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Thread: Passivating stainless at home...

  1. #1
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    Default Passivating stainless at home...

    I want to make some arty bits in 304 stainless to add to my garden products range, they will be plasma cut, some will be welded.

    I know i need to keep a set of tools strictly for stainless to stop iron contamination and also use stainless wire brushes etc.

    I have been told i need to passivate the edges to stop rust - i cant get a brush wheel or disc in to these edges due to the design, what is the best way to achieve this?

    All of my stuff so far is plain mild steel so this is a learning curve

    I have got stainless MIG wire and also know i need 98/2 gas at a minimum, these are basket brackets so not stairs or handrails etc.

    The surface finish desired is achieved by using a cup-brush in the grinder, a bright, swirly effect.

    Parts vary in size but generally 18" dia or so, 1/8" thick or less.

    Any suggestions

    Thanks

  2. #2
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    Would you show a pic of the stuff?Scratches are always a problem compared to polished surfaces. Would you consider sending it for electro polishing.

  3. #3
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    I would try googling passivating SS. Citric acid can be used which is more environmentally friendly than other acids, but I don't know the strength, temperature or pretreatments required.

  4. #4
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    Its stuff like this...



    Can't really afford to add any treatment that i can't do myself.

  5. #5
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    Quote Originally Posted by old mart View Post
    I would try googling passivating SS. Citric acid can be used which is more environmentally friendly than other acids, but I don't know the strength, temperature or pretreatments required.
    Yes found stuff about citric, its easy to get hold of too, seems 4-10% by weight as a guide. Not found out yet how to actually do it

  6. #6
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    They make special passivating acids and coming from darkest third world S Africa we dont care about the environment.I soppose it would be safer to do that in 316 seeing that it has rough plasma cut edges and grind marks on the flat areas that would soak up salt if its in a seaside environment. Looks good.

  7. #7
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    That's a very nice piece, Dave.

    Citric acid in powder form is easy to find and easy to dispose of. It's used in cooking so no hazards involved. I get five pound bags for periodic cleaning of my dishwasher (keeps the spray holes and impeller from plugging up with mineral salts).

    -js
    There are no stupid questions. But there are lots of stupid answers. This is the internet.

  8. #8
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    I have used phosphoric acid but maybe that is not what you need.

    -Doozer
    DZER

  9. #9
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    Thanks for the compliments guys,

    I think it can be done with Nitric, Phosphoric and a couple of other acids but for a home setup i think the citric acid is looking best.

    I have also been looking electro-passivation where you pass a current between a carbon fibre brush wet with acid and the work, it seems easy to set up and pretty fast too, might take that further and see what it does.

    Anyone know if white vinegar/acetic acid would remove the plasma cut edge? I know it removes mill-scale pretty well but not tried much else with it

  10. #10
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    You could keep the acid in a polypropylene container with a lid, and it would probably work for six months or more. Passivating SS will not use up the acid fast as the actual amount of chemical reaction each time is tiny. A good soak in a detergent followed by a thorough rinse in running water should suffice before the passivating, then another rinse and a final dip in hot water to finish off.

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