Exposed! Test Method for Air Permeability Resistance of Butyl Inner Tubes

Tires are the main load-bearers of automobiles, and their air tightness has a greater or lesser impact on the overall performance of the vehicle: tires with good air tightness can improve vehicle safety, driving performance, and comfort; reduce tire rolling resistance, thereby reducing fuel consumption; due to reduced fuel consumption, carbon dioxide emissions are reduced; and the frequency of tire inflation is reduced, facilitating vehicle maintenance. Tires maintain their optimal shape and performance when properly pressurized internally. Therefore, the air permeability resistance of the airtight layer is crucial for automotive applications.

Test Basis:

Butyl rubber inner tube manufacturers can test the air tightness of the airtight layer of butyl inner tubes according to GB/T 7755-2003 "Determination of air permeability of vulcanized rubber or thermoplastic rubber". This standard provides a method for testing the air tightness of rubber materials, which can quickly and accurately test the air permeability resistance of rubber, thus providing a reliable basis for the selection of materials during tire manufacturing.

Test Principle:

The test employs the differential pressure method. A pre-treated sample is placed between the upper and lower test chambers. First, the low-pressure chamber is evacuated, and then the entire system is evacuated. Once the specified vacuum level is reached, the lower test chamber is closed, and a test gas at a certain pressure is introduced into the high-pressure chamber, ensuring a constant pressure difference is formed on both sides of the sample. Due to the existence of the pressure gradient, the gas permeates from the high-pressure side to the low-pressure side. By monitoring the pressure in the low-pressure side, the barrier properties of the tested sample can be obtained.

Sample Selection:

The degree and rate of gas diffusion and permeation in polymers are related to the molecular thermal motion of the polymer. Butyl rubber molecules have densely packed side methyl groups, restricting the thermal motion of polymer molecules. Therefore, butyl rubber has good gas permeability resistance and is a commonly used material for tire inner tubes or airtight layers. This article uses the testing of butyl rubber as an example to introduce the test method for the airtightness of tire inner tubes.

Sample selection: 

Samples should be flat, free of scratches, punctures, or other defects.

Instrumentation:

Based on the differential pressure method, this instrument is a professional instrument for testing gas permeability. Its three test chambers are completely independent, allowing simultaneous testing of three identical or different samples. It boasts high accuracy, with the test temperature controllable between 5℃ and 95℃, achieving an accuracy of ±0.1℃. Humidity control ranges from 0%RH, 2%RH to 98.5%RH, and 100%RH, with a humidity control accuracy of ±1%RH. This allows for accurate testing of the gas permeability of high-barrier materials.