MIL-DTL-45204D
correspond as nearly as possible to those affecting the significant surfaces of the articles
represented. For barrel plating, rod specimens shall be used approximating the dimensions of the
parts contained in the barrel, but of a size that can be easily separated from the bulk of the
product.
4.4.3.1.1 Separate specimens for hardness. When separate specimens are prepared for hardness
tests they shall be approximately 0.5 by 1 by 0.04 inch. The specimens shall be plated
concurrently with the articles represented plus additional plating under the same conditions to a
plating thickness necessary to accurately determine the Knoop hardness number. Plating
thicknesses for measuring hardness shall be as listed in Table V. All specimens shall be
overplated with at least 0.0005 inch of nickel or copper.
TABLE V. Hardness vs. minimum plating thickness.
Hardness (Grades)
Minimum Plating Thickness
Grades A and B
0.002 inch
Grades C
0.001 inch
Grades D
0.0005 inch
4.4.3.1.1.1 Frequency of hardness test using separate specimens. Hardness testing of deposit
(gold plating) shall be determined initially on a weekly basis and should be continued until
process stability and control are demonstrated (see 4.6.3). Documented process performance
(data) shall be the indicator that the process is in control. Unless otherwise specified in the
contract or purchase order (see 6.2), once the hardness test data is in conformance with the
hardness range specified for the purity (type) and hardness (grade) designation, the frequency of
the test can be revised to allow adjustment based upon process history. Once there is evidence
that the process is stable and in control, the frequency of the hardness test shall be preformed on
a monthly basis, unless there is evidence that the process is no longer in control (see 4.8). If data
indicates that the hardness is out of range, the weekly test should be reinstituted until the process
is stable and in control.
4.4.3.1.1.2 Frequency of testing versus process control. The hardness of the deposit is directly
related to the condition of the bath. Process control procedures and process parameters have
been developed by the suppliers of the chemical plating solutions to ensure that the plated
products will meet the requirements of the military specification. Process control recommended
by these suppliers involve measurement of the gold content, evaluation of the pH, verification of
solution density, and analysis of the alloy hardening additives and other metal impurities in the
bath. A spectrographic analysis of the electrodeposited gold coating will confirm that the purity
of the deposit relates to the composition or purity specified for use (see 3.6.7 and 4.6.7).
NOTE: These process controls assure that the process and product remain consistent at each
plating facility. With adequate control, the purity and hardness of the plated deposits will be
consistent, and testing once a month will be sufficient to assure that the plating will perform as
intended.
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