304 Stainless signs.....rusting! - Page 3
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  1. #51
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    Oct 2015
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    Aurora, CO
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    Re: 304 Stainless signs.....rusting!

    From what I've heard that sounds legit based on my experiences, getting stainless really hot will burn off some of the chromium content. If you notice, the problem areas are in the heat affected zones where it was cut.

    I don't recall all the properties of the different grades of stainless, but in my experience, 304 isn't meant to stay rust free. Its used a lot in exhausts where looks don't really matter. 316 tends to be the most common for cosmetic fixtures.

  2. #52
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    If that was the case only the plasma cut edges would have rusted. The signs were reblasted in a shop that only handles stainless. It has been a couple years and they all still look great. No clearcoat.

    Cutting with an abrasive waterjet would have made signs with a tighter tolerance, not at all necessary. They still would have needed shot blasting for the desired finish.

    Jim Colt Hypertherm
    The rest of the rust could just be transfered from where it originated from. Water will move rust staining around. These ARE outside. It's pretty obvious the worst spots are in the HEZ.

  3. #53
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    Re: 304 Stainless signs.....rusting!

    i am guessing you cut those on the same plasma table you cut steel (maybe water table after cutting steel), or on a steel stand off and now you are contaminated. stainless only need mixed with stainless. We pressure test items, and if we pressure test steel in our tank it contaminates the water and we see similar issues with our stainless products. gotta segregate.
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  4. #54
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    I don't think so....I am the original poster on this thread. Was looking for advice....which I got a couple years ago when it was first posted! Not sure where you see a product being promoted?

    Jim Colt
    They were referring to a spam post where a guy was trying to push electropolishing equipment, which was removed by the moderators. I can see where the misunderstanding came from.

  5. #55
    Join Date
    Nov 2012
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    481

    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by sjames View Post
    im no expert on the process, but it involves a heated bath in a nitric acid solution.

    one source lists 20% nitric acid at 140F for 30 minutes.
    Also not an expert but the aerospace company that I used to worked for called for it on EVERYTHING that they made from SS. My understanding is that by briefly soaking in strong acid, the SS forms an oxide layer that will protect it from further oxidation by weak acids, weather, etc. However they did it, the process worked WELL. I seem to recall that they used Potassium Dichromate in addition to Nitric Acid.

  6. #56
    Join Date
    Jan 2009
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    236

    Re: 304 Stainless signs.....rusting!

    I work in food process sanitary stuff ..308..316..it rusts..most of it is also magnetic

  7. #57
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    Jan 2008
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    Richmond, Virginia
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    Re: 304 Stainless signs.....rusting!

    If the signs get a little grody again, clean them off with Barkeepers Friend cleanser.
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  8. #58
    Join Date
    Oct 2014
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    Re: 304 Stainless signs.....rusting!

    The media blasting leaves a rough surface that is not ideal for stainless steel especially if you are leaving it outside. The rough surface allows contaminates that are naturally blowing around to rest on your sign and rust. If you want the look of the media blasting you will have to clean it often. To make it more ideal it would be better to go with a 400 grit finish or greater smother is always better. You should still clean it and apply a product like Sheila Shine.

  9. #59
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    Jan 2011
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    W. Wisc
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    Re: 304 Stainless signs.....rusting!

    Jim, any idea what media they used to blast this? I'm looking for finish ideas for some outdoor SS railings I will be doing on my house next summer. Right now I'm thinking glass beads, 60-120 grit to get a nice uniform light matte finish.

    Thanks,
    Dave
    -Dave
    XMT304, 22A Feeder

  10. #60
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    Re: 304 Stainless signs.....rusting!

    @ davec - recommend you explore the "why?" of 'free iron' associated with stainless steel by reading post #66 in the metallurgy thread.

    SS is typically cleaned with Nitric and HF acids to remove 'free iron', and then neutralized with baking soda {critical}. The preferred mechanical removal technique incolves are flapper and unitized wheels, with unitized being optimal.

    Glass beading SS, nor using wire brushes, is not/not recommended as the approach will induce micro pits into the SS and further promote corrosion.
    "Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi

  11. #61
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    Oct 2007
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    New Hampshire
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    Re: 304 Stainless signs.....rusting!

    It has been a few years since this was posted....I do not know what the stainless signs were blasted with. Jim Colt


    Quote Originally Posted by davec View Post
    Jim, any idea what media they used to blast this? I'm looking for finish ideas for some outdoor SS railings I will be doing on my house next summer. Right now I'm thinking glass beads, 60-120 grit to get a nice uniform light matte finish.

    Thanks,
    Dave

  12. #62
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    Jan 2011
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    W. Wisc
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    Re: 304 Stainless signs.....rusting!

    Thanks Jim, It was just a shot to see if you recalled.

    Manokai, I am fully aware of the issues with free iron on SS, the interaction of that with welding, and the need to isolate tools and equipment from plain steel work to avoid contamination of SS. My intention is to pickle all HAZ areas first, but then I need to do something to get a uniform finish as most components will be mill finish. I am going to make something very much like the "crap" that Barn118 did for fence panels in this thread: http://weldingweb.com/showthread.php...+i+like+making

    (Yes, I fully understand railing codes also.) Now looking at this, I see no possible way of polishing that all up. Plus i really don't want a bright shiny finish. There are just too many individual thin components to be able to polish all that. I suppose the "grass" could be pre-polished by making some sort of a multiple-buffing wheel setup that you could pull a rod through prior to welding, and then you just have to hit the HAZ and other affected areas after it is welded up, but my experience in finishing is to do it all at once, or it will not look uniform. So my intention was to pickle the welded areas to get them back up to full SS level protection, and then to blast the entire assembly to get a uniform, light matte finish. I would probably also pickle any other areas that seemed to be showing or indicating rust, prior to any blasting. Probably with Citristrip products to make the hazards of pickling reasonable.

    Blasting will need to be from a clean system that never touched plain steel. Right now I am thinking of using 60-120 grit glass beads based on a thread I saw on Practical Machinist on this topic. I have also considered electropolishing, but that is not easy to come by for very large parts like 3.5'x8'+ railing sections, and those sort of places only want to deal B to B, not with dorks like me.

    These are residential porch/deck railings and not in a coastal area, so salt exposure is nil. Based on the fact that Jim is saying the signs look great 2-3+ yrs later after a proper blasting with clean SS-only equipment, I am confident that that level of finish will not be a major headache in this application.

    With that said, i am still open to and exploring options. You build railing panels from many rod pieces like in the linked thread, and how would you recommend/handle a finish?

    Thanks,
    Dave

    Edit: I reviewed the link you posted, and was familiar with everything in there with the exception of the methods of testing for free iron, so thank you for that.
    Last edited by davec; 01-14-2017 at 12:19 AM. Reason: Add info
    -Dave
    XMT304, 22A Feeder

  13. #63
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    Mar 2014
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    NH
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    304

    Re: 304 Stainless signs.....rusting!

    I know Jim got his answer but for what its worth; I've seen vinyl siding, concrete and an aluminum sign "rusting", it was the high content in the water common in NH sprayed from irrigation sprinklers .
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