Indian Journal of Fibre & Textile Research Vol. 29, September 2004, pp. 3 1 3-3 17

Study on drafting force of roving: Part IV - Correlation between drafting force, .

roving strength and yam quality

A Das·, S M Ishtiaque & Rajesh Kumar

Depa·rtment of Textile Technology, Indian Institute of Technology, New Delhi 1 1 0 0 16, India

Received J May 2003; accepted 7 July 2003

The effect of fibre-to-fibre friction, roving hank and roving twist multiplier, which directly affect· the roving drafting force, on the properties of yarn has been studied. A fairly good correlation (R2

= 0.900 1) has been observed between roving strength and drafting force. The yarn tenacity is found to be better correlated with fibre and roving parameters as compared to yarn breaking elongation. Yarn irregularity and total imperfections have very good correlation with the fibre and roving parameters.

Keywords: Cotton, Drafting force, Fibre friction, Roving strength, Yarn irregularity

IPC Code: Int. CI.7 D02G 3/00, DOI H 1 3/26, G01N 33/36

1 Introduction In the earlier papers l .3, the effects of various

process and material related parameters on the drafting force and its variability have been reported. Drafting force of sliver and roving is dependent both on fibre composition and machine / process variables used to draft the material during spinning. These machine or process variables include draft, drafting speed and roller setting. The drafting force is determined by inter-fibre friction, fibre crimps4, fibre parallelization, incidence and direction of hooks5, and twist of roving. Drafting force of roving has been found to affect spinning efficiency. The variability in drafting force appears to be more correlated with spinnability and yam quality than absolute value of drafting force. As a matter of fact, the drafting force can be used as a tool to evaluate the spinning performance or an optimum drafting force is required for a smooth spinning operation.

Apparently, it seems that the drafting force of slivers or rovings can be obtained by measuring the breaking strength. But measurement of breaking strength with the help of a tensile tester does not simulate the actual process of drafting and thus the results may create confusion. The instrument for

"To whom all the correspondence should be addressed. Phone: 2659 1413; Fax: +9 1 - 1 1 -2685 1 103; E-mail: apurba_das@hotmail.com / apurba@textile.i itd.ernet.in

measuring the drafting force should be able to simulate the actual dynamic condition of drafting.

The process of attenuation of linear fibre assemblies by roller drafting causes a tension to be generated in the fibres in the drafting zone. The force necessary to give rise to the average tension in the moving fibre mass in the drafting zone is referred to as the drafting force. The way a fibre behaves during drafting depends very much on the variation in cohesive forces acting on it in the drafting zone. Since the drafting waves are caused by the irregular movement of fibres, once it is known that how a fibre moves in the drafting zone during drafting, it may be easier to comprehend the nature and formation of drafting waves. The interaction between fibre properties and fibre behaviour during drafting becomes increasingly important, as the modifications of fibre properties become prevalent. For with every fibre or fibre modification, question arises as to how the new fibre will draft or what process changes must be made to improve its performance during drafting. The knowledge of the resistance of a given fibre to the drafting of its assembly should provide a sound basis for answering such questions.

The interaction between single fibre and fibre assembly properties, keeping the drafting condition constant, causes variation in cohesive forces acting on floating fibres, resulting in irregular movement of fibres in the drafting zone. This irregular movement,

3 14 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004

in turn, causes variation in mass per unit length of the drafted material. The significance of drafting force during staple fibre spinning cannot be undermined. It is, however, the variation in drafting force which significantly affects the yarn quality. This leads to a difficult situation as the drafting force is a highly sensitive factor which depends on various process parameters and more significantly the single fibre and fibre assembly characteristics. Thus, the relative measurement of the effect of different factors on drafting force assumes huge significance.

The main objective of the present study is to investigate the combined effect of single fibre and fibre assembly parameters (fibre-to-fibre friction, roving hank and roving twist multiplier), which directly affect the drafting force, on the properties of yarn. The correlation between drafting force and roving breaking strength has also been established.

2 Materials and Methods

2.1 Materials

Medium grade cotton (1-34) was dyed in three shades with natural dyes to get different levels of frictional coefficients. The reason for using natural

Table I-Actual values of material variables corresponding to coded levels

Variable

Fibre friction (Xl) Roving hank (X2) Roving twist multiplier (X3)

Coded level - 1 0 + 1

0.3 0.4 0.5 0.9 1 . 1 1 .3 0.9 1 . 1 1 . 3

dyes is that they are mainly surface deposition type, resulting in change in frictional properties of fibre and also the tensile properties of cotton are least affected by these dyes. The static frictional coefficients of the fibres were measured on a friction tester6• The selected samples were grey, linen colour dyed and royal colour dyed cottons with static frictional coefficients of 0.3, 0.4 and 0.5 respectively. The properties of cotton are given below:

2.5% span length 50% span length Fibre fineness Bundle strength

2.2 Experimental Design

: 26.8 mm : 1 3 .3 mm : 3 .9 Ilglinch : 2 1 .63 g/tex

As reported in earlier studies 1 .2, a three-variable factorial design proposed by Box & Behnken has been used to investigate the influence of material variables. The actual values of three variables (fibre­to-fibre friction, roving hank and roving twist multiplier) corresponding to coded levels are given in Table 1 and the fifteen roving samples with different combinations prepared, as per the experimental design, are shown in Table 2.

2.3 Roving and Yarn Preparation

The grey and dyed cotton fibres were processed in blowroom, card, draw frame (two passages), speed frame and ring frame. The finisher draw frame slivers with three different friction levels were processed in speed frame to produce fifteen different combinations of rovings (Table 2). All the fifteen types of roving

Table 2 - Roving drafting force, strength of roving and quality of yarn for different material variables

SI. Variable Roving gualit� Yarn gualit� No.

XI X2 X3 Drafting Roving Tenacity Breaking Irregularity Total imperfec-force, W strength, g g/tex elongation, % U% tions 11000 m

1 0.3 0.9 1 . 1 0.92 1 59.3 9.92 5.30 9.57 479 2 0.5 0.9 1 . 1 3.760 1 1 1 .7 1 2. 10 5.69 1 2.23 9 12 3 0.3 1 .3 1 . 1 0.746 45.3 9.86 5.32 9.34 462 4 0.5 1 .3 1 . 1 2.987 88.67 1 1 . 1 3 5.7 1 1 1 .98 870 5 0.3 1 . 1 0.9 0.5 1 0 33.0 9.84 5.70 1 0.0 1 538 6 0.5 1 . 1 0.9 1 .024 67.3 9.27 5.05 1 2.28 952 7 0.3 1 . 1 1 .3 1 .289 7 1 .3 1 1 .60 6.07 1 0. 1 2 551 8 0.5 1 . 1 1 .3 3.575 103.0 12.42 4.9 1 1 2.37 948 9 0.4 0.9 0.9 0.840 47.7 8.25 4.88 1 1 .05 757 1 0 0.4 1 .3 0.9 0.690 38.0 8.82 4.91 1 0.75 736 1 1 0.4 0.9 1 .3 3.680 1 07.0 1 0.87 5.99 1 1 .26 796 1 2 0.4 1 .3 1 .3 3.432 98.3 1 1 .37 5.77 10.9 1 754 1 3 0.4 1 . 1 1 . 1 1 .019 64.3 1 1 .56 5.02 1 0.99 753 14 0.4 1 . 1 1 . 1 1 .020 65.3 1 1 .83 5.30 1 1 .06 743 1 5 0.4 1 . 1 1 . 1 1 .0 1 9 65.0 1 1 .63 5.33 1 0.95 750

DAS et at.: STUDY ON DRAFfING FORCE OF ROVING: PART IV 3 15

bobbins were then processed in ring frame to produce 20s Ne yarns with 3 .8 TM.

2.4 Testing of Rovings and Yarns

The drafting force of roving was measured with the help of draftometer7 . The breaking strength of rovings was measured by SOL Universal tensile tester with 100 mm gauge length and 1 00 mm/min traverse speed of the jaw. Twenty readings per sample were used to obtain the average breaking strength. The irregularity and imperfections of all the yarns were tested on Uster Tester-3 at 400 m/min for 1 min. Yarn tenacity and breaking elongation were measured on SOL Universal tensile tester using 500 mm test length and 100 mm/min extension rate. Average of 20 readings was taken for each sample. The drafting force and breaking strength of rovings and different yarn properties corresponding to these rovings are given in Table 2 .

3 Results and Discussion

3.1 Drafting Force and Strength of Roving

Table 2 shows the values of drafting force and strength of rovings for different combinations of fibre friction and roving parameters. It is clear from Table 2 and Fig. 1 that the roving strength is very well correlated with the drafting force (R2 = 0.9001) . This shows that the roving with higher breaking strength requires higher drafting force. Both the roving strength and the drafting force depend on the fibre-to­fibre friction, roving twist and roving hank. Low roving strength will result in stretching of roving at ring frame creel because of very low drafting force. On the other hand, a very high roving strength will again become problematic because of improper draftablity at ring frame and very high drafting force will be required which ultimately deteriorates the yarn quality. Hence, a roving should have optimum

strength for better drafting at the back zone of the ring frame. B esides these factors, the roving strength also varies in different position along the length because of the variation in roving twist at the speed frame and due to the irregularity of roving. It has already been reported3 that the variation in irregularity of roving does not affect the average drafting force significantly. Therefore, it can be stated that the roving strength may be an indication of drafting force to some extent but sometimes it can be misleading. This is due to the fact that the strength is measured in static mode and the drafting force is a dynamic phenomenon. The present system of measurement of drafting force simulates the actual roller drafting system.

3.2 Effect on Yarn Quality Parameters

The contour plots (Figs 2 - 4) and the response surface equations (Table 3) show the combined effect of fibre and roving parameters (fibre-to-fibre friction, roving hank and roving twist multiplier) on the properties of yarn.

120

100

c:n � 80 c: ., � 60 c:n c: � '" � 40 CD

20

o

y =18.813x + 37.759 R2 = 0.9001

o o

0.5 1.5 2 2.5 Drafting force. W

3 . 3.5

o

4

Fig. l-Relationship between drafting force and strength of roving

Table 3-Response surface equations for various yarn characteristics

Yarn characteristic

Tenacity, g/tex

Elongation. %

Irregularity, U%

Total imperfections

Response surface equation

1 1 .68+0.46 I X/+ 1 .26X,r0.938X/-0.9 1 lX/

5.39+0.274X,i

1 1 .00+ 1 .23XrO. 1 43XrO.209X/+ 0.20 I X,?

748.7+206.5Xr 1 5.25X2+8.25X,r40.7 1 X/-27.2 1 X/+39.29X/-6.25X/Xr5.25X2Xr4.25X3X/

Coefficient of determination (R2)

0.888

0.265

0.993

0.998

3 1 6 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004

The response surface equation for yarn tenacity (Table 3) shows that the yarn tenacity is reasonably well correlated with all the chosen single fibre and fibre assembly parameters. Fig. 2 shows the increasing trend of yarn tenacity with the increase i n fibre friction and roving twist multiplier. Roving hank shows relatively less influence, but at mid coded value ( 1 . 1 ) a marginal increase in the yarn tenacity is observed. In case of coarser roving with constant roving twist multiplier, the actual twist per unit length

o

-0.5

-0.5

...

....

....

...... . .........

........ . ...... .

.....

.... ....... .. .............

" '''''' ....... .

.. ....

.....

" ,

...... -.. -........ ' .

,/,., ..

(

...... ..........

..........

: :� , . ,�� ...........

...... " -.-..... ................

.................. . .. -1 .0 L-_---L-=_-I....�_....I..-�"---' -1 .0 -0.5 0 0.5 1 .0

Fibre friction

Fig. 2--Effect of fibre friction and roving hank on yam tenacity [roving TM: (a) 0.9, (b) 1 . 1 and (c) 1 .3]

will be less. Hence, during drafting the fibre tension will be very less and proper fibre straightening and parallelisation will not take place. On the other hand, at higher value of roving hank (finer rovings) with same roving twist multiplier, the roving twist will be very high and cause i mproper drafting because of excessive drafting force; hence i t may cause buckling of fibres in the drafting zone. Thus, the yarn tenacity decreases when the roving hank becomes either too coarse or too fine. The increase in yarn tenacity with the i ncrease in fibre friction is due to the increase in inter-fibre cohesion. The increase in roving TM causes increase in drafting force in the break draft zone, resulting i n proper removal of fibre hooks and more straightening of fibres, which, in turn, results in increase in yarn tenacity.

The response surface equation for yarn breaking elongation (Table 3) shows that the yarn elongation is correlated only with the roving TM and the correlation is very poor.

The response surface equation for yarn irregularity (Table 3) shows that it has very good correlation with the chosen s ingle fibre and roving parameters which

1 .0 r----.,....-�-.,..,..-..,.......-""T"'-.,.....,.._.

0 / 0.5 f /

I 0 , ,

-0.5 � \ c:: \ ' � ,

..c -1 .0 ........ ---"-_J..--'---4-.t-:._�"'----I.---'-' CI c:

& I

0.5 i i

-0.5

-1 :.� .0 -0.5

i i

I I

I 1 I

\ \

0 Fibre friction

I i (

I

2

0.5 1 .0

hg. 3--Effect of fibre friction and roving hank on yam irregularity [roving TM: (a) 0.9 or 1 .3 and (b) 1 . 1 ]

DAS et al.: STUDY ON DRAFfING FORCE OF ROVING: PART IV 3 17

1 .0

0.5

0

-0.5

-1 .0 1 .0

0.5 � c: tll J::.

: i ! ! f§1

i j/ / / i

'(a)

Cl 0 c: .:; 0 0:: -0.5

-1 .0 '---'--'-'-"--'---'-''--'-'--'-.:.........!.-..i..L....L--'-.:...:.l 1 .0 ,-----r;-,,,-;-.,-,..--,--,. ....... ---,-....-71

0.5

o

-0.5

\ (c) -1 .0 '--'--'-'-'-.........,-->-........... '-LJ.---'---'-........ ....I..-___. .........

-1 .0 -0.5 0 0.5 1 .0 Fibre friction

Fig. 4-Effect of fibre friction and roving hank on total imperfections in yam [roving TM: (a) 0.9, (b) 1 . 1 and (c) 1 .3]

directly affect the drafting force. It is evident from Figs 3a and 3b that the fibre friction significantly affects the yam irregularity as compared to roving TM and roving hank. The increasing trend of yam irregularity with the increase in fibre friction may be due to the improper drafting of rovings. The roving prepared from fibres with higher fibre-to-fibre friction requires higher drafting force and thus the draftability of such roving becomes very poor. Figs 3a and 3b a1so show that for a constant fibre friction and roving TM, the increase or decrease in roving hank, within

the present experimental range, results in marginal improvement in yarn irregularity but the improvement is found to be insignificant. Too high or too low roving TM results in increase in yam irregularity. When roving TM is very low, the yam unevenness is high because the low twist in the roving may results in undue stretching in the creels. This causes increase in yarn unevenness. In case of higher roving TM, the drafting force will be high which results in improper drafting, thereby increasing the yam irregularity.

Table 3 also shows that the total imperfections have very good correlation with the fibre and roving parameters (R2 = 0.998). It can be observed from Fig. 4 that the fibre-to-fibre friction, roving hank and roving TM have the similar effect on total imperfections of yam as that of yam irregularity.

4 Conclusions 4.1 Roving strength is very well correlated with the drafting force (R2= 0.9001 ) and hence the roving strength may be an indication of drafting force.

4.2 Yam tenacity is well correlated with the a1l chosen single fibre and fibre assembly parameters. With the increase in fibre-to-fibre friction and roving TM the yam tenacity increases.

4.3 Yarn breaking elongation is poorly correlated with material variables (R2 = 0.265).

4.4 Yarn irregularity and total imperfections increase with the increase in fibre-to-fibre friction. Also, too high or too low roving TM results in increase in yam irregularity and yarn imperfections.

References 1 Das A, Ishtiaque S M & Kumar Rajesh, Indian J Fibre Text

Res, 29 (2004)1 73. 2 Das A, Ishtiaque S M & Kumar Rajesh, Indian J Fibre Text

Res, 29 (2004) 179. 3 Das A, Ishtiaque S M & Kumar Rajesh, Indian J Fibre Text

Res, 29 (2004) 308. 4 Dutta B, Salhotra K R & Qureshi A W, Blended Textiles

[The Textile Association (India)], 198 1 , 136. 5 Martindale J G, J Text Inst, 38 ( 1947) T153. 6 Ishtiaque S M., Das A & Sharma V, Design and development

of a friction tester for measuring the frictional characteristics of staple fibres and fabrics, paper presented

at the 43rd Joint Technological Conference of ATIRA, BTRA, SITRA and NITRA, IIT- Delhi, 2-3 March 2002.

7 Das A, Ishtiaque S M, Yadav P & Kumar Rajesh, Design and development of draftometer and a critical study on drafting force of roving, paper presented at the 44th Joint Technological Conference of ATIRA, BTRA, SITRA and NITRA, Coimbatore, 8-9 March 2003.