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Cleaning alloy castings

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Kenneth Deighton02/05/2014 20:59:18
69 forum posts

I need to clean some old aluminium cast stepping plates that sit on the running boards of a vintage car that I am restoring, what is the best cleansing liquid that I can use,?. sorry no sand blasting available.

RJW02/05/2014 21:28:31
342 forum posts
36 photos

I've used this stuff recently to good effect on well corroded camshaft covers and intake manifolding!

(No connection other than a happy customer)!

You could also google 'alloy cleaning with phosphoric acid' or 'Caustic Soda + Nitric acid' which brings up results of more agressive mixtures and alternatives to the stuff sold via Raceglaze, but I decided against it, pretty nasy stuff if you get it wrong!

Beware if you go the caustic soda route, the alloy goes as black as night before the nitric strips it off and takes some shifting!



Bill Pudney03/05/2014 03:59:28
483 forum posts
16 photos

Caustic soda and al.alloy are generally a no-no. A friend once tried to clean his Ariel Arrow barrels (cast iron) and cylinder heads in a caustic soda solution and found that his cylinder heads had disappeared! The barrels were nice and clean though.

best of luck



Involute Curve03/05/2014 06:40:10
337 forum posts
107 photos

Soda blasting makes old bike engine casings look better than new, and is quite common in the restoration market.

RJW03/05/2014 09:06:16
342 forum posts
36 photos
Caustic soda is perfectly ok to clean alloy as long as you don't leave objects stewing in the brew, the hard graft is getting rid of the blackened residue!
Blasting is certainly my preferred method, but you need a suitable cabinet with lighting and dust extraction, plus a decent compressor - either deaf or very understanding neighbours are a major plus if doing this at home, it's not a quick job!


Edited By RJW on 03/05/2014 09:08:13

robjon4403/05/2014 10:01:03
127 forum posts

Hi all, remember well from my motorcycling years when cleaning very heavily soiled alloy engine castings, cut up several large Rhubarb leaves & boil them up in a pan big enough to get the castings in, we naturally got the gear together & did the job over a wood fire at the bottom of the garden, you then have a strong hot solution of Oxalic Acid, that which causes Oak to eat iron nails. They came out clean enough to eat your dinner off, but nowhere as dangerous as Caustic Soda & its ilk. There is also to be considered that one can make a pie out of the red bits the leaves come attached to, if you cant do this find someone who can (no point in having a dog & barking yourself)


Ady103/05/2014 10:29:30
4134 forum posts
576 photos

Some of those high pressure water cleaners have a sand blasting attachment

All you need is a bucket of sand

The nozzle has a flexi-tube with a stick-it-in-the-sand alloy tube on the end


Gordon W03/05/2014 10:44:15
2011 forum posts

I use Gunk or similar stuff. Scrub well in and leave for a few minutes, then wash off with water, pref. a pressure washer. This gets the old stuck-on crud off and leaves a nice clean casting to work on. Depends what you want to do with them next. Acetone scrubbed in gets them very clean for painting.

JA03/05/2014 11:13:51
1055 forum posts
54 photos

Boil in non-biological washing powder. You will need quite a lot of powder! Do not use detergent or washing up liquid (these are very different).


GaryM03/05/2014 11:23:00
314 forum posts
44 photos

How about car alloy wheel cleaner?


RJW03/05/2014 11:36:58
342 forum posts
36 photos

Most alloy wheel cleaners are acid based and just for removing baked on brake dust rather than corrosion, generally there will be a warning on the bottle (if acid based) Not to be used on wheels where the lacquer coating is damaged such as from kerbing etc, it has the same effect on alloy as caustic soda and will turn it black - and it's a bugger to get back to bright alloy again!!

Whichever method is used to brighten the alloy, it will need spraying with something like clear lacquer, beeswax or the dreaded WD40 very soon after cleaning, otherwise the surface will quickly fuzz up with corrosion and need doing again!


GaryM03/05/2014 16:54:43
314 forum posts
44 photos

I'll get me coat.



RJW03/05/2014 17:08:30
342 forum posts
36 photos

Only reason i know Garry, is I got caught ........... as the saying goes 'if all else fails read the instructions ........' and we all do that don't we! blush
Some alloy cleaners have no effect on bare alloy and safe to use where the lacquer has been scraped off, just wish they'd make the damned labels and print bigger so you can read them without a loupe to know what you're actually buying!


peter walton04/05/2014 10:18:42
84 forum posts

Best thing I have found to clean aluminium is boiled rhubarb is also fairly gentle on the ally.

Rhubarb contains some oxalic acid, even more in the leaves, use warm and it will clean off the oxide layer! wash well afterwards.


Tim Stevens04/05/2014 18:07:19
1308 forum posts

In case it helps someone ... the black or grey residue on Al castings when cleaned with alkali (or some acids) is mainly silicon, along with any other alloying elements. And silicon is fairly inert stuff, which is why cleaning is not so easy. The same problem causes some light alloys to look dull or dirty after anodising.

Strong nitric acid is seriously noxious, but can be very useful as it attacks iron and steel but not aluminium. Ideal for removing broken taps or engine bolts that have corroded in place.

Cheers, Tim

Kenneth Deighton05/05/2014 19:52:09
69 forum posts

Thankyou for all of the different solutions, the Rubarb sounds interesting.


V8Eng05/05/2014 20:38:51
1509 forum posts
30 photos

Make sure you buy some extra Rhubarb to eat.

Rhubarb Crumble, yum yum!

Edited By V8Eng on 05/05/2014 20:40:07

"Bill Hancox"06/05/2014 00:30:43
257 forum posts
77 photos

Or rhubarb wine! (Hic)

Ian S C06/05/2014 10:28:06
7468 forum posts
230 photos

You could try something like Frost's Ali Clean, or Wonder Wheels, think it's sold by Halfords. Ian S C

Toys4boys07/05/2014 20:54:23
10 forum posts
1 photos

If castings don't need to be highly polished or have awkward hard to reach pockets, my first choice is vapour blasting. For anything else, I scrub up with neat acetone using a stiff brush and finish of with super fine wire wool soaked in oil or soapy water which gives a nice semi polished finish. Depending on the final result I'm after, I may also buff until they gleam.

If anything just needs a little clean up, I'll use Simple Green diluted with hot water and scrub like mad, then give a good rinse.

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