Indian Journal of Fibre & Textile Research Vol. 27, June 2002, pp. 135-141

\\

Apron slippage in ring frame: Part II-Factors affecting apron slippage and their - - --

-- effect on yam qualit

e.\basj & lp ' adav ')

r- Northern India Textile Research Association, Sector-23, Raj Nagar, Ghaziabad 201 002, ndia

and

\ S M Ishtiaque 1-.

r " Department of Textile Technology, Indian Institute of Technology, New Delhi I IO 016, India

'-Received 6 September 2000; revised received and accepted 22 February 2001

LThe effect of various roving and drafting parameters like roving hank, roving TM, top arm pressure, spacer size and break draft on apron slippage has been studied. It is observed that both bollom apron slippage and apron-to-apron slippage change with the change in the above parameters. With the change in these parameters, when the apron slippage increases the yarn quality in general deteriorates and vice versa.

Keywords: Apron slippage. Break draft, Roving T M, Spacer size, Top arm pressure

1 Introduction A detailed study on apron-to-apron slippage in ring

frame has already been reported I. The phenomenon of apron-to-apron slippage and its effect on yarn proper­ties has also been studied. It has been established that the slippage between bottom apron to top apron dis­turbs the movement of fibres in the apron zone which results in deterioration of yarn quality . Apart from the apron-to-apron slippage, another apron slippage i.e. slippage between middle bottom roller to bottom apron, termed as bottom apron slippage, has also been reported. The bottom apron faces friction from the bottom apron bridge, the tension bracket and the top apron unit, giving rise to considerable slippage2

• The slippage between bottom roller and bottom apron re­sults in the change in draft distribution which affects the yarn quality.

Both apron-to-apron and bottom apron slippages depend on various factors and it is very important to know the effect of these factors on apron slippage to improve the yarn quality. In the present work, the ef­fect of various factors, like roving hank, roving TM, lap arm pressure, size of spacer and break draft, on bottom apron and apron-to-apron slippages has been studied. The effect of these factors on yarn properties

'To whom all the correspondence should be addressed. Phone: 4783586; Fax: 0091 -0120-4783596; E-mail: nitra @ndc. vsnl.neLin

has also been studied. 2 Materials and Methods

2.1 Preparation of Yarn Samples

All the carded yarns (24 Ne) were spun from 100% cotton (134 SG) with 4.2 TM at a spindle speed of 10,500 rpm. The details of sampling plan along with the yarn reference number are given in Table I. The yarn samples were prepared by changing one parame­ter at a time, keeping all the other parameters con­stant. Ten ring bobbins were prepared for each sample and tested afterwards for different properties.

2.2 Measurement of Apron Slippage

The apron-to-apron and bottom apron slippages were observed with and without roving in the drafting zone. In the present study, ten spindles were selected in such a way that their apron slippage values were very close to each other so that the mean of these ten spindles could be taken as representative slippage value. The details of slippage values both with and without materials are given in Table 2.

2.2.1 Bottom Apron Slippage

To measure the slippage between bottom roller and bottom apron, a mark was put on the bottom apron and another reference mark was put on the frame. The surface speed of the bottom roller was calculated from roller rpm and diameter. The time taken to make five complete revolutions by the bottom aprons was meas­ured with the help of stop watch. The process was

136 INDIAN J. FIBRE TEXT. RES., JUNE 2002

repeated for five times to get the average time. Then, the length of the bottom apron was measured. From the values of time and length, the surface speed of bottom apron was calculated. The bottom apron slip-page (Sb) was calculated by the following formula:

Table I - Sample details

Sample Roving Roving Middle Spacer Break re f. no. hank TM top roller size draft

pressure mm kg

SH I 0.80" 1.5 15 3.5 1.4 SH2 1.10" 1.5 15 3.5 1.4 SHJ 1.40" 1.5 15 3.5 1.4

STI 1.10 1.2" 15 3.5 1.4 ST2 1.10 1.5" 15 3.5 1.4 ST) 1.10 1.8" 15 3.5 1.4

SPI 1.10 1.5 13" 3.5 1.4 SP2 1.10 1.5 15" 3.5 1.4 SP3 1.10 1.5 17" 3.5 1.4

SSI 1.10 1.5 15 3.0" 1.4 SS2 1.10 1.5 15 3.5" 1.4 SS) 1.10 1.5 15 4.0" 1.4

SOl 1.10 1.5 15 3.5 1.1 "

S02 1.10 1.5 15 3.5 1.25" SO) 1.10 1.5 15 3.5 1.4"

Sample codes SH, ST, SP, SS and SO arc the samples prepared by changing roving hank, roving TM, top arm pressure, spacer size and break draft respecti vel y. "Yariable parameter.

Bollom apron slippage (Sb), % =

Surface speed of - Surface speed of middle bOllom roller bOllom apron

x 100 Surface speed of middle bOllom roller

2.2.2 Apron-to-Apron Slippage The slippage between bottom and top aprons was

measured by the method described earlier' . The apron-to-apron slippage (Sa) was calcu lated using the following equation:

Apron-to-apron slippage (Sa), % =

BOllom apron surface speed - Top apron surface speed x 100

BOllom apron surface speed

2.2.3 Backward and Forward Slip In the backward slip, the rovings in the roller nip

are held by the back roller, causing the bottom and the top apron to run more slower than [he bottom roller. On the other hand, the fibre strand in the front roller nip tries to pull the aprons at a faster speed, causing forward slip of apron. In the present study, always backward slippage of aprons is observed which is due to the fact that the number of fibres in the back roller nip are much higher than that in the front roller nip.

2.3 Measurement of Yarn Characteristics The irregularity and imperfections of all the yarns

were tested on Uster Tester-3 at speed of 400 m/min for I min. The thin places, thick places and neps per

Table 2 - Effect of different factors on apron slippage

Sample Middle Apron speed Apron slippage Apron speed wilh Apron slippage with ref. no. bOllom roller without roving without roving, % roving, mmls rovi ng, %

surface mrnls speed BOllom Top BOllom roller Boltom apron BOllom Top Bottom roller BOllom apron mrnls apron apron to boltom to lOp apron apron apron to bOllom 10 top apron

apron (Sb) (Sa) apron (S b) (Sa)

SH I 10.08 9.85 9.73 2.34 1.23 9.51 9.06 5.67 4 .71 SH2 13.86 13.53 13.37 2.39 1.19 12.59 12.17 9 .1 8 3.35 SH3 17.65 17.23 17.02 2.36 1.21 16.98 16.55 3.77 2.54

STI 13.86 13.53 13.37 2.39 1.19 13.38 12.98 3.49 3.03 ST2 13.86 13.53 13.37 2.39 1.19 12.59 12. 17 9. 18 3.35 ST) 13.86 13.53 13.37 2.39 1.19 12.14 11.6 1 12.46 4.34

SPI 13.86 13.32 13.17 3.92 1.14 12.06 11.59 13 .01 3.92 SP2 13.86 13.53 13 .37 2.39 1.19 12.59 12. 17 9. 18 3.35 SP3 13.86 13.45 13.31 2.97 1.10 12.93 12.56 6.72 2.85

SSI 13.86 13.40 13.28 3.32 0.96 12.66 12.33 8.68 2.62

SS2 13.86 13.53 13.37 2.39 1.19 12.59 12. 17 9 . 18 3.35

SS3 13.86 13.59 13.38 1.97 1.57 12.72 12. 15 8.28 4.49

SOl 10.89 10.63 10.51 2.45 1.15 10.20 9.90 6 .33 2.96

S02 12.38 12.09 11.96 2.30 1.10 11.56 11.17 6 .63 3.38 SO) 13.86 13.53 13.37 2.39 1.19 12.59 12. 17 9.18 3.35

DAS el al.: APRON SLIPPAGE IN RING FRAME: PART II 137

kilometer were measured at -50%, +50% and +200% levels. Yarn tenacity and breaking extension were measured on SOL Universal Tensile Tester using 50 cm test length and 10 cm/min extension rate. Average 100 readings were taken for tensile testing from each sample (10 readings from each bobbin x 10 bob­bins/sample). Hairiness index and diameter U% were measured in Keisokki Hairiness Tester, LASERS POT Model LST at a speed of 25 m/min. The details of the test results are given in Table 3.

3 Results and Discussion

3.1 EO'eet of Roving Hank on Apron Slippage Table 2 and Fig. 1 show that as the hank of the rov­

ing increases the bottom apron slippage (Sb) increases initially and after 1.1 hank it decreases, whereas the apron-to-apron slippage (Sa) always decreases. At lower hank, i.e. for coarser rovings, the thickness of the fibre strand at middle roller nip point is higher which increases the effective pressure at that point. The higher pressure at nip point causes more friction of bottom apron with bottom roller, which results in lower bottom apron slippage at roving hank of 0.8 . When the roving hank becomes finer (1 . 1), the effec­tive pressure on bottom apron decreases. This leads to the increase in bottom apron slippage. But, further increase in roving hank to 1.4 results in the reduction

E <!: '" c 0

13 (!)

"t: <Il a. S c (;j >-

10 ,--~---------~

$. 8 4> rn

'" a. ,g. 6 ·

'" c: e · a.

<{ 4

2 ·

1000

775

550 -

325

100

........ So

- '- Sa

........ Thin places (-50%)

--- Thick places (+50%j

......... Ncps (+200%)

-----..----

in slippage. This is due to the reduction in drafting force at back zone which acts as retarding force on aprons for finer hank roving. Coarser the roving the higher will be the drafting force3

. The apron-to-apron slippage depends on the thickness of the fibre strand in the apron zone. For coarser roving, more number of fibres are in between the aprons, causing less trans­mission of motion from bottom apron to top apron, resulting in higher apron-to-apron slippage and vice versa. The effect of roving hank on yarn quality is shown in Table 3 and Fig. 1. Keeping the break draft constant at 1.4, as the roving hank becomes finer the total front zone draft required to spin 24 Ne yam re­mains lower.

With the increase in roving hank, as the apron-to­apron slippage gets reduced, the yarn quality in terms of irregularity, imperfections and tenacity improves (Fig. 1). As the apron-to-apron slippage decreases, the fibre movement gets more and more smooth which results in improvement in yarn quality. Keeping the break draft same, as the roving hank becomes finer, the draft at the main draft region gets reduced to pro­duce same count of yarn. At lower level of draft, the control over the floating fibres improves which also results in improvement in yarn quality. The similar findings have also been observed by earlier work­ers4.5. Breaking elongation and hairiness have not been found affected by roving hank (Table 3).

17.2 .,------ ----'-----,

~ 16.8

>: "" Iii -g, 16.4

.~ c: Iii 16 >-

15.6 '----_ _ --' _____ --.J

11 .2 r------------,

)("10.8 2 Z o ;:: 104 . 1i m c Gl .... 10

9 .6 .. - - --- _-'-____ ---1

0. 8 1.1 1.4 0 .8 1.1 1.4 Roving hank

Fig. I - Effec t of roving hank on apron slippage and yarn irregularity, imperfec tions and tenacity

138 INDIAN J. FIBRE TEXT. RES., JUNE 2002

Table 3 - Effect of apron slippage on yarn quality

Sample Apron slippage Irregu- Imeerfections/km Tensile ero~rties Hairiness Diam. ref. no.

SH I SH2

SH}

STI ST2 STJ

SPI SP2

SPJ

SSI SS2 SS}

SDI SD2 SD}

with roving. % lari ty Sb Sa U%

5.67 4.71 16.77 9. 18 3.35 15.93 3.77 2.54 15.67

3.49 3.03 15.03 9.18 3.35 15.93 12.46 4.34 16.22

13.01 3.92 17. 12 9.18 3.35 15.93 6.72 2.85 15.71

8.68 2.62 15.96 9.18 3.35 15.93 8.28 4.49 17.20

6.33 2.96 15.80 6.63 3.38 15.82 9.18 3.35 15.93

14

~Sb

'ii 11 ___ Sa Q) (J)

'" a. n. 8 Vi c o

~ 5

Th in places

(-50%)

242 167 131

159 167 165

275 167 151

102 167 236

175 146 167

Thiek Neps Tenacity Breaking index places (+200%) eN/tex elongation. % (HI)

(+50%)

826 779 9.62 4.65 711 82 1 644 10.24 4.93 704 607 536 10.88 4.88 708

785 589 11.06 4.84 720 82 1 644 10.24 4.93 704 830 674 9.92 5.03 697

945 657 9.43 4.62 682 821 644 10.24 4.93 704 824 520 10.19 5.15 695

833 659 10.99 5.27 660 821 644 10.24 4.93 704 897 731 10.28 5.22 688

736 682 10.07 4.46 752 793 704 10.44 4.72 686 821 644 10.24 4.93 704

17

~16.5 .~ iii :; 16 (J)

.~ c iii 15.5 >-

2 L-_____ ~ ______ ~ 15

900

E ~ 700 VI c o :u ~ 500 4l a.

.~

~ 300 >-

100

r-

-+- Thin placs (-50%)

--- Thick places (+50%)

__._Neps (+200%)

1.2 1.5

11.2

~ 10.85 )( QJ ~ Z ~

10.5 ~ ·5

'" c QJ

I- 10.15

9.8 L-_____ --'-_____ _

1.8

RovingTM

1.2 1.5 1.8

U%

16.92 15.66 15.41

14.94 15 .66 15.89

17 .0 1 15.66 14.92

15.82 15 .66 17. 11

15.70 15.63 15.66

Fig. 2 - Effect of roving TM on apron sl ippage and yarn irregularity . imperfections and tenacity

3.2 Effect of Roving 'I'M on Apron Slippage

With the increase in roving TM , both apron-to­apron slippage and bottom apron slippage increase (Table 2 and Fig. 2). As the roving TM increases, the drafting force also increases6 and thi s acts as retarding force on the aprons which results in reduction in their

surface speed. The increase in bottom apron slippage with the increase in roving TM causes decrease in break draft and increase in front zone draft, so that the complete removal of roving twist in the break draft zone may not be possi ble. At the sa me time, the in­crease in roving TM results in turbulent movement of

DAS el al.: APRON SLIPPAGE IN RING FRAME: PART II 139

fibres in the apron zone due to the increase in apron­to-apron slippage. The increase in roving TM also increases the inter-fibre friction due to the more inter­fibre contact force which creates problem during smooth drafting and ultimately deteriorates yarn qual­ity. Both the above factors are responsible for the de­terioration in yarn quality (Table 3 and Fig. 2). For 24 Ne cotton yarn, the TM of 1.2 is normally on the lower side, but our repeated experimentation shows that in the present set-up it gives the optimum results.

3.3 ElTect of Top Arm Pressure on Apron Slippage The effect of top arm pressure on bottom apron and

apron-to-apron slippage is shown in Table 2 and Fig. 3. With the increase in top arm pressure, the frictional contact between bottom roller to bottom apron and bottom apron to top apron increases, which results in better transmi ss ion of mot ion from bottom ro ller to bottom apron and from bottom apron to top apron. Due to the better motion transmission, the bottom apron and apron-to-apron slippages decrease with the increase in top arm pressure when there is mate ri al in drafting zone. No clear trend is observed in apron slip when there is no mate ri a l. At the hi gher top arm pres­sure, the bottom apron and apron-to-apron s lippages get reduced and at the same time there will be better gripping of fibres at roller nip as well as within the

14

'i 11 Q)

'" ro Q.

.9- 8

c o

~ 5

--Sb

--- Sa

2 L-________ ~~ ________ ~

950 'F.::::=---- - -------,

E ~ 750 c .2 U ~ 550 OJ Q.

S ~ 350 >-

-- Thin places (·50%)

--Thick place (+50%)

- - Neps (+200%)

150 L-______ --=:!===~ _ __!

13 15 17

apron zone, which avoids fibre slippage during draft­ing. These factors result in improvement in yarn qual­ity in terms of evenness, imperfections and tenacity (Table 3 and Fig. 3).

3.4 Effect of Spacer Size on Apron Slippage Table 2 and Fi g. 4 show the effect of apron spacer

size on bottom apron and apron -to-apron slippages. With the increase in apron spacer size, the pressure between aprons in the drafting zone decreases which results in increase in apron-to-apron slippage, but no clear trend is observed in bottom apron slippage. As the apron-to-apron slippage increases with the in­crease in apron spacer size, there appears uncontrolled movement of fibres in the apron zone. The wider apron spacer size also results in uncontrolled fibre movement in the mai n draft zone due to the improper control over the fibres at the apron ex it point. Both these factors result in deteriorat ion in yarn quality which is evident from Table 3 and Fig. 4 . The simil ar trend was also reported by earlier workers7

.8

•

3.5 Effect of Break D.·aft on Apron Slippage

Table 2 and Fig . 5 show the effect o f break draft on bottom and apron-to-apron s li ppages. As the break draft increases, the bottom apron s lippage increases . This may be due to the increase in draftin g force with

17

~ ~ 'E- 16.6 . ~

:; . ~ 16.2

c

~ 15.8

15.4 '---------'---------~

10.4 r-------------~

- 10.15 x 2! Z u 'E- 9.9 o '" c OJ

I-- 9.65

9.4

13 15 17

Top ann prcssur~ (kg)

Fig. 3 - Effec t of top ann pressure on apron s lippage and yarn irregul a rity, imperfec ti ons and tenac ity

140 INDIAN J. FIBRE TEXT. RES. , JUNE 2002

10

~ Q) 8 0> co a.

.Q-Ui 6 c 0 Q. <t:

4

--Sb

---Sa

17.5 ,----------__ -:-_

:!!. 17 ::J

~ ;;; ~ 16.5

. ~ c

~ 16 f-.--- -----<I

2 15.5 '---------4. _ ___ _ ---.l

1000 11.2 ,--------------~

~ 775 -;;; .Q 13 OJ

~ 550 a. .!:' <:

~ 325

~ Thin places (-50%)

---- Thick places (+50%)

-- Neps (+200%)

100 k=========-____ -.J 3.0 3.5 4.0

~ 10.9 )( <I>

~ u 1S 10.6 'u co c

'" I-- 10.3

10 L-_________ ~ _________ ~

3.0 3.5 4 .0

Spacer size (mm)

Fig. 4 - Effect of spacer size on apron slippage and yarn irregulari ty, imperfections and tenaci ty

E ~

-;;; c 0

U ~ <I> a. .!:' c ;;; >-

10 ,---- -------------,

--Sb / ;j 8 ----- Sa ., ~ L---

.9- 6 "iii c e :t 4

2 '-------~-------.J

1000

775

550 -+-- Thin places (-50%)

----- Thick places

325 ~50%)

-r- eps

100

1.10

(+200%)

1.25

-

1AO

15.95 ,-------------- -,

~ 15.9 ~ .~ ;;; ~ 15.85

.~ c ;;; 15.8 >-

15.75 '---------'------~

10.6 ,---------- - ---,

~ 10.45 x Q)

~ o ~ 10.3 u <II c: Q)

I-- 10.15

10 '---------'-------

1.10 1.25 1.40

13reak draft

Fig. 5 - Effect of break draft 011 apron slippage and yarn irregulari ty, imperfections and tenacity

the increase in break draft at reasonably low level of draft rati03

, i.e. from 1. 1 to I A. But, on the other hand, the apron-to-apron slippage initia lly increases and then decreases after break draft of 1.25. The amount of break draft a ffects both twist and size of the s lubbing sandwiched between aprons. As the

break draft increases, the drafting force increases, which is responsib le for the increase in apron-to­ap ron slippage in itia ll y but, at the same time, the thick ness of the f ibre strand within the apron zone reduces with the break draft , resulting in red uction in apron to apron s lippage in the later stage . Also, the

DAS et al.: APRON SLIPPAGE IN RING FRAME: PART II 141

optimum break draft gives both the optimum fibre arrangement as well as minimum fibre spread at the front roller nip. The former contributes better yarn uniformity and strength and the latter reduces the end breakage rate and hairiness through increased fibre density in the cross-section of the emerging strand of fibres at the delivery roller.

Table 3 and Fig. 5 show the effect of break draft on yarn irregularity, imperfections and tenacity. With the increase in break draft, the apron slippage is found to be increased, but the changes in U% are non­significant. No clear trend is observed in yarn imper­fections and tenaci ty .

4 Conclusions Both the bottom apron slippage and apron-to-apron

slippage change with the change in various factors, like roving hank, roving TM, top arm pressure, apron spacer size and break draft, and hence the yarn qual­ity. The observations made within the experimental range are given below: 4.1 As the roving hank becomes finer, both the apron slippages get reduced and hence the yarn quality, in general, improves. 4.2 With the increase in roving TM, the bottom apron and apron-to-apron slippages increase. The irregular­ity, imperfection and tenacity also get deteriorated as the apron slippage increases with the increase in rov­ingTM.

4.3 The increase in top arm pressure results in im­provement in yarn properties, which is due to the re­duction in apron slippage with top arm pressure.

4.4 With the increase in spacer size, the apron-to­apron slippage increases, but no clear trend is ob­served for bottom apron slippage. For wider apron spacer, the deterioration in yarn properties has been observed.

4.5 As the amount of break draft increases, the bot­tom apron slippage also increases, but the apron-to­apron slippage initially increases and then decreases. The yarn irregularity deteriorates with the increase in break draft, but no clear trend is observed for imper­fections and yarn tenacity .

4.6 Apron slippage does not have any significant ef­fect on breaking elongation and yarn hairiness.

References Das A, Ishliaque S M & Yadav P, III dian J Fibre Text Res, 26 (2002)38.

2 Singh A K, Effect ofspeed-J;'(//lIe aproll slippage 011 yam qllal ­ity, M.Tech. lhesis, Indian Insli lule or Technology , Delhi , 1999.

3 Plonsker H R & Backer S, Text Res J, 37 (1967) 673. 4 Audiverl R & Vidiella J E, Text Res J, 32 (1962) 652. 5 Newlon FE & Burlcy S T, Text World, March (1964) 42. 6 Hannah M, J Textillst , 41 (1950) T57. 7 Aucliverl R, Villaronga M & Coscolla R, Text Res}, 37 (1967) I. 8 Balasubramanian N, Text Res J, 39 (1969) 155 .