Specification/information for Black Oxide finish callout

[SwinnyGG]

One of my ongoing tasks is reviewing, and in many cases making large changes to, my company's standard Scope of Requirements and Engineering Standards documents.

They were in a sorry, neglected state when I started almost a year ago, but are slow approaching a state where they might become useful again.

I'm in the midst of the specification set for coatings, and have had no problem specifying platings, paint, and anodizing all of which I have a lot of experience with.

However, I need to develop an internal standard callout (and a standard drawing note to match) for black oxide finish on machined and fabricated steel parts.

The existing callout from the last version of this document reads:

6.4.1: Black Oxide coatings on Ferrous Components​

6.4.1.a When 'Black Oxide' is specified for machined or fabricated components comprised of ferrous base material, the supplied coating shall conform to MIL-13924​

Two thoughts here. One, I'm used to callouts with more detailed information; the similar section for anodized aluminum parts, for example, reads:

6.4.7.a If 'Anodize XXXXXXX' is specified for machined or fabricated components made from aluminum alloys, supplied coatings shall conform to MIL-A-8625, Type II, Class 2, minimum thickness 0.8 mil unless otherwise specified. Callouts which require Anodize finishes but do not specify color shall be returned for clarification and correction. Clear anodize must be specified directly.

Two, I know that an important part of specifying Black Oxide finishes is specifying after treatment, which is not a component of MIL-DTL-13924 (which covers the processes for creating the conversion coating only, as far as I can tell)

So, for those of you using black oxide all day long, what do your callouts look like? How do you specify aftertreatment in such a way that there is a standard to compare to?

I do not have the time or budget to create my own test, results, and derived specification for aftertreatment of black oxide- so I'm trying to find an existing one that supplements MIL-DTL-13924 correctly.

 

[hydtools]

At one time, maybe still, it was known as Parkerizing.

https://en.m.wikipedia.org/wiki/Parkerizing

Ted

 

[SwinnyGG]

Black oxide and parkerizing are actually very different finish types. Parkerizing creates a layer of porous phosphate salt on the surface of the base metal. Black oxide is a conversion coating.

 

[3DDave]

I'd suggest asking over at finishing.com. Also the page

https://en.wikipedia.org/wiki/Black_oxide

seems helpful; it lists some ASTM and ISO alternatives.

I see it referenced in MS16995, which does not specify any further treatment. I don't recall having a use for it as it isn't a corrosion preventative finish.

 

[XL83NL]

Call a company speciailized in this process, ask them which standards they apply for the process, and then ask how they would like to see the call-out.

 

[Screwman1]

Unless you really need the exact MIL spec coating I would try to not use that as a call out because it cuts out a lot of firms that do commercial quality black oxide but don't meet the requirements of the MIL spec. For our black oxide parts we simply call out black oxide with the appropriate top coat ( oil (brand name if required) , wax (UV tracer if required), etc.) We always try to keep it simple on finish call outs, you can add a lot of cost and lead time as well as sourcing issues by putting unnecessary details into the call out. We deal with commercial industrial parts, your situation may differ.

 

[MintJulep]

http://www.ahkm.fi/images/AHKM_oxide_coating_web.pdf[/URL]]The most commonly used standards include ISO 11408, MIL-DTL-13924,
AMS 2485 and ASTM D769.

 

[SwinnyGG]

it cuts out a lot of firms that do commercial quality black oxide

This is the sort of problem I'm trying to avoid.

I need the MIL spec, but I don't know:

1) how to call out an appropriate after treatment- I don't want to wind up with suppliers rejecting bids or adding cost because I specify a certain brand of oil or whatever

2) How to capture my top coat requirement (which is usually just that it is dry to the touch and tack-free) without, again, adding in cost by specifying something specific.

With callouts like this I generally try to make the specification as wide as possible while still meeting the need; not being well versed in black oxide, I need to find that balance on the callout of the after treatment.

 

[3DDave]

You are somewhat stuck. If you specify a performance spec for the after treatment, that gets expensive and suppliers won't like that, plus you need to either repeat the test all the time or audit the supplier to make sure they don't change anything. If you specify an exact process then suppliers won't likely use that exact process.

 

[pylfrm]

A supplementary water displacing preservative coating such as MIL-PRF-16173, grade 3 or comparable material which will provide equal or superior corrosion protection may be specified.

Have you investigated this specification and the Qualified Products List associated with it?


pylfrm

 

[SwinnyGG]

Have you investigated this specification and the Qualified Products List associated with it?

Well now I feel pretty dumb.

The hard copy of 13924E we had on file did not contain section 6. I now have a complete copy thanks to everyspec.

This is what I needed, thanks to all who tried to help me out.

 

[pylfrm]

jgKRI,

I wonder why they mentioned Grade 3 specifically. Grade 4 seems like it might be a better match for your tack-free requirement, but I'm not sure how it compares otherwise.

If you care to share, I'd be interested to see how you end up writing the specification.


pylfrm

 

[SwinnyGG]

Grade 4 is, in fact, what I will be specifying. Transparent and non-tack is what we are after in a black oxide finishing step 99.99999% of the time.

Our internal spec will list reasons for exceptions, which I'm still working on.

The base callout will read:

Black Oxide per MIL-DTL-13924 Class 1
Supplementary Coating per MIL-PRF-16173 Grade 4