Ders notları (Lecture notes)

Eng.Des.1 ENGINEERING APPROACH TO DESIGN PROBLEM

For the solution of a design problem by an engineering approach one should make this approach in a systematic way and should also use some mathematical methods. These methods will be applied with a certain objective in mind which represents the properties and behaviour of an engineering product. The solution to such a design problem will be to determine the structural parameters of the product which will give existence to a product that shows the required behaviour or that meets certain demands concerning aesthetic and physical values and performance criteria in relation to the purpose of use. Thus the solution to the design problem will be to select those structural parameters which are called design parameters that are the right parameters giving the structure satisfying the design objective. This process is like a process of bringing together the components of the required product as if making a synthesis. In other words it is a process of selecting the right variables describing the structure. It is clear that there will be certain relations between these variables and the expected values that the product will possess and also the behaviour expected from the product. These relations may not be simple and direct relationships. Therefore for an engineering approach to the solution of this problem will be a mathematical approach. Before examining how a mathematical approach may be made to design problems it would be useful to examine main approaches adopted in industry by designers. Design approaches adopted in industry may be examined under three headings:

Analysis Approach

This is the approach widely used in industry and it may be applied with a view to obtain. –Exact reproduction –Modified version of similar product

Technical Approach

We usually apply this approach to design simple fabrics to be used for shirtings, sheetings, workclothes … etc. This usually involves obtaining a fabric of certain unit weight with a given weave and specified raw material. This is an approach somewhat near to engineering design. For this we can use –Certain tables, formulae and other useful information –Standard construction data In industry designers or design bureau managers will produce sample fabrics based on a certain design solution but in doing this they may produce a series of samples each representing a certain modification or variation af the design so as to choose the best item satisfying the requirements and expectations. This part of the process is a trial and error approach.

Aesthetic Approach

This is the approach of artists and art students and is not an approach for engineers. It is neither an approach widely used an industrial design. It is a process starting from surface appearance of the fabric and going through the technical work. -This is an approach valid for printed fabric design, jacquard fabric design and for carpet design -The technical parameters may be fixed before the design work as in the case of designing printed fabrics and carpets. -In dobby and jacquard fabrics suitable solutions are tried to be found during the process of designing In dobby designs it is more difficult to find the most suitable solution because of the fact that the number of heald shafts to be used will be fixed and limited but this affects the fabric weight and the counts of yarn that can be used. Note: Design capacity of a loom may be expressed as -Number of maximum available warp movements that can be obtained -Maximum number of heald shafts or hooks (in jacquard looms)

Engineering Approach

It will be a mathematical approach. The above approaches may sometimes be satisfactory for simple fabrics or standard fabrics with given constructions. There may however be a lot of requirements such as strength, handle, permeability, other than aesthetic and weight requirements. In this situation there are many objectives which may be represented by many objective functions and the problem is to select a set of design variable that will fulfil these objective functions. Thus the problem becomes multi-objective or multi-criteria optimisation problem.

DESIGN THEORY

In design work we assign values to a set of parameters each denoting a property of the product. These values may be numbers, colours, shapes, smells, …, etc. We may assign to these parameters countable or uncountable values. Thus we make selections from many alternatives or we assign values within a certain range which are suitable and in conformity with the requirements or design aims. We aim at a certain product which can be defined by values to be attached to certain properties.

Rules to follow selecting values:

The values should be selected within a given range for each property. Each selected value should be in harmony or compatible with all the other selected values (mutually inclusive, they must be able to exist together). The selections must be in the right direction with the aim of design. A design solution will be a set values assigned to the properties of the product provided that the above rules are obeyed. This means we will probably have more than one solution. Mathematical Formulation of Design Problem ai ≤ xi ≤ bi We must find the best solution, or the most suitable solution. Some of the variables may be dependent upon some other variables such as

Eng.Des.2

where xj is a dependent variable and xq, xr, xs,… etc. may be independent or not. x1, x2, x3, ….., xn will represent a solution with n variables obeying the restrictions Eng.Des.3 Eng.Des.5

This is an optimization problem If we have more than one objective function than we shall have a multipurpose or multi-criteria optimisation problem.

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Unit weight of fabric (g/m2)= Objective Function (Target function)

G1≤W≤G2 k1=Crimp factor (warp), k2=Crimp factor (weft), S= Yarn density (Sett), Fw= Weave value, d= Yarn diameter Eng.Des.8

GarmentDesign-1

PRINCIPLES OF GARMENT DESIGN

Garment: A garment is a three dimensional structure constructed using a certain fabric supported by auxiliary materials with a purpose to fit a human body or a part of a human body.

In garment design the factors involved (design steps) are:

USAGE-MARKET DEMAND-FASHION-MATERIALS-MODEL-DIMENSIONS-PRODUCTION TECHNOLOGY

ACCESSORIES AND ORNAMENTATION-COST

PRINCIPAL COMPONENTS OF GARMENT DESIGN:

Principal components of garment design are: material, form, construction and dimensions.

They are the factors which define a certain garment or garment type or more precisely the product type. The starting point of a design work for garments is a thorough (extensive) market research.

GarmentDesign-2

The product type will depend on the usage in relation to market research.

The garment will be defined by dimensions, materials (including accessories), form and construction.

The dimensions will be determined as based on market research and on the characteristics of the target population.

The materials will be influenced by usage, technology, fashion and cost.

The form and materials will also affect each other because we have to select right materials for the required forms and also the properties of the material may affect the form.

CONSTRUCTION

The construction will be defined as based on materials and form, because if we have a light weight material as the main fabric we might have to use some supporting material or select simpler constructions etc.

The construction is affected by the technology, fashion, dimensions, model and by the cost.

GARMENT MEASUREMENTS

Having determined the dimensions of the body we have to derive the dimensions for the actual garment, which will be termed as garment measurements. Garment measurements are effected by the form and the construction of the garment which themselves are effected by fashion and also by technology in relation to fabric characteristics and to mode of use of the garment.

Production will be affected by the materials, construction and garment measurements.

Production process will include the works to be done for pattern development to define the final shape and to select the cutting, sewing and pressing techniques as well as production planning.

In the design process there will be feedbacks or reconsiderations to complete the design, which will satisfy the requirements. These feedbacks may lead us to change our decisions abut materials, forms and construction and in some cases the production processes.

ASPECTS OF GARMENT DESIGN

Having determined the dimensions of the body we have to derive the dimensions for the actual garment, which will be termed as garment measurements. Garment measurements are effected by the form and the construction of the garment which themselves are effected by fashion and also by technology in relation to fabric characteristics and to mode of use of the garment.

Production will be affected by the materials, construction and garment measurements.

Production process will include the works to be done for pattern development to define the final shape and to select the cutting, sewing and pressing techniques as well as production planning.

In the design process there will be feedbacks or reconsiderations to complete the design, which will satisfy the requirements. These feedbacks may lead us to change our decisions abut materials, forms and construction and in some cases the production processes.

FASHION

The fashion, also, is defined  by these components. It is usually declared one or one and half years earlier.

This is because the fabric will have to be produced first, which may take some six months and the garment will be produced in a certain time before the season starts.

There must also be time for delivery and presentation to the customer which may include advertisements, fashion shows, exhibitions etc.

FASHION DESIGN

Fashion design is making a fashion drawing together with preparing garment specifications.

Fashion drawing does not actually show how the garment will be seen actually on the body, but it aims at showing the reflections rather of the aesthetic design components namely image, colour, model etc. Therefore it does not have to reflect the real garment dimensions and fabric characteristics.

Fashion drawing may exaggerate certain features of the model and materials to bring out into focus the image to be created. Thus it is necessary to provide a technical drawing along with it to give adequate information for pattern development work.

COMPONENTS OF A GARMENT DESIGN WORK

Components of a garment design prepared as a project may be in the following order and structure:

Fabric specifications (depending on usage, aim of the garment  and season)

Garment construction (with a view to usage and fashion)

Accessories

Stylistic drawing (Fashion drawing)

Block patterns

Unit material costs

Process flow (flow chart)

Operations list (list of operations including diagrams, machine types, workforce requirement, standard times

Estimated unit cost

PATTERN DEVELOPMENT

The first step in pattern preparation is to develop a “Block Pattern”. This is the basic pattern and it is a pattern to fit a body of average size irrespective of model or fashion. It is prepared from body measurements to give a good fit to the body defined by measurements.

There are various relations or proportions between various body measurements. Thus body measurements are not independent  of each other. This leads to the belief that there must be certain fixed proportions between them. For example, if we take the chest circumference and shoulder width, there will be a fixed ratio between them in the same person.

However,  we know that people have different body shapes. Some people are tall, some are short and some are fat. So there must be different proportions between body measurements of people of different body shapes. In this case the proportions between related measurements may vary depending on body shapes. Conversely, body shapes may be defined by these differing proportions.

BODY SHAPES

However, it is the usual practise to classify the bodies into categories based rather on anatomical characteristics first and then to define these categories by the proportions of certain body measurements. Even then there will be different body sizes within these categories giving different body measurement values.

So the best is a statistical approach to a certain population represented by a sample and this sample must to have been based on market research.

The anatomical way of classifying bodies is by “Somatotypes”. This approach defines three different body types:

Mesomorphism, Endomorphism, Ectomorphism

BODY TYPES

Endomorphy   Mesomorphy  Ectomorphy

Mesomorphism defines an athletic or sportive body with muscular structure.

Endomorphism defines a body with high fat content with round features.

Ectomorphism defines a body with less fat content, tall stature and thin limbs

Body Types

Another way of classifying body types is classifying bodies in four categories as:

Short-stocky

Normal

Fat with belly

Tall and thin

Another type of classification is according to body height in three categories:

Short

Medium

Tall

In all these classification systems a size is also specified which is expressed by half the chest circumference in cm.

A measurement called “drop” which is half the difference between chest circumference and waist circumference may also be stated. This reflects to some extent the body shape and may be considered as another system of classification of the body shape.

 

 

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ÖRNEKLER

 

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Bu örnekte “Dubldra” olarak da bilinen iki yüzlü çift katlı bezayağı kumaşın sıkıştırılmış bölümler ve fantezi iplikler içeren bir türünün yüzey görünümü ve örgü yapısı gösterilmiştir. Verilen tarak planı ile kumaş yüzeyinde parlak bölümlerle çizgi efektleri elde edilmektedir. Kumaş esnek bir yapıdadır.

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Burada motifte kullanılan çerçeve sayısının yarısı ile aynı motifin simetrik düzenleme ile elde edilişi gösterilmektedir. Ancak, tek katlı olarak elde edilen bu kumaşın zemin örgüsünde motifin yerleştiği bölümde dimi çizgilerinde yön değiştirmeler ortaya çıkmaktadır. Diğer yandan, aynı çerçeve sayısı ile motifler iki kat daha büyük boyutta da elde edilebilir.

 

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Bu örnekte tek katlı motifli bir kumaş yapıya zemin örgüyü bozmadan artık atkı ve çözgü iplikleri kullanarak elde edilmektedir. Bu iplikler yalnızca motif oluşturma amacıyla kumaş yüzeyine çıkarılmakta, zemin bölümlerinde kumaşın arkasında yer almaktadırlar. Bu ipliklerin kumaşın arkasında uzun iplik atlamaları oluşturmaları durumunda zemin atkı ya da çözgü iplikleriyle bazı noktalarda yüzeye çıkarılarak bağlantı yapmaları sağlanarak kumaş yapısının dayanıklılığı sağlanır.

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Bu çift katlı motifli kumaş yapısında kumaş yüzeyini oluşturan atkı ve çözgü iplikleri ile kumaş arkasını oluşturan atkı ve çözgü iplikleri motif çevresinin aynı çizgisi üzerinde yer değiştirtilerek hem motif konturu ortaya çıkmakta, hem de iki kumaş katı birbirine bağlanmaktadır. Kumaşın yüzünü ve arkasını oluşturan ipliklerin farklı renklerde düzenlenmesi ile motif renkli olarak elde edilecek, iplikler yer değiştirdikçe renkler de yer değiştirecektir.

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Bu simülasyon 3D-Max yazılımı kullanılarak iki boyutta çizilen iplik eğrileri ve bunlarla oluşturulan kumaş kesit diyagramlarından  üç boyutlu kumaş yapısını göstermek için geliştirilmiştir (Soydan ve Başer, 2005).

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Karmaşık yapılı kumaş kesitlerinin video gösterimi (Soydan ve Başer, 2005).

Türkhavlusu

 

Yüzyüze Halı

AtkıKadifesi

WEAVING  TECHNOLOGY  AND RECENT  PROGRESS  ON  WEAVING  MACHINERY

Prof. Dr. Güngör BAŞER Dokuz Eylül University, Faculty of Engineering, Department of Textile Engineering- İZMİR, 2006

  1. GENERAL INTRODUCTION

Weaving is an ancient technique to make up a fabric by the intersection of two sets of yarns at right angles to each other.  These sets of yarns, namely the warp and weft are interlaced with each other in a certain manner to form a structure which must be stable and uniform. The manner in which warp and weft yarns are interlaced together by passing over and under each other is called the WEAVE. Such a structure is known as a WOVEN FABRIC, but there are other ways of obtaining a fabric. A TEXTILE FABRIC may, essentially, be considered as a sheet of fibrous material with a uniform surface and a rather soft and flexible structure. Therefore it is possible to form fabrics directly by fibres having the abovementioned properties. Such fabrics are called NON-WOVEN fabrics. The method of knitting, however, achieves the formation of a fabric structure by joining  sets of yarn loops by passing each newly formed loop through the previous one. Whatever method has been used to form a fabric,  a certain degree of  COVER must be provided on the fabric surface, because a textile fabric has the primary function to cover surfaces such as of  a human body, furniture, floors etc. The structures like fishnets with insufficient cover and like a wire mesh with no flexibility will not conform with the definition of a textile fabric. In woven and knitted fabrics the cover is obtained by the yarns lying on the surface of the fabric. Stability, on the other hand, is obtained by the structural character of the weave plus the DENSITY or SETT of the yarns on the fabric surface. Uniformity is, hovever, obtained, by the orderly arrangement of interlacings of the yarns in the weave and by the perfection of the actual weaving process. A final requirement for a fabric, especially for those that are woven, is the STRENGTH and ELASTICITY. A fabric must stand up to various strains during use and should also recover from deformations after the deforming effects are removed. Weaving is also an art, and a very ancient art too. The way the warp and weft yarns interlace form certain patterns on the fabric surface. These WEAVE EFFECTS impart the fabric different appearances and will be the source of a certain TEXTURE on the fabric surface. Thus, surface texture is considered, also,  as an AESTHETIC property. Surface texture will affect the handle and certain physical properties of the fabric, such as moisture absorption, warmth, air permeability etc., as well as fabric appearance. The appearance characteristics are very important for textile fabrics. Apart from the weave effects, COLOUR, COLOUR AND WEAVE EFFECTS, FIGURE OR MOTIVE EFFECTS and SHINE are other aesthetic surface properties of woven fabrics. The basic properties for a woven fabric can be summed up as STRENGTH, STABILITY, UNIFORMITY, ELASTICITY, FLEXIBILITY, COVER, AESTHETIC VALUE and APPROPRIATE SURFACE PROPERTIES.

Woven fabrics have superiority in many aspects associated with these requirements, over both knitted and non-woven fabrics. They have strength, good cover, fine texture, stability and wide possibilities to be furnished with aesthetic values. Nevertheless, it may be said that it is a more costly way of making fabrics. This has been the driving force in such remarkable progress in the knitting and non-woven technologies. But with recent  developments in modern weaving technology, weaving has revived its high status once more. However, the superiority of the knitted fabric to adapt itself better to the sape of human body is worth mentioning as an exception to the general rule. The unique properties of the woven fabric stem from the fact that sections of yarns can be placed parallel and much closer to each other in a woven fabric and the fabric thickness is less influenced by factors like type of weave, sett, yarn count etc. than in knitted fabrics. The three dimensional structure of the knitted loop and the effect of yarn rigidity on the size of the loop tend a knitted fabric of the same yarn count to be thicker. A denser structure in the woven fabrics , however, results in higher material cost. Thus two important problems in the manufacture of woven fabrics are HIGH MATERIAL COST and LOW PRODUCTION RATE. Therefore, the main task of the woven fabric manufacturer will be to produce a fabric of low material cost at a sufficiently high production rate without endengering any of the abovementioned basic quality requirements. 2. PRINCIPLES OF WEAVING The basic principles of weaving can be explained in the following way: In order to form a woven fabric structure one set of yarns, namely the warp, must be prepared and placed on the weaving machine, called the LOOM, as a sheet of parallel yarns under some tension . The weft yarn is, then, to be inserted in between the warp yarns at right angles in a way to make the required interlacings.

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Figure 1:The basic principle of weaving

To achieve this, warp yarns have to be separated into two groups, one group being above the other, thus forming a gap in between through which the weft yarn can be placed by a certain means. This gap is called the WARP SHED and the means used to insert weft may be a SHUTTLE or some other instrument. Dokuma-002  

Figure 2: Shed formation

The formation of the fabric is achieved by the loom with the application of the following five basic motions: 1- SHEDDING: Separation of the warp yarns into two sheets 2- WEFT INSERTION ( PICKING): Insertion of the weft yarn between the warp yarns 3- BEATING UP: Pushing the weft in between the warp threads to be entrapped in the cloth structure 4- WARP LET OFF: Feeding in of the warp by letting off the warp beam 5- CLOTH TAKE UP: Drawing of the fabric to be wound on the cloth beam

The first three of these motions are the MAIN MOTIONS for the fabric formation and the last two are COMPLEMENTARY MOTIONS to ensure the continuation of the weaving process under stable conditions. Beating up motion is affected by the forward movement of the REED between the warp yarns which have previously been separated into two sheets to carry the weft to the line at which fabric forms. This is so synchronised that the beating up action takes place when the shed just starts to change and thus at the completion of this motion the weft is entrapped between the warp yarns in the cloth structure . The let off motion is a feeding action, whereas cloth take up means the production of the cloth. All the looms whether handloom or powerloom must have all these five motions, the first three of them for the formation of an interlacing, the last two for ensuring the continuation of the weaving process. The semi-automatic looms, on the other hand, will have additional motions which are called AUXILIARY MOTIONS to enable the effective control of the weaving machine by the loom itself. These are such motions as WARP STOP MOTION and WEFT STOP MOTION to stop the loom automatically when breaks occur, SHUTTLE CONTROL to ensure that there is sufficient weft yarn left on the pirn and BOX CONTROL to ensure that the shuttle is properly placed in the box- both of them incorporating automatic stop motions- SHUTTLE PROTECTION, WARP PROTECTION or REED PROTECTION MOTIONS as safety measures. There will also be a SELVEDGE CONTROL provided by temples. In weaving with coloured yarms on shuttle looms, a multiple shuttle box arrangement to weave with more than one shuttle, each carrying a a weft of different colour is provided. It will, then, be necessary to have a SHUTTLE  BOX  MOTION that will bring the shuttle carrying the weft of the desired colour to the picking position. Automatic looms, on the other hand, have a WEFT REPLENISHMENT MOTION  and usually weave with single colour weft. This motion will either be a PIRN  CHANGING or a  SHUTTLE  CHANGING operation. The shuttleless looms on which the insertion of weft is achieved by other means have special colour selection mechanisms.

2.1. CLASSIFICATION  OF  LOOMS

The classification of looms as HANDLOOM, POWERLOOM, SEMI-AUTOMATIC  LOOM and AUTOMATIC  LOOM  is one based on the way man and machine work together to perform the weaving process. In a handloom all the motions of the loom are performed by the weaver using manpower. The weaver opens the shed, picks the weft, beats up the weft and also performs the tasks of letting the warp and winding the cloth as weaving proceeds. He will also control the pickspacing and  selvedge formation. In a powerloom the movement of loom parts are achieved by the power supplied by a motor. But, still, the weaver will control the process and will repair the broken picks and ends as these will be frequently occurring events in weaving with a powerloom. In the semi-automatic looms the control of the process is achived by the machine itself through certain motions called automatic stop motions and various control  and protection mechanisms. In automatic looms, however,  there will be a weft replenishment motion in addition to all the auxiliary motions provided in semi-automatic looms. As the machine becomes more automatic, the tasks of the operator, weaver in that particular case, are reduced, and it, then, becomes possible for the operator to tend more than one machine. In such a situation, however, there will be some losses of the productive time of the machine due to a phenomenon called MACHINE INTERFERENCE. This is because the operator may be busy in repairing a machine while a second machine may stop within that span of time and will need repairing. Thus an optimum number of machines to be assigned to one operator has to be found, which will reduce labour cost without giving rise to significant production losses. It may also be pointed out here that the method of servicing the machine will depend on both the type and number of  machines assigned. Another way of classifying looms is based on the shedding motion which  follows: 1.  TAPPET LOOMS 2. DOBBY LOOMS 3. JACQUARD LOOMS In tappet and dobby looms warp yarns are controlled by HEALD SHAFTS which carry those warps that will move up or down together  through all successive sheddings(or pickings). In tappet looms the heald shafts are pulled by connections activated by eccentric cams called TAPPETS.  There will be a tappet for every different warp movement. The number of tappets used does not generally exceed eight due to physical limitations. This limits the types of weaves that can be obtained with a tappet loom. Dokuma-3

Figure 3: Positive tappet shedding mechanism ( 1. Treaddles, 2. Tappet-eccentric cam, 3. Fulcrum, 4. Follower, 5. Heald shaft, 6. Pulley system, 7. Warp )

For more complicated weaves a dobby loom  will be needed which gives up to 24 warp movements (Figure 4). Although dobby looms providing 36 warp movements were used in the past, this did not become common practice. Dokuma-4

Figure 4: Negative dobby shedding mechanism ( 1. Driving rod, 2. T- lever, Knives, 4. Hooks, 5. Dobby arm, 6. Connecting lever, 7. Stoppers, Needles,  9. Feeler levers, 10. Pattern Wheel, 11. Heald connections, Heald shaft, 13. Spring

For more complicated weaves and larger figured and motive designs a jacquard loom is needed which provides a much larger number of independent warp movements (Figure 5).   Dokuma-5

Figure 5: Simple Jacquard shedding system ( 1. Lifting table, 2. Hook, 3. Knife, 4. Needle, Card cylinder, 6. Guide board, 7. Spring box, 8. Control board, 9. Harness cord, Harness thread, 11. Comber board, 12. Heald eye, 13. Shed

One can get precise and secure warp movement with tappet looms. Thus for heavy industrial fabrics and high speeds of weaving a tappet motion is preferred. The shedding motion obtained with a jacquard mechanism is comparatively slow, but when high DESIGN CAPACITY,  for example 400, 600, 1200, 1800 warp movements, is required there is no other alternative. There are jacquard mechanisms like DOUBLE LIFT and DOUBLE CYLINDER to give a higher rates of picking but this will make the weaving process  more complicated. So slowness was considered as  an inherent character of jacquard shedding, but after the introduction of electronic jacquard mechanisms in recent years this is not a valid argument any longer. An equally important way of  classifying looms is one based on the type of  the picking motion. From this point of view  looms are grouped into two large groups as CONVENTIONAL  and  MODERN LOOMS. The conventional looms use a shuttle for picking and are thus named also as SHUTTLE LOOMS. Although modern looms are most often named as SHUTTLESS LOOMS not all of the modern or non conventional looms may be regarded as shuttles. In conventional picking the weft yarn is carried in a shuttle which is a box carrying the weft yarn as it is pushed across the shed at a great speed by the striking action of picking stick. The shuttle has the shape of a vessel  with pointed tips and carries the weft inside its hollow part. The weft is placed in the shuttle in the form of a  package  called the PIRN or QUILL as weft yarn wound onto a cop ( Figure 6 ).  In modern picking a different type of  shuttle may sometimes be employed ( as in circular looms), but the shuttle is usually eliminated. The principle is to draw  the weft  directly from the weft bobbin by means  of weft carriers such as projectiles,  needles, rapiers. etc. There are also systems in which the weft is pushed across the shed by the drag of a strong water or air stream created by the action of JETS.

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Figure 6: Shuttle and pirn types

A general classification of looms according to picking motion is as follows: CONVENTIONAL LOOMS 1. WHIP PICKING LOOMS 2. PUSH PICKING LOOMS a. Underpush Picking b. Overpush Picking MODERN LOOMS 1. GRIPPER LOOMS ( PROJECTILE LOOMS ) 2. RAPIER LOOMS a. Single Rapier * Needle Type *  Hooked Rapier Type b. Double Rapier *  Rigid Rapier * Flexible Rapier * Telescopic Rapier 3.  JET LOOMS a. Water Jet Looms b. Air Jet Looms 4.  MULTI PHASAE LOOMS a. Circular Looms b.  Straight Multi-Phase eLooms In conventional weaving the whip picking in which the shuttle is pushed by the pulling action of a leather strap fixed to the picking stick placed above the weaving level is no longer in use. Underpush picking is usually preferred in which picking is achieved by the pushing action of the picker attached to the end of a picking stick  (Figure 7). In both cases the picking stick is activated by a picking cam of appropriate design to obtain a sudden movement. Although the shuttle looms are rapidly being replaced by the modern looms which have now all the versatility, there are still many shuttle looms being in use all over the world in many countries. In the class of modern looms called gripper looms a small shuttle which is also termed as projectile carries the weft yarn that it draws from the bobbin through the shed. This projectile catches the end of the yarn by its clips at its end and is accelerated by a picking arm activated by a torsion rod ( Figure 8 ).

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Figure 7: Picking mechanism ( 1. Picker, 2. Picking stick, 3. Lug strap, Vertical shaft, 5. Horizontal shaft, 6. Picking cam, 7. Cone, 8. Shuttle )

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Figure 8: Sulzer projectile picking system ( 1. Picking arm, 2. Picking cam, Torsion rod, 4. Connecting lever, 5. Cam shaft, 6. Shaped lever arm, 7. Follower, 8. Fulcrum, 9. Guide element )

In rapier looms the weft yarn is drawn from the bobbin by either the eye of a needle shaped long  rapier or by a hoook attached to the end of a rapier ( Figure 9 ).

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Figure 9: Weft insertion by needle rapier system (Jurgens loom)

In double rapier systems there are two hooked rapiers working in opposite sides. One of them takes the weft from the bobbin and brings it half way through the shed. The other moving in the opposite direction takes over the weft yarn and carries it to the edge of the fabric, as a conseqeence, a weft transfer action being performed. In flexible rapier version the hooks are carried on flexible bands of metal whereas in telescopic version the rapiers are moved outwards from inside a cylindrical pipe each,  thus occupying a narrower space over the loom frame ( Figure 10 ).

Figure 10: Telescopic rapier weft insertion system ( 1. Rapier, 2. Moving tape, Pulleys, 4. Loom frame )

In jet looms a water or an air jet is provided through which the weft yarn passes and is carried through the shed by the water or air blown out of the jet nozzle at a high pressure. In multi- phase looms, however, more than one shed are opened across the warp sheet and more than one weft yarn are inserted into the appropriate shed at the same time as being carried by special carriers or shuttles. In shuttless looms there are special selvedge forming and colour selection mechanisms to make them as versatile as shuttle looms. These looms are usually provided also with a weft feeder or weft accumulator. The weft feeder  draws the weft yarn from the bobbin in a measured length and accumulates it in order to insert the same length of weft at each picking, since picking is done from the same side of the loom. The weft inserted is cut off at each time. There is also another way of classifying shuttle looms which is based on the box motion. If picking is done alternatively, it is called ALTERNATIVE PICKING and the loom is termed as a PICK-AND-PICK LOOM. In colour weaving with shuttle looms picking has to be done freely from any side of the loom instead of once from one side, second time from the other. Looms with this construction are called AT WILL PICKING  LOOMS. In this type of looms there will be a CLUTCH mechanism on the picking system to disengage the picking mechanism when picking is to be done from the other side of the loom. Looms are also defined in terms of the cloths that can be woven on that particular loom, e.g. CARPET LOOM, COTTON LOOM, RIBBON LOOM, etc. A loom should be built up with certain auxiliary mechanisms needed for  weaving  certain types of fabric and should be rebust  enough to withstand the mechanical strains occurring during weaving .This necessitates different loom designs for different fabric types. This sort of classification of looms  helps to define a particular loom in its mechanisms and characteristic features. It will also help in choosing a particular loom to weave a particular fabric. The best choice of the loom may only be made from among those that are suitable to weave the cloth in question. Only then the factors such as speed, cost of labour and maintenance may and should be considered. This attitude will also secure the fabric quality to some extent.

2.2. PROCESSES PREPARATORY TO WEAVING

Warp and weft yarns have to be prepared , prior to weaving, in a certain way which makes them suitable for transportation and convenient to be placed on the loom in a certain fashion. The warp is prepared on a flanged roller called the WARP BEAM as a set of yarns  wound side by side in equal spacing and under equal tension. Requirements for the warp are as follow: The warp yarns should be PARALLEL  TO  EACH OTHER, EQUALLY  SPACED, EQUALLY  TENSIONED, PLACED  IN  THE  ORDER  AS  THEY  WILL  APPEAR  ON THE FABRIC, STRONG  ENOUGH  TO  WITHSTAND  STRAINS  AND  FRICTION DURING  WEAVING The last requirement may necessitate, as in weaving with single’s cotton yarns or  filament yarns, covering the warp yarns with a suitable material such as starch, glue etc. This process is called SIZING. The preparation of the warp on the warp beam may be done in two different ways: DIRECT TO BEAM WARPING SECTIONAL WARPING In direct to beam warping the warp yarns which have been placed in the bobbin form on a CREEL of large capacity are drawn off and wound on to the warp beam directly in a single process. This will only be possible when the total number of warp ends is not so high and when weaving a uniform colour fabric. In cases when sizing is to be done, however, direct to beam warping is an intermediary step before sizing to prepare warp for this process. Then a number of beams are prepared to feed the sizing machine from a beam creel. The sizing machine, which is in fact a set of machines, is sometimes called the SLASHER . The sizing is achieved by passing the warp yarns taken from the beams as sheets of yarns and passing them through one or two size boxes containing hot size solution. The excess of the sizing material is squeezed off by a pair of rollers after which the warp yarns are dried over hot cylinders. The separate sheets of the warp coming out of the drying chamber are joined as a single sheet and finally wound on the warp beam which is sometimes termed as the WEAVER’S BEAM. Thus the sizing set must incorporate a warping unit ( Figure 11 ).

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Figure 11: Section view of a slasher with double size box ( 1. Beam creel, Size boxes, 3. Drying chamber, 4. Beamer )

In sectional warping there is a two stage operation. In the preliminary stage of the process, the warp yarns drawn from the bobbin creel are wound on to a large cylinder to make a section of the warp and the whole warp is built up by repeating this operation to lay successive sections side by side over this cylinder. Of course, each time a section has been wound the ends of warps have to be secured and the next section must be laid without leaving any space in between to make a single sheet of warp.  This is achieved by careful adjustments. This stage is called  WARPING. In the second stage known as BEAMING, sections are drawn off altogether and wound on the warp beam. Whatever the method is, the spacing of the warp yarns and width of the warp sheet are adjusted by means of certain arrangements on the machine. In order to be able to build a whole continuous warp sheet from a number of sections, each section is wound over the previous one as forming cross sections of the shape of a parallelogram by means of inclined plates or a conical surface at the starting end of the drum, usually called the CONE DRUM ( Figure 12 ). It is  also the general rule that the width of the warp sheet and the setting of the warp yarns are the same as those obtained on the reed. Another point is that in preparing sections on the drum a lease is formed each time before the start of winding by means of a special  reed called the HECK and a special lease cord running across the sections on the drum. Dokuma-16

Figure 12: Formation of warp sections on the sectional warper

Weft yarn is wound on two different kinds of package named as the PIRN or WEFT COP. A HOLLOW COP may also be wound for woollen weaving or in weaving heavy fabrics like carpets and certain industrial fabrics with low count yarns. The weft is wound directly on to the spindle in this case, and when it is drawn off the spindle a hollow centre is formed through which the spindle inside an appropriate type of the shuttle passes. The pirn is pressed into the shuttle and held in it with the aid of spring lid on top ( Figure 6 ). This arrangement enables maximum amount of yarn to be contained in the shuttle. In the majority of cases the weft is wound on to a wooden or plastic cop in which case it should have the following requirements: UNIFORM WINDING, SUFFICIENT  AND  UNIFORM  TENSION  ON  WINDS TO PREVENT SLOUGHING, RESERVE YARN should be provided serve yarn is particularly useful in automatic weft replenishment. In shuttless weaving weft bobbins should be wound on what is called PRECISION  WINDING  machines  because of similar requirements in so far as the insertion of the weft is concerned. These requirements are such that THE WEFT  IS INSERTED  IN  THE  SAME  LENGTH  AND  TENSION. 2.3. MECHANICS  OF  WOVEN  FABRIC  FORMATION The process of weaving may be defined as the bending of straight yarns into a certain form or shape so as to form a uniform structure, as designated by the weave, when this process is applied simultaneously on two sets of yarns placed at right angles to each other. Thus it is a process of deformation; but as this process is applied while the yarns are under some tension, it is a deformation taken place in tension. The tension on the warp yarns prior to and during cloth formation has two functions:

1- To provide a supporting point for the bending of the yarn sections,

2- To secure the parallelism of the yarns or to keep yarns in the same direction.

The weft tension, on the other hand, develops as the weft is deformed during weaving, but prevented from moving by the action of selvedge control. Initial tension of the weft prior to beat up is a small one just to keep the weft straight and to feed equal lengths of weft at each loom cycle. Now what are the forces acting on the yarns during beat up? The main force is provided by the warp tension which is balanced by the cloth tension. Prior to beat up the resultant of the tensions on individual warp yarns along the plane of the cloth is equal to the cloth tension. During beat up warp tension increases due to the movement of  cloth fell in consequence of which the warp yarns stretch and the cloth contracts. As the weft is pushed forward between the two warp sheets, by the force supplied by the reed called the BEAT-UP FORCE, there also develops a frictional force acting in the  opposite direction ( Figure 13 ). The beat up force will increase and attain a  maximum value until the reed is at its furthermost position. As the reed begins the reverse its motion, the beat up force will fall suddenly. The changes  in the warp and cloth tensions are shown in a graph of actual recording due to Snowden and Chamberlain ( Figure 14 ). Neglecting frictional forces the beat up force is equal to the difference between the warp and cloth tensions.

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Figure 13: Forces acting during cloth formation

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Figure 14: Tension  variations  within the weaving cycle ( 1. Tension, Warp tension, 3. Fabric tension, 4. Closed shed, 5. Open shed, 6. Beat-up )

When T1-T2 = 0 , i.e. R=0, the insufficient weaving conditions described by the term “ BUMPING ” occur. Then the required pick density will not be achieved. It is also important to keep the correct cloth fell position. In stoppages the cloth fell position receeds and if no adjustment is made a thin place will form on the fabric. This gives rise to a fabric fault called STARTING MARK or SETTING PLACES. To prevent bumping conditions the basic warp tension To should not fall below a minimum value shown by the inequality ,

k/( P – D ) ( E1 l2 / E2 l1 + 1 ) > To ,

where P is the amount of cloth take-up, D is the weft yarn diameter, k is a constant given by the inverse distance equation

R  = k/(r-D)

in which  r  is the distance between the reed and its final position. The constant  k  is an empirical one. The way  k  depends on the weave parameters, the shed angle and the frictional force is explained by a more comprehensive thory by Plate and Hepworth ( 1973 ). There are also conditions that will cause the inserted weft to slip back due to insufficient friction between warp and weft. Factors such as yarn rigidity, the shed angle at the time of beat-up, the pickspacing achieved by the preceding picks, the frictional properties of the yarns play important roles in this phenomenon that affects the value of the final pickspacing obtained.

3. WOVEN FABRIC STRUCTURES

Simple structures in woven fabrics are formed by two sets of yarns intersecting at right angles to each other and the way these yarns interlace with each other is called the WEAVE. The smallest unit of the weave structure that forms the whole structure when repeated is called the WEAVE UNIT. The weave structures of fabrics are shown symbolically on point paper. In the weave structure shown on the point paper the horizontal spaces represent the weft yarns and the vertical spaces the warp yarns. Each square on the point paper is a POINT  OF  INTERSECTION  and a mark shows that the warp up, a blank shows that the weft is up.

3.1. SIMPLE STRUCTURES

The simplest weave is the PLAIN WEAVE which repeats on a square weave unit of size 2×2. In plain weave the number of interlacings is the most frequent one in that each yarn goes once over and next under the intersecting yarn ( Figure 16 ).

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Figure 16: Plain weave (1- Weave structure and Symbolic representation,2- Fabric appearance and cross sectional views)

In TWILL weaves the YARN FLOATS  which are the sections formed by passing over more than one intersectig yarns run in the diagonal direction. Apart from SIMPLE TWILLS there are also FANCY types of twill weaves developed by a combination of different float lengths. There are also the RIGHT and LEFT versions of twill weaves ( Figure 17 ). STEEP and FLAT TWILLS are obtained by applying a STEP greater than one as shown in Figure 18a. When this is done to interlacings like 1/4, 1/6, 1/7… or  4/1, 6/1, 7/1, .. then SATEEN and SATIN weaves are obtained respectively ( Figure 18b).

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Figure 17: Right and left twill

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Figure 18a : Steep and flat twills

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Figure  18b: Sateen and satin weaves

Apart from these THREE BASIC WEAVES namely plain, twill and sateen weaves, there are DERIVATIVES of these weaves. The idea behind developing these weaves is to obtain physical and aesthetic characteristics in the fabric somewhat different than those obtained with the basic weaves. The predominant characteristics of the plain weave structures are stability, fine and open structure and dull appearance, those of the twill structures flexibility, thick and dense structure, characteristic twill lines, a smoother and brighter surface, those of the sateen structures stability, thick and dense structure, a smooth and bright surface. In derivative weaves properties intermediary between these main groups are obtained. This is achieved  by rearranging the basic weave structures by the application of certain methods to give the desired result. In this way, RIDGES, INDENTATIONS, CELLS,  PORES etc. can be obtained on the fabric surface  by certain arrangement of floats in the weave unit of these simple single structures ( Figure 19 ). Also, by applying higher settings a denser and thicker fabric may be obtained provided that the weave structure is suitable for doing this.

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Figure 19: Surface effects obtained by different arrangement of floats In addition to the weaves derived from basic weaves

HERRING BONE and DICED WEAVES may be obtained by combining different weaves as forming different sections of a small weave unit ( Figure 20 ). Furthermore WEAVE COMBINATIONS  may be arranged in larger weave units to give STRIPE  AND  CHECK  WEAVES ( Figure 21 ).

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Figure 20: Development of a diced  weave

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Figure 21: Stripe and check weaves

Thus by combining the yarn properties with those of the weave, fabrics of a wide variety of physical and aesthetis properties can be obtained. Moreover, apart from the simple single structures described briefly above, there are other more complicated structures to obtain heavier and thicker fabrics for special purposes of use as winter dressings, home textiles and industrial fabrics.

3.2. COMPOUND  STRUCTURES

In backed and double fabric structures, in addition to the usual sets of warp and weft, extra sets of warp or weft or both are introduced into the structure. If these extra sets of threads are used partly ( or sparingly ) in parts of the structure for the purpose of figuring, then EXTRA WARP,  EXTRA WEFT and EXTRA WARP  AND  WEFT  structures are obtained, which are considered as single structures. These extra yarns will lie over the ground fabric formed by the actual warp and weft yarns when they are required to form the figure, otherwise they will remain on the back of the fabric  ( Figure 22 ).  The number of extra yarns used in the figured area of the fabric may be in certain proportions as compared with the number of ground yarns used in the same section like 1 to 1, 1 to 2, 2 to 2,  2 to 4 or 2 to 1 etc. In certain design the extra yarns may be used in full over the fabric surface. Dokuma-27 Exstra warp structure               Extra weft structure                        Extra warp and weft structure

Figure 22: Extra yarn structures

If the extra yarns are used in full and in a way to lie mostly on the back to obtain a heavier or thicker fabric, then we obtain a class of fabrics called  BACKED CLOTHS. If the use of  extra threads is full in a certain proportion to the ground threads, then we get the WARP BACKED and WEFT BACKED STRUCTURES.

If  this is done in both warp and    weft  directions  we obtain  DOUBLE CLOTHS.

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Figure 23: Backed Structures (a,b:Warp backed structure, others: weft backed structure)

EXTRA WARP or EXTRA WEFT  or both EXTRA WARP AND WEFT yarns are used  for figuring, these can be spot effects or in some cases FIGURE ( motive ) effects. WARP BACKING or WEFT BACKING is applied, on the other hand, to give weight and thickness to the cloth without changing its surface appearanca and its soft handle. In using extra warp or in warp backing,  the principle is to sett the warp in the reed in such a way that  the extra or backing threads would be sett in the same dent that the ground thread or threads are sett in as extra (or in excess) without changing the warp setting as calculated for a single structure ( excepting a small reduction made to allow for the easier movement of yarns during weaving ). For extra weft or weft backed structures the arrangement of the weave in the  proper way and a stronger beat up will give the required result. In double structures two single cloths are arranged to be woven one on the top of the other on the loom, but shown on the same point paper design by arranging the face and the back threads side by side in a proper order. The problem is binding of the two structures in some way. As shown in Figure 24, in the SELF STITCHED DOUBLE CLOTHS this is done by certain threads, in either face or back or both, interlacing with certain intersecting threads on the other structure. Special STITCHING THREADS are used in CENTRE  STITCHED  DOUBLE  CLOTH structures ( Figure 25 ).

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Figure 24: Self stitched double cloth (a. Surface structure, b. Cross sectional view; Point paper design) Dokuma-28   Dokumja-29

Surface and cross sectional views                              Point paper design

Figure 25: Centre stitched double cloth

Self stitching makes the cloth hard, and lower settings than those in single cloths must be employed for both face and back so as to allow room for stitching, whereas in centre stitching this is not necessary. Furthermore, self stitching has the drawbacks of the stitching points to show themselves on the fabric face and of the difficulty of finding perfect stitching points that are fully covered by the yarn floats. Another way of obtaining a double structure is the interchange of warp and weft of one layer, in groups, with that of the other layer. These are called INTERCHANGING  DOUBLE  CLOTHS  or  DOUBLE FACED DOUBLE CLOTHS, the most common version of which is the DOUBLE PLAIN CLOTH used in dressing fabrics ( Figure 26 ).

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Figure 26: Double plain fabric structures

3.3. SPECIAL  WOVEN  FABRIC STRUCTURES

We have so far mentioned of the conventional woven fabric structures. There are also more complex structures which necessitate the use of special looms that are equipped with special arrangements to achieve certain structural features. These fabrics are also quite different in appearance and in some of their physical properties. These fabrics can be grouped in six main categories according to the fabric structure and method of weaving. 3.3.1. GAUZE  AND  LENO  FABRICS In order to make open structures special threads are used in the warp direction to bind and secure the intersection points. These threads come cross with the ground warp and this movement is achieved by the use of a special HALF HEALD. Two crossing healds are employed, the front one carrying the half heald and the crossing warp passes through the eyes of both ( Figure 27 ). The ground warp passes through the eye of the standard heald which is placed in between the crossing healds, thus the special thread crosses the standard warp thread in passing from back to front and thus the special thread will lie in the cloth at an angle to standard warp thread. Structures obtained by using this technique are called GAUZE  WEAVES. If the crossing thread moves over more than one standard warp through successive picks, it can be used to obtain motive effects and such structures are known as LENO  WEAVES. Dokuma-32

Figure 27: Gauze weaving ( 1. Half heald, 2. Front crossing heald, Back crossing heald, 4. Standard heald, 5. Easer bar )

  3.3.2. VELVET  AND  VELVETEENS

If the extra threads, as warp or weft, are introduced into the cloth structure to make loops at right angles to the plane of the cloth, then a  PILE  FABRIC  is obtained. One way of doing this is to arrange extra wefts making long floats in orders as three or more extra picks to the ground, and to weave at high pick densities.  When these extra floats are cut in the middle by special machines or knives a weft pile fabric will be obtained which is called a VELVETEEN ( Figure 28 ).

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Figure 28: Formation of a plain velveteen

Velvets are warp pile fabrics. Extfa warp threads called PILE WARPS  are woven into the ground structure in greater lengths. In one system they pass over wires which are inserted into the shed as pick and form LOOPS over these wires carrying a blade at one end. When the wires are withdrawn from the shed one by one, they will cut the loops formed by the pile warps and a CUT  PILE  VELVET  structure will be obtained ( Figure 29 ). Dokuma-33 Figure 29: Design and cross section of wire velvet structures

In another system called  FACE  TO  FACE  WEAVING  pile warps interchange between two ground cloths woven face to face with a suitable distance in between them. The fabric is woven on a double cloth principle and the pile threads which bind the two cloths together are cut at the same time during weaving to form the cut pile structure ( Figure 30 ). Dokuma-34

Figure 30: Face-to-face velvet structures

3.3.3. TERRY  OR  TOWEL  STRUCTURES

In towel structures known by the general term TERRY  pile thread is fed at a greater speed by an independent let-off system from a separate beam. By a special  TERRY  REED  MOTION  two picks are inserted by leaving the beat-up motion incomplete in the first stage. The third pick is then beaten up fully and at the same time a slackening of the pile warp is achieved by the action of an easing lever. Thus a loop is formed by the extra length of the pile warp due to lack of tension at this second stage ( Figure 31 ). Dokuma-35

Figure 31: Weave and cross sectional view of Turkish towel structure

3.3.4. MACHINE CARPETS

Machine carpets can be woven on the principle of wire weaving or face-to-face weaving as in velvets. These carpets are known as  WILTON  CARPETS ( Figure 32 ). In carpets the ground warps are cotton, the weft is either cotton or jute, the pile yarn is wool or a wool mixture. There is also a FILLING yarn used in the warp direction to support the pile and to fill in the space between the pairs of warp yarns. There are various Wilton carpet structures woven on the face-to-face weaving system  according to the the type of the loom and the number of colours used in the pile ( Figure 33 ). Dokuma-36

Figure 32: Wire Wilton carpet structure Dokuma-37

Figure 33: Three colour face-to-face Wilton carpet structure

In another group of machine carpets called  AXMINSTER  carpets there are special mechanisms to form the loops. In this system the loops are formed by small lengths of the pile yarn which are drawn and cut off by looping elements as shown in Figure 34 and various  Axminster structures are given in the cross section in Figure 35. Dokuma-38 Figure 34: Formation of pile in Gripper   Axminster carpet Dokuma-39

Figure 35: Various Axminster carp structures  ( A:Imperial, B: Corinthian, C: Kardax )

3.3.5. TRIAXIAL  FABRICS

They are the outcome of space research giving uniform tensile properties to the fabric. Two series of warp yarns crossing each other at some angle are intersected and interlaced with weft yarns in a special loom. Some varieties of structure may be obtained ( Figure 36 ).

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Figure 36: Some triaxial fabric weaves

3.3.6. THREE  DİMENSIONAL  STRUCTURES

There are various forms of three dimensional woven structures made on specially designed looms. In principle a group of yarns placed in the vertical direction to a multi layer woven structure are employed in these fabrics but othes sets lying in various directions may also be incorporated. These fabrics are used for special industrial uses ( Figure 37 ). Dokuma-41

Figure 37: Sectional views of various three dimensional fabric strucrıres

3.3.7. NARROW  FABRICS

These are fabrics of widths less than 45 cm used for various purposes as industrial fabrics or as materials of ornamentation and trimmings for the clothing industry. 3.3.8. HAND  WOVEN  FABRICS Hand made carpets, rugs, soumaks and other kind of structures are handicraft products which still have important economic and aesthetic value ( Figure 38 ).

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Figure 38: Various handwoven fabric structures

3.3.9. CLASSIFICATION   OF  WOVEN  STRUCTURES

A full classification of woven fabrics based on structural features and on the method of weaving is given in Figure 39. This classification includes a broad distinction between fabrics which can be woven on a common weaving loom termed as NORMALLY  WOVEN  FABRICS  and those which require special loom designs to provide certain structural features termed as SPECIALLY  WOVEN  STRUCTURES.

  1. DESIGN OF WOVEN  FABRICS

Designing a fabric means specifying all the important characteristics of the finished fabric. These characteristics may be stated in certain categories which follow:

DIMENSIONAL PROPERTIES:  Length, width, weight, thickness

STRUCTURAL PROPERTIES:  Weave, thread density, thread diameters or yarn counts

PHYSICAL PROPERTIES:Strength, wear, warmth, moisture absorption, handle, drape, crease resistance, permeability CHEMICAL PROPERTIES: Colour fastness, washability, flammability, dyebility

AESTHETIC PROPERTIES: Colour, colour and weave effect, figured design, shine, surface texture

Some of these parameters are concerned with the performance of the fabric during use.Properties such as the weight, the weave, he colour design etc. are the actual design parameters which influence and in fact determine the performance characteristics such as strength, permeability, handle  etc. In principle the properties which can be independently chosen are those that should be taken as design parameters. Others will depend on these independent parameters. There will be certain relations between the design parameters and those which are functions of them, but these relations may not always be easily definable. What are, then, the principal design parameters for a woven fabric? Weight per unit area of a fabric is a very important parameter. Especially in dress fabrics light weight materials are used in warm climate and in summer. A rather light weight fabric is required for shirting, whereas for suitings a heavier fabric is needed. For furnishings and for the dress fabrics to be used in winter still heavier fabrics are needed. But it is rather difficult mathematically to start with the fabric weight and calculate the yarn counts and theread densities due to the two dimensional structure of  a woven cloth. Having chosen the count and sett of warp or weft, the count and sett of the other set of threads may be adjusted to give the required weight. But even then there will not be a single solution to the problem since there are four variables affecting the weight.  Another difficulty stems from the fact that in weaving there occur contractions in length and width due to crimping of yarns to form the weave structure of the fabric.  Unless  the magnitudes of these contractions are known the actual lengths of of the threads placed in the unit area of cloth cannot be calculated accurately. If we employ constants k1 and k2 for warp and weft respectively to allow for contractions occurring in weaving and finishing and also to adjust units, then the weight per unit area of fabric may be expressed by the formula,

Formül 1

where S1 and S2 are warp and weft setts, N1 and N2 are warp and weft counts respectively. Therefore, although weight is an important parameter it is a function of four other parameters which would be taken as design parameters if there were no interrelation between them. But there is another relation between the yarn count, the sett and the weave which is defined by what is called  SETTING  THEORY. This relation stems from the fact that given a yarn of certain diameter and weave there is a limit to the sett or density of yarns in the cloth. The limitations are both geometrical and mechanical. The geometrical limitations arise from the fact that there must be room between two consecutive threads for the interlacing threads to pass through. The mechanical limitations, on the other hand, are such that the equilibrium of forces during fabric formation may not allow certain pick densities. This will be affected by both fabric parameters and mechanical conditions of weaving. It shouls also be born in mind that the sett applied in one set of yarns will affect the sett to be applied in the other set of yarns in an inverse manner. The setting theories may be expressed by the general formula,

Formül 2

where S is the set of warp or weft, Fw  is the  WEAVE  FACTOR,  K is a constant depending on the type of yarn,  C is the count of the yarn used as warp or weft. R. Ashenhurst ( 1884 ) expressed the weave factor for SQUARE WEAVES, which have the same number of warp and weft threads in the weave unit, as

Formül 4

where  w is the number of threads in one repeat of waeve,  i  is the number of intersections. Thus for a plain weave Fw = 0.5 , for a 2/2 twill weave Fw = 0.67. The original formulae of Ashenhurst for the diameter of yarns in terms of yarn count expressed in unit of inches are: for worsted yarns

Formül 3

for cotton yarns

Formül 5

for woollen yarns

Formül 6

In the metric system, if metric count, Nm, is used, the constant  K  will take the values 7.9, 8.3 and 7.3 for worsted, cotton and woollen yars respectively. Another important setting theory is that due to Brierley ( 1931 ) who expresses the threads Per inch, T, as

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where F  is the average float, m is a constant depending on the weave type. m  takes on values  0.39,  0.42  and 0.45 for twill, sateen and plain or matt weaves,  K takes on values  134, 200, and 60 for worsted, cotton and woollen yarns respectively. In metric system and using the general formula by putting  Fw = Fm , the value of K will approximately be 4.25 with no great differences between the yarn types. So we have two important relations between weight, yarn count, setting and weave type. It is usual to consider the setting as a dependent parameter in the general design approach.

4.1. LOOM  PARAMETERS  AFFECTING  FABRIC  DESIGN

There are also factors to be taken account in the design of a fabric concerned with the construction of the loom. In figured designs quite important limitations may confront us. One such factor is the DESIGN  CAPACITY  of the loom which may be defined as the number of independent warp movements that can be obtainen in a given loom. Thus, given a loom, only the weave units of figured designs of certain dimensions may be employed. This is so even in jacquard weaving. A particular jacquard machine will have a certain design capacity. The dimensions or the width of the figured design depend on the number of different warp interlacings used in the design together with the warp setting applied. As the yarn count gets higher, a higher setting has to be used, and consequently the width of the design will decrease. If  is the width of the design, S  is the warp setting and  n  is the design capacity used of the loom, whether a dobby or jacquard loom,  then the relation

Formül 9

will hold. Conversely, this relation also means that the warp setting to be employed in a figured design will be a function of both design width and the design capacity of the loom. The particular loom used will limit the cloth width and and may also limit the fabric weight. In colour weaving the box arrangement on the two sides of a shuttle loom will limit the colour plans that can be used. In pick-and-pick weaving only the colour plans 2:2, 4:4 and like can be applied. A 1:1 colour plan can only be applied in at will picking where there are box movements on both sides of the loom. In shuttless weaving also the number of weft calours used will be limited. Having thus determined the principal parameters, other parameters depending on them will be determined or calculated. These will include all the quantitative information necessary to carry out production processes at all stages going from the finish cloth back to the supply of raw materials. Thus fabric design work should finally take the form of a project for production. 4.2. DESIGN  APPROACHES There are two basic approaches to woven fabris design namely, CLOTH ANALYSIS and TECHNICAL DESIGN In cloth analysis a sample of cloth is analysed in many ways to extract all the information necessary to reproduce the desired cloth. In the technical design approach the weave, the raw material, the counts of the yarns to some extent and approximate weight per unit length or area may be pre determinerd. Nevertheless, some mathematics will be needed to insure that  the design is compatible with the technical conditions and the final fabric characteristics aimed, the most important and critical one being the fabric weight. The fabric weight is calculated and controlled as it is a measure or criterion for the compatibility of the design with the design aims or with the intended use. It is also quite important because of cost considerations. A third approach namely AESTHETIC  DESIGN  APPROACH  is possible but very difficult indeed. This can be expressed as designing the fabric to have a surface appearance as drawn or painted on paper. This is a difficult task for woven fabrics because of limitations imposed by structural requirements for the fabric and of constructional features of the loom. It is, however, quite possible with some technical skill and experience.

4.3. DESIGN METHODS

The reproduction of fabrics based on the information obtained from a piece of sample cloth require these following steps: A visual inspection of the fabric sample to determine the face and back of the fabric, to find the warp and weft direction, to determine surface properties and to determine the fabric type as regards its structural characteristics.

  • To determine the actual unit fabric weight by weighig and finding the area of the sample fabric.
  • Carrying out a thorough YARN ANALYSIS  by extracting some threads from the sample and determining their types, raw materials, counts, twists and  ply numbers.
  • To determine the uncrimped straight lengths of the extracted threads, to be used in count and twist calculations as well as in calculating crimp factors by setting ratios of uncrimped lengths to crimped lengths in the sample fabric.
  • To find the weave by WEAVE
  • To determine warp and weft setts.
  • To determine colouring plans and denting used in coloured and fancy design fabrics.
  • To calculate warp and weft weights to be used in the manufacture of the fabric according to types and colours of the yarns used.
  • To calculate the finished weight and -from this- the unit fabric weight.
  • Comparing this calculated unit fabric weight with that determined on the onset of cloth analysis and making the necessary corrections.

All the information necessary to produce a reproduction of the sample fabric can be obtained from such a full cloth analysis followed by certain weaving calculations carried out in the usual way. In the calculations of the yarn weights the crimp factors as calculated in the abovementioned way and as shown by k1 for warp and k2 for weft will be of great help. Using these constants the weight of a fabric of sides 1 m in warp and weft direction, the unit fabric weight will be given by the formula given in Section 4 (The Technique and Art of Weaving, Vol I, G.Baser, 2004).

To design a fabric of given unit fabric weight by the technical approach, hovever, the weave type and yarn counts have to be determined first, and then the settings can be calculated using a convenient setting theory. As there will be three unknowns there will be many solutions to this design problem. To reduce the unknowns a convenient approach is to start off with a chosen weave and make the assumption that the same count of yarn will be used in both warp and weft and the crimp ratios in both directions are the same. This will also mean that the warp and weft settings will be the same. Thus the formula giving the weight per unit square of fabric will become as,

Formül 10

Substituting the setting theory as given by the formula  S= kFwK, instead of  S= FwK, which gives the thread setting on the loomstate fabric, we obtain

Formül 11

and from this we can obtain a value for the yarn count given by the formula

Dokuma-24 

Having a value for the yarn count and applying the setting theory it is possible to find appropriate settings and from here on the usual weaving calculations may be carried out to calculate production particulars as to the reed width, warp length, reed count, grey fabric dimensions etc. As for the aesthetic design approach applied sometimes in the design of figured fabrics the main difficulty is obtaining a given figure width with a given unit fabric weight. This is a more difficult problem to solve when designing for dobby looms. In this case the number of heald shafts available for figuring together with the figure  width will give a fixed warp sett. And when the setting theory is applied for a given ground weave the yarn count will be obtained as a fixed value. These known parameters, namely yarn count, weave and sett will give a certain unit fabric weight which may be quite different than those required. In such a situation certain modifications in these parameters will be necessary, the easiest and the most reasonable one being to change the figure width. Although a change of the weave type with a higher weave factor, resulting in  a higher sett and consequently a greater weight, or vice versa, may be made, but this will change the yarn count as well. It will, therefore, be necessary to either apply a suitable algorithms to make these adjustments in a predictable way, or else a trial and error approach will be applied. Such an algoritm has been developed by the use of the formula

Formül 12

Constant where  A  is the number of heald shafts used in the figure, a is the figure width and the other parameters being defined as before ( Başer, 1994 ).

5. PROGRESS IN THE  WEAVING  MACHINERY

From the introduction of the first powerloom the progress in the weaving machines has been quite rapid. The non conventional ways of inserting pick by other than with a shuttle was not new in 1950’s, but there were still problems that had not yet been solved in the weaving of ordinary fabrics. In the weaving of some some industrial fabrics, however, some of the non conventional weft insertion systems had quite been well established. The shuttle loom was, still, essential for most fabrics, especially for  those which required a selvedge. The competition to shuttle weaving was from the knitting industry which ,in turn, gave impetus to many researches on non conventional ways of weaving and on other ways of forming fabrics that looked more like a woven fabric. Progress in engineering design of machines and increas in speed of  weaving , with the introduction of new continuous filament yarns also resulted in the warp and weft preparation machinery. The progress of the last 30 years will be dealt here in a systematic way pointing out the lines of research and progress in relation to various weaving machinery.

5.1. PROGRESS  IN  WARP  PREPARATION  MACHINERY

The progress in the warping machines has been on these lines: The speed of warping

  • Tension control on the individual warp ends
  • Automatic and instant stop of the warping drum when an end breaks
  • Uniform build-up of conical sections on the warping drum of e sectional warper
  • Measurement of the length of warp wound
  • Design of the creel

Developments Exibited in 1999 ITMA Milan In modern sectional warping machines automatic loose end finding and computer control of the precision of the winding are provided. The problems in the sizing machines are the following: Regular take-up of the size

  • Tension control on warp ends
  • Efficient drying
  • Prevention of the dried warp ends from sticking to each other

In modern sizing machinesautomatic control systems to regulate the rate of uptake of size and automatic feeding of the size box are provided. Problems related to drying are solved. 5.2. PROGRESS  IN  WEFT  WINDING The winding of weft yarn is achieved in three ways, namely as winding on pirns, winding on flanged bobbins and as precision winding of the weft bobbins.  The progress in the weft winding machines has been on the following lines: * Greater winding speeds

  • Automatic winding without ribbonning
  • Precision winding on large bobbins
  • Unifil winding, that is winding pirns for an automatic pirn changer loom

5.3. PROGRESS  ON  LOOMS

The progress made on looms can be examined in the following areas: IN  SHEDDING * Shedding speeds in dobby looms

  • Controlled movement of the heald shafts in dobby shedding
  • Speed in Jacquard shedding
  • The maximum number of the heald shafts employed in the shuttleless weaving
  • The application of Jacquard shedding to shuttlless looms
  • Electronic dobby
  • Electronic Jacquard

IN  PICKING * Picking speeds

  • Drives to the rapiers
  • Tip transfer for coarse and twistless yarns with cleaning arrangements
  • Strength of picking in air jet weaving
  • Accumulation of the weft for air jet picking
  • Design of the nozzles for the air and water jet looms
  • Automatick pick finding arrangement
  • Automatic running back of the loom for cloth fell correction
  • Double pick insertion

IN  BEATING  UP * High speed beat-up for shuttleless weaving

  • Double beat-up and cam controlled sley movement

IN  WARP  CONTROL * Electronically controlled warp let-off

  • Independent warp let-off for half beams in multi width weaving
  • Special selvedge motions for shuttless weaving such as leno motions
  • Sophisticated warp tensioners
  • Electronically controlled warp tension

IN  TAKE  UP * Cloth take-up by the floating roller

  • Automatic cloth fell correction

IN  MULTY  COLOUR  WEAVING * Weft mixing in shuttleless weaving

  • Up to 12 weft colours in shuttleless weaving
  • Computer controlled colour selection

IN  REDUCING  NOISE  AND  VIBRATION IN  LUBRICATION IN  MAINTENANCE IN  MONITORING  LOOM  PERFORMANCE Any progress made on a loom is evaluated as based on two criteria: ACTUAL  REVOLUTIONS  PER  MINUTE  ATTAINED; EFFICIENCY. As the fabric widths have increased and multi-width weaving has been introduced, the first criterion now has left its place to the LENGTH  OF  WEFT  INSERTED  PER  MINUTE. The NUMBER  OF  WEFT  COLOURS  and the NUMBER  OF  HEALDS  are secondary, but important criteria for a versatile loom.  Another important criterion of versatility is the capability of the loom to weave fine and twistless yarns, coarse and hard yarns such as glass fibre yarns. The progress for the last ten years has been mainly through the applications of electronics and the introduction of computer control. Electronic dobby and jacquard mechanisms, the transfer of the design information to looms by computer, on line control of the weaving process by an integrated computer system are the main advances. However, there have also been further progress in the method of weft insertion  as in multy phase weaving applied by Sulzer in their latest  Sulzer N 800 loom. Another area of progress has been in three dimensional weaving for producing technical fabrics and preforms ( Bilişik, 1994).

 

INTRODUCTION TO THE POST GRADUATE COURSE TITLED “FIBRE AND YARN MECHANICS”

ScP-1 AIM OF THE COURSES ON FIBRE AND YARN MECHANICS

  • To examine the mechanical properties of fibres and yarns as well as to show how scientific approach is made in investigating a topic of research.

SCIENTIFIC APPROACH

  • An approach to provide information, in the way of an explanation of a certain structure, event or behaviour, based on reason.
  • Such events may be any natural phenomena, namely a physical, chemical or biological happening, a behaviour of any material, of structure or organism, including social happennings.

SCIENTIFIC METHOD

  • Methods based on observations and experiments or on some theoretical analyses based on certain likely assumptions and worked out by mathematical reasoning, being subject to experimental verification.

THEORY

  • Experimental results and evaluations can be used in a limited area and cannot be generalized easily.
  • In order to generalize experimental results, rules and formulae, one must have , first, a theoretical model of the related natural event or problem. Secondly, analyses should be carried out, based on the constructed model, giving certain results which are subject to experimental verification. For this, one needs to carry out certain planned and controlled experiments.
  • In this way, one understands more about the mechanism of the event or behaviour studied and may, consequently, develop some means (instruments or methods) to control that event.

THEORETICAL MODEL

  • It is possible to construct a very complex and detailed theoretical model, but, then, this model may be very difficult to analyse.
  • Thus, it is customary to construct, first, a very simple model, analyse it, and then, after some efforts of verification, to try to construct a better model to improve upon the first one.
  • The simpler is the model, the easier to analyse it and the better is to use it for practical applications.

GENERAL METHOD OF RESEARCH

  • 1- Make observations and collect as much information as possible
  • 2- Carry out small scale preliminary examinations or experiments
  • 3- Design your first simple theoretical model based on the most general and acceptable assumptions deduced from prior observations and information
  • 4-Analyse the problem using the theoretical model and obtain some results
  • 5- Design and plan a set of experiments to verify the theory and collect experimental data
  • 6- Compare the calculated theoretical results with the experimental data using certain statistical methods of analysis
  • 7- Criticize the theory in the light of this comparison and also check the experimental results obtained and the methods used
  • 8- If the agreement is not satisfactory, construct an improved theoretical model and revise the experimental methods. If necessary redesign and enlarge the experimental work
  • 9- Follow the same procedure from item 4 downwards as before until you reach at a satisfactory agreement between theory and experiments
  • This research cycle is shown in the following diagram
  • ScP-2

EXAMPLES ON TEXTILE RESEARCH ASSUMPTIONS:

  • -Yarn cross section is circular
  • -Twist angle is very small or tan θ ≈ θ in radians ≈ sin θ
  • – Fibre has an infinite length
  • – The number of fibres in yarn cross section is very high etc.

MODEL A model should – Define characteristics or shape (structure) or – Define mechanical behaviour Models will be based upon assumptions such as stated above TYPES OF MODELS

  • MATHEMATICAL MODELS
  • – Geometrical
  • – Algebraic
  • – Statistical
  • PHYSICAL MODELS
  • -Structural Models
  • -Geometric – Mechanical Models
  • -Mechanical Models
  • ANALYSES
  • 1- Algebraic analyses
  • 2- Geometrical analyses
  • 3- Statistical analyses
  • RESULTS
  • They are functions expressing or describing
  • 1- Structure or shape
  • 2- Static or dynamic behaviour

 

 

 

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