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Black oxide solutions and equipment

I am looking for info on Black Oxide (tanks & chemicals). I would like any info that you could give me regarding the building of the tanks and the make-up of the solution. I have been told that you can build your own tank and that you can make your own solution.

Thanks,

David Nay
1996

I assume you are talking about black oxide on steel parts. The solutions contain caustic soda [affil links] and sodium or potassium nitrates. Typical formulations can be found in the Metal Finishing Guidebook. These solutions operate at about 300 °F., well above the boiling point of water. Usually this means they need to be gas heated.

Since the tanks can be built of plain steel and 'a tank is a tank is a tank', there is clearly a temptation to build your own tanks. But because water boils at 212, it can 'flash' to steam if introduced improperly, which can result in a blowup or eruption of the tank contents, splashing people with boiling hot caustic! For this reason, the operation is rather dangerous and I wouldn't advocate building your own tank just to save a few dollars, but only if there is a really good reason and you were willing to do a lot of research into the details. Military handbook MIL-HNDBK-205 is a good starting point.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


1996

I know of a plater who worked in the Philadelphia Navy Yard as a welder who built his own tanks, so it is certainly possible.

If you are an engineer, you can design your own tanks, but I have seen lots of homemade tanks with funny bows in them from the weight of the liquid inside, so make sure your calculations are correct.

The calculations for a black oxide tank are that much more critical because of the high temperatures and extremely hazardous contents.

Making your own solutions:

You can make your own home brew, but the chemical suppliers have their hands full doing this, and they are professionals. Again, you picked one of the nastiest processes to try this.

I believe, from trying it myself, that no competitive advantage accrues to the finisher who tries to save money by making tanks and home brews.

While I was at M&T Chemicals, my boss once caught me adding all kinds of garbage to a Hull Cell, trying to invent a new nickel brightener. He looked at me, patiently, and said "Don't you think someone has tried that already? People (a lot smarter than me) have spent hundreds of man-years systematically testing every chemical known to man, and as soon as a new one was invented, they threw that in the Hull Cell for good measure."

There may be some advantage for the very largest plating houses to develop their own additives, but even then, they probably recruit someone who has spent time at a proprietary chemical supplier who carried away at least the basic formulas. And just like the person who uses pirated software, it's obsolete in a short time, and where do you go when you get in trouble?

  
Tom Pullizzi
Falls Township, Pennsylvania

Fabricating Tanks: