ISO 1432:2021 pdf download – Rubber, vulcanized or thermoplastic — Determination of low-temperature stiffening (Gehman test).
5.4 Heat-transfer medium, liquid or gaseous, which remains fluid at the test temperature and which does not appreciably affect the material being tested, as prescribed in ISO 23529. Gases may be employed as the heat transfer medium provided the design of the apparatus is such that results obtained using them duplicate those obtained with liquids. NOTE The following fluids have been used satisfactorily: a) for temperatures down to –60 °C, silicone fluids of kinematic viscosity of about 5 mm 2 /s at ambient temperature, which are usually suitable owing to their chemical inertness towards rubbers, their non- flammability and their non-toxicity; b) for temperatures down to –73 °C, ethanol; c) for temperatures down to –120 °C, methylcyclohexane cooled by liquid nitrogen (found to be satisfactory with the use of suitable apparatus). 5.5 Temperature-measuring device, capable of measuring temperature to within 0,5 °C over the whole range of temperature over which the apparatus is to be used. The temperature sensor shall be positioned near the test pieces. 5.6 Temperature control, capable of raising the temperature as per 8.2 and 8.3 and maintaining the temperature of the heat-transfer medium to within ±1 °C. 5.7 Container for heat-transfer medium, a bath for a liquid medium, or a test chamber for a gaseous medium, with means of heating and cooling the coolant to the minimum temperature required. 5.8 Stirrer, for liquids, or fan or blower, for gases, which ensures thorough circulation of the heat- transfer medium. It is important that the stirrer also moves the liquid vertically to ensure a uniform temperature in the liquid. 5.9 Stopwatch, or other timing device, graduated in seconds.
7.2 Conditioning of test piece 7.2.1 The minimum time between forming and testing shall be 16 h. For non-product tests, the maximum time between forming and testing shall be 4 weeks and, for evaluations intended to be comparable, the tests should be carried out, as far as possible, after the same time interval. For product tests, whenever possible, the time between forming and testing should not exceed 3 months. In other cases, tests shall be made within 2 months of the date of receipt by the customer of the product. 7.2.2 Samples and test pieces shall be protected from light as much as possible during the interval between forming and testing. 7.2.3 Prepared test pieces shall be conditioned in accordance with ISO 23529 immediately before testing for a minimum of 3 h at a standard laboratory temperature, the same temperature being used throughout any one test or series of tests intended to be comparable.