Function & performance of AFI System in EOUs
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Function & performance of AFI System in EOUs
 
Article Introduction
Afis, once considered to be exclusive process control equipment, has been effectively used by some eous in cotton selection as well. Here are some of the interesting findings.

Article Description
Indias textile exports stand at US$ 12.6 billion during 2003- 04 with the contribution of cotton textiles alone to the tune of US$ 4.3 billion. Within cotton textiles, the cotton yarn contributes to US$ 1.7 billion. These figures show that Indian mills make world-class yarns. It was anticipated that the further growth in yarn export would be seen after the quotas were removed since January 1, 2005.

Making a quality yarn as per the importing countrys specification and free from defects is a major concern to export oriented units (EOU). To meet the stern specifications of an importer, one has to carefully select the raw material, maintain the process in control and carry out final inspection such that the yarn delivered satisfies the customer. For such an attempt, EOUs not only need the state-of-the-art spinning machines but also the sophisticated testing equipment, which are capable of carrying out preferably online testing, not with-standing the advantages in offline estimation.

The two instruments, which play major roles in cotton selection and process control, are the High Volume Instrument (HVI) and Advanced Fibre Information System (AFIS). HVI has been used by the EOUs for quite a long time. However, AFIS started entering Indian market in the early 90s. Although AFIS gives a lot of information about fibre quality in a short time, the parameters exploited by the EOUs for maintaining yarn quality are limited.

On the other hand, EOUs and other mills use majority of the attributes measured by using the HVI. AFIS parameters give information about length, fineness, maturity, trash and neps. As some of the parameters supplied by the two equipment, vis, HVI and AFIS are overlapping, one is interested to understand, which is more useful, where and how this knowledge about the fibre parameters is practically helpful.

Despite the fact that many earlier works [1-9] have discussed the relationship between AFIS and HVI parameters, and AFIS parameters and yarn property relationships, not much work is reported about the current status with regard to utilisation of AFIS parameters in maintaining yarn quality. Hence, a survey was conduced to understand the practical utility of AFIS parameters and this paper reports the results of the survey.

Survey locality
The survey was conducted in and around Kolhapur in Maharashtra, where the conglomeration of EOUs can be seen. All these EOUs possess the latest test equipment including AFIS. The data presented here are based on the information gathered during the personal visit of the authors. In order to maintain confidentiality, the names of the EOUs are not given. The number of EOUs visited was 6 and the English alphabets A-E are consistently used to refer to these EOUs.

The spindelage of EOUs varies from 13,000 to 50,000. Even the one EOU, which is having lowest spindles, also is under expansion and hence one can say that minimum size of an EOU is around 25,000 spindles. The turnover goes upto a maximum of 120 crores and the average cost of the yarn sold at the export market works out to around 4-5 US$ per kg of yarn. This is almost double that of the average price of yarn in the local market.

The yarn realisation achieved by these units is around 70% This low yarn realisation is due to the reason that all the EOUs are producing combed yarns, in which case the comber noil removed is on an average varies from 15 to 20%. These EOUs consume around 2.19 lakh bales of cotton accounting for about 1.4% of Indias cotton production. Yarn production of these EOUs mainly is from ring spinning and two mills also have compact spinning machines, which are nothing but modified ring spinning systems. None of these Units has open-end spinning machines.

It can be seen that some mills use a single variety in their mixings, which is expected to give a uniform product than one with multiple variety in mixings. However, majority of EOUs mix different varieties of cotton in appropriate proportions. Even mixing of foreign and Indian cotton is also observed. One EOU uses a mix of 80% Giza and 20% MCU 5 for the production of 60s combed yarn.

Advanced Fibre Information Systems
All the contacted EOUs possessed HVI and AFIS. One unit has the state-of-the- art Uster instrument like HVI spectrum for testing cotton. The main difference between AFIS and HVI is that while AFIS does single fibre testing, HVI carries out testing on bundle of fibres. The one important information that AFIS does not provide is fibre strength. Hence, one cannot have only AFIS in an EOU without having HVI for raw material selection and process control. Generally, AFIS is employed for process control and HVI for selection of raw material.

AFIS works on the principle of first individualizing the fibres by mechanical action then separating into three components namely fibre, trash and dust by passing through perforated pinned roller and finally electro-optical sensing and micro- processing of signals generated through different components.

The AFIS report The AFIS report contains 21 columns of fibre parameters. This can be classified under the headings, vis, length, trash, maturity, fineness and neps. The length and trash related measurements alone come around two- third of parameters measured. 9 cells containing fibre length parameters falls under the heading length and under trash heading there are 5 cells, adding up makes to 14 cells of parameters under these two headings alone.

Testing atmosphere and sampling
All the EOUs have the latest air-conditioning systems in their laboratory for maintaining standard relative humidity and temperature. Conditioning of samples is essential as atmosphere affects the textile materials; it becomes necessary to bring the samples to moisture equilibrium status before testing.

As far as conditioning is concerned, each EOU follows its own procedure as far as duration of conditioning concerned. There is no uniform practice followed in this case. Some EOUs keep the sample for a day in conditioning room. Although AFIS does not measure fibre strength and it is known that this is the parameter that is highly sensitive to moisture, even then it is advisable to condition until moisture equilibrium is reached. A uniform conditioning practice is required among the EOUs and then only one can compare ones results with either norms or with other suppliers.

EOUs test 20% of their bales for AFIS fibre parameters. The prescribed standard number of readings is 5 per sample. Out of 6 EOUs only two follow the standard replications and the remaining mills consider 4 readings per sample. The five readings cover 15.000 fibres in total, whereas 4 readings would cover only 12,000 fibres, and hence the result is bound to be less accurate.

Most used fibre measurements
It can be seen that the mills regularly use only 8 parameters. Among these 8 parameters, neps/gram is used by all the EOUs and the least used parameters are the 5.0% length and fibre millitex.

Upper Quartile Length (UQL) by weight is the length of the 25% of longest fibres. It is used for comparing the 2.5% span length obtained from HVI. Four mills use this parameter and as per their experience, HVI 2.5% span length plus 1 mm will give UQL of AFIS. This is used as a check for HVI and if this relation does not come then the instrument is checked for calibration.

The 5.0% length by number is the length of the longest 5% of fibres. Out of the 6 EOUs under survey, one uses it for draw frame setting. The 5.0% length of the combed sliver is measured and used for setting purposes. In the case of breaker draw frame, 5% length is kept for front zone and for back zone it is 5% length + 4 mm. Finisher draw frame front zone kept at 5% length + 2 mm and back zone is kept at 5% length + 6 mm. The remaining EOUs use 2.5% span length + allowance for their draw frame setting.

For short fibre content, AFIS gives two values, one based on weight and the other on number of fibres. All the surveyed EOUs use only Short Fibre Content by number [SFC (n)]. This is defined as percentage of short fibres less than 0.5 inches. SFC (n) is mainly used for checking comber performance in deciding the amount of noil to be removed. One EOU cautioned that it should not be used for carding performance study, as the card sliver that comes as output contains hooks, and the SFC (n) measured would be misleading as a result of this.

AFIS gives fibre fineness in millitex. The mill E uses it for crosschecking the micronaire value of cotton obtained from HVI. Fineness measured by AFIS is equivalent to gravimetric fineness and can be different from millitex value derived from micronaire.
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Posted : 9/8/2005

 
 
Function & performance of AFI System in EOUs