Study of loop formation process on 1 x1 v bed rib knitting machine

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

259

STUDY OF LOOP FORMATION PROCESS ON 1X1 V-BED RIB

KNITTING MACHINE: THE FACTORS AFFECTING LOOP LENGTH

AND VALIDATION OF MODEL

1SRINIVASULU K,

2MONICA SIKKA,

1J HAYAVADANA

1Department of Textile Technology,Osmania university, Hyderabad, India,500007.

2Department of Textile Technology, National Institute of Technology, Jalandhar, India,

144011

ABSTRACT

A study of loop formation process on 1x1 V-bed flat knitting machine is initiated with

experiments designed by considering three knitting process variables: Yarn input tension,

Cam setting and Take down load. The interaction between these factors and their effect on

loop length and the percentage of contribution of variables on Final loop length is

determined. It was observed from the results that the contribution of cam setting on loop

length is more than the take down load which have a marginal effect only.

The proposed model is validated both experimentally and statistically. The unroved

loop length, the theoretical loop length were linearly related with an average of 5% error at

95% significance level.

Key words: Yarn input tension, cam setting, Takedown load, Unroved loop length,

Theoretical loop length.

1. INTRODUCTION

For the last twenty years by far the most important development in knitting

has been the extraordinary rise in popularity of double jersey cloth, particularly for ladies’

outwear and even more recently in outer wear garments for men. For instance, the

amount of double jersey(Rib) fabric produced today is at least three times than that

of ten years ago.

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Properties of the knitted fabrics are mainly governed by two parameters (i.e. length of

loop and shape of the loop), the shape of the loop can be finalized during relaxation treatment

but the loop length is decided during formation process only. So it is important that the stitch

length of knitted fabric should be uniformly controlled to produce a superior fabric.

Loop length plays an important role in knitted fabric production in order to meet buyer

specifications and consumer satisfaction and the investigation of geometrical loop length or

theoretical loop length which makes the production of knitted fabric easy for knitter and it

consumes time to produce the fabric of different specifications. Ultimately the rate of

production will increase if we know the theoretical calculations of knitted fabric parameters.

The loop formation process became a subjective matter of research from past 50 years,

and some studies related to loop formation process are available in literature. The mechanism

of single jersey loop formation process as explained by Knapton and Munden (1966) was

based on the concept of robbing back (%). A mathematical model of the single jersey weft

knitted process involving flat bottom stitch cam was formulated by Alsaka. Peat and Spicer

developed a geometrical model of single jersey loop formation process. A mathematical

model of single jersey loop formation process involving non-linear stitch cam and

incorporating five different stages of initial geometry of knitting zone was developed by Lau

and Knapton.

A model of single jersey loop formation process based on the concept of balancing forces

acting on needle that decides the loop forming point by Ghosh and Banerjee, and a model of

1x1 rib loop formation developed by Sadhan Chandra ray and Banerjee on dial and cylinder

machine.

In present work an attempt has made to study the impact knitting processing variables like

yarn Input tension, Cam Setting, and Take down Load on loop length and developed a

mathematical model of loop formation on 1x1 rib loop formation process on V-Bed flat

knitting machine.

The model is developed by considering two-dimensional coordinates of knitting elements by

rotating both front bed and back bed to 450 and considering the tuck point as an origin of

coordinate system. Based on 2D geometry a mathematical model has been developed for rib

loop length. The model is validated experimentally and statistically.

2. EXPERIMENTAL

2.1. Materials

The material selected for producing samples is three-ply Acrylic yarn of count 229TEX.

Experimental samples were produced on Hand driven V-bed machine by combinations of 3

processing variables (i.e. Yarn input tension, Cam setting, Take down load). For identifying

the role of one variable, and other variables kept as constant.

2.2. Methods

2.2.1. Measurement of Yarn input tension To identify the effect of yarn input tension, 9 samples were produced by varying input

tension from 5g, 15g, and 25g by keeping cam setting and takedown load constant for a set.

The unroved loop length was subsequently measured for all samples. The Tensioner used for

varying yarn input tension is spring disc type and tension variation can be measured by

tension meter as shown in figure 1.

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, M

Figure 1. Position of tension meter along yarn path

2.2.2. Measurement of Cam settingThere are 18 samples produced in order to identify the role of cam setting on loop length. The

samples are produced by keeping yarn input tension, Take down load as constant and cam

setting varying from 5mm-15mm. Out of 18 s

front bed cam setting, keeping back bed setting constant and vice versa for remaining

samples. The unroved loop length can be measured simultaneously after producing

samples.cam setting is change by rotating

Figure 3.


6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

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f tension meter along yarn path Figure 2. Digital tension meter

Cam setting There are 18 samples produced in order to identify the role of cam setting on loop length. The


15mm. Out of 18 samples 9 sample are produced by varying



samples.cam setting is change by rotating cam jack screw as in figure 3.

3. Cam jack in V-bed knitting machine


April (2013), © IAEME

Digital tension meter

There are 18 samples produced in order to identify the role of cam setting on loop length. The


amples 9 sample are produced by varying





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C1*a C2*a

β α

Stitch cam

Figure 4. Take down load set up

2.2.3. Measurement of Take down load Sample fabric were knitted over a range of 1500g, 2000g, 2500g of take down load

this is achieved by maintaining yarn input tension, cam setting as constant. There are 9

samples produced by hanging dead weights over width of 25 needles. The unroved loop

lengths are measured simultaneously after removal of weights. The take load is varied by

changing weights as shown figure 4.

3. MEASUREMENT OF STITCH CAM CHARACTERISTICS

The length of the yarn in the kitted loop is decided by stitch cam the characteristics as

shown in figure 5. Where a represents distance between neighboring Front bed and Back bed

needles, while α, β represents cam angles and C1 &C2 are some constants. The stitch cam

angles can be determined by observing movement of yarn up to knitting point.

Figure 5. Stitch cam characteristics of V-bed flat knitting machine



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4. MEASUREMENT OF YARN NEEDLE DIMENSIONS

The dimensions of yarn and needles like diameter, movement of yarn path can be

measured by using image analyzer. For each sample, one hundred readings were taken for

working out the average value. The modulus of yarn is tested on Zwick tensile tester.

The movement of yarn and configuration inside the knitting zone are taken as images by

digital camera and the dimensions of needle, wrap angles (ѲL, ѲT and δL) around the front bed

and back bed needles, angle of path (ψ) of yarn between bed verges were measured.

4.1. Observation of yarn and needle movements under Quasi-static condition By moving the hand lever very slowly, one front bed needle (FN) is made to catch the

feed yarn. In that position, a mark was applied on the yarn lying across the preceding back bed

needle (BN) with indelible ink. The coordinates of marked point and of relevant FN and BN were

recorded. The machine was moved to short distance and the new positions of the marked point

and relevant needles were recorded. This procedure was continued till the FN under observation

reached the running position after passing through the knitting points

5. DETERMINATION OF UNROVED LOOP LENGTH

The fabric was prepared in such a manner that the length of yarn forming complete

knitted courses can be unroved. The lengths of yarn are measured in a straightened state under

suitable tension (B S: 5441). The straightened state is achieved by removing the knitting crimp

and/or yarn crimp as found in textured filament yarn.

The stitch length can be calculate by counting the number of Wales available for fabric sample

and divide the course length by the number of needles used and express the results in cm.

6. RESULTS AND DISCUSSION

6.1 Effect of process variables on loop length

6.1.1 Effect of yarn input tension on loop length Loop lengths are calculated over a range of yarn input tension (from 5g to 25g) and cam

setting (from 5mm to 15mm), and take down load kept constant. The values are plotted in graph

(figure 6). And the 3-Dimensional graphs were plotted with help of MATLAB software

Figure 6 Effect of yarn input tension on loop length



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It is observed form the graph 6 that, at a constant value of take down load and cam

setting, an increase of yarn input tension level from 5g to 25 g always results in linearly

decrease in loop length. And the trend is same in all 3 level of cam setting (5mm, 10mm, and

15mm).For higher cam settings, the curves shifts upwards, the shape remains the same. In

general, the rate of increase in loop length with an increase in input tension decreases for

higher cam settings.

6.2. Effect of cam setting on loop length

6.2.1. Effect of front bed cam setting on Loop length The samples were produced in order to see the effect of cam setting on Loop length.

Loop lengths were measured over a range of cam setting (from 5mm to 15mm) and the input

tension and take down load kept as constant. And the measured values were plotted in graph

(figure 7)

Figure 7. Effect of front bed cam setting on Loop length

It is observed from the graph 7 that at constant values of input tension, take down

load, an increase in the stitch cam setting results in linearly increase in loop length at 3 levels

of back bed cam setting (5mm, 10mm, and 15mm).

The trend of the graph is nearly same as the authors worked on single jersey(Banerjee P K,

and Ghosh S,1999) and 1x1 circular Bed knitting machine (Ray S C, 2003) but the slope of

curve is different because of linear cam profile of 1x1 V-bed flat rib knitting machine.

6.3. Effect of back bed setting on loop length The samples were produced by varying back bed cam setting from 5mm to 15mm

at three levels of front bed cam setting (at 5mm, 10mm, and 15mm), the variables input

tension, take down load kept constant. The measured values were plotted on

graph (figure 8).


6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, M

Figure 8 Effect of back bed setting on loop length

From the graph it shows that the increase

cam setting but the slope of the curve is exactly linear as compared to front bed cam setting it

is due to cam profile of V-bed machine.

6.4. Effect of Take down load on Loop length Loop lengths were calculated ov

cam setting levels at 5mm, 10mm, and 15mm, and yarn input tension kept as constant value.

There were 9 samples produced in order to see the effect take down load on loop length. The

values of loop length are on graph (

Figure 9 Effect of Take down load on Loop length

It is observed from the graph that there is a nearly linear increase of loop length with

an increase in take down load. Compare to other variables there is

down load on loop length (Banerjee P K, Ray S C, 2003) and (Banerjee P.K, Ghosh.S, 1999).


6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

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Effect of back bed setting on loop length

From the graph it shows that the increase in loop length trend is same as front bed


bed machine.

. Effect of Take down load on Loop length Loop lengths were calculated over range of take down load from 1500g to 2500g and



re on graph (Figure 9).

Effect of Take down load on Loop length


an increase in take down load. Compare to other variables there is marginal effect of take



April (2013), © IAEME

in loop length trend is same as front bed


er range of take down load from 1500g to 2500g and




marginal effect of take




266

7. STATISTICAL INTERPRETATION OF EFFECT OF VARIABLES ON LOOP

LENGTH

To determine the impact of Input variables on output variable (Loop Length) the

complete data (Measured Loop length values) was analyzed by using STATISTICA

SOFTWARE. The result in terms of contribution of each variable on loop length is

determined. And the analytical data is explained by plotting graphs of input variables in terms

of chi- square value (Figure 10).

During loop formation process an interaction takes place between these three input

variables over loop length, and this interaction is explained in terms of regression equation.

The interaction result is show through regression equation in terms of F-value.

The equation as follows

�� 1.719341 � 0.0785�� 0.626�� 0.0001�� 0.00147��

Where

FCS- Front bed cam setting, BCS-Back bed cam setting, TL-Take down load, IT-

Input tension.

7.1 Impact of input variables over Loop length

0 5 10 15 20 25 30 35 40 45 50

Importanceof variables (Loop lenghth (Chi-square))

TL

IT

FCS

BCS

Figure 10. Impact of input variables over Loop length



267

8. VALIDATION OF THE MODEL

8.1 Comparison of Unroved and Theoretical loop length (From Mathematical Model)

In order to validating the model the values of unroved loop length and theoretical

values should be compared. The computed or theoretical values were determined by

generating a JAVA programme (Sinivasulu K, 2013) and the actual values for calculation of

theoretical loop length are taken from machine (angles and distances) for every combination

of samples. The computed value s of 3 variables of samples is given in table

Table 1: Experimental and theoretical (from the model) values of output variables

S.No

Unroved Loop

length(Lu)(cms)

Theoretical Loop

length(Lt)(cms)

% Error

1 2.40 2.45 -2.083

2 2.23 2.31 -3.587

3 2.10 2.16 -2.857

4 3.05 3.12 -2.295

5 2.84 2.91 -2.465

6 2.68 2.72 -1.493

7 3.65 3.70 -1.370

8 3.45 3.53 -2.319

9 3.35 3.42 -2.090

10 2.30 2.41 -4.783

11 2.60 2.65 -1.923

12 2.95 3.12 -5.763

13 2.56 2.65 -3.516

14 3.00 3.06 -2.000

15 3.40 3.45 -1.471

16 2.95 3.05 -3.390

17 3.35 3.41 -1.791

18 3.72 3.84 -3.226

19 2.25 2.41 -7.111

20 2.75 2.81 -2.182

21 3.05 3.14 -2.951

22 2.60 2.68 -3.077

23 2.80 2.96 -5.714

24 3.35 3.42 -2.090

25 3.30 3.38 -2.424

26 3.86 3.89 -0.777

27 4.60 4.71 -2.391

28 1.95 2.05 -5.128

29 2.15 2.20 -2.326

30 2.30 2.35 -2.174

31 2.60 2.61 -0.385

32 2.72 2.84 -4.412

33 2.83 2.89 -2.120

34 3.20 3.30 -3.125

35 3.42 3.52 -2.924

36 3.60 3.68 -2.222



268

Scatterplot with Histograms of theoritical loop length against unroved loop length

0

10

20

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

unrov ed loop length

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5T

he

ori

tic

al

loo

p l

en

gth

0 10 20

Figure 11. A scatter plot between theoretical and unroved loop length

From the table and graph it is observed that there is an average of 5% error between

theoretical loop length and unroved loop length, and the linear relation is given by graph

�� 0.0784 � 1.006 � �

And it is concluded that both experimentally and statistically the proposed model (Srinivasulu

K, 2013) on 1x1 V-bed rib knitting machine is feasible.

9. CONCLUSIONS

Following are the conclusions drawn from the experimental work conducted.

� An increase of yarn input tension results in linearly decreasing loop length. For

higher cam settings, the curves shifts upwards, but the shape remains the same. In

general, the rate of increase in loop length with an increase in input tension decreases

for higher cam settings.

� Back bed cam setting gives more loop length value as compared to front bed cam

setting, and the variation is due to difference in profile of stitch cam for both the beds.

� Effect of take down load on loop length is very marginal as compared to other

variables.

� The results of the work suggest that suitable combinations of variables can be used

(i.e the critical adjustment of the yarn input tension , stitch-cam setting and take down

load in conjunction with the properties of the yarn to be knitted.) to produce high

quality fabric and to meet the requirements or specifications of the buyer.

� A two dimensional mathematical model is proposed to determine the loop length of v-

bed rib knitted structure. This theoretical value can be used to produce a knitted fabric

of particular specifications. (G.S.M and Tightness factor).



269

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Study of loop formation process on 1 x1 v bed rib knitting machine