FED-STD-791D
d. Mark each piece for future identification by cutting small pieces from one
or more corners.
e. Attach wire hooks to each piece.
6.5 Weigh each rubber test sheet (and its hook) in air to the nearest 0.1 mg by
suspending it from the balance by its hook. Record the weights.
6.6 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 to prevent
the sheet from touching the water container. Record the weights.
6.7 Determine (and record) the displacement weight of each piece by subtracting
the weight in water from the weight in air.
6.8 Fill a 400-mL beaker with 350 mL of the sample.
6.9 Attach the rubber sheets to the suspension device, and submerge the sheets in
the sample so that the top edges are no less than 1.3 cm (1/2 in) below the surface. Make
certain that the sheets do not touch each other or contact the sides or bottom of the
beaker.
6.10 Place the beaker in oven at the required temperature for the specified time.
6.11 At the end of 72 h, remove the beaker from the oven and allow it to cool at
room temperature for 30 5 min.
6.12 Remove the rubber test sheets from the sample and wash them in ethyl
alcohol, rubbing them gently with the fingers to remove all oil from the surfaces.
Caution - wear protective gloves.
6.13 Wipe the rubber pieces dry with soft lint-free cloth, and allow them to air
dry for several minutes.
6.14 Repeat 6.5 to 6.7 to determine the displacement weight of the rubber sheets
after immersion in oil.
7. CALCULATION
7.1 Displacement weight
Weight of test sheet in air
- Weight of test sheet in water
Displacement weight
246
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