DIPLOMA THESIS

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Faculty of Textile Engineering

DIPLOMA THESIS

2010

Syed Zameer Ul Hassan

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Faculty of Textile Engineering Department of Textile Technology

Analysis of fabric defect

Syed Zameer Ul Hassan

Supervisor: Prof.Petr Ursiny, MSc. PhD. DSc.

Consultancy: Ing. Petr Tumajer, MSc. PhD.

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Statement

I have been informed that my thesis is fully applicable by the Act No. 121/2000 Coll. about copyright, especially section 60 - school work.

I acknowledge that Technical University of Liberec (TUL) does not breach my copyright when using my thesis for internal need of TUL.

I am aware that the use of this thesis or award a license for its utilization can only be with the consent of TUL, who has the right to demand an appropriate contribution of the costs incurred by the University for this thesis work (up to their actual level).

I have elaborated the thesis alone utilising listed literature and on the basis of consultations with the supervisor.

Date: 10th May 2010

Signature: Syed Zameer Ul Hassan

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Acknowledgement

“An expression of thanks or a token of appreciation”

In the order

God

My parents and loving wife Prof. Petr Ursiny

Prof. Sayed Ibrahim Prof. Jiri Militky Ing. Monika vysanska Ing. Petr Tumajer Ing. Vladimir Quacic Tereza Jonaskova

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ABSTRACT

Air-jet texturing is a well-established filament yarn processing technology that has been around for more than half a century. This project analyzed a serious warp streak problem in a woven fabric produced for car seats composed of 100 % Polyester air textured yarn.

Yarn variability regarding stress-strain properties, force elongation relation, yarn diameter variations, thermal shrinkage and the structural behavior of two samples of yarn is being investigated. One of the yarn samples was producing these defects in the fabric and the other not producing this defect. Moreover the comparison of the influence of these parameters on both the samples is also being monitored. Variation in the behavior of these samples is observed.

Key words: Textured, Bulk, False twist, Streaks, Tensile strength, Elongation.

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List of Figures

Figure 1 False twist formation as [1] ... 15

Figure 2 Process flow of air jet texturing according to [5] ... 19

Figure 3 Radial Jet (a) and Axial Jet (b) according to [2] ... 20

Figure 4 Comparison for Force and Elongation... 30

Figure 5 Comparison for Tenacity and Elongation ... 31

Figure 6 Upper row is comparison of the Force values with relative frequencies and the lower row is between Elongation values... 31

Figure 7 Upper row is the comparison of the Normal P-P plot of Force and the lower row is for P-P plot of Elongation... 32

Figure 8 Upper row is the comparison of the Normal Q-Q plot of Force and lower row is for Q-Q plot of Elongation ... 33

Figure 9 Comparison of Cumulative sum Force and Elongation... 33

Figure 10 Mean stress strain curve of sample A ... 34

Figure 11 Mean stress strain curve of sample B... 34

Figure 12 Comparison of both samples for Force and Elongation ... 36

Figure 13 Comparison of both samples for Tenacity and Elongation ... 36

Figure 14 Upper row is comparison of the Force values with relative frequencies and the lower row is between Elongation values... 37

Figure 15 Upper row is the comparison of the Normal P-P plot of Force and the lower row is for P-P plot of Elongation... 38

Figure 16 Upper row is the comparison of the Normal Q-Q plot of Force and lower row is for Q-Q plot of Elongation ... 39

Figure 17 Comparison of Cumulative sum Force and Elongation... 39

Figure 18 Mean stress strain curve of sample A ... 40

Figure 19 Mean stress strain curve of sample B ... 40

Figure 20 Force Elongation curves of sample A ... 42

Figure 21 Force Elongation curves of sample B ... 42

Figure 22 Upper row is the comparison of the Force values with relative frequencies and the lower row is the comparison of the Elongation values with relative frequencies... 43

Figure 23 Force Elongation curves of sample A ... 45

Figure 24 Force Elongation curves of sample B ... 45

Figure 25 Upper row is the comparison of the Force values with relative frequencies and the lower row is the comparison of the Elongation values with relative frequencies... 46

Figure 26 Appearance of sample A on the left hand side at magnification (a)2 mm (b)1 mm (c)500 µm (d)200µm (e)100 µm (f)50µm (g)20 µm (h) 10 µm and sample B on the right hand side at same magnification (i)2 mm (j)1 mm (k)500 µm (l)200µm (m)100 µm (n)50µm (o)20 µm (p) 10 µm... 49

Figure 27 Temperature dependence of maximum shrinkage rate ... 52

Figure 28 Temperature dependence of maximum shrinkage rate ... 52

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List of Tables

Table 1 The measured values of the sample A ... 29

Table 2 The measured values of the sample B ... 30

Table 3 The mean values of force and elongation of sample A... 35

Table 4 The mean values of force and elongation of sample B... 35

Table 5 The measured values of breaking force and elongation of sample A... 41

Table 6 The measured values of breaking force and elongation of sample B... 41

Table 7 The measured values of sample A ... 44

Table 8 The measured values of sample B ... 44

Table 9 Comparison of the calculated parameters of both samples of 1^sttesting ... 50

Table 10 Comparison of the calculated parameters of both samples of 2^ndtesting... 50

Table 11 Shrinkage rate measured values of related temperature ... 51

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1 Introduction

Bulkiness has been traditionally one of the main requirements of textile manufacturers regarding protection and thermal insulation. There are several techniques used to impart bulk among which the false twist texturing and air texturing technology are much significant.

Air textured technology has the advantage of processing not only the thermoplastic filament yarns but also the other manmade and natural fibers such as viscose, viscose filament yarn and natural silk. Air textured yarns are very stable; do not show increased stretch, bulkier, softer handle and high absorption capacity.

The Literature review shows also that there is a reduction in the elongation and tenacity of air textured yarn as compared to the supply yarn and if this reduction is not in a proper order or manner then it may cause the defects in the fabric made by these textured yarns including the streakiness. The aim of this work is to analyze this problem of streakiness by realizing the relationship of breaking force and elongation of the yarns and their variations on different testing equipments. Moreover the behavior of the stress strain curves and the dispersion of the statistical observations are also discussed in this work.

Variability can arise in textured yarns from many causes. The Thermal shrinkage and structural geometry of the yarns with respect to their variability is also investigated regarding the arrangement and orientation of the fibers.

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2 Literature Review

2.1 Texturing

The basic constructional element of a yarn and of any textile product is the fibre.

The specific weight of a textile fibre and particularly its geometric properties determine the performance characteristic of a textile product from the view point of its bulkiness.

In the majority of textile products two important functional properties are required:

protection and thermal insulation. Both these can be satisfied by adequate bulkiness of the product. In general a bulky product will have to be made of bulky raw material, i.e. fibre, yarn. Thus bulkiness has been traditionally one of the main requirements of textile manufacturers.

As due to their geometric properties a great number of textile raw materials lack the necessary bulkiness there have been efforts made since long ago to impart higher bulk to such fibres. Smith and Sons Carpet Company was using stuffer box technique to improve the crimp in wools for carpet manufacture many years ago. However texturing has been always an exception of improving the bulkiness of textile raw materials.

The synthetics have low specific weight and the extremely important inherent property of thermo plasticity, which means they can be texturized and subsequently heat set (stabilized) in this textured configuration and contraction can be chemically controlled by modification of the chemical structure. For this reason synthetic fibres have become an ideal material for the production of high bulk textiles. The process in which the bulkiness of synthetic fibres, yarns and products is developed and increased is generally called “the texturing process”. Together with the progress in the development of new synthetic fibres the importance of texturing has become more and more significant. Among the synthetics the polyamides and polyesters considered to be most attractive for texturing. [1]

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2.2 Background

The first attempts were made to impart bulkiness as the continuous cellulose filament was made available. Before the Second World War Swiss company, Heberlein AG, developed a texturing method for filament yarns. According to this method a twisted or twist less filament yarn is wound onto a bobbin while at least a four times higher twist is imparted to it to be humidified eventually at a higher temperature and dried while still on the bobbin and to be untwisted subsequently through the zero point. Heberlein produced a crimped viscose filament by this method which was marketed under the name Nigrila.

The method did not find much acceptance because it did not provide a sufficiently stable crimping effect with the cellulose fibres, i.e. the viscose, cuprammonium and acetate filament yarns respectively.

However with the advent of synthetic fibres, of which polyamides were the first to be generally available, this method could establish itself firmly and it was soon followed by several other new texturing methods developed instantly one after the other.

After the Second World War the heberlein method was tried successfully with polyamide filament. Thus, e.g. according to a British patent polyamide filament can be twisted, allowed to shrink in relaxed condition and subsequently heat set and untwisted. This texturing method, which has become classical by now, imparts to the filament high bulk and stretch and guarantees a good stability of the imparted bulk. At the same time, however, it involves high cost and low productivity. Nevertheless the positive textile properties of the first textured filament yarns extended greatly the scope of applications of synthetics in a wide range of textile products. This made helpful to improve the productivity of the existing synthetic filament texturing methods.

Within a few years a number of new more productive texturing methods appeared which were based, contrary to the conventional texturing method, on continuous processing. As a matter of fact, however, these new methods provided new texturing effects in the textured synthetic filament yarns. [1]

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2.3 Properties of Textured Yarns

The products made of textured yarns have the following characteristics:

a. At a similar weight products made of textured yarns are bulkier, i.e. they are more porous, they entrap greater amounts of air and their volume weight is, therefore.

lower.

b. Higher thermal insulation.

c. Absorb moisture better and faster.

d. Air permeability is better.

e. More pleasing handle.

f. More luster and appearance. [1]

2.4 Types of Textured Yarn Technologies

Several techniques have been introduced for the increment of the bulkiness; some of them are discussed below.

2.4.1 Conventional Process

This process involves the number of turns imparted to the yarn along one meter of its length and by the heat setting process (Heberlein method).There is no exact rule defining the number of turns per meter to be imparted. The suitable number of turns per meter is a matter of individual choice and depends on the desired appearance of the fabric into which the yarn will eventually be formed. [1]

According to Heberlein the number of turns per meter can be calculated from the following formula:

T = 275,000 + 800 (1) D + 60

Where T is the optimum number of turns, and D is the denier of the yarn.

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The production of textured yarn by conventional method includes seven operations which are as follows.

2.4.1.1 Rewinding

The yarn is prepared on the convenient bobbins for the twisting machine. This operation is not obligatory if uptwisters are being used in the next step.

2.4.1.2 Twisting

The twisting operation is being done on uptwisters or on machines with double twist spindles. The amount of twist is determined by the above mentioned formula. The yarn is twisted simultaneously in both directions. Sometimes the twist is imparted in two steps. A perfectly uniform spindle rotation must be maintained throughout the twisting operation.

2.4.1.3 Heat Setting

The quality of the texturing effect is determined by the action of heat applied to the twisted yarn. It is important that the same heat be applied to the yarn on the surface of the package, in the intermediate package layers and in the bottom layers which rest on the tube. The heat setting operation is carried out in a pressure vessel, an autoclave, which is provided with pressure and temperature controls within the setting area.

Higher setting temperatures and longer setting times would result in considerable losses in the strength, elasticity and softness of the textured yarn. On the other hand, however, if lower setting temperatures and shorter setting times were used the textured yarn would not be stabilized properly and the individual yarn layers in a package would show different affinity to dyes.

2.4.1.4 Rewinding

The heat set yarn will have to be rewound only if the untwisting is carried on uptwisters. Basically it is important to choose the proper flange bobbin and the proper tension. It is also important to choose a proper rewinding machine with efficient tensioners.

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2.4.1.5 Untwisting

The untwisting operation requires particular care. Though determined by the number of turns inserted in the yarn the yarn bulk will not develop if the imparted twist were untwisted completely so the withdrawal and winding speeds must be calculated keeping in mind this phenomenon.

2.4.1.6 Doubling (plying)

The twisted yarn was heat set in its twisted form .During untwisting it was forced to uncoil, i.e. the single filaments in it were forced to open owing to their different lengths and opposite helix sense. The latent residual forces in an untwisted yarn make it return to the form in which it was heat set. This phenomenon is counteracted by doubling yarns with opposite residual forces.

2.4.1.7 Winding

The doubled textured yarn must be wound on to bobbins suitable for subsequent processing stages. They should be wound under the appropriate tensions. It is important that the cleaner blades be adjusted properly so that all knots present in the passing yarn are caught during winding process. [1]

2.4.2 False Twist Process

The false twist texturing principle makes it possible to join all the basic operations involved into a continuous process. The operations are: twisting, heat setting and untwisting and in the latest machines even plying and doubling.

The great advantage of the false twist principle is that supply bobbin need not rotate which makes it possible to diminish the twisting spindle and to have it rotating at considerably higher speeds. Another advantage is that S twist and Z twist are imparted simultaneously to two yarn sections which correspond to the respective working sections so that actually two twist turns are inserted within one spindle revolution. In the false twist principle the spindle no longer rotates the yarn package: In this case it is called a twist tube, if the yarn passes through it in the centre, or a twist pin, if the twisted yarn is wound around its rotating part.

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False twist will be inserted in a yarn if a section of it whose two ends cannot rotate simultaneously is twisted. The Figure 1shows the principle of false twist formation. It is expected that one S twist turn and one Z twist turn are inserted within one twist tube revolution. While the twist tube performs one revolution, there will be a Z twist formed in the section A and S twist in the section B. The formed twist will extend between the first point of contact, i.e. in this case between the end of the coil on the feed mechanism 2 (I) and the first bent inside the twist tube 3.within the B section it will extend between the outlet bent inside the twist tube 3 and the starting portion of the coil on the delivery system 4 (II). When the process is repeated further twist turns will be formed in the same way simultaneously in both sections I and II. The heat setting A1is applied in the section A.

If we make the twisted yarn move in the direction of the arrow in Figure 1, i.e. from the supply bobbin 1 till the final package 5, the number of twist turns imparted within the section A will be

Z = n (2) v

Where n is the number of revolutions per minute v is the speed of the yarn passage in m/min

Z is the number of turns per inserted in a 1 meter length

of the yarn.

When the yarn length containing true twist has left the section B the S twist will begin to decrease gradually until the number of Z twist turns coming from the section A into the section B balances completely the number of the opposite twist turns S. At that moment twist will be zeroed completely and the yarn will leave the delivery system 4 in its initial smooth form. The section A does not affect the number of twist turns. Within that section only that number of Z turns is distributed which corresponds to the length proportion contained in a 1m length of fed yarn and it may be expresses with the formula

Figure 1 False twist formation as [1]

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l . Z = Z1 (3) Where

Z is the number of turns corresponding to a 1m length l is the length of the section A expressed in cm

Zt is the number of turns corresponding to the section A. [1]

2.4.3 Stuffer box texturising

Stuffer box is the oldest among texturising technologies. Texturising consists of stuffing the drawn yarn which is fed against the surface, it means that the yarn is continually bended, possible broken and thus texturized.

The yarn is transported into a stuffing box. The stuffing in the box takes place either on the yarn layer already being formed or on the stuffing surface. Heating of yarn is done before this process. The stuffed yarn creates a yarn layer and it must be stabilized. The stabilization is carried out in the accumulation zone where the yarn layer is situated and where quite often a pre heated yarn is heated to the final temperature and then cooled. The layer is relieved at the end of the accumulation zone and the yarn textured and fixed is being created. This yarn is possibly properly processed in the modification drawing zone and finally wound.

The technology of stuffer box crimping (texturising) may be characterized from three aspects:

a) According to the kind of supply package material.

b) According to the yarn transport and stuffing.

c) According to the linear density of textured yarns.

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The first two aspects have a decisive influence on the device performance, properties of the texturized yarn as well as the type of technology being applied, Where as the third factor is decisive for the application of texturized yarns.

Supply package material, yarn transport, yarn layer opening, yarn heating and the yarn winding are the important parameters to be monitored for effective processing. [3]

2.4.4 Knit de knit texturing system

The synthetic filament yarns may be textured by the knit de knit method on small diameter circular knitting machines. The plain knitted fabric is heat set and subsequently de knitted. In the knitted fabric the synthetic filament yarn is shaped into loops which make a certain thickness of the fabric. After de knitting the yarn is deformed according to the loop shape and thickness of the initial knitted fabric into a three dimensional structure.

The number of crimp is determined by the gauge of the machine on which the fabric was produced.

The yarn textured by the knit de knit method has special features and its strength in comparison to yarns textured by other methods is lower due to the effect of knitting and the effect of steam on the relaxed yarn in the fabric. On the other hand it has a higher elasticity than the yarns textured by other methods. [1]

2.4.5 Air textured technology

The production of air textured yarns was launched in late 70s at the Hedva n.p. in Liberec and the yarns have been marketed under the trade mark MIRLAN. The system is covered by a Czechoslovak patent No.106, 675. [1]

Air-jet textured yarns are produced from thermoplastic, cellulosic or nonorganic filaments yarns using a turbulent fluid, which is usually compressed air. Loops are formed on the surface of the filament yarn, giving it a voluminous character. [3]

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Air-jet-textured yarns partially simulate the spun yarns because of their surface loops. The structure of an air jet textured yarn depends on the texturing parameters: air pressure, overfeeds of core and effect components, filament denier, number of filaments and positioning of coarse and fine filaments in core or sheath and vice versa. Fabrics produced from these yarns are affected by their structures and fabric construction parameters. [7]

2.4.5.1 Principle of Air jet texturing

The most widely quoted general description of the process is from Acar [6].

“When the overfed filaments enter the texturing nozzle, they are carried along through the nozzle, blown out from the texturing end, and are formed into loops which are mutually trapped in the yarn structure by the effect of the supersonic and turbulent air stream and forms a textured yarn structure. The supply yarn is normally wetted just before it is fed into the texturing nozzle by passing it through a wetting unit. Wet texturing improves the quality of textured yarn produced. Textured yarn is taken up at right angles to the nozzle axis by the delivery rollers located after the nozzle. Another set of take-up rollers, running at slightly higher speeds than the delivery rollers, may be used before the high-speed winders to apply tension to the textured yarn in order to stabilize the loops formed during the process. The textured yarn is then wound up by means of a high-speed winding unit.

Heaters can optionally be used to impart further desired properties to thermoplastic yarns, but this is not essential for the process”.

The above description is a comprehensive summary of the process. The main principles of air jet texturing system are as follows:

A. Overfeeding

Provides excess length that can be bent or twisted to be formed into loops i.e. the new surface element (bulk).

B. Bending, rotating, displacing, opening

 Transforming the excess length into loops.

 Distributing the loops three dimensionally around the three axis.

 Forming a central core that supports the surface loops by mixing the fibers.

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C. Wetting

 Imparts cohesion thereby facilitating the formation of stable core.

 Combines fibers thereby helping very fine/long fibers achieve critical stiffness to form into loops rather than being locally crinkled.

 Removes spin finish

D. Stretching

Removes any slack that may be present in the core structure thereby minimizing the instability of the structure. [5]

The process flow of air jet texturing is shown in the Figure 2.

Figure 2 Process flow of air jet texturing according to [5]

2.4.5.2 Air Jet Nozzles

The nozzle is the heart of the air texturing process. Increase in production speeds in air texturing over the years have been attributed to the development of newer more efficient nozzle designs. These newer designs have also lead to the production of more stable and uniform yarn structures. [5]

Most important is the selection of the correct jet, since the Stahle RMT-D machine is capable of processing yarns from 50–5000 denier (55–5500 dtex) but individual jets are

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limited to a narrower range. Furthermore the choice of jet is determined by the material to be processed and by the end-use and characteristics of the yarn to be produced.

There are two basic types of texturing jet, the axial and the radial. The Figure 3 shows these two types side by side. The ﬁrst is the axial jet (Figure 3 (b)). This was the ﬁrst type of jet to be developed for air-jet texturing, initially by the DuPont Company, using the trademark Taslan. The principle of the jet has remained the same for many years, but there have been many detailed improvements. There are still many Taslan jets in use from Mark XIV onwards and there is also the equivalent made by Heberlein, which has the designation EO52.

The second generic type is known as the radial jet (Figure 3 (a)).This jet was developed originally in Czechoslovakia using the Mirlan name but has been manufactured by Heberlein since 1977. Radial jets are made from both ceramic and tungsten carbide materials. [2]

Figure 3 Radial Jet (a) and Axial Jet (b) according to [2]

Function of Nozzles

When supplied with compressed air, a complex airflow pattern is produced inside the nozzle that along with rest of the air texturing machine components produces a high bulk yarn structure.

The functions of the nozzle are:

i. To push the yarn out of the main nozzle channel, thereby assisting in tensioning the yarn up to the plane of air inlet and maintaining process stability.

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ii. 3D spatial displacement of discrete as well as multi-filament groups around the axis of the yarn and within the central core. The former gives rise to the 3D surface bulk of an air textured yarn, while the latter helps form the intermingled core that not only assists in supporting the surface loops against being pulled out, but also forms the barrier regions into which subsequent filaments run into, forming loops.

iii. To open & separate discrete elements as well as multi-filament groups from the main body of the yarn thereby assisting in distributing them three-dimensionally around the yarn axis.

iv. Along with water, nozzle helps remove spin finish from the filament surface. Since the position of individual filaments of the yarn within the nozzle channel may be random along the cross section of the nozzle channel, it may be assumed that this removal of spin finish may be non-uniform along the filament length as well as between different filaments from periphery to the inner core of the yarn. This non- uniform removal of spin finish may influence the fiber to fiber frictional properties in the final air textured yarn and may be one of the contributing factors to the instability of the yarn. This fiber to fiber frictional relationship may also be responsible for the overall non-uniform structure of air textured yarns and may also serve to explain the difference between wet textured and dry textured yarns. [5]

2.4.5.3 Properties of Air textured yarns

The main properties of the supply yarn that are affected by texturing are:

a) Linear density: The linear density of an air textured yarn is always higher than that of the supply yarn

b) Elongation: The elongation of an air textured yarn is always lower than the supply yarn

c) Tenacity: The tenacity of an air-textured yarn is always lower than the supply yarn.

d) Yarn diameter: The overall yarn diameter of the textured yarn is always higher than the supply yarn. This may be considered as a statistical feature of the yarn and the comparison with supply yarn is usually based on an idealized supply yarn diameter.

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e) Appearance: Air textured yarns are always flatter in appearance compared to the supply yarns

f) Feel: An air textured yarn always feels softer compared to a flat yarn. [5]

Mechanical properties of polyester multifilament yarns are reasonably changed by air texturing. Breaking tenacities of polyester air textured sewing threads are markedly less than that of the raw polyester thread. This is due to core-wrap structure of the air-textured threads and the disordering of filaments of core threads during air texturing. Polyester threads are pretty less responsive to loop testing if comparing with straight thread test than the raw polyester yarn. Air-pressure and overfeed in texturing are influential factors in respect of stress-strain properties. [8]

Due to an increase in air pressure, the tenacity and breaking elongation of air textured yarns is reduced where as by increasing the texturing speed the yarn tenacity and breaking elongation are both dropped initially then begin to increase. [9]

2.4.5.4 Process Variables

The main processing variables in air texturing are overfeed, air pressure, stretch, operating condition, production speed, and air pressure. The variation of these parameters is believed to influence the final air textured yarn structure to varying degrees. [5]

According to Hearle [2] the process variables consists of draw ratio, hot pin or draw-pin, yarn overfeed, yarn wetting, air-texturing jet , mechanical stabilization , heat-setting, yarn lubrication and package build.

2.5 Determination of Faults (Streakiness) in Textured Yarns

Textured yarns always show variation in their behavior. “Variability can arise in textured yarns from many causes – in the feed yarn, in process conditions, or in subsequent handling and manufacturing. There may be differences in ﬁber linear density (tex) and ﬁber internal structure, which then show up in bulk and crimp. The major problem is that very small differences in shade, which are not easy to pick up by analytical methods, can be detected by the eye, particularly in uniform shades of critical colors. These differences

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may be due to physical form, e.g. bulk differences affecting luster, or to variability in dye uptake. The consequence consists of faults called barre or streakiness in fabrics”. [2]

A difference in a single yarn from its neighbors may be of too small, a size to be resolved by the eye and so will not be detectable, but when several similar yarns happen to come together, the barriness or streakiness will be objectionable. If each yarn is itself very regular, then differences between yarns are very apparent; but, if the yarns have appreciable short term variability, which is not objectionable, then the differences between yarns are less apparent. [2]

The faults in the textured yarns regarding texturing process are due to the following factors as discussed by Piller [1].

a. Irregular bulk in textured yarns.

b. Causes of uneven dyeing.

c. Yarn deterioration due to texturing.

Irregular bulk in textured yarns

This fault is apparent at sight and can be seen through. This is due to not receiving sufficient amount of twist, unequal residual twist and the temperature variation in the heat setting process.

Causes of uneven dyeing

Insufficient and incompatible dyes can cause a broader change of shade in the consequent processes. Different dye take up may be due to the more extended fibers, different density and different bulkiness in the yarn.

Yarn deterioration due to texturing

In textured yarns there is always a decrease of strength and elongation by the process. This factor of decreasing the strength and variation in it can cause defects in the further processes.

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Air textured yarns made from manmade continuous filament yarns are to be processed as warps in weaving it is usually necessary to size them to improve their tensile behavior. The main requirement in warping textured synthetic yarns is to keep a low, even and regular yarn tension as well as accurately controlled warp end tension. For a proper processing of textured yarns in all stages of textile mechanical processing the following parameters must be monitored:

a) Yarn Tension b) Yarn Path

c) Surface quality in yarn guides d) Yarn package

e) Tensioners

2.5.1 Causes of barriness

One of the most frequent faults in textile fabrics composed of textured yarns is barriness or stripiness. The main causes of stripiness during the texturing process are mentioned below as discussed by petr ursiny. [3]

(a) Fluctuation of yarn temperature at the outlet of heater.

(b) Irregular yarn tension.

(c) Irregularity of the mechanical structure of the final package.

Warp streaks may be a cause of variations in the yarn fineness, differences in the yarn twist, different volume or bulk and inappropriate texturized process. [4]

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3 Experimental Work

The aim of experimental part of this thesis was to analyze the sources of fabric defects (strip pines). The mechanical and stress strain properties of the air textured yarns were observed. Moreover the structure of the yarns was also observed under the electron microscope. The last observed parameters were the diameter of yarns with the help of NIS Elements and thermal shrinkage.

These fabrics are produced by the Fezko Industry Strakonice and they were facing the problem of warp streaks in the fabric. During our visit to the Fezko Industry on 6^th November 2009, the following observations were noted:

a) 100% polyester air textured dyed yarn of 520 dtex was being used as a raw material. The Fezko was purchasing this yarn from “AUTOFIL” company.

b) Karl Mayor machines were being used for warping. The number of ends set on warping was 4748. No sizing material was being applied during warping.

c) Jacquard Looms of “Dornier” were being used for fabric manufacturing.

d) The temperature throughout the whole process was being maintained at 25⁰C and the range of relative humidity was 40- 45%.

e) The raw material (yarn bobbins) was being tested in the testing Laboratory for dyeing uniformity, color shade, tensile strength, fineness, elongation before processing, but the frequency of the testing was very low.

f) These warp streaks were continuous on the same yarns, by moving the yarn into the selvedge area the fault disappeared in the fabric.

g) This fault occurred randomly.

h) Unfortunately access to the technological parameters of the machines and the testing reports was restricted due to some privacy policy.

i) Fabric with warp streaks was not provided which was necessary for checking the uneven dyeing.

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3.1 Material

We have been provided two samples of yarn by Fezko industry. One sample is creating the warp streaks in the fabric and the other one without creating any streaks. Both samples were 100% Polyester Air Textured Dyed Yarn of 520 dtex.

3.2 Methodology

All the testing was carried out on the basis of comparison between these two provided samples:

 Yarn creating no streaks in the fabric, Sample A.

 Yarn creating streaks in the fabric, Sample B.

3.2.1 Stress Strain Properties

The force and elongation tests were being conducted on two different testing machines i.e. Instron 4411 and Labortech.

3.2.1.1 Instron 4411

Instron 4411 testing machine was used performing the tests. The tests were provided at gauge length (500 ±1) mm, testing speed 250 mm/min and the specimen pretension of 0.260 N. The temperature and humidity of the lab was 22.6 ^OC and 60%

respectively. All the tests were processed with blue hill software.

Two tests were conducted by taking 150 measurements for sample A and sample B each and the following parameters were obtained:

 Breaking Force (N)

 Elongation at break (mm)

 Breaking Tenacity (cN/tex)

 Young’s Modulus (gf/tex)

Matlab and SPSS programs were used for the evaluation and graphical representation of these parameters.

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3.2.1.2 Labortech

Labortech testing machine was used performing these tests. The tests were provided at gauge length (500 ±1) mm, testing speed 400 mm/min and the specimen pretension of 0.260 N. All the tests were processed with Labtest software.

Two tests were conducted by taking 50 measurements for sample A and sample B each and the following parameters were obtained:

 Breaking Force (N)

 Elongation at break (mm)

 Elongation at break (%)

 Young’s Modulus (MPa) 3.2.2 Structural properties

The longitudinal view of both the yarns was observed using the Digital Microscopy Imaging, TESCAN. The yarn samples for this study were prepared precisely on SCD 030 (Balzers) quoted with gold and the images were taken at different scales; 2 mm, 1 mm, 500 µm, 200 µm, 100 µm, 50 µm, 20 µm and 10 µm.

3.2.3 Diameter Measurement

The both samples of yarns were tested for measuring the diameter using NIS Elements. Two tests were conducted by taking 850 images for sample A and sample B each for one test. The dilation was carried out with the recommended length of 51 pixels and calibration was being done at 3.67µm/pixel. These images were then processed on matlab for the measurement of the diameter.

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3.2.4 Evaluation of Thermal shrinkage

The both samples were being investigated for thermal shrinkage test using Thermal Shrinkage Tester 2 (TST 2). The samples are extracted according to the standard CSN EN 12751 (80 0070). After calibration the pretension was adjusted according to the prescribed standard which was 10.4 grams. Sixteen measurements were taken for temperature range of 50 ⁰C, 70 ⁰C, 90 ⁰C, 100 ⁰C, 120 ⁰C, 140 ⁰C, 160 ⁰C, 180 ⁰C, 200 ⁰C and 220 ⁰C for sample A and sample B, each.

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4 Results and Discussions

4.1 Stress Strain Properties

The Force and elongation test results are discussed below.

4.1.1 Results of Instron 4411

Two tests were performed on this machine. We will discuss it in steps.

4.1.1.1 First Testing

The mean values of the measured parameters are shown in the Table 1 and Table 2 for sample A and sample B respectively where as the complete tested values can be seen in the Appendix 1 and Appendix 2 for the sample A and sample B respectively. It was seen that the standard deviation, variance and coefficient of variation is on the higher side in case of sample B.

Table 1 The measured values of the sample A Elongation at

Break (mm)

Breaking Force (N)

Breaking Tenacity (cN/tex)

Energy at Break (mJ)

Young’s Modulus

(gf/tex)

Total No of Tests 150 150 150 150 150

Mean Value 132.92 16.04 30.85 934.90 154.58

Standard deviation 8.42 0.54 1.04 41.40 2.95

Variance 171.95 1.87 6.92 27353.01 159.87

Coefficient of variation 6.34 3.38 3.38 4.43 1.91

Minimum value 116.14 14.49 27.86 839.90 144.40

Maximum value 159.58 17.27 33.21 990.53 160.95

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Table 2 The measured values of the sample B Elongation at

Break (mm)

Breaking Force (N)

Young’s Modulus

(gf/tex)

Total No of Tests ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀

Mean Value 138.99 16.64 32.01 1276.89 154.57

Standard deviation 19.20 1.43 2.76 299.52 7.79

Variance 368.55 2.06 7.60 89713.56 60.61

Coefficient of variation 13.81 8.61 8.61 23.46 5.04

Minimum value 83.43 11.63 22.37 491.04 141.87

Maximum value 165.09 18.22 35.03 1679.41 188.53

The comparison of both samples for the relation between Force-Elongation and Tenacity- Elongation on the basis of the above results is shown in the Figure 4 and Figure 5 respectively. We can see the variation and more dispersion of the values in sample B as compared to sample A.

Figure 4 Comparison for Force and Elongation

11.00 11.50 12.00 12.50 13.00 13.50 14.00 14.50 15.00 15.50 16.00 16.50 17.00 17.50 18.00 18.50 19.00

0.00 50.00 100.00 150.00 200.00

Force [N]

Elongation [mm]

Comparison chart

sample B sample A

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Figure 5 Comparison for Tenacity and Elongation

The Histograms for Force and Elongation parameters with the relative frequencies is shown in the Figure 6 with sample A on the left hand side and sample B on the right hand side. The variation can be seen in case of sample B.

Figure 6 Upper row is comparison of the Force values with relative frequencies and the lower row is between Elongation values

2223 2425 2627 2829 3031 3233 3435 36

0 50 100 150 200

Tenacity [CN/ Tex]

Elongation [mm]

Comparison chart

sample B sample A

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The Normal P-P plot and Normal Q-Q plot of Force and Elongation for both samples (sample A on the left hand side and sample B on the right hand side) are drawn by using SPSS as shown in Figure 7 and Figure 8. The dispersion of the values from the mean is quite far in the case of sample B.

Figure 7 Upper row is the comparison of the Normal P-P plot of Force and the lower row is for P-P plot of Elongation

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Figure 8 Upper row is the comparison of the Normal Q-Q plot of Force and lower row is for Q-Q plot of Elongation

Also GGraphs are made for both yarn samples as shown in Figure 9 (sample A on L.H.S and sample B on R.H.S).

Figure 9 Comparison of Cumulative sum Force and Elongation

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Finally the mean stress strain curve of both yarn samples was derived with the help of MATLAB as shown in Figure 10 and Figure 11 for sample A and sample B respectively.

We can see the difference of lower strength and lower elongation in the case of sample B.

Figure 10 Mean stress strain curve of sample A

Figure 11 Mean stress strain curve of sample B

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4.1.1.2 Second Testing

The testing was repeated on the same instrument i.e. Instron 4400 and the mean values of the measured parameters are shown in the Table 3 and Table 4 for sample A and sample B where as the complete tested values can be seen in the Appendix 3 and Appendix 4 for sample A and sample B respectively. It is clearly observed that in case of sample B, the greater values of standard deviation, variance and coefficient of variation are observed.

Table 3 The mean values of force and elongation of sample A Elongation at

Break (mm)

Breaking Force (N)

Young’s Modulus

(gf/tex)

Total No of Tests ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀

Mean Value _131.83 _16.07 _30.91 _950.54 _155.61

Standard deviation _6.45 _0.47 _0.91 _35.86 _2.44

Variance _41.54 _0.22 _0.83 _1285.82 _5.96

Coefficient of

variation 4.89 2.95 2.95 3.77 1.57

Minimum value _116.13 _14.95 _28.75 _884.21 _149.39

Maximum value _152.18 _17.24 _33.15 _997.96 _162.35

Table 4 The mean values of force and elongation of sample B Elongation at

Break (mm)

Breaking Force (N)

Young’s Modulus

(gf/tex)

Total No of Tests ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀ ₁₅₀

Mean Value _136.74 _16.57 _31.87 _790.92 _154.16

Standard deviation _19.48 _1.53 _2.95 _126.70 _5.74

Variance _379.55 _2.35 _8.68 _16052.98 _33.00

Coefficient of variation _14.25 _9.25 _9.25 _16.02 _3.73

Minimum value _70.85 _9.83 _18.91 _358.79 _144.62

Maximum value _165.67 _18.18 _34.96 _974.39 _201.69

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The comparison of both samples for the relation between Force-Elongation and Tenacity- Elongation for above results is shown in Figure 12 and Figure 13.

Figure 12 Comparison of both samples for Force and Elongation

Figure 13 Comparison of both samples for Tenacity and Elongation

9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00

0.00 50.00 100.00 150.00 200.00

Force [N]

Elongation [mm]

Comparison chart

sample B sample A

18.00 20.00 22.00 24.00 26.00 28.00 30.00 32.00 34.00 36.00

0.00 50.00 100.00 150.00 200.00

Tenacity [CN/ Tex]

Elongation [mm]

Comparison chart

sample B sample A

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The Histograms for Force and Elongation parameters with the relative frequencies are shown in the Figure 14.

Figure 14 Upper row is comparison of the Force values with relative frequencies and the lower row is between Elongation values

The Normal P-P plot and Normal Q-Q plot of Force and Elongation for both samples are drawn by using SPSS as shown in Figure 15 and Figure 16, sample A on L.H.S and sample B on R.H.S. We can see the same behavior of sample B, as first testing, of being more dispersed from the mean values as compared to the sample A.

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Figure 15 Upper row is the comparison of the Normal P-P plot of Force and the lower row is for P-P plot of Elongation

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Figure 16 Upper row is the comparison of the Normal Q-Q plot of Force and lower row is for Q-Q plot of Elongation

Also GGraph is made for both yarn samples as shown in Figure 17.

Figure 17 Comparison of Cumulative sum Force and Elongation

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Finally the mean stress strain curve of both yarn samples was determined with the help of MATLAB as shown in Figure 18 and Figure 19.

Figure 18 Mean stress strain curve of sample A

Figure 19 Mean stress strain curve of sample B

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4.1.2 Results of Labortech

4.1.2.1 First Test

The mean values of the measured parameters are shown in the Table 5 and Table 6 for sample A and sample B, where as the complete tested values can be seen in the Appendix 5 and Appendix 6 for sample A and sample B respectively.

Table 5 The measured values of breaking force and elongation of sample A Breaking

Elongation (mm)

Breaking Force (N)

Breaking Elongation (%)

Young’s Modulus (MPa)

Total No of Tests 50 50 50 50

Mean Value 138.81 16.91 27.76 103.69

Standard deviation 7.66 0.41 1.53 3.21

Variance 58.71 0.17 2.35 10.30

Coefficient of variation 5.52 2.44 5.52 3.09

Minimum value 121.31 15.82 24.26 96.16

Maximum value 152.96 17.57 30.59 111.75

Table 6 The measured values of breaking force and elongation of sample B Breaking

Elongation (mm)

Breaking Force (N)

Mean Value 128.85 16.45 25.77 106.75

Variance 381.44 2.72 15.25 21.30

Minimum value 83.66 12.52 16.73 93.90

Maximum value 156.16 18.07 31.23 116.58

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The standard deviation, variance and coefficient of variation

B as compared to sample A. The graphical distribution of these tests is shown in the following Figure 20 and Figure

distributions of the values where as in case of sample B there is much variation.

Figure 20 Force Elongation curves of sample A

Figure 21 Force Elongation curves of sample B

The standard deviation, variance and coefficient of variation are greater in case of sample B as compared to sample A. The graphical distribution of these tests is shown in the Figure 21.we can see that in case of sample A there is symmetrical distributions of the values where as in case of sample B there is much variation.

Force Elongation curves of sample A

Force Elongation curves of sample B

greater in case of sample B as compared to sample A. The graphical distribution of these tests is shown in the we can see that in case of sample A there is symmetrical distributions of the values where as in case of sample B there is much variation.

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The Histograms made on the basis of the above data are shown in Figure 22 with sample A on the left hand side and sample B is on the right hand side.

Figure 22 Upper row is the comparison of the Force values with relative frequencies and the lower row is the comparison of the Elongation values with relative frequencies

4.1.2.2 Second Test

The testing is repeated on the same instrument i.e. Labortech and the mean values of the measured parameters are shown in the Table 7 and Table 8 for sample A and sample B where as the complete tested values can be seen in the Appendix 7 and Appendix 8 for sample A and sample B respectively.

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Table 7 The measured values of sample A Breaking

Elongation (mm)

Breaking

Force (N) Breaking

Elongation (%) Young’s Modulus (MPa)

Total No of Tests 50.00 50.00 50.00 50.00

Mean Value 144.91 16.93 28.98 107.35

Variance 44.58 0.12 1.78 11.96

Minimum value 131.82 15.95 26.36 100.71

Maximum value 158.23 17.63 31.65 116.34

Table 8 The measured values of sample B Breaking

Elongation (mm)

Breaking Force (N)

Mean Value 129.91 16.54 25.98 104.97

Variance 320.58 2.06 12.82 23.01

Minimum value 92.03 12.96 18.41 93.02

Maximum value 154.71 18.29 30.94 118.02

We can see the same trend of greater variation in the sample B as in the first testing. The graphical distribution of these tests is shown in the following Figure 23 and Figure 24. We can see the difference of behavior of sample B having more variation than sample A.

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Figure 23 Force Elongation curves of

Figure 24 Force Elongation curves of

The Histograms made on the basis of the above data are shown i on the left hand side and sample B

sample B is observed as in the first testing, having sample A.

Force Elongation curves of sample A

Force Elongation curves of sample B

istograms made on the basis of the above data are shown in Figure 25

on the left hand side and sample B is on the right hand side. Almost the same behavior of as in the first testing, having more dispersion as compared to the 25 with sample A lmost the same behavior of as compared to the

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Figure 25 Upper row is the comparison of the Force values with relative frequencies and the lower row is the comparison of the Elongation values with relative

frequencies

4.2 Structural Parameters

The images taken from the electron microscope were viewed in comparison of the sample A (left hand side) and sample B (right hand side). From the following Figure 26 it is quite obvious that the sample B shows quite different structural behavior of texturing.

The bulk is more as compared to the sample A and we can see the arrangement of fibers not oriented and the helix angle is increasing at yarn surface where as in the case of sample A there is more orientation. If we compare (h) and (p), we can observe the scales and quite rough appearance of the fibers of the sample B where as in case of sample A there is smooth and rather clean surface.

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(a) (i)

(b) (j)

(c) (k)

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(d) (l)

(e) (m)

(f) (n)

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(g) (o)

(h) (p)

Figure 26 Appearance of sample A on the left hand side at magnification (a)2 mm (b)1 mm (c)500 µm (d)200µm (e)100 µm (f)50µm (g)20 µm (h) 10 µm and sample B on the right hand side at same magnification (i)2 mm (j)1 mm (k)500 µm (l)200µm (m)100 µm (n)50µm (o)20 µm (p) 10 µm

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4.3 Diameter Analysis

Two tests were performed .The comparison of the calculated values are shown in the Table 9 and Table 10. The parameters Maxs (the longest possible distance between yarn boundaries), Mins (the longest possible distance between yarn boundaries) and Diameter D1 are calculated using Matlab program. We can observe the higher values and higher variation in sample B which shows more unevenness as compared to the sample A.

Table 9 Comparison of the calculated parameters of both samples of 1^sttesting

Maxs µm Mins µm D1µm

Sample A Sample B

Sample A Sample B Mean Value _601.912 _597.847 _370.268 _384.352 _637.507 _640.254 Standard

deviation ^91.0538 ^93.7562 ^55.1604 ^58.2931 ^93.0204 ^97.3794 Co efficient

of Variation ^15.1274 ^15.6823 ^14.8974 ^15.1666 ^14.5913 ^15.2095 Upper Limit _608.234 _604.352 _374.103 _388.406 _643.965 _647.003 Lower Limit _595.591 _591.342 _366.434 _380.297 _631.049 _633.506 Median _601.88 _601.88 _370.67 _385.35 _634.91 _645.92

Table 10 Comparison of the calculated parameters of both samples of 2^ndtesting

Maxs µm Mins µm D1 µm

Sample A Sample B

Sample A Sample B Mean Value _574.008 _591.264 _388.059 _381.744 _612.491 _639.504 Standard

deviation

90.2215 88.092 57.8156 59.2161 89.7364 94.3321 Co efficient of

Variation

15.7178 14.8989 14.8987 15.512 14.6511 14.7508 Upper Limit _580.052 _597.162 _391.934 _385.707 _618.506 _645.816 Lower Limit _567.964 _585.366 _384.183 _377.782 _606.476 _633.192 Median

572.52 590.87 389.02 381.68 605.55 638.58

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4.4 Thermal shrinkage Results

The measured values of all the tests can be seen in the Appendix 9 and Appendix 10 for sample A and sample B respectively. However the mean values for each sample are mentioned in the Table 11 which were being calculated by using matlab program.

Table 11 Shrinkage rate measured values of related temperature

Sample A Sample B

Temperature ⁰C

Max Shrinkage

rate [%/min] Temperature ⁰C

Max Shrinkage rate [%/min]

50 0.1200 50 0.0091

70 0.1439 70 0.2454

90 0.088 90 0.079

100 0.1201 100 0.0728

120 0.0789 120 0.0548

140 0.0945 140 0.4246

160 0.7782 160 0.8955

180 1.4671 180 1.4523

200 9.0611 200 5.7302

220 26.5516 220 35.5956

The above mention values are plotted on a scale to describe the relationship between these parameters as shown in Figure 27 and Figure 28.

DIPLOMA THESIS

Faculty of Textile Engineering

DIPLOMA THESIS

2010

Syed Zameer Ul Hassan

Faculty of Textile Engineering Department of Textile Technology

Analysis of fabric defect

Syed Zameer Ul Hassan

Supervisor: Prof.Petr Ursiny, MSc. PhD. DSc.

Consultancy: Ing. Petr Tumajer, MSc. PhD.

Statement

Acknowledgement

ABSTRACT

Table of Contents

List of Figures

List of Tables

1 Introduction

2 Literature Review

3 Experimental Work

4 Results and Discussions

Comparison chart

Comparison chart

Comparison chart

Comparison chart