anyone know black oxide mil-std-171 3.3.4? parts are undercooked!

[qcboy]

I'm the QC tech at a machine shop. We just got some parts back from an outside vendor. Cert says they underwent black oxide per mil-std-171, 3.3.4. HOWEVER, our purchase order (from the owner) requested they not give the parts an acid bath before the black oxide, to preserve the tight tolerances. (on a previous job they used an aggressive acid bath that put those parts out of tolerance on the O.D.). So these parts don't even look like they've been treated. As our sole QC guy, I flagged the parts, because they way I see it, we instructed them to omit a step in their process (rather than having them CONTROL their process), and the cert isn't worth a hill of beans, if on visual inspection the parts have barely a trace of black oxide (they look just about the same as they did before we sent them out). The boss (owner) says, don't worry about it, we just have to supply the cert, that is our only obligation and that "cosmetic" appearance is not a requirement. I would think uniform application of the surface treatment would be an implied if not explicit requirement. I wouldn't sign off on the parts and the owners shipped them anyway. We're the sub-contractor..the part is for military use...I'm not putting my name on anything that we know is sub-standard. I would assume the black oxide is for corrosion and wear resistance, and if it's not complete, the part will wear/deteriorate prematurely. any opinions?

 

[MintJulep]

Good for you for not signing off.

Black oxide is pretty much useless. It doesn't provide any meaningful corrosion protection and doesn't improve the wear performance of anything.

You're boss sounds like a scum bag. You seem like you've got your act together. You should start looking for another job.

 

[qcboy]

thanks for the moral support. Unfortunately, in this economy, I"m just thankful I have a job of any sort, period. And also, sadly, the parts are so late that the customer (the direct contractor) will probably accept them without batting an eyelid. Perhaps that's how the big bad world of manufacturing really works. A wink here, and a nudge there and a a little desperation thrown on top. I document what I can and hopefully my butt is covered. I'm glad we aren't involved with aircraft parts. thanks again.

 

[mcgyvr]

There are other methods to clean the base metal prior to black oxidizing besides an acid bath.. Who's to say they didn't use those methods and that your material cert is still 100% valid.

 

[qcboy]

well...let's say you hire a house painter, and the drywall shows through their paint job on 90% of the wall surface, but they have a piece of paper that says they did everything correctly. Would you go with the piece of paper? or what you can see instantly?

The basic definitions of black oxide that I've found say a uniform black appearance is part of the end product. In this case, we have parts that look vaguely like they were badly gun-blued with barely a hint of color change. Unfortunately, nothing I can see in Mil-std-171 says explicitly how the black oxide should appear or any other test requirements to validate it was done correctly. I think there's a spec somewhere that says there is minimum coverage (percentage of surface area), but I don't believe it's specific to black oxide.

 

[mcgyvr]

Try ASTM D769 or MIL-DTL-13924 and MIL-HDBK-205
Or really what Spec was called out in the documents from your customer?

I agree with you that the coating should typically be "uniform shade of black" in appearance. But the standard you called out is really vague.

Regardless the only thing you can do now is document that you wanted to scrap the parts and you were "over ruled" by upper management in case it ever comes back to bit you.

Oh and welcome to the wonderful world we live in..money rules.

It does sound like your company needs to be a little more specific/informed on finishes so you have a little more than a rotten peg leg to stand on.

Good luck..
You seemed to have done the right thing to start with

 

[qcboy]

thanks. mil-std-171 3.3.4 is the only referenced requirement.

I think mil-dtl-13924 is more specific, but if it's all about meeting the paperwork requirement, it's all kind of moot.

I"ve learned in my time in the QC business, that if it doesn't look right, it probably isn't. I need to trust that instinct.

thanks again.

 

[redpicker]

Welcome to the world of QC. I tell people all the time that I am too concerned with the integrity of our products to get involved with quality. I understand the QA/QC folks have a job to do, it's just one I don't like. I quit the last job I had in quality (over 20 years ago) over a similar, but more egregious situation. No, I don't like to get involved in quality.

If you want to stay in QC, remember it is all about keeping your tail covered (with paperwork) and not about the actual parts.

If it is any consolation to you, the purpose of the coating, in all likelihood, is purely aesthetic. If it was for a more critical purpose, then the vendor would not have issued the certification in the first place. I'm not trying to justify the actions of management (management actions are justifications by themselves), just saying that in the big picture, this really isn't that important. If you can't buy into that, you don't belong in quality (I didn't).

rp

 

[qcboy]

Thanks, Redpicker. I've pretty much come to the conclusion that our ISO cert on the wall is b.s.. Without a doubt, there are quality policies and procedures that have real impact on the end product, but the "system" is so screwed up...the more you get into it, the more it becomes a self-serving bureaucracy that does more to obscure problems than it does to solve them.

 

[gtaw]

If the situation you described is for a military contract, it would fall under the definition of malfeasance. If the parties involved know the item does not meet the requirements, there is an obligation to notify a higher authority and if that fails to get the proper response, there is an obligation to notify the customer.

Best regards - Al