FED-STD-228A
Method 4021.1
18 APRIL 2014
AIR PRESSURE TEST, INSULATION AND SHEATH
1. SCOPE
1.1 This method is intended for use in determining the effect of elevated temperature and air pressure on
rubber and rubber-like insulation and sheaths of insulated wire and cable. This test is not recommended
for compounds that have not been specifically designed to withstand elevated temperatures in service.
The test is sensitive to small temperature variations.
2. SPECIMEN
2.1 The specimen should be as described in methods 3021 and 3031 or other method of test required for
determining the amount of deterioration, 4.2.
3. APPARATUS
3.1 The apparatus shall be as follows:
3.1.1 An air-pressure chamber consisting of a metal vessel designed to maintain an internal atmosphere
of air under uniformly controlled pressure and temperature as required in 4.1. The size of the chamber
shall be such that the specimens may be suspended vertically therein without undue crowding and
without touching each other or the sides of the chamber. Provisions shall be made for rapid opening and
closing of the apparatus for introduction and removal of specimens. Two suitable designs are shown on
figures 4011A and 4011B.
3.1.2 A pressure gage attached to aging chamber for registering the pressure.
3.1.3 A safety valve, attached to chamber, set for release at approximately 200 pounds per square inch
pressure.
3.1.4 A source of heat which is optional shall be located outside of the aging chamber proper.
3.1.5 The heating medium is optional but a liquid medium is preferred because of more rapid heat
transfer.
Caution: Special safety precautions are necessary if oil or other combustible organic fluids are used as
the heating medium because of danger of fire or explosion. When the design shown on figure 4011A is
used, the entire chamber shall be immersed in the heating medium. If air is used, the following special
precautions shall be taken in order that accurate, uniform heating is obtained in all parts of the aging
chamber: (1) The heated air shall be thoroughly circulated around the vessel by means of mechanical
agitation, (2) baffles shall be used as required to prevent local overheating and dead spots, and (3) the
preferred location of the temperature control shall be adjacent to the recording thermometer.
3.1.6 A thermo-regulator for automatic temperature control of the heating medium.
3.1.7. A recording thermometer shall be located in the heating medium during the test. Preferably the
thermometer bulb should be close to the pressure chamber but not touching it. If air is used as the
heating medium, an actual check of temperature shall be made by means of maximum reading
thermometers placed in various parts of the oven housing to verify the uniformity of heating.
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