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Author: Subject: Need advice from some Mad Chemist
Fenwick6
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[*] posted on 11-3-2021 at 12:38
Need advice from some Mad Chemist


Hello Mad Chemist,

I am a machinist with a company that rebuilds large DC mill motors. Last year we had a fire that destroyed our facility. See "Huntingdon Electric Motor Fire". We were able to salvage some items and have several tons of cast brass brush-holders that we would like to reuse as some of them are no longer available. Problem is they are coated with a well adhered blackening that I assume is baked on smoke residue. It seems it can only be removed with labor intensive bead blasting. I am looking to find a chemical dip method to restore them to bright finish. I have tried ZEP 7961 phosphoric acid cleaner but it only etches the non blackened areas and does nothing to the bulk of the residue. I believe this is due to the caustic nature of the residue forming a sort of inhibiting barrier. I have thought about heating the acid bath but I don't fave a fume hood in place and am not sure if this would have an effect. Does anyone have any ideas about other dip chemicals which may dissolve the blackening without heavy removal of the base material? I can acquire a fume hood and PPE if necessary.

Thanks in advance for you consideration and responses,
Fenwick6

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zed
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[*] posted on 11-3-2021 at 13:24


Try Acetone, or Methylene Dichloride. These solvents will dissolve most types of organic crud, while hopefully leaving the metal alone.

Such formulations usta be used in "Paint Strippers". I've seen guys spray whole house exteriors with stripper, let it sit for a while, until all off the paint blistered, and then follow up with pressure washing.

In SF, we used a local product labeled "Green's". Until a few years ago, "Jasco" offered a similar formulation.

Bare wood!

If however, the surface of the metal was oxided by excessive heat. Maybe electrolysis, and/or electroplating is the answer.

Or perhaps, a product like "Tarn-X"

[Edited on 11-3-2021 by zed]

[Edited on 11-3-2021 by zed]
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Texium
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[*] posted on 11-3-2021 at 13:41


My first recommendation would be tetrachloroethylene. It does as well or better than DCM, but is less volatile and less toxic. It is sold as brake parts cleaner, so you can buy a spray can of it at any automotive store if you just want to test it out, but it should also be readily available from industrial chemical suppliers if it works and you need a larger amount. It's the most common solvent used in dry cleaning as well.

This is the stuff you'll want: https://www.amazon.com/Brake-Maintenance-Tools-Set/dp/B08TMS...
You can tell that it's tetrachloroethylene since they adverstise it as non-flammable. The non-halogenated stuff is not the same and will not work as well.

If that doesn't work, another good option that would be very cheap would be a nice caustic soak in a concentrated sodium hydroxide bath. Only issue there is you might end up with some pitting on the parts since they are brass, but the organic crud would likely react and slough off much faster, before the parts are damaged significantly. Sodium hydroxide is used in heavy duty oven cleaners though, so that's a testament to how good it is at liquifying burnt on crud.




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macckone
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[*] posted on 12-3-2021 at 10:07


I second automotive brake or electrical parts cleaner both are basically the same.
The brake cleaner may contain other hydrocarbons but the electrical parts cleaner is usually straight TCE.

If the coating is straight carbon, not much will dissolve it without damaging the metal.
Elbow grease is sometimes the best way to remove stuff like this.

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Texium
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[*] posted on 12-3-2021 at 10:10


Quote: Originally posted by macckone  
The brake cleaner may contain other hydrocarbons but the electrical parts cleaner is usually straight TCE.
The brake cleaner that I linked to is straight TCE with no hydrocarbons.



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violet sin
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[*] posted on 13-3-2021 at 00:16


Ive found brake fluid itself useful for stripping baked on enamel from a scroll saw casing, especially if its got some scratches through the surface and isnt just attacking a perfect membrane. i wouldnt want to have to dispose of multiple tainted gallons of it though, sounds like a headache. best of luck.
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Swinfi2
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[*] posted on 13-3-2021 at 01:28


I can't see the bronze burning but carbon definitely should. Could you burn it off? That said a lot of heat will soak into the metal before its hot enough to burn the carbon so might be impractical at scale.
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Amos
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[*] posted on 13-3-2021 at 06:16


Quote: Originally posted by Texium (zts16)  
Quote: Originally posted by macckone  
The brake cleaner may contain other hydrocarbons but the electrical parts cleaner is usually straight TCE.
The brake cleaner that I linked to is straight TCE with no hydrocarbons.


TCE is trichloroethylene, while tetrachloroethylene is usually referred to as PCE or PERC (perchloroethylene)
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[*] posted on 18-3-2021 at 17:46


goto a marine shop, or ask some fisherman, or in a snob club of "sailors"... these guys have a lot of brass in their boats and known very well how to clean and polish it.
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