New developments in spinning, weaving, & processing
The textile industry has been developing rapidly and newer technologies are introduced and the only formula for survival is encapsulating those innovations into the manufacturing process and making the best of use them for increasing the productivity and quality, says Chitra Siva Sankar. Textile industry is a traditional and a very old industry, and has been amidst almost all kinds of culture around the world from the very beginning, which almost proves the point that the history of human culture and the textiles, are the same. A wide spectrum of processes is involved in the textile industry. Starting from fibre manufacturing to the final processing and garmenting stage, involves a lot of technologies and skills, which leads to a quality conversion of fibres into the ultra modern fashion or a high performance commodity in the case of technical textiles. The first major change in the textile industry took place somewhere during the industrial revolution which lead to the advent of the machines in to the manufacturing processes in the textile industry. This major breakthrough lead to reduction in the work load of the labours and pronounced the dawn of machines in the textile industry. After that there have been a lot of developments in the various sectors of the textile industry, and the following would throw light on the latest developments that have taken place in the major segments of textile industry, namely spinning, weaving, knitting and processing. Spinning Spinning is the industry, which provides raw material for the knitting and weaving industry. The main driving factor of the companies today is to achieve and improve yarn quality that will ensure better competitiveness and higher yarn prices. The developments that are coming up in the industry today are mainly for maintaining higher productivity with effective quality control, by selecting suitable equipment and spinning conditions to match with the raw materials. One of the very important concepts that has revolutionised the spinning industry is the compact spinning concept. After the advent of the compact spinning, yarn quality parameter has changed, especially in respect to yarn hairiness, strength and to some extent imperfections. The compact spinning system has been designed to meet the challenges faced by the high-end spinning mills. • Optimum and sustained yarn quality. • High consistency of all yarn parameters. • Minimal variations between spinning positions. • Easy handling. • Raw material cost saving. • Increased production. Compact spinning attachment can be accommodated on the existing machine types. Some advantages of the compact spinning system (EliTe®CompactSet V5): •Yarn o Tenacity increases by 25%. o Zweigle (S85) hairiness (fibres exceeding 3 mm) reduced by 3% and Uster (H) Hairiness reduced by up to 30%. o Elongation increased by 15% to 20%. o Work capacity increased by up to 50%. o Improvement in yarn irregularity. •Spinning  o Optimum utilisation of fibre substance. o Improved spinning stability. o Ends-down rate reduced by up to 60%. o Fibre loss reduced up to 0.01%. o Fibre fly reduction in the spinning room. o Possibility of reducing the twist by 10% and corresponding increase in the production. Other players in the compact spinning system are Toyota Way, Zinser, RocoS. Weaving The most innovative developments, which have taken place in the field of weaving machinery, have changed the weaving sector completely. The weaving sector was said to be labour intensive in the past but now because of the advent of the shuttleless weaving technologies and other innovations, the scenario is changed, and now it is capital intensive. The shuttleless technologies have many advantages over the conventional weaving systems. • Excellent quality fabrics with high productivity. • Versatility, consistency and reliability of the machines. • Better fabric engineering and creative weave patterns possible. It is not just the three major concepts; Rapier, Air-jet and Projectile, but also a new one in the race, ‘Multiphase Weaving Concept’. Several features are common for the three weaving systems. All of these possess; • Electronic monitoring and control systems, which increases the quality of the fabric and productivity. • Cam, dobby and jacquard shedding systems can be used. • Quick style change mechanism, which reduces downtime. • Use of weft accumulators which almost provide a tension free weft insertion. • Low vibrations due to rigid and sturdy frames. When considering the multiphase weaving concept, the buzz name in the weaving industry is the Sulzer. Sulzer Ruti’ M8300. There is a warp-wise shed formation in this instead of weft-wise shed formation as found in the other weaving systems. One can insert four weft yarns simultaneously at a constant uniform yarn velocity of 22 m/s with minimal weft loading. One can go up to a maximum of 5,500 m/min of weft insertion rate, which is several times higher than that of the other single phase weaving systems. There are several advantages of the multiphase weaving concept over the single phase technologies: • Minimum specific energy consumption. • Small footprint. • Reduced room air treatment requirement and less dust production (made possible by the integrated dust extraction system and air conditioning system). • Substantially lower noise emissions. • 20 to 30 per cent lower production costs. Knitting Knitting is the process of looping and inter-looping or inter-meshing the loops to form a fabric. Knitting by hand is an ancient art whose actual origin is not clearly known. The advent of knitting machines enhanced the speed of production and different designs. Knitting is becoming more and more popular because of the low cost of production and also of its single stage ornamentation. There are two main kinds of knitting; One is weft knitting and the second is warp knitting. The following throws light on the developments that have taken place in the weft-knitting sector. Creel unit The main concern in the creel unit is the fly removal. The fly removal system, mounted at one end of the creel removes the fly, which affects the quality, which also when arising in large quantity jams the entire running of the machine. A tube is provided starting from the yarn-mounting place the wheel that feeds the threads in the formation of the cloth. This way the production quality does not deteriorate. The air is compressed for threading, and the material is bit polished, which offers very less friction that maintains thread quality. Yarn feeder The yarn feeder pulls out the yarn from the package and adjusts it, so that the needles are placed with uniform tension for knitting. This is the only job the yarn feeder does. It is very essential that the tension is maintained uniformly, as the length of yarn per stitch has to be unique for the whole length of the cloth. The machine has attained super efficiency with its improved feed wheel and the tensioner. The present day’s super-positive feed wheel with yarn tensioner, with a motion stopper, along with multiple looping has increased efficiency. Less or nil amount of slippage helps the cloth quality to upgrade. Latest positive feeders for circular knitting are easy to navigate, needs less maintenance and are quite durable. The whole unit is housed with a plastic cover, and is very light in weight, results in less vibration and elimination of static charge. Some of the machines have electronic controls with enhance yarn feed process. Materials used in the spooler are always being researched so that filamentation is less in amount. The coating is hard to resist corrosion and wearing off. A clutch is provided with open-design, which is helpful while cleaning. The ceramic yarn guide prevents short-circuiting of the vibration tensioner that contains magnetic rings. All these mechanisms are to ensure perfect tension. For irregular or intermittent feed the yarn feeders have to stop periodically in between the weave as in case of the jacquard machine. All these specifications have been achieved in the storage yarn feed, developed by IRO. Cams and needles The heart of the knitting machine is the cams and needles. The machine efficiency looks after design and the quality of fabrication. The cam and the needle, which have been arranged as the cylinder and the dial move in unison to move the needle which makes them involved with the knitting process in more direct manner. The backup system ensures that there are almost double knitting arrangements. It makes knitting a no-trouble operation. Cam boxes that have been manufactured by Amtek, using high strength alloys, are good conductors of heat, which implies that heat is removed promptly from the system. The needles that weave smooth patterns are very delicate in nature that can withstand certain amount of tension but not much. Designing is very important part, so that the needles work for longer. Various parameters for the making of needles to resist different fabrics are: Modern improved surface quality, head geometry, heat treatment and shape of the shank. With circular stitching styles, the bending of the needles is the main problem. The needle hooks are made circular for this kind of stitching. To increase efficiency of the needle without compromising the space for the yarn, designers have devised the cone-shaped needle hooks. The shank design holding three needles have been improved geometrically to take care of the machine vibration. A needle with special latch and extra saw slot for smooth operation with rest surface at the back of the latch, was designed by Groz Beckert who has been manufacturing needles for years. At the end of the latch there is a spring that helps regulating the tension. Sinkers The sliding movement provided by the sinker supports the loop. The curves have been properly designed and there is surface finish. The yarn tension is reduced with this design. Take-down The tension has to be almost the same everywhere throughout the circumference of the unit. There is an open-width fabric cutter and take-up with black-and-white Lycra wheels appearing gray as long as the fabric is running and clear black and white when the yarn breaks. This helps in enhancing fabric take-down performance. The centre puncturing of the roll is ceased, and the calculation is done with EPA for even take down and rolling of yarn for without a crunch for the entire width of the fabric. Apart from the technological developments on the machine, there have been developments in the case of patter designing also. Other developments which has to be mentioned here are the Mayer and Cie’ Relanit technology. For faster change in fine gauge machines, open width take down with quality has been developed by Terrot. Four track feeders for every cam box instead of the three track feeders have been introduced by Santoni, which helps in easy cam replacement. ProcessingTextile processing industry is one of the largest industrial users of process water and huge quantities of complex chemicals that are used in different stages of processing. There have been a lot environmental concerns for the processing sector in the last few years. Hence the wet processing industry of the future should be cost effective, environmental-friendly and also very gentle to the textile materials. The following will throw light on a very innovative environmental-friendly concept of dyeing, supercritical carbon dioxide dyeing. Supercritical carbon dioxide has been tried in different areas of textile treatments and has very high potential because this dyeing medium completely avoids water pollution and use of conventional auxiliaries in dyeing as well as after treatments. The drying after dyeing is also not required. The CO2 dyeing technology is now on its way to become an industrial application. Hence, it is a new technologically profitable process. Supercritical fluid Supercritical fluids are advantages in textile processing as they combine the valuable properties of both gas and liquid. The solvating power of supercritical fluid is proportional to its density, whereas its viscosity is comparable to that of a normal gas. Such a combination leads to highly remarkable penetration properties. The increased power of solvation with the increase in density is desirable in the dyeing process as it has a decisive effect on the dissolution of disperse dye in the supercritical carbon dioxide medium. The following is the phase diagram for CO2. Further increases in pressure, for example, will greatly increase the dielectric constant of such system, thus imparting dissolving powers even to a system that under normal condition of p and T has almost none. Reasons for selecting CO2 Carbon dioxide is the best choice. It is non-toxic; It is used in the food and beverage industry; It is inflammable; It is supplied in large amounts either from combustion processes or volcanic sources without the need of producing new gas and it can be recycled in a closed system. Carbon dioxide is frequently used as a solvent because of its special and unique properties; • Virtually inexhaustible resources (atmosphere, combustion processes, natural geologic deposits). • Since carbon dioxide is a constituent of natural metabolic processes occurring in the biosphere it is consumed by assimilation and is returned to the natural circuit by dissimilation. It is not only biodegradable as nutrient promoting the growth of plants, but is an essential element of natural processes. • Carbon dioxide does not affect the edibility of foodstuffs and will only have toxic effects at extremely high concentrations. • It is produced on the commercial scale and is readily available together with the necessary logistics. Concepts for dyeing equipment using supercritical fluids The machine is an extraction plant modified for processing with the supercritical fluids. In contrast to conventional extraction plants the dyestuff are applied to the substrate instead of being removed, ie, the fluid will have to be loaded with dyestuff prior to coming in contact with the goods to be dyed. This can be done in two manners; 1. The dyestuff is filled into the pressure vessel in defined quantities. The dyestuff is filled into an additional small autoclave in the desired (surplus) quantity regulating the carbon dioxide content via, pressure, temperature and/or flow control instruments. The absorption of the dyestuff by the fibre, ie, the diffusion into the inner parts of the fibre, has to meet high levelness standards. The necessary convection of the liquor can be achieved by an agitator within the dyeing autoclave or by moving the substrate. 2. Another option is to penetrate the goods, either by the circulation of the liquor or by utilising the current produced by continuous replenishment of carbon dioxide. In the latter case, the flow of replenished carbon dioxide will have to be continuously loaded with dyestuff. Residues of dyestuff or fibre admixtures to be extracted prior to dyeing will be collected in a conventional separator. The separation of phase will in this case be initiated by expansion or by raising the temperature. Dyeing apparatus An apparatus for dyeing in supercritical carbon dioxide consists of a temperature controller, a vessel heater which surrounds the vessel, a stainless steel dyeing vessel of 50 ml capacity (with a quick release cap), a manometer, a Varex HPLC carbon dioxide pump and a cooler for cooling the head of the carbon dioxide pump. The apparatus was pressure-tested for use up to 350 bars and 100°C. A side arm connects the top and the bottom of the cell outside the heater to allow the supercritical carbon dioxide to circulate by thermal convection. Procedure for fabric dyeing with SC-CO2 method The fabric sample to be dyed (size = 10 to 25 cm) is wrapped around a perforated stainless steel tube and mounted inside the auto clave around the stirrer. Dyestuff without auxiliary chemicals was placed on the bottom of the vessel and closed & purged with gaseous CO2 and preheated. On reaching working temperature CO2 was compressed to the working pressure under constant stirring. Pressure maintained during the dyeing period of 0 to 60 min and afterwards the fabric is rinsed with acetone to remove residual dyestuff. The technical parameters of the dyeing procedure is given below: Table 1 Description Actual used Capacity Maximum Capacity Pressure 250 bar 500 bar Temperature 103" C 350" C Procedure for yarn packages with SC-CO2 method Dyeing temperatures and volume flow rates are similar to the conventional dyeing methods, but the advantage here is that the actual dyeing time requires is less. The procedure of the yarn package dyeing is given below. Table gives an actual comparison between the conventional dyeing procedure and the supercritical CO2 procedure. Table 2 Super Critical CO2 Dyeing Conventional Dyeing Procedure No waste water. Dye remains as powder. No need for dispersing, levelling agents High volumes of waste water with residual dye and other process chemicals Only 20% of the energy requirement High energy requirement Only 2 hours’ time is required for dyeing Dyeing, washing, and drying time is around 3-4 hours/batch Advantages of supercritical CO2 dyeing • Contaminated wastewater streams and other effluents are not produced. • Dispersants are not required to solubilise a disperse dye in water. • Solubility is controllable by pressure, allowing control of the dyeing intensity and colour. • Diffusivities in the fluid are higher, making mass transfer in the fluid faster. • Take up of carbon dioxide by the polymer fibre causes it to swell slightly giving faster diffusion within the polymer. • Viscosities are lower making the circulation of the dye solutions easier. • Penetration of voids between fibres is fast because of the absence of the surface tension and the miscibility of air with carbon dioxide under pressure. • No preparation of processing water (by desalting). • Low energy consumption for heating up the liquor. Energy preservation because drying processes are no longer required (conventional dyeing processes consume about 3,800 kJ per kg of water evaporated). • No air pollution due to recycling of the carbon dioxide (the gas is not contaminated by the processes). • Substantially shorter dyeing times. • No chemicals such as levelling agents, pH regulations etc, have to be added. • No need for auxiliary agents, disposing agents, adulterants, etc. • For polyester, no reduction clearing is needed. • Higher diffusion coefficients lead to higher extraction or reaction rates. Though there are some disadvantages in this kind of dyeing method, like high pressure requirement for dye solubility, impact of dyeing machine weight on the circulation etc, research work is going on to make them completely viable in the process industry. The supercritical system is also being tried with ammonia for application in mercerizing process. The textile industry is developing rapidly and newer and newer technologies are introduced day by day. The only formula for survival is encapsulating those innovations into the manufacturing process and making the best of use it for increasing the productivity, and quality.  Article presented by Chitra Siva Sankar