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कपास फाइबर गुणों के लिए नमूनाकरण विधि
Sampling method for cotton fibre properties:
The selection of
the sampling method for testing fibre properties depends upon the form of
the available fibres. In this way, different types of sampling methods or
techniques are used for fibre bale, sliver, carding wave, and yarn etcetera.
The test results obtained from different forms of fibre do not get necessarily
identical. There may be two sources of errors during sampling:
1 - Random error
2 - Error due to
bias
When we do a sampling of fibres, the degree of fibre mixing and blending gets very crucial.
If we pick up the sample from the draw frame sliver and the sample is picked
from one region of the bulk, we assume that the picked sample contains fibres
from all of the original supply.
In case of limited
fibre mixing, the samples are taken from all parts of the bulk in order to
achieve a representative test sample. It is called zoning sampling.
Types of
techniques for fibre sampling:
The types of
techniques for fibre sampling are given below:
Squaring
technique:
In this sampling
method, the sliver is opened out into a web. Now his web is placed on a black
velvet pad. The end of the sliver is squared off. A plate of glass is placed
over these fibres to control them. A small fringe is left projecting beyond the
plate. Now, all the protruding fibres are removed and discarded.
The glass plate is
moved back to little and a second fringe is removed. Apparently, the extent of bias has been avoided. Since all the ends of the fibres have been terminated in
a given volume. It is necessary to repeat the operation until the final
position of the plate edge was at least a distance equal to the length of the
longest fibre present from its original position. This is necessary because
whenever a strand gets broken there is a bias of long fibres at each broken
fringe.
Cut squaring
technique:
Where the material
is composed of fibres in the parallel order (sliver, roving, and yarn) a
modified squaring technique can be used. First of all, the twist of material is
untwisted then is opened out a little. Now, the fibres are laid in parallel
order on a black velvet pad. A glass plate is placed over these fibres with its
leading-edge at right angles to the strand axis. The fringe is cut across with
scissors as near to the glass plate as possible and the fibres whose cut ends project
are removed by force and discarded. This operation is repeated. finally, after
the third movement of the glass plate, the fringe is removed and used as a
sample.
Zoning technique
for raw cotton:
If the bulk of the
material is not homogeneous, a number of subsamples are taken at random from
different places in the bulk.
The number of
subsamples depend upon the degree of heterogeneity of the bulk and may be
found by experiment or known by experience.
When sampling from
bulk material, such as a bale of raw cotton, the required number of fibres
should be taken one by one at random from different parts of the bale. Since it
is impracticable, we use a system whose object is still to sample from as many
parts of the bulk as possible. The sampling procedure of the zoning technique
is given below:
1 - A sample of approximately two ozs. is
prepared by selecting about eighty large tufts chosen, so far as is possible,
over the bulk.
2 - This sample is
divided into four equal parts
3 - Now, sixteen
small tufts (each 20mgs.) are taken from each quarter.
4 - Each tuft
is halved four times and is discarded alternately with right and left hands
and turning the tuft through a right angle between successive halvings. Sixteen
wipes are thus produced from each quarter sample.
5 - Now, each set
of wipes is combined into a tuft.
6 - Now each tuft
is mixed in turn by doubling and drawing between the fingers.
7 - Next, each
tuft is divided into four parts.
8 - Four new tufts
are obtained by combining a part of each of the former tufts.
9 - Now each new
tuft is mixed again by doubling and drawing.
10 - Now, a
quarter from each tuft is taken to make a final sample.
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