Indian Journal of Fibre & Textile Research Vol. 29, June 2004, pp. 173- 178

Study on drafting force of roving: Part I - Effect of process variables

A Das". S M Ishtiaque & Rajesh Kumar

Department of Textile Technology, Indian Institute of Technology, New Delhi 110016, India

Received 4 April 2003; revised received Gnd accepted 4 July 2003

The effect of process variables, namely draft, drafting speed and roller setting, on drafting force of polyester/viscose (65:35) roving has been studied. A reasonably good correlation (R2 = 0.855) between process variables and drafting force has been observed. The drafting force at first increases with the increase in draft but after reaching a maximum value, it de­clines sharply. The drafting force increases with the increase in drafting speed and the same trend is also observed at lower draft and roller setting. But when the draft and roller setting further increase, initially the drafting force remains unchanged with the increase in drafting speed and then it declines. The roller setting has been found to be inversely proportional to the drafting force for all the experimental combinations.

Keywords: Drafting force, Drafting speed, Roller setting, Polyester fibre, Viscose fibre

fPC Code: Int. Cl.7 D02G 3/00; DOIH 5/00

1 Introduction The drafting force in roller drafting system has

been the subject of research for many years. Various research workers l

- '4 have reported theoretical as well as practical aspects of measuring drafting force and its relationship with the material and machine parame­ters. The main material parameters which influence the drafting force are fibre length, fibre fineness, fibre crimp, fibre-to-fibre friction, number of fibres present in the strand, fibre parallelisation, packing factor, twist and material irregularity. The machine parame­ters which influence the drafting force are draft ratio, drafting speed and roller setting.

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 force2

. The way a fibre behaves during drafting depends very much on the variation in fric­tional forces acting on it in the drafting zone. Since the drafting waves3 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 single-fibre

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properties, fibre assembly properties and drafting pa­rameters causes variations in frictional forces acting on short fibres which move in an irregular manner in the drafting zone, thereby causing a variation in mass per unit length of the drafted material. Drafting force and its variabilit/·5 are important characteristics that determine the irregularity added during drafting, the number of faults generated and the drafting failures . Measurement of drafting force is therefore a useful aid in raw material selection, optimization of spray oils used in cotton, and optimization of crimp and spin finish level in synthetic fibres and other process parameters during synthetic fibre manufacturing.

Drafting force of sliver and roving is dependent both on fibre properties and mechanical variables of the system used to draft the material during spinning. These mechanical or process variables include draft, drafting speed and roller setting. The drafting force is determined by inter-fibre friction, crimps, fibre paral­lelisation, incidence and direction of hooks, and twist of roving. Drafting force of roving has been found to affect spinning efficiency5. The variability in drafting force appears to be more correlated with spinnability and yarn 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, i.e. an op­timum drafting force is required for a specific yarn. The present paper was, therefore, aimed at investi­gating the correlation between drafting force and pro­cess variables, i.e. draft, drafting speed and roller set-

174 INDIAN J. FIBRE TEXT. RES., JUNE 2004

ting, in connection with their individual as well as combined intluence on drafting force .

2 Materials and Methods 2.1 Sample Preparation

Polyester (51 mm x 1.4 denier) and viscose (51 mm x 1.5 denier) fibres in 65:35 blend proportion were used to prepare roving with 0.45 ktex linear density and 1.0 twist multiplier. The fibres were blended in blow room and then processed through card and two passages of draw frame. The finisher draw frame sliver was then processed on simplex to get roving with required linear density and twist. The roving bobbins were first conditioned at standard atmos­pheric condition and then taken for the measurement of drafting force .

2.2 Measurement of Drafting Force

The drafting force of roving was measured using Draftometerl5

. The drafting force measurement is based on the power demanded by the drafting roll motor to draft the material. The power is measured by using a sensitive wattmeter transducer connected in series with drafting roll motor. Since power is a func­tion of torque required at fixed roller speed, wattage becomes a direct measure of drafting force. The in­strument consists of two pair of rollers, i.e. single zone drafting system. The front and back pai rs of roll ­ers are getting individual drive from two separate speed controlled motors. The power required to drive the front roller is first stored in computer and when any roving is drafted, the difference in the power re­quirement to drive the frcnt roller will be the measure of actual drafting force. The draft and drafting speed can be controlled by changing the speed of individual motor. There is also a provision for changing roller setting in the instrument. The roving is fed in the drafting zone and corresponding drafting force, in terms of wattage, is recorded through a dedicated PC attached to it.

2.3 Experimental Design The experiment was carried out in two different

phases. In the first phase, the impact of individual parameters, i.e. draft, drafting speed and roller setting, on drafting force was studied. Then in the next phase, the impact of above parameters in combination was studied.

2.3.1 Impact of Individual Process Parameters The individual effect of process variables, i.e. draft,

drafting speed and roller setting, on drafting force was studied. To study the impact of draft at different roller

settings, five different representative draft values (1.1, 1.3, L5, 1.7 and 1.9) suitable for break draft zone in ring frame and five roller settings (55mm, 60mm, 65mm, 70mm and 75mm) for each draft were used. To study the impact of drafting speed at different drafts, three drafting speeds (6 m1min, 9 m1min and 12 m1min) and five drafts (1.2, 1.4, 1.6, 1.7 and 1.8) were used. In this second set of experiments, the draft of 1.7 was used because of the fact that the drafts 1.6 and 1.8 were producing entirely different trends. To study the complex phenomenon with in this zone 111

detail, an intermediate draft of 1.7 was used.

2.3.2 Impact of Combined Parameters

A three-variable factorial design technique proposed by Box & Behnken (Table 1) was used to investigate the influence of three Pfo<:ess variables, i.e. draft, drafting speed and roller setting, on drafting force of roving. The actual values of the three variables corresponding to coded levels are given in Table 2.

Table I - Box and Behnken design for three variables

Expt No.

2

3

4

5

6

7

8

9

10

II

12

13

14

15

X,

- I

- I

I

- I

- I

I

0

0

0

0

0

0

0

Variable

Xl

- I

- I

I

I

0

0

0

0

- I

- I

I

0

0

0

o o o o

- I

- I

- I

- I

I

o o o

Table 2 - Actual values of process variables corresponding to coded levels

Vari able Coded level -I 0 + I

Draft (X,) 1.2 1.5 1.8

Drafting speed (Xl). m/min 6 9 12

Roller selling (X3). mm 60 65 70

DAS el al.: STUDY ON DRAFfING FORCE OF ROYING: PART I 175

3 Results and Discussion From the results of drafting force (Table 3) and re­

sponse surface equation (Table 4), it is evident that the drafting force has reasonably good correlation with process variables (R2 = 0.855). Also, it can be derived from the response surface equation that the maximum drafting force can be achieved at draft, drafting speed and roller setting of 1.42, 12 rn/ min and 60 mm respectively when other two parameters are at mid coded value.

3.1 Effect of Draft

The effect of draft individually, keeping the draft­ing speed constant at certain level, on the drafting force for different roller setti ngs is shown in Fig. 1. It is evident from Fig. 1 that the drafting force initially increases with the draft and then declines sharply as the draft increases further. The contour plots (Figs 2 and 3), showing the combined effect of different pro­cess variables, also depict the similar trend. This is due to the fact that at the lower level of draft, very

Table 3 - Drafting force at different combinations of process variables

Expt No.

I

2

3

4

5

6

7

8

9

10

II

12

13

14

15

1.2 6

1.8 6

1.2 12

1.8 12

1.2 9

1.8 9

1.2 9

1.8 9

1.5 6

1.5 12

1.5 6

1.5 12

1.5 9

1.5 9

1.5 9

X.l

65

65

65

65

60

60

70

70

60

60

70

70

65

65

65

Drafting force

W

0.6313

1.1780

1.7285

0.7548

1.6451

0.5213

1.1613

0.4413

0.9915

2.9834

0.9885

0.8379

1.6093

1.6202

1.6126

Table 4 - Response surface equation for drafting force

Yariable Response surface equation

Drafting force 1.520 - 0.284 XI + 0.314 Xz - 0.339 X.l 0.855

- 0.5 13 xl - 0.536 XZX3 - 0.380XI Xz

little fibre slippage occurs due to elastic behaviour of fibre strand and the fibres are simply straightening out (removal of crimp and hooks/. So, the principle mode of drafting of roving at lower level of draft is by straightening of fibres which results in consolidation of fibre strand and hence the effective cohesion in­creases sharply. So, it causes increase in drafting force due to the resistance for further deformation. In the later stage, fibres slip partially as the draft increases, but the static friction has not yet been fully over­comed and thus the drafting force reaches its maxi­mum value with the increase in draft. The maximum drafting force is observed at different draft for differ­ent roller settings (Fig. I). With further increase in draft, the principle mode of roving deformation is due to the sliding of fibres relative to one another because the static friction is fully overcomed and hence after the peak region the drafting force declines quickly. At the higher level of draft, the drafting force generated is due to the dynamic friction of fibre which is lesser than the static friction. All the above trends are valid within the draft range used in the experiments and may vary if the draft range changes.

3.2 Effect of Drafting Speed Fig. 4 shows the effect of drafting speed individu­

ally, keeping the draft and roller setting at certain level, on the drafting force of roving. It is clear from Fig. 4 that the relation between drafting speed and drn :ling force mainly depends on the draft. It is also observed that at lower level of draft the value of drafting force increases with the increase in drafting speed. But at comparatively higher draft (1.7), the drafting force initially increases and then decreases with the increase in drafting speed. When the draft is

3

2.5

3 2

~J' -E 1.5

Cl c '2 1 r'! D

.0.5

1.1

Roller settings -<>-55mm

~60mm

--65mm

--70mm

--75mm

1.3 1.5

Draft -1.7 1.9

Fig. I-Effect of draft and roller setting on drafting force at drafting speed of 12 mlmin

176 INDIAN J. FIBRE TEXT. RES., JUN E 2004

u Q) Q) a.

(f)

01 e £ <tl L-

0

· · t~·::.'~~:~.';; ,'_~~ :::~::: :.~- -: _1L---·~~~~-L--~~~--~

-1 o 1

- 1 ~~~~~~~~~~=-~.

-1 o Draft

Fig. 2-Effcct of draft and drafting speed on drafting force [roller setting: (a) 60 mm, (b) 65 mm, and (c) 70mm]

Ol e

:;:;

W (/) I-

~ (5 0:::

-1~~==~~~~~~

-1 0 Draft

Fig. 3-Effec t of draft and roller sett ing on draft ing force [draft­ing speed: (a) 6 In/min , (b) 9 mlmin, and (c) 12 In/min]

DAS et al.: STUDY ON DRAFfING FORCE OF ROVING: PART I 177

2.5

~ 2 Q)~

0 .E 1.5

OJ c 1 <E ~ 00.5

0

Draft

~1.2

-0-1.4

--1.6

--1.7 --lIE-1 .8

6 9 Drafting speed, m/min

12

Fig. 4-Effect of drafting speed and draft on drafting force at roller setting of 65 mm

high enough (1.8), the drafting force starts decreasing with the increase in drafting speed and then stabilizes. The contour plots (Fig 5) showing the combined ef­fect of different process variables, also depict the similar trend. The increase in drafting force with the increase in drafting speed at lower level of draft may be due to the fact that the floating fibres are more likely to take up intermediate speeds at high drafting speed than at low drafting speed and also due to the increase in the ratio of dynamic frictional force to static frictional force. This can also be due to the in­termediate velocities of fibres in the drafting zone, causing shuffling or randomization of fibres as draft­ing speed increases which results in origination of fibre tension and thus the drafting force" . But at higher draft and drafting speed, the control over the fibres goes down and chances of fibre shuffling be­come less, thereby reducing the drafting force.

3.3 Effect of Roller Setting

Fig. 1 and the contour plots (Figs 2, 3 and 5) also show that the drafting force always reduces with the increase in roller setting. The above trend is due to the fact that at lower roller setting, the control over the movement of floating fibres becomes more because of the more inter-fibre cohesion. But as the roller setting increases the inter-fibre cohesion goes down and hence drafting force reduces. The similar trend has also been observed by other researchers7

.

4 Conclusions

4.1 The correlation between drafting force value and the process variables is reasonably good (R2 = 0.855) .

4.2 Within the draft range studied, the drafting force increases initially with the increase in draft but

0> C B

<1> en

o

-1L-~~~~~--~~~~1 -1 0

Drafting Speed

Fig. 5-Effect of drafting speed and roller setting on drafting force [draft: (a) 1.2, (b) 1.5, and (c) 1.8]

178 INDIAN J. FIBRE TEXT. RES., JUNE 2004

after certain value it declines sharply. The maximum drafting force reaches at different draft for different roller settings.

4.3 At lower level of draft, the value of drafting force increases with the increase in drafting speed. But at comparatively higher draft, the drafting force initially increases and then de­creases with the increase in drafting speed. When the draft is high enough, the drafting force starts decreasing with the increase in drafting speed and then stabilizes.

4.4 At lower roller setting, the drafting force al­ways increases with the increase in drafting speed, but at higher roller setting the effect of drafting speed on drafting force becomes insignificant. On further in­crease in roller setting, the drafting force reduces with the increase in drafting speed.

4.5 The drafting force always decreases with the increase in roller setting.

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(1998) 559. 10 Su Ching-Iuan & Lo Kuo-Jung, Text Res J, 70 (2000) 93. 11 Grosberg P, J Text Inst, 52 (1961) T91. 12 Audivert R & Vidiella J E, Text Res J, 53 (1962) 652. 13 Audivert R, Villoranga M & Coscolta R. Text Res J, 37

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