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By Paul_Sengupta
#1820018
And then the last reply has a question mark before it.

There's a group of icons ^^^^ up there you can choose from to post. I'm not really sure of their purpose.
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By skydriller
#1820045
...is that why the thread has a warning symbol..?? :cyclopsani:
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By Kemble Pitts
#1820051
cockney steve wrote:AIUI, Aircraft aluminium skin -sheet is actually coated with a thin layer of alloy which abrasive is likely to wear-through.


Actually it's the other way around.

Not germain to the discussion, but for education purposes only.

The 'aluminium' used in aircraft construction is actually a mixture of about 95% aluminium and various other elements; often largely copper or zinc. These other elements are referred to as the 'alloying elements', and you end up with an 'aluminium alloy', also known as 'light alloy' or just 'alloy' in hangar slang (or even 'ali' - yuck and very confusing).

Aluminium alloy has much better strength than pure aluminium (which is pretty useless in this regard) and is capable of being 'heat treated' and hot or cold 'worked' (stretched, bashed, squashed, etc.) to improve its strength or hardness, as required.

The down-side is that aluminium alloy is more prone to corrosion than pure aluminium. So, the sheet material used in aircraft has a very thin layer of pure aluminium hot-rolled onto each face and this provides a good corrosion protection layer.

Such sheet material is 'aluminium-clad aluminium alloy sheet', usually shortened to 'alclad'.

OK, break time.
NickC, cockney steve, Aerials and 1 others liked this
By Peter Kelly
#1820576
Hmmm...

The cladding on 'Alclad' aluminium is very thin, typicaly about 0.001" (it varies depending on the sheet thickness, specification etc.).

Mechanical abrasives remove the protective layer in the blink of an eye. One stroke of 80-grit sandpaper scratches right through. Mechanical abrasion to remove paint on aluminium aircraft skins is fraught with danger, hence the preference for chemical stripping.

Blasting GRP is a fairly complex issue involving gel-coat thickness, grit type and size, pressure etc. The good guys do boats really quickly and very effectively with minimal removal of gelcoat.

On this moulded composite components used in aircraft, I'd always use abrasive, either by hand or on some kind of mechanical tool.