indian Journal of Fibre & Texti le Research Vol . 3 1 , December 2006, pp. 529-536

Analysis of controlling force at the double apron drafting system of ring frame

S Subramanian" & A Peer Mohamed

Department of Textile Technology. A C College of Technology, Anna University, Chennai 600 025, India

Receil'ed 29 Jllly 2005; accepted 15 Decelllber 2005

Contro l l ing of floating fibres at the double apron drafting system of ring frame to avoid formation of drafting wave has been analysed. The l imitation of existing double apron roller draft ing system in control l i ng the floating fibres has becn discussed. The cradle of the drafting system has been modified to achieve higher control l ing force towards the front roller nip to execute better control over the floating fibres and lower control l ing force away from the front roller nip to reducc the drafting resi stance in order to avoid undrafting. The imperfections and total classified yarn faults are lower for the yarn produced using modified cradle wi thout spacer compared to that of normal cradle with least possible thickness spacer.

Keywords: Aprons, Controll i ng force, Drafting wave, Floating fibres, Spacer IPC Code: Int. Cl .8 DO I H5/00

1 Introduction The 'drafting wave' is formed as a result of non­

steady motion of the fibres in the drafting field. When all the fibres are not of the same length, the shorter ones are released by the back rol lers before their front ends have reached the front rollers. These fibres tend to come out of the front rollers in clots and so cause an alternate thick and th i n places in the drafted material . This is called the drafting wave. I The drafting wave formation can be restricted by suitable control over the floating fibres in the main draft zone. The motion of floati ng fibres during drafting and controll ing of fibre movement has been studied by many researchers.:!- 1 2 Taylor l 2. u has studied the fibre movements in the drafting zone and for the worsted sliver he found that under normal drafting conditions, fibres at any t ime during their passage through the drafting zone may be retarded or accelerated, depending on the change in distribution of their contacts with surrounding fibres. The pressure between the aprons in the drafting zone governs the degree of control exerci sed on the floating fibres and has influence over the drafting i rregularities. 14 In the present work, the analysis has been carried out on the controlling of floating fibres to avoid formation of drafting wave. The l imitation of existing double apron roller drafting system in controll i ng the floating fibres is discussed. The cradle of the drafting system has

"To whom all the correspondence should be addressed. E-mai l : ssubbu@annauniv.edu

been modified to achieve favourable distribution of controlling force at the double apron zone for better controll ing of floating fibres.

2 Theoretical Consideration

Mechanics of Drafting Wave Formation In the double apron roller drafting system of ring

frame, control over the floating fibres is obtained by a pair of aprons. The design of nose bar and cradle, the position of nose bar and cradle wi th respect to the drafting plane, gap between the aprons, the property and thickness of the apron, and the thickness of the strand in between the aprons decide the amount of control exerted over the floating fibres.

In Fig. I , f is the fibre gripped by the front roller nip moving at the veloc i ty of VI (fast moving front­fibre) ; b, the fibre gripped by the back roller n ip moving at the velocity of V2 (slow moving back-

Front roller Middle Roller

Fig. I - Double apron roller drafting system

530 INDIAN 1 . FIBRE TEXT. RES . . DECEMBER 2006

fibre); and s is the floating short fibre, neither gripped by the front nor by the middle roller nip and move with the velocity of e ither VI or V2 based on the frictional resistance between short fibre & front fibre, and short fibre & back fibre.

During normal drafting of fibres in an apron zone of a roller drafting system (Fig. 1 ) the force equation, assuming uniform acceleration, i s given below:

Pf= F fb + F fa + Mf (VI - V2)/l'1t Pr= Ftb + F fa + Mr VI [ 1 - ( I /DI )]/l'1t . . . ( 1 )

where Pr i s the pull ing force exerted by front roller nip; Ftb , the frictional resistance between fast moving front fibre and slow moving back fibre; Fra, the frictional resistance between fast moving front fibre and slow moving aprons ; Mr, the mass of fast moving front fibre; VI , the veloci ty of front roller; V2, the velocity of middle roller; I'1t, the t ime for acceleration ; and DJ , the draft i n the apron zone.

Lower value of Pr compared to RHS of Eq. ( I ) results in roller slip and leaves the strand undrafted. The short fibres wil l be accelerated before they reach the front roller nip and the drafting wave wil l be created when

. . . (2)

where Fsf is the frictional resistance between floating short fibre and fast moving front fibre; Fsb, the frictional resistance between floating short fibre and slow moving back fibre; Fsa. the frictional resistance between floating short fibre and aprons, i .e . the controlling force exerted by the aprons over the floating short fibres; and I11s, the mass of floating short fibre.

The Eq. (2) shows that the formation of drafting wave can be avoided by (i) exerting controll ing force over the floating fibres using aprons and ( i i ) i ncreasing the inertial force of drafting fibres. From Eq. (2), it is further clear that either Fsa and Fsb have to be increased and/or Fsf has to be reduced i n order to avoid formation of drafting wave for a given draft and front roller speed. The controlling force exerted by the aprons on the floati ng short fibre Fsa can be i ncreased by reducing the gap between the top and the bottom aprons, i .e . by reduc ing the spacer thickness. This reduction in gap between the aprons will , on the other hand, increases the value of Fra manifold in Eq. ( l ) . Under extreme conditions, the fall-outs of the reduction of gap between the aprons are given below:

( i ) I f PI' i s less than the RHS value of the Eq. ( I ), it wil l result in roller s l ip and undrafting.

( i i ) If Pr i s sti l l greater than the RHS value of the Eq . ( l ), it would cause increased tensioning of the drafting fibres and may lead to fibre breakage. Moreover, to keep Pr at greater level, the loading on the front roller has to be i ncreased at the cost of l ife of cots and other rotating elements.

The yarn uniformity increases due to the reduction in gap between the aprons up to a certain level . Beyond that level, reduction i n spacer thickness leads to deterioration instead of i mprovement in yarn quality. I S. 1 6 Hence, for the better control of floating fibres without undrafting, the controlling force Fsa has to be increased without causing manifold increase of Fra and it can be achieved by suitably distributing the controlling force over different regions of main draft zone according to the requirement.

Reducing friction between fibres in the drafting strand reduces both Fsr and Fsb in Eq.(2) and Fib in Eq . ( I ) , and with the reduction of fibre-fibre friction i t i s possible to increase Fsa in Eq. (2) by reducing the spacer thickness in order to avoid drafting wave formation. The effect of i ncrease in Fsa will be reflected in Eq . ( I ) by the increased Fra, whose adverse effect can be suppressed by the reduction in Fib.

The above analysis shows that the reduction in spacer thickness to exert higher controll ing force on the floating fibres without causing undrafting and fibre damage can be achieved by ( i ) suitably distributing the controll ing force over different regions of main draft zone according to the requirement, and ( i i ) reducing the friction between the drafting fibres.

Distribution of Controlling Force between Aprons The distribution of controll ing force between the

aprons was measured using a specimen made out of fabric strip of uniform thickness as explained below. A groove was made in the front top roller of a ring frame. The specimen was kept between the top and bottom aprons and the top arm was pressed to apply load. The speci men was taken through the groove of the front top roller and load was appl ied gradually at the end of the strand (Fig. 2). The load ( W) at which the specimen slips out of the aprons was noted. The force exerted by the aprons on the specimen was measured at different positions, viz . 5 mm, 1 0 mm, 1 5mm, 20 mm and 25 mm from the tip of the nose bar using the fol lowing relationship:

W/P = e �e

SUBRAMANIAN & PEER MOHAMED: CONTROLLING FORCE AT THE DOUBLE APRON DRAFTING SYSTEM 53 1

p

w

Fig. 2 - Measurement of control l ing force

where Il is the coefficient of friction between fluted roller and the specimen; e, the angle of wrap (45°); and P, the controll ing force exerted by the aprons over the specimen.

The method of finding the coefficient of friction between fluted roller and speci men strand (Il) is described as follows. The speci men was mounted over the fluted roller as shown in Fig. 3. A known weight TI was balanced by applying a load h The load T2 was i ncreased gradually till the specimen started moving and was noted.

The value of Il can be calculated using the following equation :

The calculated value of Il was found to be 0.4. Figure 4 shows the control l ing force measured between the aprons for normal and the modified cradle with 2.75 mm spacer and without spacer.

Limitation of Existing Double Apron Drafting System In the Fig. 5 , 0' A'B' shows the variation of drafting

strand thickness from m iddle roller nip to the front roller nip. The various terms used in figure are explained below:

O-Middle roller nip,

B -Front roller nip,

N-Tip of the apron,

OB -Distance between front and middle roller nips (C),

00' -Roving strand thickness at the middle roller nip (R),

BB' -Yarn strand thickness at the front roller nip (Y), and

E -Mean length of fibres.

230

'" g 180 ... '" � ] 8 1: 1 30 'iii '3

Fig. 3 - Measurement of coeffic ient of friction

-- Nonnal cradl� - 2.75 mm spacer

-'-Nonnal cradle - No spacer

-·-Modified cradle- 2.75 mm spacer -A-lvlodified cradle - No spacer

�.'-----A-------,------U§ �------- --------.--------.--------

80 J...I --_--'--__ -L ___ -'--__ ---L..

B'

y B

10 I S 20 Distance from the tip of apron. mm

Fig. 4 - Cumulative contro l l ing force

I • • '

3 2

N

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

. .... ..

E c

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

A '

A

25

.' 3

2 CCF

R

o

Fig. 5 - Strand thickness and cumulative control l i ng force (CCF) in main draft zone

532 INDIAN 1 . FIBRE TEXT. RES., DECEMBER 2006

The attenuation starts, on an average, at distance E from the front roller n ip (A in Fig. 5) . The cumulative controll ing force exerted by apron on the drafting fibre is shown as 1 - 1 , 2-2 and 3-3 in Fig. 5 . In the recent conventional double apron drafting arrangement, the cumulative controll ing force exerted by the aprons is s imilar to either 2-2 or 3-3 for two different thickness of the spacer in between the aprons. If the thickness of the spacer is more, the controll ing force towards the exit of the apron, i .e. tip of the apron, will be less (2-2 in Fig. 5). This reduces F,o in Eq.(2), which faci l i tates the formation of drafting wave. On the other hand, if the spacer thickness is reduced below a certain level , the controll i ng force avai lable towards the exit of the apron increases, and also the controll ing force acting on the whole length fibre in the drafting strand (3-3 in Fig. 5) . This will i ncrease Fra i n Eq . ( I ) , and if the pul l ing force P,. i s not sufficient, rollers slip and hence undrafting of fibre strand would occur.

The control l ing force acting on the fibre strand should be h igher nearer the front roller ni p to execute better control over the floating fibres in order to avoid formation of drafting wave. However, it should be lower away from the front roller n ip to reduce drafting resistance in order to avoid undrafting of fibre strand and fibre damage ( I - I i n Fig. 5), which is opposite to what i s available in recent conventional drafting system (2-2 and 3-3 in Fig. 5) . Hence, the recent design of the double apron drafting system has a l imitation in controll i ng the floating fibres and therefore, on the prevention of formation of drafting wave, the level of control obtained is not sufficient particularly when h igher draft i s to be employed with more short fibre content. The design modification of apron system becomes essential to provide the . required controll ing force only at the required position, i .e. h igher control l ing force towards the exit of the apron with lower controll ing force away from it. The design of cradle was modified to ach ieve the favourable distribution of controll ing force at the apron zone.

Design of Cradle Fol lowing points are taken care of while designing

the modification i n cradle:

(i) Higher control l ing force to be appl ied on the drafting strand towards the exit of the apron with lower control l ing force in all other pos i tions i n the apron zone.

Front roller Middle roller

Fig. 6 - Stepped nose bar with modi fied cradle

( i i ) Smooth rotation of the bottom and top aprons without apron-to-apron slippage.

( i i i ) No hi ndrance to the flow of drafting strand in the apron zone.

The diagram of the modified cradle is shown in Fig. 6. The top apron was l i fted for a height of 1 .6 mm at a distance of 1 8 mm from the tip of the apron, so that the control l ing force exerted on the drafting strand by the aprons becomes nearly zero, except at the exit and entry of apron. S ince the distance between the front and middle roller nips is 46 mm, in normal case the cotton fibres will not be simultaneously gripped by both middle rol ler and front roller n ips at any instant during drafting. Due to the above modification, the controll ing force exerted by the aprons on the whole length of fibres i n the apron zone becomes less for the modified cradle compared to normal cradle for the same thickness of spacer. Thi s reduction in controll ing force exerted on the whole length of fibre in the drafting strand can be advantageously exploited by exerting stil l higher control l ing force towards the exit of the apron for the same pull ing force offered by the front rol ler nip without caus ing undrafting.

3 Materials and Methods

3.1 Measurement of Apron-to-Apron Slippage

The apron-to-apron sl ippage causes uncontrolled movement of fibres in the apron zone, resulting in poor yarn quali ty . 1 7. 1 8 The sl ippage can be measured using the following expreSSIOn for different experi mental condit ions:

Bottom apron Top apron

Apron-to-apron =

surface speed surface speed x 1 00 slippage (%) Bottom apron surface speed

SUBRAMANIAN & PEER MOHAMED: CONTROLLING FORCE AT THE DOUBLE APRON DRAFTING SYSTEM 533

Table I - Raw material properties and process parameters used for producing yarn samples

Yarn sample Cradle Yarn count Rovi ng count Spacer no. Ne Ne thickness

mm

I N Normal 80 C 2.7 2.75

2M Modified 80 C 2.7 2.75

3M Mod i fied 80 C 2 .7 No spacer

4N Normal 30 K 1 .05 3 .25 5M Modified 30 K 1 .05 No spacer

C - Combed. and K - Carded.

The time taken for 1 0 revolutions of bottom apron and 20 revolutions of top apron was measured.

3.2 Production of Yarn Samples

Carded cotton yarn of 1 9 .7 tex (30 NeK) and combed cotton yarn of 7 .4 tex (80 NeC) were produced with different experimental arrangements using a modern high speed ring frame having pneumatically loaded top arm with double apron drafting arrangement. The material properties and process parameters used for the production of yarn samples are given in Table 1 . The quality of yarn would be better with minimum possible spac ing between the aprons, provided the undrafting of fibre strand does not occur for the given properties of roving and ambient atmospheric condition at the laboratory . For the preparation of yarn samples, the spacer thickness was selected in such a manner that i t was the least possible value below which undrafting of fibre strand occurred. The spacer thickness values, selected based on the above prescriptions to produce different yarn samples, are given in the Table 2. Yarn sample (80 NeC) was produced using modified cradle with 2.75 mm spacer to compare the qual i ty of yarn with the normal cradle at the same experimental conditions.

3.3 Yarn Quality Measurement

The yarn samples were tested using a Premier IQ tester for hairiness, unevenness and imperfections. The i mperfections were measured at all the sensit ivity levels, viz. th in -30%, -40%, -50%, -60%; thick +35%, +50%, +70%, + 1 00%; and neps + 1 40%, +200%, +280%, + 400%. The tests were carried out using the specifications: test speed, 400 mlmin ; test time, 1 min ; and number of tests, 20 per sample .

The tensile properties were studied using a Premier Tensomaxx tester working on constant rate of elongation principle. The testing conditions were :

Fibre QroQerti: 2. 5 % span 50% span length Micronaire Bundle strength length, mm mm �lg/inch gltex

3 1 . 1 1 5 .7 3 .2 20.7

3 1 . 1 1 5 .7 3.2 20.7

3 1 . 1 1 5.7 3 .2 20.7

27.4 1 2 .4 3 . 1 1 9.4

27.4 1 2.4 3. 1 1 9.4

Table 2 - Least possible thickness of spacer for the production of yarn samples

Yarn Cradle Spacer thickness mm

Normal 2.75 80 NeC Modi fied No spacer

Normal 3 .25 30 NeK

Modified No spacer

specimen length, 500 mm; test speed, 5000 mm Imin ; and number of tests, 1 00 per sample.

The yarn faults were measured using a Uster Classimat 3 (Model V2. 1 0) tester for the sample length of 1 lakh metre. As imperfections were higher for sample 2M compared to samples I N and 3M, the classified faults were measured for samples 1 N and 3M for 80 NeC yarn. Samples 4N and 5M were tested for classified faults of 30 NeK yarn .

4 Results and Discussion

4.1 Controlling Force

The proposed favourable distribution of controlling force at the main draft zone is to provide higher controlling force towards the front roller nip to execute better control over the floating fibres and lower controll i ng force away from the front roller nip to reduce drafting resi stance. For the normal cradle. the cumulative controll ing force is increasing towards the middle roller n ip as shown in Fig. 4. The cumulat ive controll ing force i n modified cradle remains nearly constant from exit of the apron to the position closer to middle roller nip, i .e. higher control l ing force towards the exit of the apron with lower controll i ng force acting on the remaining positions in the apron zone. Due to availabil i ty of favourable distribution of controll ing forces at the apron zone with modified cradle, greater controll ing

534 INDIAN J. FIBRE TEXT. RES., DECEMBER 2006

force is exerted on the floating fibres towards the front roller nip w ithout causing undrafting by employing no spacer, which i s not otherwise possible.

4.2 Apron-to-Apron Slippage

Apron-to-apron s l ippages for normal and modified cradle with different spacers are given in Table 3. It is observed that the s l ippage increases with the i ncrease in spacer thickness. As the spacing between the aprons increases, the frictional contact between the aprons decreases which results in increase in apron­to-apron sl ippage. Apron-to-apron sl ippage depends on the thickness of the fibre strand in the apron zone . 1 8 Hence, it can be seen from the table that the sl ippage is more with drafting strand in between aprons compared to that of without drafting strand. The apron-to-apron sl ippage is marginally h igher in modified cradle compared to that in normal cradle for same experimental arrangements. The reason for marginal increase i n s l ippage in modified cradle may be due to the less contact between the top and the bottom aprons and friction between top apron and cl ip used for l ift ing the top apron. However, the 80 Nee yarn sample was produced using ( i ) normal cradle with 2.75 mm spacer and ( i i ) modified cradle without spacer, and 30 Ne yarn was spun using ( i i i ) normal cradle with 3 .25 mm spacer and ( iv) modified cradle without spacer. I n both the yarn preparations, the apron slippage i s less with modified cradle without spacer.

4.3 Evenness, Imperfections and Hairiness

The evenness, imperfections and hairiness values of the yarn sample produced at different experimental conditions are given i n Table 4. Since modified cradle without spacer provides higher controll ing force on the floating fibres towards the front roller nip, the unevenness and i mperfections (in most of the sensitivity levels) of the yarn is lower compared to the yarn spun using normal cradle with 2.75 mm spacer. The study on comparison between modified cradle and normal cradle with same 2.75 mm spacer shows that the imperfections are h igher for the yarn produced using modified cradle with 2.75 mm spacer due to very low controll ing forces available towards the front roller nip. The same trend is observed in the case of 30 NeK yarn also. The imperfections of the yarn produced using modified cradle without spacer are lower than the yarn samples produced using normal cradle with 3 .25 mm spacer.

Table 3 - Apron-to-apron sl ippage

Yarn Spacer AQron-to-aQron sliQQage, % thickness With draft ing strand Without drafting strand

mm Normal Modified Normal Modified cradle cradle cradle cradle

80 NeC 0 3.07 3.34 2.4 2.93 2.75 3.84 3.59 2.86 2.93

30 NeK 0 2.84 3.29 2.44 2.84

3.25 4.84 4.84 3.24 3.24

Table 4 - Effect of modification of cradle on yarn properties

Yarn property Yarn samQle no. I N 2M 3M 4N 5M

U nevenness. U % 1 2.47 1 3 1 2 .24 1 2 .24 12 . 1 6

Unevenness, CV% 1 5 .84 1 6.52 1 5 .56 1 5 .59 1 5 .45

Thin (-50%) 38 46 20 1 3 8

Thick (+50%) 1 55 25 1 1 27 226 166

Neps (+200%) 285 304 248 253 1 79

Sub total (-50% +50%) 1 93 297 1 47 239 1 74

Sub total 478 60 1 395 492 353 (-50% +50%+200%)

Thin (-30%) 2866 327 1 2638 2684 2580

Thick (-40%) 490 585 398 307 285

Neps (+35%) 788 1 1 22 676 1 1 57 923

Thick (+ 1 40%) 846 892 754 1 474 1 075

Sub Total 4 1 44 4978 37 1 2 4 1 48 3788 (-30%+ -40%+35%)

Thin (-60%) 2 I 0 0

Thick (+70%) 3 1 48 24 26 20

Thick (+ 1 00%) 7 I O 6 3 2

Neps (+280%) 104 1 16 93 47 33

Neps (+400%) 36 36 30 I I 7

Sub total 39 60 3 1 29 22 (-60%+ 70%+ I 00%)

Hairiness index 3.5 3.3 3.66 6.25 7.29

Tenacity, g/tex 1 8. 3 1 1 9.3 1 19 .32 1 5 . 1 5 1 4.65

Elongation-at-break, % 3.75 4 3.89 4.67 4.8 1

Table 4 shows that the hairiness value of the 30 NeK yarn spun using modified cradle without spacer is higher as compared to normal cradle. This may be due to the occasional disturbance to the edge fibres by the metal clips used at the sides for l ifting the top apron (Fig . 6), though care has been taken to avoid the same. In the case of 80 Nee yarn, the increase in hairiness i ndex i s not appreciable due to the lower width of the drafting strand of 80 Nee yarn compared to that of the 30 NeK yarn.

SUBRAMANIAN & PEER MOHAMED: CONTROLLING FORCE AT THE DOUBLE APRON DRAFfING SYSTEM 535

Table 5 - Effect o f modification of cradle on classified yarn faults

Type of fault Yarn salllEle no. I N 3 M 4N 5M

A I 1 090.6 1 043.2 388 303.7 A2 266.4 229.5 59.3 77.7

A3 28.9 40.2 14. 1 I 1 . 1 A4 7.9 8.9 5.5 1 .4 B I 20.2 1 6.4 10.6 1 2 .5 B2 2 1 23.8 5 .2 6 .9 B3 7.9 7 .5 3 .3 4.2

B4 3.9 8.9 1 0.9 0

C I 1 0.5 1 7.9 5.4 I 1 . 1 C2 5.2 1 0.4 4.7 2.8 C3 3.9 3 0 1 .4

C4 1 .3 8.9 1 .8 0 D I 6.6 7.5 1 .5 4.2 D2 3.9 1 .5 4.9 2.8 D3 2.6 3 0 0 D4 1 . 3 0 3.0 0

Total short faults 1488. 1 1 430.6 5 1 8.8 439.8 E 34. 1 1 1 .9 7 .3 4 .2 F 40.7 1 3 .4 4.9 5.5 G 5 .2 1 .5 0 0 H I 49.9 32.8 6.7 1 3 .9 H2 1 49.6 1 07.3 1 2 .6 1 2 .5 I I 0 0 0 0 12 6.6 0 0 0

Total faults 1 774.2 1 597.5 550.3 475.9

4.4 Classified Yarn Faults

The classified faul ts of the yarn samples are shown in Table 5. The table shows that the total faul ts are less in the case of yarn produced with modified cradle for both 80 Nee and 30 NeK yarns. The objectionable long thick (E+G) and objectionable long thi n (H2+I l +12) faults are lower for the 8 0 Nee yarn and marg inally lower for 30 NeK yarn spun uSl l1g modified cradle.

These results corroborate the concept that the application of greater controll ing force on the floating fibres by way of reducing the spacing between the aprons, which is made possible by sui table distribution of controll i ng force i n the apron zone, would produce better quality yarn.

4.5 Tensile Property of Yarn

The breaking strength and elongation-at-break of yarn samples produced w ith d ifferent experimental arrangements are given i n Table 4. The results show

that the elongation-at-break is marginally higher for the yarns produced using modified cradle. This may be due to the lesser controll i ng force acting on the whole length of fibre in the apron zone and hence some residual elongation of fibre still present in the yarn . The breaking strength of yarn is higher in the case 80 Nee yarn and lower in 30 NeK yarn produced using modified cradle. The h igher breaking strength of 80 Nee yarn may be attributed to lower breakage of longer fibres during drafting, as the controll ing force acting on the whole length of fibre i s less with modified cradle (yarn sample no. 3M) . In the case of 30 NeK yarn, the length of fibre used for the yarn production is shorter and hence the fibre breakage may probably be not a major factor i nfluencing the breaking strength of yarn, rather less straightening of the fibres may have resulted in lower breaking strength with modified cradle.

S Conclusions 5.1 The formation of drafting wave can be avoided

by i ncreasing controlling force acting on the floating fibres, which can be achieved by reducing spacing between the aprons. H igher reduction in spacer thickness to exert h igher control l ing force on the floating fibres without causing undrafting and fibre rupture i s possible by suitably distributing the max imum possible controll ing force over different regions of main draft zone accordi ng to the requirements. The favourable d istribution of controll ing force at the main draft zone i s to provide higher controll ing force towards the front roller nip to execute better control over the floating fibres and lower controll ing force away from the front roller nip to reduce the drafting resistance in order to avoid undrafting and fibre damage. The recent conventional double apron roller drafting system has l imi tation in achieving the favourable distribution of controll ing force and warrants design modification of nose bar and cradle.

5.2 The formation of drafting wave can also be avoided by reducing the fri ction between the drafting fibres and thereby reducing the spacing between the aprons to increase the controlli ng force exerted over the floating fibres wi thout caus ing undrafting and fibre damage.

5.3 The imperfections are lower for the yarn produced using modified cradle without spacer compared to that of normal cradle w ith least possible thickness spacer due to higher controlling force towards the front roller n ip obtained with modified

5 36 INDIAN 1 . FI BRE TEXT. RES .. DECEMBER 2006

cradle. The total classified yarn faults are lower for the yarn spun using modified cradle wi thout spacer.

5.4 The strength-at-break of yarn depends on the fibre rupture during drafting particularly in the case where longer fibres are used. The elongation-at-break is higher in the yarn produced using modified cradle without spacer.

Acknowledgement The authors are thankful to AICTE, New Delhi , for

financial support towards the purchase of necessary machine and equipment and to Mis Kirloskar Toyoda Textile Machinery Ltd, Bangalore, for cooperation extended to conduct the experiments.

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