Application and Operation of Gurley Method in Measuring Air Permeability of Paper and Cardboard
The Gelley method is a standard method used to determine the air permeability of paper and cardboard, which is evaluated by measuring the time it takes for air to pass through a specimen at a certain pressure. The test was carried out using a Gelley Tester, which included an inner and outer cylinder and a clamping device, to ensure the tightness and accurate calibration of the instrument. The experimental procedure includes sample preparation, instrument setup, permeability measurement, and result calculation, and the results are expressed in microns per Pascal second (μm²/(Pa ·)).
definition
Air permeability is a measure of a material's ability to pass through gas under specific conditions. It is defined as the average air flow per unit area of a specimen per unit of time at a unit differential pressure. This indicator can reflect the air permeability of the material and is essential for evaluating the breathability of paper and cardboard. The unit of air permeability is usually microns per Pascal second (μm/(Pa ·)).
Unit Conversion – The unit of permeability is microns per Pascal second (μm/(Pa·s)) which can be used for conversion in the International System of Units. The specific conversion relationship is as follows: 1 μm/(Pa·) = 1 mL/(m²· Pa·s) is a unit used to represent the volume of gas passing through a 1 square meter specimen per second at a pressure difference of 1 Pascal. This unit makes the measurement of air permeability compatible with the standard system of units, allowing for comparison and application across laboratories and industries.
principle
The determination of air permeability is achieved by smoothly lowering the inner cylinder in the sealing oil. The descent of the inner cylinder compresses the air around it, allowing it to pass through the specimen. This method relies on the mass and differential pressure of the inner cylinder to create a steady flow of air between the surface of the specimen and the sealing oil in the test instrument to determine the breathability of the specimen.
The relationship between air permeability and air permeability – The magnitude of air permeability directly affects the amount of air that passes through the specimen. When the air permeability is large, the specimen can let air through in a shorter time, so the time required is shorter; With less air permeability, it takes longer for the same amount of air to pass through the specimen. This relationship makes the air permeability inversely proportional to the time for air to pass through the sample, that is, the greater the air permeability, the shorter the time; The less air permeability, the longer it lasts.
instrument
Gelley Tester
Main components
Outer and Inner Cylinders – The outer cylinder is 254mm high and 82.6mm inner diameter and is used to contain the sealing oil and apply pressure. The inner cylinder is 254 mm high, 76.2 mm outer diameter and 74.1 mm inner diameter and is used to pass through the specimen and measure the air flow.
Sealing oil – at 38°C, the density is about 0.86 g/ml, the dynamic viscosity is 10-13 mm²/s, and the flash point is not less than 135°C. The oil is used to seal and provide a stable test environment.
Clamping device - including upper and lower clamping rings, outer diameter 28.66mm, there are holes in the upper clamping ring for clamping specimens, liner thickness 0.70-1.00mm, elastic, oil and oxidation resistance properties to ensure tightness and accuracy.
Ancillary Equipment
Stopwatch or motorized chronograph – used to accurately measure the time required for a breathability test, accurate to 0.2 seconds, to ensure the accuracy and reliability of the data.
Instrument calibration
Tightness calibration, a thin, smooth, impermeable sheet of metal or rubber sandwiched between the clamp rings is checked according to the air permeability test method. If the gas leakage does not exceed 50ml within 5 hours, the tightness of the instrument meets the requirements. Otherwise, all air leaks should be inspected and sealed, and neoprene or other adhesives should be used to treat the air leak to ensure the accuracy and stability of the instrument.
Experiment preparation
Samples were collected according to standard methods, and samples were treated with standard temperature and humidity to ensure the accuracy and reproducibility of experimental results.
Cut no less than 10 specimens with a size of 50x50 mm to ensure the representativeness of the results.
Air permeability testing is performed under standard temperature and humidity conditions to ensure consistency and accuracy of the test environment.
Experimental Procedure
Alignment of the instrument and addition of oil volume - ensure that the instrument is placed horizontally, add the sealing oil to the outer cylinder, and the oil volume should reach the marking line of the inner cylinder.
Gripping and measuring of specimens
The 50x50 mm specimen is clamped in a gripper to ensure that the specimen is flat and wrinkle-free.
Remove the carriage, lower the inner cylinder into suspension, start the timer and measure the amount of air passing through the specimen.
Avoid instrument vibration to prevent affecting the measurement accuracy.
Each specimen is tested face up and back up to obtain comprehensive data.
Test results
Calculate Air Permeability – Calculate the air permeability of each specimen based on the measured time, using a formula to convert the time into air permeability values.
Data processing – Statistical analysis of measured air permeability values is performed and standard deviations and coefficients of variation are calculated to assess the degree of dispersion and reliability of the data.
Directional Differences – If there is a significant difference in the permeability of the specimen in different directions, the positive and negative permeability results should be reported separately to provide detailed directivity data for analysis.
summary
The Gelley method provides a method for accurately measuring the air permeability of paper and cardboard, reflecting the air permeability of materials by determining the time it takes for air to pass through a specimen at a certain pressure. Accurate calibration of the instrument and standardized test procedures are key to ensuring reliable results. This method is widely used to evaluate the air permeability characteristics of paper to help improve the properties and application of materials.
