"dazed and confuzzed" wrote in message
news
THe issue with aluminum is that the bond is usually to the oxide layer
that forms rather than to the aluminum itself.

Indeed. And therefore an etching ALU primer must be used, prior to applying
epoxy. See www.westsystem.com for more info.

Meindert

William R. Watt wrote:

THe issue with aluminum is that the bond is usually to the oxide layer
that forms rather than to the aluminum itself. Some folks have had good
luck with epoxy and some form of "brillo" type pad or sandpaper to break
this layer so that the epoxy can bond to the aluminum. With a cast part,
you might get enough"tooth" to make 5200 work.


If it breaks and he puts it back a few days later there won't be
an oxide layer yet.

THere will be an oxide layer thick enough to cause a poor bond in less
than a second after the part breaks again.




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--
“No battle plan survives first contact with the enemy”
Sun Tzu

--For grins you might post this problem over at
sci.engr.joining.welding Maybe you'll get lucky and have a hotshot from
that group within driving distance..

--
"Steamboat Ed" Haas : A greasy donut, a cup of
Hacking the Trailing Edge! : coffee and thou...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

steamer wrote:
For grins you might post this problem over at
sci.engr.joining.welding

My news server doesn't carry it. I put in a request for it though.
We'll see what happens.
Thanks. Didn't know it even existed.

"William R. Watt" wrote in message
...

THe issue with aluminum is that the bond is usually to the oxide layer
that forms rather than to the aluminum itself. Some folks have had good
luck with epoxy and some form of "brillo" type pad or sandpaper to break
this layer so that the epoxy can bond to the aluminum. With a cast part,
you might get enough"tooth" to make 5200 work.

If it breaks and he puts it back a few days later there won't be
an oxide layer yet.

Aluminum oxide forms within minutes....

Meindert

West Systems 860 Aluminum Etch Kit
A two-part treatment for preparation of aluminum surfaces for bonding
with epoxy. Our research shows adhesion to aluminum is significantly
improved with this process. Also improves paint adhesion.
860-8 Two 1/4 pint bottles (treats about 50 sq. ft.)
860 Two 1-pint bottles (treats about 200 sq. ft.).

http://www.westsystem.com/

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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William R Watt National Capital FreeNet Ottawa's free community network
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On 15 Oct 2005 14:53:26 GMT, (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

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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William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
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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.”

dazed and confuzzed wrote:


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.

I wonder how the Lotus Elise stays together then? It has an aluminium
tub-chassis, constructed from aluminium extrusions bonded together with
epoxy resin.

--

Geoff