2 Fibre length.pdf

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1. Fibre Length

2. Importance of fibre length
•Length and fineness are related to each other in natural fibres .
(For example in cotton fibre longer the fibre finer the fibre)
•For manufactured fibreslength and fineness can be controlled
separately.
•In cotton, fibre length decides the commercial value. Longer the
fibre higher the price.
•Fibre length decides spinnability that is the maximum count that
can be spun from the fibre with acceptable level of quality.
•The process parameters like drafting roller setting, yarn twist are
chosen based on the fibre length.

3. Nature of cotton fibre length
•Cotton fibre properties vary for different varieties of cotton,
for different growth areas, for different climatic conditions
and season to season.
•For cotton fibre as the length variation is higher, a large
number of fibreshas to be considered to get a reliable result.
•In addition to the fibre length measurement, the fibre length
distribution is also taken into consideration.

4. Cotton fibre length measurement
Stapling Method
•This method was recommended by USDA.
•It was a system of length measurement used by classers in earlier
days to class the fibres.
•The length obtained by this method is called Staple length.
•
This concept is still used by some people for the approximate
estimation of fibre length.

5. Hand stapling of cotton fibre

6. Comb Sorter Method
•This method is used to judge the fibre length distribution visually
and numerically.
•It gives a fairly accurate measurement if followed properly.
•This method uses set of top and bottom combs for the
preparation of cotton tufts of different length groups with in the
same fibre sample.
•Collection and placing of of fibre tufts of varying length
distribution on a velvet pad, which provides a diagram called
sorter diagram
•From the sorter diagram various length parameters can be
obtained

7. Baer Sorter Instrument

8. Fibresare arranged based on their length
Sorter Diagram

9. Fibre length measurement in Baer Sorter

10. Optical Scanning Method
•This is the most widely used method of
cotton fibre length measurement.
•It is faster than the methods discussed
earlier and more number of samples can be
tested.
•The test results are not influenced by
personal judgement.
•This method uses a fibre sampler and a set
of combs for the measurement of fibre
length.

11. Optical scanning of test specimens
•Fibre combs are brushed carefully to remove the loose fibres
and the clamed fibres are straightened.
•The fiber combes moves into the light zone and the fibre
beard is scanned photo electrically from base to tip.
•The amount of light being used to measure the number of
fibresthat extend various distance from the comb.
•From this a diagram, Fibrogramis reported.
•
The fibre length is reported as span length.

12. Span length concept

13. Span length indices
•2.5% Span length
the distance of 2.5% of the fibresextending from the clamps in which
they have been caught at random along their length. It is numerically
nearer to the staple length as determined by American classers.
•50% Span length
the distance of 2.5% of the fibresextending from the clamps in which
they have been caught at random along their length.
•Uniformity ratio
the ratio of 50% span length to 2.5% span length and it is expressed
as a percentage.

14. Flat & Triangle distribution of cotton fibre

15. Different modes of fibre length testing in HVI
ICC Mode HVI Mode
2.5% Span length Upper Half Mean Length
Uniformity Ratio % Uniformity Index