Say what you want about hot caustic soda, it's seriously fast...

[rcx132]

I thought I'd put hot caustic to the test. I got my bits and bundled them into bundles so I know what goes with what and the long cable tie lets me fish it back out the stainless container. Dipped it into hot caustic soda and totally stripped in 30 min!

Note I'm doing this outdoors under a roof, on a stainless table. Fumes aren't too bad. The rust isn't removed, so a phosphoric overnight dip will sort that.

 

[Henrik]

Is there a picture missing? I can't see the end result

 

[Turbo]

Why not use washing soda & electrolysis? It's a single process that removes paint & rust plus you're not trying to work with nasty chemicals like caustic soda & phosphoric acid. Another danger with the acid is that it will dissolve good metal if you leave it in too long, electrolysis is 100% safe.

 

[slim_boy_fat]

Note I'm doing this outdoors under a roof, on a stainless table.

Hope none of your neighbours have looong arms.....

 

[rcx132]

Why not use washing soda & electrolysis? It's a single process that removes paint & rust plus you're not trying to work with nasty chemicals like caustic soda & phosphoric acid. Another danger with the acid is that it will dissolve good metal if you leave it in too long, electrolysis is 100% safe.

It's just quicker..

 

[rcx132]

It's just quicker..

With electrolytic each part needs to be wired, I've got dozens of small parts so thought I'd try hot caustic. It's also quicker, one of the bolts had thick silicone on it, that came off after two hours. I know acid can eat healthy metal. But electrolytic also has problems because of hydrogen embittlement.

There's no after photo sorry, the bits still have bad sections where there's rust, so just popped it all into a half sealed bucket of 30% phosphoric.

 

[Turbo]

It's just quicker..

I can have most things cleaned after an overnight soak in an e-bath. Sometimes if it's very rusty or my sacrificial electrodes are dirty it will need a second soak. Cheap too as it uses very little electricity & you can re-use the solution 100's of times.

 

[Turbo]

With electrolytic each part needs to be wired, I've got dozens of small parts so thought I'd try hot caustic.

I use the basket from a chip pan to hold small items, a metal sieve would also work.

 

[rcx132]

I use the basket from a chip pan to hold small items, a metal sieve would also work.

Awesome idea with the chip basket. I do have an electrolytic tank set up but I found it slow. This was just an experiment to see how hot caustic compares. The other advantage of electrolytic is there's less flash rusting when you take parts out.

 

[rcx132]

A few after photos. So this is after maybe 90 min in hot caustic soda and 90 min in phosphoric acid. The parts have come up awesome but there's still a few spots where the rust and grease were thicker. I'm going to go at them with a wire brush a bit and then put them through the process again.

I've got dozens and dozens of bits from my restoration so once I get a process going it should go quick.

Once stripped and derusted they will go into the zinc plating tank.








upload pics

 

[balmerchris]

With electrolytic each part needs to be wired, I've got dozens of small parts so thought I'd try hot caustic. It's also quicker, one of the bolts had thick silicone on it, that came off after two hours. I know acid can eat healthy metal. But electrolytic also has problems because of hydrogen embittlement.

There's no after photo sorry, the bits still have bad sections where there's rust, so just popped it all into a half sealed bucket of 30% phosphoric.

How does it cause hydrogen embrittlement?
Surely the hydrogen can't permeate beneath the surface, it's just water and soda crystals.

 

[123hotchef]

i cant see any of the pics?

but we use to have a hot dip caustic soda tank for removing carbon from pans, griddles ect worked wonders

 

[rcx132]

How does it cause hydrogen embrittlement?
Surely the hydrogen can't permeate beneath the surface, it's just water and soda crystals.

I know virtually nothing about it except that it happens, it's due to the hydrogen gas that forms on the metal, it happens in acid dips as well (hydrogen ions in the acid I think) it affects hi tensile more than mild steel. I only know what I read on finishing.com. I don't know how serious a problem it is and how long it takes before the metal is affected.

 

[rcx132]

i cant see any of the pics?

but we use to have a hot dip caustic soda tank for removing carbon from pans, griddles ect worked wonders

Maybe the photo site it down. How does your tank look? What's it made of, how's it heated and how do you deal with fumes?

 

[123hotchef]

it was kept outside, heated by eletrical element in a big stainless tank with a hinged lid

 

[123hotchef]

 

[Henrik]

A few after photos. So this is after maybe 90 min in hot caustic soda and 90 min in phosphoric acid. The parts have come up awesome but there's still a few spots where the rust and grease were thicker. I'm going to go at them with a wire brush a bit and then put them through the process again.

I've got dozens and dozens of bits from my restoration so once I get a process going it should go quick.

Once stripped and derusted they will go into the zinc plating tank.








upload pics

That looks pretty good actually

 

[Aerohead]

What do you do with the liquid when you are done?

 

[rcx132]

What do you do with the liquid when you are done?

Haven't got that far. There's nothing on any council or UK gov websites about whether it can be disposed of down the drain, though considering it's used for unblocking drains it probably can. Our local council accepts chemicals, they don't even ask what it is half the time, just put the bottle with the other bottles.

 

[Aerohead]

Sounds easy enough.

Lost a lot of the first electrolysis tank down the driveway.

Second batch of water is the base level of my rat water trap, pictures if there's interest.