Yarn Conditioning Process : An Overview

   

Yarn Conditioning Process : An Overview

High speed spinning machines generate more friction thus giving additional heat to the yarn and as a result of such heat transfer the yarn moisture content is vaporized. Rising speeds in spinning result in decreased yarn quality for other processes and it is well known that dry yarns have worse properties. For quality reasons it is absolutely important to have even distribution of this recuperated moisture throughout the entire yarn package. Only the vacuum technology provides the conditions for the required moisture regain. This paper attempts to comprehensively review the yarn conditioning mechanism, process parameters of conditioning and applications of yarn conditioning.

Moisture in atmosphere has a great impact on the physical properties of textile fibres and yarns. A high degree of moisture improves the physical properties of yarn and it helps the yarn to attain the standard moisture regain value of the fibre. Yarns sold with lower moisture content than the standard value will result in monetary loss. Therefore the aim of yarn conditioning is to provide an economical device for supplying the necessary moisture in a short time, in order to achieve a lasting improvement in quality.

In these days there is a dramatic change in the production level of weaving and knitting machines, because of the sophisticated manufacturing techniques. Yarn quality required to run on these machines is extremely high. In order to satisfy these demands without altering the raw material, it is possible to make use of the physical properties inherent in the cotton fibres. Cotton fiber is hygroscopic material and has the ability to absorb water in the form of steam. It is quite evident that the hygroscopic property of cotton fibers depends on the relative humidity. The higher the humidity is, more the moisture absorption. The increase in the relative atmospheric humidity causes a rise in the moisture content of the cotton fiber.

The fibre strength and elasticity increase proportionately with the increase in humidity. If the water content of the cotton fibre is increased, the fibre is able to swell, resulting in increased fibre to fibre friction in the twisted yarn structure. This positive alteration in the properties of the fibre will again have a positive effect on the strength and elasticity of the yarn.

Problems in conventional yarn conditioning method

The standard conventional steaming treatment for yarn is chiefly used for twist setting to avoid snarling in further processing. It does not result in lasting improvement in yarn quality. The steaming process may fail to ensure even distribution of the moisture, especially on cross-wound bobbins (cheeses) with medium to high compactness (Fig. 1).

The absence of vacuum in conventional conditioning chambers prevents Conventional homogeneous penetration. The outer layers of the package are also too moist and the transition from moist to dry yarn gives rise to substantial variations in downstream processing of the package, both with regard to friction data and strength.

Since the moisture is applied superficially in the wet steam zone or by misting with water jets, it has a tendency to become re-adjusted immediately to the ambient humidity level owing to the large surface area. Equipment of this kind also prevents the optimum flow of goods and takes up too much space.

CONTEXXOR conditioning process by Xorella

The thermal conditioning process of the yarn according to the CONTEXXOR process developed by Xorella, is a new type of system for conditioning the yarn package (Fig. 2). Thermal conditioning uses low-temperature saturated steam in vacuum. With the vacuum principle and indirect steam, the yarn is treated very gently in an absolutely saturated steam atmosphere. The vacuum first removes the air pockets from the yarn package to ensure accelerated steam penetration and also removes the atmospheric oxygen in order to prevent oxidation. The conditioning process makes use of the physical properties of saturated steam or wet steam (100% moisture in gas-state). The yarn is uniformly moistened by the gas. The great advantage of this process is that the moisture in the form of gas is very finely distributed throughout the yarn package and does not cling to the yarn in the form of drops. This is achieved in any cross-wound bobbins, whether the yarn packages are packed on open pallets or in cardboard boxes.

Effect of conditioning process parameters on yarn properties

Although yarn conditioning machine can add the moisture of yarn, one must consider different raw material and yarn counts to make different yarn conditioning programs. In spite of higher moisture, if there is high vacuum condition, the low quality of raw cotton, coarse count and higher ratio of short fibre would make yarn over relaxed and thus will have less strength. Thus cotton yarn less than Ne 21s, needs less vacuum, low steam temperature, longer heating up time and constant temperature. For PC or pure polyester fibre as well as combed yarn. It requires high vacuum degree and high steam temperature. The time for heating up and constant temperature is related to the actual twist but maximum should not exceed 70 minutes.

Steam temperature is set according to the types of fibers. If cotton fiber is conditioned under 100 for 20 days, it would have only 92% strength left, but polyester fibre under the same conditions would retain 100% strength. For different fibers, there is a big difference in the flow temperature, fusion, resolution and other index of thermo logy. Maximum temperature for cotton fiber in yarn conditioning machine should not exceed 85 but pure polyester could reach 140. Otherwise it will have negative effects on breakage strength and colors. 

P. V. Kadole et al found that, the cycle with first cycle temperature 58C - 05 min. and second cycle temperature 62C - 25 min. (with total time for the cycle 55 min.) gives optimized yarn properties for 20KW (4.26 TM), 20KH (3.78) waxed, 20 CH waxed. (3.6 TM) yarns. They also stated that in case of conditioning waxed and unwaxed yarn simultaneously with same programme, care should be taken while selecting maximum temperature in second cycle. Always it should be less than melting point of the wax. They showed that the combined programme helps in achieving best yarn results at low power cost and higher production rate.

Sibel Sardag et al studied the effects of vacuum steaming process parameters (temperature and duration) on tenacity properties of 1 00 % cotton and 100 % viscose yarns. For this purpose, the yarns with different twist coefficients and numbers were twisted and exposed to vacuum steaming at different temperatures and for durations appropriate to their raw material properties. Tenacity properties of the yarns were measured before and after vacuum steaming. They found that vacuum steaming temperature has significant effect on tenacity properties of 100% cotton and 100 % viscose yarns but vacuum steaming duration has been found to be statistically insignificant on tenacity properties of cotton yarns, and viscose yarns.

In another study, these authors showed that tenacity, elongation at break (in per cent), and work of rupture of 30 tex and 20 tex PES/viscose yarns were to be enhanced due to heat-setting. They also showed that the tenacity and elongation at break values of the yarns decreased after dyeing; however, these values are still high when compared with those of the pre-heat setting. The increase of temperature from 90C to 110C caused a decrease in the strength values of the yarns. For this reason, they considered the heat- setting at 90C to be sufficient to enhance the strength properties of PES/viscose yarns - consisting of 67% PES and 33% viscose.

Yarn conditioning machine does improve the CV of yarn and also it does not make it worse. It is the fact that CV and neps of yarn detected by yarn evenness tester is raised rapidly for yarn, just taken from the yarn conditioning machine. However, leaving it for 24 hours, later the data will remain as before. The reason is after processing, a part of water gets into the inner core of yarn and becomes relatively steady crystal water, and water attached to the surface of yarn becomes unsteady. The difference in each part of the surface water would result in different dielectric coefficient, which makes the yarn evenness tester give inaccurate results.

In case of cotton fiber, absorption of moisture is delayed after processing in the yarn conditioning machine. It is therefore, better to pack or use the yarn after 30 minutes rest in the yarn stock room. This would allow enough time for the surface water to evaporate and also to retain the same moisture level both inside and outside of the yarn. The yarn that has been processed in the yarn conditioning machine should not be mixed with the one which has not been processed; otherwise, there will appear long and narrow shadow on the final product after dyeing, especially for knitted fabric. 

Major applications of the yarn conditioning In spinning process yarn conditioning machine is used to adjust the moisture of yarn and to improve efficiency in the next process. After processing, when the moisture level of yarn would reach about 8.5 %, strength and elongation can be increased greatly, which help the performance at processing line. The dealing of cone yarn would improve the efficiency on winding, doubling and twisting and also reduce the yarn hairiness. It will be also helpful to improve warping efficiency and to reduce the defects from rewinding and warping. Owing to the conformity of moisture of the yarn, the efficiency of sizing and weaving will also improved ensuring the quality of the final fabric. The yarns after processing by yarn conditioning machine would improve the working process as well as the quality of final fabric. Because of fixed twisting and shaping of the yarn, it will give equal height of rising and looping, reduce the unwinding tension, stable the structure and size of the end fabric and give better appearance. Especially it is the key process for setting the seamless underclothes. The process of conditioning will not only stabilize the twist, but also fully relax the yarn to reduce the shrinkage of final product. In dyeing industry, processing after yarn conditioning machine can remove the stress on grey fabric, which will be helpful for uniform absorption of dyes to obtain bright color as well as uniform shade of the fabric. In garment industry, yarn conditioning machine can make fabric with stable size, reducing the shrinkage and improving the quality. Processing yarn, especially the chemical fiber, in the conditioning machine can greatly improve the quality and appreciation of product. Conclusion Textile market is becoming sensitive buyer's market. Weaver is demanding dimensioned quality with consistency from spinners. Therefore in order to satisfy these demands without altering the raw material; the hygroscopic nature of cotton fibers can be used. Therefore most of the spinning mills are now going for YCP. These modern YCP gives us even penetration of steam into all the layers of yarns on cone & ensures even conditioning effect throughout the package. The yarn conditioning plant supply the yarn with increased strength & elongations, that have reduced snarling of yarn, improved working at post spinning processes like warping, weaving, knitting, etc. Yarn conditioning reduces invisible loss to the spinners. Though its initial cost of investment is high, but its payback period is very less. This article was originally published in the Textile Review magazine, January, 2013, published by Saket Projects Limited, Ahmedabad.

Improving the quality of spinning machines in textiles

Improving the quality of spinning machines in textiles

Globalization has led to tough competition in the textile industry than ever before. New and improved yarn spinning machines have been developed so that the textile companies can enhance the quality of yarn, have better production control, and sustain in the market. In the past few years, one can notice a tremendous improvement in the quality of yarn especially in countries like China, India, Bangladesh, Vietnam, and Indonesia.

All are aware that spinning is a part of textile manufacturing process. It is a process where strings of fibres are converted into yarn. Further the spinning process involves many functions like cotton mixing, carding, combing, drawing and the last step is winding. In this process the small amount of yarn is wound into big cones.

However, it is important to maintain the quality in any textile process. The quality of the textile depends on the quality of the yarn. Therefore, it is essential for the manufacturers to produce good quality yarn to sustain in the competitive market.

Along with the quality aspect one should not ignore productivity as it is equally important in the spinning process. Manufacturers must concentrate on both these aspects. In this respect, the manufacturers should see that methods adopted to improve the quality of the yarn do not affect the productivity. There are different spinning techniques and machines developed for each technique.

Ring spinning is considered as the most trustworthy, cost effective, and successful yarn manufacturing method. Ring spinning system has gone through many changes in the past 30 years. This spinning technique has improved continuously in the past years with its goal on higher production, along with speed and superior quality. The quality of yarn produced by this technique is considered to be the best and is accepted worldwide.

It is broadly used because of its high speed and the quality of yarn it produces. This technology produces yarns which are structurally stronger. It produces softer yarns and fabrics. It can be used to spin any material. Its operational functions are very simple to learn and understand. Moreover as the speed in the drawing section can be properly managed, the uniformity of the yarn is very well maintained.

In addition to these benefits, as the yarns are stronger they break less during spinning or at later stage. Also, the yarns are less hairy and it is beneficial for fabric manufacturing. This spinning system is extensively used in Europe and Asia. There are about 1000 spindles and 500 drafting systems in today's ring spinning machine for wool.

Another new invention in spinning is the vortex spinning technology. It is one of the most promising technologies in recent times. In this method, with the help of air jets, false twist is developed. The chief advantage of the vortex spinning machine is that it has the ability to spin carded cotton fibres at a phenomenal speed of 400m/min. Furthermore, the cost of maintenance is low as there are fewer moving parts.

The older roving frame process is removed and a fully automatic piecing system has been established. Moreover, yarn produced with this technique is less hairy compared to the normal ring spinning machines. In addition, the fabrics made from these yarns have exceptional qualities like resistance to scratch, absorbs moisture, has color fastness, and dries quickly.

The spinning machines are continuously being developed to achieve the main goals of spinning. Such as high productivity, low maintenance cost, and best quality yarn. The new air jet spinning machine has been developed recently with high performance theory. This air jet machine has achieved the targeted spinning speed of 450m/min compared to the normal delivery speed of the ring spinning machine which is 15-27m/min.

The rotor spinning machine and air jet spinning machine are almost similar in construction. However, this new air jet machine has four robots to do the functions like changing the bobbin, arrangement of yarn piecing, and cleaning. Also, it has the provision to simultaneously produce two different qualities of yarn without getting mixed up. The robots are highly reliable. Any faults or problems are sorted out without waiting for manual instruction.

The quality of cotton yarns produced in Poland was not good compared to the yarns produced in countries like India, Turkey and China. This had posed a big challenge to the Polish manufacturers as these yarns had already entered the Polish textile market. To improve the quality of their yarns, the local manufacturers purchased new machines.

These machines included carding machines, combing machines, cleaning machines and latest spinning frames. Today, the polish yarns are at par or even better than the imported yarns. Their effort to improve the quality of the yarn by using new types of spinning machines and techniques has yielded them positive results.

Rotor or open end spinning has been established since 1960s and the technology has grown over these years. The new automatic rotor spinning machine provides many additional benefits that the older machines did not have. The new machine is set to produce better, softer and more yarns. Its intrinsic features will further increase the speed and improve efficiency at the same time will consume less energy.

This machine has become very successful as it produces superior quality yarn. The buyers have accepted it as its benefits are clearly visible. It is easy to operate and very reliable. Moreover, its elements can be replaced without using the tools. Further, its new structure prevents fibre accumulation or changing the spinning conditions and has very low hairiness. The 'cool nozzle technology' keeps the surface cool.

All these features result into higher productivity with different types of synthetic fibres. The manufacturers have already experienced the benefits of the new spinning technology with better yarn strength and evenness.

The new age spinning technology has widely caught the interest of the manufacturers around the globe. The high speed rotor spinning machine is giving tough competition to other machines in the market. Innovative spinning techniques have tremendously changed the performance of different types of spinning machines. The benefits of the improved machines are not limited to producing high quality yarns or increase in productivity but have completely changed the scenario of the spinning sector.

References:

1.              Cottonyarnmarket.net

2.             Indiantextilejournal.com

3.             Slideshare.net

4.             Cottonyarnmarket.net

5.             Evolution.skf.com

Problems, Causes and Remedies in Blow Room Section

Problems, Causes and Remedies in Blow Room Section

Blow Room: Blow room is the initial stage in spinning process. The name blow room is given because of the "air flow" And all process is done in blow room because of air flow. Blow room is consisting of different machines to carry out the objectives of blow room. In blow room the tuft size of cotton becomes smaller and smaller. In a word we can say a section in which the supplied compressed bales are opened, cleaned & blending or mixing to form uniform lap of specific length is called Blow room section. During the opening, cleaning, blending or mixing different faults or defects occur in blow room. Now I will discuss about faults/defects, causes and way to remedies in blow room section. Problems/Faults/Defects in Blow Room: 1.      Low cleaning efficiency 2.      High nep generation and fibre rupture 3.      High variability in the delivered hank 4.      Formation of cat's tail 5.      Conical lap 6.      Lap licking 7.      Patchy lap 8.      Holes in lap 9.      Soft laps 10. Ragged lap selvedge Causes and Remedies are discussed below: Low cleaning efficiency: Lower extraction of wastes than required for that mixing considering the trash content is one of the main reasons for low cleaning efficiency. Increase the wastes if the lint in the wastes is normal or nil. If the beater speeds are lesser than required, we get lower cleaning. Check the beater settings and correct them if needed. Increase the space between the grid bars. Close slightly the air-inlets under the grid bars towards the cotton entry side, and open those on the delivery side. Reduce the fan speed following the beaters by 100 to 200 RPM. If the grip of the feed roller is less, we shall get low cleaning efficiency. Therefore check for the grip. Also check the sharpness of the beaters. Check the synchronization of the machine working. The blending bale openers should work for 80 to 85% of the time of working of the final machine. If there is a back draught because of not cleaning the wastes under the machines, the cleaning efficiency shall come down. High NEP generation and fibre rupture: The main reasons are blunt beaters, burrs in grid bars, bent pins on beaters, higher beater speed, lower fan speed and excessive feed. A higher beater speed shall give more neps, if the material is not moved out of the beating area effectively. If materials return back to beaters, neps shall generate, hence check the setting of leather flaps, stripper knife etc. Excessive of soft wastes fed, and cottons with more immature fibres are major reasons for neps in opened material. Therefore have a control on the issue of soft wastes to mixing and spread them uniformly throughout the mixing. High variability in the delivered hank: Improper levels in the hoppers, improper action of feed regulators viz, cone drums, pedals, photocells, direct driving gear motors, etc are the normal reasons for variability in delivered hanks. Formation of cat's tail: If material movement is less and cottons are over beaten, we get this defect. By sharpening beater edges, increasing fan speeds, increasing the air in-let below the grid bar area of cotton entry, closing the striping knife and beater setting shall avoid cat's tail. The very important step in avoiding cat's tail is to avoid chocking of materials in beaters. Excessive use of cotton-spray oil, water etc., also causes cat's tails. Conical lap: Conical laps are due to, either higher quantity of cottons coming on one side of the lap, or due to unequal calendar and rack pressures in scutchers. Ensure equal opening of air-inlets under grid bars, replace torn leather lining at the cage, clean the cage thoroughly with emery paper, make pressure on lap spindle uniform on both the sides, remove the pedals and clean thoroughly, and check the pedals where it rests on fulcrum and also pedal fulcrum bar. Lap licking: Lap licking can be due to excessive addition of soft wastes in mixing, higher rack pressures, lower compacting of laps and excessive dampness in cotton. In case of polyesters, this problem shall be mainly due to static charges and higher bulk of fibres. The problem of lap licking can be reduced by increasing the pressure on calendar rollers, reducing the pressure on racks, increasing the quantity of antistatic, use of roving ends or lap fingers behind the calendar roller nip, blocking of top cage and by reducing the lap length. Patchy lap: Patchy lap is a result of unopened tufts. Ensure that the mixing is opened thoroughly, and increase opening points if feasible. Check tuft size at the delivery of each beater, and adjust the setting between feed roller and beaters, reduce the gauge between evener roller and inclined lattice, clean the cages, and increase effective suction at cages. Holes in lap: Holes in the lap can be due to different reasons. Check the cages for damage, and reduce tension draft. Soft lap: Lower calendar pressure makes the laps soft. Increase the calendar roller pressure. Ragged lap selvedge: Ragged lap selvedges are mainly due to uneven spots at the edges. Check for the rough spots on the sides of the feed plates, leather linings for the cages, and keep the edges of the scutcher clean.