ZIG ZAG OR WAVY TWILLS

ZIG ZAG OR WAVY TWILLS:

Pointed Twill

These are also known as pointed twills. In these classes of twill weaves the twill progresses in one direction for half of the repeat and then is reversed for the next half of the repeat. The reversal of the twill may be done in a regular or irregular manner. Ideally the reversal of the twill should be done considering the series of threads that predominate the face of the fabric. Thus warp way reversal is done in cases where the warp predominates over the weft and weft way reversal is done in cases where the weft predominates over the warp.

Figure 4.6 shows a design of the pointed twills.

THE ANGLE OF TWILL | FACTORS DETERMINING THE PROMINENCE OF TWILL WEAVES | COMPARISON OF THE FIRMNESS OF TWILLS

THE ANGLE OF TWILL:

The angle of twill is the angle between the diagonal twill line and an imaginary horizontal line or axis parallel to the weft. This angle is dependent on the ratio between the ends/inch and picks/inch in the cloth. When the warp ends/inch is equal to the weft picks/inch, the twill angle will be 45°. When the warp ends/inch exceeds the weft picks/inch the twill angle will be an obtuse angle i.e., >45° (high angle or steep twill). When the weft picks/inch exceeds the warp ends/inch, the twill angle will be an acute angle i.e., <45° (low angle or flat twill).

FACTORS DETERMINING THE PROMINENCE OF TWILL WEAVES:

The following factors determine the relative prominence of twill weaves

• Nature of the yarn
• Nature of the weave
• The warp and weft threads/inch, and
• The relative direction of twill and yarn twist

Nature of the yarn:

The fineness of yarn and the amount of twist given to it influence the prominece of the twill. A coarse yarn of lower twist produces a greater effect on the twill as compared to a fine yarn of higher twist. On the other hand doubled or ply yarns have a stronger effect on the twill as compared to single yarns.

Nature of the weave:

Twills with longer floats will give more prominence as compared to those with shorter floats. For example, a 3/1 twill will be more prominent as compared to a 2/2 twill. It is to be noted that an increase in float length has to be balanced by proportionately increasing the corresponding threads/inch.

The warp and weft threads/inch:

The twill prominence increases proportionately with the increase in warp and weft threads/inch.

The relative direction of twill and yarn twist:

Another important factor that influences the prominence of twill is the direction of twist in the yarn. When the direction of yarn twist is same as the twill direction, the prominence is reduced and when them direction of the the yarn twist is opposite to the twill direction, the prominence of the twill is increased. In other words a Z twill with Z twist yarn or an S twill with S twist yarn shows less prominence. On the other hand a Z twill with S twist yarn or S twill with Z twist yarn gives more prominence.

COMPARISON OF THE FIRMNESS OF TWILLS:

The firmness of a weave depends on the number of intersections. The greater the number of intersections, the better the firmness. On the other hand lesser the number of intersections, greater will be the cover of the cloth. This is due to the increase in the floats of the threads. Increase in the number of intersections restrict the thread density and vice versa.

The illustration in Fig. shows three cases in which an 8 thread repeat of twill weave is chosen.

Case 1: In this case shown at A, a floating weave of 4/4 twill is chosen.

Case 2: In this case shown at B, a combination of 3/2 and 1 /2 twill is chosen

Case 3: In this case shown at C, a combination of 3/1, 1/1 and 1/1 weave is chosen

The corresponding cross sections are shown at D, E and F, respectively. The distance between the dotted lines represent a distance equal to the diameter of a single thread. It can be seen that design A occupies a space of ten threads (D), design B occupies a space of twelve threads (E) , and design C occupies a space of fourteen threads (F). It can be seen that a spacing of 10 threads in G is occupied as against the spacing of 14 threads at F.

The following conclusion can be drawn on observing the interlacings in the three above cases:

Relative firmness of Twill Weaves

In case 1, the cloth will have the minimum level of firmness and maximum cover.

In case 2, the cloth will have firmness and cover intermediate between 1 and 2.

In case 3, the cloth will have maximum firmness and minimum cover.

CONTINUOUS TWILL AND THE TYPES OF CONTINUOUS TWILL | ANGLE OF TWILL.

CONTINUOUS TWILLS:

Warp Faced Twills:

In these types of twills the warp thread floats over all the picks in a repeat except one pick. The minimum repeat size required is 3. Examples of warp faced twills are 2/1, 3/1, 4/1, 5/1 etc.

Some examples of warp faced twills are shown in Fig.

Fig. A, C and D show a right handed or Z twill and Fig. B shows a left handed or ‘S’ twill.

Weft Faced Twills:

Weft Faced Twill

These twills are the reverse of the previous ones. In these weaves the weft thread floats over the warp on all picks in a repeat except one. Examples of weft faced twills are 1/2, 1/3, 1/4, 1/5 etc. Some types of weft faced twills are shown in Fig. 

Fig. B, C and D show a right handed or ‘Z’ twill and Fig. A shows left handed or ‘S’ twill.

Balanced and Unbalanced Twills:

Balanced and unbalanced Twill

In these types of twills the warp and weft floats may be equal or unequal. In other words the twills may be of the reversible or irreversible types. Accordingly they may be known as balanced and unbalanced twills. Examples of balanced twills are 2/2, 3/3, 4/4, 5/5 etc. Examples of unbalanced twills are 2/3, 4/2, 5/3 etc. The 2/2 twill is popularly known as “Gaberdene” weave. Fig. 4.3 A and B show designs for balanced and unbalanced twills and C and D show the interlacement diagrams of a 4/1 twill and 1/4 twill (warp faced) (weft faced).

Warp and Weft Faced Twills:

Warp and Weft faced Twill

In these twills the warp and weft floats may be equal or unequal with either the warp floats

predominating the weft floats and vice versa. Some examples of these twills are shown in Fig. 4.4 A, B and C respectively.

THE ANGLE OF TWILL:

The angle of twill is the angle between the diagonal twill line and an imaginary horizontal line or axis parallel to the weft. This angle is dependent on the ratio between the ends/inch and picks/inch in the cloth. When the warp ends/inch is equal to the weft picks/inch, the twill angle will be 45°. When the warp ends/inch exceeds the weft picks/inch the twill angle will be an obtuse angle i.e., >45° (high angle or steep twill). When the weft picks/inch exceeds the warp ends/inch, the twill angle will be an acute angle i.e., <45° (low angle or flat twill).

TWILL WEAVE | CLASSIFICATION OF TWILL WEAVES

TWILL WEAVE:

Twill weaves are the weaves that find a wide range of application. They can be constructed in a variety of ways. The main feature of these weaves that distinguishes from other types is the presence of pronounced diagonal lines that run along the width of the fabric.

The basic characteristics of twill weaves are :

• They form diagonal lines from one selvedge to another.

• More ends per unit area and picks per unit area than plain cloth.

• Less binding points than plain cloth

• Better cover than plain weave

• More cloth thickness and mass per unit area.

 CLASSIFICATION OF TWILL WEAVES:

 The twill weaves are produced in a wide variety of forms. They are however classified broadly into
important categories, namely :

1. Ordinary or continuous twills
2. Zig zag , pointed or wavy twills
3. Rearranged twills such as satin/sateen weaves and corkscrew weaves
4. Combination twills
5. Broken twills
6. Figured and other related twill weaves

The above types of twills are further subclassified as:

1. Warp face twills
2. Weft face twills
3. Warp and weft face twills

MODIFICATION OF PLAIN WEAVE | WARP RIB WEAVE | WEFT RIB WEAVE | MATT RIB WEAVE

MODIFICATION OF PLAIN WEAVE:

The plain weave may be modified by extending it warp or weft way or both. The extension of the plain weave thus produces a rib effect. A warp rib results from extending the plain weave in the warp direction and a weft rib structure results from extending the plain weave in the weft direction. A matt rib results from extending the plain weave in both directions.

The chart below shows the derivatives/modifications of plain weave :

WARP RIB WEAVE:

These are produced by extending the plain weave in warp wary direction. Fig 3.2 shows the warp rib weaves constructed on regular and irregular basis.

Warp rib Weaves

At A, B and C are seen regular warp rib weaves and at D, is shown the irregular warp rib weave. E and F show the interlacing of D and A respectively.

WEFT RIB WEAVE:

These are constructed by extending the plain weave in weft direction as shown in Fig.

 In both the warp and weft rib weaves, the appearance of the cloth depends on the respective threadsettings, and to achieve good effects, it is necessary to weave a weft rib with a high number of picks per inch and a comparatively low number of ends per inch. Similarly the warp rib effect can be enhanced with a high number of ends per inch and a comparatively low number of picks per inch. The prominence of the rib can be increased by suitable use of coarse and fine yarns. The dependence of all rib constructions upon the correct thread settings is marked.

The typical constructional particulars for a weft rib structure is given below:

Warp - 2/14s & 36s
Ends/inch - 56
Weft - 18s
Picks/inch - 100
The typical constructional particulars for a warp rib structure is given below:
Warp - 30s cotton
Ends/inch - 126
Weft - 15s cotton
Picks/inch - 38

  Uses:

Rib weaves are used in gross grain cloths, matelasse fabrics, repp cloth which is extensively employed for window blinds in railway carriages and other vehicles, upholstering furniture, and cambric picket handkerchief.

MATT RIB WEAVE:

These weaves are also variously known as hopsack or basket weaves. The matt rib structures result from extending the plain weave in both directions.
The regular and irregular types are shown in Fig.

In case of regular matt weave, the plain weaves are extended equally in the warp and weft directions, where as in case of irregular matt weaves, the plain weave is extended unevenly or irregularly in the warp and weft directions.

Uses:

Matt weave finds extensive uses for a great variety of fabrics such as dress materials, shirtings, sailcloth, duck cloth etc.

PLAIN WEAVE AND ITS CHARACTERISTICS

PLAIN WEAVE:

The plain weave is variously known as “calico” or “tabby” weave. It is the simplest of all weaves having a repeat size of 2. The range of application of this weave is wide.
The plain weave has the following characteristics :

• It has the maximum number of binding points
• The threads interlace on alternate order of 1 up and 1 down.
• The thread density is limited
• Cloth thickness and mass per unit area are limited.
• It produces a relatively stronger fabric that is obtained by any other simple combination ofthreads, excepting that of “gauze”or “cross weaving”.

The principle involved in the construction of plain cloth is the interlacement of any two continuous threads either warp or weft in an exactly contrary manner to each other, with every thread in each series passing alternately under and over consecutive threads of other series interlaces uniformly throughout the fabric. By this plan of interlacement, every thread in each series interlaces with every thread in the other series to the maximum extent, thereby producing a comparatively firm and strong texture of cloth. A complete unit of the plain weave occupies only two warp threads and two picks of weft, which is the design for that weave.

Plain or Tabby Weave

TEXTURAL STABILITY OF PLAIN WEAVE IN RELATION TO OTHER WEAVES:

The firmness of any woven structure depends on the frequency of interlacing between the warp and weft threads. The greater the number of intersections the better will be the firmness of the cloth. Let us consider the case of two fabrics woven with identical warp and weft counts and thread settings. Consider that one is woven as plain weave and the other with any other weave such as twill, sateen etc. It will be seen that the latter will be less firm, and therefore of weaker texture than the former, because the threads composing it would be bent in a lesser degree than those of the plain weave, thereby causing them to be less firmly compacted. Thus it is important that the counts of warp and weft, the number of warp threads and picks per inch, and the weave, should be properly proportioned, in order to obtain the best results.

RANGE OF TEXTURE PRODUCED IN PLAIN WEAVES: 

The plain weave is produced in a variety of forms and textures, possessing totally different
characteristics, which adapt it for specific purposes. A variety of forms in textures are produced :

• By causing a differential tension between the warp threads during weaving.
• By using various counts of yarn for weaving different types of fabrics,
• By using warp and weft yarns of different counts in the same fabric,

The term ‘texture’ is related to type of material, counts of yarn, relative density of threads, weight,bulk, feel during handle, and other properties. The range of textures produced in plain cloth is wide. An ideal plain cloth is one which has identical or similar warp and weft constructional parameters.

END USES:

Plain weave finds extensive uses. It is used in cambric, muslin, blanket, canvas, dhothi, saree, shirting,suiting, etc.

WOVEN DESIGN | CLASSIFICATION OF WOVEN STRUCTURES | METHOD OF WEAVE REPRESENTATION | WEAVE REPEAT | BASIC ELEMENT OF WOVEN DESIGN

WOVEN DESIGN:

A woven cloth is formed by the interlacement of two sets of threads, namely, warp and weft threads. These threads are interlaced with one another according to the type of weave or design. The warp threads are those that run longitudinally along the length of the fabric and the weft threads are those that run transversely across the fabric. For the sake of convenience the warp threads are termed as ends and the weft as picks or fillings.

CLASSIFICATION OF WOVEN STRUCTURES:

Woven structures are classified into the following categories:

1.  Simple structures
2.  Compound structures

In case of simple structures, there is only one series of warp and weft threads. These threads interlace with one another perpendicularly. All the neighbouring warp and weft threads are parallel to one another and play an equally important role in determining the properties of the fabric. In case of compound structures, there may be more than one series threads, of which one set forms the body or ground and the other forms the figuring or ornamentation. Unlike the simple structures, the neighbouring threads need not be parallel to one another.

METHOD OF WEAVE REPRESENTATION:

A weave is the interlacing pattern of the warp and weft. Two kinds of interlacing are possible :

1.  Warp overlap in which warp is above weft
2.  Weft overlap in which weft is above warp

When the warp is lifted above the inserted weft, a warp overlap is obtained. When the warp thread is lowered, the weft thread is inserted above the warp thread and the weft overlap is obtained.

There are two practical methods of weave representation :

1.  Linear
2.  Canvas

In the linear method each warp thread is represented by a vertical line and each weft thread by a horizontal line. The point of intersection of lines corresponding to a warp overlap is marked by the dot, and the point of intersection corresponding to weft overlap remains unmarked.. Though this is a simple method, it is seldom used because the designer has to draw plenty of horizontal and vertical lines, which is time consuming.

In the canvas method, a squared paper is employed, on which each vertical space represents a warp thread and each horizontal space represents a weft thread. Each square therefore indicates an intersection of warp and weft thread. To show the warp overlap, a square is filled in or shaded. The blank square indicates that the weft thread is placed over the warp i.e. weft overlap. Several types of marks may be used to indicate the warp overlap. The ‘x’ mark is most commonly used.

Weave representation (Canvas method)

WEAVE REPEAT (REPEAT SIZE):

The repeat of a weave is a quantitative expression of any given weave. It indicates the minimum number of warp and weft threads for a given weave. It comprises of warp and weft repeat. The size of the repeat may be even or uneven depending upon the nature of the weave. In elementary weaves such as plain, twill, satin etc. the repeat size is normally even. However in weaves such as honey comb, huck a back the repeat size may be even or uneven. For any weave the repeat size is the sum of the warp and weft floats. Thus in case of a 2/1 twill the repeat size is 3 ¥ 3. It is common practice to denote one repeat of a weave on design paper.

BASIC ELEMENT OF WOVEN DESIGN:

The three basic elements in a woven design are :

1.  Design
2.  Draft or drawing plan
3.  Peg or lifting plan

The design indicates the interlacement of warp and weft threads in the repeat of the design. It is made up of a number of squares, which constitute the repeat size of a design. The vertical direction of the squares indicate the picks and the horizontal direction indicates the ends. A blank in a square indicates that a warp goes below the corresponding weft and ‘X’ mark in the square indicates that the warp floats above the weft.

The draft or drawing plan indicates the manner of drawing the ends through the heald eyes and it also denotes the number of heald shaft required for a given weave repeat. The choice of the type of drafting plan depends upon the type of fabric woven.

The peg or lifting plan provides useful information to the weaver. It denotes the order of lifting of heald shafts. In a peg plan the vertical spaces indicate the heald shafts and the horizontal spaces indicate the picks. The peg plan depends upon the drafting plan. In the case of a straight draft, the peg plan will be the same as the design. Hence no peg plan is necessary in the case of a straight draft. 

The design, draft and peg plan are illustrated with the aid of an example shown below

Basic elements of a Woven Design (2/2 twill weave)

BASIC LOOM MECHANISM | GENERAL PASSAGE OF THROUGH A LOOM | DESCRIPTION OF IMPORTANT PARTS OF A LOOM

BASIC LOOM MECHANISM:

The basic mechanisms in any type of loom can be classified as follows:

1. Primary motions
2. Secondary motions, and
3. Auxiliary motions.   

Primary motions: 

The primary motions can further be divided as shedding, picking and beat up motions. The shedding opens the warp sheet into layers to facilitate passage of shuttle. The picking motion causes the shuttle carrying weft to be propelled from one end of loom to another. The beat up motion lays the previously laid weft to the fell of the cloth.

Secondary motions:

The secondary motions comprise of take up and let off motions. The take up motion helps to wind the cloth on to the cloth roller and also influences the pick density in the cloth. The let off motion helps to let the warp from the weaver’s beam at an uniform rate thus maintaining the warp tension constant throughout the weaving process.

Auxiliary motions:

The auxiliary motions consist of the warp stop motion, weft stop motion and warp protector motion. The warp stop motion is used to stop the loom in the event of warp breakages. This is necessary to prevent fabric defects such as missing ends and floats. The weft stop motion is used to stop the loom in the event of weft exhaustion or weft breakages. This is necessary to prevent missing weft threads called cracks, in the fabric. The warp protector is used to prevent multiple warp thread breakages in the event of shuttle getting trapped in the middle of the warp sheet.

GENERAL PASSAGE OF THROUGH A LOOM:

The passage of warp through a loom is shown in Fig. 1.1. The warp after leaving the weaver’s beam 1 passes over two bars 2 and 3 connected by a bracket at each end. One half of the warp end now passes under the back lease rod 4, and the other half passes over this rod. Those warp ends which pass under the back lease rod pass over the front lease rod 5, and ends from over the back lease rod pass under the front lease rod. Therefore, the warp is completely divided as it passes through the lease rods, and facilitates the straightening of any warp ends which may break and become entangled before they reach the healds 6 and 7. The lease rods also assist in forming an even shed. Leaving the lease rods, the warp ends next pass through the healds. Odd numbered pass through the front heald 7, and the even numbered ends pass through the back heald 6. The healds consists of heald wires with eyes at the centre through which the warp ends are passed, the warp ends being thus controlled in their upward and downward movement. The warp ends next pass through the reed 8, this being comprised of a flat wire comb with the teeth secured at both ends. Usually two ends pass between one tooth and the next—this space being termed “dent”. In the figure, two warp ends are represented as being in the same dent.

Passage of warp in a loom

At the point 9 is what is known as the ‘Cloth fell’. It may be considered as the point where the warp and weft become cloth, because it is at this point where the last pick of weft, which was left by the shuttle, becomes beaten up. Passing forward, the cloth is held at each side by a temple 10 which holds the cloth fell out to the width of the warp yarn, in the reed. From the temples the cloth passes over the breast beam/front rest 11, partly round the sand or emery roller K, over the steel roller, or tension rod L, and then on to the cloth roller M.

DESCRIPTION OF IMPORTANT PARTS OF A LOOM:

Heald shaft:

This part is related to the shedding mechanism. The heald shaft is made of wood or metal such as aluminium. It carries a number of heald wires through which the ends of the warp sheet pass. The heald shafts are also known as ‘heald frames’ or ‘heald staves’. The number of heald shafts depends on the warp repeat of the weave. It is decided by the drafting plan of a weave. The main function of the heald shaft is as follows:

•  It helps in shed formation
•  It is useful in identifying broken warp threads
•  It maintains the order or sequence of the warp threads.
•  It determines the order of lifting or lowering the required number of healds for a pick. In other words it helps in forming the design or pattern in a fabric.
•  It determines the warp thread density in a fabric, i.e. the numbers of heald wires per inch determine the warp thread density per inch.

Sley or. lay:

It is made of wood and consists of the sley race or race board, reed cap and metal swords carried at either ends. The sley mechanism swings to and fro. It is responsible for pushing the last pick of weft to the fell of the cloth by means of the beat up motion. The sley moves faster when moving towards the fell of the cloth and moves slower when moving backwards. This unequal movement is known as ‘eccentricity of the sley’. It is needed in order to perform the beat up and also to give sufficient time for passage of shuttle to pass through the warp shed. The beat up of the lastly laid pick of weft is accomplished through a metal reed attached to the sley.

Shuttle:

It is basically a weft carrier and helps in interlacement of the weft with the warp threads to form cloth. The shuttle which is made of wood passes from one end of the loom to the other. It travels along the wooden sley race and passes between the top and bottom layers of the warp sheet. The shuttle enters a shuttle box fitted at either ends of the loom, after passing through the warp shed. A shuttle normally weighs about 0.45 kgs.

Shuttle Box:

It is the housing for the shuttle and is made of wood. It has a spindle and a picker. It may also

accommodate the picker without spindle. The top and side of the box towards the sley race are open. The shuttle dwells inside the box for the intermediate period between two successive picks.

Picker:

The picker is a piece made either of leather or synthetic material. It may be placed on a spindle or grooves in the shuttle box. It is used to drive the shuttle from one box to another. It also sustains the force of the shuttle while entering the box.

Reed:

It is a metallic comb that is fixed to the sley with a reed cap. The reed is made of a number of wires and the gap between wires is known as dents. Each dent can accommodate one, two or more warp ends. The count of the reed is decided by the number of dents in two inches. The reed performs a number of functions which are enumerated as follows:

•  It pushes the lastly laid pick of weft to the cloth fell.
•  It helps to maintain the position of the warp threads.
•  It acts as a guide to the shuttle which passes from one end of the loom to the other.
•  It determines the fineness of the cloth in conjunction with the healds.
•  It determines the openness or closeness of the fabric.There are various types of reed such as ordinary reed, gauze reed, expanding reed, V reed etc.

Warp Beam:

This is also known as the weaver’s beam. It is fixed at the back of the loom. The warp sheet is wound on to this beam. The length of warp in the beam may be more than a thousand metres.

Back Beam:

This is also known as the back rest. It is placed above the weaver’s beam. It may be of the fixed or floating type. In the first case the back rest merely acts as a guide to the warp sheet coming from the weaver’s beam. In the second case it acts both as a guide and as a sensor for sensing the warp tension.

Breast Beam:

It is also known as the front rest. It is placed above the cloth roller at the front of the loom and acts as a guide for the cloth being wound on to the cloth roller. The front rest together with the back rest helps to keep the warp yarn and cloth in horizontal position and also maintain proper tension to facilitate weaving.

Cloth Beam:

It is also known as the cloth roller. The woven cloth is wound on to this roller. This roller is placed below

the front rest.

LOOMS | CLASSIFICATION OF LOOMS | BRIEF DESCRIPTION OF VARIOUS LOOMS

Loom: 

"A loom is a device that causes interlacement two sets of threads, namely, warp and weft threads, to form a fabric."

Hand Loom

The very first loom in history is the pit loom. Subsequently the handloom was developed and

then the power loom. After the advent of power looms, a number of developments have taken place. The very first power looms that had been developed were of the non automatic type. These looms had neither a positive let off device nor warp stop mechanism or a weft changing mechanism. This demanded a great deal of attention from the weaver. The semi automatic loom was then developed which incorporated two out of the above three mentioned mechanisms. Then the automatic loom was developed which had all the three essential mechanisms, namely, positive let off device, warp stop mechanism and weft replenishment mechanism. The last century saw the development of shuttle less weaving mechanisms.

Classification of Looms:

BRIEF DESCRIPTION OF VARIOUS LOOMS:

The hand loom was operated by the weaver using his hands to propel the shuttle from one end to another. The weaver used his foot to operate the healds. The production in this type of loom was obviously very less and thus varied from weaver to weaver.

The power loom was operated by power. This reduced the strain of the weaver. Considerable
automation has taken place which resulted in lesser strain of the operatives and increasing the production and efficiency of the loom. The shuttle less looms are good examples.

The tappet, dobby and jacquard are warp patterning mechanisms. Among the shuttle looms, the tappet loom is the simplest. It is suitable for weaving up to 8 heald shafts. The dobby loom is suitable for figuring up to 40 heald shafts and the jacquard is suitable for elaborate designs running to several picks. The advantage of the jacquard mechanism is that it can control individual warp ends and hence has a large figuring capacity.

•  The multiple box mechanism is suitable for weft patterning, particularly in creating checked effects in the fabric. The colouring capacity of the multiple boxes ranges from 2 to 24.
•  The shuttle less looms have the advantage of higher speed and efficiency than the conventional shuttle looms. Also larger weft packages minimize the frequency of weft changes thus improving the loom efficiency