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Old 07-16-2011, 02:39 PM   #15
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Originally Posted by Nuvite-F View Post
No, it's probably intact. Pure aluminum is more corrosion resistant than the underlying alloy, but not infinitely so. Most old trailers have ghosts of the old numbers on them. The other thing you will discover when you start polishing is that each sheet of aluminum is a little different, and at least on the one trailer I polished, the compound curved panels of the end shells seem to have "stretch marks" that are hard to polish out.

Good luck!
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What do your stretch marks look like? I looked on mine (which has not been buffed) and couldn't find anything. This aluminum thing is getting complicated.
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Old 07-17-2011, 07:52 AM   #16
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I think this may have already been said, but the numbers do not cause any damage to the skin. What does cause the issues is the area around the numbers that actually is exposed. The numbers, when stripped, do not remain, the clean perfect aluminum is exposed. You see the oxidation around the numbers. The more exposer, the deeper the ghost image will be. Sometimes this is impossible to remove and just has to be looked at as history.
Nuvi is very correct about the stretch marks. The seven panel end caps have the least due to less stretch forming required. The five panel end caps will show even more due to each segment being a wider span and having required more tonnage to form it. The modern aluminum used today does not form these stretch marks due to it being a totally different alloy of aluminum (it is the same as license plates are made from) but cannot be polished as Alclad can. Any metal can be polished. Some polish better than others.
I always wonder though, why the center panel on a new Airstream is a totally different color than the rest of the end cap. I asked someone from Colonial this and they kind of side tracked the answer. I assume they did not know either.
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Old 07-17-2011, 09:57 PM   #17
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What do your stretch marks look like? I looked on mine (which has not been buffed) and couldn't find anything. This aluminum thing is getting complicated.
The "stretch marks" I mentioned are kinda hard to describe. They don't show up till you start cutting through the oxide. After a couple passes with coarse polish (you will probably find it will take several passes to get through to clean aluminum--at least I did) you will notice thin dark streaks where the oxide is thicker. I suspect this is where the pure aluminum layer stretched out a little thinner when the panel was formed. It's not a problem aside from the fact that those panels will take more polishing to get the oxide off than the other panels. Or you can do like I did and let some of the oxide stay--I didn't want to polish right through the cladding.

And yeah, you're right--"this aluminum thing" is a lot more complicated than most people realize! I found a lot of variation in polishing behavior between one panel and another. It's more of an art than a science.

Dale (Pee Wee) Schwamborn worked for Airstream, and purchased their aluminum for a number of years. He has a lot of good stories to tell about it. I've forgotten the details, but I recall Airstream bought the aluminum they used for single-curved panels from one manufacturer (Reynolds, I think) but the aluminum for the compound-curved end shells from another (Kaiser) because the different brands worked better in those uses. (I may have Reynolds and Kaiser reversed.) Nobody knew why.

The other Pee Wee story is that if you look at the pictures of new 60's Airstreams, they looked like they had been polished. They weren't--that's what the aluminum looked like when it came from the rolling mill.

And therein lies a tale. The quality of the surface finish of the sheet depends on the surface finish of the rollers in the rolling mill. The rolls are reground at frequent intervals and the first batches of aluminum sheet that come off the new rolls are better than later batches.

Aluminum is purchased to a specification, and all the aluminum meets the specification. But Boeing paid extra to get the first batches off new rolls so they had the best surface finish.

But there was one relatively small customer that got their aluminum even before Boeing--Airstream.
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Old 07-18-2011, 06:11 AM   #18
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Attached should be a before pic. I did get a promising amount of the etching to smooth out through compound cut. Will post more later.

Got a little over half of the first cut done this weekend.
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Old 08-15-2011, 12:19 PM   #19
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I have had some success with 1000 grit wet sandpaper, and then brown tripoli. The numbers are almost totally invisible now.
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