Author Topic: Aluminium Galling.  (Read 4680 times)

Offline Stilldrillin

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Aluminium Galling.
« on: April 06, 2009, 02:26:55 AM »
I know I shouln`t a done it......  ::)

But, I had a nice piece of 1" aluminium, and an alloy tube candle stick. So I made a chimney assembly for me Mamod.  :wave:

With an O ring around the spigot to stop dribbles.
I`m very pleased with how it fits smoothly together, without any built in wobbability factor.  :thumbup:











But, it will soon gall together!

Anyone any ideas?

My thoughts are, a smear of Coppaslip might help.

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

bogstandard

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Re: Aluminium Galling.
« Reply #1 on: April 06, 2009, 04:29:51 AM »
Your thoughts are correct David.

But it isn't galling, it will be corrosion that is the problem. With copper pipes and a nice humid atmosphere, it will start to become like a very low voltage battery (galvanic action). As you used to do with battery posts on your car, a thin smear of petroleum jelly on the slip joint should stop it causing any problems. But expect it to break out in little patches of white dust almost anywhere. After it has dried out after a run, a little polish with Mr Sheen or any other waxy type stuff should keep the shine and stop the rot appearing.

Now to explain galling in laymans terms.

When you see a nice shiny lump of ali, it looks like it is perfectly smooth. In fact, even under a fairly low powered microscope, it will look like a mountain range on the surface.

So in a piston/cylinder configuration, when the two parts rub together, with normal lubrication, gradually the mountain peaks get worn down, and the parts slide together more easily, and the more it beds in.
If you put it in there without a good lubrication film, the peaks rub together, and the friction between the two surfaces will cause them to fuse together, similar to a very low temperature welding. That is galling.

It isn't just aluminium that does it, almost all metals will gall together under certain conditions.

In fact, I use that to my advantage. You will find on my little engines, I almost exclusively use stainless cap headed fastenings. When tightened up in a metal threaded hole, or the point of a grub screw, stainless has a 'grab factor' built in (very minor galling), and it saves me having to use Loctite. In fact sometimes, on small cap screws, it is too efficient, and I round the hex out when trying to break the grip of the screw.

Even though you didn't ask for it, I hope this has explained it.

John




Offline Stilldrillin

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Re: Aluminium Galling.
« Reply #2 on: April 06, 2009, 04:40:12 AM »
Concise & to the point again John, thank you!  :headbang:


The only time it will be assembled is at steaming time.
Spending most of it`s life apart, on a shelf.......

I`m dreading that sinking feeling........ As the 2 parts take hold......  :bang:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline John Hill

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Re: Aluminium Galling.
« Reply #3 on: April 06, 2009, 04:47:30 AM »
I am not sure the Vaseline will be really effective at stopping the electrolytic reaction, you need to really isolate those two dis-similar metals. Could you manage a short stainless steel sleeve over the copper when it enter the aloy?  Rubber gromets would do the trick too but might not look that good.  Just my tuppence. :med:
From the den of The Artful Bodger

bogstandard

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Re: Aluminium Galling.
« Reply #4 on: April 06, 2009, 05:36:16 AM »
Here my thrupence worth John  :lol:

It is not to stop the electrolytic action, that would require a major rethink, and my brain hurts enough at the moment, but to stop the two parts sticking together. It wouldn't look as bad as copperslip everywhere, as David suggested.


John

Offline HS93

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Re: Aluminium Galling.
« Reply #5 on: April 06, 2009, 08:02:09 AM »
How about turning it down a bit more and superglueing a strip of clear acetate on to separate, it is very thin , Easter eggs may have some if you cannot get a sheet.

Peter
« Last Edit: April 06, 2009, 08:04:53 AM by HS93 »
I am usless at metalwork, Oh and cannot spell either . failure

Offline Stilldrillin

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Re: Aluminium Galling.
« Reply #6 on: April 06, 2009, 08:33:29 AM »
Hmmm.
Thanks guys...... I hadn`t thought about the reaction between pipes & collector base!  ::)

It is all an experiment really. Changing/ rebuilding year on year.

The pipes are Loctited into the cyl blocks, and Golden Hermatited into the collector.

Good thinking re acetate & super glue Peter!  :thumbup:

I think the thing to do, is to leave it as is, with fingers crossed & a smear of something greasy on the spigot.
Then to "re bush" any problem areas as & when.

It will probably all be redesigned again, by this time next year!  :lol:

David D

« Last Edit: April 06, 2009, 08:35:20 AM by Stilldrillin »
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!