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Definition of HVI Parameters

High Volume Instrument is used to test fibre quality

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Spinning Consistency Index (SCI)

Spinning Consistency Index (SCI) is a calculated value based on a regression equation. This equation takes into account all HVI properties and calculates one value to be used on each sample tested. The SCI is an index derived with data from a large number of cotton samples having a wide range in properties that is related to test data from yarn spun from each sample.

The following are SCI equation for the most important HVI measurements:

SCI = – 414.67 + (2.9 x Strength) – (9.32 x Mic) + (49.17 x Length in inch) + (4.74 x Uniformity Index) + (0.65 x Rd) + (0.36 x +b)

Moisture Content (Mst)

Cotton is a hygroscopic fibre, it absorbs moisture from a high humid atmosphere and evaporates it when stored in dry atmosphere. For smooth spinning operation, the cotton fibre should have moisture in the range of 6 to 8 per cent. Moisture content below this limit causes high fluff generation and higher end breaks, while cotton having high moisture content is difficult to open and clean in Blow Room-carding, hence creating very high imperfection and yarn slubs which again cause end-downs at ring frame stage, lowering the production efficiency with increase in yarn imperfection and defects.

Fineness/Micronaire of fibre (Mic)

The second most important factor for spinning mills to decide the count pattern is fineness of cotton fibre that is commonly known as micronaire. Same as fibre length, it is also the deciding factor for cotton selection and spin plan of a spinning mill.

Maturity (Mat)

Maturity of cotton fibre is related with its growing process. A fully mature fibre means the fibre has achieved its complete growth process and has developed in all respects. Mature fibres achieve and exhibit better fibre properties in all respect as per their origin of variety characteristics.

In HVI testing, the maturity index is a relative value that is calculated by using a sophisticated algorithm including other HVI measurements, such as micronaire, strength and elongation. It indicates the degree of cell wall thickness within a cotton sample.

Upper Half Mean Length (UHML)

UHML is the mean length by the number of fibers in the largest half by weight of fibers in a cotton sample, usually measured from the fibrogram. Upper half mean length is normally equivalent to the staple length.

Uniformity

Settings of spinning drafting rollers depends on the length of fibres. To obtain optimized and correct spinning draft roller settings fibre uniformity is very important factor. Cotton fibre with low uniformity causes very high variation in process and creates difficulties for spinners to set the right setting for particular cotton mixing.

Short fibre (SF)

Fibre lengths below half inch, ie, below 12.5 mm are considered as short fibres. High short fibre % in cotton leads to many problems in spinning process such as high-end breaks, excessive yarn defects, very high fluff generation, lower machine efficiency, lower yarn realization and higher worker turnover.

Fibre strength (Str)

Fibre strength is an important factor for working of spinning process and yarn strength. Fibre strength is directly proportionate to yarn strength and working performance of spinning machines. However, it seems that strength of fibre is also related to others cotton properties like fibre length, micronaire and maturity. Fibre bundle strength is a deciding factor for spinning machine speeds. If fibre is not adequately stronger, then there has to be a compromise with production rate and force to reduce speed of machines. Similarly, ultimate yarn strength will be less as required.

Elongation (Elg)

Elongation is specified as a percentage of the starting length. The elastic elongation is of decisive importance since textile products without elasticity would hardly be useable. They must be able to deform and also return to shape. The fiber elongation should therefore be at least 1-2% and preferably slightly more.

The grater crease-resistance of wool compared with cotton arises for examples from the difference in their elongation cotton 6-10%, wool 25-45%.

Reflectance (Rd)

Reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at an interface. The reflectance spectrum or spectral reflectance curve is the plot of the reflectance as a function of wavelength.  Usually in Indiana cotton Rd values lie between 72 and 82. For better Control, it is advisable to maintain Rd value range below 5 in daily mixing plan.

Yellowness (+b)

 +b value significantly differs region-wise and variety-wise. In Indian cotton, +b lies in Range of 6.0 and 11.0. It is better to maintain the +b range between 2.5 in one variety of Cotton mixing.

Colour Grade (CGrd)

Variation in color grade is a major responsible factor for shade variation in cotton yarn and fabric.

Trash Content (TrCnt)

High trash content in mixing causes higher waste extraction, high end breaks rate at ring frame, higher yarn imperfection and Classimat faults. It also appears as black dots in greige fabric, usually known as kitti particles.

Co-efficient of Variation (CV%)

The coefficient of variation (CV) is a statistical measure of the dispersion of data points in a data series around the mean. The coefficient of variation represents the ratio of the standard deviation to the mean, and it is a useful statistic for comparing the degree of variation from one data series to another, even if the means are drastically different from one another. [9]

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