Indigo Dyeing Machinery The Concept Dyes Chemicals Express Textile

Indigo dyeing machinery: The concept - Dyes & Chemicals - Express TextileIssue dated - 4th September. 2003

Choose a Section ... - News & Views - Product Portfolio - Tex Talk Dyes & Chemicals - Yarns & Fibres - Events & Trends - Edit & Oped Corporate Update - Foreign Trade - Fabrics & Garments - Energy Conservation - Fashion Folio - Last Word Home > Dyes & Chemicals > Full StoryE-Mail || Print Indigo dyeing machinery: The concept Indigo in its natural form has been used for dyeing for about 5000 years. Today, most indigo is used for dyeing cotton yarns for the warp of woven denim fabric on continuous dyeing ranges. Prakash D Pardeshi elucidates on the concept. The indigofera plant yields large amount of purer dyestuff. Indigo was extracted from plants later to be replaced by synthetic indigo onto the market. Actually, the principle of dyeing indigo has never changed. Dissolving the dye by reduction involving vatting and loosening up. Dyeing from the vat. Oxidising in the air. Since indigo has a low affinity for cotton, deep blue dyeings are only obtained when dyeing and oxidising are repeated several times. Today, most indigo is used for dyeing cotton yarns for the warp of woven denim fabric on continuous dyeing ranges. These ball warps, 300-400 threads per rope, are placed in holders in front of the machine in a staggered arrangement, so that when the rope runs into the first wetting bath, the feeding angle of the individual ropes differs only slightly. This prevents varying thread tensions. Continuous dyeing, without stopping the machines lots of changes are possible since at the end of the ball warps, the rope can be joined to the warp ends of new ball warps. The thread tension is of special significance, because different thread tensions cause varying dyeing effects in the yarn, resulting in reediness. Normally, a rope dyeing machine has 3-4 wetting troughs. Depending on the required extent of precleaning, additional scouring at the boil is necessary and in this case, four troughs are required for post-rinsing. Approximately 10-18 kg warp/minute can be dyed on rope dyeing machines. For complete oxidation of dye, also inside the rope, this must be followed by an extended air passage - over two levels, if necessary. The oxidation time is about 1-2 minutes on rope dyeing ranges. Until now, it was usual to work with five dye becks. However, new machines have eight becks, the advantage being that the indigo bath concentration is less and the same depth of colour is obtained. This means that finer indigo layers are formed on the yarn, giving two advantages. They are: During the first immersion passage, less indigo penetrates into the yarn, achieving a higher white content of the yarn core, ultimately leading to ring dyed effect. The fine indigo layers give a somewhat better fastness to abrasion and washing. Dyeing and oxidising are followed by 2-3 rinsing baths. Normally, rinsing at room temperature is adequate. It should be ensured that

per kg of warp yarn, at least 3-4 litres of water per rinsing beck is sprayed with some force against the warp. It has already been mentioned that to achieve full colours, indigo has to be applied in several steps. There are basically two different types of machines namely: rope and open warp dyeing machines. Rope dyeing was started in the US. Later in Europe, dyeing of the open warp started, this being dried, sized and wound directly onto the warp beam for weaving, all in one operation. These two types of dyeing machines are still used today with some modifications when dyeing the open warp. Rope dyeing machines These are very conspicuous by virtue of their dimensions. Machines of this kind can be upto 60 metre long. The yarns for the warp rope are drawn-off of cross wound bobbins and wound onto ball warps, on so called ball warpers. The rope length can be upto 25,000 metres. If rising is carried out at temperatures of around 50 degree C, an unnecessary amount of dye is removed. Rope dyeing does not finish with the rinsing process. This is followed by a softening bath in which usually 0.5-1 per cent dry substance of a cationic softener is applied to the yarn. This application serves to aid opening of the rope to give a long chain beamer. Here the rope is opened sufficiently so that individual threads, which are paralleled by means of a comb, can be wound onto the sizing beam. Even with a perfect yarn and an effective softener, the efficiency of such a beamer is often below 50 per cent. The capacity of rope dyeing machine is between 12, 24 and 36 ropes, depending on the size and width. If the number of threads of a dyeing machine for open warp dyeing is compared with that of a rope dyeing machine, the following ensues: Rope dyeing machine: 4800/9600/14400 threads. Open warp dyeing machine: 3800-4200 threads. With 36 ropes, the material through flow is three and a half times as great as an open warp dyeing machine. The squeezing units on rope dyeing machines are of appropriate dimension. These squeezers have a rubber roll with counter steel roll. The pressures depend on the function of the squeezer. After the last wetting bath, squeezing takes place at 10 bar and the following squeezers have a slightly lower pressure, so that the yarn can pick up dye liquor. With 10 bar pressure, the rinsing liquor of the last rinsing bath is squeezed out before the ropes enter the softening bath. All other squeezing pressures are around 4-6 bar. Open warp dyeing machine In the first half of 1970s, a second type of dyeing machine was developed in Europe, on which in stead of ropes, the warp threads are processed lying parallel to each other. Sizing directly follows dyeing. This type of dyeing machine is also called a �slasher� like sizing machine. The reason of this is probably that sizers also experimented on their machine with combined sizing and dyeing. Hence trials were carried out both with pigment dyestuffs and with indigo. If indigo is applied as a pigment in the size, a dull blue grey results. It was, therefore, obvious that the machine builders were called on to design a separate dyeing machine to be installed in front of the sizing machine. As with the rope dyeing machine, the slasher machines also have advantages and disadvantages. Advantages are; The open warp dyeing machine is smaller than a rope dyeing machine, which means that the prime costs are lower. Rope opening is avoided.

Owing to the paralleled warp threads, the wetting process is shorter and a wetting trough may be adequate. The immersion and oxidation times are much shorter. Setting up or stabilisation of the dye baths is effected faster. The holding capacity of the vat is seldom more than 800 litres. Disadvantages are: Unlike rope dyeing, when dyeing the open warp, there is no friction between the threads in the vicinity of the guide rollers. Hence the rub and wash fastness standards of rope dyeing are often not achieved. The hydrosulphite consumption is much higher owing to the greater surface of the textile goods. If the individual processing stages of a slasher are considered, 1-2 wetting vats, 4-8 dye becks and 3 rinsing troughs are required. The immersion and oxidation times lie between 10-20s or 45-60s. Double sheet dyeing By this method, a further development from sheet dyeing - the dyeing and sizing processes are performed separately. Twice the numbers of single warps are presented to the dyeing range. The dyed, oxidised and dried single warps are taken upon two batches corresponding to the total number of ends. These are then presented to sizing machine. Production is almost doubled in this way. Loop dyeing machine A variation of the open warp dyeing machine is the �Loop dye 1 for 6� dyeing machine built by Kusters, USA. During the immersion passages, the warp is fed back to the same dye bath following oxidation. This makes the machine much shorter and the hydrosulphite consumption is much lower. It comprises 8 to 16 warp beams, threading-in feature, pre-wetting or pre-mercerising sections or pre-dyeing unit, the �Twin Pad� colour applicator, an integrated airing passage and two rinsing sections as well as an accumulator scray. Black and coloured warp dyeings The machine is particularly suitable for black and coloured warp dyeing with sulphur dyestuffs. By means of a few valve adjustments, the dye bath volume in the dyeing trough �Twin Pad� can be reduced to only 250 litres from the 750 litres of dye liquor required for indigo. This prevents the dreaded, so called head-tail shading, which can ccur due to the relatively high sulphur/dyestuff affinity with large dye bath volumes. The repeated immersion and oxidation of the sulphur dyestuff produces deep and full shade which can only be achieved with an additional steamer, in the case of black denim warp threads on sizing ranges. Multicolour dyeing machine For many years, Sucker-Muller has been among the largest sellers of indigo dyeing lines. They have undertaken modification of conventional indigo ranges to accommodate multicolour dyeing system. Thanks to the shape of the troughs and the circulation configuration, deposits of sediments and lint are avoided. The immersion time and trough content can be widely varied, like one to eight seconds immersion time and 150 to 600litres capacity, corresponding to the build-up rate of the dyestuffs. Modifications are made to the liquor circulation in the troughs, the liquor holding capacity and dispensing of dyes and auxiliaries to facilitate multicolour dyeing. Indigo and other colours are fed from two separate circuits. In case of indigo dyeing, the dye is applied in �thin layers� without considerable dyestuff excess, which then has to be reduced

again. Thus hydrosulphite is economised, and the small amount of free, not fixed indigo dyestuff, which has to be removed, is washed off in the subsequent washing process. More and more often, a caustic soda/mercerising device is incorporated between the wetting trough and the indigo dyeing line. Subsequently, the warp must be neutralised again in 2-3 washing troughs, whereupon it is fed into the indigo liquor with a pH value of 8-9. Owing to the swelling process of the yarn, dyeing can only takes place at the marginal zones of the threads, since the macromolecular indigo dyestuff cannot penetrate any deeper into the inner yarn cross section. The ring dyeing process is beneficial to the fashionable effect, which can be achieved by abrasion as in the case of stone washed fabric. Often pre dyeing with sulphur dyestuff results in a darker colouring of the denim. By appropriate metering of the dyestuffs and liquor channeling into separate troughs, it is possible to compose multi colour vessel lines for different colourings. Thus plants could be designed where, apart from indigo dye and depending on market trends and demands, dyeing with vat, sulphur, naphthol or other dyestuffs is feasible. Continuous dyeing machine Classic indigo dyeing is more in demand than ever before. The focus has shifted, however, over the last 20 years from indigo dyed working cloths to denim fashion wear and practical leisure wear. Fashionable clothing requires machine technology to adapt flexibly to changing trends. The modular multi-vat design and new, improved technology of Sucker-Muller-Hacoba continuous warp dyeing machine helps to achieve supreme dyeing and sizing quality. Exact metering, measured use of dyes, and low dye and chemical losses make certain of economical and environmentally compatible dyeing. The salient features of the machine include: Optimum dye fastness and uniform dyeing. Perfect yarn and warp control from the package to the loom. High dye batch stability ensured by cross flow circulation and continuous metering. Reproducible computerised process management. Multi color capability achieved by flexible process engineering. Individual warp pre-treatment. Environmentally compatible, due to low consumption of dyes and chemicals. User friendly design with low maintenance requirement. Optimum sizing and residual stretch. High output. Indigoflow dyeing machine Indigoflow is a continuous dyeing range for denim warps. Its continuous evolution and its constant modernisation made it the machine with the highest technological content, allowing the maximum flexibility in use. Various kinds of pre-treatments, mercerising, pre-dyeing, indigo dyeings, over dyeings, dyeings with vat and sulphur dyestuffs, etc with intermediate pre-drying facility and steaming, can be carried out in the machine. It is the only machine equipped with the exclusive twin low vats for the short bath dyeings of the coloured denim, with the revolutionary oxidation enhancers �Rapidsky� and with the new �Rapidwash� which enhances the washing efficiency with notable water savings. The machine is easy to manage and is designed for a high quality production with reduced costs, suitable for a wide range of warps and counts. Other characteristics include the semicircular bottom dyeing vats

for an easy cleaning, the squeezing pads with special rollers for a uniform squeezing at each work pressure, the double automatic dyestuffs feeding system, the particular finning on the rollers on air that drastically reduce the cleaning operations, the hydrosulphite and soda automatic feeding systems, the control electronic devices etc. The compactness with space availability for all the intervents, the completeness of the installations, even on the colour kitchen, for air, water, steam and condensate return are other features. Built with the modern modular concept, with best quality components easy to find on international market and with the parts in contact with the bath and the yarn in stainless steel, the running of the machine is absolutely reliable. It is supplied complete with a sizing machine or linked in perfect synchronisation with any kind or brand of sizing machines. Ben-Indigo dyeing machine In Ben-Indigo dyeing machine, the preparation of the vat stock is made in-situ in a reactor of 160litres, in accordance with the requirements of the dyeing machine, but without excess hydrosulphite or the ingress of air. The dye concentration in the dye baths can be raised to 7-8 gm/litre. The vatting rate is maintained at >95 per cent, whereby the ingress of air and hydrosulphite replenishing are reduced to a minimum. Additional dye fixing after leaving the dye bath - before oxidation - gives a high dye yield. The small amounts of hydrosulphite have a positive effect in ensuring that oxidation is fast and complete. The number of immersions can, therefore, be reduced to three. Immersion times are shortened and the content of each bath reduced to around 200-300 litres. The speed and dynamism of the system facilitates automatic monitoring. Disturbances are recognised immediately and the cause can be determined and rectified. The subsequent rinsing process requires less water since there is little non-fixed dye and a considerably lower salt load on the yarn. An indigo recovery plant is not absolutely necessary. The technique results in a dyeing range with only three dye baths, a dyestuff content of about 600-900 litres overall and a high dye fixation rate. The subsequent washing process requires thereby less water or washing compartments. The reduced sulphide load on the yarn results in better running characteristics in the following sizing and weaving processes. There are advantages. Sophisticated chemical and process engineering control is made available to the user in the form of control programs. Oxygen free just-in-time vatting permits a reduction in dyestuff with minimum use of chemicals. The process control software gives the machine a learning capability. It can make early deviation, fault diagnoses and provide warning messages. The use of the automatic monitoring system makes it possible to optimise quality and minimise costs using the analyses of the operation data logged.

Edit A right move The efforts towards formation of confederation of Indian textile and clothing industry by Mr Nikhil Meswani, president, Association of Synthetic Fibre Association should be fully supported by the textile trade and industry which is currently undergoing a transformation.

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