Cotton fibre fineness test (airflow method)
The fineness of fibre plays a very important role in yarn characteristics. It directly affects the yarn quality to be spun. The tensile strength, degree of yarn hairiness, lustre, feel, and softness of yarn depends upon the fibre fineness. The value of the fibres is also decided according to the fineness of a fibre. If all the fibres present in the bulk have a similar diameter, then the fibre fineness may be determined easily. In the case of cotton fibres, the different fibres have different diameters. The diameter of the fibre may even vary at different places in the same fibres. This is the reason why we cannot measure the diameter of the fibres accurately.
The weight per unit length of fibre is termed the fineness of a fibre. Normally, it is measured in microgram/inch.
In the bulk of cotton fibres, there are millions of fibre present. We cannot be determined the weight per unit length of every fibre. It is not possible at all. An airflow method is used to determine the average weight per unit length of the fibres in the bulk.
Airflow method of fibre fineness test:
This method can be understood by an example. Suppose that we take an equal amount of two fibres having different fibre fineness. We keep those in two cylinders and compress them. Now we pass the air through both samples at equal pressure. Here, we observe that airflow through the fine fibres are less than coarse fibres. It all happens due to the difference between the total surfaces area of coarse and fine fibres. In the case of fine fibres, the air faces more obstructions and hence the airflow rate gets dropped.
Now, we can say that airflow rate and specific surface area is inversely proportional to each other. This method is very useful and gives quick result
Cotton fibre fineness test by Shirley fineness tester:
1- Shirley cotton fibre fineness tester
2- Weighing scale
3- Cotton fibres
6 grams plus or minus cotton is weighed accurately. if the new version of the instrument is used the specimen weight is kept at 5 grams. The sample is fluffed properly to eliminate any tangled part.
If the Shirley trash analyser gets available, the material is opened, cleaned and blended with the help of a trash analyser before weighing the specimen.
*First of all, the specimen is packed in the cylindrical holder A.
*Now the specimen is compressed to a constant volume by perforated plunger P.
*The flow control valve V is kept closed at this stage.
*Now, the power supply of the exhaust pump E is switched on. The exhaust pump starts to suck the air immediately.
*The airflow is regulated by flow control valve V until the manometer M indicates that a pressure difference of 18cms of the water exists across the end of the plug of cotton.
*The new version of this instrument is supplied with the engraved scale in micronaire values. The reading of the top of the flow meter is recorded now.
*If the new version is used, the specimen weight is kept at 5 grams.
*A repeat observation is made after removing the old specimen and repacking a new specimen in the cylindrical holder.
*Four different specimens are tested and the mean value is calculated. Thus the final micronaire value is determined.