Types of yarn
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- yarn
- fibre
- cloth
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Classification based on number of strands
Yarns can be described as single, or one-ply; ply, plied, or folded; or as cord, including cable and hawser types.
Single yarns
Single, or one-ply, yarns are single strands composed of fibres held together by at least a small amount of twist; or of filaments grouped together either with or without twist; or of narrow strips of material; or of single synthetic filaments extruded in sufficient thickness for use alone as yarn (monofilaments). Single yarns of the spun type, composed of many short fibres, require twist to hold them together and may be made with either S-twist or Z-twist. Single yarns are used to make the greatest variety of fabrics.
Ply yarns
Ply, plied, or folded, yarns are composed of two or more single yarns twisted together. Two-ply yarn, for example, is composed of two single strands; three-ply yarn is composed of three single strands. In making ply yarns from spun strands, the individual strands are usually each twisted in one direction and are then combined and twisted in the opposite direction. When both the single strands and the final ply yarns are twisted in the same direction, the fibre is firmer, producing harder texture and reducing flexibility. Ply yarns provide strength for heavy industrial fabrics and are also used for delicate-looking sheer fabrics.
Cord yarns
Cord yarns are produced by twisting ply yarns together, with the final twist usually applied in the opposite direction of the ply twist. Cable cords may follow an SZS form, with S-twisted singles made into Z-twisted plies that are then combined with an S-twist, or may follow a ZSZ form. Hawser cord may follow an SSZ or a ZZS pattern. Cord yarns may be used as rope or twine, may be made into very heavy industrial fabrics, or may be composed of extremely fine fibres that are made up into sheer dress fabrics.
Novelty yarns
Novelty yarns include a wide variety of yarns made with such special effects as slubs, produced by intentionally including small lumps in the yarn structure, and synthetic yarns with varying thickness introduced during production. Natural fibres, including some linens, wools to be woven into tweed, and the uneven filaments of some types of silk cloth are allowed to retain their normal irregularities, producing the characteristic uneven surface of the finished fabric. Synthetic fibres, which can be modified during production, are especially adaptable for special effects such as crimping and texturizing.
Textured yarns
Texturizing processes were originally applied to synthetic fibres to reduce such characteristics as transparency, slipperiness, and the possibility of pilling (formation of small fibre tangles on a fabric surface). Texturizing processes make yarns more opaque, improve appearance and texture, and increase warmth and absorbency. Textured yarns are synthetic continuous filaments, modified to impart special texture and appearance. In the production of abraded yarns, the surfaces are roughened or cut at various intervals and given added twist, producing a hairy effect.
Bulking creates air spaces in the yarns, imparting absorbency and improving ventilation. Bulk is frequently introduced by crimping, imparting waviness similar to the natural crimp of wool fibre; by curling, producing curls or loops at various intervals; or by coiling, imparting stretch. Such changes are usually set by heat application, although chemical treatments are sometimes employed. In the early 1970s bulky yarns were most frequently produced by the “false twist” method, a continuous process in which the filament yarn is twisted and set and then untwisted and heated again to either stabilize or destroy the twist. The “stuffing box” method is often applied to nylon, a process in which the filament yarn is compressed in a heated tube, imparting a zigzag crimp, then slowly withdrawn. In the knit-de-knit process, a synthetic yarn is knitted, heat is applied to set the loops formed by knitting, and the yarn is then unraveled and lightly twisted, thus producing the desired texture in the completed fabric.
Bulk may be introduced chemically by combining filaments of both high and low shrinkage potential in the same yarn, then subjecting the yarn to washing or steaming, causing the high shrinkage filaments to react, producing a bulked yarn without stretch. A yarn may be air bulked by enclosing it in a chamber where it is subjected to a high-pressure jet of air, blowing the individual filaments into random loops that separate, increasing the bulk of the material.
Stretch yarns
Stretch yarns are frequently continuous-filament synthetic yarns that are very tightly twisted, heat-set, and then untwisted, producing a spiral crimp giving a springy character. Although bulk is imparted in the process, a very high amount of twist is required to produce yarn that has not only bulk, but also stretch.
Spandex is the generic term for a highly elastic synthetic fibre composed mainly of segmented polyurethane. Uncovered fibres may be used alone to produce fabrics, but they impart a rubbery feel. For this reason, elastomeric fibre is frequently used as the core of a yarn and is covered with a nonstretch fibre of either natural or synthetic origin. Although stretch may be imparted to natural fibres, other properties may be impaired by the process, and the use of an elastic yarn for the core eliminates the need to process the covering fibre.
Metallic yarns
Metallic yarns are usually made from strips of a synthetic film, such as polyester, coated with metallic particles. In another method, aluminum foil strips are sandwiched between layers of film. Metallic yarns may also be made by twisting a strip of metal around a natural or synthetic core yarn, producing a metal surface.
For additional information about the production, characteristics, and uses of modern synthetic novelty yarns, see man-made fibre.
Classification based on use
Fabric construction yarns
Almost any textile yarn can be used to produce such interlaced fabrics as woven and knitted types. In weaving, the warp, or lengthwise, yarns are subjected to greater stress and are usually stronger, smoother, and more even and have tighter twist than the weft, or crosswise, yarns. A sizing (stiffening) material such as starch may be applied to warp yarns, increasing their strength to withstand the stresses of fabric construction operations. Weft yarns, subjected to little stress during weaving, may be quite fragile.
Warp and weft threads used in the same fabric may be of differing diameter, producing such special effects as ribbing or cording in the fabric. Special effects may also be obtained by combining warp and weft yarns of fibre from differing origin, or with different degrees of twist, or by introducing metallic threads into weaves composed of other fibres.
Yarns for machine knitting are usually loosely twisted because softness is desired in knit fabrics.
Yarns used in handwork
Yarns used in hand knitting are generally of two or more ply. They include such types as fingering yarns, usually of two or three plys, light to medium in weight and with even diameter, used for various types of apparel; Germantown yarns, soft and thick, usually four-ply and of medium weight, frequently used for sweaters and blankets; Shetland yarns, fine, soft, fluffy, and lightweight, frequently two-ply, used for infants’ and children’s sweaters and for shawls; worsted knitting yarn, highly twisted and heavy, differing from worsted fabric by being soft instead of crisp, and suitable for sweaters; and zephyr yarns, either all wool, or wool blended with other fibres, very fine and soft, with low twist, and used for lightweight garments.
Embroidery floss, used in hand embroidery, generally has low twist, is of the ply or cord type, and is made of such smooth filaments as silk and rayon. Yarn used for crocheting is frequently a loose cotton cord type; and darning yarns are usually loosely spun.
Sewing thread
Sewing threads are tightly twisted ply yarns made with strands having equally balanced twist, producing a circular cross section. Thread for use in commercial or home sewing machines and for hand sewing should allow easy movement when tension is applied and ease in needle threading; should be smooth, to resist friction during sewing; should have sufficient elasticity to avoid the breaking of stitches or puckering of seams; and should have sufficient strength to hold seams during laundering or dry cleaning and in use.
Threads for special uses may require appropriate treatment. Garments made of water-repellent fabrics, for example, may be sewn with thread that has also been made water-repellent. Thread is usually subjected to special treatment after spinning and is then wound on spools. Thread size is frequently indicated on the spool end, and systems for indicating degree of fineness vary according to the textile measurement system used locally.
Silk thread has great elasticity and strength combined with fine diameter. It can be permanently stretched in sewing, and is suitable for silks and wools. Buttonhole twist is a strong, lustrous silk about three times the diameter of normal sewing silk, and is used for hand-worked buttonholes, for sewing on buttons, and for various decorative effects.
Cotton thread is compatible with fabric made from yarn of plant origin, such as cotton and linen, and for rayon (made from a plant substance), because it has similar shrinkage characteristics. It is not suitable for most synthetics, which do not shrink, or for fabrics treated to reduce shrinkage. Its low stretch is useful for woven fabrics, but not for knits, which require more stretch.
Nylon thread is strong, with great stretch and recovery, does not shrink, and is suitable for sheers and for very stretchy knits. Polyester thread has similar characteristics, and is appropriate for various synthetic and preshrunk fabrics, and for knits made of synthetic yarns.
Measurement systems
Yarn measurements are expressed as yarn number, count, or size, and describe the relationship of length and weight (or approximate diameter). Because methods of measurement were developed in various areas of the world, there has been a lack of uniformity in such systems.
Indirect systems
Indirect measuring systems are those employing higher number to describe finer yarns and are based on length per unit weight. Most countries measure yarns made from staple fibres according to the weight of a length of yarn. If one pound is used as a standard unit, for example, a very fine yarn will have to be much longer than a coarser yarn to weigh a pound, so higher counts indicate finer yarns. The size number is an indication of the length of yarn needed to reach a weight of one pound.
In the United States, the system is based on the number of hanks per pound, with a hank of 840 yards for cotton and spun silk, 300 yards (a lea) for linen, 256 yards for woollen yarns, and 560 yards for worsted yarns. A widely used Continental system is based on the number of hanks of 1,000 metres (one kilometre) required to reach a weight of one kilogram.
Denier system
The denier system is a direct-management type, employed internationally to measure the size of silk and synthetic filaments and yarns, and derived from an earlier system for measuring silk filaments (based on the weight in drams of 1,000 yards). Denier number indicates the weight in grams of 9,000 metres of filament or filament yarn. For example, if 9,000 metres of a yarn weigh 15 grams, it is a 15-denier yarn; if 9,000 metres of a yarn weigh 100 grams, it is a 100-denier yarn and much coarser than the 15-denier yarn. Thus, a smaller number indicates a finer yarn. This system is not convenient for measurement of staple yarns because their greater weight would require the use of very large numbers.
Tex system
The tex system, originally devised in 1873, is a universal method developed for the measurement of staple fibre yarns and is also applicable to the measurement of filament yarns. It is based on the weight in grams of one kilometre (3,300 feet) of yarn.
