Chapter Ten Jacquard Fabrics 10.1 Elements of Jacquard Shedding 10.2 Preparation for Designing the Jacquard Fabrics 10.3 Steps in construction of Jacquard Design
Jacquard Fabric sample:
Jacquard Fabric sample:
10.1 Elements of Jacquard Shedding Introduction: To weave a fabric on loom, forming a shed is necessary. The tappet shedding is the simplest one. It can be used to weave plain, twill etc. Later, the dobby was invented. It can be used to weave more complicated weaves, such as diamond, diaper and some compound weaves.
But dobby shedding can not fit the requirement of large pattern which need not only a small group warp threads lifting in same way, but also the single thread lifting as well. See Fig. above. So another loom is to be created to satisfy the demand.
2. Jacquard machine and Jacquard shedding Fig. 10.1 1: hooks 2: knife 3:knife frame 4: neck cord 5: rod 6: grade 7: horizontal needle 8: needle broad 9: cylinder 10: spring box 11: spring 12: card
The principles of the Jacquard shedding are described as below: (flash) The warp threads are lifted by hooks 1, which are arranged in rows. The hook is made of wire. The top bent part of hook can be engaged by the knife 2. The knives are mounted in the knife frame 3, which reciprocates vertically once every pick. Each hook is connected with horizontal needle 7, which can deviate the hook to the left.
The right-hand ends of the needles protrude at the side of the machine, passing through the holes of needle board 8, which holds the ends of the needles in the proper position against the holes of cylinder 9. The left-hand end of the needles is positioned in the spring box 10. The spring 11 is intended to return the needle to initial position after the needle has been deviated by the card 12. If there is no hole in the card against the needle, the card presses the needle, moves the needle and shifting the hook to the left. The hook will not be engaged by the lifting knife. The warp thread remains in the lower position, forming the bottom part of the shed.
If there is a hole in the card opposite the needle, it is not deflected. The hook remains over the knife and at the next moment, the knife grasps it while going up, and lifts it. As a result, the harness cord and the warp thread are lifted. The warp thread forms the top part of the shed. The number of holes in the card determines the number of warp threads to be lifted in the particular shed, when this card operates. And the number of cards in the chain equals the number of weft threads in the repeat.
10.2 Preparation for Designing the Jacquard Fabrics 1. Calculate the repeats The warp repeat of the weave can be obtained by multiplying the warp density by the width of the pattern, and the weft repeat can be reached in the same way.
Warp repeatr O = warp density width of the pattern The total number of hooks should be equal to or more than the warp repeat. Weft repeatr y = weft density length of the pattern One weft thread corresponds with one card.
2. Select the design paper A design paper is characterized by the count, which is a ratio of vertical spaces to horizontal ones in each block. In order to retain correct proportions and shapes of figure designs, the ratio of vertical spaces to horizontal ones should be equal to the ratio of warp density to the weft density in the finished fabric.
Count of design paper can be calculated by the formula: a = PO b P y Where: a = number of vertical spaces in the block, which is usually assumed equal to the number of hooks in short row of Jacquard machine; b = number of horizontal spaces in the block; P O = warp density of the finished fabric; P y = weft density of the fabric.
Next step is to find the number of blocks, which in horizontal direction is calculated by the formula: M = R O Where: R O is the warp repeat of the Jacquard weave. a
The number of blocks in vertical direction is calculated in the similar way: Where: R y is the weft repeat of the weave. The total number of block is M N. N The purpose for selecting design paper is to retain correct proportions and shapes of figure designs = R y b
Different design papers are shown below: 8/8 8/10 8/12 8/13 8/16
One block of the design paper:
10.3 Steps in construction of Jacquard Design Studio techniques/conventional system. Ⅰ. Designer: creating new ranges, pattern sketches Ⅱ. Drafter: transferring sketch on to point paper complete with structure Ⅲ. Cutter: semi-mechanical cutting methods, reading in weave structure from point paper.
Ⅰ.The first step The first step is to draw the picture or to copy it from the art book or any other source. A copy can be made by using the tracing paper. The figure of any shape can be chosen, and as an example of figure the flower has been chosen, which is shown at A in Fig. 10.3.
The picture should be divided by vertical lines into a certain number of spaces equal to the number of blocks in horizontal direction of the design paper, which have been calculated before constructing the design.
Ⅱ. The second step The second step is to transfer the outline of the figure from tracing paper to design paper. It can be done easily, since the number of squares of the tracing paper equals the number of blocks of the design paper. See Fig. B at next page:
Ⅲ. Cutter: Before cutting, the type of weave for the figure and the ground should be chosen. For this example at B in Fig.10.3 B plain weave is chosen for the figure, and twill l/7 for the ground.
The 17th and 92nd horizontal space are cut as below:
2: Electronic data processing system Fig.10.4 Construction of jacquard design by electronic way
In jacquard weaving, computer technology is now successfully employed. Designer: creating new ranges. Pattern sketches or designs can be either created on the color monitor or images from any media can be scanned into the system. Programmer: structures added, exchanged, repeated, rescaled, contours adjusted. The information is transferred into the electronically controlled cutting machine or directly record on magnetic tape cartridge.
Home works 1. Get to know each part of the Jacquard machine at Fig.10.1. 2. Get to know how the design paper is selected.