Re: Anodized planes ?

Date:         27 Aug 99 03:08:13 
From:         Richard Mlynarik <Mly@pobox.com>
Organization: ITS Preservation Society
References:   1
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JF Mezei <jfmezei.spamnot@videotron.ca> wrote:
> Bicycles and airplanes use a lot of similar technologies. Both need to
> be strong and light.
>
> One example is bicycle wheel rims. Most are high tech aluminium (and
> some now carbon-fibre).
>
> For rims and other parts, anodisation is often used. It not only
> provides a very long lasting and clean finish, but, i am told, also
> strengthens the aluminium. (is that true ?).

No.  It's false.

Like nearly everything in the bicycle industry, anodization is a
cosmetic and technically useless (in fact, technically harmful)
operation driven solely by marketing.

> Has this ever been considered for an aircraft ? I realise that the
> anodisation process would have to be done during the construction, but
> the finish would be very hot, long lasting, and very light (no paint
> needed).
>
> Would the change in characteristics of the aluminium sheets from the
> anodisation process improve the aircraft or make the aluminium less
> flexible and more likely to crack after many cycles ?

The latter.  This is well known and well-studied.
The brittle anodized layer facilitates crack formation and
propagation.  Fatigue kills airframes.

If there were a dollar to be saved the mettalurgists of the aircraft
industry, who know more about aluminium than anybody else, would have
latched on this long ago.

Anodized bicycle parts -- wheel rims in particular -- suffer from such
embrittlement.  Unlike airliners, the overwhelming majority of
bicycles are not used intensively or anywhere near their design
limits.  Those of us who do ride more than average or who weigh more
than average and have ridden for years are well aware of the many
technical problems of the bicyling industry and the outright nonsense
which is foisted upon ignorant and largely uncaring consumers.

There have been hundreds of messages over the years hashing and
rehashing this on rec.bicycles.tech.  The best informed ones are from
Jobst Brandt jbrandt@hpl.hp.com author of The Bicycle Wheel.)