Frazier air permeability test method (ASTM D737 testing)of textiles

1.Air permeability definition

What is the permeability of air? The air permeability is the volume of air passing a fabric under pressure. There are two types of air permeability tester for textiles, Frazier air permeability tester and Shirley air permeability tester. In ASTM D737 test method, we take Frazier differential pressure air permeability tester as example.

2.Test Objectives:

To determine the air permeability of textile fabrics by calculating the air permeability value.

3.Test Materials:

Woven, knitted and non woven textile materials. eg.  cotton.

4.Air Permeability Test Procedure:

4.1 The specimens must be adjusted to the standard atmosphere with  21 +/- 1°C (70 +/- 2°F) and 65 +/- 2 % relative humidity unless there is otherwise specification of contract order.

4.2 Process the specimens carefully and prevent it from changing its’ natural state.

4.3 Place each specimen on the test head of the air permeability tester, and control the test as the operation manual.

4.4 At the conditioned water pressure, making tests accord to the operation manual. In the absence of an operation manual, use a water pressure 125 Pa (12.7mm or 0.5 in. of water).

4.5 Read and record the test results. The air permeability units should be noted. Record the test results respectively in SI units as cm^3/s/cm^2 and in inch-pound units as ft^3/min/ft^2 rounded to three significant digits.

4.6 Take out the tested specimen and continue to test next specimen until the ten specimens have been tested in accordance with the flow of 4.3-4.5.

4.7 In order to make sure a high accuracy, the number of test is at least four.

5.Air Permeability Calculation

5.1 Calculate air permeability of every specimen by reading directly from the tester in SI units as cm^3/s/cm^2 and in inch-pound units as ft^3/min/ft^2, rounded to three significant digits. Please follow the instructions which the manufacturer provides when calculating air permeability.

Note-If air permeability test results are 600m (2000 ft) above the sea level, it needs correction factors.

5.2 When data are calculated by computer automatically, the calculation of air permeability rating is included in the software. Therefore, it is suggested to verify against the known values and the description of the software which is used in the test.

6.Report

The data which is needed to report is as follows.

6.1 Report whether the air permeability is in accordance with the Test Method D737.

6.2 Report the standard deviation and the variation factor while calculating.

6.3 The difference in pressure of fabric surfaces.

6.4 Report the model and the manufacturer of the air permeability test equipment.

What important points should be paid attention to when measuring air permeability?

1.Calibration board must be used before each test (all boards should be checked). Mainly air circuit, liquid circuit, air leakage, liquid leakage, position moving will cause error to the air permeability tester.

2.The sample should be fixed at the intake hole naturally and smoothly. Usually it does not need to distinguish between positive and negative, but if the positive and negative differences of structures (such as umbrella cloth, filter cloth, pile fabric) are big, air flow direction should be decided according to the actual use.

3.The caliber is selected in order of large to small to avoid the excess of liquid in the pressure gauge. The final selected caliber should be under the indication range of the 15%~85%.

4.Moderate pressure regulation makes the pressure gauge slowly change from low value to constant pressure value. If the liquid level has exceeded the constant pressure value, it must be adjusted back to a lower pressure level and re-adjusted. The pressure has to be stable for a period of time and then can be read.

5.Make sure that the end of the pressure gauge passes through the atmosphere without clogging. Some instruments have covers and should be taken down when measuring.

6.There is a nonlinear relationship between the air permeability and the differential pressure of two sides of the fabric (constant pressure value). The air permeability under differential pressure can be compared according to the following formula:

Q_M=Q_N（∆P_M/∆P_N）^b

The air permeability under the same differential pressure is converted, Q_M and Q_N of which are the air permeability under the constant pressure value of ∆P_M and ∆P_N, and the B is determined by the fabric category and ∆P_N.

7.Different countries have different air permeability unit of measurement. Therefore, please pay more attention to the air permeability units conversion. If you need to convert 1/ dm^2/min to m^3/ m^2/ minor convert l/ dm^2/ min to l/ m^2/ s, here is the air permeability conversion chart as follows for your reference.