ZāGO
offers numerous
platings the choice of which depends upon the
screw material you are seeking to coat:
BLACK CHROME (MIL-C-14538B) Black Chrome is a hard, non-reflective
coating which is resistant to abrasion, heat and
erosion. The Black Chrome surface is a dull,
dark grey and may be waxed or oiled to darken
surface.
Thickness: As specified by drawing.
BLACK OXIDE COATING (MIL-C-13924B) Black oxide is a uniform black coating for
ferrous metals. Generally it is considered a
decorative coating and provides only very
limited corrosion protections under mild
corrosion conditions. Black oxide coatings
should normally be given a supplementary
treatment. Black Oxide is appropriate for
moving parts which can not tolerate the
dimensional change of a more corrosion-resistant
finish. It can also be used to decrease light
reflection.
Thickness: No dimensional change
CADMIUM (QQ-P-416C) Type I = No supplementary treatment
Type II = Supplementary chromate treatment
Type III = Supplementary Phosphate Treatment
Cadmium is a bright silvery white plating.
Supplementary treatments for Type II can be
golden, iridescent, amber, black or olive drab.
Corrosion resistance is very good, especially
with Type II finish. Type II is specified to
show no surface corrosion products after 96
hours (20%) salt spray exposure. Parts with
hardness greater than re-40 are stress-relieved
before cleaning and plating. Parts subject to
flexure, over RG-40 hardness are given a 375° &
25° post bake.
Type II is best for corrosion resistance and is
used as a paint base. It is excellent for
plating stainless steels that are to be used in
conjunction with aluminum to prevent galvanic
corrosion.
PASSIVATE (QQ-P-35/MIL S-500SC) Passivation is a process designed to remove
foreign metals from the surface of stainless and
corrosion resistant steels. Passivation does
not change the appearance of the base metal but
it does purify the surface and therefore
improves corrosion resistance.
Six types of passivation are available:
Type I Low temperature (70°–90°, 30
minutes)
Type II Medium temperature (120°-130°, 20
minutes)
Type III High temperature (145°-155°, 10
minutes)
Type IV For steels containing large amounts
(³0.15%) of sulfur or selenium
Type V Anodie-for high carbon martenaitis
(?) (440 steels)
Type VI Low temperature (optional)
PHOSPHATE COATING: LIGHT (TT-C-00490B) A light coating for use as a base paint
GOLD (MIL-G-45204B) Yellow to orange color depending on
proprietary process used. Will range from matte
to bright finish depending on basis metal.
Good corrosion resistance and high tarnish
resistance. Provides a lower contact resistance
and is a good conductor. Has excellent
solderability.
NICKEL (QQ-N-290A) Corrosion protective plating for steel, zinc
and zinc alloys as well as copper and copper
alloys.
Nickel will be plated to specified thickness
ZINC (QQ-Z-325C) The primary use of chromate finishes on zinc
is to retard or prevent formation of white
corrosion products on zinc surfaces.
Either a bright or dull finish is acceptable.
Bright zinc plating closely resembles bright
chromium. However, bright zinc does not have the
permanence of surface appearance. Zinc coated
steel will not rust even when exposed to
scratches because of the galvanic protection of
the zinc. On weathering, Zinc turns to a drab
grey color. Zinc should be deposited directly
on the base metal. Nickel is a permissible
undercoat if base metal is a corrosion resistant
steel. Parts having a hardness greater than
RC-40 must be given a heat treatment prior to
plating. Springs having a hardness over RC-40
must be given an after-plating baking at 375° +
25° for 3 hours.
