The standard test method for air permeability of textile fabrics is defined by ASTM International as ASTM D737 - Standard Test Method for Air Permeability of Textile Fabrics. This method is widely used to measure the air permeability or breathability of fabrics, which is an important property for many textile applications.
Here is a summary of the procedure outlined in ASTM D737:
1. Test Specimens:
- Cut circular or square specimens from the textile fabric using a template or cutting machine.
- The standard specifies the dimensions of the specimens based on the intended application or specific requirements.
2. Conditioning:
- Condition the specimens in a controlled environment (e.g., 21±1°C and 65±2% relative humidity) for a specified time to achieve moisture equilibrium.
3. Test Apparatus:
- Use an air permeability testing instrument, such as a Shirley air permeability tester or an equivalent device, that conforms to the requirements of ASTM D737.
4. Calibration:
- Calibrate the air permeability testing instrument according to the manufacturer's instructions or using a reference standard fabric with a known air permeability value.
5. Test Procedure:
- Place the conditioned specimen on the test instrument's testing head or clamping device, ensuring it is flat and wrinkle-free.
- Apply a specified pressure difference across the fabric specimen, typically using a differential pressure gauge or manometer.
- Allow sufficient time for the air to flow through the fabric until a stable airflow rate is achieved.
- Measure and record the airflow rate (expressed as air volume per unit area per unit time) using the instrument's calibrated scale or digital display.
- Repeat the test with multiple specimens to ensure accuracy and repeatability.
6. Calculation:
- Calculate the air permeability of the fabric using the recorded airflow rate and the effective test area of the specimen.
- The air permeability is typically reported in units of cubic feet per minute per square foot (CFM/ft²) or liters per second per square meter (L/s/m²).
7. Reporting:
- Report the test results, including the identification of the fabric, the test conditions (temperature, humidity), and the air permeability value obtained.
It's important to note that the specific details and requirements outlined in ASTM D737 may vary depending on the version of the standard being referenced. Always refer to the latest version of the standard and follow the instructions provided therein for accurate and reliable testing.