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  1. #1
    Join Date
    Jul 2006
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    215

    Acid Cleaning

    I posted this in another thread but I don't think its getting much attention so I'll just start a thread on the subject similar to my tumbler thread.

    I have more questions on the acid and want to try this out more. How would I go about self P&Oing steel? soak it in some acid and water then take it out, and dip it into baking soda water then dry it off and wipe some wd 40 onto it? Alot of the parts I sell need a nice clean finnish and some are welded on by the customer such as tabs and brackets and things. Anybody have any input? It's taking to much time now grinding mill scale off to clean up my parts. Thanks.

  2. #2
    Join Date
    Jul 2005
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    2415
    Sorry, Too busy trolling for customers to help you out.

    TOM Caudle
    www.CandCNC.com

  3. #3
    Join Date
    May 2007
    Posts
    111
    From what I have read. Use a diluted acid mix of muriactic and water. Soak overnight. Rinse with water,dry and oil. But I wouldnt use wd-40. A regular oil or even something like evaporust.

  4. #4
    Join Date
    Jul 2006
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    215
    Quote Originally Posted by Torchhead View Post
    Sorry, Too busy trolling for customers to help you out.

    TOM Caudle
    www.CandCNC.com
    ok? why bother posting that?

  5. #5
    Join Date
    Jul 2005
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    2415
    It was sarcasm. Probably wasted. Go back and review your thread http://www.cnczone.com/forums/showthread.php?t=89747

    I pretty much came up with the acid cleaning process for my commercial steel cutting business. I try to help guys with my experience. Being attacked for posting an opinion about technology related to plasma leaves me less than enthused to take time to answer questions.

    TOM Caudle
    www.CandCNC.com

  6. #6
    Join Date
    Jul 2006
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    215
    I never attacked you, I told everybody to quit jacking the thread that had a spacific question and got way off topic. And I highly doubt you came up with acid cleaning process since people have been doing it in different fields of metal work for years. The guy who got me into cnc plasma years ago told me about it but I never really looked into it much. This thread was created to be informational to not only me but users in the future who may use the search feature looking for an answer. Oh and thanks to those that have PM'ed me with good information.

  7. #7
    Join Date
    Jul 2005
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    2415
    I didn't say I invented the acid cleaning process. I came up with it for my plasma cutting business and have used it for years. I didn't invent the powder coating we use or the copper flame finish either, but I am a minority in the DIY plasma world that is willing to share the information. I had to dig it out myself and try, try and retry on a lot of the "tricks".

    The acid process is a variation of how the P & O process is done. In the PO process They run it through highly concentrated and HOT acid and the process works as fast as the rolled material is being pulled through it. Then it's neutralized and washed, dried and sprayed with a organic type oil (they used to use whale oil). It's a very nasty dirty process (and dangerous).

    The key to doing it in the small shop is to rinse it very well and dry it quickly. Even a few minutes exposed to the air and rust starts to form. It will rust naturally even after it is dry. We go straight to sanding and paint. A light spray of a wax type product to prevent rust for later welding works. For powder coating, a pre-heat in the oven will burn off wax but conventional liquid painting has to have no wax or grease.

    For informational searches I have posted multiple times about cleaning off mill scale and the advantages of acid over hand grinding. The process was discussed at the first of the other thread you said was being ignored.

    It's not hard to try it on a small scale: Just get a 5 gal bucket and put in 4 gal of water. Buy a gallon or muratic acid (dilute Hcl) and carefully (wearing eye portection and rubber gloves) pour in the acid. You don't have to mix it. Setup another bucket with some water and baking soda. Get a hose ready. Suspend the parts in the acid with aluminum or non-metalic hangers and keep checking it every few minutes. Once the mill scale has come off remove, dip in the neutralizer and then hose it off REALLY well. Any residual mill scale should rinse off. Then towel dry it and get it into a dry environment quickly. If you do get a light layer of rust you can dip in the acid for a few minutes , rinse and dry then get it to the table for gringing or coated with something that stops the rust. The things like Navel Jelly are Phosphoric or other acids that are won't burn you if you get it on your hands but are not as agressive and cost a lot compared to Muratic and water. You will find that leaving it too long will start etching the surface and amplify any pits or scratches. You can leave it a longer than just to get the mill scale off and it will start to loosen the slag on the back of the cuts. The time is not real critical but is dependant on the concentration of the acid. You can reuse the same acid over and over and refresh it by adding in more concentrate as it starts to take longer.

    I let my tank get more dilute so it tooks hours to work and just hung the product in there while I was doing other stuff.

    I tried sandblasting and for lightly rusted material it's a good process but for the sized cuttings we were doing My cabinet was too small and to low volume. To get the equipment i needed would have cost thousands.

    TOM Caudle
    www.CandCNC.com

  8. #8
    Join Date
    Jul 2006
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    215
    Thanks for the post. I posted this in a PM but it is basically what I m doing.
    I have messed around with it alittle bit in the past to clean up some rust and had to clean a garage floor with it at my old job once. I am starting to work on speeding up my production and sitting there with a grinder cleaning off the scale is just a PITA lol and too time consuming. I have started ordering P&O plate lately to aid in the production process but I still buy hot roll flat stock for some things because its cheaper than cold roll.

    So if I can find a way to "automate" the cleaning process with acid or a tumbler or something it would deffinatly help me out. I actually had a little acid left in a jug in my garage, so yesterday I took a coolwhip bowl and put some water and the little bit of acid that was left in there, put a scrap of 3/8 x 2" bar stock half way submerged in it and left it out overnight. I just went and checked it but it does not seem like it really did anything a little bit of the scale has flaked off but not much at all. I would say maybe its like 1/16 or so acid so maybe it was just too dillutted?

    The reason I ask about oiling it as well is because the parts would need a "shelf life" so I can stock up an inventory and not have to worry so much about them rusting if there on a shelf for a year or something like that (just throwing out a number), right now I'm just building parts to order but I would like to start building a decent inventory to increase turn around time. I also thought maybe after oiling wrapping the parts with plasic wrap (the industrial seran wrap stuff) to keep the moisture out maybe and keep the oil from drying up? Would wd40 do the job do you think or soemthing else?

    I also just went and bought some more acid and added a tad bit to the bowl I have setting out for the testing. I also bout a 3' section of 4" PVC pipe and attached a cap for the bottom and I have a second cap for the top that will slide on and off for a cover, I also picked up a couple small boxes of baking soda for nuturalizing the acid. So I guess well see what happens.

  9. #9
    Join Date
    Jul 2005
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    You need a higher concentration. When you drop the piece in you should start to see bubbles (small ones) on the surface of the metal. Be careful with the concentrated stuff. It will burn your skin and the vapors will send you into a coughing spasm. Never add water to acid. Add the acid to the water.

    Try a mix of about 25% (1/4 acid) to start with. I have been know to use a 50/50 mix on jobs that had to get done right away. It was outside with ventilation and a hose for running water.

    Keep the uncovered "bath" away from anything you don't want instantly rusted.

    Some of the old gunsmiths used "Rust Bluing" that was a series of building rust over a vat of acid then boiling the piece then rubbing it and doing the process over and over to get a deep blue.

    Another interesting finish to steel is to polish it nice and shiny (leave the swerl marks from the sander) and take a torch with a small tip and blue flame and heat the back of the steel. If you are very quick and careful you can get a nice range of light to dark blues and blacks. You have to pretty quickly get the finished product clear coated or the pretty colors all turn flat and brown. It works REALLY well on Stainless with reds, yellows and blues based on how long you heat. The trick is to remove the heat BEFORE you get the color you want!

    There are very few dip finishes or patinas for mild steel like there are for copper or aluminum.

    TOM Caudle
    www.CandCNC.com

  10. #10
    Join Date
    Mar 2009
    Posts
    924
    Couple of questions:

    1: Whats P&O or PO?
    2: what type of acid? (muratic?)


    Couple of ideas,

    1: use a "bubble" abrasive, it is designed to remove scale. I'll post a pic if anybody is interested.
    2: Try the "heat color trick in your oven, color starts to change around 450f on mild steels,higher on SS and hi-carbon.
    3: Use bone meal and/or wood ash mixed and packed around it to give that case hardened look.
    4: Ask plain ol Bill for help.
    www.metaltechus.com

  11. #11
    Join Date
    Jul 2006
    Posts
    215
    Well I used the pvc cement and put a bottom cap on the tube and let it dry for a couple hours, put a peice of stock in the tube i think its like a 50/50 mix maybe a little more acid than water. Lol the one thing that sticks out in my mind from high school chemistry is allways add acid to water. well needless to say I think the acid cut its way through the pvc cement and keeps bubbling out of the bottom, I keep putting baking soda on it to keep it from being a hazard but its a pain. I need to figure out a better way to seal the bottom with an O ring or something that the acid won't eat. I also have a second cap on the top to keep the fumes in I hope it dont build up pressure or something and blow off haha. I just need to go get a poly drum if I decide to stick with this.

    P&O mean pickled and oiled, you can buy steel from your supplier like that its just a few pennys per pound more than regular hot roll.

  12. #12
    Join Date
    Nov 2007
    Posts
    343
    Someone has likely said this before but DO NOT use acid inside your shop or store it in there unless you want all your nice shiny tools to have a coat of red rust all over them (don't ask how I know -OK).

  13. #13
    Join Date
    Jul 2006
    Posts
    215
    yea its sitting outside

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