Removing Black Oxide Coatings

A. I thought that 50% muriatic acid would do the trick. Black oxide is usually oiled, have you tried a presoak in a hot alkaline cleaner first?

A. Grit blasting with a fine grit with a basket modification to your blast cabinet will work. You might try a tumbler with small media and a more caustic compound than normal.

After you get the black off the parts will rust fairly rapidly. What are you going to do then.

Have you considered just buying new screws?

A. I assumed that the screws would then be subjected to a new finish. The oxide seems to come off easily when it is fresh, maybe it sets up after a time. I have seen it stripped in a few minutes when black oxide is reprocessed. How about reverse electrocleaner if any smut is left (make the part the anode)?

Q. Mr. Watts, your suggestion works well, because that is what we are doing before further coating. But that contaminates my blasting system. And you will be surprised, it is not that easy to blast it off either. It takes time. Buying new screws has been tried. No one seems to make socket head cap-screws w/o black oxide! I did not know that. So I bought zinc plated screws at one time and stripped them.

A. Consider buying a small used cabinet and modify it with a basket that mounts on a shaft powered by a fractional horse about 6 RPM motor on the back of the cabinet with pillow block bearings. Use worn out grit from your regular blaster. We would put upwards of 20 lbs in the basket and run it for 4-5 min unattended. Will remove soft platings also.

I prefer it to stripping, because you do not have to bake the parts before further processing if they are hard.

A. SHC screws are readily available in stainless steel. Although the price is higher (and there is a slightly increased risk of thread galling) you will end up paying less than sandblasting for example.

A. You can use 50% (vol/vol) hydrochloric (muriatic) acid to remove the black. HCl will dissolve copper also but slowly so don't let the parts sit in it all week...

A. If you're looking to simply strip a black oxide coating from steel, 30% hydrochloric acid will work just fine. If however you are stripping from tool steel or other alloyed steels you might stay away from HCl to avoid hydrogen embrittlement.

A. Alan - A black oxide coating is easily removed by using a hydrochloric dip. It generally only takes a few minutes. Make sure that the part is thoroughly cleaned first - so that no residual oils are left in the oxide layer. Good Luck.

A. If it's a hot oxide you can use a 25-50% Hydrochloric acid pickle. If it's one of those room temperature oxide coatings it's a little more difficult. For those we have to use a mixture of Sodium Cyanide and Sodium Hydroxide at 125 °F. I wouldn't recommend this for you if you don't already have a plating line that uses Cyanide. You can tell right away by dipping a part in the Hydrochloric acid. If it comes right off you're okay. If it stays black then start blasting (sand or glass bead). Note: If it has an oil film you should degrease it first in some type of cleaner ... it keeps your acid lasting longer. The parts will rust very quickly once they're out of the acid so a rust preventative is a good idea.

Thanks for all of your help. HCl does not remove the type of black oxide we tend to come upon. That leaves cyanide, and I think we will leave cyanide as far away as possible.

So we will stick to blasting. If anyone has anything else to suggest, please don't hesitate. All suggestions are welcome, and will be tried.

Thanks, Alan.

A. Use a medium to rough grit piece of emery cloth and lots of cutting oil. I have done this myself to remove black oxide from a 3/16 inch piece of steel and it worked great.

A. Hi Roy. You are probably using the words "black oxide" in a slightly different context than the previous writers. I think the short answer is that you use oxalic acid / wood bleach [affil links], but if you search the site for "wood bleach" you'll find some threads on the subject. Good luck.

Regards,

A. Dear Mr.Partha

Is it black coating or Black oxide?
What types of coatings are you doing. Then I can be able to suggest something for stripping.

Regards,

A. The coating could be black nickel (probably unlikely), black zinc or zinc-iron, black chrome, a black PVD coating, black oxide (likely) or, my first guess, salt bath nitriding.

Please find out from the manufacturer what the coating is, or take it to a lab for XRF or auger or other analysis, and tell us what the tools are, and what you want to ultimately coat them with. Thanks!

A. Dear Mr.Partha

As Mr.Ted mooney rightly indicated ,it will take years to come to a final conclusion.
So please understand from your manufacturer what exactly it was so one can suggest how to come out of that.

Regards
Murali

A. Dear Mr Partha
1st thing if the blackodise is due to Nitriding then micro blast with #520 (SiO2/Al2O3, then polish & do PVD coating you will get good adhesion

2nd thing if blackodise is due to oxidation apply Con.HCL/HF it will remove by looks the tools you can decide but shining will goes down.

3rd thing If blackodise is due to rust(Fe2O3/Fe3O4) apply K.C-15/2, for that you can contact me.

4th thing If there is a problem there is a solution.

okay, Thanks

A. Hi Gokulraj. We appended your inquiry to a thread which discusses the issue. As you will read, it is possible to remove the black oxide, but it will not necessarily be as easy as a dip in HCl. You might be better off buying stainless steel fasteners.

Yes, zinc plating and passivation will be more corrosion resistant than black oxide.

Although no one has mentioned it yet, so I may be wrong, it seems to me that if zinc plating is unavailable on a certain type of fastener, there may be a reason -- for example the screws may be too hard to safely zinc plate without embrittlement.

Regards,

A. Hi Dylan. A lot of the black jack chain is painted or powder coated rather than black oxided. But if you're sure that yours is black oxide, just removing the wax or oil on it with strong caustic detergent should let it rust pretty quickly. Or you can blast it; the black oxide is only millionths of an inch thick.

Regards,