Anybody tried glueing cast aluminum parts together with ep..

External Since: Jul 09, 2005 Posts: 32

William R. Watt wrote:
> I didn't know aluminum oxidized within minutes so I did a test.
>
> Part of a piece of aluminum was scraped removing any oxidation and making
> the scraped part bright and shiny. Two hours later the scraped part was
> still just as bright and shiny. Eighteen hours later the scraped part was
> not as bright and shiny. Part of the surface which had been scraped the
> day before was rescraped and the difference was noticeable, the newly
> scraped surface was brighter than the surface scraped the day before, but
> both scraped surfaces were still a lot brighter than the part of the
> surface which had not been scraped at all.
>
> I would conclude that there is some oxidation in the first 24 hours.
>
>
>
> --
> ------------------------------------------------------------------------------
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THe thin layer of oxide that forms in the first seconds is nearly
transparent. Try again, this time using a white piece of cloth. Polish
until the area seems as "bright and shiny" as you want. Notice the
black stuff on the cloth. That is aluminum oxide. Wait 30 seconds and
use a clean portion of the rag to polish the "bright and shiny" part you
just polished. Notice the black stuff? That is more aluminum oxide.

Aluminum is like silver. It oxidizes almost instantaneously.

It is this thin layer that fails when gluing parts. The adhesive bonds
to the oxide layer and the oxide fails, not the glue.

--
“The darkest places in hell are reserved for those who maintain their
neutrality in times of moral crisis.”

External Since: Jun 22, 2003 Posts: 434

On 15 Oct 2005 14:53:26 GMT, ag384 DeleteThis @FreeNet.Carleton.CA (William R.
Watt) wrote:

>
>I didn't know aluminum oxidized within minutes so I did a test.
>
>Part of a piece of aluminum was scraped removing any oxidation and making
>the scraped part bright and shiny. Two hours later the scraped part was
>still just as bright and shiny. Eighteen hours later the scraped part was
>not as bright and shiny. Part of the surface which had been scraped the
>day before was rescraped and the difference was noticeable, the newly
>scraped surface was brighter than the surface scraped the day before, but
>both scraped surfaces were still a lot brighter than the part of the
>surface which had not been scraped at all.
>
>I would conclude that there is some oxidation in the first 24 hours.

If you can't see the film, doesn't mean it's not there.
Astro mirrors are aluminized, these days.
In a vacuum chamber, a small aluminum sample is vaporized off a
filament onto the glass.
Then they let the air back in. That mirror surface looks good for
years. And if they hard coat it, it lasts even longer.

Brian W