Indian Journal of Fibre & Textile Research Vol. 30, March 2005, pp. 94-98

Short Communication

Studies on combined effect of heating of roving and space between the aprons of ring

frame drafting system on yam quality

S Subramanian" & A Peer Mohamed Department of Textile Technology, A C College of Technology,

Anna University, Chennai 600025, India

Received 18 August 2003; revised received 8 December 2003 and accepted 29 March 2004

The combined effect of heating of roving at the break draft zone and space between the aprons of ring frame drafting system on yarn quality has been studied . Heating of roving at the break draft zone of ring frame reduces the friction between the draftlIlg fibres which can be advantageously utili zed by reducing the spacing between the aprons, thereby improvi ng the control over the floating fibres. It is observed that the yarn imperfections, faults and elongation - at - break are affected by the heating of roving at the break draft zone and vary ing the space between the aprons.

Keywords: Classimat faults, Yarn hairiness, Yarn imperfections

IPC Code: Int. C I7 DOIH 5/00, D02G 3/00

In the ring frame drafting system, to avoid formation of drafting wave, the fibres should accelerate at the speed of roller only when they are gripped by it. The control over the floating fibres is effected by set of aprons. The friction between the fibres plays very important role in causing irregularity of the strand.

One of the causes of irregularity in the drafted strand is draggi ng of undrafted strand into the nip of the front roller due to the increase in drafting force and its subsequent retreat under the action of internal elastic forces when the drafting force decreaes I .

Cavaney and Foster2 studied the effect of draft, compactness of sliver, direction and speed of drafting and fibre properties on the drafting force. The drafting wave can be avoided if the frictional resistance between the fast moving front fibre and the floating fibre is maintained less than the combined force of frictional resi stance between the floating fibre and the slow moving back fibre and the frictional resistance between floating fibre and aprons3

.

Tn the present work, the roving is heated at the break draft zone of the ring frame drafting system and

"To whom all the correspondence should be addressed. Phone: +9 1-44-22203562; E-ma il: ssubbll @annallni v.edu

the effect of heating and spacing between the aprons on yarn quality has been studied. The heating is done at 45°C and 55°C, well below the temperature at which physical and chemical properties of cotton change.

Two sets of yarn samples were prepared. In first set of samples, 30 tex (20 Ne) carded yarn and 7.4 tex (80 Ne) combed yarns were spun from cotton roving of 0.59 ktex (1.0 Ne) and 0.219 ktex (2.7 Ne) respectively to study the effect of heating at the break draft zone of ring frame drafting on yarn quality. The details of process parameters and properties of both yarn and roving samples are given in Tables 1 and 2 respectively. The yarn samples were prepared (i) at normal condition (32 - 34°C and 55 - 60% RH) , and (ii) by keeping the break draft zone at two different temperatures 45°C and 55 °C. The heating lamps were used for this purpose. At normal condition, minimum possible spacing between the aprons was selected such that there was no undrafting of fibres. In the case of 20 Ne carded yarn (yarn samples 1 and 2), the spacing between the aprons was kept same in both normal and heated conditions. As there was no improvement in yarn quality in 20 Ne yarn due to the heating alone, the spacer thickness was reduced in 80 Ne yarn at the heated condition (yarn samples 5 and 6). It was found that under heating, the spacer thickness upto 2.25 mm was possible without undrafting of fibre strand, which was not possible at the normal condition .

Second set of yarn samples, 14.8 tex (40 Ne) carded and 7.4 tex (80 Ne) combed yarns were prepared at normal condition and by heating the break draft zone at 45°C with same and lesser thickness spacers to study the combined effec t of heating and spacing between the aprons on yarn quality.

The breaking force of roving at 60 mm gauge length was studied using Instron tester. The study was conducted for sixty tests per samples at normal condition by heating the break draft zone at 45°C and 55 °C for 1 min. The testing speed was 80 mm/min. For heating, the heating lamp was focused directly on the roving between the jaws of the Instron tester.

The yarn evenness, imperfections and hairiness were eval uated on an Uster evenness tester (Model TTl) with 400 m/min speed and I min testing time. The

SHORT COMMUNICATION 95

Table I-Process parameters and properties of yarn samples

Yarn Yarn Roving Roving sample specification specification twists

No. lex (Ne) ktex (Ne) per inch

Set 1 1 30 (20) K 0.59 (1.0) 1.50 2 30 (20) K 0.59 (1.0) 1.50 3 30 (20) K 0.59 (1.0) 1.50 4 7.4 (80) C 0.22 (2.7) 1.96 5 7.4 (80) C 0.22 (2.7) 1.96 6 7.4 (80) C 0.22 (2.7) 1.96

Set 2 7 14.8 (40) K 0.39 (1.5) 1.65 8 14.8 (40) K 0.39 (1.5) 1.65 9 14.8 (40) K 0.39 (1.5) 1.65 10 14.8 (40) K 0.39 (1.5) 1.65 11 7.4 (80) C 0.22 (2.7) 1.96 12 7.4 (80) C 0.22 (2.7) 1.96 13 7.4 (80) C 0.22 (2.7) 1.96

K - Carded, and C - Combed

Tempe- Spacer rature thickness 2.5 % span

°C mm length mm

32 3.5 24.5 55 3.5 24.5 45 3.5 24.5 32 2.75 31 55 2.5 31 45 2.5 31

32 3.0 28.5 45 3.0 28.5 45 2.5 28.5 45 2.25 28.5 32 2.75 31 45 2.75 31 45 2.25 31

Fibre properties 50% span Micronaire

length mm

12.8 4.4 12.8 4.4 12.8 4.4 14.9 3.4 14.9 3.4 14.9 3.4

14.0 3.2 14.0 3.2 14.0 3.2 14.0 3.2 14.9 3.4 14.9 3.4 14.9 3.4

Bundle strength

g/tex

16.5 16.5 16.5 21 21 21

20 20 20 20 21 21 21

Table 2-Process parameters and properties of roving samples

Roving Roving Twists Tempe- Gauge sample specification per inch rature length

No. ktex (Ne) °C mm

1 0.59 (1.0) K 1.50 32 60 2 0.59 (1.0) K 1.50 55 60 3 0.59 (1.0) K 1.50 45 60 4 0.37 (1.6) C 1.52 32 60 5 0.37 (1.6) C 1.52 55 60 6 0.37 (1.6) C 1.52 45 60 7 0.25 (2.4) C 1.96 32 60 8 0.25 (2.4) C 1.96 55 60 9 0.25 (2.4) C 1.96 45 60

K- Carded and C- Combed

yarn samples were also tested on Uster Classimat 3(Model V2.10) to classify the faults. The single yarn tensile properties were studied using Uster Tensorapid 3 with 500 mm gauge length, 5000 mm / min testing speed and 100 tests per sample.

Significance tests were conducted for roving breaking strength, yarn tensile strength, elongation-at­break, hairiness and imperfections. Multiple comparisons between the samples have been can-ied out at 5% significance level.

The breaking force of roving has been measured at 60 mm gauge length under normal condition and two different temperatures (45°C and 55°C) and the results are given in the Table 2. The breaking force reduces by 53-59% in the case of 1.0 Ne carded and

Fibre properties Breaking 2.5 % span 50% span Micro Bundle strength length mm length mm naire strength of roving

g/tex ()" 0

24.5 12.8 4.4 16.5 213 24.5 12.8 4.4 16.5 101 24.5 12.8 4.4 16.5 129 29 15.5 3.3 19 248 29 15.5 3.3 19 108 29 15.5 3.3 19 161 31 14.9 3.4 21 236 31 14.9 3.4 21 87 31 14.9 3.4 21 128

1.6 Ne combed rovings and by 63-66% in the case of 2.4 Ne combed roving at 55°C. The breakage of twisted strand is due to the slippage and breakage of fibres4

. The breakage of roving is mainly due to the slippage of fibres. The slippage of fibre, in turn, depends on friction between the fibres . On heating, the moisture content of the cotton fibres reduces and hence the frictional force between the fibres 5

. The reduction in frictional resistance between fibres results in easier slippage of fibres upon loading and thus breakage occurs at lesser load.

The reduction in breaking force due to heating is higher in 2.4Ne combed roving compared to that in LONe carded and 1.6Ne combed rovings. The reason may be discussed as follows . The number of fibres in

96 INDIAN J. FIBRE TEXT. RES. , MARCH 2005

the cross - section is less in finer roving. For the same temperature and time, the decrease in moisture content and hence the frictional resistance between the individual fibres is more in finer roving compared to that in coarser roving. It is also observed that the reduction in breaking force is 35-41 % in 1.0 Ne carded and 1.6 Ne combed rovings and 41-45% in 2.4 Ne combed roving at 45°C. The reduction in breaking force is less while heating at 45°C compared to that while heating at 55°C due to the relatively higher moisture in the fibre and hence frictional resistance between the fibres at lower temperature.

Table 3 shows the effect of heating of roving at the break draft zone and variation in space between the aprons of ring frame drafting on yarn evenness, imperfections at different sensitivity levels, hairiness and tensile properties. The results show that there is 12-1 8% reduction in imperfections measured at different sensitivity levels in the case of 80 Ne combed yarn (yarn samples 4 and 5). This is due to the better control of floating fibres by the reduction in spacer thickness, which was possible due to the heating of roving at the break draft zone. The improvement in imperfections is not significant in the case of 20 Ne carded yarn (yarn samples 1,2 and 3). The reason is that the spacer was same in both normal

and heated conditions. The table also shows that there is no significant difference in the yarn imperfections between heating at 45°C and 55°C and hence 4~oC

was selected for the second set of experiments. It can be seen for the 40 Ne carded yarn (yam

samples 7, 8, 9 and 10) that there is no improvement in imperfections due to heating alone. But the combined effect of heating and subsequent reduction in spacer thickness improves the imperfections, more particularly the thin places . The reduction in spacer thickness to the tune of 2.25 mm was tried with heating and it was not found to be practicable at normal condition. The reason is explained as follows . The pulling force required at the front roller should be more than the addition of frictional resistance between the fibres and the force exerted by the aprons over the fibres, otherwise roller slippage and undrafting of fibre strand occur3

. Due to heating, the frictional force between the fibres decreases, which may be advantageously compensated by increasing the controlling force by the aprons on the fibres. The reduction in spacing between the aprons increases the controlling force acting on the fibres strand in the apron zone and results in more control over floating fibres. It can be seen from the table that the change in hairiness of the yarn due to heating is not significant

Table 3 - Effect of heating of roving and space between the aprons on evc: nness, imperfec tio ns, hairiness and tensile properties of yarn

Property Yarn samEie No. 2 3 4 5 6 7 8 9 10 11 12 13

U% 13.54 13 .69 13.66 14.8 1 14.5 14.62 15.85 15.9 1 15.47 15.20 13.73 13.76 13.5 1 Thin (-50%) 37 37 31 150 127 136 143 152 108 92 138 135 98 T hick (+50%) 375 401 382 688 597 602 1044 1058 895 816 244 274 222 Neps (200%) 168 173 170 597 539 520 1404 1492 1299 1239 345 354 315 Sub total 442 438 413 838 724 738 11 87 1210 1003 908 382 409 319

(-50% +50%) Sub total 580 611 583 1435 1263 1258 259 1 2703 2302 2146 726 763 634

(- 50%+50%+200%) Thin (-30%) 3675 3763 3804 5416 4944 5165 5758 5932 5355 5093 4159 4108 3763 Thin (-40%) 604 635 623 135 1 1149 1232 1363 1437 11 82 1059 1112 1006 845 Thick (+35%) 1595 1674 1662 2232 2055 2113 2935 2966 2673 2476 1200 1263 1100 Neps (140%) 972 924 986 222 1 191 2 1956 4479 4775 4279 4019 1237 11 72 1017 Sub tota l 5874 6072 6089 8999 8148 85 10 10056 10335 9211 8628 6471 6376 5708

(- 30%+-40%+35%) Thin (- 60%) 3 0 0 6 5 4 4 5 2 3 9 10 7 · Thick (+70%) 52 43 48 160 126 11 3 251 275 206 184 44 47 41 Thick (+100%) 3 4 2 26 19 15 36 50 33 31 8 12 8 Neps (280%) 33 35 34 186 166 156 407 439 379 368 112 122 11 2 Neps (400%) 6 8 6 54 46 44 109 125 110 98 35 38 36 Sub total 58 47 50 192 150 132 291 330 241 218 61 69 55

(- 60%+70%+100%) Hairiness index 6.62 6.73 6.51 4.28 4.05 4.12 :' .36 5.63 5.46 5.51 4.21 3.72 3.85 Tenacity, g/tex 13.44 13.00 13.48 15.25 16.98 16.46 14.15 14.79 14.08 14.64 17.17 16.97 16.69 Elongation, % 5.72 6.55 6.09 3.77 4.35 4.20 4.30 4.5 1 4.29 4.62 3.62 4.4 4.15

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Table 4-Effect of heating of rovi ng and space between the aprons on yarn faults

Classimat faults 7 8

Al 6256 6438 A2 1055 1183 A3 116 122 A4 20 29 BI 129 122 B2 81 65 B3 22 22 B4 12 9 C1 43 12 C2 16 4 C3 3 3 C4 3 Dl 14 3 D2 10 12 D3 2 1 D4 2 1

Total C and D faults 91 39 E 6 10 F 58 15 G 13 1

Long thick faults 77 27 (E + F + G)

HI 64 23 H2 194 127 ]1 0 0 12 0 0

Long thin faults 258 150 (H 1 +H2+Il +12)

in most of the cases. The change in imperfections and hairiness in 80 Ne combed yarn (yarn samples 11,12 and 13) follows the same trend as shown in 40 Ne carded yarn.

It can be seen from Table 3 that the change in tensile strength of yarn is not significant, but the improvement in elongation-at-break due to heating is observed in most of the cases. The drafted strands are twisted when they are in heated condition. Differential shrinkage of fibres takes place during heat dissipation and this may be the reason for the improvement in elongation-at-break of yarn.

Table 4 shows the Classimat faults of 40 Ne carded and 80 Ne combed yarns. The results of 40 Ne carded yarn show that the faults C, D, long thick and long thin are less in sample 8. The reason is that the heating of roving at the break draft zone and thereby the reduction in friction between the fibres facilitate easier drafting. The lesser resistance to drafting reduces the drafting - related faults and long faults. As the spacer thickness is reduced to 2.5 mm and 2.25

Yarn samQle No. 9 10 11 12 13

6182 6772 1687 1860 1258 1106 1163 418 548 308 109 124 65 66 34 16 20 16 16 24 119 218 43 34 21 61 98 32 34 26 14 28 19 7 19 16 11 14 6 8 20 32 22 13 10 11 9 7 10 5 2 7 6 7 3 4 2 10 4 3 8 10 9 6 10 8 11 7 3 8 0 2 4 4 3

5 4 3 3 54 78 69 50 45 6 17 25 21 8

27 27 22 18 13 0 0 4 0 0 32 44 51 39 21

51 54 31 42 38 226 157 144 170 134 0 0 0 0 0 0 0 2 0 0

277 211 177 212 172

mm, the force on the fibres at the apron zone increases. Though it helps in controlling the floating fibres, the resistance to drafting increases which may have caused the apron and front rollers slippage occurring rarely. These slippages may have resulted C, D and long faults . However, these faults are lesser than the faults found in the yarn produced at normal condition. In the case of 80 Ne combed yarn, the faults are lesser in the yarn produced at heated and smaller spacer condition (yarn sample 13). The reason may be discussed as follows. The number of fibres in the cross-section is less in 80 Ne yarn and hence the thickness of fibre strand at the apron zone. Therefore, the spacer thickness of 2.25 mm used at heated condition may have not significantly increased the drafting resistance compared to 2.5 mm spacer thickness used at normal condition .

The results show that the yarn with lesser imperfections and faults can be produced by heating the roving at the break draft zone of ring frame, thereby reducing the friction between the fibres and

98 INDIAN 1. FIBRE TEXT. RES., MARCH 2005

subsequently selecting the optimum spacing between the aprons to have better control over the floating fibres.

Heating at the break draft zone of ring frame reduces moisture content present in the roving and hence the friction between the fibres . This can be advantageously utilized by reducing the spacing between the aprons, thereby improving the control over the floating fibres. The combination of heating at the break draft zone and subsequent increase in controlling force on the floating fibres at the apron zone by reducing the spacing between the aprons improves the evenness and imperfections of yarn. The yarn faults, mainly the long thick and long thin faults, reduce by heating due to the lesser drafting resistance. Reducing the spacing between the aprons increases long thick and long thin faults in 40 Ne carded yarn; the faults are however lesser than the yarn produced at normal condition. In the case of 80 Ne combed yarn,

the reduction in spacer thickness along with the heating at break draft zone reduces long faults.

Acknowledgement The authors are thankful to Mr. P S Karthikeyan,

Indra Cotton Mills Ltd, Chennai, and GEM Spinners Ltd, Chennai, for cooperation extended to conduct the experiments.

References 1 Grosberg P, J Text Inst, 52 (1961) T91. 2 Cavaney B & Foster GAR, J Text Illst, 45 (1954) T390. 3 Subramanian S & Peer Mohamed A, Proceedings, 17'"

National Convention of Textile Engineers [The Institution of Engineers (India), Chennai] , 2002, 94.

4 Hearle J W S, in Structural Mechanics of Fibres, Yams alld Fabrics, by Hearle J W S, Grosberg P & Stanley Backer (John Wiley & Sons. Inc, New York), 1969, 277

5 Morton W E & Hearle J W S, Physical Properties of Textile Fibres (The Textile Institute, Manchester) , 1993, 624