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Analysis of GB/T 11048 Test Method for Moisture Absorption and Perspiration
1. Testing principle GB/T11048 introduces two methods for testing the thermal resistance of fabrics-evaporative hot plate method and static flat plate method. The principles of the two test methods are the same. The static plate method requires that the air velocity of the climate chamber is not greater than 0.1m/s, while the former requires 1m/s. Among them, the evaporative hot plate method can also test the moisture resistance of the fabric, and the test component is slightly different from the thermal resistance method. Thermal resistance: The sample is covered on an electric heating test board, and the test board and the thermal guard ring around and at the bottom can maintain the same constant temperature. The entire test device is placed in a climate chamber with constant temperature, humidity and wind speed. The temperature on the electric heating test board and the temperature of the climate chamber form a temperature gradient. The electric heating test board dissipates heat to the surroundings through the sample, and the power consumed in this heat dissipation process is brought into the corresponding formula to obtain the thermal resistance value. Moisture resistance: For the measurement of moisture resistance, a breathable but impermeable film should be covered on the porous electric heating test plate. The water entering the electric heating plate evaporates and passes through the film in the form of water vapor (no liquid water is in contact with the sample). After the sample is placed on the film, the heat flow required to maintain the constant temperature of the test class under a certain water evaporation rate is measured, and the water vapor pressure of the passing sample is substituted into the formula to calculate the moisture resistance of the sample. It can be known from the principle of the test that the moisture resistance test requires the test board to be a through-hole structure, and it must be equipped with a water supply system. 2. Evaluation of thermal resistance and moisture resistance Thermal resistance: the calculation formula is, where Tm and Ta are the surface temperature of the test board and the surface temperature of the climate chamber, respectively. A is the area of u200bu200bthe sample, these are certain. H is the power value consumed by the fabric to dissipate heat under a temperature gradient. △Hc is the power correction value. Rct0 is the thermal resistance value calculated when no sample is added, that is, when the plate is empty, which is called the empty plate value. , Hct0 is the power value of direct heat dissipation under the temperature gradient. The calculation formula for the humidity resistance is that the surface temperature of the test board and the surrounding air temperature are both controlled at 35°C, and the air flow rate is 1m/s. The humidity of the air should be maintained at 40%, and its water vapor pressure Pa should be 2250Pa. The saturated steam pressure Pm is 5620Pa. Ret0 is the wet resistance value calculated when no sample is added, which is called the empty plate value. , Het0 is the power consumption value of the instrument under the water vapor concentration gradient. 3. Analysis of test instrument components This section mainly introduces the components in the evaporative hot plate method. 1. Temperature and water vapor control and measurement device (with the test board as the main body) The test board is placed in the thermal guard ring (to prevent heat dissipation). The test board mainly consists of the following components: 1. Metal plate; 2. Temperature sensor; 3. Temperature controller; 4. Heat measuring device; 5. Quantitative water supply device; 6. Metal body with heating element. It can be seen from the figure that 6 generates heat and transfers to 1 metal plate, and the two constitute the test board. The function of 5 is to supply water when measuring humidity resistance (source of water vapor). It should be noted here that the moisture resistance test is that the metal plate is in a porous form, and the surface of the electric heating wire metal component in contact with the porous plate is a groove, so that the water provided by the water supply device 5 can enter the electric heating plate. 2. There are two types of thermal guard ring with temperature control. The numbers in the figure indicate: 7. Temperature and water vapor control and measurement device; 8. Thermal protection ring; 9. Temperature controller; 10. Temperature measurement device; 11. Sample table; 12. Test board; 13. Thermal protection Plate; 14 bottom plate; 15. wooden frame; 16. cork strip; 17, 18. temperature measuring device. The size of the specific device is described in detail in the standard. Fourth, the test process and the condition of the test before the empty plate value is determined. Record the measured value once within 3min, and the test time can reach stability at least 30min (not including warm-up time). Thermal resistance: adjust the temperature Tm of the test panel to 35℃, the temperature of the climate chamber Ta to 20℃, the relative humidity to 65%, and the air flow rate to 1m/s (the static plate method is not more than 0.1m/s). After placing the sample on the test board, after Tm, Ta, relative humidity, and H are stable, record the value and substitute it into the formula calculation. Moisture resistance: Place a film that can permeate water vapor but not water on the test board. Adjust the surface temperature Tm of the test board and the air temperature Ta to 35°C, the relative humidity to 40%, and the air flow rate to 1m/s. After placing the sample on the test board, after Tm, Ta, relative humidity, and H are stable, record the value and substitute it into the formula calculation.
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1. ISO 5402-1: Specifies the flexometer method for testing leather flex resistance under repeated bending.
2. ISO 17694: Defines test methods for footwear upper and lining flex resistance, simulating real-world bending stress to assess long-term durability.
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