BS ISO 188:2011 pdf download – Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests.
4 Apparatus 4.1 Air oven 4.1.1 General 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 10 mm from each other and, in cabinet ovens and ovens with forced air circulation, at least 50 mm from 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 specified tolerance for the specified ageing temperature (see Clause 8) for the whole ageing period. A temperature sensor shall be placed inside the heating chamber close to the samples to record the actual ageing temperature. No copper or copper alloys shall be used in the construction 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 ten air changes per hour. Care shall be taken to ensure that the incoming air is heated to within ±1 °C of the temperature of the oven before coming in contact with the test pieces. The ventilation (or air change rate) can be determined by measuring the volume of the oven chamber and the flow of air through the chamber. NOTE To ensure good precision when doing ageing and heat resistance tests, it is very important to keep the temperature uniform and stable during the test and to verify that the oven used is within the temperature limits with regard to time and space. Increasing the air speed in the oven improves temperature homogeneity. However, air circulation in the oven and ventilation influence the ageing results. With a low air speed, accumulation of degradation products and evaporated ingredients, as well as oxygen depletion, can take place. A high air speed increases the rate of deterioration, due to increased oxidation and volatilization of plasticizers and antioxidants.
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 time- interval. 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.