FED-STD-791D
6.7.5 Insert the air tube (orifice-end down) through the condenser and into the
sample and support it so that its orifice is within 0.3 cm (l/8 in) of the bottom of the tube.
(When testing spindle oil, orifice should be within 0.6 cm (l/4 in) of the junction of the
metal square.)
6.8 Connect the source of clean, dry air (3 0.2 L/hr for spindle oils; 5 0.5 L/hr
for other oils) to the air tube and allow the air to flow for 168 h.
6.9 At the end of the specified period, shut off the air-flow, and disassemble, and
check test setup as follows:
6.9.1 Remove air tube and disconnect condenser.
6.9.2 Remove test tube from constant-temperature bath, and wipe off the outside
of the tube with a naphtha-dampened cloth.
NOTE 7:
Caution. Naphtha is flammable. Use only in a well ventilated area. Keep
all flames away from naphtha.
6.9.3 Reweigh the air tube, test tube, and contents to within 0.1 g, determine
weight of sample remaining, and compute the percentage of weight loss resulting from
evaporation of sample (see 7.1). (If the evaporation loss is greater than 8%, leakage is
present. Correct the leak, and repeat the determination, using fresh sample and new
metals squares.)
6.9.4 Using forceps, withdraw the metal squares from the test tube, and remove
the cords holding them together. (Retain the test tube and sample for further
examination.)
6.10 Prepare squares for examination as follows:
6.10.1
Using forceps, wash each square
individually
in
warm
1,1,1-trichloroethane (approximately 54C [130F]).
6.10.2 Repeat the washing, using fresh 1,1,1-trichloroethane and scrubbing the
squares with the short-bristled brush, until the 1,1,1-trichloroethane shows no additional
discoloration, and allow the squares to air-dry.
6.11 Examine each square as follows:
6.11.1 Reweigh each square to the nearest 0.1 mg and compute (in mg/cm2 of
surface) the change in weight of each square (see 7.2).
6.11.2 Using the 20-power microscope, carefully examine each square, and note
any evidence of pitting or etching.
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