Details About Fiber Fineness

R Fiber Fineness: - Fiber fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. The fineness determines how many fibers are present in the cross-section of a yarn of given thickness. Additional fibers in the cross-section provide not only additional strength, but also a better distribution in the yarn. Thirty fibers are needed at the minimum in the yarn cross-section, but there are usually over 100.

R Why Fiber Fineness is so Important:-

It has been known since long that fiber fineness plays an important role in determining the quality of resultant yarn and hence that of the resultant fabrics. In general fiber fineness is important due to the following factors:

1.  It affects Stiffness of the Fabric: - As the fiber fineness increases, resistance to bending decreases. It means the fabric made from yarn of finer fiber is less stiff in feel. It also drapes better.
2.  It affects Torsional Rigidity of the Yarn: -Torsional rigidity means ability to twist. As fiber fineness increases, torsional rigidity of the yarn reduces proportionally. Thus fibers can be twisted easily during spinning operation. Also there will be less snarling and kink formation in the yarn when the fine fibers are used.
3. Reflection of Light:- Finer fibers also determine the luster of the fabric. It is so because they there are so many number of fibers per unit area that they produce a soft sheen. This is different from hard glitter produced by the coarser fibers. Also the apparent depth of the shade will be lighter in case of fabrics made with finer fibers than in case of coarser fibers.
4.  Absorption of Dyes: -The amount of dye absorbed depends upon the amount of surface area accessible for dye out of a given volume of fibers. Thus a finer fiber leads to quicker exhaustion of dyes than coarser fibers.
5.  Ease in Spinning Process: -Finer fibers lead to more fiber cohesion because the numbers of surfaces are more so cohesion due to friction is higher. Also finer fibers lead to less amount of twist because of the same increased force of friction. Which means yarns can be spun finer with the same amount of twist as compared to coarser fibers. This also means that the yarns will be softer.
6. Uniformity of Yarn and Hence Uniformity in the Fabric: -Uniformity of yarn is directly proportional to the number of fibers in the cross fibers. Hence finer the fiber, the more uniform is the yarn. When the yarn in uniform lit leads to other desirable properties such as better tensile strength, extensibility and luster. It also leads to fewer breakages in spinning and weaving. In fact fiber fineness is one of the dominant factors in determining the limiting count to which a yarn can be spun.

R Following are some methods of determining fiber fineness.

• gravimetric or dimensional measurements
• air-flow method
• vibrating string method

R Fiber Fineness is Measured by the Airflow Method:

Principle: - In this method, fiber fineness is measured by air flow. If large amount of air is blown, the fiber will be coarse and if small amount of air is blown, the fiber will be fine. The method based on this principle.

Description: - Let us, consider two cylinders ‘a’ & ‘b’ of similar dimensions, one filled with circular rods of large diameter (a) & the other with circular rods of small diameter (b) as shown figure. The number & the diameter of the rods are so chosen that the total cross sectional area is equal in both the cases. If air is blown through two cylinders at the same pressure it will be found that the rate of air flow through ‘b’ would be less than through ‘a’ even though the space through which air has to pass is the same in both cylinders. The reason for this is that the air flowing through ‘b’ has more rod surface to flow past. This rod surface acts as drag on the air & therefore the resistance increases.

     Hence, a difference in the rate of air flow is a measure of the difference in the surface area of the large diameter 7 small diameter rods. This leads to consider a term called specific surface. Specific surface is defined as the ratio of surface area to volume.

  i.e. Specific surface = Surface area / volume

To calculate the specific surface of the cylinder:

Let, V             is the volume of the cylinder.

V = Cross sectional area A × Length of the cylinder L.

   =  QUOTE  

Where ‘d’ the diameter of the cylinder.

The surface area of the cylinder =  QUOTE  

Specific Surface S =  QUOTE  

                                 =  QUOTE  

                                 =  QUOTE  

Also   S =  QUOTE  

             =  QUOTE  

             = 4/d

Thus, S  QUOTE  

Therefore it can be said that the specific surface S is inversely proportional to the fiber diameter and it can also be said for fibers of circular cross section of specific surface is inversely proportional to the fiber diameter. Therefore by the measuring the rate of airflow under controlled conditions, the specific surface of the fiber can be determined & consequently the fiber diameter.

R Fiber Fineness Rating:-

Micronaire Value	Rating
Below 3	Very fine
3-2.9	Fine
4-4.9	Average fine
5-5.9	Coarse
6-avobe	Very coarse