anyone know black oxide requirements? mil-std-171 3.3.4?

I'm hoping there's some QC people in this section that might know black oxide surface treatments.

We had a job requiring black oxide (mil-std-171 3.3.4). The parts came back from out outside vendor and looked totally undercooked. The parts were barely changed in appearance. It looks like a bad gun-bluing job at best. A black sharpie would've been better. However, I can't seem to find any specific requirement for uniform appearance or color in mil-std-171 (although I have not read it cover to cover). I would think that uniform appearance and color would be implied, if not explicitly stated for any surface treatment, coating, etc...

I flagged the parts, but was overruled by the owner of the shop and said there is no appearance or cosmetic requirement...and he shipped the parts anyway. He said as long as there was a cert for the black oxide, all was good.

seems kinda shady. Especially since we seem to have consistently bad luck with our outside vendors, across the board, who screw up on heat treating, anodization, you name it. I pretty much don't trust any of our outside vendors.

of course, perhaps I'm just naive, and this is how the big bad world of conformance and contracts work.

any thoughts? thanks.

Little blurb from our quality procedures manual.... which intails the MIL standard and then some..

The coating shall cover the base metal completely. The color shall be a uniform black. A reddish, mottled finish instead of a deep, jet black
finish, as the result of too high salt concentration, is unacceptable.

The coating shall have no indication of reddish–brown or green smut.

The black oxide coating of Type 1&2, prior to application of a preservative, shall pass the oxalic acid spot test. Spot tests shall be made on at least
two test specimens to be processed concurrently with production parts.

Before testing, the Type 1 coated test specimens shall be clean and free of contaminants, or otherwise they shall be cleaned with acetone or by vapor degreasing.

Each sample piece shall have deposited, on one flat spot of the black oxide surface, three drops (0.2 ml) of a 5% solution of oxalic acid. Allow the oxalic acid to react for 8 minutes. After 8 minutes, the test panel shall be rinsed and examined for a quality coating:

(a) A black or dark brown center with a light border indicates a good quality coating.

(b) A light grey center with a light border indicates a poor quality coating.

(c) All reactions will show a light border, indicating exposure of metal around the drops. Parts should be judged only on color under the drop and
exposure of metal under the drops.

This is a management issue, not a metrology question.

Moved to Shop Management.

- Leigh

thanks. I was hoping to find some QC folks in the metrology section that would have more specific info. on black oxide specs. The shop management and owners issues seemed like it was for issues faced owners and managers.

thanks, Rossco, for the info. That seems to jibe with other info. I've found. However, seems like the name of the game is to justify how we did it, rather than doing it right in the first place.

qc_tech said:

thanks, Rossco, for the info. That seems to jibe with other info. I've found. However, seems like the name of the game is to justify how we did it, rather than doing it right in the first place.

Click to expand...

Sounds like a Quality Escape to me. What's the point of having a QA, if noted discrepancies are over ruled, not corrected, and shipped?

If I was customer paying to get black oxide parts and they showed up looking like a "blued" part, you can bet I would dumping them back on supplier with a big "WTF" regardless of paperwork is supplied.

I will venture a guess they saved some outsourcing dollars and did it in house with one of those kits that Caswell sells. I tried that myself, it won't produce the desired result if you follow instructions. Not following instructions by acid dipping to get them clean and running some parts through 4 times the parts I did came out ok. I actually talked to a government contracting officer and they said as long as my brass parts were uniform black and it won't rub off they are fine. As for your vendor I would ask them to send pictures of their process. I bet they charged you professional rate and used a homemade kit, that is what your description tells me. A lot of these government jobs aren't even inspected, if they fit, work, look ok and aren't a critical application item, they are fine and dandy.

most definitely not a black oxide kit. The parts were sent to a vendor that is a black oxide specialist with one of the bigger facilities in the area. Our PO specified no acid pre-wash (on previous parts their acid wash adversely affected a critical O.D.), so they deviated from their process...so I suspect our instructions gives them an out for less the poor result.

Only time I have seen any variance in parts if required to be pickled before blacking.

qc_tech said:

most definitely not a black oxide kit. The parts were sent to a vendor that is a black oxide specialist with one of the bigger facilities in the area. Our PO specified no acid pre-wash (on previous parts their acid wash adversely affected a critical O.D.), so they deviated from their process...so I suspect our instructions gives them an out for less the poor result.

Click to expand...

Not an expert at all on the process, I am just good at trial and error and learning by my mistakes. Mind you I was black oxiding brass. I discovered the secret to a good end result was the cleanliness of the brass before dipping. I monkeyed around for 30-40 hrs trying to figure it out. Acid was the only thing that would clean them well enough and not leave a residue as it will rinse off with distilled water. I tried a half dozen solvents and even though the part looked clean under a microscope they weren't clean enough. Most common black oxide jobs we see wouldn't pass the test I gave my finished parts when I finally had a good result. I think your right that the "no acid" mandate didn't leave the parts clean enough. The parts I did had +/- .005 tolerances on them so I didn't worry about the acid bath. Since the acid etches the surface I wonder if a soda, or bead blast would be a suitable surface preparation before oxiding? That is about the only thing I didn't try. That was the next idea if the acid didn't do the trick. I wonder if a quick dip in a highly diluted solution would be good enough with out removing too much metal.