to lower the cost of certain fabrics by combining lessexpensive yarns with the more costly. They can be used to add strength to a weak yarn, such as adding nylon to a metallic yarn. A mixture is sometimes referred to as a combination fabric. Special Types of Yarns Textured Yarns The appearance and touch of multifilament yarn can be altered from smooth, lustrous, and flat to crimped, dull, and soft (somewhat like the appearance of spun yarn). This modification yields entirely new yarn properties, which in turn provide entirely new fabric properties. The filament yarns are modified before they are woven or knitted. Because the modified yarn takes on an entirely new surface or texture, it is called textured yarn. The ability of filament yarns to be modified to give them new shape, crimp, and bulk derives from the thermoplastic nature of the fibers from which they are produced (see p. 28). The various methods for making textured yarn involve shaping the yarn to some desired configuration of crimp or bulk by setting the yarn, heating it to near its melting point, and then cooling the material. (The exception to this is the air-jet method, described on p. 74.) Favorable Properties The following are favorable properties of textured yarns. u Possess high stretch and/or bulk u Provide greater cover (opacity) than regular filament yarns u Afford greater breathability and absorption than regular filament yarns u Afford greater insulation than regular filament yarns u Provide softer and drier hand than regular filament u Provide spunlike yarn characteristics u Are more wrinkle resistant than spun yarns or regular filament yarns Unfavorable Properties The following are unfavorable properties of textured yarns. u They have a tendency to snag on broken fingernails, chair seats, and similar objects. Because it is FABRIC SCIENCE A 76 F a long filament rather than a short-spun fiber that snags, the likelihood of damaging the fabric is high. Textured yarns should, therefore, be avoided in such garments as children’s playwear, where hard, rough use is anticipated. u Possible growth problem u Poor abrasion resistance u Easy soil penetration Types of Textured Yarn There are several methods of producing textured yarns. They are classified into three main categories: stretchtextured, bulk-textured, and set-textured type. (See Figure 4.10.) Stretch-Textured Stretch-textured yarn is made primarily from nylon and used extensively in leotards, stretch ski pants, stretch hosiery, and similar items. These yarns can be stretched from 30 to 50 percent of their relaxed length. Stretch-textured yarns are produced by several methods. The false-twist method is the most widely used technique for producing textured yarns in finer deniers. Yarns are twisted, heat-set, and untwisted in one operation. Stretch-textured yarns are also produced by the knife-edge method. This process consists of passing the filaments over a heated roll and then pulling them over a sharp edge at an acute angle. When relaxed, the filaments take the form of coiled springs, but the spiral direction reverses itself at random, which helps produce a balanced yarn. Gear crimping is a third method for producing stretch-textured yarns. This method consists of passing the filament yarn through a series of heated rollers or sets of heated gears that deform the filaments. Variations in crimp can be obtained by controlling the number of crimps per inch as well as the depth of gear deformation. Bulk-Textured The most important property of bulktextured yarns is their high bulk with low or minimal stretch. A method for producing bulk-textured yarn is the stuffer-box method, which produces an increase in bulk from 200 to 300 percent and can be found in yarns used for carpets. In this process, the filaments are compressed into the confined space of a heated chamber and heat-set with a wavy, random crimp. The resultant yarn is relatively bulky, possesses some degree of stretch, and is torque-free. Torque-free means the yarn will stay flat and motionless as opposed to a yarn that has a tendency to curl around itself.
textured yarn a b heater c d high pressure/ high-velocity air heater textured yarn guide rollers regular yarn heated chambers guide rollers regular yarn textured yarn regular yarn e f Figure 4.10 Methods of producing textured yarn: (a) false twist (b) knife-edge (c) stuffer box (d) gear crimping (e) high-pressure/high velocity air-jet and (f) knit-deknit. YARNS AND SEWING THREADS A 77 F regular yarn edge point heater regular yarn heater textured yarn heater textured yarn guide rollers circular knit fabric unraveled textured yarn
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