Electrounrusting New question,old topic

[Lee Cordochorea]

The problem with using electrolysis on the mystery metals you described is some of them will probably contain cadmium, chromium, nickel, and other metals. Those will end up in the solution, and I think they call that Hexavalent Chromium. That's very bad stuff, and it is verrry difficult to dispose of properly.

Flunked chemistry, did you?

[ed_h]

There is an ASTM standard for baking after electroplating, but I'm not sure how well it applies to electro de-rusting.

The standard requires baking at 190 degC for at least 3 hours for steels of 1200 MPa or higher.

Low strength steels aren't really susceptible to hydrogen embrittlement.

Ed

[J Tiers]

Fair enough.

Throw it in he oven and see if that helps. If so, then you have GOOD evidence.

[MattiJ]

A blade that does not hold an edge.... in shat way? does it dull? Or does the edge break off and chip? If it chips off, that is evidence for embrittlement, but if it just dulls, there is more chance that it is just softer steel.

Chips off.

[J Tiers]

Plenty of references if you check google for it. I have only personal experience from one plane iron that seemed to lose ability to hold edge after derusting. But truth to be told I can't remember how good it was even orginally 15 years ago.

http://www.misumi-techcentral.com/tt/en/surface/2009/07/0005-hydrogen-embrittlement---pickling.html

Bake should work if you choose to do it.

They give a "rate", but it is not clear what the "rate" means in actual change in material properties. After all, that is the real issue. I did google it......

As for baking.... Dunno about that "" you sort of HAVE to do the baking, or not clean/put up with rust, or have fragile steel.

The common zinc-electroplated "drywall screw" is an example of what happens with a rough plating process and absolutely no care taken to deal with embrittlement. At last I assume so, since the standard ones do not break, but plated ones from the same manufacturer have broken off as much 3 times out of 5 when driving them (they are somewhat better now).

A blade that does not hold an edge.... in what way? does it dull? Or does the edge break off and chip? If it chips off, that is evidence for embrittlement, but if it just dulls, there is more chance that it is just softer steel.

[MattiJ]

This is repeated over and over and over and over. It has been repeated so often "that everyone knows it". And I certainly am not denying it.

Has anyone actually done any testing to see to what degree this occurs? Is there any reference for it?

It makes sense, as there can be electrolysis of the water, and that end at the object to be de-rusted will be where the hydrogen goes to accept electrons. With a larger concentration of hydrogen around the object, diffusion into the metal is possible.

The question is whether it becomes a significant issue in the time needed for de-rusting. There must be some depth to which the diffusion reaches in a given time.

And, if so, why would a post-treatment baking not drive out the hydrogen?

Plenty of references if you check google for it. I have only personal experience from one plane iron that seemed to lose ability to hold edge after derusting. But truth to be told I can't remember how good it was even orginally 15 years ago.

http://www.misumi-techcentral.com/tt/en/surface/2009/07/0005-hydrogen-embrittlement---pickling.html

Bake should work if you choose to do it.

[1-800miner]

+ anything that has sharpened edge or is (was?) hardened would be suspect to hydrogen embrittlement in electrolytic cleaning. Same problem with acids.

Any lathe or mill cutters are not getting the bath. When needed I am scotchbriting the shanks clean, then trying them out .
If they are trash, into the Chinese recycle bin they go.

[J Tiers]

+ anything that has sharpened edge or is (was?) hardened would be suspect to hydrogen embrittlement in electrolytic cleaning. Same problem with acids.

This is repeated over and over and over and over. It has been repeated so often "that everyone knows it". And I certainly am not denying it.

Has anyone actually done any testing to see to what degree this occurs? Is there any reference for it?

It makes sense, as there can be electrolysis of the water, and that end at the object to be de-rusted will be where the hydrogen goes to accept electrons. With a larger concentration of hydrogen around the object, diffusion into the metal is possible.

The question is whether it becomes a significant issue in the time needed for de-rusting. There must be some depth to which the diffusion reaches in a given time.

And, if so, why would a post-treatment baking not drive out the hydrogen?

[lakeside53]

did you have to take the lid of that pot again?

[MattiJ]

It seems to be true that most "tools" and hardware will be already damaged sufficiently to be very questionable.

Any Allen, Grade 8 or other heat treated alloy steel bolts etc will be back to a state which is probably about that of ordinary A-36 steel. Relatively low strength due to being annealed. Actual will depend on alloy.

I agree that electrolysis is a good cheap solution which has less chance of impact damage.

+ anything that has sharpened edge or is (was?) hardened would be suspect to hydrogen embrittlement in electrolytic cleaning. Same problem with acids.

[1-800miner]

I have an old, ruined job box in the corner. As I sort and organize I am finding lot of useless, soft as butter tools.
They get tossed into the box for a new life as Chinese milling machines.

Much of the bolts that I will derust used to be grade eight. now they are grade two. But they are better than nothing at the moment.

One of the hard parts of this process is tossing a custom tool or jig that I spent time building and now is worthless.
And trying to figure the best layout of this new shop. How to make efficient use of the space.
The old shop grew by one piece at a time and got shoved into an available space. Organized chaos.
New one is all open space asking me what to do. Well sort of open space. I put stuff under the roof to protect it until I can figure out a permanent home for it.

Speaking of a home. This Nichols horizontal mill is in my way and if you come with a truck I will load it for you and give you a complimentary beer.

[Glug]

I found this thread about derusting from a reliable source. Check it out for yourself.

Interesting, but I'm not sure that is very authoritative, given the many other sources and how high the stakes are on this. Also, what about the cadmium and other plating? Doesn't that get stripped and end up in the water?

I don't think you should pour something on the ground unless you're comfortable growing vegetables in that spot.

[ironmonger]

The problem with using electrolysis on the mystery metals you described is some of them will probably contain cadmium, chromium, nickel, and other metals. Those will end up in the solution, and I think they call that Hexavalent Chromium. That's very bad stuff, and it is verrry difficult to dispose of properly.

Hexavalent chrome is bad stuff, but as I understand it, it is more of a problem when welding.

One of the original threads that described electrolytic de-rusting warned about the hex chrome, but the author later retracted his comments about the generation of hexavalent chrome.

I found this thread about derusting from a reliable source. Check it out for yourself.

https://www.finishing.com/340/01.shtml

seems to lay to rest the hexavalent chrome problem. I started using a plastic pail with iron an iron anode and have since moved on to a stainless soup pot for small stuff. Anode and pail all in one :>)

[J Tiers]

It seems to be true that most "tools" and hardware will be already damaged sufficiently to be very questionable.

Any Allen, Grade 8 or other heat treated alloy steel bolts etc will be back to a state which is probably about that of ordinary A-36 steel. Relatively low strength due to being annealed. Actual will depend on alloy.

Many tools which one does not initially consider to be "hardened steel", are actually somewhat hardened, as they must be to do their job. They will also be more-or-less annealed.

Anything HSS is a crapshoot. It "probably" did not get the special heat profile needed to actually anneal it, but you do not know.

So, I would use the cheapest process to attack the problem, which also promises to be effective. That is probably the tumbling in some form of mild abrasive, such as sand. I'd use a good deal of sand, to minimize the amount of pounding of one part against another. That normally does a bolt or a tool no good, especially if it may be softer than standard. It is not great for hard HSS, let alone anything else.

I agree that electrolysis is a good cheap solution which has less chance of impact damage. The problem I see is getting electrical contact. Rust is not a good conductor, to say the least. So a bucket of rusty items may, or may not, get effective contact and participate evenly in the de-rusting process.

Your best bet may be a combination. Do some tumbling, which should get off a lot of "bulk rust", and then follow up with the electrolysis for final cleaning. You may find that you will discard some items and not NEED to go further with them.

[reggie_obe]

The problem with using electrolysis on the mystery metals you described is some of them will probably contain cadmium, chromium, nickel, and other metals. Those will end up in the solution, and I think they call that Hexavalent Chromium. That's very bad stuff, and it is verrry difficult to dispose of properly.

I recall that the problem occurs when you use stainless steel for the electrodes. Have not heard that is an issue when cleaning plated materials.