FED-STD-791D
6.4.4 Determine original volume of silicone test specimens.
6.4.4.1 Weigh each rubber test specimen and its hook in air to the nearest 0.1 mg by
suspending it from the balance by its hook. Record the weights.
6.4.4.2 Reweigh (to the nearest 0.1 mg) each sheet while suspended in distilled water at
room temperature, being careful to remove all air bubbles from the sheet and prevent the sheet
from touching the water container. Record the weights.
6.4.4.3 Determine (and record) the displacement weight of each piece by subtracting the
weight in water from the weight in air.
6.5 Testing.
6.5.1 Fill a 600-mL beaker with 500 mL of the oil sample.
6.5.2 Attach the rubber specimen to the suspension device, and submerge the sheets in
the sample so that the top edges are no less than 0.635 cm (1/4 in) below the surface. Make
certain that the sheets do not touch each other or con-tact the sides or bottom of the beaker.
6.5.3 Place the beaker in the oven at 121 1C (250 2F) for 96 h.
6.5.4 Insert a thermocouple in a glass thermocouple holder and place assembly into oil.
The temperature of each oil should be recorded during the test.
NOTE 1:
Test liquids must not be reused.
6.5.5 At the end of 96 h, remove the beaker from the oven and allow it to cool at room
temperature for 30 5 min.
6.6 Post test determination of physical properties.
6.6.1 Remove the rubber test specimens from the sample and wash in a fresh beaker of
methyl alcohol, then rub gently with the fingers to remove all oil from the surface and rinse with
a jet spray of methyl alcohol. Caution: Wear protective gloves.
6.6.2 Allow the rubber pieces to air dry for several minutes.
6.6.3 Volume swell.
6.6.3.1 Measure the displacement weight of the rubber test specimens per 6.4.4
6.6.4 Hardness.
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