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Letter 42063
MIL-P-23377 suitable for Inconel?
[Colorado]
August 29, 2006
I am reviewing an older drawing (2001) that calls for a coated
area per MIL-P-23377. I read through the MIL spec & could not
find any references to the type of material that this epoxy primer
can be applied to except aluminum. The problem is that my part is
made of Inconel 718. Can this primer be used on Inconel 718? Is there
another MIL spec that has a similar epoxy primer that is used on
Inconel 718?
Thank You!
Denny Falls
Genesis 3 Engineering - Woodland Park, CO, USA
First of two simultaneous responses -- September 1, 2006
Denny,
MIL-P-23377 should be able to be applied successfully to Inconel. It
has more to do with the preparation of the surface to produce a key
for the paint rather than the suitability of the paint.
We currently apply MIL-P-23377 to various materials including
stainless steel, titanium, nickel, aluminium (usually anodised or
alodined), alloy steels of various types and even to various
composite and plastic materials.
What you need to do is probably to either mechanically work the
surface such as alumina blast, bead blast or similar, or to
chemically etch the surface, one of the nickel etches will probably
do the job for you.
As always, when developing a process, run some test pieces first and
optimise your conditions, ensuring you get good adhesion before you
start applying it to production parts.
Brian Terry
Aerospace - Yeovil, Somerset, UK
Second of two simultaneous responses -- September 1, 2006
1) Yes, and 2) Maybe yes, depending on use, if authorized.
MIL-PRF-23377J-A1 PRIMER COATINGS: EPOXY, HIGH-SOLIDS, Paragraph
6.1:
"...These primer coatings are formulated for the unique performance
requirements of military aircraft. These requirements include
adhesion to a wide variety of metals and composites..."
Paragraph 6.1.1 Compatibility. "For some applications, and only when
authorized by the procuring activity, MIL-PRF-85582, Primer Coatings:
Epoxy, Waterborne, may be substituted for MIL-PRF-23377..."
But MIL-PRF-85582 is another primer used mostly for aluminum, with
the limitation (Para. 6.1):
"However, primer coatings containing water, such as these coatings,
should not be used on iron or bare carbon steel, nor for the wet
installation of fasteners or faying surfaces."
Inconel 718 is mostly Ni-Cr, so no flash rusting problem but maybe
limited adhesion. And, no substitution if MIL-PRF-23377 is required
for wet installation of slip fits or press fits, etc; see
MIL-STD-7179 for more information.
Note Paragraph 3.11f. "Apply over pretreated metal..." The only
referenced pretreatment suitable for non-aluminum metals and FRP is a
wash primer in accordance with MIL-C-8514.
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Ken Vlach
- Goleta, California
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