Bulk Continuous Filament Continuous Filament

Fibre to Yarn

C. Lawrence , in Textiles and Fashion, 2015

Abstract

Continuous-filament yarns (or filament yarns) are used to produce a wide range of woven and knitted fabrics for various textiles and clothing. A classification is given for these yarns and the yarn-count system used for specification is described. The extrusion-spinning systems for producing filament yarns and the various texturing processes for imparting visual and tactile characteristics to them are also described. The properties of continuous-filament yarns and means for imparting added functionalities are discussed, and examples of applications for these yarns and future trends in their development are outlined.

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Yarn structural requirements for knitted and woven fabrics

H.M. Behery , in Advances in Yarn Spinning Technology, 2010

Modified continuous filament yarns

Continuous filament yarns are made from straight filaments which are smooth and slippery to the touch. They lack the bulk, comfort and tactile hand of yarns spun from staple fibers. Producers of continuous filament yarns tried to simulate the effects obtained by staple fiber yarns. First, they modified the luster of the filament from bright to semi-bright to dull. Second, they modified the structure of the filament by adding bulk and stretch, by various texturing processes. These processes are primarily to increase bulk for comfort, resilience and hand or to provide stretch to the yarn. The subject of texturing and the different technologies used with the resultant yarn structures obtained are discussed by Demir and Behery (1997).

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Developments in rope structures and technology

J.W.S. Hearle , in Specialist Yarn and Fabric Structures, 2011

3.2.1 Continuous filament yarns

Continuous filament yarns do not need twist to transmit stress from one fibre to another. In principle a tow of parallel filaments would support a load. In practice, the tow would not be easy to handle. The filaments would spread out, could become entangled or snag on neighbouring objects. Some structure is needed to give a coherent rope but, whereas in staple fibre ropes a substantial level of twist is needed to generate a self-locking structure and more to maximise strength, in continuous filament structures maximum strength is achieved at the low level needed to give support to weak places in filaments. This was an opportunity for rope-makers to exploit with new low-twist structures.

The first cellulosic continuous filament yarns, rayon and acetate, did not impact on the rope industry, though high-tenacity viscose became important in tyre cords. The low wet strength may have been a contributory factor.

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Conversion of Fibre to Yarn

R. Alagirusamy , A. Das , in Textiles and Fashion, 2015

8.2.2 Continuous-Filament Yarns

Silk was the first natural continuous-filament yarn in use before the introduction of man-made fibres. Man-made filaments are manufactured by extruding polymer solution through a spinneret, at which point the solution solidifies by coagulation, cooling or evaporation. The number of orifices in the spinneret dictates the number of filament in the bundle. The diameter and amount of drawing provided will subsequently decide the diameter of the filament. The filaments are cut and crimped according to the required length for conversion to staple fibre, which will undergo further staple-yarn production.

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The development of textured yarns

C. Atkinson , in False Twist Textured Yarns, 2012

1.4 Achieving desirable fabric properties through texturing

Fabrics manufactured from filament silk, and indeed unmodified continuous filament synthetic yarns, have characteristics that are very different to yarns spun from staple fibres such as cotton or wool, staple synthetic fibres, or staple fibre blends such as cotton and polyester or wool and nylon. Continuous filament yarns, when simply drawn after spinning to produce desirable mechanical properties, tend to exhibit smoothness, evenness, and parallelism compared to the less regular, more bulky and hairy staple-fibre spun yarns.

Of course, continuous filaments from synthetic fibres can be cut into staple lengths through a separate filament cutting process to form filament staple suitable for a conventional spinning process using raw synthetic- or blended-staple fibres. This is known as 'tow to top' conversion. However, this is a multi-stage process, which is costly, utilising an end-spinning process that was developed for natural fibres. As a consequence, in the 1950s and 1960s, processes referred to as 'texturing' were developed. Texturing imparts desirable textile properties to continuous filament yarns without destroying their continuity through introducing distortions or crimp along their lengths. As a result, textured yarns have suitable volume, stretch and recovery, and air porosity for every day use in fabrics for a wide range of textile end-uses. Initially, the process comprised the insertion of twist into nylon or polyester yarns, thermally setting the twist by steaming in an autoclave, cooling and then untwisting the yarn by the same number of turns as originally inserted. Texturing processes are aimed at capitalising from raw material yarn properties rather than producing a material that fits the traditional yarn process routes.

Thermoplastic, melt-spun continuous filament yarns provide the ideal platform for texturing, as imparted filament distortions can be softened through heat and set by cooling. The texturing process, therefore, evolved around key synthetic thermoplastic filament yarns, which soften when heated and reset when cooled, namely:

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polyester,

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nylon,

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and, to a lesser degree, polypropylene.

Throughout the 1960s and 1970s, various texturing methods were introduced commercially to the yarn manufacturing industry: ¹⁸

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Edge Crimping – drawing a thermoplastic yarn over a heated edge, creating differential internal stresses in the filament cross-sections (Fig. 1.11). Edge-crimp yarns exhibit high stretch; they were used for ladies hosiery and circular knit fabrics.

1.11. Edge-crimping principle. (a) Thermoplastic yarn fed over heated knife-edge (b) Knife-edge heater.

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Knit-de-Knit – knitting the thermoplastic yarn on a small diameter circular knitting machine. The plain knit fabric is then heat set and subsequently de-knitted and wound onto a package. After de-knitting, the yarn is deformed according to the knitted loop shapes, forming a three-dimensional structure.

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Stuffer-box – thermoplastic yarn is overfed into a heater cylinder, under a pressure from the feed-roller delivery that exceeds that of the controlled outlet resistance (Fig. 1.12). As a result of this process, the filaments are heat-set in a buckled/crimped form before exiting the stuffer-box and being wound onto a package.

1.12. Stuffer-box texturing principle. (a) Thermoplastic feeder yarn (b) Heated chamber (c) Crimped yarn under pressure from overfeed (d) Pressure control (e) Output roller feeds (f) Crimped, heat-set yarn.

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False Twist Texturing – inserting high twist levels into thermoplastic yarns, setting the twist by heating and cooling prior to de-twisting.

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Air Jet Texturing – air-entangling of continuous filament yarns, applying overfeeds, draw and heat set to the individual component yarns to create filament loops and entanglements.

Of the above methods, the most significant texturing processes to evolve over the last 50 years are False Twist Texturing and Air Jet Texturing. False Twist Textured Yarns (Fig. 1.13) comprise a multitude of crimp in the individual filaments and are inherently elastic. The degree of crimp and hence elasticity can be determined largely by the amount of twist applied to the yarn in the heat-set process. The modern process for false twist texturing is based on a technique patented by Finlayson and Happey in 1933, whereby temporary twist is imparted to a moving yarn upstream of a spindle (twist applicator). The twist is thermally set and cooled before becoming automatically untwisted after the spindle. ²¹

1.13. POY and false twist textured nylon 66 yarns.

Air Jet Textured Yarns (Fig. 1.14) provide a staple fibre appearance due to the multitude of filament distortions and entanglements brought about by a high-pressure air flow as they pass through a purposely designed air jet. ²⁰ They exhibit low elasticity due to their filament construction and because of their filament entanglements, and they have good abrasive characteristics.

1.14. Scanning electron micrograph of air jet textured yarn. ²⁰

Regarding Edge Crimping, Knit-de-Knit and Stuffer-box Texturing, only the Stuffer-box technique has continued to be developed; it is used for high decitex carpet yarns. Old Knit-de-Knit machinery is still, however, used today in very limited applications for textured yarn specialities and where fashion demands a low crimp/low elasticity appearance.

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Common principles

Peter R. Lord , in Handbook of Yarn Production, 2003

3.2.6 Twisted filament yarns

It is unnecessary to twist continuous filament yarns to impart strength; nevertheless, some small amount of twist is inserted merely to control the fibers. An untwisted bundle of filaments is difficult to handle because odd filaments and loops project from the surface of the bundle. These tend to catch up in guides, tangle with adjacent yarns, or otherwise cause difficulty. Some man-made fibers tend to balloon out quite severely because they accumulate electrical charge. Filaments or loops protruding from the yarn are often called wild filaments. Even a low level of twist in the yarns helps to reduce the number of these wild filaments; twist inserted for this purpose is called producer twist.

Filament yarns are sometimes twisted to a fairly high level to break up the luster of the yarn or to impart some other attribute to the yarn for effect purposes. However, high twist levels reduce the tenacity of the yarn and make the yarn leaner (i.e. have a smaller diameter).

Another use of twist in filament yarns is to create texture. A false twisted yarn will coil or snarl if it is subject to the correct sequence of twist, set, and untwist. If properly relaxed, these textured yarns become bulky and have many desirable features. A major advance was made when it was realized that the process of false twisting provided the opportunity to carry out such a sequence in a continuous manner. To understand how that works, it is necessary to be knowledgeable about false twist.

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Types and properties of fibres and yarns used in weaving

P.K. Hari , in Woven Textiles, 2012

1.8.1 Filament yarns

With the exception of natural silk, continuous filament yarns are man-made. They can be sourced from natural polymers such as paper pulp to produce viscose, rayon, etc., or from synthetic polymers such as polyester, polypropylene, polyethylene, polyamide, etc. A filament yarn can be either monofilament or multifilament. There are also flat yarns.

Monofilament yarns can be solid or hollow. Monofilament yarns have a single filament with a cross-section which can vary depending on the end use. It is normally circular but can be altered to a range of other shapes (e.g., triangular, multilobal, serrated, oval or dogbone-shaped). A non-circular cross-section prevents close packing and helps wicking. Monofilament diameters are typically in the range of 0.1–2   mm. The filament yarn is chopped to a suitable length to produce staple fibres, and these staple fibres are spun alone or blended with natural fibres in to yarn.

Continuous filaments are invariably used as a multi-strand and termed a multifilament yarn. A multifilament yarn consists of a bunch of monofilaments with a nominal twist to provide coherence to the structure. Alternatively, fibres in multifilaments can be held together by intermingling or entanglement. A non-circular cross-section prevents the close packing of multifilament yarns.

Flat filament yarns can be textured to increase bulk or extension by false twisting, intermingled by an air-jet or crimped by a stuffer box. Flat yarns can be twisted or interlaced to produce different effects. Tape yarn is produced by splitting up a thin ribbon-like narrow width of polymer film. Tape yarns are used, for example, for making fabric for packaging applications. A tape yarn can be further split or fibrillated mechanically to produce a regular network of interconnected fibres, a texture similar to multifilament yarn.

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Modelling and simulation of fibrous yarn materials

X. Chen , in Computer Technology for Textiles and Apparel, 2011

Continuous filament yarns

The tensile stress–strain curve of twisted continuous filament yarns is the most successfully modelled example of the mechanics of a textile material, based on the idealised geometry of Fig. 5.1. According to the definition, the strain of yarn is expressed as

5.5 ${\epsilon }_{\mathrm{y}}=\frac{\mathit{\delta h}}{h}$

where δh is the extension of yarn length h corresponding to one turn of twist. From Fig. 5.1(b),

5.6 $l^2=h^2+4{\pi }^2{r}^2$

Assuming that the yarn radius R does not change under the tensile loading leads to

5.7 $\frac{\mathrm{d}l}{\mathrm{d}h}=\frac{h}{l}$

In this process of tensile loading, the strain of a filament can be described as

${\epsilon }_{\mathrm{f}}=\frac{\mathit{\delta l}}{l}=\frac{1}{l}\cdot \frac{\mathrm{d}l}{\mathrm{d}h}\cdot \mathit{\delta h}=\frac{h^2}{l^2}\cdot \frac{\mathit{\delta h}}{h}$

In this simplest approximate form, modelling goes from the strain distribution in fibres, which reduces approximately as cos² θ, to give a contribution to stress reduced by a further factor of cos² θ through the axial component of tension and the oblique area on which fibre tension acts. The ratio of yarn to fibre modulus is thus the mean value of cos² θ, which is cos² α for the ideal helical geometry. For a more exact model, an energy method is both simpler than the use of force methods and easily adapted to cover large strains and lateral contraction. An important simplification in modelling is that most fibres extend at close to constant volume, i.e. Poisson's ratio being 0.5. This means that the deformation energy is the same when the fibre is extended at zero lateral pressure in a tensile test as it is when the fibre is subject to combined tension and pressure within a yarn. Consequently, the measured fibre stress–strain curve is a valid input. Except for a small deviation at low stresses where some buckling of central filaments reduces their contribution to tension, there is good agreement between the theory and experimental results.

Twisted yarns break when the central fibres, which are the most highly strained, reach their break extension. Consequently, yarn and fibre break extensions are similar and the strength reduction is similar to the modulus reduction.

In the case where the yarn radius reduces under tensile loading, the strain of the filaments is expressed as follows, where σ _y is the yarn stress:

5.9 ${\epsilon }_{\mathrm{f}}={\epsilon }_{\mathrm{y}}\left({cos}^2\theta -{\sigma }_{\mathrm{y}}{sin}^2\theta \right)$

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Yarn and thread manufacturing methods for high-performance apparel

M. Tausif , ... I. Butcher , in High-Performance Apparel, 2018

3.4.2 Wrap spinning

A parallel strand of fibers is wrapped by a continuous filament yarn on a hollow spindle machine ( Fig. 3.32). A roller drafted roving is fed through a rotating hollow spindle, with a small filament bobbin mounted on it, and a false twisting element. The false twisting is introduced to provide structural integrity to a loose strand of drafted fibers. The pin-type false twister can be placed at the base or top of the hollow spindle. The anticlockwise rotation of spindle generates twist from the twisting element towards the nip of the front drafting rollers. The continuous filament, nipped between the delivery rollers and the twisting element, is wrapped around the untwisted/parallel core of staple fibers in a helical path. To provide additional support for weak fibers, a filament core can be introduced with the drafted fiber strand. The wrap-spun yarn offers low level of hairiness and good covering power. The commercial success of this technology has been limited.

Fig. 3.32. Principle of hollow-spindle wrap spinning (Stalder, 2016b).

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A brief description of the manufacturing processes for medical textile materials

Yimin Qin , in Medical Textile Materials, 2016

4.2 Yarn processing

Yarn is a long continuous length of interlocked fibers, suitable for use in sewing, crocheting, knitting, weaving, embroidery, and ropemaking. Yarns are made by utilizing either staple or filament fibers, or by combining both. Filament yarn is a term applied to a long rope-like bundle of raw fibers which is extruded from the spinneret in the chemical fiber production process. Filament yarns can be monofilament or multifilament. Spun yarn is made by gathering a bundle of staple fibers and spinning the spindles at a very high speed to twist the staple fibers together to form a piece of yarn.

In the textile industry, yarn spinning was one of the very first processes to be industrialized. Spun yarns may contain a single type of fiber or a blend of various types. Combining synthetic fibers (which can have high strength, luster, and fire-retardant qualities) with natural fibers (which have good water absorbency and skin-comforting qualities) is very common. The most widely used blends are cotton-polyester and wool-acrylic fibers. Blends of different natural fibers are common too, especially with more expensive fibers such as cashmere. Yarns are selected for different textile products based on the characteristics of the constituent fibers, such as wool for warmth, nylon for durability, cashmere for softness, etc.

Technically, yarns are made up of a number of singles, which are known as plies when grouped together. These singles of yarn are twisted together in the opposite direction to make a thicker yarn. Depending on the direction of the final twist, the yarn can be S-twist or Z-twist.

Filament yarn consists of filament fibers either twisted together or simply grouped together. In order to develop stretch and bulk in subsequent processing, filament yarns are often texturized. When woven or knitted into fabric, the cover, hand, and other aesthetics of finished fabrics made from texturized filament yarns resemble the properties of a fabric constructed from spun yarn.

Texturing is the process of crimping, imparting random loops, or otherwise modifying continuous filament yarn to increase cover, resilience, abrasion resistance, warmth, insulation, and moisture absorption, or to provide a different surface texture. Texturing methods fall roughly into the following six groups.

1.

Air-jet method: In this method, yarn is led through the turbulent region of an air jet at a rate faster than it is drawn off on the far side of the jet. In the jet, the yarn structure is opened, loops are formed, and the structure is closed again. Some loops are locked inside the yarn and others are locked on its surface.

2.

Edge-crimping method: In this method, thermoplastic yarns in a heated and stretched condition are drawn over a crimping edge and cooled. Edge-crimping machines are used to make Agilon yarns.

3.

False-twist method: This continuous method for producing textured yarns utilizes simultaneous twisting, heat-setting, and untwisting. The yarn is taken from the supply package and fed at controlled tension through the heating unit, through a false-twist spindle or over a friction surface that is typically a stack of rotating discs called an aggregate, through a set of take-up rolls, and on to a take-up package. The twist is set into the yarn by the action of the heater tube and subsequently is removed above the spindle or aggregate, resulting in a group of filaments with the potential to form helical springs.

4.

Gear-crimping method: In this method, yarn is fed through the meshing teeth of two gears. The yarn takes on the shape of the gear teeth.

5.

Knit-de-knit method: In this method, the yarn is knit into a two-inch-diameter hose-leg, heat-set in an autoclave, and then unraveled and wound on to a final package. This texturing method produces a crinkle yarn.

6.

Stuffer box method: The crimping unit consists of two feed rolls and a brass tube stuffer box. By compressing the yarn into the heated stuffer box, the individual filaments are caused to fold or bend at a sharp angle, while being simultaneously set by a heating device.

The physical, chemical, and mechanical properties of yarns are characterized in methods similar to those used for fibers. To describe the fineness of the yarn, textile engineers often use the unit tex, which is the weight in grams of a kilometer of yarn, or decitex, which is a finer measurement corresponding to the weight in grams of 10   km of yarn. Many other units have been used over time by different industries.

Yarn quantities are usually measured by weight in ounces or grams. In the United States, Canada, and Europe, balls of yarn for handcrafts are sold by weight. Common sizes include 25, 50, and 100   g skeins. Some companies primarily measure in ounces, with common sizes being three-ounce, four-ounce, six-ounce, and eight-ounce skeins. These measurements are taken at a standard temperature and humidity, because yarn can absorb moisture from the air. The actual length of the yarn contained in a ball or skein can vary due to the inherent heaviness of the fiber and the thickness of the strand. For instance, a 50   g skein of cotton yarn may contain several hundred meters, while a 50   g skein of bulky wool may contain only 60   m.

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