About Fineness:::::
Fineness:
By
fineness we can know how fine a fibre is. It is expressed in terms of average
linear density (weight per unit length) of a fibre.Fibre fineness is an important quality characteristic
which plays a prominent part in determining the spinning value of fibres. If
the same count of yarn is spun from two varieties of cotton, the yarn spun from
the variety having finer fibres will have a larger number of fibres in its
cross-section and hence it will be more even and strong than that spun from the
sample with coarser fibres.
Fineness denotes the size of the cross-section or
dimensions of the fibre. As the cross-sectional features of cotton fibres are
irregular, direct determination of the area of cross-section is difficult and
laborious. The Index of fineness which is more commonly used is the linear
density or weight per unit length of the fibre. The unit in which this quantity
is expressed varies in different parts of the world. The common unit used by
many countries for cotton is micrograms per inch (MIC) and various instruments
are developed for the measurement of fibre fineness.
Importance/Effect of fineness:
Fibre
fineness impacts on a wide range of other properties like………
On yarn count:
Finer fibres can produce finer yarn
On yarn strength: Finer fibres give
stronger yarn
On
yarn regularity/uniformity: Finer fibres give more regular/uniform yarn
On
weight of fabric: Finer fibre can give less weight of fabric
On
spinnability: The finer the fibre the easier to spin (because the greater
the total surface area available for inter-fibre contact hence less twist is
needed to provide the necessary cohesion)
On
fabric property: The coarser the fibre the more stiff/rigid the fabric.
System of fibre fineness Measurement:
Generally fibre
fineness is expressed in linear density method. The fineness of cotton fibre is
measured by the following two systems-
Ø
British or
English system:
In this system linear density is expressed in the
units of mgX10-5 per cm. It is denoted by H. The unit of weight is
mgX10-5 or gmX10-8 and the length unit is cm.
Ø American system:
In this system linear density is expressed in the
units of microgram per inch. It is denoted by A. The unit of weight is
microgram or gmX10-6 and the length unit is inch.
Relation between British and American system of fibre
fineness measurement:
Fibre linear density =
Fibre weight or Hair weight in (milligram x 10-5) per cm
= Fibre weight in (mg x 10-5)
/ cm
= Fibre weight in (gm x 10-8)
/ cm
= H
x 2.54x 10-8 x gm / inch (let)
American system:
Fibre linear density = Fibre weight in μg per inch
=
Fibre weight in (gram x 10-6) /inch (let) [1μg (microgram) = g x 10-6]
= A x 10-6 x gm /
inch
Now
we can write, H X 10-8 X 2.54 = A X 10-6
Or, A = H X 10-2 X 2.54
[For
example, H = 192, A= 192 x 2.54 x 10-2 = 4.9 μg/inch]
MIC value:
In American system, fibre
fineness is measured by micro gram per inch. So the weight in microgram of one
inch fibre is termed as micronaire value (MIC).
That
is, MIC value = microgram or (gmX10-6)
Inch
Rating of Cotton fibre with respect to fineness:
Micronaire
value (MIC) Fineness rating
< 3.0 Very fine
3.0-3.9
Fine
4.0-4.9
Average
5.0-5.9
Coarse
6.0 & above Very coarse
Measurement of
fibre fineness:
§
Air-flow method
(for bulk fibre like cotton, wool)
§
Gravimetric
method
§
Vibroscopic
method (for single fibre)
§
Microscopic
method (for single fibre)
§
Optical method
Air Flow
Principle:
A sample of a known weight is
compressed in a cylinder to a known volume & subjected to an air current at
a known pressure. The rate of air flow through the porous plug of fibre is measured,
the flow meter calibrated in terms of fineness- microns for wool, micrograms
per inch (MIC value) for cotton.
We know,
The mass of a cylinder is
given by-
mass= volume x density
= x-sectional area x length x density
then,
then,
=>mass/length
= x-sectional area x density
=> Fibre linear density = πd2 x
density [d=fibre diameter]
4
=> Fibre linear density ∞ d2 …………… (1)
If air blown through the above two cylinders at he
same pressure, the rate of air flow through (b)
would be less than through (a).The reason is that the
air flowing through (b) has more rod surface to flow past.
Hence,
Airflow ∞ fibre diameter ………………. (2)
Fibre linear density ∞Airflow
The rate of air flow will be less for fine fibres than
for coarse fibres.
Theory/principle: Air flow principle
Machine diagram
& description: Follow reference book
Working procedure:
Step-1:
5 gm sample is weighed to accuracy.
Step-2
The sample is then packed into the cylinder holder &
compressed to a constant volume by the perforated plunger.
Step-3
With the flow control valve shut the exhaust pump is
switched on.
Step-4
The air flow is then regulated by the control valve until
the manometer indicates a pressure difference 18 cm of water.
Step-5
The flow meter tube is graduated in MIC value. The top of
the floating indicator indicates the result of fineness.
KM MIRAZUR RAHMAN MURAD
BSC IN TE
DAFFODIL INTERNATIONAL UNIVERSITY
EMAIL:kazimurad_bd@yahoo.com
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