DETERMINATION OF STITCH LENGTH RANGE AND STITCH LENGTH VARIATION FOR PLAIN KNITTED FABRIC PRODUCED IN A

HAND DRIVEN SMALL DIAMETER WEFT KNITTING MACHINE

SUBMITTED BY

MD. JUBAIDUR RAHMAN 050206016 MD. ABDULLAH AL MASUM 050206028 MD. BOADRUL ISLAM SHAWON 050206096 MD. MONIRUZZAMAN 050106068 MD. RASHED IMRAN 040106079

(STUDENTS OF 4th YEAR 2nd SEMESTER, SPRING-2009)

A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF TEXTILE TECHNOLOGY OF AHSANULLAH UNIVERSITY OF

SCIENCE & TECHNOLOGY

SUPERVISED BY

A.K.M MOBAROK HOSSAINASST. PROFESSOR

DEPARTMENT OF TEXTILE TECHNOLOGY

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ABSTRACT

Stitch length is the most important knitting variable that influence knitted fabric dimensions and other properties, including weight. It is essential that the average stitch length is maintained at the required value during the entire production of a particular fabric quality. Knitting machines may be fitted with either positive or negative yarn feed system. In a positive feed system, yarn is supplied at the correct rate under low tension speed.

A negative feed system allows the knitting machine to take in as much yarn as it requires and with such a system, control of stitch length is virtually impossible since the feed rate is influenced both by yarn tension and speed.

The use of positive feed device is strongly recommended for most weft knitted structure to ensure uniform stitch length which result s in superior fabric quality and appearance.

However negative feed system holds its own significance clearly too.

Large area jacquard and similar structures whose individual needle selection causes larger fluctuations in feed rate requirements (both between feeders and at the same feeder from one revolution to the next) could be supplied from positive feed device.

So study on fabric stitch length produced by machine with a negative feed system is of greater importance for a knitter.

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By this project work values of maximum and minimum possible the stitch lengths has been found out for a hand driven socks knitting machine and also stitch length variations have been observed for different yarn counts.The work thus gives a basis to deal with negative feed system used in modern knitting technology.

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ACKNOWLEDGEMENT

Firstly we wish to convey our heartiest gratitude to almighty ALLAH.

Secondly we are indebted to Professor Dr. MUSTAFIZUR RAHMAN,

head of the department of Textile Technology of AHSANULLAH

UNIVERSITY OF SCIENCE & TECHNOLOGY.

We acknowledge our profound indebtedness & express sincere

gratitude Mr. A.K.M MOBAROK HOSSAIN, Asst. professor of

Department of Textile Technology for his constant guidance,

supervision and suggestion at all stages in the conduct of this project.

Finally we like to thank all our respected teachers of the department of

textile technology and those people who directly or indirectly helped us

in this project.

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Table of content

Chapter Topics Page no.Chapter 1 Introduction

1.1 Introduction1.2 The socks machine1.3 Research area1.4 Aims and objectives

679

1213

Chapter 2 Background study 14

Chapter 3 Organization of the project 18

Chapter 4 Result & discussion4.1 Charts and graphs4.2 Discussion

202127

Chapter 5 Limitation 28

Chapter 6 Conclusion 30

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CHAPTER: 1

INTRODUCTION

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1.1 Introduction :

The art of knitting has been rapidly progressing in the world. In our country knit sector already holds the highest position, if compared with weaving or other small sectors related to textile. Knit RMG is the highest foreign currency earning sector of Bangladesh. The industry is also growing very fast due to strong backward linkage, less capital investment requirement and higher profitability.Sock is a hosiery knit-good used for foot covering generally covers from ankle to toe. It is one of the most used hosiery products by human being. There are many sock industries in Bangladesh in which conventional hand driving sock machines are used for producing export quality socks although it is very tough to maintain uniformity across the length and width so most of these industries are importing automatic sock machines of China and India origin.In hand driving sock machine negative feeding mechanism is used. In a negative feeding mechanism the yarns are pulled into the knitting area by the needles. So stitch length varies because the tension is notuniform during knitting. This stitch length variation depends on several other vital factors such as package condition, cam position, yarn count, yarn path, tension on yarn guide, yarn type etc. It also depends on the speed of cylinder rotation especially for hand driving machine. Stitch length is an important factor for knit-goods which directly affects the GSM and draping quality of fabrics.This loop length or stitch length combines in the form of course length and it influences all other properties. Course length variation between one garments to another provide size variation within a structure produce horizontal barriness.Weft knitted structure of hosiery, knit-garments and under-garments have unique properties of form fitting i.e. body fitting based on the ability of knit loop to change shape after subjected to tension. But

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unfortunately this dimensional change occurs during production, washing and wearing which leads to customer dissatisfaction. The three basic laws for controlling loop length and loop shape are….

a) Loop length is the fundamental unit of weft knitted structure.b) Loop shape determines dimensional property; it depends upon

the yarn used and the treatment that the fabric has received.c) Loop length and loop shape relations can be expressed in term of

a simple equation.

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1.2 The Socks Knitting Machine:

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1. Clamp screw2. Needles3. Crank wheel4. Tension nut5. Heel spring6. Bobbin7. Yarns stand top8. Take-up lock9. Yarn Carrier10. Tension cam11. Cam cylinder12. Bed plate13. Cog ring14. Yarn stand rod15. Tension cam spring16. Crank wheel stud17. Crank wheel handle18. Crank wheel pin19. Needle cylinder20. Spiral band

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1.3 Research Area :

The experiment was executed at the Fabric Lab of AUST with a hand

driven socks knitting machine.

So the project work was basically dependent on the available knitting

and finishing facilities of those factories.

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1.4 Aims and Objects :

a) To learn the knitting action of a small diameter manually operated

weft knitted machine

b) To determine the maximum and minimum values of stitch length

that may be achieved while knitting with the mentioned socks

knitting machine

c) To observe the feed system of the machine and its effect on stitch

length variation due to change of yarn fineness

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CHAPTER: 2

BACKGROUND STUDY

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Some Important technical Terms:

Knitting: Knitting is the process of producing fabric by the intermeshing

loops of yarn.

Knitted loop: A basic unit of weft knitted fabrics consisting of a loop of

yarn meshed at its base with a previously formed loop.

Course: A row of knitted loops across the width of a flat fabric, or

around the circumference of a circular fabric or, a course is a horizontal

row of loops produced by the needle during same knitting cycle.

Wale: It is a vertical column of loops produced by the same needle

knitting at successive knitting cycle.

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(In this fig. the length of the curved line is stitch length)

Stitch length (SL): The length of yarn in a knitted loop.

SL=CL/total no. of needles used CL=course length

Course length: The length of yarn in a knitted course.

Feed system:

a) Positive feed: For the production of the vast majority of basic construction, positive yarn feeding is only reliable method for accurately controlling the average stitch length in a knitted fabric. This is because a positive feed system consistently delivers a predetermined length of yarn to all the needles knitting in one complete revolution of the machine cylinder.

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b) Negative feed: It exerts no control over the length of yarn which is fed to the needles. It allows the machine to take in as much as yarns required. For some complicated construction (e.g. jacquard), the length of yarn required at each feeder varies significantly. So the use of negative yarn feed is necessary.

Standard deviation (SD): It is a statistic that tells how tightly all the various examples are clustered around the mean in a set of data. When the examples are pretty tightly bunched together, the standard deviation is small. When the examples are spread apart, the standard deviation is large.

∑=summation, µ=mean, N=total no. of data, X1=1st data, XN=Nth data

Coefficient of variation (CV): It represents the ratio of the standard deviation to the mean, and it is a useful statistic for comparing the degree of variation from one data series to another, even if the means are drastically different from each other.

CV=SD/µ, expressed in percentage (%)

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CHAPTER: 3

ORGANIZATION OF THE PROJECT

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The project work was conducted in the following ways:

1. Yarns of different counts were collected from different sources.

2. Needles were arranged in the machine.

3. Stitch cam was set at different positions/heights.

4. Double yarn of same count was fed from two packages at a time.

5. Socks of different stitch length and of different yarns were

produced, i.e. each sock was produced from a fixed yarn count

and at a fixed cam position; no intermixing of count and cam

position for particular sock.

6. Course length of different socks was measured by HATRA COURSE

LENGTH TESTER.

7. Average course length was measured for particular yarn count

and for particular cam height/position.

8. SD value was calculated.

9. And finally CV% value was measured.

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CHAPTER: 4

RESULTS AND DISCUSSIONS

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4.1 Charts and graphs:

Different Course Lengths (cm):

(stitch cam at upmost position)

(20/1*2)Ne

(24/1*2)Ne

(26/1*2)Ne

(32/1*2)Ne

(50/1*2)Ne

100.5 101.5 100.0 101.5 100.5 101.5 100.5 99.5 100.5 101.0 101.5 102.0 100.5 100.0 99.5 100.0 99.5 99.0 100.0 99.5

100.5 102.5 104.5 106.5 104.0 103.0 103.5 103.0 104.5 101.5 103.0 103.0 103.0 103.5 103.5 102.5 104.5 102.0 101.5 102.5

113.5 113.5 112.5 113.0 112.0 110.5 110.5 113.0 112.0 111.5 113.0 111.0 111.5 112.0 112.0 111.5 113.0 113.5 112.5 112.0

108.0 108.0 107.5 107.5 108.5 107.0 107.0 108.0 108.5 108.5 108.0 106.0 107.0 106.0 106.0 107.0 106.0 107.5 106.5 106.5

115.0 116.0 115.75 115.5 113.5 119.75 115.75 113.5 115.0 116.0 114.5 115.25 113.0 118.5 116.5 115.0 113.25 114.0 115.75 115.0

µ 100.35SL 7.59SD 0.807CV 0.80%

103.125 7.81 1.283 1.244%

112.2 8.5 0.913 0.81%

107.25 8.125 0.858 0.80%

115.325 8.736 1.608 1.39%

µ=average course length (cm); SL=stitch length (mm); SD=standard deviation (cm); CV=coefficient of variation; Ne=English count; Total number of needles was 132

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Different Course Lengths (cm):

(stitch cam at a normal position)

(20/1*2)Ne

(24/1*2)Ne

(26/1*2)Ne

(32/1*2)Ne

(50/1*2)Ne

69.75 68.0 68.75 69.75 69.25 69.0 68.75 69.25 68.5 69.25 68.5 69.5 68.25 68.75 69.25 69.75 68.5 68.25 68.0 68.75

69.75 70.0 70.0 69.75 68.75 68.0 68.5 68.5 69.5 68.25 69.75 70.5 71.0 69.5 68.75 68.5 69.0 69.75 68.5 68.25

74.75 74.75 74.5 74.5 75.5 74.5 75.0 75.0 74.75 75.5 74.75 74.5 75.0 75.25 74.5 74.5 74.75 74.25 75.0 74.75

76.5 75.25 75.25 75.75 76.0 75.5 74.75 76.5 75.75 76.0 76.5 74.5 75.75 75.25 76.0 76.75 75.5 76.25 76.0 76.25

84.0 83.75 83.75 83.25 83.75 83.5 84.0 83.0 82.75 83.0 82.75 83.5 82.5 83.5 83.25 83.75 83.5 83.25 84.0 84.25

µ 68.825SL 5.214SD 0.597CV 0.867%

69.225 5.244 0.813 1.175%

74.8 5.66 0.331 0.44%

75.8 5.74 0.584 0.77%

83.45 6.321 0.465 0.557%

µ=average course length (cm); SL=stitch length (mm); SD=standard deviation (cm); CV=coefficient of variation; Ne=English count; Total number of needles was 132

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Different Course Lengths (cm):

(stitch cam at downmost position)

(20/1*2)Ne

(24/1*2)Ne

(26/1*2)Ne

(32/1*2)Ne

(50/1*2)Ne

67.75 67.0 67.25 66.75 66.25 66.5 67.25 65.5 67.0 65.75 66.75 67.0 67.25 66.75 65.75 67.5 66.75 65.5 67.25 67.0

68.25 66.5 66.75 69.5 67.0 68.5 67.25 67.0 68.75 67.25 67.0 68.5 67.75 67.25 68.0 67.75 68.75 67.5 67.75 67.0

71.0 70.25 71.5 70.75 71.75 71.75 71.0 71.5 70.5 71.0 70.75 71.5 71.25 70.0 70.75 71.0 71.25 70.5 71.5 70.75

70.5 72.0 71.5 71.75 71.0 71.75 71.75 70.0 71.0 71.75 72.5 72.0 71.75 71.25 70.5 70.75 70.5 70.25 71.0 71.75

80.0 80.5 81.0 80.25 80.5 81.25 80.5 80.75 81.0 80.5 80.25 80.5 80.0 80.25 81.5 80.75 80.0 81.0 80.5 80.0

µ 66.725SL 5.054SD 0.641CV 0.96%

67.7 5.128 0.777 1.14%

71.013 5.38 0.527 0.742%

71.26 5.398 0.668 0.937%

80.55 6.102 0.422 0.524%

µ=average course length (cm); SL=stitch length (mm); SD=standard deviation (cm); CV=coefficient of variation; Ne=English count; Total number of needles was 132

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4.2 Discussion:

From the above experiment we have observed that stitch length changes with the change in counts of yarns i.e, stitch length is higher for finer yarn and lower for coarser yarn. This is due to the covering ability possessed by the yarn; finer yarn gets more space and makes larger loops in a fixed area than that of a coarser yarn. Obviously all the knitting parameters (no. of needles, gauge, cam setting etc) should be remained unchanged to watch this phenomenon. Although we have observed in the graph for “cam height maximum” that stitch length of (26/1*2) Ne yarn is more than that of (32/1*2) Ne; it is due to the softness and fullness of the yarn package. The package was softly wound and full so more amount of yarn was fed into the needle. We have observed another thing that for same yarn, stitch length varies with the change in cam height or position. It happens because when cam is raised on an upper position, the needle track becomes bigger across the width so needle gets more space to move. Moreover the frictional force between the needle butt and the cam plate gets minimized with this phenomenon.

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CHAPTER: 5

LIMITATION OF THE PROJECT

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Limitations:

a) Sources were different, TPI (twist per inch) were assumed same.

b) Package size was not fully same.

c) Yarn tension was not possible to measure at different points due to change in yarn count.

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CHAPTER: 6

CONCLUSION

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Conclusion:

Finally we can say in a word that in negative feeding mechanism stitch length will be higher for higher count of yarn (English count) and also for higher position of cam.

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