Sunday, July 18, 2021

Sampling method for cotton fibre properties:

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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