FED-STD-791D
4. Allow the wax coating to cool and harden. Cut a groove in the wax coating
with a knife to expose the masking tape.
5. Remove the masking tape to expose the area to be plated.
6. Lightly sand blast the exposed portion of the test gear using No. 30 grit
aluminum oxide.
7. Immediately following the sand blast, the gear must be rinsed thoroughly with
distilled water and placed in the nickel strike for 2 min.
8. Rinse the gear again with distilled water and place in the nickel plate bath. The
nickel is plated to a thickness of approximately 0.0025 cm (0.001 in)
(approximately 6 min).
9. Rinse the gear thoroughly with distilled water. It is important that all of the
liquid nickel solution be removed from the gear and wire holder prior to
proceeding to the chrome plate bath.
10. After thoroughly rinsing the gear in distilled water, place it in the chrome
plate bath and plate until the nickeled area is uniformly covered with black
chromium (approximately 20 min).
11. Rinse the gear thoroughly with distilled water. Remove the platers wax from
the gear.
12. Clean the gear with dry cleaning solvent and rinse with petroleum ether.
13. Dip the cleaned test gear in standard reference oil and store in suitable
container until required for test.
NOTE 3:
Organic contamination of the nickel solution will produce a wrinkled,
brittle-plated surface which flakes easily.
Organic or chloride
contamination of the chrome bath will produce a yellowish-brown plate
which is unacceptable. If contamination of either bath exists, discard the
solution and prepare new plating solution.
4.2.2 Test gear nickel strike and plating solution. Approximately 4 L of nickel
strike and plating solution is required, as follows:
a. Prepare the nickel strike and plating solution in a clean borosilicate glass beaker.
b. Add 3 L distilled water to 896 g purified crystalline nickelous chloride (NiC12)
and dissolve the crystals.
c. Add 308 g reagent grade hydrochloric acid (HC1) to the solution.
d. Add additional distilled water to make approximately 3.785 L of solution.
4.2.3 Black chromium plating solution. Approximately 3.8 L (1 gal) of black
plating solution is required, as follows:
a. Prepare the chromium plating solution in a clean borosilicate glass beaker.
b. Dissolve 1 kg reagent grade crystalline chromium trioxide (Cr03) in 3.785 L
distilled water.
c. Add 1/4 g reagent grade crystalline silver nitrate (AgNO3). Stir solution, cover
and place in a dark area for 4 h.
d. Decant and discard precipitate.
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