Fiber Fineness | Way to Measure Fiber Fineness.

     Fiber fineness is important quality characteristic which plays a prominent part in determining the spinning value of cottons.

If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibers will have a larger number of fibers 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 dimensions of the

fibre. As the cross-sectional features of cotton fibres are irregular, direct

determination of the area of cros-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 and the various air-flow instruments

developed for measuring fibre fineness are calibrated in this unit

The fibre fineness is expressed in wt. per unit length or length per weight.

According to “Textile Institute”, the fineness of cotton, silk and manufactured

fibres is usually expressed in terms of average linear density.

A single fibre has variable cross-section along its length and varies in cross-

section shape from fibre to fibre. To overcome their effect in calculating

fineness, same index of fineness is derived.

 Mass = Volume x Density

 = Cross-section area x length x density.

For a known length or unit length,

 Mass 8 Cross-sectional area.

For this suitable fineness index is taken by measuring the wt. of a known

length of fibre is called linear density and this is expressed in terms of wt. per

unit length.

Importance of fineness:

1. Lower irregularity of yarn:

With a greater number of fibres in the cross-section the basic irregularity is

reduced. The finer the fibre the higher the number and the lower the

irregularity. Fine fibre gives more regular yarn than the coarse fibre.

2. Uniformity of count:

A fine fibre can be spun to finer than coarse fibre measurement of fineness.

In other words the finer the fibre, the higher the yarn count will be.

3. Uniformity of strength:

 In a given cross-sectional area, if a given count is spun a fine and coarse

fibre, a more and a stronger yarn will result from the fine fibre because of

being large no. of finer fibre.

4. Uniform of fabric characteristics:

 As fine fibre gives more uniform yarn, so it gives good quality fabric with

uniform property.

5. Less twist:

The finer the fibre the greater the total surfaces area available for inter fibre

contact and consequently, less twist is needed to provide the necessary

cohesion.

6. Spinning performance:

 The fineness of the fibre affects several mechanical properties and therefore

influences the behaviour of the fibre during processing.

7. Good appearance:

The finer yarn produced by finer fibre is good appearance.

8. Less neps:

In the finer yarn, less neps present.

 Principle of fibre fineness measurement:

1. Gravimetric method.

2. Optical method.

3. Air flow method.

4. Vibroscope method.

Air Flow Method:

Principle:

 In this method, fibre fineness is measured by air flow. If large amount of air is

blown, the fibre will be coarse and if small amount of air is blown, the fibre will

be fine. — The method based on this principle.

 Procedure:

. A sample of known weight is taken and compressed in a cylinder to a

known volume and subjected to an air current at a known pressure.

. The rate of air flow through the porous plug of fibre is measured.

. Suppose, two cylinders of similar dimensions were filled with:

a) A few cylinder rods of large diameter.

b) Many rods of small diameter.

. If air were blown through the two cylinders at the same pressure, it

would be finding that the rate of air flow through (b) was less than

through (a).

. The reason is that the air flowing through (b) has more rod surface to

flow past.

. The difference in the rate of air flow is a measure of the difference in the

surface area of the large diameter and small diameter rods. This leads us

to consider the specific surface.

For fibres of circular cross-section specific surface is inversely proportional to

the fibre diameter. Therefore by measuring the rate of air flow under controlled

condition, the specific surface S, can be determined and consequently the fibre

diameter. Then by using a value for the density of the material, the fibre wt. per

unit length/ fineness could be derived.

The WIRA cotton fineness meter:

This instrument is a modified version of the Wool fineness meter and is

manufactured by Shirley Developments Ltd. The diagram of the general

arrangement of the apparatus is shown in fig.

Wira fineness tester

 Construction:

. In this apparatus, A is a cylindrical holder with a perforated false bottom.

. M is a manometer which indicates the pressure difference in cm;

. V is a control valve which controls air flow through cotton plug.

. F is a flow meter indicating air flow in litre per min.

. In this chamber, a sample of fixed wt (5 gm) is compressed to a fixed

volume by piston P.

Working principle:

. 6 gm sample weighed to an accuracy of 0.05 gm is fluffed up to

eliminated any tangled parts.

.

. The sample is then packed into the cylindrical holder and compressed to

a constant volume by the perforated plunger.

. With the flow control valve shut, the exhaust pump is switched on.

. The air flow is then regulated by the control valve until the manometer

indicates that a pressure difference of 18 cm of water across the ends of

the plug of cotton.

. The flow meter to be is graduated in Micronaire and the reading at the

top of the indicator float is recorded.

. A repeat observation is made after removing the sample and repacking it

into the holder.

. For greater accuracy, a third observation is operated.

. Then the mean value is taken. Therefore direct reading of cotton fineness

is got.

 Gravimetric method:

1. Cotton:

 For carrying out this experiment, at first the comb sorter diagram is

made. Then 5 tufts of fibre are taken at intervals down the diagram and

from each tuft a section is sliced out by means of two razor blades set in a

holder at a spacing of 1 cm. then using a large lens and good lighting, 100

fibres are counted from each of the tufts. Each group of 100 fibres is

collected and weighed on a sensitive micro balance. The mean fibre weight

per centimeter is calculated. After determining the maturity of cotton, this

may be corrected to give the standard fibre weight per centimeter, Hs.

2. Bast fibres:

 At first five tufts from the staple diagram are taken. Then they are

combed straight and a known length is from the middle of each tuft and

weighed to an accuracy of 1 in 100 and the number of fibres counted. The

mean fibre wt. per unit length is then calculated.

3. Man made staple fibre:

 The length of individual fibre is measure by a scale on a velvet pad. Two

pairs of tweezers are used to remove the crimp. Each fibre is weighed on a

micro bale and the results used to calculate the fibre weight per unit length.

 4. Wool:

 After completing a fibre length test the fibres are collected and thoroughly

cleared of oil, allowed to condition and then weighed on a micro balance. The

total fibre length is calculated and knowing the number of fibres the fibre wt.

per unit can be derived.

Micronaire value:

The term micronaire value is now a widely used expression and where as

originally the figure meant fibre wt. in micrograms per inch.

The micronaire value regarded as indication of maturity and fineness. The

units are commonly ignored.

The higher micronaire value of the fibre, the fibre regarded coarser.

Micronaire value plays a vital role during mixing of different grades of fibres for

Yarn preparation. The higher micronaire value difference of fibre, higher yarn

irregularity.

The fibres are classified in different grades on the basis of micronaire value.

 Micronaire value Classification of fibre

 2.9 or below very fine

3.0 to 3.9 fine

4.0 to 4.9 average

5.0 to 5.9 coarse

6.0 to above very coarse

 System / Unit of measuring fineness:

The fineness of cotton fibre is measured by following two systems:

1. British System:

 In this system, the linear density is either the fibre wt, per cm or the hair

wt. per cm, H.

 Here the unit of wt.= milligram x 10-5

 And the unit of length = cm.

 The unit of fineness = H x 10-5 mg/cm.

Example: The fibre wt. per cm for an American upland cotton may be 142

i.e. 192mg x 10-5/cm

2. American System:

 In this system, the linear density is expressed in microgram per inch.

 Here, the unit of wt. = microgram (gm x 10-6)

 The unit of length = inch.

Example: the linear density of American Upland would be 4.9 i.e. 4.9

microgram per inch.

In this system, fineness is expressed in micronaire.

Relation between two fineness measuring systems:

 American linear density = fibre wt in gm x 10-6 / inch

 = A x 10-6 gm / inch

 British linear density = fibre wt. in mg x 10-5 / cm

 = fibre wt. in gm x 10-3 x 10-5 / cm

 = H x 10-8 gm/cm

 = H x 10-8 x 2.54 gm / inch

 We have, A x 10-6 = H x 10-8 x 2.54

 A = H x 10-2 x 2.54

 This is the derived relationship between them.

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Writer and editor SABBIR

I am Nur Mohammed From comilla,Bangladesh.I studied in Textile Engineering and very much fond of blogging; so try to write about Textile