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Department Of Textile Engineering
Assignment on
Cotton Fibre Length Measurement By Using
Fibrograph.
Course Code: Tex-2031
Course Title: Textile Testing & Quality Control-1
Submitted To:
Mr. S.M. Masum Alam
Lecturer, Southeast University.
Submitted By:
Name : Sagor Saha
Id : 2015100400006
Batch : 29th
Section : A
Submission Date: 19.04.2017
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Introduction:
Fiber length is one of the most important quality of cotton contributing to higher
yarn strength, spin ability and reduced end breakages in spinning. Short fibre
content has pronounced effect on waste, yarn irregularity, appearance and end
breakages Conventional and HVI instruments used for testing fibre length
parameters of cottons are briefly reviewed here. The determination of fibre length
is of a greater importance both for the trader and technician. Several instruments
are available for determining the fibre length characteristics of cotton. However,
each instrument is based on a different principle. The fibrograph is an optical
instrument employing photovoltaic cells for scanning samples of parallel fibers and
tracing a type of length- frequency curve. The theory is developed for a sample of
parallel fibers in which the fibers are positioned at random. Due to the method of
holding the sample in the comb, the instrument does not include in its
measurement those fibers of approximately ¼ inch and shorter. Therefore, the use
of the instrument for determining the length of machine waste results in entirely
erroneous and misleading measurements, inasmuch as a large proportion of the
fibers in waste is made up of very short fibers.
Objects:
1.To know about different length of fibres.
2. To know about the Fibrograph m/c and its different parts.
3. To find out the fibre length by using Fibrograph.
Principle:
It is an optical instrument with light sensitive cells for scanning cotton fibres and
simultaneously drawing a length- frequency curve. The height of the vertical axis
of the fibro gram is equal to the total fibre length if it is assumed that the fibres
have the same linear density, it can be state that the height of the fibrograph is
proportional to the weight of the fibre.
The horizontal axis of the fibrograph:
The horizontal axis of the fibrograph is expressed in percentages of amount of
fibres. A span length is that length which a certain percentage of fibres from the
original fibre population would spam when caught at random along their length.
i.e, span length is a distance from a line where the fibres are caught randomly to
a point where only a certain percentage of fibre extend. Thus, 2.5%span length is
that length which 1/40th of the fibres would span when randomly caught along
their lengths. The figure represents a state of fibres caught by a clamp all loose
fibres to the right of the clamp are removed. The clamp moves from this position
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to the right till only 225 fibres, i.e, 2.5% of 9000. The distance D is the 2.5% span
length. In this way 50%SL, and 67.7%s.l can all be determined. This method of
measuring fibre length is more realistic than can sorter technique, since it is a
measure derived from the fibre oriented in a similar fashion to fibre in process.
i.e, randomly arranged rather than the fibre ends co-terminus along base line.
Difference between Fibre length and Span length:
Span length is the fibre extension distance and it is not the fibre length. The staple
diagram is universally accepted as the ultimate in expression of the end- to- end
length of fibre. The sorter test is the laboratory method of expressing fibre length
in staple diagram configuration. Fibre arrangements of the staple diagram relate
to end-to-end fibre length but not so easy to yarn spinning. Fibre arrangements of
the fibrogram relate to spinning but not so easy to end-to-end fibre length. Actual
fibre extension in yarn manufacture cannot be easily determined from the staple
diagram.
Similarly span length cannot be used to determine the end- to-end fibre length.
The staple diagram represents fibres as observed in the laboratory the fibrogram
represents the same fibre as they would appear in spinning.
Fibrograph measurements are based on the assumptions that a fibre is caught on
the comb in proportion to its length as compared to total length of all fibres in the
sample and that the point of catch for a fibre is at random along its length.
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Apparatus:
B- Photocell, L-Light Source,
C- Fibre length, p- Pen,
D-Card, H- Card Holder,
E- Comb, G- Galvanometer,
S1- Scanning slit, S2- Glass Screen,
W1- LH Hand Wheel, W2- RH Hand Wheel.
Preparation of test samples:
Select small tufts of fibres at random from the lab sample. The weight of the test
sample is around 400 milligram. The small tufts are placed one above the other
and entire bundle is pulled apart into two parts with thumb and fore finger.
The two parts of the sample are superimposed over each other with the broken
edges of two parts in one line. Using one comb, comb all the broken edges until
the fibre sample is uniformly distributed over the full length of the comb. Then
holding this comb with its teeth pointing upwards, comb the fibre gently with
other comb, increasing the depth of penetration of the teeth for each stroke.
The hold both the combs with their teeth pointing upwards, place one comb in a
position such that its teeth almost touch the base or the teeth of the other comb.
Deposit the fibre on the teeth of the bottom comb by pushing straight down the
top Comb. Repeat this combing and transferring three times. At the last transfer,
the fibres will be distributed evenly over the length of the combs, with an equal
amount being on each comb.
Combing Strokes for cotton
20 for initial combing,
10 after first transfer and 10 after second transfer.
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Description and working:
The combs are placed in the instrument as shown in fig. so that the fibres can be
scanned. A narrow slit is provided in which the photo electric cell A is placed. Over
the slit, the combed fibres are placed. Above the fibres, a fluorescent tubular light
is provided. Another light from an incandescent lamp through a glass screen falls
onto a second photo cell B. The intensity of this light can be varied by rotating the
right hand-hand wheel. If the current passing through the photo cell A is matched
by the current passing through the photo cell B then the system is in balance and
the galvanometer will show null deflection. The fibre fringe is so positioned that
the centre line of the scanning slit coincides with a line ¼ inch away from the
comb teeth. In this condition, the right hand- hand wheel is turned to give an
optical balance.
The fringes are now traversed upwards by the left hand – hand wheel which
imparts corresponding movement to a pen. The vertical displacement of the pen
thus registers the fibre length.
As the fibres are going up, the obstruction to the light by the fibres becomes less
and the amounts of light through the photo cell a increases. The extent of increase
is measured by rotating the right hand –hand wheel, which not only adjust the
current through the cell B but also traverses the card horizontally. The horizontal
displacement of the pen relative to the card is thus taken to represent the changes
in relative number of fibres during scanning. By rotating both LH and RH wheels
simultaneously, we get a smooth length – frequency curve which is called as
Fibrogram. Time taken for one test is 10 minutes.
Analysis of the Fibrogram:
The fibrogram obtained from fibrograph is shown in fig. From the point X which is
either the starting point of the pen ¼ inch above the base line, a tangent is drawn
to the curve, which meets OX at the point N and OY at the point A. Measure OA
which is the mean length. Measure ON, take a point S which is half of ON . Draw
another tangent from S to the curve meeting the like OY at T. Measure OT ie,
Upper Half Mean length.
The upper Half Mean length is the mean length of the longer 50% of the fibres in
the sample from which the clamped fibre test specimen was prepared. Getting the
two values, mean length and upper half mean length, uniformity ratio of the
sample can be measured which is the ratio between mean length and upper half
mean length expressed as a percentage.
2.5% Span length:
It is defined as the distance spanned by 2.5% of fibres in the specimen being tested
when the fibres are parallelized and randomly distributed and where the initial
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starting point of the scanning in the test is considered 100%. This length is
measured using "DIGITAL FIBROGRAPH".
50% Span length:
It is defined as the distance spanned by 50% of fibres in the specimen being tested
when the fibres are parallelized and randomly distributed and where the initial
starting point of the scanning in the test is considered 100%. This length is
measured using "DIGITAL FIBROGRAPH".
For the span lengths measured, average the results for all specimens in inches to
two decimal places or in millimeters to one decimal place. Calculate the
Uniformity ratio by dividing the average of the shorter span lengths by the average
of the longer span lengths. Multiply the ratio by 100 to convert it to a percentage
and round it off to a whole number
I.e., Uniformity Ratio = 50% span length /2.5% span length*100
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Classification of cotton according to Staple Length and Span Length Values:
At present five staple length categories are used for classification of cotton as follows:
No category Staple length range in mm
01 Short 19 and below
02 Medium 20 to 21.5
03 Superior Medium 22 to 24
04 Long 24.5 to 26
05 Superior Long 27 and above
According to 2.5% span length values cotton is classified into the staple length categories as
follows:
No Category 2.5% span length in inch
01 Short Below 1
02 Medium 1 to 1.14
03 Long 1.15 to 1.29
04 Extra long Above 1.29
Merits:
1. Simulates beard formed by fibres held by back or front roller nip of a drafting
system
2. Very rapid (about 1 - 4 min per sample)
3. Does not depend much upon operator skill.
4. Effective length is close to graders staple length
5. Provides accurate estimate of short fibre content
Limitations:
Fibrograph: Beard of fibres is prepared by picking the fibres randomly from the
sample by a comb and loose fibres brushed aside. The beard is optically scanned
from the base to tip from which a fibrogram is drawn. The comb has 28 needles/inch.
Since long fibres have a proportionally higher probability to be caught by comb this
results in a length biased sample. The instrument based on this principle was
developed by Hertel. Upper half mean length, mean length and Uniformity index are
determined from the fibrogram by drawing tangents to the curve.
ASTM D1447 - 07(2012)e1 gives the Standard Test Method for Length and Length
Uniformity of Cotton Fibers by instruments like Fibrograph. Mechanisation of
measurement of length in
the instrument resulted in
servo fibrograph.
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Conclusion:
Fibrograph measurements provide a relatively fast method for determining the
length uniformity of the fibres in a sample of cotton in a reproducible manner.
Results of fibrograph length test do not necessarily agree with those obtained by
other methods for measuring lengths of cotton fibres because of the effect of fibre
crimp and other factors.
Fibrograph tests are more objective than commercial staple length classifications
and also provide additional information on fibre length uniformity of cotoon fibres.
The cotton quality information provided by these results is used in research studies
and quality surveys, in checking commercial staple length classifications, in
assembling bales of cotton into uniform lots, and for other purposes.
THE END
