Fibre Length.pdf

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Fibre Length
Evaluation of Textile Materials

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Why fibre length?
 Quality assessment
 Quality prediction
 Fibre breakage study
 M/C settings ??
 Combing efficiency etc.
Fibre Length

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Fibre Length
Fiber length can be expressed as,
Staple length (STPL)
Mean length (ML)
Upper quartile length (UQL)
Effective length (EL)
Modal length (MoL)
Span length (SL)
Upper half-mean length (UHML)

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Fibre Length
The parameters used to estimate fiber length
variations
Dispersion%
Uniformity index (UI)
Uniformity ratio (UR)
Short fiber content (SFC), and
Floating fiber index (FFI)

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Staple Length
The staple length is defined by USDA as “the
normal length of typical portion of staple fibers
having relative humidity of 65% and temperature
of 70°F without regard to value or quality.”

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Mean Length
The mean length of the fibers is defined as “the
average length of all fibers in the test specimen
based on weight–length data”.
It can also be calculated by number–length data
as an alternative.

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Upper Quartile Length
According to ASTM, upper quartile length (UQL)
is defined as “the fiber length which is exceeded
by 25% of fibers by weight in test specimen”.

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Effective Length
The effective length is longer than the average length
and is a measure of the length of the majority of longer
fibers in a sample.
The effective length is described statistically as the
upper quartile of the fiber length distribution obtained by
ignoring short fibers whose length is less than half of
the effective length of fibers.
Animation

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Modal Length
The modal length is the length of the high frequency fiber
in the sample obtained from the fiber length frequency
diagram.
The modal length of long staple cotton is higher than the
mean staple length due to the progressive increase in
skewness with increasing staple length in the fiber length
distribution

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Span Length
The span length is the length of fibers at a
distance spanned by a specific percentage of
fibers (it can be by number or by weight) in the
test beard, considering the reading as 100% at
the starting point of scanning.
The most common span lengths used
commercially are 2.5% and 50% span length

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Span Length
Animation: Fibrogram

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Span Length
 The 2.5% span length is defined as the length of
fiber at which only 2.5% of long fibers are excluded
It provides the reference length for roller settings to
be adjusted so that few, if any, fibers are broken
The 2.5% span length is close to upper half-mean
length (UHML) for long staple cotton
The 50% span length is more valuable as a
potential measure of yarn quality and spinning
performance

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Animation: Fibrogram Analysis
Upper Half Mean Length

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Dispersion%
LL´ = Effective length
LL´ - MM ´ = NL ´ = Inter-quartile range
Dispersion%=NL ´ /LL ´
(for flatter middle zone, dispersion is minimum)
Animation

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Uniformity Index
The uniformity index (UI%) is the ratio of the mean
length to the upper half-mean length

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Uniformity Ratio
The uniformity ratio (UR%) is the ratio of the 50% span length
to the 2.5% span length.
Uniformity ratio (U.R.) = 50 % span length /2.5 % span length
= S50% / S2.5%
Uniformity ratio (U.R.) in %= [50 % span length /2.5 % span length ] *100
= [S50% / S2.5% ] * 100
It is a smaller value
than the uniformity
index by a factor
about 1.8

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Short Fibre Content
Short fibre content (SFC%) is the percentage by
weight of fibers having a length less than half of an
inch.
It can also be measured in percentage by number
of fibers having a length less than half of an inch.

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Short Fibre Content
The % of short fibers in cotton increases the cost of
processing (combing) and waste %.
Also contributes to weaker yarn and less efficient
spinning.
Long length fibers are mostly preferred due to the reduced
number of fiber ends with a higher yarn strength in the same
length

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Floating Fiber Index
Floating Fiber Index (FFI) is an alternative to
short fiber content
It explains the number of short fibers which are
not clamped between the nips of a pair of rollers
in the drafting system
These fibers are floated on long fibers to pass
through the drafting zone without the influence of
the applied drafting mechanism

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By trained classers
I. Selecting a sample and preparing the
fibres by hand doubling and drawing to
give a fairly well straightened tuft of
about ½ inch wide.
II. This is laid on flat black background and
the staple length is measured.
Cotton Fibre Length
a) Hand stapling method:

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III. The shorter fibres will lie in body of the
tuft and extreme ends (tips) will not be
the limits used for measurement of
staple length.
IV. The classer choose the length where
there are reasonably well defined edges.
V. Subjective in nature, so difference in
results between classers.
Cotton Fibre Length
a) Hand stapling method …..cont

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b) Shirley photoelectric stapler
For quicker measurement of length
(staple length)
Objective measuring technique of earlier
staple length measuring method. (classer
judges by eye)
Cotton Fibre Length

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b) Shirley photoelectric stapler Animation

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Fringes of fibres are prepared by hand
and carefully placed over black velvet pad
The density of the fringe should be such
that traces of the black velvet can be seen
through central part where density is
highest.
 The photoelectric stapler detects the
distance between the points where the
density gradients are maximum (on either
b) Shirley Photoelectric Stapler

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Two photoelectric cells connected
opposition to each other
Depending on light intensity, the opposed
cells pass a current which is proportional to
the difference in the intensity.
b) Shirley Photoelectric Stapler … cont

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b) Shirley photoelectric stapler

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Variation in current are shown in sensitive
indicator
As the fringe is advanced inside the instrument,
two maximum density gradient point will be there
and this distance is “Staple Length” (max.
deflection of galvanometer in opposite direction)
E.L. = P. E. Staple length × 1.1
b) Shirley Photoelectric Stapler … cont

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SF%=(RB/OB)×100% and LL´ =Effective length
LL´ - MM ´ = NL ´ = Inter-quartile range
Dispersion%=NL ´ /LL ´
(for flatter middle zone, dispersion is minimum)
c) Comb Sorter
Cotton Fibre Length
OQ =½ OA OK = ¼ OP
KS =½ KK´ OL = ¼ OR
OM = ¾ OR
Animation

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American staple length = 0.91 × Effective length (LL’)
c) Comb Sorter
Cotton Fibre Length
OQ =½ OA OK = ¼ OP
KS =½ KK´ OL = ¼ OR
OM = ¾ OR

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Frequency distribution in opposite way, i.e. the
curve is known but the frequency distribution is
to be obtained (Y-Axis: Fibre length in 1/8th inch)
Mean Length from Comb Sorter

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Mean Length from Comb Sorter

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d) Single fibre length measurement
Each fibre is taken separately and gently
straightened over the slide
Length is recorded
o tedious & time consuming;
o not used in mill practice,
o used where number of fibres are small
Fibre Length

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e) Length measurement by weighing method
 After combing, the fibres are placed on a velvet
pad.
 Then ranked into groups so that length range in
each group is about 3 mm
 Groups are then weighed on a sensitive
balance.
Mean length = WL/ W
where L = Group length
W = Mass of fibre in length group
Upper Quartile Length ? - 1/4th of the fibres by
mass is longer than that length
Fibre Length

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f) Clamp tuft method (Weighing method)
 Clamping
 Combining to remove loose un-gripped
fibres
Fibre Length

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 The protruding tufts are cut from edge of the
clamp and weighed.
 The clamps then opened and fibres inside the
clamps are weighed separately.
Fibre Length
f) Clamped tuft method (Weighing method)
Total mass of combed tuft =
Mass of cut edge fibres + Mass of Clamped fibres

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Mean fibre length/Total mass of combed tuft
= Width of clamp (W) / Clamped tuft mass
Mean fibre length (mass biased)
= W × Total mass of combed tuft
Mass of clamped tuft
Mean fibre length α Total mass of combed tuft
Fibre Length
f) Clamped tuft method
(Weighing method) …cont.

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g) Photoelectric method (Fibrograph)
Optical method of measuring the density
along the length of a tuft of parallel fibres.
Samples are prepared by “fibrosampler”
The Final Tuft
Fibre Length (Cotton) Animation

Fibre Sampling by Fibrosampler
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Assumptions:
 A fibre is caught on the comb in proportion to
its length as compared with the total length of
all fibres in the sample (longer fibre has greater
chance)
 The point where it is caught is at random along
its length
Fibre Length (Cotton)

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Typical Fibrogram
Superimposition
of Fibrogram and
Sorter Diagram

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Typical Fibrograms (Cotton & Cut Staple Fibre )
Fibrograms Analysis

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Capacitive Method
Fibre Length (Wool)
h) WIRA fibre diagram machine (length
for combed wool fibre)

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 Parallel fibres have one end sealed
between strips of plastic
 Measurement carried out by pulling the
fibres “draw” through measuring
slots.
 M/c measures the capacitance as the
‘draw’ passes through slots.
(capacitance is proportional to amount
of material)
WIRA fibre diagram machine

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 Mean Length (ML) is calculated from ten
length reading taken at 10% interval between
5% and 95% (=  Li / 10)
WIRA fibre diagram machine
Animation

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 Automatic version of WIRA fibre
diagram m/c, with modification.
 Sample is prepared by fully automatic
m/c known as “Fibroliner”.
i) Wool fibre length - by Almeter
(Capacitance method)

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 During measurement
the sample is moved
(trapped between two
plastic films) at a
constant speed with
longest fibre entering
the capacitor first.
 Change in capacity
caused by amount of
fibre.
Wool fibre length - by Almeter
(Capacitance method)

Fibre Length.pdf

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