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Spinning & Weaving
  Contamination-controlled cotton & yarn

Improvement of Indian cotton quality with respect to contamination level is the responsibility of all cotton growers, traders & processors, affirms Sunil Kumar Sharma.

Indian cotton is popular but considered one of the most contaminated and unclean cottons in the world. An ITMF Survey in 2011 described the Indian cottons as the "most contaminated" cotton. Sometimes the level and type of contamination in cotton bales have shocked the global buyers. Spinners have been taking many steps to fight this problem, but still it is an unresolved matter for all cotton processors.

Contamination complaint in cotton yarn has been a major customer complaint in the recent times and spinners either pay huge amount to settle claims or they spend a lot of money and manpower to remove the contamination from cotton. Studies show that contamination complaints and claims shares approximately 15% of total yarn complaints. Nowadays when labour shortage is also a major issue for spinning mills, fighting the contamination problem has become more difficult as it requires huge labour deployment for contamination removal. Yet there is no established measurement and monitoring systems available at various stages of cotton processes.

The object of this article is to describe the origin, kind of contamination and how to control it, establishing various measurement and monitoring systems throughout the cotton processing from its origin to spinning stage. A broad road map is presented for creating awareness among the entire stakeholders for dealing with contamination problem. By adopting these systems ginners may produce "Contamination-Controlled Cotton" & spinning mills may produce "Contamination-Controlled Yarn" for contamination sensitive end uses.

Origin & kind of contamination in cotton

The source of contamination is spread in a very wide spectrum, adding into each process, from cotton growing to cotton spinning. Contamination in raw cotton according to their origin can be described as in Chart 1.

Cotton growing field, storage & transportation

During picking, storage and transportation of raw cotton, farmers normally use hessian bags or HDPE bags, and the thread pieces of these bags get added to cotton, significantly contributing to increase in the contamination level. Part of birds feathers, insects, mosquitoes, hairs, dust, small stone pieces, etc may also get added during these processes as cotton trade is done in a multi-fold manner in India. It is assumed that some pesticides and chemical fertilisers also affect the basic colour of raw cotton fibre. Usually it is not visible at grey stage of raw cotton, yarn and grey fabric, and it appears only after processing in dye-house as pink or green spots in fabric. However it is not an clearly established fact and researches are still continuing in their efforts in identifying the exact reason for pink and green spots after bleaching.

Ginning & pressing

Ginning & pressing factories are the highly contributing places for cotton contamination. In ginning and pressing, sand, stone pieces, etc get added if raw cotton is unloaded at a place where concrete platform is not available. Use of HDPE bags for various purposes also contributes to increasing contamination level. Workers engaged in ginning and pressing operations may also be responsible for addition of contamination level. Many times by mistake or negligence workers leave their personal belongings such as hair bands, small handkerchief, chapels, pocket holdings, key chains, tobacco gutkha pouches, etc in cotton. These contamination breaks into thousands of small pieces during ginning and spinning processes. Some ginners mark cotton bales by permanent colour markers which leave their impression on raw cotton.

Spinning

In spinning mills due to higher temperature and humidity, workers hairs frequently fall and get added into process material. Use of HDPE bags for various purposes in spinning mills is also responsible for increasing contamination level.

HDPE: Lower cost, higher lifecycle, lightweight, easy to carry and maintain, these specialities of HDPE materials are being increasingly used day by day. Presence of HDPE in throughout the cotton supply chain has become a severe problem for textile industries as HDPE fibres or thread pieces get added into each and every process of cotton supply chain which is very difficult to remove, especially white HDPE threads. Even new generation cotton contamination sorters & electronic yarn clearers are unable to remove them.

Contamination Control Systems

TMC rated ginning & pressing

Technology Mission on Cotton - TMC's star rating initiated by the Ministry of Textiles for modernisation of ginning & pressing factories has now become a benchmark for raw cotton processing. This is a unique system in the world for grading of ginning-pressing units based on its available machinery, infrastructure, management practices and additional qualification for upgrading the raw cotton processing facilities. The concrete platform for keeping the raw cotton and direct automatic feeding to ginning machines and pressing is a mandatory requirement for TMC rating. By conducting several studies now it has been established that cotton processed through "TMC" plant is having less contamination level. The list of TMC grade assigned ginning & pressing factories is available on Textile Committee’s website.

Controlling at ginning & pressing stage

Ginner should ensure following systems for better contamination control. Spinning mills should also pressurize ginners for strictly following these system when they purchase cotton bales:

  1. Ginning & pressing units should be TMC rated. Full concrete platform & automatic cotton feeding system are a must requirement.
  2. Ginner should pressurize and ensure that farmers & traders should not use HDPE material for cotton storage & transportation. Ginner should also ensure that these should not be used at their end too.
  3. Pre-cleaner & post-cleaner machines should run in ginning factories so that heavy particles are removed at ginning stage itself.
  4. Ginner should create awareness for "Contamination" among their labour for taking proper care and remove visible contamination.
  5. Cotton bales should be covered with cotton cloths only.
  6. Cotton bales should not be marked with colour markers. Cotton cloth label or thick printed papers may be used for bales identification.
  7. It is advisable to put "On-line Cotton Contamination Sorter - CCS before pressing machine for better performance.

Control by spinning mills

At the time of purchasing raw cotton usually spinners are more concerned over cotton quality parameters only and not addressing contamination issue properly as this does not affect working and yarn characteristics. But ultimately it is related with their end-product quality. Monitoring by customer at supplier-end always gives better results and effective control. Hence at the time of selection and purchasing cotton bales, spinners should also ensure above mentioned points at ginner stage.

This will definitely create a better environment for producing contamination controlled cotton as well as spinners will also get better quality cotton. Before purchasing cotton bales, spinners must visit the ginning factories and should ensure all above guidelines suggested for ginning and pressing units. If required it must be implemented on a timeframe basis. Ginning unit which follows these guidelines should be selected in approved vendor list. An appreciating premium may be paid at the initial stage for motivating the ginners for adopting these systems. Once the system is adopted and implemented, it will pay you lifelong.

Cotton bales iron strips, GI wires or plastic strips should be removed outside the blow room and workers engaged for this work should also be educated for pickup all small pieces of iron or plastic strips before shifting cotton bales for lay-down or for mixing bin. Two cotton ropes may be used for tying the opened loose bales for shifting bales to blow room.

Online contamination control systems for spinning mills

The following hi-tech online monitoring systems are available for detection and removal of contamination from cotton and yarn:

Cotton Contamination Sorters (CCS)

Online cotton contamination sorters have become a necessary mechanism for cotton spinning mills. CCS may be looped into blow room line just before carding feed. Cotton contamination sorters analyse the cotton moving in the illuminated zone by the fluorescent lights. The detected contamination is ejected out by the nozzle driven by the Electro Valve using the compressed air. The continuous running contamination collection fan sucks the ejected materials, which are thrown into the collection bag. User may set size and contrast of contamination in system PC as per their end use requirement. An average ejection in range of 1500 - 2000 per hours is a reasonable setting for contamination removal.

Electronic Yarn Clearer

Latest new generation Electronic Yarn Clearers are also equipped with foreign matter detection and removal facilities. Colour foreign matters are measured against the contrast between the yarn body and foreign matter. The signal which is generated by the foreign matter is defined as the intensity of the foreign matter. The intensity of foreign matter depends on change of the light reflection. Electronic yarn clearers may be set according to length of foreign matter and contrast intensity. Contrast intensity of more than 20% and defect length of more than 2 cm are to be removed for a reasonable quality yarn. Figure 3 shown foreign matters removed by electronic yarn clearers.

Manual Sorting

It is the most effective method for removing contamination in blow room at the time of bale opening. Usually 1.5 - 2.0 bales/shift/worker is allotted for manual sorting where pre-opened bales are fed into blow room line. In direct bale feeding system at least four persons are to be engaged at bales lay-down, ie, one each both side of bales lay-down in forward move of Belndomat/Uniflock and one each both side to backward move. At least one person round the clock must be engaged for contamination sorting from CCS ejected material for each collection point.

Monitoring & measurement of cotton contamination

Monitoring and measurement of contamination in tangible form is very difficult as these seldom occur and also in different forms and shapes. Lightweight and dark colour contamination is very serious for yarn and fabric which is multi-fold after ginning & spinning operation. While heavy particles such as stone, metal pieces, heavy substances may cause damage to spinning machinery or fire incidence. Measurement of raw cotton contamination cannot be obtained by applying one simple system. Therefore contaminations are being measured thoroughly by weight and by both methods. The following methods may be helpful in establishing trends for cotton contamination:

1. Manual checking of per bale contamination: Usually this method is adopted where cotton is fed into blow room line through manual operation. In this method cotton bales of different lots, stations or suppliers are being thoroughly inspected manually for contamination and removed contamination are classified by numbers and by weight per bales. This method is very appropriate for grading the cotton bales contamination according to supplier/station and variety wise. Mills equipped with automatic direct bale feeding system may adopt this method for contamination grading on random sampling basis, prior to use of any new supplier lot.

2. Overall mixing contamination level: This method is used for monitoring the overall trend of contamination in running mixing per shift or per day through by weight method. Overall contamination is removed throughout the shift collected by labour engaged for contamination removal whether it is from manual bale opening system or from direct bale feeding system. Totally removed contamination is weighed and divided into number of bales consumed and calculated as Contamination/Bales in gms.

3. Cotton Contamination sorters: Average number of ejection per minute/hr in a shift or day by the "CCS" is to be monitored on daily basis. If there is significant variation observed in ejection level trend it should be diagnosed properly and corrective action to be taken accordingly. Similarly ejected contamination is also to be analysed and monitored as by weight method w.r.t. blow room production (ie, contamination in gms for 1000 kg cotton). Operating and cleaning systems suggested by CCS suppliers should be followed strictly for consistent and better performance of CCS.

4. Foreign matter electronic yarn clearers: Count-wise foreign matter cuts per 100/km is to be monitored regularly. This will provide the trend for contamination level in ring yarn. This is the final action point for contamination monitoring in spinning division and hence according to foreign matter cuts level user may set CCS setting in blow room and EYC setting at autoconer.

5. FD/km through Uster Evenness Tester-5: The Uster Tester-5 provides a new sensor, ie, "FM sensor" that is able to measure foreign fibres in yarn in order to extend the analysis possibilities to the laboratory. Besides the measurement of coloured foreign fibres, the sensor can also differentiate vegetable matter.

The sensor FM provides the following results:

a. Foreign matter dark FD: Coloured foreign matter, the number of FD, ie, foreign matter dark may be divided into 23 classes. The number FD/km in the result Table gives the overall number of foreign matters.

b. Vegetable matter: Vegetable matters are residual of plants. In contrast to artificial matter like plastic, vegetable matters have a higher mass increase and can therefore be separated from the other foreign matter. As they consist of cellulosic material, it is assumed that vegetable matter can be dissolved or bleached in subsequent processes after spinning.

User may classify foreign matter classes as their own requirement and obtain report accordingly. A sample test report is shown here for ready reference in Chart 2 and Chart 3.

5. Classimat Uster Quantam: This also provides the classification for foreign matter defects with 21 classes, which help the user to set right adequate electronic yarn clearer setting and for monitoring of foreign matter defects. Users may also configure different classes according to their own requirements.

6. Consolidation of all data: After conducting all above measurement and monitoring activities through different channels and at various stages, user should prepare a consolidated report in which contamination level at different stages may be compiled in a single page report, so overall performance of different processes may be obtained at a glance. A model report is shown in Chart 4 for ready reference.

Social responsibility

India is the second largest producer of cotton & yarn in the world. We should realise this fact that characteristic-wise our cotton is far better but we are spoiling it by adding contamination in different stages knowingly or unknowingly. Improvement of Indian cotton quality with respect to contamination level is the responsibility of all cotton growers, traders and processors. By taking appropriate initiatives and contribution whatever possible at our end, we can get desired respect and value for Indian cotton and yarn in textile world and may save a lot of money and manpower that are involved in removing contamination in downstream processes. Many a time contamination in cotton also causes wears & tears and fire incidence in spinning, which results in huge financial losses and heavy reduction in productivity. Hence by taking proper care and creating awareness among all stakeholders related with cotton trade we can contribute a lot to textile industry's growth in our country and society.

Conclusion

Characteristic-wise Indian cotton is among the best available cottons in the world, most suitable for medium count range. However the contamination level present in it has downgraded the overall rating. Now is the time to take serious efforts to resolve this burning problem before it hits our targets. The concept behind "Contamination-Controlled cotton" & "Contamination-Controlled yarn" is to provide globally competitive Indian cotton and yarn with respect to lower contamination level by improving whole supply chain from fibre to finished yarn. Various monitoring and measurement systems in different stages of cotton processing, applying with various quality monitoring tools were explained here for better control. Ultimately it is our social responsibility too to improve the quality of Indian cotton and yarn to face the competitive global market, by increasing productivity of spinning and downstream by-products in this complete process.

References

  1. www.itmf.org.
  2. Vetal Scan - Instruction Manual.
  3. Uster Tester 5 - Application Handbook.

Sunil Kumar Sharma
Manager-QAD
Loknayak Jayprakash Narayan Shetkari Sahakari Soot Girni Ltd
Shahada, Dist, Nandurbar
Maharashtra-425 409.
Mobile: 09552596742, 09921417107.
Email: sunil_ku67@yahoo.com.

published August , 2013
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