MIL-DTL-13924D
3.6 Alkaline oxidizing (class 4). The black coating of class 4 shall be
processed in accordance with instructions furnished by the suppliers of the raw
materials and the resulting coating shall conform to the applicable requirements of
this specification.
3.7 Coverage and color. Class 1, 2, 3, and 4 coatings
(see 1.2) shall cover the
basis metal completely and shall pass the smut test. The
color shall be a uniform
black. A slight amount of smut, which is inherent in the
process, shall not be
cause for rejection. There shall be no indication of any
reddish-brown or green
smut when tested as in 4.4.1. Smut "spottiness" shall be
classified as
unsatisfactory requiring reprocessing.
3.8 Oxalic acid spot test (class 1, 2, and 3). The black oxide coatings of
classes 1, 2, and 3, prior to the application of a preservative, shall pass the
oxalic acid spot test for a good quality coating (figure 3) as specified in 4.4.2.
3.9 Resistance to salt spray (fog) (class 4 AISI type 300 series corrosion
resistant steel only). The black coating, of class 4 (300 series only), prior to
the application of a preservative, shall show no signs of corrosion after 96 hours
of exposure in the salt spray test (see 4.4.3).
3.10 Hydrogen embrittlement relief treatment. Steel parts that are surface or
through hardened at 40 HRC and above shall be given a hydrogen embrittlement relief
treatment after application of the oxide coating. Coated springs or other parts
subject to flexure shall not be flexed prior to the embrittlement relief treatment.
If an embrittlement relief treatment is required, it shall follow the chromic acid
rinse. The embrittlement relief treatment precedes the supplementary preservative
treatment.
3.11 Supplementary preservative. Materials for supplementary preservative
treatments and methods of application shall be in accordance with the applicable
requirements of the end item specification, or as otherwise specified. Unless
otherwise specified, the supplementary preservative treatment shall be applied to
the clean and dry parts immediately after the final stage of processing.
3.12 Workmanship. The surface of the coated part shall be uniform in appearance
and free of visible coating defects, such as blisters, pits, roughness, nodules,
burning, cracks, or uncoated areas, and other defects that will affect the function
of the coating. The coated parts shall be clean and free of damage.
4.
VERIFICATION
4.1 Responsibility for inspection. Unless otherwise specified in the contract or
purchase order, the contractor is responsible for the performance of all inspection
requirements (examinations and tests) as specified herein. Except as otherwise
specified in the contract or purchase order, the contractor may use his own or any
other facilities suitable for the performance of the inspection requirements
specified herein, unless disapproved by the Government. The Government reserves the
right to perform any of the inspections set forth in this specification where such
inspections are deemed necessary to ensure supplies and services conform to
prescribed requirements.
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