FED-STD-228A
3.1.2 The temperature shall be measured by means of a thermometer or thermo-couple mounted so as
to indicate the temperature of the specimen. However, if the container is completely surrounded by
steam or by a liquid bath maintained within the specified temperature range, the temperature of the
specimen shall be considered to be the same as that of the bath.
3.1.3 Radiation shields shall be placed between the specimen and any portions of the walls of the
container not maintained within the specified temperature limits.
3.1.4 Provisions shall be made for suspending the specimens vertically without touching each other or
the sides of the chamber.
3.1.5 Automatic temperature controls shall be used and a recording thermometer employed to record the
temperature.
3.1.6 The test chamber shall be preheated to the exposure temperature before the specimen is placed in
it. If the temperature within the container changes while the specimen is being placed in it, the container
and contents shall reach the specified temperature within 15 minutes after the specimen has been placed
in the chamber.
3.1.7 The exposure period shall start at the time the specimen is placed in the chamber. At the end of
the exposure period, the specimen shall be removed from the chamber and permitted to rest at room
temperature for not less than 16 nor more than 96 hours before determining its properties.
3.1.8 The material used for marking bench lines or other markings on the specimen shall not be
detrimental to the rubber compound.
3.1.9 Copper or brass parts shall not be exposed to the atmosphere used in the aging chamber.
3.1.10 If a liquid heating medium is used, the liquid or its vapors shall not come in contact with the
specimen.
4. CONDITIONS OF EXPOSURE
4.1 The conditions of exposure shall be as described in the detail specification. Many combinations of
temperature, pressure, and time of exposure may be used. As an aid towards standardization, it is
recommended that the temperature and pressure specified in the detail specifications be selected from
the following suggested conditions. In general, the conditions selected should be such that the
deterioration will not be so great as to prevent the determination of the final physical properties unless the
aging characteristics of the compound are known to be poor.
4.2 In the oxygen pressure test the increase in temperature from 70° to 80° C. would be expected to
approximately double the rate of oxidation of the rubber or other oxidizable material.
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