of wraps per unit length, and AL - average length of wrapped portion)

surface, some part of which is caught by the yarn core. Some of them get twisted when untwisted by the twist tester and get untwisted when yarn is retwisted by the twist tester. It is observed that there is a difference between the measured twist (untwist - retwist method) and the machine twist. Also, this deviation is not uniform. The deviation of twist from the machine twist can be expressed by the term percentage twist deviation (PTD) which is calculated by the following relation­ ship: PTD

=

Machine twist - Measurement twist x 100 Machine twist

The experimental results show that the PTD value is affected by the rotor speed. At lower twist multi-

360

INDIAN J. FIBRE TEXT. RES., DECEMBER 200 1

plier (TM), PTD value increases with the increase in rotor speed but at higher TM, the PTD value de­ creases with the increase in rotor speed (Fig. 2). On the other hand, the opening roller speed has no dis­ tinct effect on PTD values within the experimental range of speeds (Fig. 3).

30 ,

25

3.2 Structural Parameters v s Yarn Properties

The yam properties are shown in Tables 3 and 4. The correlations between the structural parameters and the major physical properties have been worked out. The relationship between the structural parameters and the physical properties of the yams are as follows: 6s Ne Cotton 1

c 0

:g .

:;;

I 0

20

15

Vi .�

t-

� 10

CSP=1 O.22 TPI+ 1 820.39 R=0.08

5

Tenacity= 1 3.57-0. 1 2 TPI R=O. l 3

. 45 000 rpm G 50000 r pm 0 5 5000 r pm

0

4·0

4·9

T w i st Mult iplier

Elongation=6.96-O.09 TPI R=0.06

5·5

Fig. 2-Effect of rotor speed on PTD

Hairiness (H)=0.84 TPI-0.273 R=0.52 When structural parameters are considered

CSP=30.38 1-28.78 AN+ 1 30.27 AL+205 1 .39 R=0.80 Tenacity=0.99 1-0.20 AN+0.38 AL+ 1 4.5 1 R=0.78 Elongation=0.69 1-0.36 AN+2.80 AL+3 .80 R=0.87 Hairiness (H)=3 .59-0.08 1+0.34 AN-O. 1 2 AL R=0.8 1 When both TPI and structural parameters are considered

CSP=45 .45 TPI+ 1 6.26 1-30.67 AN+49.38 AL+ 1 798.30 R=0.86 Tenacity=O. l l TPI+O.07 1-0.20 AN+0. 1 9 AL+ 1 3 .90 R=0.78

0 5000 r pm � 6500 r pm � 7000 r pm o

�--�----��

49 5'5 Multi p lie r

Twist

Fig. 3-Effect of opening roller speed on PTD

361

BASU: OBJECTIVE MEASUREMENT OF STRUCTURAL PARAMETERS OF ROTOR-SPUN YARNS

Table 3 -Yam structure-property relationship (Cotton I ) Sample No. 6s Ne 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 lOs Ne

I

2 3 4 5 6 7 8 9 10

II

12 13 14 15 16 17 18 19 20 21 22 23

Yam tenacity g/tex

Elongationat-break %

CSP

TPI

Hairiness

Incidence of wrapsll 0 cm

Av. no. of wraps/cm

Av. length of wraps, cm

1 3 .45 1 2.40 1 2.9 1 13.10 1 2.76 12.81 1 2.27 1 2.52 1 2.69 1 2.24 1 2.22 1 2.58 1 2.33 1 1 .74 1 2.56 12.14 1 2.34 1 2.50 1 1 .86 1 1 .95 1 2.09 1 1 .89 1 1.17 1 1 .9 1 1 1 .89 1 1 .94 1 1 .77

7.04 6.50 6.94 6.82 7.08 6.5 1 7.02 6.60 7. 1 2 6.80 5.80 6.06 6.0 1 5.77 5.84 5.58 6.23 5.5 1 5.04 4.64 5.00 4.98 5.38 5.40 5. 1 5 4.83 4.77

2055 1947 2020 20 19 20 1 3 1950 1 949 1 859 2037 1 979 1 937 2006 1988 1913 1 906 1 925 1 905 1 898 1 897 1 83 1 1 882 1915 1 800 1 856 1 857 1 839 1 923

1 0.52 9.60 1 1 .49 1 1 .06 1 0.61 9.66 1 0.8 1 9.82 1 1 .43 1 1.14 1 0.20 10.54 1 0.69 1 1.19 1 0.24 10.47 1 1.19 1 0.95 1 0.87 10.60 1 0.48 1 0.79 10.53 1 1.14 1 1 . 32 1 1 .30 1 0.65

7.90 7.70 8.03 8.28 7.99 7.24 8.00 7.76 8.40 8.66 8.0 1 8.76 8.52 9.8 1 8.39 8.48 9.76 8.58 9.27 1 0.34 9. 1 4 8.90 9.69 9.37 9.40 1 0.47 9.04

6.70 5.95 6.40 5.60 9.35 8.05 8.75 5.35 4.65 5.35 6.00 6.85 6.80 6.25 5.45 5.75 7.50 5.00 4.75 5.60 5.55 5.60 4.90 5.50 5.05 4.20 4.75

1 3 .70 1 3 .94 14.76 1 5.75 15.38 1 5.98 16. 1 5 1 6. 1 1 1 5 .62 1 6.48 1 5.28 1 6. 1 6 1 5.28 1 6.74 1 6.94 1 8. 1 7 1 8.57 17.15 1 8.87 1 8.97 1 8.39 1 9.57 1 9.77 1 8.48 1 8.93 20.73 1 8.92

1 .23 1 .39 1 .30 1 .47 0.89 1 .01 0.93 1 .55 1 .8 1 1 .57 1 .40 1 .22 1 .23 1 .35 1 .53 1 .44 1.1 1 1 .66 1 .75 1 .49 1 .49 1 .47 1 .7 1 1.51 1 .65 2.00 1 .75

1 1 .66 1 1 .60 1 1 .76 1 2.05 1 2.07 1 2.40 1 1 .89 1 0.74 1 1 .04 1 1 .80 1 1 .67 1 1 .00 1 2.9 1 1 2.94 1 2.04 1 2.65 1 2.30 1 2.63 1 1 .63 1 2.22 1 2 .09 1 2.56 1 2.60

4.56 4.75 5.06 4.41 5.14 4.83 5.01 4.25 4.54 4.75 4.38 5.00 4.80 5.24 6.80 5.83 6. 1 9 6.56 5.96 5.92 6.36 6.09 6.58

1 632 1737 1 722 1 867 1 830 1 8 10 1 744 1 670 1 643 1 805 1 738 1 747 203 1 1 977 1 865 1 942 1 907 1989 1 992 1957 2023 2037 2082

1 2.36 1 2.60 1 2.93 1 3.22 1 4.41 1 4.35 1 3.48 1 3.45 1 1 .68 1 2.70 1 3 .40 . 1 3.76 1 2.56 1 3.72 15.15 1 5.03 1 6.00 1 5.89 1 5.98 1 5 .48 14.52 1 4. 1 7 14.60

6.5 1 6.60 6.54 6.43 6.60 6.70 6.23 6. 1 0 7.06 6.44 6.66 6. 1 8 7.54 7.22 7.67 7.64 7.46 6.36 6.43 6.82 6.69 6.48 6.36

6.55 8.05 6.40 7.50 7.65 8.80 1 0. 1 5 1 1 .00 1 1 .05 8.50 8.80 9.60 1 2.95 1 3.40 1 2.50 1 2.70 1 2.50 1 1 .40 1 1 .40 1 3.60 1 3.55 1 5.55 1 4.00

2 1 .68 2 1 .00 20.79 2 1 .90 2 1 .8 1 23.50 23.07 24. 1 0 23.46 22.59 25. 1 7 26.73 28.62 27.7 1 28.00 29.35 29. 2 1 29.32 30.52 29.83 30.68 30.83 . 3 1 .43

1 .27 1 .03 1 .29 1 . 10 1 .07 0.96 0.80 0.74 0.74 0.97 0.94 0.87 0.63 0.6 1 0.65 0.64 0.66 0.72 0.72 0.59 0.60 0.52 0.58 (Cantel)

INDIAN 1. FIBRE TEXT. RES., DECEMBER 200 1

362

Table 3-Yam structure-property relationship (Cotton I )-Con�d Sample No.

Yam tenacity gltex

Elongation­ at-break %

CSP

TPI

Hairiness

Incidence of wraps! I 0 cm

Av. no. of wraps/cm

Av. length of wraps, cm

24 25

1 1 .52 1 1 .34

5.70 6.2 1

20 1 0 191 1

1 5.22 1 5.37

6.80 6.36

1 4.00 1 3.30

30.76 30.30

0.58 0.61

1 1 .75 1 2.76 1 3.4 1 1 0.58 1 0.37 1 0.59 1 0.80 1 1 .05 1 1 .37 1 1 .89 12.06 1 1 .67

5.95 6.42 6.7 4.89 5.03 4.94 5.58 5.42 5.18 5.58 5.38 5.49

1 908 2 1 64 2240 1 62 1 1 608 1 65 1 1 729 1 770 1 804 1 860 1 87 1 1851

1 1 .88 1 3.53 1 5.22 15.40 1 5.87 1 4.60 1 6.47 1 6.20 1 5.22 1 6.42 1 6.09 1 6.56

5.30 5.26 5.02 5.43 5.46 5.60 5.30 5.26 5.19 5.16 5.16 5.19

1 1 .82 12.10 1 l . l5 9.50 8.95 7.25 1 0. 1 0 7.70 7.45 6.95 5.75 5. 1 5

1 1.14 1 1 .27 1 1 . 82 1 1.10 1 1.10 1 1.10 1 1 .30 1 1 .80 1 1 .40 1 1 .80 1 2.00 1 2. 1 0

0.55 0.59 0.64 0.73 0.83 1 .0 1 0.66 0.98 1 .00 1 .12 1 .40 1 .57

12s Ne 1 2 3 4 5 6 7 8 9 10 II 12

Table 4--Yam structure-property relationship of rotor-spun yams (Cotton 2) Sample No.

Yam tenacity g/tex

Elongation­ at-break %

CSP

Hairiness

TPI

Incidence of wraps/J O cm

Av. no. of wraps/cm

Av. length of wraps, cm

1 2. 1 9 1 0.97 1 1 .66 1 1 .24 1 1 .86 1 1 .27 1 1 .86 1 1 .52 1 0.70

7.49 6.68 5.97 7.09 6.77 5.86 7.35 6.52 5.44

181 1 1 74 1 1 797 1 672 1 765 1738 1 782 1 787 1 709

5. 1 3 5 .27 5.19 5.25 5.20 5.33 5.4 1 5.44 5.31

18.19 1 6.68 1 7. 1 1 1 7.83 1 6.67 1 6.29 1 6. 8 1 1 6.76 1 6.45

25.65 35.97 31.12 33.30 27.70 36.01 33.44 28.22 48.54

33.83 32.04 33.04 33. 1 2 32. 1 7 32.3 1 33.59 32.72 33.25

0.29 0.2 1 0.24 0.2 1 0.27 0.2 1 0.22 0.26 0. 1 5

1 1 .32 9.65 9.22 1 1 .21 1 1 .24 1 1 .4 1 1 1 .46 1 1 .89 1 0.35

7.43 6.55 5.77 7.32 6.85 6. 1 1 7.40 7.00 5.92

1740 1612 1 662 1 706 1 762 1 765 1 750 1818 1749

5.3 1 5.32 5.26 5.46 5.52 5.56 5.55 5.50 5.42

1 5. 1 3 1 5. 9 1 1 5.84 1 6.47 1 5.03 1 4. 1 7 1 5.21 1 5 .47 1 5.22

36.35 32.09 36.23 27. 1 0 28.25 3 1 .35 28. 1 7 24. 1 0 40. 1 1

35.93 32.57 3 1 .00 33. 1 2 32.56 33.08 33.00 34.85 32.36

0. 1 9 0.23 0.20 0.27 0.26 0.22 0.26 0.32 0. 1 8

12s Ne 1 2 3 4 5 6 7 8 9

lOs Ne I 2 3 4 5 6 7 8 9

Elongation=0.30 TPI+0.60 1-0.37 AN+2.27 AL+2. 1 3 R=0.89 Hairiness (H)=0.52 TPI-0.24 1+0.32 AN-l .04 AL+0.7 1 R=0.86 In general, the relationship between the structural parameters and physical properties of rotor-spun

yarns i s better than that between TPI and physical properties. The findings are similar for all other counts and mixings studied (Tables 5 and 6). The relationship between the predicted and actual physical properties is shown in Figs 4-7. Fig. 4 shows the relationship between predicted value using only TPI and actual values. Figs 5-7 show the relationship between predicted value using TPI and other struc­ tural parameters and actual physical properties.

BASU: OBJECTIVE MEASUREMENT OF STRUCTURAL PARAMETERS OF ROTOR-SPUN YARNS

Table 5-Relationship between yam structural parameters and physical properties (Cotton 1 ) Regression equation

Yam property

Correlation coefficient (R)

10s Ne CSP Tenacity, gltex Elongation-at­ break, % Hairiness

7 1 .75 TPI + 859.57 1 6.40 TPI + 45.56 I + 23.46 AN + 477 . 1 6 AL + 1 36.87 0. 1 3 TPI + 1 0. 1 7 0.09 TPI + 0.34 I - 0. 1 3 A N + 3.28 A L + 4.67 0.5 1 TPI - 1 .84 0.38 TPI + 0.32 I + 0.04 AN + 3.02 AL - 6.73 0.05 TPI + 6.09 om TPI + 0. 1 0 I - 0.04 AN - 0.01 AL + 6.46

0.64" 0.86" 0.27 0.45 b 0.80" 0.83" 0. 1 2 0.35

12s Ne CSP Tenacity, g/tex Elongation-at­ break, % Hairiness

2549.38 - 46.42 TPI 98.33 1 - 42.82 TPI + 464.53 AN + 267.27 AL - 3942.83 1 4.003 - 0. 1 6 TPI 0.39 I + 2.36 AN + 1 .0 1 AL - 0.23 TPI - 1 6.54 7.82 - 0. 1 5 TPI 0.33 I + 1 .24 AN + 0.69 AL - 0.06 TPI - 1 1 .20 7.84 + 0. 1 6 TPI 0.01 TPI - 0.0 1 1 - 0.50 AN + 0.24 AL + 1 0.75

0.33 0.92" 0.24 0.9 1 " 0.37b 0.96" 0.68" 0.87'

'Significant at 1 % level of significance bSignificant at 5% level of significance I-Incidence of wrappers per 1 0 cm of yam AN-Av. number of wraps per cm of wrapped portion AL-A v. length of wrapped portion Table 6--Relationship between yam structural parameters and physical properties (Cotton 2) Regression equation

Yam property

Correlation coefficient (R)

lOs Ne CSP Tenacity, gltex Elongation-at­ break, % Hairiness

25 1 7.74 - 5 1 . 1 0 TPI 1 1 0 1 . 1 4 - 64. 14 TPI + 1 5 .02 I + 16. 1 5 AN + 2234.42 AL 1 8.60 - 0.50 TPI 9.30 - 0.52 TPI - 0.08 I + 0.36 AN + 1 . 1 5 AL 0.29 TPI + 2.2 1 0.38 TPI + 0. 1 7 + 0.28 AN - 14.87 AL - 0.73 6.94 - 0. 1 0 TPI 7.52 - 0. 1 1 TPI - om I - om AN + 0.5 1 AL

0.54" 0.88b 0.36 0.9 1 b 0.28 0.89b 0.56" 0.87 b

12s Ne CSP Tenacity, gltex Elongation-at­ break, % Hairiness

8.77 TPI + 1 606.89 776.38 - 50.54 TPI + 2.93 I + 4 1 .93 AN + 1 574.64 0.37 TPI + 5 . 1 6 2.43 - 0.26 TPI - 0.04 + 0.4 1 A N + 5.28 A L 0.73 TPI - 5.80 0.29 TPI - 0. 1 3 I + 0.22 AN - 1 3.26 AL + 1 .98 6.85 + 0.09 TPI 6.99 - 0. 1 8 TPI - 0.03 1 + 0. 1 1 AN - 4.53 AL

"Significant at 1 % level of significance bSignificant at 5% level of significance I-Incidence of wrappers per 10 cm of yam AN-Av. number of wraps per cm of wrapped portion AL-Av. length of wrappe d portion

0. 14 0.9 1 b 0.50 0.96b 0.66 0.80b 0.58" 0.8 1 b

363

INDIAN J. FIBRE TEXT. RES .. DECEMBER 200 1

364 2 000

1�

65 Ne O E Yarn

R

=

6 s N e D E Yarn

0.08

R

Q. Vl U "1J ...

�

·u 0 c

U

0.78

1�

,!!!

�

�

.Q.

'§

... Q.

1 900 L1 800

� __ __ __ �__ __ __ �

__ __ __

1 9 00

2 0 00

Actual C5P

2100

Fig. 4-Relationship between actual and predicted CSP (from twist only)

=

:

_ __ L_ _ __ � _ __ __ __ �__ �

11

12

11

.------,

6s Ne DE Yarn

0.86

R

10

2 000

14

13

Actual Tenacity

Fig. 6-Relationship between actual and predicted tenacity

6s Ne DE Yarn

R

12

11

2100 ,----,

Q. Vl U· "0

=

=

0.86

III III '" C .;:

�

.c:;

Q;

U '6

J: "0 .,

.!2 "0 ...

9

'"

1 900

0:

8 1 800 �---�-----L-----� 1 800 1 900 2 000 2100 Actual C5P

7 1...-____-'-_ _ --' '--_ -'__ _ --' _ 7

F\

'I

Actual Hairiness

1n

11

Fig. 5-Relationship between actual and predicted CSP (all parameters)

Fig. 7-Relationship between actual and predicted hairiness

From the above results, it can be observed that TPI alone does not explain the tensile properties and hairiness of rotor-spun yarns. In ring-spun yarns, the development of tension during tensile strain increases the inter-fibre frictional interaction and more and more fibres are constrained to rupture before the fail­ ure of the yarn. In rotor-spun yarns, such a consoli­ dating effect is available mostly to the fibres com-

prising the core. The wrappers or belts extend on axial straining of the yarn and thereby reinforce the yarn matrix to restrict the fibre slippage. The measures used in this study to quantify the wrappers of the yarn generally cover the wrappers in total. Figs 4-7 show that the correlation of yarn twist (measured by conventional method) and physical properties, such as tensile and hairiness, is poor. The

BASU: OBJECTIVE MEASUREMENT OF STRUCTURAL PARAMETERS OF ROTOR-SPUN YARNS

correlation improves considerably if the structural parameters (1, AN and AL) are included with twist. The incidence of wrappers per unit length of yam (1) and the average length of wrapped zone (AL) repre­ sent the total length of yam covered by wrappers, while the average number of wraps per unit length of wrapped zone (AN) indicates how closely the core fibres are held by the wrappers. The addition of TPI enhances the correlation in some cases. The measured twist generally represents the estimation of twist of the core fibres in yarn which has a structure similar to ring-spun yam and thereby this inclusion improves the accuracy. The incidence of wrapper fibres per unit length and the average length of wrapped zones are negatively related to hairiness, i .e. the more is the length of yam covered by wrappers, the less is the hairiness. In yams, the fibre ends not held by twist protrude out­ side the yam and produce hairs. The wrappers hold those loose fibre ends and disallow them to protrude outside, resulting in decreased hairiness. 4 Conclusions 4.1 The structures of rotor-spun and aIr-Jet spun yams are quite different from that of ring-spun yam. The twist testers designed for ring-spun yams are not very useful for the assessment of twist in rotor and air-jet spun yams. 4.2 The correlation between the measured yam twist (TPI) and the physical properties of the rotor-spun yams, such as esp, tenacity, elongation-at-break and hairiness, is poor. 4.3 The structural parameters of rotor-spun yam, such as incidence of wrappers per unit length of yam, average length of wrapped portion and average num-

365

ber of wraps in each wrapped zone, are highly corre­ lated with the physical properties, viz. esp, tenacity, breaking elongation and hairiness, of the rotor-spun yams. Inclusion of TPI along with the structural pa­ rameters enhances the correlation. 4.4 The measurement of TPI is not enough for pre­ dicting the physical properties of rotor-spun yams. Acknowledgement

The author is thankful to the Ministry of Textiles, Government of India, for sponsoring the project. He is thankful to Ms Indra Doraiswamy, Director, SITRA, for continuous encouragement and to Mr T.V. Rat­ nam, Advisor, SITRA, for valuable guidance in pre­ paring this report. References 1 Salhotra K R

& I shtiaque S M, Rotor Spinning, Its Advan­ tages, Limitations and Prospects in India (NICTAS, Ahmed­

abad), 1 995. 2 Ratnam T V, Doraiswamy I & Rajamanickam R, Working of Spinning Mills, SITRA Research Report, 43 ( 1 0) ( 1 998) 2. 3 Audivert R, ] Text Inst, 79 ( 1 988) 333. 4 Sengupta A K, Dutta B & Radhakrishnaiah P T, Text Res ], 5 1 ( 1 98 1 ) 70. 5 How V L, Cheng K & Wong S, Text Asia, 22 ( I I ) ( 1 99 1 ) 5 1 . 6 Basu A & Oxenham W, Indian Text ], 1 02 ( 1 1 ) ( 1 992) 60. 7 Chasmawala R J, Hansen S M & Jayaraman S, Text Res ], 60 ( 1 990) 6 1 . 8 Xie y, Oxenham W & Grossberg P, ] Text Inst, 77 ( 1 986) 295. 9 Krause H W & Soliman H A, Text Res ], 59 ( 1 989) 546. 1 0 Holdaway H W, ] Text Inst, 56 ( 1 965) TI 2 1 . 1 1 Holdaway H W& Robinson M S , ] Text Inst, 56 ( 1 965) T 1 68. 12 Barella A, Melliand Textilber, 67 ( 1 986) 779. 1 3 Barella A , Manich K M , Castro L & Hunter L, ] Text IIlSt, 76 ( 1 985) 293. 14 Basu A, ] Text Inst, 91 (2000) 1 79.