Stripping powder coating from cast aluminum???
Posted 22 June 2007 - 03:12 PM
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.
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.
Posted 22 June 2007 - 06:24 PM
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!
Posted 22 June 2007 - 07:48 PM
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.
Posted 22 June 2007 - 08:07 PM
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.
Posted 23 June 2007 - 02:29 AM
Posted 23 June 2007 - 02:32 AM
Posted 23 June 2007 - 12:12 PM
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.
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.
Posted 23 June 2007 - 04:49 PM
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.
Posted 23 June 2007 - 10:18 PM
Posted 23 June 2007 - 10:33 PM
Posted 24 June 2007 - 01:17 PM
Posted 28 June 2007 - 04:46 PM
How long has the powder coating process been around?
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.
Posted 28 June 2007 - 11:05 PM
Posted 29 June 2007 - 08:31 AM
Posted 30 June 2007 - 02:31 PM
Posted 30 June 2007 - 03:14 PM
Posted 30 June 2007 - 05:49 PM
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,