Accordion renovation

[Kiwi BlokeParticipant @kiwibloke62605]

For some reason, which I don't fully understand, I have set myself the task of renovating an elderly Italian piano accordion. It has suffered from damp storage, but was cheap and, being from one of the better makers, is worth restoring. Like some expensive Italian classic cars, it looks pretty, is full of ingenuity, some 'engineering' is rather suspect, its execution leaves a bit to be desired, and it seems to have been designed to corrode. Fortunately, it contains nothing electrical…

The thing contains slides, to select reed banks. These are thin, delicate strips of aluminium alloy, sliding in aluminium alloy channels, held captive by an aluminium alloy plate – an aluminium alloy sandwich. There's quite a bit of corrosion, which has caused the slides to be stuck. I've mechanically cleaned off as much corrosion as possible, but there will be traces of oxide left in corrosion pits in the material.

Small brass screws have been used in aluminium, with corrosion making some (so far) stuck fast.

Q 1. Is there a non-aggressive chemical treatment to 'kill' aluminium corrosion? It must not leave an oily or sticky residue. Anodising isn't practicable.

Q 2. Any suggestions for removal of corroded-in brass screws (which seem to be made from crumbly cheese)? I'm hoping to release them chemically, and preserve the screws, so not wanting to drill them out.

Q 3. Accordion repairers warn against oiling any of the mechanism because of the risk of fluff and dust build-up. In any case, oil or grease would produce too much drag in the slide mechanism, but would a PTFE-based 'dry' lubricant work, or does it eventually peel off surfaces? Ideally, something is required to prevent corrosion.

[Kiwi BlokeParticipant @kiwibloke62605]

(Don’t ask…)

[Nigel Graham 2Participant @nigelgraham2]

Aluminium-alloy is not happy with other metals in sufficiently electrolytic conditions. Combine it with mild or stainless-steel, and the aluminium corrodes instead.

I think your only recourse is careful cleaning with wire-wool followed with the plastic equivalent. There may be no harm in starting with a "Brillo" pad in warm water, so you are not putting fine aluminium-oxide dust everywhere, but you must wash in hot water, and dry, the metal immediately afterwards.

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The only safe approach for the screws is likely to be Plus-Gas (better than WD-40 as a releasing-agent, as indeed shown by these product's design intentions). Any such product of course will soak into any wood or fabric still in contact with the components.

Even then you may have to be prepared to fit new screws, assuming appropriate ones are available / can be made / can be swapped with nearest equivalents. If made of "cheese" their alloy and the aluminium alloy would seem to have been fighting it out with injury on both sides.

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If the professional repairers warn against oily lubricants, what do they suggest instead? Anything else probably will scrape off in time, inevitably; but PTFE or silicone seems the best candidates. A furniture-polish containing either of these might be suitable.

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I'd suggest experimenting with samples before touching the instrument parts themselves.

[Nick WheelerParticipant @nickwheeler]

Are you a restorer that has to put things back to how it was no matter how bad the original design, or can you change things? Replacing the aluminium channels with plastic would be an example.

We see this counter productive idea a lot with church bells, where we're frequently forced to patch up old and worn out wooden frames or fittings simply because they're old, rather than replace them with modern parts that would render the bells good for another 150years without any extra work.

[Nick Clarke 3Participant @nickclarke3]

Posted by Kiwi Bloke on 17/07/2022 11:10:13:

Q 3. Accordion repairers warn against oiling any of the mechanism because of the risk of fluff and dust build-up. In any case, oil or grease would produce too much drag in the slide mechanism, but would a PTFE-based 'dry' lubricant work, or does it eventually peel off surfaces? Ideally, something is required to prevent corrosion.

Graphite powder as used on locks, sparingly applied perhaps?

[old martParticipant @oldmart]

If you can remove the aluminium parts and separate them from any other metals, you might try anodising them. That would kill any corrosion and leave a resistant coating. Try googling "anodising at home", the bath is very simple and easy to run. The PTFE sprays would be the best lubricant, The WD40 one is not sticky to attract dust.

[Merddyn’s DadParticipant @merddynsdad]

In a previous life I used to apply a chromate conversion coat to aluminium components already part of an assembly using a 'space qualified' cotton bud and Alochrome solution as part of a rework process.

The process was controlled well enough to satisfy an Nasa inspector.

A chromate conversion coating will provide resistance to corrosion and abrasion.

[old martParticipant @oldmart]

I used to Alochrome lots of aircraft parts, because the anodising is non conductive electrically, and the Alochrome gives corrosion protection and allowed electrical bonding as protection from lightening strikes. The spark must not be allowed to jump. I would not think there is any abrasion resistance, though, you can pretty much rub it off with your finger.

[Kiwi BlokeParticipant @kiwibloke62605]

A silicone wax polish sounds like a good idea. Anyone know whether there are long-term compatability issues with Al?

I'd prefer to stay well away from hexavalent chromium compounds, so Alodyne/chrome isn't a very attractive option. Also, I'd need only a few ml and it's expensive, even in minimum quantities sold.

Graphite sounds attractive, but would it form an electrolytic cell with the Al, as it does with Cu, leading to pin-hole corrosion in plumbing pipes?

I believe that wire wool should be avoided on soft Al alloys, because tiny bits of steel get embedded into the Al – and you're off with an electrolytic cell again.

I guess the answer is to avoid damp atmospheres…

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