Director dept. of textiles Dr.J.S Muralidhara – principal of white pencil college of fashion Bangalore.
Cotton cost forms the largest single component (60%-70%) of the total cost of yarn. Even a small saving in the cotton cost, therefore, means a considerable increase in the gross profits of the mill in absolute terms. for example , a medium sized mill spinning 30s average count can increase its annual gross profits by Rs 1.5 lakh if it can save just 1% on the cotton cost.
A mill can control the total cost of cotton cy selecting cottons of the right quality by buying them at the most appropriate time. Though cotton prices fluctuate substantially over the year, and efficient formulation of mixings for the various counts of yarns that are being spun, is of utmost importance in industrial practice, cotton quality continuous to be evaluated mostly on the basis of hand stapling and visual grading; decisions on when to purchase are taken on the basis of intuitive judgment. The type and proportions of the cotton that are to be used in making a mixing are decided upon by tacking in to account the cotton prices as well as the previous experience of the mill with the working of different cotton.
There is, of course, an increasing use of instrument to supplement the evaluation of cotton and in formulating mixings. While these methods certainly help in controlling mixing cost , they cannot assure that it is reduced to the minimum without any sacrifice in the quality. Any improvement in the methods of evaluation- purchase of cottons and in the formulation of the mixings-is therefore desirable. The evolution of cotton on the basis of instrument testing of fibre properties and the use of the test results in formulating mixings of minimum cost and desired quality are described in this article.
INSTRUMENTAL EVALUATION OF COTTON
It is generally true that the prices of cotton are governed by its quality when one considers different varieties of cotton. For example, the price of digvijay is invariable more than that of kalian 320F, while Shankar-4 sells at a higher price than digvijay.
But when several lots from a given variety of cotton, such as those sold at different stations, grown in different areas of cultivation are considered for purchase, the price is no more a reliable index of the value or quality of the cotton. Such a situation arises.
- firstly, because the existing system of grading and pricing of cotton id based on human judgment.
- Secondly, in the system of grading, fiber length has traditionally been given more importance than the other properties such as fineness and strength.
- Thirdly, the pricing of cotton in relation to its trash content is approximate. Any improvement in the precision of assessing the different aspects of cotton quality can result in consign of assessing the different aspects of cotton quality can result in considerable economic gains to a mill and instrument testing of cotton for fiber properties is, therefore, very desirable.
The important properties of the fiber are length, strength, fineness and maturity. Several other properties are measurable. But they are either poorly correlated with any yarn property or are closed associated with length, strength or fineness. Hence, they need not be measured for assessing cotton quality in mill routine some useful information regarding the testing of cotton properties is given below. The number of tests given under sample size is the minimum required for obtaining reliable results. The values of “real different” are to be used as illustrated in the following example.
Results to tests of mean length of two cottons based on two patterns for each are as follows: cotton A-22.3mm; cotton B-23.3mm. then, one concludes that cotton B has the greater means length.
To answer this question, the difference 23.1=0.8 has to be compared with the table value of 4%. Since the difference is less than 4% of 22.7mm (average of 23% and), the conclusion is that the mean lengths of cottons A &B are not different.
The following are some of the important point that should be remembered while interpreting the results on the cotton properties:
- Effective length
- Short fiber content
- Length tests with different instruments
- Fineness and maturity
- Bundle strength
- Fiber characteristics of some cottons
MODEL VALUES OF FIBRE CHARACTERISITICS OF SOME SELECTED VARIETIES OF COTTON
LIMITATION OF INSTRUMENTAL EVALUATION OF COTTON:
Although the above-mentioned fiber characteristics provide much useful information regarding the processing behavior and yarn quality of cotton, there are instances in which a cotton gives troubles during processing that would not have been anticipated on the basis of test result, or gives a yarn much weaker than expected. One has to depend on past experience in deciding upon the use of such exceptional cotton.