3.1.1 Cam Shedding . Figure 9. Hand or manual drawing-in. Hand Drawing Cam shedding (courtesy of NC State College of Textiles). 3.1.2 Dobby Shedding.
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Tex tile Weaving 1 INTRODUCTION .. 3 2 WARP PREPARATION . 4 2.1 Direct Warping .. 4 2.2 Indirect Warping 4 2.3 Slashing 5 2.4 Drawing -In 8 2.5 Tying -In . 9 3 WEAVING . 9 3.1 Shedding .. 9 3.1.1 Cam Shedding . 9 3.1.2 Dobby Shedding 10 3.1.3 Jacquard Shedding . 11 3.2 Filling Insertion 12 3.3 Shuttle Weaving . 12 3.3.1 Rapier Filling Insertion .. 13 3.3.2 Projectile Filling Insertion . 15 3.3.3 Air Jet Filling Insertion 15 3.3.4 Water Jet Filling Insertion . 16 3.4 Beat -Up .. 17 3.5 Let-Off and Take -Up 17 3.6 Weaving in Combination with Embroidering 17 4 BASIC WOVEN DESIGNS 19 4.1 Plain Weaves .. 19 4.1.1 The Basket Weave .. 20 4.1.2 The Oxford Weave .. 21 4.2 Twill Weaves 21 4.2.1 The 2 x 1 Twill Weave 21 4.2.2 The 2 x 2 Twill Weave 22 4.2.3 The 3 x 1 Twill Weave 23 4.3 The Satin Weave .. 24
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Textile Weaving, © 2012 Cotton Incorporated 3 1 INTRODUCTION Weaving is the process of interlacing sets of yarns together to form a woven fabric structure. As diagrammed in Figure 1, one set of yarns run along the fabric length or machine direction; these are called warp yarns, warp ends, or simply ends. The other set of yarns run along the fabric width and are called weft yarns, picks, or filling yarns. Figure 1. Compone nts of a woven fabric structure The warp yarns unwind from a loom beam and move forward at a fixed rate as the woven fabric is formed. The weft yarns typically are inserted one at a time across the warp yarns. The warp yarns are under tension and undergo stress, strain, and abrasion as they move up and down and follow a path through the various parts of the loom. The tension is necessary in order to form a clear opening, or shed, for insertion of the weft yarns. This booklet covers the preparation of the warp yarns for weaving, the basic motions of a weaving machine, and basic woven designs. Red yarns: filling weft picks Green yarns: warp yarns warp ends Transitional selvage and outer selvage with identification threads
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Textile Weaving, © 2012 Cotton Incorporated 4 2 WARP PREPARATION Because the warp yarns are under high tension, are in very close proximity to one another, and go through various weaving machine elements, they must be properly prepared for the rigors of weaving. The warp yarns go through several processing steps before being wound onto a loom beam that will be inserted at the back of a weaving machine. The processes to prepare the warp yarns for efficient weaving comprise what is called warp preparation; they include warping, slashing, and drawing- in or tying-in. 2.1 Direct Warping This method of warping transfers yarns from many cones or tubes and winds them simultaneously onto a section beam in a parallel arrangement called a yarn sheet. The yarn packages are held on a device called a creel. For spun yarns, a creel typically holds 400 to 800 yarn packages, while filament yarn creels can hold over 1,000 yarn packages. Each section beam contains the same number of yarns. Because most woven fabrics contain well over 2,000 warp yarns, several section beams are needed to provide the required number of warp yarns for a given fabric construction. For a fabric requiring a total of 4,000 warp yarns, 10 section beams need to be formed, each containing 400 warp yarns. It is critical that the warp yarns be wound with equal tension, that they not be crossed or rolled over one another, and that none be lost (broken and not tied back together) or missing. Various elements of the warping machine, such as tension devices, static eliminators, broken yarn detectors, wild yarn (yarn waste) detectors, eyelet boards, and expansion combs help ensure that the warping machine forms high-quality beams. For most fabrics, all section beams must have identical yarn tension, uniform yarn count, and equal numbers of yarn ends. The warping operation shown in Figure 2 is transferring 400 yarns from cones onto a section beam. In the background is the creel holding the yarns as they make their way to the warper. Above the section beam is an expansion comb, which helps to keep the yarns straight and parallel as they wind onto the section beam. 2.2 Indirect Warping This method of warping uses smaller creels with fewer yarn packages and therefore requires less space. Bands or sections of parallel yarns are wound onto a pattern drum. The bands are wound parallel to one another, contain the same number of yarns, and are identical in make-up. Indirect warping is preferred for sample work, short runs, and fabrics with pattern stripes. The total required number of warp yarns is wound onto the drum, eliminating the use of section beams. However, the yarn on the pattern drum must be then be rewound onto a flanged loom beam suitable for use in further processing.
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Textile Weaving, © 2012 Cotton Incorporated 5 Figure 2. Direct warping from yarn packages to a section beam Figure 3 . Indirect warping of bands or secti ons of yarn onto a pattern drum 2.3 Slashing The purpose of slashing spun yarns is to encapsulate the yarn in a film of size in order to reduce yarn hairiness, improve yarn abrasion resistance, and increase yarn strength. Figure 4 illustrates how slashing reduces the hairiness of spun yarns. For spun cotton yarns, size is typically starch or a blend of starch and polyvinyl alcohol (PVA). In the case of filament yarns, the size is formulated not to encapsulate the yarn, but to hold or glue the individual filament together. PVA is commonly used as size for filament yarns.
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Textile Weaving, © 2012 Cotton Incorporated 6 Slashing may be omitted with coarse plied spun yarns or heavier-denier filament yarns, or in production of fabrics with a low-density warp (in which the yarns are not close to one another). Figure 4. Reduction of yarn hairiness by slashing In the case of direct warping, the required number of section beams are placed on a slasher creel. Figure 5 shows section beams loaded on a slasher creel for the weaving of denim. To produce a yarn-dyed woven fabric with a striped pattern, section beams of yarn are dyed on a special beam and then placed on the slasher creel, as shown in Figure 6. The different colors of yarn are aligned in an expansion comb at the front end of the slasher in the correct order to form the desired color pattern in the fabric. Figure 5. Slasher creel loaded with 12 section beams for weaving denim Before Slashing SlashingCross-Section of Spun Yarn Yarn Hairiness Size Film AfterSlashing Section Beams in Slasher Creel
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Textile Weaving, © 2012 Cotton Incorporated 8 2.4 Drawing -In The last warp yarn preparation step is to draw each warp yarn through the appropriate loom elements, as illustrated in Figure 8. If a given yarn breaks, the associated drop wire makes an electrical contact that stops the weaving machine. The heddles are necessary to control the weave design, and the reed helps to space the yarns equally and provide a means of pushing, or beating, each weft yarn into the fabric. Each opening or space in a reed is called a dent. Drawing-in is sometimes done by hand (as shown in Figure 9), but can be done electronically. If all yarns are drawn in properly, then weaving will be more efficient, fabric design will be accurate, and the overall fabric appearance will be acceptable. Figure 8 . A warp yarn drawn through a drop wire, heddle, and reed dent Figure 9 . Hand or manual drawing -in Hand Drawing
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Textile Weaving, © 2012 Cotton Incorporated 9 2.5 Tying -In In mass production of a fabric in the same fabric design, it is not necessary to redraw the warp yarns in order to replace a loom beam that has run out with a new beam of the same style. Instead, the much faster process of tying-in can be used. A tying-in machine takes each end of warp yarn on the existing loom beam and ties it to the associated yarn on the replacement loom beam. 3 WEAVING Forming a woven fabric requires five basic loom functions or motions: shedding, filling insertion, beat-up, let-off, and take-up. The first three motions take place in a set time interval and follow one another sequentially. Because these motions cannot happen simultaneously, conventional weaving is a single-phase process. Some machines can insert a number of picks almost simultaneously into a number of shed openings and beat each pick into the fabric. However, these multiphase (multished) machines have limited design potential and generate more lint when weaving spun yarns. 3.1 Shedding This loom function separates all the warp yarns into a weave shed (opening) formed between a top shed (yarns that are raised) and a bottom shed (yarns that are not raised). Each weft yarn is inserted into the opening created by shedding of the warp yarns. Devices called harnesses contain a certain number of heddles through which warp yarns are drawn (see Figure 8, above). Harnesses are raised and lowered to produce a particular woven design. There are three general methods of shedding, each with specific design capabilities. 3.1.1 Cam Shedding Cam shedding typically uses 6 to 8 harnesses, though sometimes up to 12. As illustrated in Figure 10, each harness is controlled by a rotating cam that forces the connected harness to move up and down in a prescribed manner to produce a particular fabric design. The profile or shape of each cam and its position on the camshaft dictate the movement of the connected harness. With cam shedding, designs are limited to basic weaves such as plain weave, simple twill weaves, and common satin weaves.
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Textile Weaving, © 2012 Cotton Incorporated 10 Figure 10 . Cam shedding (c ourtesy of NC State College of Textiles) 3.1.2 Dobby Shedding Dobby shedding typically uses 12 to 32 harnesses, which allows for a broader range of woven designs than with cam shedding. In addition to the basic weaves, dobby shedding makes it possible to weave small geometric figures, spot weaves, and more complex pattern stripes. Many machines with dobby shedding use plastic sheets with punched holes to direct the harnesses to be lifted in a certain sequence to produce a given design. A punched hole allows a pin to penetrate the sheet and initiate lifting of the associated harness. The weave design is thus controlled by the positioning of the holes in the pattern sheet. Figure 11 shows a weaving machine using this type of dobby shedding. Figure 11 . Dobby shedding Today, many weavers are investing in electronic dobby shedding machines that work in a much simplified manner, with no punched sheets. Connected with a computer-aided design system, these machines can quickly download and weave a developed design. Figure 12 shows an electronic dobby shedding machine.
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Textile Weaving, © 2012 Cotton Incorporated 11 Figure 12 . Electronic dobby shedd ing machine with cover removed 3.1.3 Jacquard Shedding Instead of using harnesses to control the weave design, Jacquard shedding employs draw cords that drop down from a Jacquard head; each cord is connected to an individual heddle or a small group of heddles. This type of control makes it possible to form large design repeats and very intricate designs. A given Jacquard machine will have a certain number of hooks that control the lifting of warp yarns. Having more hooks makes it possible to weave larger design repeats and more intricate designs. Figure 13 shows a Jacquard machine and its associated draw cords. Figure 13 . Weaving machine with Jacquard shedding (courtesy of Picanol) Dobby with cover off Jacquard Fabric Filling Yarn Packages Filling Yarn Feeders Jacquard Harness Assembly (Draw Cords) Gantry Jacquard Head
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