Tuesday, August 6, 2019

EVALUATION OF COTTON FIBRE FINENESS

EVALUATION OF COTTON FIBRE FINENESS:

                                                                         
The fineness of cotton fibre is a very important characteristic of fibre. It directly affects the yarn quality to be spun from a particular cotton variety. If two yarns of same count are spun by using two cotton varieties having different fibre fineness, the remarkable difference results among the strength, evenness, and hairiness of those yarns there.
We can understand the reason behind this difference betbeen yarn qualities to be produced.
Suppose that a yarn of 10 s count is spun with coarse fibres,  the number of fibres in cross section area of yarn gets lower than required number of fibres. Thus the low yarn strength results in the yarn.  If the number of fibres of cross section area of the yarn gets increased more than required,  these fine fibres results in the form of improved yarn strength.
The coarse fibres also results in the form of unevenness. How does it happens? The cotton fibres differ in fineness  one to another within the variety. Here more number of fibres of finer fibres always have grater chances to result in the form of improved evenness than the yarn spun with lower number of fibres of coarse fibres.


Fineness of fibre tell us about diameter of fibre or dimensions of cross section of fibre. Since cotton fibres does not have rregular diameter or cross-sectional dimension, so that it gets almost impossible to to determine the cross-sectional dimensions or diameter accurately. The linear density of fibre is measured. “Weight per unit length of fibre or linear density of fibre is called fibre fineness”. The unit of fibre fineness micrograms / inch is commonly used.



A mironaire instrument working based on air flow is commonly used to examine the fineness of cotton fibre. “This instrument works on resistance offered to the flow of air through a plug of fibres. It mean how much air gets passed through the plug of cotton fibres to be tested. The resistance to air flow depends upon the specific surface area of fibres”. The maturiy  ratio of fibres also affects the specific surface area. If matur   ity ratio of cotton fibres sample varies highly thereadings of  micronare meter are a treated with high degree of cautions. In the micronaire meter, an amount of 3.24 grams of cotton from the sample is taken. Now this weighed amount of cotton is well opened. This well opened cotton is compressed into a cylindrical container of fixed dimensions. The compressed air is passed through sample at a definite pressure and the volume-rate of flow of air is measured by a rotometer type air flowmeter. The sample for micronaire test should be well opened cleaned, and thoroughly mixed ( by hand fluffing and opening method).  The low meter reading indicates that fibre is fine. The gradding is done as below:

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