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Stripping powder coating from cast aluminum???

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#1 twhite

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Posted 22 June 2007 - 03:12 PM

All,

I recently bought a Unitron 150 mount from a fairly respected/respectable seller. He took it to a UPS Store that he uses frequently to ship it to me. However, inexplicably and VERY unfortunately, they did NOT wrap it in bubble wrap before putting it in a box to ship to me... so the counterweight and the mount head came into contact and decided to have a party. Now I have a dime-sized area of finish missing on what used to be a like-new mount head. :foreheadslap:

So, I sent photos to the seller, which in turn he showed to the UPS store -- and they said 'we're sorry, no problem, get estimates and we'll take care of it'. (There's NO WAY in he-DoubleHockeySticks I'm shipping it back to them. I don't want to lose it.)

So, I took the head to a local powder coating shop I've done business with before (excellent little shop!) and talked to the owner, and showed him the mount head. Normally they do sandblast/prep before coating, but he took one look at that Unitron head and said 'I won't strip it'. Why? Because it's cast aluminum, and powder coating is a very hard coating which is difficult to remove, and he believes the sandblasting process would damage the aluminum -- and, once I thought about it, I'd have to agree. (He did, by the way, confirm that the Unitron mount WAS powder coated rather than painted, which I had always believed.)

Now, he DID suggest that I use some sort of chemical stripper -- and, specifically, an 'aircraft-grade' stripper -- which he said would remove the powder coating. It would then have to be bead-blasted in preparation for re-coating.

So... my question to the group is: Does ANYONE have any experience doing this? What did you have to do? What product did you use, and how well did it work? I need to benefit from experience here -- it's got to be something that will remove the finish but not damage the aluminum castings.

This mount is obviously valuable and difficult to replace, and this was such a nice mount before United Package Smashers got their paws on it... and I need it to be right again.

Thanks to all in advance for your assistance.

#2 gnabgib

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Posted 22 June 2007 - 06:24 PM

Tony;
The powder coatings I have had removed in the past had to be "burned off" in a high temp oven. (around 750 Degrees f).
I have not found a paint stripper that will remove powder coatings. Some paint strippers will "soften" the surface of powder coatings and that is about all!
Kevin

#3 JWW

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Posted 22 June 2007 - 07:48 PM

Tony,

I am not a sandblasting expert but I have had a TON of stuff powdercoated over the years. I would think damage is dependent on the blast media being used. I would suggest contacting a blast media supplier/expert that has a variety of different medias to offer. I am sure they will suggest a plastic media if you want to keep the aluminum surface untouched, instead of using a aggressive media like aluminum oxide, garnet, etc.) which would leave the surface rough. Of course this would take longer to blast which would cost more.

Since I worked in the semi-conductor and pharmaceutical for many years, I know they make a chemical stripper because I have seen it used. I can't recall what company we used but here is a link to start with. You might email them or call them. I am sure it will be expensive but then again, they are going to pick up the tab, right? Anyway, I know nothing about them, but they say their product does not attack the aluminum surface during the stripping process.

Regards,
-JWW:

#4 dave b

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Posted 22 June 2007 - 08:03 PM

StripFast eats powder coat paint in a hurry (in 2 minutes its wrinkled up)

eats plastic too.

http://www.caswellpl...s/clearcoat.htm

#5 twhite

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Posted 22 June 2007 - 08:07 PM

James,

One of my things to follow up on is to talk to a shop here in Tulsa called Blasting Specialties. I think it's obvious what they do. :)

Thanks for the suggestion.

#6 clintwhitman

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Posted 23 June 2007 - 02:29 AM

Tony I have been working on a 150 head and scope for months the head is not powder coated. Powder coat it 7 time harder than paint and will not sand very easy in fact none of the unitron or and other telescope have powder coating on them.

#7 clintwhitman

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Posted 23 June 2007 - 02:32 AM

Lenny and both have found that rustolian semi gloss black almost matches the stock paint exactly in properties and finish.

#8 2manyscopes

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Posted 23 June 2007 - 12:12 PM

Hi,
I just finished restoring my Cave scope here which has a number of powder coated Unitron parts on it. Powder coat is definitely harder than paint.

I used 220 grit aluminum oxide for the parts I stripped myself. No damage to the cast aluminum parts at all except for a uniformly even frosted appearance. For some other parts I used a company that uses a soda blasting process. Those came out as if the parts had just come from the casting foundry.

Compared to the painted parts, the powder coated ones took about 4 timers longer to strip with the aluminum oxide 220.

Good luck!

BTW, the 6" Cave refractor will be ready soon. I had a hard time locating the right sized tubing to make a dewshield out of. (the only missing original part) I made both a 6" long dewshield (original) and a 16" long one that I will use daily. Both of these are off being powder coated so it will be a couple more weeks.
Bill

#9 Preston Smith

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Posted 23 June 2007 - 02:06 PM

How long has the powder coating process been around? :question:

#10 twhite

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Posted 23 June 2007 - 04:49 PM

Clint,

This is a VERY hard finish. The damage would have been a lot worse otherwise, IMO... the damage was where the edge of the cylindrical counterweight was allowed to rub -- a lot; probably in several UPS trucks -- against the mount.

The guy at the powder coating shop was quite sure it was a powder-coated finish. It doesn't just sand off... or flake off, either, like paint would.

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#11 clintwhitman

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Posted 23 June 2007 - 10:18 PM

That strange I didnt find it hard to sand out in fact I used it a a primer coat under the black on all the parts there is a grey dark grey primer under the paint. My mount and other parts are from the early 60s. All the parts Ron pastory sent me Unibalance and a bunch of other rings had the same back paint with a grey primer. and my 114 is from the mid 50s I have not touched it its mint! I also think lennys is a 50s

#12 clintwhitman

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Posted 23 June 2007 - 10:19 PM

What mount is that in the picture??

#13 twhite

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Posted 23 June 2007 - 10:33 PM

That's my 150 mount -- Unitron 4" Alt-Az, with counterweight.

#14 clintwhitman

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Posted 23 June 2007 - 10:37 PM

Sorry I ment 152 mounts EQs

#15 Lew Chilton

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Posted 24 June 2007 - 01:17 PM

At one time, telescope manufacturing in Japan was a cottage industry. Separate parts were made by a great number of family-run businesses who sent the completed components to an assembly plant. Is it possible that Unitron parts (in this case) came from different suppliers and that different methods of paint application were employed by those different suppliers?

#16 Preston Smith

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Posted 28 June 2007 - 04:46 PM

How long has the powder coating process been around? :question:


I found an answer: :)


Powder coating was invented in the 1950s, when Erwin Gemmer, a German scientist, developed a more-efficient way to coat wire baskets with nylon, according to The Powder Coating Institute Inc., a trade association.

#17 clintwhitman

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Posted 28 June 2007 - 11:05 PM

The other reason is my 114 is form the mid 50s and the 152 is late 50s s and powder coating didnt come around much as I remeber even in the 60s I dont remeber seeing it on things until the 70s

#18 Rcade

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Posted 29 June 2007 - 08:31 AM

Sorry to hear of your damage on such a nice old mount. I hope it can be solved easily for you. I use TuffStrip from Lowe's and it works great on aluminum and brass. I used it on my aluminum cast Cave mount. It is solvent based and not acid or caustic so it will not harm the softer metals. Strips all paints I've come across in less than an hour with water washup. I have not tried it on powder coated aluminum but it did strip powder coating off a motorcycle frame. Be careful to only use solventss on aluminum, No Acids Or Caustics. Good Luck and let us know what works for you.

#19 danmesloh

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Posted 30 June 2007 - 02:31 PM

Tony it's hard to tell from your picture but the finish looks thinner then the motorcycle or auto parts I normally see powder coated. Could it be a baked enamel:question: which still has a harder finish then normal paint but not quite as hard as powder coating

#20 twhite

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Posted 30 June 2007 - 03:14 PM

I guess it's possible. It seems pretty thick to me... and the guy at the local powder coater thought it was powder coat as well...

#21 highertheflyer

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Posted 30 June 2007 - 05:49 PM

Tony:
I've got a feeling that the finish on your Unitron mount is not a powder coating at all, but layers and layers of lacquered coatings.
I have a 5 inch Unitron, and it has a mount and spreader yoke that is in that familiar lacquered finish. When dinged, it will always chip right down to the gray undercoating underneath.
I would get a black lacquer paint to match, and build up the thickness in layers, with a brush coat and fine 600 sanding between.
Then polish and buff it to blend in.
Just my two cents,
Jim

#22 mikey cee

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Posted 30 June 2007 - 06:28 PM

Just do it....there ain't no tooth fairies! :smirk: :smirk:Mike

#23 Preston Smith

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Posted 30 June 2007 - 06:31 PM

:funny: :rofl5:


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