A CIRCOT study[5] revealed that within varieties, the relationship between AFIS fineness and micronaire value gave substantially high correlation with r values ranging from 0.92-0.98.
However, pooled data for more than 100 samples, which comprised different varieties as well, showed a relatively low "r" value. But, the correlation still remained significant at 1% level. This of course affects the predictability of micronaire from AFIS fineness or vice versa. This is understandable, as AFIS fineness would depend only on wall-thickness, while micronaire value would depend both on perimeter and wall-thickness. So long as the former remains the same, (true for a given variety) a higher correlation can be expected between micronaire and AFIS fineness.
Immature Fibre Content (IFC) is the percentage of fibres possessing less than 0.25 degree of thickening. This value is mainly used by EOUs in deciding the mixing of cottons in the production of yarns meant for knitting. According to one mill B, two cotton varieties differing more than 10% in IFC should not be mixed. This is done to avoid dyeing defects in knitted fabrics. IFC is also used to check the comber performance and it is expected that comber should preferably remove undeveloped fibres and bring about reduction in IFC by at least 25%.
Maturity Ratio (MR) is the ratio of number of fibres with degree of thickening of 0.5 (or more) to that of with degree of thickening of 0.25 (or less). Like IFC, this parameter is also used by the EOUs for choosing cottons for the production of hosiery yarns. Mills B and C insist for a minimum MR of 0.8, while mill E will not buy cotton if the MR is less than 0.86. This is mainly done to avoid stripping effect known as barre in finished fabrics.
Neps per gram indicates the number of neps present in one gram of cotton. This is the parameter most extensively used by all the EOUs to study the performance of blow room, card and comber. One mill E uses this parameter for cotton selection as well. As per the norms adopted by these mills, for roller-ginned cotton, the neps per gram should be less than 180 and for saw-ginned cotton it should not be beyond 250.
Higher neps are allowed for saw-ginned cottons, as the treatment in saw gin is harsh and produces more neps than roller gin. All the EOUs agree to the point that blow room neps per gram in lap should not exceed more than double that of raw cotton and card and comber should work at least with a minimum nep removal efficiency of 75% and 55% respectively.
Seed Coat Neps (SCN) are the seed coats attached with fibres that remain even after opening. Mill E puts a condition in their contract that the procurement will be accepted only if the SCN is less than 25 per gram in the cotton. Normal neps are easily removable during carding unlike SCN, which is difficult to remove while carding as they break into small fragments. These SCNs that remain after carding and combing create yarn faults, finally resulting in defective fabric.
Conclusion
This survey has revealed that UQL, 5.0% L, SFC (n), mTex, IFC, MR, Neps/g and SCN/g are parameters that are put in use daily by EOUs in their routine operations. It does not mean that the other parameters are less useful for practical applications. It is up to the researchers and machinery manufacturers to establish the effectiveness of other parameters for mechanical processing.
AFIS, once considered to be exclusive process control equipment, has been effectively used by some EOUs in cotton selection as well. Even with all these controls, mills sometime land in quality complaints like neppiness and barriness in fabrics. There is a need to establish tolerances for mixing of different cottons for AFIS parameters as has been currently done for measures of HVI.
Controlling yarn neps seems to be still a problem even after the use of sophisticated testing instruments. Research efforts are needed to establish concrete relationships between fibre-yarn-fabric neps and the outcome of such studies are expected to improve the competitiveness of our export-oriented units further.
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