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Old 27th Jun 2019, 11:56 am   #1
Radio_Dave
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Default Polishing aluminium

Hi,

I'm restoring a vintage desk fan and would appreciate any tips on how to remove the corrosion and polish the aluminum fan blades to a high shine.

Regards
Davids
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Old 27th Jun 2019, 12:11 pm   #2
G6Tanuki
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Default Re: Polishing aluminium

The spidery "snail tracks" are very difficult to get rid of because the corrosion goes somewhat more than just skin-deep.

I would start by using fine [1200] Wet&Dry paper - wet - and lots of elbow-grease!

Then something like Solvol Autosol once you've got back to good metal.
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Old 27th Jun 2019, 1:01 pm   #3
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Default Re: Polishing aluminium

That looks like it goes deep and is indicative of poor grade aluminium sheet in the first place. Be careful, the stuff may be seriously lacking strength n the affected areas.

David
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Old 27th Jun 2019, 1:08 pm   #4
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Default Re: Polishing aluminium

Soap filled steel wool, e.g. Brillo pads, are generally very good for producing a fine finish on aluminium but David's warning is very relevant.

The probelm with fan blades, assuming the material is basically sound is that any serious abrasion may possibly affect the balance. Scotch Brite pads are available in a variety of grades and will not remove as much metal, if any, as emery based abrasives. Again if the material can stand it, gentle bead blasting would be effective and could be followed by the steel wool.

PMM
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Old 27th Jun 2019, 1:19 pm   #5
davyrocket2
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Default Re: Polishing aluminium

Try T Cut, Brasso or even toothpaste and buff accordingly.
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Old 27th Jun 2019, 1:45 pm   #6
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Default Re: Polishing aluminium

I'd seriously consider spray painting those - starting with a suitable etch primer. Sacrilege to some but pragmatism occasionally makes sense in my view. Choice of colours and finishes too!

Alan
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Old 27th Jun 2019, 2:34 pm   #7
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Default Re: Polishing aluminium

Some of those marks look like they could be the beginnings of cracking, especially the one on the third rivet up from the centre. If you wet them and work them with abrasive it may encourage them to go that way, and they do look like they will need a good deal of material removing. As suggested, a good paint job may be the lesser evil.

B
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Old 27th Jun 2019, 4:43 pm   #8
emeritus
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Default Re: Polishing aluminium

At Plessey, the workshop used to use a rag mop wheel on a bench grinder for polishing aluminium alloy. I don't know if this involved any cutting fluid or whether the rag itself was sufficient, but it was used to good effect on the die cast aluminium alloy eddystone boxes used extensively in one of our projects. The highly polished finish avoided the need for painting or other surface preparation.
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Old 27th Jun 2019, 5:05 pm   #9
Ian - G4JQT
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Default Re: Polishing aluminium

How about dipping in caustic soda solution? Although if wire wool doesn't do the trick, not sure what will.
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Old 27th Jun 2019, 5:10 pm   #10
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Default Re: Polishing aluminium

Quote:
Originally Posted by Ian - G4JQT View Post
How about dipping in caustic soda solution?
It'd have to be a very quick dip and a weak solution otherwise you'd have nowt left, just the stump
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Old 27th Jun 2019, 5:18 pm   #11
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Default Re: Polishing aluminium

Progressive grades of wet n dry with a little clean engine oil.
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Old 27th Jun 2019, 5:24 pm   #12
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Default Re: Polishing aluminium

Quote:
Originally Posted by Ian - G4JQT View Post
How about dipping in caustic soda solution?
The blades would have been formed by pressing, so you'd have to believe there could be some residual stress in there, and they already show signs of corrosion. So, it's not hard to believe that it wouldn't take much to initiate stress-corrosion cracking.

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Old 27th Jun 2019, 8:05 pm   #13
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Default Re: Polishing aluminium

Linishing wheel (may be too thin for that)

Looking at the spidery patterns makes me think that a clear lacquer may have been applied, then later corrosion started at a defect- and crept laterally. The pitting at the centre of the spider could indeed be quite deep.

Dave
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Old 27th Jun 2019, 11:12 pm   #14
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Default Re: Polishing aluminium

Thanks for all the replies.

As feared, it doesn't sound like it's going to be easy. I think I'll start with some wet and dry paper and see how deep the corrosion goes.

Regards
David
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Old 28th Jun 2019, 8:05 am   #15
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Default Re: Polishing aluminium

Quote:
Originally Posted by Radio_Dave View Post
Thanks for all the replies.

As feared, it doesn't sound like it's going to be easy. I think I'll start with some wet and dry paper and see how deep the corrosion goes.

Regards
David
Good Idea.

If that works out I would go for 3M aluminium Polish:

https://www.academy.com/shop/pdp/3m-...rer-and-polish

I used it on the aluminium chassis of a Bush TV22, which was quite corroded before I started. I used 1200 & then 2000 grade paper prior to the polish:

http://worldphaco.com/uploads/BUSH_TV22.pdf

It took some hours. Get ready for black-grey hands, which will wash up with detergent.

The thing I like about the polish (despite that it works really well) on the label it says; 3M will not be responsible for any damage caused by the polish regardless of any theory put forward by a Lawyer ! After reading that I was even more devoted.
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Old 28th Jun 2019, 9:02 am   #16
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Default Re: Polishing aluminium

The other possibility is that the original surface finush was anodisation. It is hard to tell from photos.

If you start applying abrasives to anodised aluminium then you have a big job as you then have to abrade it all off before you can get a nice finish.
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Old 28th Jun 2019, 9:59 am   #17
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Default Re: Polishing aluminium

600 grade wet/dry, used with T-Cut. Do NOT use Caustic Soda dip, as already warned, unless you wish a textured dull grey finish (if there's anything left to show a finish). Could cracks be sealed with superglue? Just a thought.

Tony
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Old 28th Jun 2019, 10:34 am   #18
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Default Re: Polishing aluminium

Quote:
Originally Posted by Argus25 View Post



The thing I like about the polish (despite that it works really well) on the label it says; 3M will not be responsible for any damage caused by the polish regardless of any theory put forward by a Lawyer ! After reading that I was even more devoted.
I like that. Did you know that if you laid all the lawyers end to end, it'd be a jolly good start? I can't remember who said that.
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Old 28th Jun 2019, 11:17 am   #19
Radio Wrangler
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Default Re: Polishing aluminium

I don't like the thought of pieces of thin aluminium sheet getting thrown at speed from a disintegrating fan.

A kid at school once threw a 7 inch single record at someone (who ducked in time) and the record embedded itself edge on into a plywood blackboard. Close call! decapitated by Mr Tambourine Man.... doesn't bear thinking about.

David
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Old 28th Jun 2019, 2:29 pm   #20
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Default Re: Polishing aluminium

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..decapitated by Mr Tambourine Man.... doesn't bear thinking about.

David
So that is how the senses have been stripped and the hands can't feel to grip
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