Saturday, May 2, 2020



Air permeability of fabric:

 “The volume of air passed per second through per unit area of the fabric is called air permeability of fabric”It is measured in cubic centimetres per second per square centimetre (cm3/second/cm2).
It depends upon the count of yarn, construction of fabric and weight per square unit of the fabric. If the warp and the weft count of two fabrics are identical, then the fabric having more threads per square inch give poor air permeability than lower threads count fabric.

If the threads count per square inch of two fabrics is the same, then the fabric made of coarse count yarn gives poor air permeability. 

Testing of air permeability of the fabric:

The testing procedure of air permeability of the fabric is given below:

Apparatus used:

1- Shirley fabric air permeability tester

2 - Fabric

3 - Scissor

4 - Marking pen

Specimen's preparation:

The specimen size is kept according to the size of specimen fixing plate. Normally, a circle of 2.54 centimetres is marked on the fabric. The enough clamping margin is also left with specimen. If you take a rectangular fabric which has length and width more than 2.54 centimetres and extra clamping margin, it can be directly used without cutting a circle. Five specimens are prepared.

Testing procedure:

The whole testing procedure gets completed in below steps:

1-  first of all, open the specimen clamp 'j'. Place the specimen on the specimen fixing plate ' I'. Now tighten the specimen clamp securely.

2- Now instrument is connected to a suitable electric power supply. Now the power supply switch is pushed on position. The air suction pump gets started to suck the air through fabric specimen. 

3 - There are four rotameter are connected with the air circuit. Initially, the technician first brings rotameter ' A'  into the circuit by turning a knob.

4-  An specific pressure drop between two fabric surfaces ( face and back ) is achieved by regulating the various valves provided with the instrument.

5- The reading of Rotameter is observed across the top of the float.

6 - If the rate of air flow through the specimen is too low to produce an indication on the Rotameter 'A', it is switched to next Rotameter B, C, & D in sequence until an indication is obtained.

7 - The specific pressure drop is kept 10 mm of watter head.

8 - When the specific pressure drop is achieved properly. The reading of  Rotameter is recorded.

9 - Five test specimens are tested.

10 - A temperature of 20 °C plus or minus 2 ° and 65% relative humidity are kept during test.

11 - A Rubber gasket is used to prevent the air leakage.

12- The mean of all five reading is calculated.

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