9 Jacquard weaving

B. A. Muralidhar

1. INTRODUCTION

Shedding systems are the different mechanism employed to create sufficient gap between the warp layers for the uninterrupted passage of the weft yarn from one side of the loom to the other. TheJacquard shedding named after its inventor, was developed by a French weaver and merchant Joseph Marie Jacquard in the year 1804. The invention of jacquard was considered as forefather to the development of calculators and computers.As this was the first machine which could read the information contained on a punched card.

This shedding system is used for weaving designs beyond the scope of a CAM and dobby shedding systems. Jacquard is used to create elaborate, intricately woven figured designs with fine details. Jacquard fabrics have a distinct front and back, with varying fineness. With the jacquard shedding system, individual ends can be controlled independently and thus a large, intricate figured designs with several hundred or more ends working differently and repeating upon a similar number of picks can be easily produced.

Jacquards are primarily classified as:

1) Ordinary Jacquards

2) Special Jacquards

1.1 ORDINARY JACQUARDS:

These jacquards are extremely versatile and can be used to produce, figured designs in almost any type of count, construction.

1.2 SPECIAL JACQUARDS:

Special jacquards are the modified of the ordinary jacquard, these jacquards are built for a special type of construction which restricts their applicability but, may result in certain advantages in their own field of operation. These special machines include self-twilling jacquard, cross-border jacquard, banister jacquard, pressure harness jacquard,leno brocade, inverted hook, inverted hook jacquard and the fine pitch jacquard.

Jacquards are further classified based on (i) the type of shed formed; (ii) pitch; and (iii) the figuring capacity.

1.3 Shed type:

The shed formation is dependent on the mechanical action of the jacquard and it influences the speed at which the jacquard works. Further, on occasions the shedding system may have a bearing upon the construction of designs.

a) Single lift	–	Bottom closed shed
b) Centre shed	–	Centre closed shed
c) Double lift	–	Open shed / Modified open shed

1.4 Pitch:

Jacquards may be manufactured in a variety of pitches broadly distinguished as fine and coarse pitch jacquards. The pitch regulates the dimensions of the jacquard machine. Jacquards classified beneath shed type could be set in any pitch settings.

1.5 Figuring capacity:

The figuring capacity of the jacquard is the size of the jacquard and it refers to the number of independent end lifts that can be obtained, it may range from 100 to 1792 hooks. However, virtually unlimited number of picks can be introduce in weave repeat.

2. PARTS OF AN ORDINARY JACQUARD

A jacquard machine consists of the following main parts such as the needles, spring-box, needle-board, hooks, griffe, cylinder, pattern cards, card cradle, harness, comber-board coupling and lingo.

Needle: is one of the main part of a jacquard. The horizontal needle is bent at a point to secure the vertical hooks. Eight different bent position in the needle will be required by an eighth row jacquard machine as shown in Figure 2.1. The needle head rests with their head on the needle board projecting about 4 mm towards the cylinder. At the rear end of the needle is a small helical spring contained in the spring-box.

Spring-box: the rear end of the needle is passed into the spring-box and the loop in the needle permits a flat wire to be inserted to secure the needle in position. Pressing the needle at the head compresses the spring and on removal of the pressure the spring pushes the needle back to its natural position.

Needle-board: this wooden perforated board serves as a guide. It has holes corresponding to the number of needles presented to the cylinder.

Hooks: are vertical wires bent at the top to form the hook. The hook holds its position over the griffe bar, at the bottom the hooks double at the base and is turned upwards for about one third of their lengths. This doubled end is passed through a narrow slot in the grate,which prevents the hook from twisting around. The neck cords are looped to this bottom portion of the hook to which the harness cords are connected.

Griffe: strong horizontal iron knifes are contained in an iron frame called griffe. The griffe with knifes are worked vertically to rise and fall. There are as many knifes in a jacquard as there are hooks in the short row.

Cylinder: the punched cards are laced to form an endless chain and are passed over a four sided,seasoned wood prism called cylinder. Each face of the wooden cylinder is perforated corresponding to the number of needles. The function of the card cylinder is to present, one card to the needles at a time, for every 1/4th revolution of the cylinder.

Pattern cards: punched pattern cards are laced together to form an endless chain. There are lace holes at each corner and in the centre for lengthy pattern cards to increase their stability. A 400 hooks jacquard machine pattern card size would be about 6 cm in width x 40 cm in length.

Card cradle: are provided (where large number of cards are required to produce the design) below the steel girders over which the jacquard machine is mounted, to keep the punched cards in sequence and in a convenient position. The cradle consists of two curved iron rods slightly larger than the length of the cards. Metal wires are inserted in the punched card chain at regular intervals of 12, 16, 20 or more cards as suitable. These rods are slightly larger than the punched cards. These metal rods both ends rest on the curved sides of the cradle allowing the cards to form a neat stack above the warp sheet.

Harness: the jacquard harness consists of a neck cord connected to the bottom of the hook and threaded through the bottom board. The yellow harness cords are connected to the neck cord and are passed separately through the comber board, extending across the width of the loom. Top, bottom coupling, mail eye and the dead weight lingo are supported by the harness cord.

Comber board: are perforated board extending across the width of the loom, its objective is to spread the harness cords uniformly.

Coupling: are part of the harness and consists of the top and the bottom loop, a mail and a lingo.

Lingo: are cylindrical dead weigh suspended at the end of the coupling to keep the harness down.

Figure 2.1 Side view of single-lift single-cylinder jacquard

2.1 PRINCIPLES OF OPERATION

Jacquard designs are transferred from point paper to pattern cards in the form of holes and blanks. A hole in a pattern card indicates lifting of an end however, a blank indicates a lowering of an end to the bottom shed. One pattern card controls the selection of all the ends for one particular pick. Figure 2.1 shows working components of a single lift single cylinder jacquard.

Jacquard operation involves:

1) When the needle is opposed by a blank in the punch card – as the cylinder moves in and presents the card to the needle, the needle encountering the blank forces the needle back and this in turn presses the hook clear of the knife, just prior to the upward movement of the griffe bar.

2) When the needle is opposed by a hole in the punch card – as the cylinder moves in and presents the card to the needle, the needle encountering the perforations in the card enters the corresponding hole in the cylinder and no action takes place. This allows the hooks, connected to the needle to remain over the knife which in its upward movement takes the hook with it, thus lifting the ends into the top of the shed line.

Consider a 400 hooks capacity jacquard machine. This machine can handle 400 ends working independently, requiring 400 vertically arranged hooks and 400 horizontally arranged needles. The needles can be arranged in 8 rows and each row will have 50 needles. Hooks which are connected to ends through harness cords are also arranged in 8 rows and each row having 50 hooks. One knife bar is responsible for lifting and lowering one row of hooks. However, the lifting and lowering of the ends will be ascertained by the selection mechanism of the punched cards. The needles are connected with springs at the opposite side of the cylinder to enable the needles move clear off the knife bar (or) hold its position depending on the presence of a blank (or) a hole in the punched cards. The kink present in the needle, bring back the hooks tilting away from the vertical plane of the knife.

In a single lift single cylinder jacquard, if the loom speed is 300 picks/minute. The cylinder will have to turn 300 times and the knife will have to move up and down 300 times. These movements impede the speed of the loom.

In a single lift single cylinder jacquard:

a) The shed is formed when the griffe bar knife rises the hooks.

b) SLSC jacquard forms a bottom-closed shed.

c) The lifted warp ends are highly strained and may cause end breakage.

d) More time is required to form the shed.

3. HARNESS AND DESIGN CALCULATIONS

The harness is a system of connecting cords, healds and lingos for transmitting the hooks movement to the individual warp ends.

The jacquard is placed on top of the loom with the card cylinder in the front or back called the Norwich system, or at the left or right of the loom called the London system.

In the London arrangement, the card cylinder is at the sides and the long rows of hooks are at perpendicular to the comber board, therefore the harness cords are crossed with each other in its passing from the neck cords to the holes in the comber board.

Whereas, in the Norwich arrangement, the card cylinder is at the back or front of the loom, with the long rows of hooks parallel with the length of the comber board such that the harness cords are not crossed.

In tying, the harness the first hook taken when facing the cylinder is on the right, and the other hooks follow in consecutive order from 1 to 8 as indicated in Figure. 3.1

Figure 3.1 Norwich (a) and London (b) tie

If the jacquard has as many hooks as there are figuring threads in the full width of the fabric, then only one harness cord is connected to each hook and the tie is called single tie. However, if there are more figuring threads than the lay-over or repeating tie is used (Figure 3.2). In a layover tie-up the number of hooks tied up gives the maximum number of threads in the repeat in the width of a design. For Example, consider a 400 hooks capacity jacquard operating 400 independent ends. Now if the fabric has 4000 ends then 10 repeats of the design can be produced on the entire width of the fabric. Assuming that the hooks are arranged in eight rows and each row having 50 hooks. Then each hook will effectively control 10 ends (4000/400). The interlacement pattern of end 1, 401, 801. 1201, 1601, 2001, 2401, 2801, 3201, 3601 will be similar and are controlled by hook no. 1 through 10 harness tie-up. All hooks across the design are similarly tied up. This is depicted in Figure 3.2 Individual harness cords pass through the perforations of a comber board and dead weights (lingos) pull the harness (ends) down.

Figure 3.2. Straight (a) and lay-over or repeating (b) tie

Sett of the harness is decided by the number of holes in the comber board. Usually the number of holes in each short row of the jacquard and the comber board are similar. Thus, in an eight row jacquard machine there will be 8-holes in the wooden comber board for a coarse sett. For a medium sett, the holes are staggered to give as much space between the holes. However, in very fine sett harnesses, the comber board may contain twice as many holes as there are hooks in a short row of the jacquard. In tying up the harness cords from the first row of hooks are passed through the odd holes, and from the second row through the even holes.

4. SIZE OF REPEAT

The size of the repeat in weaving depends on the finished state of fabric, because the finished fabric contains more number of threads per unit space than the loom state. Jacquard design requires to be constructed in accordance with the finished condition of the cloth. For example: if a cloth contains 40 ends/cm and 40 picks/cm when finished, a design 10 cm long and 10 cm wide will repeat upon 40 x 10 = 400 picks i.e. 400 cards and 40 x 10 = 400 ends.

The repeat length in a jacquard is theoretically unrestricted, however in practice there is a limit to the number of pattern cards that can be conveniently made to work in a machine.

The width of the repeat is more restricted than the length. As in the loom it cannot exceed the space occupied by one division of the harness in the comber board. The major factors influencing the width size of the repeat are the harness tie-up, cloth construction and the sett of the harness. For example: assume that the cloth contracts 12% from the reed width  on finishing, a 400 hook tie with 40 harness cords /cm will give (400÷40)-12% = 8.8 cm width of design repeat in the finished cloth.

5. COUNT OF DESIGN PAPER

In the design paper, each horizontal space corresponds to a weft pick and each vertical space to a warp end and a hook of jacquard. For convenience the point paper is divided by thick lines usually into square blocks. For the card cutting, the vertical ruling of the design paper is arranged to coincide with the jacquard hooks i.e. the design is divided into as many vertical spaces as there are hooks in the short row of the jacquard. For example the design paper used for an 8 row jacquard will have eight vertical spaces between each pair of thick lines. To retain the correct proportion and shape of figure, the number of vertical and horizontal spaces to be in the same proportion as the ends and picks per unit space in the finished cloth. The necessity to use proper ruled paper is illustrated using a small motif of a spot in Figure 5.1. (A), (B) and (C). In (A) the spot is repeated on equal number of ends and pick, and the same spot if required in twice the number of ends as (A) would look like the one shown in (B) and (C) represents the spot repeated on twice the number of picks to (A).

6. CONSTRUCTION AND DEVELPOMENT OF DESIGN

The construction and development of a jacquard design is a very tedious and time consuming process. A considerable amount of skill and experience is required in developing and reproducing a jacquard design. Which include the following steps:

1. Selecting a design/figure from a woven sample from which the design is reproduced (or) from an original sketch.
2. Enlargement of the design/figure on the point paper, according to the sett of the cloth i.e. the number of ends and picks required for one repeat of the design.
3. The enlarged design/figure is squared out and the design part alone is painted with a light transparent colour.
4. Suitable weaves for the development / binding of the design/figure are inserted and then the ground weave is marked.
5. Preparations for card punching is carried out.
6. The punched cards to be laced according to the design and mounted on the card cylinder of the jacquard for its production.

Conclusion:

In this module on jacquard weaving, the viewers have been briefed on the different types of jacquard. Further, the main parts of the jacquard and its functions has been dealt with, followed by the working principle and operation of a single lift single cylinder jacquard. During the end of this module we have also briefed on the construction and development of jacquard designs.

References

1. Grosicki Z.  J.  Reprinted  (2004).  Watson’s  Textile  Design  and  Colour  Woodhead Publishing Limited, Cambridge, England.
2. Talukdar M. K., Sriramulu P. K., Ajgaonkar D. B. 1998. Weaving-Machines-Mechanisms-Management, Mahajan Publishers Private Limited, Ahmedabad, INDIA

Web links

• textilelearner.blogspot.com/ http://nptel.ac.in/courses/116102005/35