Undoing galvanic corrosion

[Chris152]

Hope this is in the right part of the forum.

I'm trying to release the threaded steel bar from its ally sleeve. I've tried heating and hammering the little scrap bar I've inserted at the top, no success so far. I've been spraying release stuff top, bottom and in the locking screw hole.
I've read that sodium hydroxide can help. Any other suggestions? It's worth the effort as it's part of a fairly rare modelling stand, but not the end of the world if we can't get it loose - it is a large area of contact.

Thanks for any thoughts.

 

[addjunkie]

Put it in a drum filled with diesel. Leave a month and try again!

 

[Munkul]

Have you tried heating the WHOLE sleeve? It needs to be pretty hot and pretty quickly compared to the steel below. It will need oxy propane IMO.
Sodium hydroxide will just eat away at the aluminium evenly and by the time the threads come loose, there'll be nothing left at all..

 

[zzr1200]

First thing make a thick metal ring (12/14mm) and handle, which would be bolted to a very solid non movable object(your vice just isn't up to the job). I'd also clean all the exposed threads, de-rust and almost polish them, then heat it with a roofers torch until very hot then put item into a metal bucket/tube filled with oil/diesel mix, repeat several time including leaving in soak. The heating/cooling cycle may help draw the liquid up into the threads..

That is going to be a b*t*h to release.

 

[ajlelectronics]

But WHAT have you been spraying? Water Dispersants will be useless of course. The absolute "Magic potion" is 50:50 ATF and real Acetone.

 

[Munkul]

But WHAT have you been spraying? Water Dispersants will be useless of course. The absolute "Magic potion" is 50:50 ATF and real Acetone.

A k a plusgas

 

[Keithmac]

I have this battle quite frequently (steel fasteners into aluminium).

You have a right job on your hands there!.

Worst case could you split the sleeve down one side and have it welded up after you've extracted the screw?.

I always end up either heating up the aluminium housing or drilling the steel fasteners out, the latter is not an option for you though!.

Maybe Ultrasonic cleaner with some diesel or similar in it?.

You could drill a few holes down the sides to allow lubricant to wick in.

Aluminium to steel corrosion is a pain to sort out..

 

[MattF]

You could try immersing it in white vinegar for a while. Concentrate on cleaning/derusting the iron rather than the aluminium.

As mentioned, caustic will corrode/dissolve the aluminium.

 

[Chris152]

OK, thanks all. We'll have a go at immersing it in diesel for a couple of days; if that doesn't help, we'll try the heat cycle with diesel and oil.

I started cleaning the exposed threads as per yours, @zzr1200 , and rather than ally, the whole sleeve looks to be bronze. Does that change anything? (Not sure the colour will show properly in the pics.)

 

[bricol]

You don't want to be heating the steel. Heat the alloy as has been mentioned - allow will expand muchly compared to the steel, so might just break free. Even a hot air gun/paint stripping gun will make a good difference.

Clamp the steel bit in the vice, try turning, wobbling the alloy bit.

Steel into corroded alloy is rather different than steel components rusted - if it's gone that entire length, then the alloy is probably scrap.

 

[Gareth J]

Horrible scenario.

I would focus on heating the steel, not the aluminium. I know it is logical to think of heating the aluminium to expand it and let it off the threads and that may be valuable, once it's loosened a little. But as it is, focussing heat on the aluminium is more likely to end up with it melting. That's all to easy to do and the result is likely to be game over.

If you can get both ends of the steel red hot though, there's a chance it will move things enough to break the corrosion inside and let some release fluid in to help. This will need a big torch but ideally oxyfuel. You don't necessarily need the female part to expand relative to the male part to release stuck things, just that they expand differently relative to one another. As is the case with welding things onto broken studs to remove.

If you get it moving at all, be gentle, the aluminium will want to gall on all the corrosion. Work it back and forth with very light force and lots of release fluid to try to break down and "wash" out the corroded material.

If that's a hole through to the threads on the side of the casting, use it to get more fluid in and let te corroded material out. You could consider drilling other, similar relief holes if it's not too critical.

 

[Chris152]

Thanks both. Not sure if my correction from ally to bronze (post 9) is relevant, but we'll keep working at it today trying all the above. Then it's into a bath of some for a good while sort to see where that leads!

 

[mechman]

Hope this is in the right part of the forum.

I'm trying to release the threaded steel bar from its ally sleeve. I've tried heating and hammering the little scrap bar I've inserted at the top, no success so far. I've been spraying release stuff top, bottom and in the locking screw hole.
I've read that sodium hydroxide can help. Any other suggestions? It's worth the effort as it's part of a fairly rare modelling stand, but not the end of the world if we can't get it loose - it is a large area of contact.

Thanks for any thoughts.

View attachment 475895

I think holding the threaded part in the vice would give you a better chance ( not squashing the ally onto the threads).

 

[Misterg]

Not sure if my correction from ally to bronze (post 9) is relevant

I think it is *VERY* relevant - you might actually have a chance of success now!

I think the heat / diesel and/or Plus-Gas approach still stands though.

I agree that it would be well worth your while to make up something that bolts onto the flange so that you can secure it properly when applying force to the screw.

 

[Chris152]

First thing make a thick metal ring (12/14mm) and handle, which would be bolted to a very solid non movable object(your vice just isn't up to the job).

I agree that it would be well worth your while to make up something that bolts onto the flange so that you can secure it properly when applying force to the screw.

So, a piece of steel that goes around the steel bar, bolts onto the three holes in the bronze flange, then secure that to something solid. Then continue to try to turn the steel thread (heat, diesel etc.). Is that right?

 

[Gareth J]

Thanks both. Not sure if my correction from ally to bronze (post 9) is relevant, but we'll keep working at it today trying all the above. Then it's into a bath of some for a good while sort to see where that leads!

Yeah, that makes a difference. Much less fear heating the bronze than if it were aluminium. It'll glow a bit before turning into a puddle. Sorry I missed that.

 

[Ross365]

Two approaches are cropping up; i) use of a lubricant and ii) use of a dissolving agent. If you go with the lubricant first then I don't think you will get the dissolving agent to go in after the lube (oil and water won't mix).

Nobody has mentioned citric acid yet, but it's talked about on the forum all the time for rusted tools etc. I often use citric mixed with IPA to act as a wetting agent, and that might be worth considering here.

With aluminium, I think sodium hydroxide is a choice I'd avoid. Looks like a real PIA to sort out .

 

[RichardM]

I'd bolt the flange so you can use it to hold it vertical, then make a dam around the screw, pour some diesel in so it has the chance to penetrate down. When you start to see it coming out at the bottom jog the screw back and forward.
Also check the boss at the end just to ensure there isn't a grub screw in it.

 

[Misterg]

So, a piece of steel that goes around the steel bar, bolts onto the three holes in the bronze flange, then secure that to something solid. Then continue to try to turn the steel thread (heat, diesel etc.). Is that right?

That's what I would try. You can get bronze much hotter than aluminium, too.

 

[zzr1200]

OK, thanks all. We'll have a go at immersing it in diesel for a couple of days; if that doesn't help, we'll try the heat cycle with diesel and oil.

I started cleaning the exposed threads as per yours, @zzr1200 , and rather than ally, the whole sleeve looks to be bronze. Does that change anything? (Not sure the colour will show properly in the pics.)

View attachment 475901 View attachment 475902

So, a piece of steel that goes around the steel bar, bolts onto the three holes in the bronze flange, then secure that to something solid. Then continue to try to turn the steel thread (heat, diesel etc.). Is that right?

Something like this bolted to the bench/solid item and then the outer sleeve, allows bars/tubes stillsons as required and heating while mounted... The ali or bronze will expand faster than the steel, plus once it's hot you could lift a bucket of water/oil/diesel up to cover the lower threaded part causing it a contract slightly it all helps breaking free the threaded part, heat cycling and soaking is the key here, patience is an absolute must....

And don't forget a liberal amount of engine oil around the top flange just after heating it, it may draw the oil into the top section of the threads, a bit smokey, but.....