Showing posts with label Fineness. Show all posts
Showing posts with label Fineness. Show all posts
10 November 2012
What is Micronaire Value? | Relationships Between Micronaire, Fineness, and Maturity
Micronaire is one of the two most important fiber characteristics
for international cotton classers and spinners. Micronaire is an
indicator of air permeability. It is regarded as an indication of both
fineness (linear density) and maturity (degree of cell-wall
development). For a given type of cotton, a relatively low micronaire
has been used as a predictor of problems in processing, but a low
micronaire may also indicate fine fibers with adequate maturity.
Similarly, growers may be discounted for high micronaire when, in fact,
the fibers have adequate fineness and good maturity, because high
micronaire fibers are normally coarse, which is undesirable from the
point of view of spinning and yarn evenness.
Fineness is generally expressed as gravimetric fineness or linear density (wall area times a constant), and maturity is generally expressed as maturity ratio (wall area divided by perimeter squared). One of the first practical tools to measure fineness and maturity was the determination of linear density and maturity ratio on the Shirley Developments Limited Fineness and Maturity Tester (FMT).
Although linear density, maturity ratio, and micronaire are useful to spinners, all three properties can be viewed for any given cotton in terms of wall thickness and perimeter. Wall area is a function of wall thickness and perimeter . Wall thickness and perimeter are fundamental cross-sectional characteristics of the fiber with respect to wall area, because the function cannot be decomposed further into other geometric measures. If one examines the fiber crosssection, the wall thickness is not constant but varies around the fiber, so that points must be sampled to get an averaged value. As a consequence, an averaged wall thickness and perimeter are fundamental with respect to an averaged wall area. Exploring the relationships on a fundamental level can be beneficial by demonstrating how a unique wall thickness and perimeter value together give an equivalent micronaire- fineness-maturity combination.
Cottons with a much greater genetic diversity are being developed, and a greater range of both fiber perimeter and wall thickness, and their combinations, is probable. Consequently, the relationships between micronaire, fineness, and maturity are being modified . This is because the original set of U.S. cottons that were used to calibrate the micronaire instrument had perimeters with a smaller range compared to current cultivars. The original relationships apply best to those cottons having perimeters similar to the calibration samples. For other cottons, these relationships do not apply as well, which results in modified expressions.
Fineness is generally expressed as gravimetric fineness or linear density (wall area times a constant), and maturity is generally expressed as maturity ratio (wall area divided by perimeter squared). One of the first practical tools to measure fineness and maturity was the determination of linear density and maturity ratio on the Shirley Developments Limited Fineness and Maturity Tester (FMT).
Although linear density, maturity ratio, and micronaire are useful to spinners, all three properties can be viewed for any given cotton in terms of wall thickness and perimeter. Wall area is a function of wall thickness and perimeter . Wall thickness and perimeter are fundamental cross-sectional characteristics of the fiber with respect to wall area, because the function cannot be decomposed further into other geometric measures. If one examines the fiber crosssection, the wall thickness is not constant but varies around the fiber, so that points must be sampled to get an averaged value. As a consequence, an averaged wall thickness and perimeter are fundamental with respect to an averaged wall area. Exploring the relationships on a fundamental level can be beneficial by demonstrating how a unique wall thickness and perimeter value together give an equivalent micronaire- fineness-maturity combination.
Cottons with a much greater genetic diversity are being developed, and a greater range of both fiber perimeter and wall thickness, and their combinations, is probable. Consequently, the relationships between micronaire, fineness, and maturity are being modified . This is because the original set of U.S. cottons that were used to calibrate the micronaire instrument had perimeters with a smaller range compared to current cultivars. The original relationships apply best to those cottons having perimeters similar to the calibration samples. For other cottons, these relationships do not apply as well, which results in modified expressions.
Even
though micronaire is of great practical value for trade and industry, a
literature review indicated no theoretical or experimental studies have
been reported that model the three fiber characteristics in terms of
the fundamental measures of thickness and perimeter. The specific
objectives of this research were to use fineness and maturity components
– wall thickness and perimeter to develop models for fineness,
maturity, and micronaire; to simulate the interaction of fineness and
maturity and the resultant micronaire; to quantify the relative
sensitivity of the models to changes in thickness and perimeter; and to
demonstrate variability in the coefficients of determination between
micronaire and the other variables.
http://textilelearner.blogspot.com/
http://textilelearner.blogspot.com/
18 October 2012
Fiber Fineness Measurement by Projection Microscope
The projection microscope is the
standard method for measuring wool fibre diameter, and all other methods
have to be checked for accuracy against it. The method is also
applicable to any other fibres with a circular cross-section. The method
involves preparing a microscope slide of short lengths of fibre which
is then viewed using a microscope that projects an image of the fibres
onto a horizontal screen for ease of measurement. The apparatus is shown
diagrammatically in Fig. Techniques are followed that avoid bias and
ensure a truly random sample.
Method of Test
A suitable random and representative sample is conditioned for 24 h in a standard testing atmosphere. Using a modified Hardy microtome the fibres are cut to a suitable length (0.4mm for fibres below 27 (im) and a slide is prepared by carefully mixing the fibres into the mountant. The use of short fibres gives a length-biased sample so that proportionally more of the longer fibres will have their diameter measured. The mounting agent should be non-swelling and have a suitable refractive index (for example liquid paraffin). The mixture of fibres and mountant is spread thinly on the slide and covered with a cover glass, carefully avoiding air bubbles and finger prints.
The slide is placed on
the stage, coverglass down (microscope inverted) and fibres are selected
for measurement in the following way. The slide is traversed in a
zigzag fashion, measuring every fibre that complies with the following
requirements: 1 has more than half its length visible in the 7.5cm
circle which is drawn in the centre of the field of view; 2 is not in
contact with any other fibre at the point of measurement. The traverse
of the slide is continued until the required number of fibres
has been measured. The magnification of the microscope is adjusted to
be 50Ox so that on the scale used to measure the fibres each millimetre
represents 2 um.
For accurate tests three slides should be measured from randomly selected areas of the material and not less than 150 fibres per slide should be measured. The coefficient of variation of diameter for unblended wool lies between 20% and 28%. From this value the number of tests to give certain confidence limits has been calculated .
http://textilelearner.blogspot.com/
A suitable random and representative sample is conditioned for 24 h in a standard testing atmosphere. Using a modified Hardy microtome the fibres are cut to a suitable length (0.4mm for fibres below 27 (im) and a slide is prepared by carefully mixing the fibres into the mountant. The use of short fibres gives a length-biased sample so that proportionally more of the longer fibres will have their diameter measured. The mounting agent should be non-swelling and have a suitable refractive index (for example liquid paraffin). The mixture of fibres and mountant is spread thinly on the slide and covered with a cover glass, carefully avoiding air bubbles and finger prints.
 |
| The projection microscope |
For accurate tests three slides should be measured from randomly selected areas of the material and not less than 150 fibres per slide should be measured. The coefficient of variation of diameter for unblended wool lies between 20% and 28%. From this value the number of tests to give certain confidence limits has been calculated .
http://textilelearner.blogspot.com/
6 June 2012
Fiber Fineness is Measured by the Airflow Method
Principle:
In this method, fiber fineness is measured by air flow. If large amount of air is blown, the fiber will be coarse and if small amount of air is blown, the fiber will be fine. The method based on this principle.
This is an indirect method of measuring fibre fineness which is based on the fact that the airflow at a given pressure difference through a uniformly distributed mass of fibres is determined by the total surface area of the fibres .
In this method, fiber fineness is measured by air flow. If large amount of air is blown, the fiber will be coarse and if small amount of air is blown, the fiber will be fine. The method based on this principle.
This is an indirect method of measuring fibre fineness which is based on the fact that the airflow at a given pressure difference through a uniformly distributed mass of fibres is determined by the total surface area of the fibres .
 | |
| (a) |
 |
| (b) |
Fig: Fiber Fineness is Measured by the Airflow Method
The
surface area of a fibre (length X circumference) is proportional to its
diameter but for a given weight of sample the number of fibres
increases with the fibre fineness so that the specific surface area
(area per unit weight) is inversely proportional to fibre diameter; Fig.
shows this diagrammatically. Because the airflow varies with pressure
difference it is the ratio of airflow to differential pressure that is
determined by the fibre diameter. Therefore the method can be used to
measure either the airflow at constant pressure or the pressure drop at
constant airflow.
The measurement of airflow at constant pressure is the more usual form of apparatus with wool. For fibres of approximately circular cross-section and constant overall density such as unmedullated wool, the estimate of fineness corresponds to the average fibre diameter as determined by the projection microscope with a good degree of accuracy.
http://textilelearner.blogspot.com/
The measurement of airflow at constant pressure is the more usual form of apparatus with wool. For fibres of approximately circular cross-section and constant overall density such as unmedullated wool, the estimate of fineness corresponds to the average fibre diameter as determined by the projection microscope with a good degree of accuracy.
http://textilelearner.blogspot.com/
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