Hot Citric Acid Bath

[Onoff]

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:

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:

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

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

Slung a few other bits in at the same time:

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?

 

[Wonderweaver]

Excellent results harsh on the rust kind to the metal.
You could use that set up for bluing.

 

[Onoff]

You could use that set up for bluing.

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.

 

[Wonderweaver]

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.

 

[ronan]

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.

 

[ronan]

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.

Rust bluing is the the easiest way for someone at home to blue gun bits. You can get solutions via Brownells.

 

[Wonderweaver]

Rust bluing is the the easiest way for someone at home to blue gun bits. You can get solutions via Brownells.

Is that cold bluing?

 

[Seadog]

It does etch the surface though.

It doesn't, it just exposes the corrosion from the rust.

 

[Monkey Harris]

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.

Yup citric is quite cheap ..
in kilo bags on fleabay

 

[ronan]

Is that cold bluing?

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

 

[rikrobson]

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.

 

[Onoff]

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.

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.

 

[Screwdriver]

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.

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.

 

[pedrobedro]

Your heating tank looks like our chip fryer.

 

[garethp]

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.

 

[Onoff]

Your heating tank looks like our chip fryer.

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

 

[ronan]

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

Mc cain's politically correct oven chips i trust.

 

[slim_boy_fat]

SWMBO only does oven chips here

Buy her a hot air fryer - they're the canine's genetalia.

 

[The_Yellow_Ardvark]

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.

 

[RaceDiagnostics]

I use a cup water boiler. My 40 year old Merc tool kit.