Cotton fabric manufacturing starts with the preparation of the yarn for weaving or knitting.
Weaving is the oldest method of making yarn into fabric. While modern methods are more complex and much faster, the basic principle of interlacing yarns remains unchanged. On the loom, lengthwise yarns called the warp form the skeleton of the fabric. They usually require a higher degree of twist than the filling yarns that are interlaced widthwise. Traditionally, cloth was woven by a wooden shuttle that moved horizontally back and forth across the loom, interlacing the filling yarn with the horizontally, lengthwise warp yarn. Modern mills use high-speed shuttleless weaving machines that perform at incredible rates and produce an endless variety of fabrics. Some carry the filling yarns across the loom at rates in excess of 2,000 meters per minute. The rapier-type weaving machines have metal arms or rapiers that pick up the filling thread and carry it halfway across the loom where another rapier picks it up and pulls it the rest of the way. Other types employ small projectiles that pick up the filling thread and carry it all the way across the loom. Still other types employ compressed air to insert the filling yarn across the warp. In addition to speed and versatility, another advantage of these modern weaving machines is their relatively quiet operation. There are three basic weaves with numerous variations, and cotton can be used in all of them. The plain weave, in which the filling is alternately passed over one warp yarn and under the next, is used for gingham, percales, chambray, batistes and many other fabrics.
The twill weave, in which the yarns are interlaced to form diagonal ridges across the fabric, is used for sturdy fabrics like denim, gabardine, herringbone and ticking. The satin weave, the least common of the three, produces a smooth fabric with high sheen. Used for cotton sateen, it is produced with fewer yarn interlacings and with either the warp or filling yarns dominating the “face” of the cloth. In some plants, optical scanners continuously monitor fabric roduction looking for flaws as the cloth emerges from the weave machine. When imperfections appear, computers immediately print out the location of the flaw so that it can be removed later during fabric inspection.
Knitting is a method of constructing fabric by using aseries of needles to interlock loops of yarn. Lengthwise rows of these loops, comparable to the warp yarn in woven goods, are called wales. Crosswise rows, comparable to filling yarns, are known as courses. There are numerous similarities in knitting done by hand and machine, but there are also some marked differences. Most cotton is knit on circular machines which have needles fixed to the rim of a rotating cylinder. As the cylinder turns, the needles work their way from stitch to stitch producing a tubular fabric. Its width is regulated by the size of the cylinder, which usually ranges from 9 to 60 inches in diameter. A hand knitter uses two needles forming one stitch at a time. Depending on the width of fabric desired, a modern knitting machine might use over 2,500 needles. Instead of a single cone of yarn, a knitting machine may have up to four cones per inch of fabric width. For example, a machine with a 32-inch cylinder can have over 2,700 needles and 128 cones of yarn feeding simultaneously. These are typical statistics for a machine used in making underwear knits, but figures vary according to the type of machine used and the fabrics produced.
The flat knitting machine is another basic type. Designed with a flat bed, it has dozens of needles arranged in a straight line and produces a knit fabric that is flat, similar to woven fabric. A flat knitting machine makes over one million stitches a minute, and can be set to drop or add stitches automatically in order to narrow or widen the fabric at certain points to conform to specific shapes. Knitting machines can be programmed to produce a wide variety of fabrics and shapes.
Cotton fabrics, as they come from the loom in their rough, unfinished stages, are known as greige goods. Most undergo various finishing processes to meet specific end-use requirements. Some mills, in addition to spinning and weaving, also dye or print their fabrics and finish them. Others sell greige goods to converters who have the cloth finished in independent plants. Finishing processes are numerous and complex, reflecting today’s tremendous range and combination of colors, textures and special qualities. In its simplest form, finishing includes cleaning and preparing the cloth, dyeing or printing it and then treating it to enhance performance characteristics. To produce a smooth surface in preparation for dyeing and finishing, the greige goods are passed rapidly over gas-fired jets or heated copper plates to singe off lint and loose threads. Moving at speeds that can be greater than 200 yards a minute, the material is scoured and bleached in a continuous process that involves the use of hydrogen peroxide. The time for the chemicals to do the preparation reactions occurs from piling the fabric on conveyor belts that pass through steaming chambers, or stacking in large steam-heated, J-shaped boxes before the goods are withdrawn from the bottom. If a more lustrous cloth is desired, the goods are immersed under tension in a caustic soda solution and then later neutralized. The process, called mercerizing, causes the fiber to swell permanently. This gives the fabric a silken sheen, improves its strength and increases its affinity for dye. Mercerizing also can be done at the yarn stage.
The most commonly used processes for imparting color to cotton are piece dyeing and yarn dyeing. In piece dyeing, which is used primarily for fabrics that are to be a solid color, a continuous length of dry cloth is passed full-width through a trough of hot dye solution. The cloth then goes between padded rollers that squeeze in the color evenly and removes the excess liquid. In one variation of this basic method, the fabric, in a rope-like coil, is processed on a reel that passes in and out of a dye beck or vat. Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction. One of the most commonly used yarn dyeing methods is package dyeing. In this system, yarn is wound on perforated cylinders or packages and placed on vertical spindles in a round dyeing machine. Dye solution is forced alternately from the outside of the packages inward and from the inside out under pressure. Computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy.
Printing colored designs on cotton cloth is similar to printing on paper.Long runs of the same fabric design are produced on a roller print machine operating at speeds between 50 to 100 yards a minute. As many as of 10 different colors can be printed in one continuous operation. A typical printing machine has a large padded drum or cylinder, which is surrounded by a series of copper rollers, each with its own dye trough and doctor blade that scrapes away xcess dye. The number of rollers varies according to the fabric design, since each color in the design is etched on a separate roller. As the cloth moves between the rotating drum and rollers under great pressure, it picks up color from the engraved area of each roller in sequence. The printed cloth is dried immediately and conveyed to an oven that sets the dye. Automatic screen-printing is another principal method for imparting colored designs to cotton fabrics. Although lower than roller printing, it has the advantage of producing much larger and more intricate designs, elaborate shadings and various handcrafted effects. In flat bed screen-printing, the fabric design is reproduced on fine mesh screens, one for each color. Oneach screen, the areas in the design that are not to be penetrated by the dye are covered with lacquer or some other dye-resistant coating. The screens are coated with dye on the back nd mounted in the proper sequence above a flat bed. As a belt carries the fabric along from screen to screen, a squeegee or roller presses the dye through the open area of the screen onto the fabric. The new flat bed machines can have speeds of up to 1,200 yards per hour for a fabric with a 36-inch design repeat. Faster by far are the recently developed rotary screen printing machines with production speeds of up to 3,500 yards an hour. The system combines roller and screen printing, utilizing perforated cylinders instead of flatscreens. The color paste is fed inside the cylinders and a small metal roller forces the color through the pores of the cylinder onto the fabric which is moving continuously under the cylinders. As many as 16 colors can be printed on one fabric using this method. Use of this technique is increasing since the screens or cylinders can be produced less expensively than the engravedcopper rollers used in roller printing.
Finishing, as the term implies, is the final step in fabric production. Hundreds of finishes can be applied to textiles, and the methods of application are as varied as the finishes. Cotton fabrics are probably finished in more different ways than any other type of fabrics. Some finishes change the look and feel of the cotton fabric, while others add special characteristics such as durable press, water repellency, flame resistance, shrinkage control and others. Several different finishes may be applied to a single fabric.
Cotton’s Major Uses
Cotton is used for virtually every type of clothing, from coats and jackets to foundation garments. Most of its apparel usage, however, is for men and boys’ clothing. Cotton supplies over 70% of his market, with jeans, shirts and underwear being major items. In home furnishings, cotton’s uses range from bedspreads to window shades. It is by far the dominant fiber in towels and washcloths, supplying almost 100% of that market. Cotton is popular in sheets and pillowcases, where it holds over 60% of the market. Industrial products containing cotton are as diverse as wall coverings, bookbindings and zipper tapes. The biggest cotton users in this category, however, are medical supplies, industrial thread and tarpaulins.
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