1. 0 INTRODUCTION

Evolving workable prediction formulae to relate fibre properties with yarn quality has been an interesting field of study by several research workers for more than 5 decades.

SITRA has developed expressions for predicting yarn quality (yarn strength & yarn unevenness) from fibre properties measured by conventional fibre testing instruments as early as 1972. Later on, keeping in view the improvements that have taken place in the technological performance of spinning machinery, the expressions were revised. In the event of introduction of HVI test system for fibre quality evaluation, SITRA has developed expressions for predicting yarn quality from fibre properties measured by HVI Test System (ICC Mode) in the year 19957 and by HVI Test System (HVI Mode) in the year 2002.

With the advent of high speed shuttleless looms, yarn elongation has assumed considerable significance because it is one of the major yarn characteristics affecting loom performance. Studies at SITRA have shown that most of the cotton yarns produced in Indian mills achieve 25 to 50% Uster Statistics level for yarn strength, evenness and imperfections. However, in most of the cases, yarn elongation values meet only Uster 75% statistics.

Many attempts have been made in the past to relate grey yarn elongation with fibre characteristics 12 to 15. However, very little attempt has been made to study the combined influence of fibre properties and process variables used in preparatory and spinning machinery on achievable level of cotton yarn elongation. Similarly, separate studies have been reported on (i) the effect of fibre properties like Mic. value, mean length and its variation on yarn hairiness and (ii) the effect of process variables like spindle speed, twist, traveller weight etc. on yarn hairiness. The combined influence of fibre properties and process variables on yarn hairiness is yet to be established.

To produce yarns of specified elongation & hairiness, knowledge of the combined influence of fibre properties and process variables on the same is essential. Hence, the present study has been undertaken to develop prediction expressions for elongation & hairiness of cotton yarns (spun on modern machinery) from cotton fibre properties measured by HVI Test System / AFIS Instrument and process variables employed.

A high correlation of around 0.935 (Figure 9) was found between actual and predicted values. The error of estimate was found to be around 12%. Considering the high level of natural variation associated with yarn hairiness (CV values of the order of 25%) the prediction accuracy can be considered as good.



Of the 567 yarn samples spun in this study, the difference between actual and predicted values of hairiness lies below 15% in more than 72% of the cases



3.2.3 Hairiness (S3) Values Achieved for Indian and Imported Cottons

Imported cottons exhibit lower hairiness, as compared to their Indian counterparts, by 25 to 50% in different counts.

The difference in yarn hairiness values (S3 value) and the corresponding difference in Cotton Propensity Index for Yarn Hairiness (CPIYH) values are given in Table 7 for some of the Indian and imported cottons.



Table 7 indicates that the difference in yarn hairiness between Indian and imported cottons in a given process situation is largely explained by the respective difference in Cotton Propensity Index for Yarn Hairiness (CPIYH) values.

4.0 CONCLUSIONS

- Two non-linear expressions have been derived, one for predicting cotton yarn elongation and the other for yarn hairiness (S3 value) from fibre properties measured by HVI/AFIS instruments and process variables employed.
- The agreement between actual and predicted values was found to be very close, the correlation co-efficient being 0.952 in the case of elongation and 0.936 in the case of hairiness.






of fibre properties to yarn elongation and hence this factor termed as Cotton Propensity Index for Yarn Elongation (CPIYE) can be taken as a measure of cotton quality to yarn elongation.


contribution of fibre properties to yarn hairiness and hence this factor termed as Cotton Propensity Index for Yarn Hairiness (CPIYH) can be taken as a measure of cotton quality to yarn hairiness.

- Imported cottons exhibit higher elongation by 1.0 to 1.5% (absolute values) and lower hairiness by 20 to 50% as compared to their Indian counterparts in a given process set-up. This difference is, to a larger extent, explained by the respective differences in CPIYE and CPIYH values.

__________________________________________________________________________
FL = 2.5% Span Length of fibre (mm)
FS = Bundle Strength of fibre (g/tex)
FE = Fibre elongation (%)
SFC (W) = Short fibre content by weight in comber sliver


5.0 ACKNOWLEDGEMENT
The authors are thankful to Dr. Arindam Basu, Director, SITRA for his keen interest in this project. Our special thanks are due to Ms. Indra Doraiswamy, Research Advisor, SITRA for her guidance at various stages of the progress of the work. Thanks are also due to Mr. M.P.S. Ravindran, Scientific Officer for his assistance in developing the statistical models.

6.0 REFERENCES

1. K.N. Seshan & T.V. Ratnam
Measures for Assessing Spinning Performance
Proceedings of the 10th Joint Technological Conference held at ATIRA, Ahmedabad during December 1968, p. 2.1 2.27 (Vol. 1)

2. T.V. Ratnam, K.N. Seshan & K. Govindarajulu
Some Factors Affecting Yarn Irregularity
Journal of the Textile Institute, Vol. 65, No. 2, February 1974, p. 61 67

3. T.V. Ratnam, Indra Doraiswamy & P. Chellamani
Fibre Quality Yarn Strength Relationships and Spinning Performance
SITRA Research Report, Vol. 34, No. 6, September 1989

4. P. Chellamani, K. Gnanasekar & R. Gunasekaran
Studies on Fibre-Yarn Relationships and Drafting Force and Its Variability During Mechanical Processing of Man-made Fibres
SITRA Research Report, Vol. 36, No. 5, August 1991

5. Indra Doraiswamy, P. Chellamani & T.V. Ratnam
Fibre Quality-Yarn Strength Relationships During Man-made Fibre Processing
SITRA Research Report, Vol. 37, No. 9, December 1992

6. P. Chellamani, T.V. Ratnam, Indra Doraiswamy & K. Gnanasekar
Factors Affecting Irregularity of Man-made Fibre Yarns
Proceedings of the 32nd Joint Technological Conference held at SITRA,
Coimbatore during June 1991, p. 34 - 44
7. K.P. Chellamani, K. Gnanasekar, M. S. Ravindran & T.V. Ratnam
Fibre Yarn Relationship Using HVI/FMT Measured Fibre Properties
SITRA Research Report, Vol. 41, No. 1, April 1995

8. K.P. Chellamani, V. Thanabal, Arindam Basu & T.V. Ratnam
Fibre-Yarn Relationships Using Newer Fibre Properties with USDA Cottons
for Calibration Measured by HVI Test System
SITRA Research Report, Vol. 47, No. 9, November 2002

9. N.N. Truevtsev, S.A. Grishanov & R.J. Harwood
The Development of Criteria for the Prediction of Yarn Behaviour Under Tension
Journal of Textile Institute, Vol. 88, No. 4, p. 400 414, 1997

10. K. P. Chellamani,
"Breaking Elongation of Indian Yarns - Some Considerations",
Asian Textile Journal, September, 1996, p. 53 54

11. Deepali Plawat, J.M. Grover & A.J. Sonagra
Studies on Elongation of Cotton Fibre at Various Stages of Ring
Spinning and Methods to Improve Yarn Elongation
Proceedings of the 43rd Joint Technological Conference held at NITRA,
New Delhi during March 2002, p. 141 149

12. G. Trommer and H. Grunert
Possibilities of Influencing Yarn Elongation at Break Through
the Spinning Process
Melliand Textilberichte, 78, No. 4, 1997, p. E 41 E 44

13. S.K. Agarwal
A Model to Estimate the Breaking Elongation of High Twist
Ring Spun Cotton Yarns Part I
Textile Research Journal, Vol. 59, No. 11, 1989, p. 691 - 695

14. S.K. Agarwal
A Model to Estimate the Breaking Elongation of High Twist
Ring Spun Cotton Yarns Part II
Textile Research Journal, Vol. 59, No. 12, 1989, p. 717 - 720

15. Atal Vijay Agrawal, M.M. Towari, S.M. Ishtiaque & Anita Nishkam
Impact of Ring Frame Process Variables on Physical Properties
of Compact Spun Yarn
Proceedings of the 44th Joint Technological Conference held at
SITRA, Coimbatore during March 2003, p. 129 136

16. A. Barella
The Hairiness of Yarns
Textile Progress, Vol. 24, No. 3, 1993

17. A. Barella & A.M. Manich
Yarn Hairiness : A Further Update
Textile Progress, Vol. 31, No. 4, 2002


APPENDIX - I
MACHINERY AND PROCESS DDETAILS

 

2.0 METHODS AND MATERIALS
Seven cottons differing widely in fibre properties were spun on a set of modern machinery. The cottons covered in the study include four Indian cottons viz. DCH 32, MCU 5, Brahma & S4 and 3 imported cottons viz. US Pima, Giza 88 & Russian. The major properties of these cottons as measured by HVI Test System (ICC Mode) are given in Table 1:



Each cotton was spun into 3 counts and each count at 3 different twist multipliers. In addition, each count was spun using 3 different comber noils (to get different levels of short fibre content in the comber sliver) and at 3 different spindle speeds. In all, about 567 spinning trials were carried out. The various counts spun and the process variables employed for them are given in Table 2:



Total Number of Trials = 567
(Grand Total)


* Values in paranthesis represent SFC(W) measured using AFIS instrument on comber sliver.

The entire processing was done at SITRA pilot mill and the machinery and process details are given in Appendix I. The yarn samples were tested for yarn elongation (%) using Tensojet and yarn hairiness (S3 Value) using Zweigle Hairiness Tester.

S3 value refers to total number of hairs with length 3 mm & above per 100 m. length of yarn.

3.0 RESULTS AND DISCUSSIONS

3.1 Prediction Expression Connecting Yarn Elongation with
Fibre Properties & Process Variables

3.1.1 Formulation of Cotton Propensity Index for Yarn Elongation (CPIYE)


Yarn elongation is generally influenced by (i) fibre length, (ii) fibre strength, (iii) fibre elongation, (iv) Mic. Value and (v) short fibre content in the feed material. Hence an Index called Cotton Propensity Index for Yarn Elongation has been formed and its effect on yarn elongation (YE) studied in 3 counts, 20s, 60s & 100s.








Where,

FL = 2.5% Span Length of cotton (mm)
FS = Bundle strength (g/tex)
FE = Fibre elongation (%)
Mic. Value = Micronaire Value of cotton (g/Inch)
and
SFC(W) = Short fibre content by weight in comber sliver measured using AFIS instrument

SFC(W) is better correlated with yarn elongation as compared to SFC(n) and hence SFC(W) is incorporated in CPIYE.

Higher the value of CPIYE, higher will be the YE & vice versa.

The ratio of YE to CPIYE is shown in Figures 1 & 2 for 60s and 100s yarns.



a given set of process conditions (barring exceptional values). Hence, it can safely be assumed that

YE varies as the CPIYE

i.e. YE CPIYE

3.1.2 Development of Prediction Expression

Efforts to develop linear expressions connecting YE with CPIYE & process variables have not yielded any encouraging results. Hence, attempts were made to develop non-linear expressions. As a first step, the type of relationship between YE and process variables was explored.

YE was found to vary approximately (i) in proportion with Square of TM as shown in Figures 3 (a) and 3 (b), (ii) with inverse of count as given in Figures 4 (a) and 4 (b) and (iii) with inverse of spindle speed {Figure 5 (a) and 5 (b)} at a given set of fibre & process variables.



The value of the constant K was found to be 630 by value substitution.

Hence, the final expression for yarn elongation is given by



A high correlation of 0.952 was found between actual and predicted values. (Figure 6). The average error of estimate was found to be around 6%.



Of the 567 yarn samples spun in this study, in about 92% of the cases, the difference between actual and predicted values of elongation lie below 5%.

3.1.3 Elongation Values Achieved for Indian & Imported Cottons
Imported cottons generally exhibit higher elongation to the tune of 1.0 to 1.5% (absolute values) as compared to their Indian counterparts for a given process set-up. Highest values of elongation achieved in different counts for Indian and imported cottons considered in this study are given in Table 4:



To understand the reasons for the same, an analysis of yarn elongation and fibre quality was carried out for some of the imported and Indian cottons and the values are given in Table 5.



It is clear from Table 5 that the difference in yarn elongation between imported & Indian cottons in a given process situation is fully explained by the respective difference in Cotton Propensity Index for Yarn Elongation (CPIYE) values.

3.2 Prediction Expression Connecting Yarn Hairiness with
Fibre Properties and Process Variables

3.2.1 Formulation of Cotton Propensity Index for Yarn Hairiness


Fibre fineness, fibre length and short fibre content jointly influence the formation of yarn hairiness to a great extent. Hence, an index called Cotton Propensity Index for Yarn Hairiness (CPIYH) has been formed and its effect on S3 value studied.



Higher the value of CPIYH, higher will be the yarn hairiness and vice versa.