Knit Goods

Knit Goods

 

knitted fabrics or finished articles made from such fabrics, composed of a series of interloopings of one or more yarns and produced on a knitting machine. In contrast to other textiles, knit goods have the ability to stretch in all directions because the loops are able to change their shape and size. The loose, looped structure gives knit goods softness and wrinkle resistance. Knitted fabrics are used in the manufacture of clothing, artificial fur, lace, fishing nets, and industrial and medical products.

Knit goods are classified according to fiber composition, structure, finish, and purpose. Knitwear is manufactured primarily from cotton and wool yarns and artificial and synthetic fibers, including textured yarns. Synthetic raw materials are more widely used for knit goods than for woven fabrics because knitted fabrics have an open structure and are permeable to air and moisture. Knit goods may be manufactured from fibers of a single type, from blended yarns obtained from a mixture of different fibers, or from several different yarns. Knitted fabrics composed of a mixture of cotton and a small quantity of wool wastes are often called vicuna.

Depending on their structure, knitted fabrics are classified as weft-knit or warp-knit and as single-knit or double-knit. Double-knit fabrics are denser and heavier than single knits, and they do not roll up at the edges; they are primarily used for outerwear, less often for underwear. Depending on the finishing method used, knitted fabrics are classified as raw (unfinished), bleached, solid-dyed, or variegated. The dyeing and finishing equipment used is specially adapted for processing knitted fabrics. Knit goods may have a smooth surface, or they may have a fleecy layer, or nap, which is formed by combing the yarns on the surface of the fabric with fillet wire or teasels fastened to the shafts of napping machines.

Knitted fabrics may be used for underwear, outerwear, hosiery, gloves, or kerchiefs. Knitted articles of underwear and outerwear are usually sewn from pieces of knitted fabric; other types of garments are usually finished on the machine. Knitted underwear possesses high hygroscopicity, softness, elasticity, and permeability to air and moisture. It is usually manufactured from cloth made with a cotton-polyester (cotton-Lavsan) yarn; also used are plated fabrics, in which the face is made from silk yarn and the back from cotton. Knitted fabrics for outerwear are usually thicker than those used for underwear; they hold their shape well and provide excellent warmth.

The structure of knit goods depends on the interlinking of the loops and on the loops’ dimensions and shapes—the length of the yarn in the loop, the ratio of the length of the yarn to the thickness, and the height of the loop row. Other factors include the density of the yarn (the weight in grams of 1 km of yarn), the thickness and number of layers of yarn, and the surface structure (whether smooth or napped). The quality rating of knit goods is determined by the weight per unit surface area, the number of loops per unit length along the loop column and along the loop row, and various other mechanical and physical properties.

The ratio of weight to surface area determines the amount of raw material needed to produce fabric of a given area and, indirectly, the thickness of the knitted fabric; for outerwear it is 300–600 g/m2, and for underwear 115–240 g/m2.

Several characteristics are measured in order to evaluate the mechanical properties of knit goods, including the fabric’s extensibility, elasticity, resilience, tensile strength, ability to withstand repeated washing, and resistance to abrasion, unraveling, and edge curling. The extensibility of knitwear depends on the type of interlooping and the structure of the loops; the greatest dimensional increases are found in weft-knit articles (for example, up to 400 percent for hosiery), and the least in warp-knit fabrics. In all instances, transverse stretch is greater than longitudinal stretch. Low-stretch knitted fabrics do not require special processing for the manufacture of clothing; individual parts are sewn together on chain-stitch sewing machines to form the finished article. A reduction in the extensibility of knitted fabrics used for outerwear is achieved by means of combination interlooping, in which weft yarns are sometimes used. The yarns may be laid along the loop rows or along the columns. This technique reduces extensibility to 5–10 percent.

A knitted fabric’s elasticity—its ability instantaneously to recover its original shape after the load applied is removed—and its resilience—its ability gradually to resume its shape after the load is removed—primarily depend on the type of raw material and the method of interlooping used. The greatest elasticity is found in knitwear manufactured from textured yarns of wool and elastic yarns. High elasticity and resilience help the garment retain its shape when worn, and they significantly increase the resistance to abrasion and the ability to withstand repeated stretching.

The tensile strength of knit goods is usually 50–70 percent of the total strength of the yarns in a given cross section of cloth. The resistance to abrasion depends on the fiber surface, the twist of the yarns, and the type of interlooping and finishing. Knit goods made from synthetic yarns possess the greatest resistance to abrasion; wool knits and knits with a napped surface have the least resistance. Destruction of the yarn in the loops as a result of abrasion or other damage causes the loop to unravel. The amount of unraveling depends on the type of interlooping and the smoothness of the yarn. Warp knits in which two yarns make up each loop exhibit almost no unraveling. Weft knits usually unravel easily; however, open-work, press, and intertwine knits are exceptions.

Edge curling is characteristic of all knitted fabrics produced on machines with a single needle cylinder. It is caused by the tendency of yarn to straighten out after it has been bent into a loop. The amount of curling depends on the elasticity and density of the yarn, the external conditions, and the type of finishing. This tendency makes garment-making difficult; it can be eliminated for the time being by moisture and heat treatment in calenders or presses. Knitted garments may sometimes wear out prematurely because of their inability to retain their size and shape after repeated wearing and washing; such instability is inherent in loop structures formed from yarn with a high ratio of length to thickness. An article’s extensibility is an indication of its ability to retain its shape. Knits with loops that have little movement or that are positioned close together and those that have been chemically stabilized in a stretched state are characterized by great size stability.

The hygienic properties of knit goods are usually determined by the goods’ physical properties, including the ability to absorb moisture from the environment (hygroscopicity), the permeability to air, water, and vapor, and the ability to hold an electric charge. Hygroscopicity depends on the type of fiber used: cotton knitwear possesses the best properties; articles made from synthetic fibers absorb almost no moisture. As a result of its loose loop structure, knitwear is significantly more permeable to air, water, and vapor than are woven textiles. Different degrees of permeability can be achieved from different degrees of tightness in the knit or by the use of yarns that differ in fleeciness.

The ability of an article of knitwear to accumulate charges of static electricity up to amounts that can be felt by a person depends on the article’s fiber composition. Hydrophobic fibers (the majority of synthetic fibers are in this category) will accumulate high static charges; this tendency is reduced if the knitwear is treated with chemicals called antistatics. A mixed knit in which the share of hydrophilic fiber is high will not hold an electric charge.

REFERENCES

Willkomm, W. Trikotazhno-viazal’noe proizvodstvo, part 2. Moscow, 1928. (Translated from German.)
Marisova, O. I. Trikotazhnye risunchatye perepleteniia. Moscow, 1970.
Dalidovich, A. S. Osnovy teorii viazaniia, 2nd ed. Moscow, 1970.
Kobliakov, A. I. Struktura i mekhanicheskie svoistva krikotazha. Moscow, 1973.
Paling, D. F. Warp Knitting Technology, 2nd ed. London, 1965.

I. I. SHALOV

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