Cable Ozone Resistance Testing
Ozone testing for cables is a test to determine a rubber or elastomer's resistance to ozone degradation. The test methodology for IEC 60811-403 requires an Ozone test chamber capable of generating a controlled amount of ozone, a means for circulating ozonized air under controlled conditions of humidity and temperature, and a means for determination of ozone concentration.
Ozone resistance testing for cables typically applies to cross-linked compounds. The tests are required to be carried out not less than 16 hours after the extrusion or cross-linking of the insulating or sheathing compounds. Test samples are required to be conditioned before exposure to ozone. Insulated cores are to be bent around a brass, aluminium or suitably treated wooden mandrel with a diameter according to the below table.
| Outside diameter of insulated core (mm) | Mandrel diameter (as a multiple of the outsude diameter of insulated core) |
|---|---|
| D ≤ 12.5 | 4 ±0.1 |
| 12.5 < D ≤ 20 | 5 ±0.1 |
| 20 < D ≤ 30 | 6 ±0.1 |
| 30 < D ≤ 45 | 8 ±0.1 |
| 45 < D | 10 ±0.1 |
The bent test pieces on their mandrels shall be kept in air at ambient temperature without any further treatment for between 30 to 45 minutes before being tested. Cable sheathing materials are prepared as dumbbell pieces and are then be stored in the desiccator for at least 16 h at (23 ± 5) °C.
The conditioned test pieces are then placed in the middle of the ozone test chamber fitted with a what is known as a test cock; the test pieces shall be at least 20 mm from each other. The test pieces shall be maintained at a temperature of (25 ± 2) °C, unless otherwise specified in the cable standard, and exposed to a circulating current of dry air with the required ozone concentration. The ozone concentration and the exposure time shall be as specified in the relevant cable standard. The air with the required ozone concentration shall have a flow rate of between 280 l/h and 560 l/h, and the air pressure shall be maintained slightly above atmospheric pressure.
After the specified test duration, the test pieces are removed from the test chamber and examined with normal or corrected vision without magnification and should be free from cracks and the ozone concentration is measured directly with an ozone meter. The required ozone concentration will be specified in the relevant cable standard.
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