Hot Citric Acid Bath

  1. Onoff Member

    Messages:
    672
    Location:
    Sevenoaks, UK
    After reading on here that Deox-C is likely citric acid with detergents I thought I'd have a go. I love Deox-C but not the price. So off to Wilko for 3 packs of citric acid at
    £1.75 for a 250g pack:

    IMG_20190820_114800411.jpg

    Dug out an old hot tank I made for PCB plating about 30 years ago. Random element and a cylinder stat in the side holds it all at a steady 70degC:

    IMG_20190820_115025871.jpg

    Main use today was to free up a seized bearing and derust a pulley assembly on the grass box of my ride on mower.

    IMG_20190820_134645739.jpg

    Works a treat, 5.5hrs in it's hot bath & nearly clean enough for masking and priming. Seized pulley lovely and free:

    IMG_20190820_183127007.jpg

    Slung a few other bits in at the same time:

    IMG_20190820_195616741.jpg
    Deffo a goto process for me now. Tbh smells like the Deox-C process. Did wonder about adding a squirt of Fairy to the mix for it's detergent properties?
     
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  2. Wonderweaver

    Wonderweaver Member

    Messages:
    283
    Location:
    Manchester
    Excellent results harsh on the rust kind to the metal.
    You could use that set up for bluing.
     
  3. Onoff Member

    Messages:
    672
    Location:
    Sevenoaks, UK
    How? I've only ever blued by heating the steel then quenching in oil or sawdust. Had a bottle of gel years back for gun barrels too thinking about it.
     
  4. Wonderweaver

    Wonderweaver Member

    Messages:
    283
    Location:
    Manchester
    Yeah lots of videos on YouTube from pro bluing guys. They heat the bluing solution with gas and control the heat but you could do it with a thermostat and coil. Certainly no expert but looked into it once. There's a site in the UK that sells the chemicals.
     
  5. ronan

    ronan Forum Supporter

    Messages:
    8,960
    dublin
    I bought a rusty triumph crank off ebay for next to nothing, and gave it the citric acid bath treatment. Its great. I recommend the citric acid to anyone who wants to get rid of rust. It does etch the surface though.
     
    Parm likes this.
  6. ronan

    ronan Forum Supporter

    Messages:
    8,960
    dublin
    Rust bluing is the the easiest way for someone at home to blue gun bits. You can get solutions via Brownells.
     
  7. Wonderweaver

    Wonderweaver Member

    Messages:
    283
    Location:
    Manchester
    Is that cold bluing?
     
  8. Seadog

    Seadog Forum Supporter

    Messages:
    4,517
    Location:
    NE London - UK

    It doesn't, it just exposes the corrosion from the rust.
     
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  9. monky harris Member

    Messages:
    625
    Location:
    northampton nn5
    Yup citric is quite cheap ..
    in kilo bags on fleabay
     
    ronan likes this.
  10. ronan

    ronan Forum Supporter

    Messages:
    8,960
    dublin
    Not as such, you warm the part up with a heat gun or similar, suppose you could immerse the part in boiling water, and apply the solution allowing the part to rust. The rust is then converted to black by dipping the part in boiling water and it turns to magnetite.

    https://www.brownells.co.uk/4-oz-EXPRESS-BLUE-1-MARK-LEE-575200004
     
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  11. rikrobson

    rikrobson Member

    Messages:
    3,708
    Location:
    Perth, Scotland
    So what is the benefit of heating the citric acid bath? Either use a citric acid bath or use electrolysis. A few amps @12v would be better than heating the water energy wise.
     
    Hopefuldave likes this.
  12. Onoff Member

    Messages:
    672
    Location:
    Sevenoaks, UK
    I just wanted rapid results is why I heated it plus a bit of "just for the Hell of it" as I'd only ever done Deox-C cold. I've used electrolysis too albeit only with a 24vdc 5A supply and washing soda solution. Want to try a big old arc welder!

    I did wonder how much energy I was using but then I started off with hot water from the tap and yesterday was pretty warm and the tank had a lid on. It wasn't boiling just maintaining 70degC. I reckon you could keep a big citric acid tank warm on a hot day for free using a thermo syphoning solar thermal or PV panel feeding an element.

    Whatever, hotter is quicker.
     
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  13. Screwdriver

    Screwdriver Member

    Messages:
    5,011
    UK London
    Heat almost always accelerates virtually any chemical process. Having said that, cold bluing is a chemical process entirely different from so called hot-bluing so even if you heat up a cold blue solution (Selenium dioxide) it's still a "cold blue" finish.

    With citric, I was surprised to discover while I was researching the process that heat does not break down the organic acid which I had assumed but (iirc) you can pretty much take it up to a boil without affecting it. On the other hand ramping up the amps in electrolysis does affect the result quite dramatically so rather than encouraging Iron ions to waft over to replace Iron oxides in the workpiece, you're ripping them off and splattering them instead. The upshot is greater erosion to the workpiece as less of the new Iron is bonding to the cleaned surface. Low and slow is the best way with electrolysis, heat does help as usual but ideally not by using a higher current to generate it.
     
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  14. pedrobedro

    pedrobedro Man at Matalan

    Messages:
    9,805
    Location:
    CX Derbyshire
    Your heating tank looks like our chip fryer.
     
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  15. garethp Forum Supporter

    Messages:
    832
    sw scotland
    Another vote for heat speeding it up. I use a cheap fish tanker heater and turn it off when moving stuff in or out of the tank in case I knock the glass housing.
     
    Wallace likes this.
  16. Onoff Member

    Messages:
    672
    Location:
    Sevenoaks, UK
    It was that long ago I can't remember where the ali box came from nor the element! Think I bought the stat new. Vaguely remembered the TIG on the box looked good and watertight and it was.

    SWMBO only does oven chips here :(
     
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  17. ronan

    ronan Forum Supporter

    Messages:
    8,960
    dublin

    Mc cain's politically correct oven chips i trust.
     
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  18. slim_boy_fat

    slim_boy_fat Forum Supporter

    Buy her a hot air fryer - they're the canine's genetalia. :thumbup:
     
    ronan likes this.
  19. The_Yellow_Ardvark

    The_Yellow_Ardvark If in doubt ask. Same rules for everyone

    Messages:
    10,858
    Location:
    A Padded Cell.
    The British heart foundation do a good range of deep fat fryers what are great for.

    Hot caustic baths.

    Hot washing soda de greasing.

    Hot Citric acid baths.

    For electrolysis rust remover tanks I have done hot and cold.
    Hot for quick results, cold for nice slow finish. You get a nice black oxide finish if you go slow.
     
  20. I use a cup water boiler. My 40 year old Merc tool kit.

    [​IMG]

    [​IMG]
     
    Dr.Al, Turbo, indy4x and 2 others like this.
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