Hot Citric Acid Bath

[Dcal]

Poo nah

If you don't wipe off the citric acid solution and just let it dry, that will protect till you need it, wash anf dry just before you do need
I used that AutoTek primer once, it was terrible, seemed to have silicon contamination in it that showed up when top coated.

I agree with your thinking, butt if he doesn't put decient paint on it what's the point?
Also leaving it longer than necessary before painting it (once and properly) seems silly.

 

[RaceDiagnostics]

That is interesting. So just allowing the part to air dry with no rinsing works ok?

I have never tried it and I have been impressed by the work you have shown on here. I always rinse and they wipe over with a dilute phosphoric acid solution to prevent flash rusting and to phosphate the surface of the steel. Do you think I am wasting my time?

I have found that I don't want to make up a batch of epoxy every time I have derusted a few bits and bobs, prefer to get a decent number of items together before doing the painting all at once, so I just leave the parts with the citric acid residue on till I'm ready, then I normally rinse and then bake them dry ahead of priming.

I read somewhere it was fine to do this.

 

[Onoff]

That is interesting. So just allowing the part to air dry with no rinsing works ok?

I have never tried it and I have been impressed by the work you have shown on here. I always rinse and they wipe over with a dilute phosphoric acid solution to prevent flash rusting and to phosphate the surface of the steel. Do you think I am wasting my time?

If it works carry on. What dilution phosphoric acid?

 

[Dcal]

I came back after a week and a half away to see how the parts I had immersed in the citric acid were getting on.
This citric acid solution was well used and was black before I put the parts in but seemed to be working OK.
This was just left outside with a gorilla tub over the top to keep the worst of the weather off it.



What I found was there was a thick white deposit well adhered to the upper exposed surfaces of the metal.
The underside was coated in a black coating that would wash off (This is what I would expect and had seen before.)
The deposit appeared to have just settled out and covered painted surfaces as well as the clean metal although it was easier to remove from the paint.





The deposit is difficult to remove and I tried boiling it to see if the compound dissolved in water.
This had some effect but needed to be scrapped off and an insoluble compound was left.

I used a needle gun on some of the bigger bits and it got it off but it was not easy and the deposit had a proper grip.



One of the small parts was damaged during dismantling and I had repaired it by welding and turning it down. The shiny bit seemed completely unaffected by the week and a half in the citric acid and the boiling and washing to remove the deposits.



This is what was left in the container after I decanted the citric acid solution.





Any chemists in tonight?
Anyone know whats going on?

Does the citric acid react with the rust and make a compound that settles out over time to coat the parts?
Does heating keep this compound in solution for longer?
Can the compound be removed or is it better to dump the mix and start again?
How long should the citric acid solution last?
If there is more rust to dissolve will the solution "wear out" sooner?

From a search on the inter-web it might be iron citrate? Also it might not form if the solution is heated and gives off bubbles when the rusty bits are immersed in the citric acid solution.

I accept I should have kept a closer eye on it but it's an interesting result and shows there is probably more going on here than it seems at first glance.

 

[Screwdriver]

Looks like you have brewed up a cocktail of metals. Willing to bet a lot of that is a plating (cadmium?) plus if you had any aluminium in there that will add to the weirdness. I use citric all the time and have never seen anything like that, got a thing in the tub now as it happens (will post pics in a mo) and I only ever put steel, iron or cast iron into the bucket.

 

[Onoff]

The new citric acid "tank" has arrived. I ditched the original (plated brass?) waste and fitted a plastic/stainless one:





Going for 19:1 for the big bath solution for the cross member.

Based on:

4:1 by volume = 250g / 1L

19:1 by volume = 250g / 4.75L

Rough, required volume is 1200 x 400 x 350 (cross member size) so 168L thus just under 9kg at 19:1.

It'll be unheated and just left with an old door/tarp over it.

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[Chillitt]

I have just found some similar 'stuff'.

 

[Sean]

It seems to be the remnants of zinc passivating.

Ive used a strong and hot citric to de zinc bolts before TIG welding they came out white and lumpy needed wire brushing.

 

[Onoff]

Should have done this back when it was warmer but I finally got around to filling the old bath up with 9kg of citric acid in water. The only hot was the 3 buckets from the tap that I mixed it up with, the rest was from the garden hose. Should have blocked the overflow off too to get a deeper fill as a couple of bits of the crossmember are poking above the surface.

Made a rough lid from a denailed / renailed pallet and a bit of siding (not quite wide enough).

In went the MK1 Focus rear cross member (gut feel it's too far gone to be bothering) and one of the rear trailing arms (salvageable I reckon).

No ideas what'll happen in this weather, guessing it might freeze? Assume the derusting will be really slow too with no heat?

 

[Ashley Burton]

@Onoff shame you couldn't of attached a coil & heated it

 

[Wallace]

If you have a pressure washer take the parts out daily and give them a thorough wash. The citric acid will not remove the paint but the pressure washer will help with that by removing the loose stuff. I had to apply a couple of coats of paint stripper in between dips to get 1965 paint off the 383 Chrysler block.

 

[ronan]

Or had an old cast iron or steel bath and stick a gas burner under it.

 

[Wallace]

My next big mix will be warm with air agitation to get some movement around the parts.

 

[Onoff]

@Onoff shame you couldn't of attached a coil & heated it

Imagine the heat loss on this weather!

 

[Onoff]

If you have a pressure washer take the parts out daily and give them a thorough wash. The citric acid will not remove the paint but the pressure washer will help with that by removing the loose stuff. I had to apply a couple of coats of paint stripper in between dips to get 1965 paint off the 383 Chrysler block.

Tbh the only paint left pretty much is where the frame touched the rear suspension turrets!

 

[The_Yellow_Ardvark]

I didn't go big.
I went tiny.

Just a small set of spanners, boiling water and 10 minutes.


The sound of it was enough to be heard out side of the shop.



10 minutes. From that to this.

 

[Ashley Burton]

Imagine the heat loss on this weather!

Yeah you would need a big fire to try & win the battle

 

[Mikey D]

Could ofdrilled a hole in bath and fitted an Emersion element

 

[dannyp]

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.

i made a fair size barrel for electrolosys a while back, i run it off various things depending what i want to acheve, if you want to be nice to things small battery charger and a bulb in series let it pull no more than a couple of amps , if you just want the rust gone arc welder flat out 100+ amps rips the crap off fairish then might not be so sympathetic tho

 

[Onoff]

Should I re title my thread COLD Citric Acid Bath?

It's cold out there, frost on the car one morning but I'm pleased with the results so far for minimal effort! No heating etc since the initial 3 hot buckets. I will as @Wallace suggests take the jet wash to it one night to hopefully deal with any stubborn paint: