1.3 Filament yarns Flashcards
Bulk yarn:
A yarn that has been prepared to have greater covering power, or apparent volume, than a conventional yarn of equal linear density and of the same basic material with normal twist
Processing filament yarns
Manufactured fibres are produced as long, continuous filaments. They can be cut into short staple lengths, in which case they are processed as described in section 1.3, or they can be left as filaments. When produced as a monofilament, the yarn should not be too thin because if it is, it will not be strong enough.
- Monofilaments
Monofilaments are therefore rather stiff and coarse. They are sometimes used for sewing in hems or labels, but can be uncomfortable as they tend to be scratchy.
- Multifilament
Multifilament yarns tend to be smooth and slippery to the touch. They do not have the warmth, bulk and comfort of natural and other staple yarns. By making use of their thermoplastic properties, manufactured yarns can be textured into softer, bulkier yarns with increased warmth, comfort and absorbency. Yarns that contain fibres that are not thermoplastic, such as rayon or glass, are sometimes textured mechanically, without heat, by using air-jet or fluid texturing.
Texturing methods
False-twist method
Knife-edge method
Stuffer-box method
Air-jet method
Gear-crimping method
Knit-de-knit method
Bicomponent texturing
Spinneret texturing
False-twist method
A twist is inserted into simple filament yarns. By applying heat, this twist is heat-set into the yarn. After cooling, the yarn is untwisted. A permanent kink remains in the yarn.
Knife-edge method
The yarn is passed over a heated knife edge. The yarn then curls, similar to paper gift ribbon when drawn quickly over a sharp knife or scissor blade.
Stuffer-box method
Filament fibres are forced into a container and then heat-set in this cramped condition, causing a zig-zag crimp.
Air-jet method
This method is also called fluidtexturing because a fluid stream of air is used. A stream of air or steam hits the filaments when they are in a relaxed state. Loops or curls are formed in the individual filaments making up the multifilament yarn. They become entangled and form a yarn with high bulk. No heat-setting is required.
Gear-crimping method
The filaments are passed between the teeth of two heated gears. The form of the gears is set into the fibre.
Knit-de-knit method
The filament yarns are knitted into fabric, heat is applied, and after cooling, the knitting is unravelled. The unravelled yarn now has the characteristic curl of unravelled knitting permanently.
Bicomponent texturing
In the section on bi-component yarns in the module, it was mentioned that this can also be used as a method of texturing. Two types of the same generic fibre, for example, two types of nylon, are extruded simultaneously. One type will shrink more on cooling than the other, and since they now cling together to form one filament, the filament will curl or kink.
Spinneret texturing
Filament yarns can be textured by modifying the shape of the spinneret, by changing the air flow at the spinneret or by vibrating the spinneret. These methods are not frequently used.
