Rubber vulcanized or thermoplastic- Accelerated aging and heat resistance tests- Air oven method

1. Principle:

Test pieces are subjected to high temperature and at atmospheric pressure, after which specified properties are measured and compared with those of unaged test pieces.The physical properties concerned in the service application should be used to determine the degree of deterioration but, in the absence of any indication of these properties, it is recommended that tensile strength, stress at intermediate elongation, elongation at break and hardness be measured.

1.1 Accelerated ageing by heating in air

In this method, with the low oxygen concentration, the oxygen can’t fully diffuse into the rubber to keep oxidation synchronous, even if the oxidation rate is fast. Therefore, when a sample of the thickness specified in the standard test methods is suitable for using in this method, it may give erroneous results for the rubber with poorly aging resistance.

1.2  Heat resistance test

In this test method, the test pieces are subjected to the same temperature as they would experience in service in the stipulated time, then test the appropriate properties and compare with unaged pieces.

2.Apparatus:

2.1 Aging Oven which shall be fulfilled below requirement:

• Equipped with forced air circulation device, air flow rate 0.5m/s～1.5m/s, the min. Surface area of test piece shall be against airflow to avoid the rate of airflow be interfered.

• The oven shall be of such a size that the total volume of the test pieces does not exceed 10% of the free space in the oven. Provision shall be made for suspending test pieces so that they are at least 10mm from each other and, at least 50mm the sides of the oven.

• The temperature of the oven shall be controlled so that the temperature of the test pieces is kept within the tolerances of the specified test temperature;

• A temperature sensor shall be placed inside to record the actual ageing temperature.

• No copper or copper alloys shall be used in the onstruction of the heating chamber.

• Provision shall be made for a slow flow of air through the oven of not less than three and not more than then air changer per hour.

• Before entering the aging chamber, the air should be heated to within the tolerances of the test temperature specified by the aging oven.

The Eligible GESTER Machine:

GT-KD01 Aging Oven

The other apparatus for rubber properties measurement above mentioned:

GT-K01 Universal Testing Machine

GT-KD09-LX-A Shore A Durometer

2. Test pieces

• The test pieces preparation should follow GB/T 9865.1
• It is recommended that the accelerated ageing or heat resistance test carries our on the test pieces conditioned as per GB/T 2941, and no on the completed products or sample sheet.
• The aged test piece will no be required for mechanical, chemical or heat treatment.
• The number of specimens before and after aging is usually measured in five and should not be less than three.
• Only test pieces of similar size shall be compared with each other.

Note: The test pieces shall be measured before heating but, whenever possible, marking shall be carried out after heating as some marking inks can affect the ageing of the rubber.

To prevent the migration of sulphur, antioxidants, peroxides or plasticizers, avoid heating different types of rubber samples simultaneously in the same aging chamber. It is recommended that only the

following types of materials can be heated together:

a) Polymers of the same general type;

b)Vulcanizates containing the same type of accelerator and approximately the same ratio of sulphur to accelerator;

c)Rubbers containing the same type of antioxidant;

d)Rubber containing the same type and amount of plasticizer.