GESTION DE SERVICIOS DOMICILIARIOS PARA EL PACIENTE CRÓNICO

Generally, clothing today is produced from yarns, such as woven and knitted fabrics. Laces and nets also fall into this category. Fabrics made directly from fibers without yarns include felt.

Thread is a generic term meaning textile yarn and is the elementary unit of textile construction. Thread forming, which starts with a spinning process, is a basic step for the manufacture of most textiles. The most common forms of yarns are single yarns and multiple-wound yarns, which are two or more single yarns wound together parallel.

Single yarns are produced either from staple fibers (fibers of limited and relatively short length) or from filaments (fibers of indefinite length). Examples of natural staple fibers are wool, cotton, and jute. Filaments are fibers of indefinite length. Examples of filaments are silk (a natural fiber), polyester, and nylon.

A single yarn consisting of staple fibers is described as spun yarn. Spun yarns are usu- ally held together by twist. An essential feature of spun yarn is a greater or lesser degree of hairiness. A single yarn composed of one or more filaments is referred to as filament yarn. Filament yarns consisting of more than one filament are known as multifilament yarns. There are multifilaments with and without twist.

Folded yarns include all threads in which two or more single yarns are twisted together in one operation. Depending on how many yarns have been twisted together, there are two-folded yarns, three-folded yarns, etc. Folded yarns used in hand knitting are described as two-ply, three-ply, etc., and this description of yarn is used in this book.

Manufactured fibers can be produced as a staple or a multifilament yarn. The method of tow conversion (cut or stretch broken) determines the fiber end appearance of the con- stituent staple fibers. Constituent fiber ends have been defined as the fiber appearances produced through the manufacturing processes of tow-to-staple conversion.

The concept of “hairiness” in a yarn is important also for trace evidence transfer of fibers. Sheddability, fiber transfer, and fiber persistence are principally associated with the hairiness of a fabric. The hairiness is generally determined by both the construction of the fabric and the construction of the yarns used for its manufacture. Trace evidence transfer is discussed in Chapter 8.

More information regarding the formation and analysis of yarns can be found in SWGMAT Guidelines or in other texts (e.g., Robertson and Grieve, 1999).

3.7 Fabric

A fabric is a manufactured assembly of fibers and/or yarns that has substantial surface area in relation to its thickness and sufficient inherent cohesion to give the assembly mechani- cal strength.

3.7.1 Weave

A weave is a fabric manufactured on a loom and composed of regularly interlaced threads or yarns. These threads are called the warp threads and the weft threads. The warp is ori- ented lengthwise in the fabric, whereas the weft is introduced widthwise (Figure 3.3). The individual warp yarns are called the ends and the individual yarns in the weft are called picks. The pattern of the interlacing of the warp and weft yarns is known as the weave; the repeat unit of the weave contains the smallest number of ends and picks that adequately represent the interlacing pattern.

There are three basic types of weave: the plain weave, the twill weave, and the satin weave (see Figure 3.4). The plain weave is the simplest and most frequently used in cloth- ing. It can be considered as “one over and one under.” The plain weave, because it requires less fiber mass, is often used in ladies’ blouses, business shirts, and some trousers.

A twill weave produces diagonal lines on the surface of the fabric and is considered a high fiber mass. Consequently, their durability and resistance is higher than plain weaves, and so twill weaves are often found in clothing used as workwear. The most common kind of twill weave is denim, used in jeans and jackets. Men’s gabardine suit trousers are also twill weave fabrics.

WA

RP

Preliminary Assessment 25 W ar p Weft Plain weave W ar p Weft Twill weave W ar p Weft Satin weave

Satin weaves have a smooth surface and are either weft-faced or warp-faced fabrics. These are called sateen/weft or satin/warp. They are often found in fine table linen as well as in clothing.

3.7.2 Knit

A knit is a fabric either knitted by hand by needles or on power-operated knitting machines. Knitting is a process that intermeshes loops of yarn (Figure 3.5). The diagram in Figure 3.5 shows the face of a plain jersey knit that is composed completely of face loops and one that is composed completely of back loops. Loops are formed by needles and then new loops are drawn through those previously formed — the continuing addition of new loops creates the fabric. Knitted loops are sometimes referred to as stitches when they are pulled through another loop. Consequently, yarns in knitted fabrics follow a three-dimensional configuration, contrasting with the yarn configuration in woven fabrics, which is essentially two dimensional. Loops running in the machine direction are known as wales (analogous to the warp direction in a woven fabric) and those in the cross-machine direction are known as courses (Figure 3.6).

Weft knitting, regarded as normal knitting, has loops that are made by one single thread at a time. The weft threads are fed more or less at right angles to the direction in which the fabric is produced. Hand knitting is a weft knitting procedure. Warp knitting forms loops with many parallel threads at the same time. T-shirts, sweaters, and undergar- ments are usually knitted.

D C B A H G F E Direction of knitting x W AL E S C O U R S E_S

Preliminary Assessment 27

The basic types of weft knitting are plain knit, rib, and purl structures. Plain knit fab- rics, also known as single jersey or single knit, have all loops drawn to one side or face of the fabric (Figure 3.7). A wide variety of knit fabrics are made with single jersey construc- tion, ranging from sheer lightweight hosiery to T-shirts and bulky sweaters.

Rib knit fabrics have loops in alternate groups of wales meshed on one side of the fab- ric, with the loops in the remaining wales meshed on the opposite side. Each wale contains either all plain stitches (also called face stitches) or all purl stitches. Due to the greater extensibility in the coursewise direction, rib fabrics are popular as garment body and sleeve borders (e.g., waist, cuff, and wrist) as well as socks.

Purl knit fabrics have loops in alternate groups of courses meshed on one side of the fabric, with the loops in the remaining courses meshed on the opposite side — each wale contains both plain stitches and purl stitches. The appearance of the face and back are identical, and the fabric is highly extensible in all directions. Their high extensibility has favored their use in children’s wear.

3.7.3 Felts, Leather, and Other “Non-Wovens”

Felts are produced by the compression of single fibers; leather derives from the skin of an ani- mal. We group them together because they produce similar characteristics when damaged. Leather jackets are popular today, and leather and felt are common garment trims. Other non-woven fabrics may be composed of randomly oriented synthetic fibers held together by

W C Wales cm = W=w Courses cm = C=c Stitch length = AB = 1 cm B A Course Wale

small drops of polymer, either from melting of the parent fibers or by addition to them. These are found in clothing primarily as facing or other layers beneath the surface.

3.8 Definitions

Fabric: Manufactured assembly of fibers and/or yarns

Fiber: A unit of matter characterized by flexibility, fineness, and a high ratio of length to

thickness

Yarn: Elementary unit of fabric construction; a long and thin textile product generally less

than 4 mm in diameter

3.9 Sewing Terminology