Definition of Filament yarns? | Manufacture of filament yarns

A filament yarn is made from one or more continuous strands called filaments where each component filament runs the whole length of the yarn. Those yarns composed of one filament are called monofilament yarns, and those containing more filaments are known as multifilament yarns. For apparel applications, a multifilament yarn may contain as few as two or three filaments or as many as 50 filaments. In carpeting, for example, a filament yarn could consist of hundreds of filaments. Most manufactured fibers have been produced in the form of a filament yarn. Silk is the only major natural filament yarn.

Classification Of Filament Yarn:

According to the shape of the filaments in the yarn, filament yarns are classified into two types, flat and bulk.

 

The filaments in a flat yarn lie straight and neat, and are parallel to the yarn axis. Thus, flat filament yarns are usually closely packed and have a smooth surface. 

The bulked yarns, in which the filaments are either crimped or entangled with each other, have a greater volume than the flat yarns of the same linear density.

Texturing is the main method used to produce the bulked filament yarns. A textured yarn is made by introducing durable crimps, coils, and loops along the length of the filaments. As textured yarns have an increased volume, the air and vapor permeability of fabrics made from them is greater than that from flat yarns.

 

However, for applications where low air permeability is required, such as the fabrics for air bags, flat yarns may be a better choice.

Manufacture of filament yarns:

Most manufactured fibers are extruded using either melt spinning, dry spinning, or wet spinning, although reaction spinning, gel spinning and dispersion spinning are used in particular situations. After extrusion, the molecular chains in the filaments are basically un-oriented and therefore provide no practical strength. The next step is to draw the extruded filaments in order to orient the molecular chains. This is conventionally carried out by using two pairs of rollers, the second of which forwards the filaments at approximately four times the speed of the first. The drawn filaments are then wound with or without twist onto a package. The tow of filaments at this stage becomes the flat filament yarn. Figure 3.11 shows the melt spinning process and the subsequent drawing process.

For many applications, flat filament yarns are textured in order to gain increased bulkiness, porosity, softness and elasticity in some situations. Thermoplastic filament yarns are used in most texturing processes. The inter fiber bonds break and reform during the texturing process. A filament yarn is generally textured through three steps. The first step is to distort the filament in the yarn so that the inter fiber bond is broken. Twisting or other means are used to distort the filaments within a yarn. The second step is to heat the yarn, which breaks bonds between polymers, allowing the filaments to stay crimped. The last step is to cool the yarn in the distorted state to enable new bonds to form between the polymers. When the yarn is untwisted or otherwise released from its distorted state, the filaments remain in a coiled or crimped condition.

There are many methods for yarn texturing, including false-twist, air-texturing, knit-de-knit, stuffer box and gear crimp. Among these, the false-twist is the most popular method. Figure 3.12 shows the principles of the main methods of yarn texturing.