BS ISO188:2011 pdf free download – Rubber, vulcanized or thermoplastic一Accelerated ageing and heat resistance tests.
Avoid simultaneous heating of different types of compound in the same oven, to prevent the migration of sulphur, antioxidants, peroxides or plasticizers. For this purpose, the use of individual cells is highly recommended. In order, however, to give some guidance for cases where it is not practicable to provide equipment with individual cells, it is recommended that only the following types of material 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) rubbers containing the same type and amount of plasticizer.
7 Time interval between vulcanization and testing
Unless otherwise specified for technical reasons, the following requirements shall be observed.
For all normal test purposes, the minimum time between vulcanization and testing shall be 16 h. In cases of arbitration, the minimum time shall be 72 h.
For non-product tests, the maximum time between vulcanization and testing shall be four weeks and, for evaluations intended to be comparable, the tests, as far as possible, shall be carried out after the same timeinterval.
For product tests, whenever possible, the time between vulcanization and testing shall not exceed three months. In other cases, tests shall be made within two months of the date of receipt by the purchaser of the product.
8 Ageing conditions (duration and temperature)
8.1 General
The period required to obtain a given degree of deterioration of the test pieces will depend upon the type of rubber under examination.
The ageing period used should preferably be such that deterioration of the test pieces will not be so great as to prevent determination of the final values of physical properties.
The use of high ageing temperatures may result in different degradation mechanisms than those which occur at service temperatures, thus invalidating the results.
It is crucial for the best results that the temperature be kept as stable as possible. Temperature tolerances in Iso 23529 are ±1 °C up to and including 100 °C and ±2 °C for 125 °C up to and including 300 °C. However, studies have shown that a 1 °C change in temperature corresponds to a 10 % difference in ageing time at an Arrhenius factor of 2, or 15 % at a factor of 2,5. This means that two laboratories carrying out ageing at 125 °C can have ageing times which differ by 60 % from each other and still be within the specification. To get accurate results, keep the temperature as accurate as possible by placing a calibrated temperature sensor close to the test pieces and use this to set the oven so that the temperature at this position is correct. Use the correction factor from the calibration certificate to get as close as possible to the true temperature.