Neutralising citric acid.

  1. ian_in_the_midlands Member

    Messages:
    39
    Location:
    Stafford
    I have been soaking my cold rolled steel in a citric acid bath for a day then cleaning off the scale with a paint removal disk.
    If box section, I have squirted a hose pipe through the middle to wash out the acid then pulled a cloth through to dry it and clean it out a bit.
    Is this enough, or should I be doing more to neutralise the acid?
     
  2. Barlidge

    Barlidge Forum Supporter

    Messages:
    839
    Location:
    Langford, Bedfordshire, UK
    Watching with interest as I have just discovered citric for removing mill scale, I gave mine several rinses of clean water.
     
  3. TechnicAl

    TechnicAl Member

    Messages:
    6,574
    Location:
    Rotherham
    Its not that strong so water should do it but if you want to be certain a mild alkali such as bicarb or a few limestone chippings in water will neutralise it.
     
  4. hotponyshoes Member

    Messages:
    1,264
    Location:
    Somerset. Uk
    Does it need soaking first, have you tried the removal disk without the soak?

    Just flushing with plenty of water should be enough, providing you can to all the surfaces by either rotating the tube as you flush it or get a bit of rubber/foam that you can stand against a wall, push the far end of the tube against it, fill it then pull it away and let it all rush out at once.

    I think any damp left in the tube is going to cause more problems than the weak acid that might get missed. For the odd times I need to remove large areas of mill scale I use a flap disk in a 7" angle grinder. I expect you can get paint removal disks in a larger size as well or how about a floor sander with a 40g belt?
     
  5. ian_in_the_midlands Member

    Messages:
    39
    Location:
    Stafford
    I have convinced myself that it comes of easier after a soak.
    I am only doing it on a small scale. I have 9 metres or 2"x1" box to clean this weekend. About the most I have done in one go.
    I think a floor sander would be overkill, and I havn't got one.
     
  6. bigegg

    bigegg I drink and I know things. Its what I do.

    Messages:
    6,435
    Location:
    Leeds, West Yorkshire
    i dont bother - its only acidic when wet, and once it dries, it brushes off during the subsequent surface prep.
     
  7. ian_in_the_midlands Member

    Messages:
    39
    Location:
    Stafford
    I made the comment above that I had convinced myself that it is easier to get off after a soak.
    Previously I have soaked steel for 24 hours and still needed to used the angle grinder. I found some angle iron especially stubborn.
    Today I soaked some box section and after 4 hours the scale wiped off as a sludge. Really easily. No grinding required. Just like I had read about on here.
    Using exactly the same citric acid solution in the same tube.
    Maybe there are different types of mill scale? Maybe it has warmed up a bit and that made a difference?
    As I do this all from home and don't want to make any more noise than necessary, I will keep with the citric acid.
     
  8. Screwdriver

    Screwdriver Member

    Messages:
    5,035
    UK London
    Most chemical reactions are hugely affected by temperature so yes, probably a bit warmer made all the difference. You can safely boil citric incidentally. It doesn't degrade at 100C.
     
  9. TechnicAl

    TechnicAl Member

    Messages:
    6,574
    Location:
    Rotherham
    There is a difference between rust and millscale....rust is chemically formed and millscale is heat..and there are 3 oxides of Iron FeO, Fe2O3 and Fe3O4......ive forgotten which is which
     
  10. ian_in_the_midlands Member

    Messages:
    39
    Location:
    Stafford
    Definitely mill scale.
     
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