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Doubled yarns of various types and qualities are made by combining two or more yarns of equal or differing thicknesses and then twisting those using doubling machines. The twist of the yarns (Z = right-handed, S = left-handed) is usually opposed to the rotational direction of the yarn spindles. Doubling increases the strength and uniformity of the yarn.
In order to maintain certain yarn structures, single and multiple yarns are twisted normally or over-twisted. The over-twisting of the yarns gives rise to a crimp effect, which causes a displacement of the nap of the carpet pile (twist, frisé). To ensure that this effect remains permanent, the yarn must be fixed in this over twisted state. To this end, the yarn is treated with heat and steam in a so-called heat-set process.
Dyeing is the term for the technical process of colouring textiles. Originally, textile makers were limited to natural dyes derived from vegetable, animal or mineral materials. Indigo and madder red (alizarin) are two of the most familiar examples of vegetable dyes.
Purple dye, which was extracted from a type of snail, is an example of an animal dye. The extraction of this dyestuff was highly difficult and extremely expensive – around 12,000 snails had to be processed to make just one gram of the dye! Another natural dye was cochineal red, which was gained from the female of a species of coccid. Examples of mineral dyes include chrome yellow, cinnabar, Vienna green and ultramarine. Around the mid-19th century, the first artificial dyes were manufactured. These are complex, intricately structured hydrocarbon compounds.
Today, it is possible to dye textiles virtually any colour. Consequently, not only is the attractiveness of a dye important, but also its resistance to light, water and mechanical abrasion. Resistance to acids and bases may also be important criteria in some special applications.
The hot dye bath (an aqueous solution or slurry of dyes) is brought into intense contact with the material to be dyed (pumped, saturated). In the process, the dye is absorbed into the material. It is possible to dye fibres, yarns and entire carpets. These require different dyeing processes and machines:
Production-dyed fibres and yarns
These fibres and yarns are dyed right in the spinning process – the dye is added directly to the spinning material (spinneret dyeing). The result is fully dyed filaments, which can also be produced in mottled or thrown patterns.
Dyeing fibres and yarns
The material is dyed using what are known as circulation systems, in which the fibres or yarn to be dyed are placed. The material rests motionless while the dye bath is evenly pumped through it. Fibres are always dyed in a package system (flock dyeing), while yarns can be dyed using both package and suspension systems (hank dyeing). Modern industrial circulation systems can dye up to 2,000 kg of yarn in one colour batch. When dyeing fibres, the amount of material that can be dyed a particular colour at one time is virtually unlimited, as dyed segments with slight differences in colour are mixed before spinning to ensure a uniform colour.
Unlike production-dyed yarns, this process uses multiple dyes for each yarn. The sections of each colour can be long (“long-spaced”), or very short-spaced when a dot effect is desired. Whereas in space dyeing the dye is printed on, space treating uses chemical resist substances; these cause a varied colour uptake in subsequent piece dyeing.
Fibres and yarns must already be dyed before they are made into carpets. It is not possible to respond to customers’ colour preferences on an ad-hoc basis. The solution to this problem lies in piece dyeing. Unlike the circulation process described for dyeing fibres and yarns, in piece dyeing the carpet itself is moved through the dye bath.
In the discontinuous process (vat dyeing), up to 200 running meters of carpeting 400 to 500 cm wide are run through the dye bath as an endless belt. In this process, the carpeting is manufactured from undyed (raw white) yarn and then dyed the desired colour. This piece dyeing process acquired enhanced importance with the development of tufting technology and the introduction of differential-dyed yarns.
Differential dyeing is the process of dying polyamide yarn types that have the same technological properties but different chemical structures in a non-uniform manner. This means that the yarns with the various different dyeing properties must be utilized in the production of the raw white carpeting in accordance with the desired pattern. The result is that up to three different hues can be produced in a single dye bath. Multicolour effects can be achieved using yarns treated with a dye-resist process. Piece dyeing can be performed using either a vat or a continuous dye process, in which a virtually unlimited amount of carpeting can be dyed a specific colour.
Printing (Chromo-Jet process)
As in piece dyeing, the raw-white carpeting is fed into the printing system in its fabrication width.
The material is transported to the printing table via a material buffer, a steamer and brushes. The material is then halted here, and the printing head moves transversely to the direction of travel (tuft direction) from position 1 to position 2. The printing table advances the material 1.6666 mm (1 cm/8 corresponds to a dot spacing of 1.666 mm) and the head returns from position 2 to position 1. Once the printing head has reached position 1, the material is advanced and the printing head starts again.
The printing head has 64 nozzles per colour, arranged in an 8 x 8 matrix. The printing head is equipped with a total of 768 nozzles, which means that up to 12 colours per design are possible. As the actual nozzle body has a diameter off around 2 cm, the 64 nozzles per colour are arranged diagonally. These nozzles are controlled magnetically, and can execute up to 400 open/close cycles per second. With the Chromo-Jet process, it is possible to apply spray printing designs to materials with pile weights from approx. 550 to 2000 g/m2.
To be continued...The Weaving Process.
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