Chemical cleaning of alloy parts

Discussion in 'Engines' started by Brian.G, Jun 21, 2010.

  1. Brian.G

    Brian.G Forum Member

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    I have no idea where this should go, so move it needs be:thumbup:

    Its come up a lot of times and since Ill be using it on some of my own parts in preparation for anodising I decided to throw this up here.
    Consider this a test on my behalf as I needed to figure out submersion times for other work.

    The chemicals are dangerous but can be bought easily.
    I wont go into the chemistry of it here, you can read up on it if you want to, its pretty basic but the chemicals pretty nasty but like everything if your careful its ok.
    One thing, nitric acid will eat steel containers after a while so pick your storage vessels/containers with care.

    You will need caustic soda(drain cleaner) and nitric acid (70%)

    This works great for cleaning alloy castings.
    The idea is, the caustic soda will erode the alloy very slowly, and also any gunk that is sitting on the alloy.
    But, it will not erode the copper and other stuff in the alloy so this stays on the surface as 'smut', its like black power and is pretty hard to get off after the caustic soda stage.
    Thats where you need the nitric acid, this will erode everything on there but the aluminium, leaving you with a clean new looking part, and extremely close to the original dimensions where machined faces are concerned.
    The benefits of this method is total cleaning, that is, the solution can get everywhere unlike media blasting. Its also safe for cleaning complex parts that contain oil ways or air ways where trapped media could be a disaster. There is also no work/scrubbing involved doing this, just dipping times.

    Anyway, onto the job.

    The tin pictured here is about 1.5litres. I added to that around a half inch of caustic soda.

    The gearbox bracket on the left is fairly dirty and grubby as you can see,

    [​IMG]

    Add the caustic soda to the water stirring all the time, it will get hot but wont boil, leave your part in slowly, it will fizz like hell and give of hydrogen which is flammable so do it outside,

    [​IMG]

    Give it around 20min in there or until its all dark grey/black, lift out and rinse off well with water, use gloves...

    [​IMG]

    Rinsed, lots of smut present on part,

    [​IMG]

    Next onto the acid, the acid I bought was 70%, this needs to be diluted with an equal amount of water, ALWAYS add the acid to the water. It will also get warm when you do this. Mix in a high density polyethylene container, you'll see HDPE marked on some containers, use those ones as the plastic will hold the solution for 3 or 4 yrs. Dont use steel as It will oxidise it and will not contain it, aluminium will be fine too actually,

    And left into the Nitric solution, do not get nitric acid or caustic soda in your eyes, its not good at all and will keep burning.

    The reaction is minimal here this time as Nitric wont oxidise Aluminium, only the other components in it = smut on surface.

    15min is all it needs,

    [​IMG]

    And out, still looks dirty but this rinses off easy as the smut has now been removed chemically from surface and is just sitting there,

    [​IMG]

    Rinse off well and pour nitric acid solution back into your container, it can be re-used, the caustic soda can go down the drain,

    Once rinsed it will look like this>

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Not bad hey?


    And again, The chemicals used here are dangerous, use with extreme care and keep everyone away, wash down work, workplace, and tools with loads of water when your done








    Brian.
     
    erreesse likes this.
  2. pigbladder Forum Addict

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    nice...
     
  3. altern8 Forum Junkie

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    how do you know all this
     
  4. Brian.G

    Brian.G Forum Member

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    I was good at chemistry, physics and engineering at school, thats it really, all the other subjects didnt matter:lol:
     
  5. pigbladder Forum Addict

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    25 a litre on ebay ffs
     
  6. Brian.G

    Brian.G Forum Member

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    26.13euro here off a chem supplier for 2.5L, thats enough to make 5L that can be used many times:)
     
  7. Dave

    Dave Pedantic Old Fart Paid Member

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    The thread I've been waiting for Brian!:thumbup::clap:

    Did you get the acid from the north? MISTRAL?
     
    Last edited: Jun 21, 2010
  8. neil kaye Forum Junkie

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    this is like the alluminium version of electrolysis but without needing a battery and charger,truly awsome brian,this is a revelation for inlet manifolds where you just cant get in :thumbup:
     
  9. TheSecondComing Forum Addict

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    And if you're looking to remove rust from steel or cast iron, hydrochloric acid brings it up like brand new. Again, give it a quick bath in caustic soda before you rinse and let it dry - otherwise you'll get a flash of rust that you'll need to scrub off. Hydochloric is cheap as anything, but again watch your eyes, etc. - that "smoke" it gives off when you open it will condense onto any damp surface like eyes, lungs, etc, and it's not nice stuff!
     
  10. TheSecondComing Forum Addict

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    Brian, what about oily bits? I'm thinking gearbox casings, etc. Does the caustic get rid of the greasy mank or would it need a good bath beforehand?
     
  11. Trev16v

    Trev16v Paid Member Paid Member

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    Wow, this is brilliant. Thanks for posting this Brian.

    Do you think it would be okay to clean up a completely assembled gearbox like this, if applying the chemicals by brush and being careful not to go near the oil seals and so forth?
     
  12. TheSecondComing Forum Addict

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    Applying them by brush I wouldn't do, Trev - and I'm insane. Easy to dunk stuff in a bucket and leave, but if you are brushing it on it's working, and giving off fumes all the time - and you'll be breathing them!
     
  13. Mike_H Forum Addict

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    Good work, Brian! Looks new at the end.

    The man in the shed uses a caustic tank for cleaning heads - not sure if he also has the nitric acid step.
     
  14. Brian.G

    Brian.G Forum Member

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    Dave, chemical supply place in Cork, they deliver too!

    Neil, yep, all those tricky spots are easy done, just make sure to scrub part when done with water and washing up liquid, once the smut is gone you'll know any possible nitric solution remains are gone also.

    TSC, nitric will clean steel parts too, very good infact, too good even, itll totally erode them in time to soup!! The caustic seems to cut through the crud pretty good, now if it was hardcore Id say scrape off all you can maybe, but the mount was pretty cruddy and it wiped it all, as for a gearbox the oil wont be a problem, more-so the road dirt/cv baked grease maybe? Its good tack though, maybe experiment and see on real cruddy items?

    Trev, no way, as TSC said fumes, and the fact you risk flicking solution in your eyes. Ive seen many a 'dangerous' thing in my time, and this stuff still makes me weary, if it gets in your eyes, goodnight Irene!

    Mike, does he really? Great Idea now that Ive seen it first hand, makes sense too.
     
  15. A.N. Other Banned after significant club disruption Dec 5th 2

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    I tried this today on a cam cover.

    Caustic soda easy to obtain, cheap and produced the aforementioned smut (oxidation?).

    I tried to remove this with phosphoric acid (alloy wheel cleaner, having found others on the net using it) but with limited results. Is hydrocloric any use or does it have to be nitric?

    Rather than ordering off eBay, I wondered whether the smut removal products can be obtained via mainstream outlets in whichever guise (eg brick acid = hydrocloric IIRC)?
     
  16. jchn_smith New Member

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    sorry to bump an old post but i cant find nitric acid on ebay [:^(] has legislation changed on selling this stuff or am i just not looking proprely
     
  17. StuMc

    StuMc Moderator and Regional Host - Manchester Moderator

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  18. jchn_smith New Member

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    ok im gona have to own up and admit when i serched all i got was a load of warning signs which i stupidly thought that was what they were selling, i realy should learn to read stuff properly thanks and sorry for being so dumb/lazy
     
  19. StuMc

    StuMc Moderator and Regional Host - Manchester Moderator

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  20. walkinginperu Forum Member

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    would cleaning a cylinder head using this method do any damage to the cam bearings do you think?
     

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