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Desizing Machines:
This is a singeing desizing operation in a continuous gas singeing and desize impregnator. Preparatory processing removes impurities, color bodies and size imparted in woven fabrics either naturally or during the manufacturing operations of spinning and weaving. As a result, the fabric acquires good absorbency and appearance and becomes suitable for mercerising, dyeing, printing and finishing. Steps in preparatory processing The first steps are mechanical and dry treatments, viz., shearing and singeing followed by chemical and wet treatments, viz., desizing, scouring and bleaching. The following are the features of the state of the art machines representing recent developments in each of these preparatory processing steps: Shearing Shearing machine of Kusters Calico of Germany-India can give 100% shearing efficiency with good output. Its suction mechanism is for getting optimum and all through results. It has seam protection device and a system for adjusting the distance between cloth and blade to suit different fabric sorts. The vertical shearing heads give the best results even with fabrics of loose selvedges. There is a pre-brushing unit, dust collection and cleaning unit to keep the machine as well as fabric surface clean. Singeing Singeing machine of Osthoff-senge of Germany has ‘Double-Jet’ burners capable of using all types of gases and an ideal mixture distribution system for singeing to perfection. Flame is set as per fabric width for energy saving. Singeing positions include - on to free-guided fabric, on to cooled roller or tangential singeing for different fabric sorts for the best results. Machine conforms to European Safety Regulations and has exhaust purification as well as hot air use. Desizing, scouring and bleaching Preparatory wet processing operations on cotton and blended fabrics are carried out these days mostly in open width form by continuous, semi-continuous or batch-wise methods. Continuous method ‘Mega Bleach or Flash Steam Bleach and FlexNip high-add-on application’ is the latest continuous combined 2-stage process developed by Kusters of Germany in collaboration with Ciba Specialty Chemicals of Switzerland. The first stage consists of pad-steam enzymatic cracking to thoroughly desize and also to remove the troublesome alkaline earth and heavy metal ions. Fabric is impregnated with Ciba’s enzyme Tinozym ADC and cracking agent Invatex MD followed by a short time steaming and hot wash off. This process combines acid cracking and enzymatic desizing. In its second stage, the fabric is scoured and bleached at the same time with the well established ‘Mega Bleach’ using Ciba’s Tinoclarite CBB Processor and Invatex MD cracking agent. These agents are given a high add-on application with Flex Nip followed by about 20-minute steaming and hot wash off. The well-established Mega Bleach combines the conventional steps of alkaline scouring and peroxide bleaching. The desized, scoured and bleached fabric is finally neutralised and subjected to an optimised washing process using Ciba’s Invatex AC. This process is claimed as the most efficient and economical one giving high quality goods. Semi-continuous method Kusters of Germany has also developed a semi-continuous 2-stage desizing, scouring and bleaching process with Rudolf Chemie of Germany. In its first stage, the singed fabric is impregnated with the enzyme Rucolase CML 200 at 60-95øC and padded to 100% liquor pick-up, dwelled at ambient temperature for 6-12 hr and finally washed off at boil. The second stage of combined scouring-bleaching of fabric, consists of fabric impregnation with a liquor containing 50% H2O2 (42 ml/kg), 50% NaOH (30 ml/kg), Ruco-Stab OKE, the stabiliser (6 ml/kg) and Rucogen WBL, scouring and wetting agent (2 ml/kg), padding as in the first stage followed by steaming at 100øC for 90 sec, final washing at boil, rinsing hot and cold and neutralising. Batch-wise method Open-width preparatory processing involving desizing, scouring and bleaching can also be carried out on fabric in batch form on Jumbo jiggers. jt-10 Spectra of Harish, India is an open-width Super Jumbo jigger for desizing, scouring and bleaching of cotton and blended fabrics in jumbo-size batches up to 1500 mm. Its trough is divided into three compartments with two intermediate squeeze nips. On the full width of fabric, chemicals and dyes are squeezed to facilitate rapid processing. Steam injector boxes are positioned in close proximity of fabric for flash scouring and bleaching. A chemical dosing system maintains chemical concentration in the compartment. The machine design helps to obtain temperatures up to 98øC. Its rapid hot wash with water injectors washes off soil, dirt, waxes and chemicals from fabric by water spray and thermo-mechanical energy from steam. These impurities are flushed out by an efficient filtration system. It has also a Counter Meter System with auto-reverse and a crawling arrangement during stoppage to counter any unbalancing of the wet batch. With its electronic program, the various process cycles can be pre-programmed in terms of processing conditions such as temperature, duration, speed and chemical additions. Preparatory processed fabric As a result of preparatory processing, the residual size levels in fabric come down to 0.5-1.0% in cotton and 0.2-0.5% in blended fabrics. The fabric also becomes adequately absorbent with drop test readings of 3 seconds or less. Fully bleached fabrics show brightness levels of 80-85% with yellowness levels of only 0.05-0.06%. Cuprammonium fluidity, a yardstick to check fabric deterioration or tendering during the process, will also be as per the norm of 8 or less. These quality parameters ensure that the preparatory processing is properly done to make the fabric fit for further processes of dyeing, printing and finishing. The next article in this series will focus on mercerising. Links and references: http://www.funke-jigger.com/en/produkte.html
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