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Old 17th Nov 2015, 9:41 pm   #1
SurreyNick
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Default Removing small white oxide deposits

Hi

I have a couple of Ormond slow motion dials plus variable capacitors which would be perfect except for some small white oxide deposits on the faces and vanes.

Is there an effective, fail safe and inexpensive way to bring them back to pristine condition?

Thanks

Nick
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Old 17th Nov 2015, 11:18 pm   #2
Bazz4CQJ
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Default Re: Removing small white oxide deposits

Can you confirm what the base materials are?

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Old 18th Nov 2015, 1:08 pm   #3
SurreyNick
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Default Re: Removing small white oxide deposits

I think they are aluminium. Made in the early 1930's, but I don't think they are stainless steel. I have attached a couple of pictures. The oxidisation has worsened on the slow motion dials. Somehow a bit of damp got to them in storage.

Nick
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Old 18th Nov 2015, 1:36 pm   #4
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Default Re: Removing small white oxide deposits

This is typical of aluminium when it gets damp and might be possible to clean with supermarket "Bang".
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Old 18th Nov 2015, 5:44 pm   #5
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Default Re: Removing small white oxide deposits

Many domestic cleaning products (e.g. 'Bang' ?)are based on solutions of either concentrated hydroxide or bleach and could be aggressive.

The pointer on the slow motion drive looks like plated brass to me; the condenser looks like Al. I would think about starting by cleaning them of general dirt and grease using alcohol or perhaps white spirit. At least that will make the surfaces uniformly wettable if you follow up with something water-based.

Various people have reported good results on aluminium using alloy wheel cleaner (which is hydroxide); again, start with something well-diluted. Tomato ketchup (containing both acetic and citric acid) can do great things, trick is to try brief exposure first. Among metal polishes, 'Solvol' seems very gentle.

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Old 18th Nov 2015, 6:24 pm   #6
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Default Re: Removing small white oxide deposits

Alloy wheel cleaner is good stuff for tasks like this.
It looks like the pointer can be dismantled for polishing with T-cut.
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Old 18th Nov 2015, 6:37 pm   #7
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Default Re: Removing small white oxide deposits

I'd use a pipe cleaner doused with Brasso to remove the oxide on those vanes, then a clean pipe cleaner to finish off. You'll never completely remove the marks though as the surface of the ali will be pitted, you'll just remove the looser, 'fluffier' white stuff. The process is a bit like removing rust; remove the loose surface rust and you're still left with a corroded surface below that needs mechanically removing to get back to clean metal.
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Old 18th Nov 2015, 7:53 pm   #8
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Default Re: Removing small white oxide deposits

Solvol Autosol is indeed good stuff - sometimes too good!
It very quickly imparts a shine to aluminium, which can look out of place where a 'natural' finish is expected.
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Old 18th Nov 2015, 8:56 pm   #9
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Default Re: Removing small white oxide deposits

You could try one of the little glass-fibre-bristle brushes used to burnish PCBs.

http://uk.rs-online.com/web/p/pcb-cl...ushes/0514868/

They're _very_ mildly abrasive and would help lift the powdery corrosion away.
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Old 18th Nov 2015, 9:32 pm   #10
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Default Re: Removing small white oxide deposits

I use one of those fibre glass pens for lots of surface cleaning apps (mainly contacts or small tarnished metal parts), but I can't see how it would work too well in this instance given that the oxide is on the sides of the capacitor plates with narrow gaps in between them ie the face of the brush is at right angles to the problem other than limited access at the edges.
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Old 19th Nov 2015, 10:20 am   #11
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Default Re: Removing small white oxide deposits

I was sort-of thinking you'd be dismantling the capacitor. The moving vanes should separate from the shaft, and the static vanes sepoarate from the base/insulator if it's anything like the "Wavemaster Type 5" capacitors I rescued a while back.
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Old 27th Nov 2015, 2:16 pm   #12
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Default Re: Removing small white oxide deposits

Thanks for the advice. I feel confident in giving it a go now.
Nick
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