Aluminium block meets steel mounting (galvanic corrosion...?)

[skotl]

For reasons I won't bore you with (yet!) I'll be introducing a 55mm x 30mm square aluminium face to a mild steel mount in the near future.

The fit will be a bolt from the steel plate into the alu block (the black ovals will be a bolt heading from the plate, thru the block. I'm going to use a plastic sleeve thru the alu block).

This is on a bike and I'm conscious of galvanic corrosion so my plan is to;

1. Use a plastic sheath to contain the bolt as it travels thru the alu block
2. Put rubber sheet between the alu block and the mild steel sheet (which is a good idea, anyway, as there will be a lot of vibration)

Is that enough, do you think, to combat galvanic corrosion?

 

[mr migwire]

Sounds just the job mate.

 

[Parm]

Have you considered a short section of heat shrink tubing to act as a sheath?

 

[skotl]

Have you considered a short section of heat shrink tubing to act as a sheath?

TBH, I don't exactly know what I'm going to use, but I suspect it will have to be a hard compound and glued to the ally block.
This will be part of a quick release movement, where the bolt is welded to the steel plate and then I'll de-spin(?) the nut and remove the block from the bolt. So I think the plastic sheath should be glued to the alu block.

 

[skotl]

Sounds just the job mate.

This is the first time I've ever posted a question on here and somebody has said "yep - that's it"

 

[colnerov]

Hi, A coat of paint should be sufficient between the two if you need a solid mount up.

Colin

 

[Parm]

TBH, I don't exactly know what I'm going to use, but I suspect it will have to be a hard compound and glued to the ally block.
This will be part of a quick release movement, where the bolt is welded to the steel plate and then I'll de-spin(?) the nut and remove the block from the bolt. So I think the plastic sheath should be glued to the alu block.

As you have a lathe you could make a plastic sheath, interference fit. Alternatively you could bore a hole in the block the same size as some plastic conduit, or use heat shrink lined with adhesive

 

[skotl]

Cheers, chaps. I think I'll try to get to Lidl/Aldi (which one was it?) to get some of the metal paint - pretty sure that will help, too.

OK, tangential question; how bad can galvanic corrosion get and what makes it worse / less-of-a-concern?
I'm thinking that the vibration on a bike is going to make matters worse and, if I was using paint as a barrier, then I'd have to pay attention to the paint wearing off?

 

[brokenbiker]

I'll de-spin(?) the nut .

what a pleasant way to say 'undo'. dont know if you just couldnt think of the word (i get that all the time, always with really obvious words, latest was garden, i called it the outdoor room with grass in the end) or if you just wanted a new word haha

 

[skotl]

what a pleasant way to say 'undo'. dont know if you just couldnt think of the word (i get that all the time, always with really obvious words, latest was garden, i called it the outdoor room with grass in the end) or if you just wanted a new word haha

Yep! That

 

[gordon stephenson]

You will also need a insulator between the nut/washer and the ally block, Had to do lots of this sort of thing with big power station alternators on the bearing pedestal side covers etc,

 

[skotl]

You will also need a insulator between the nut/washer and the ally block, Had to do lots of this sort of thing with big power station alternators on the bearing pedestal side covers etc,

Thanks Gordon

is that literally a poly washer between the bolt and the nut?

 

[Robotstar5]

Google "top hat insulator" - link

 

[gordon stephenson]

You got it, Would be simple to make a couple of flanged tubes and insert one from each side of the ally block,(just like some suspension bushes,

 

[Shox Dr]

You are over thinking it. It wont be a problem.

 

[bigegg]

The bolts on my MTB are steel. They go into the ali frame for the pannier racks, water bottle, saddle height adjuster, handlebar clamp, and to hold the saddle on. And the brakes! It was in storage over 20 years in a damp shed and when I came to service it, I had no problems at all with corrosion .
Just galvanised bolts afaict

 

[mr migwire]

for the amount its going to be fitted / removed, i don't think you will have much of an issue with corrosion, it tends to happen over a prolonged period of time so i shouldn't worry to much bud, however i do like parms idea of machining a sleave ...more lathe time

 

[Wendelspanswick]

So long as it's not sopping wet all the time you shouldn't have much of a problem, road salts and seawater exacerbate Galvanic corrosion but if you flush with fresh water and allow to dry it minimises any degradation.

 

[rikrobson]

As long as its dry it wont corrode. And that wont be a problem , oh wait you live in Scotland.

 

[rikrobson]

So long as it's not sopping wet all the time you shouldn't have much of a problem

You been to Scotland lately???