I tried clear powder coating, and learned the following:
1) Some clear coat powders will turn yellow when baked in the oven or exposed to the sun. Unless your powder coater is experienced with the clear powder he proposes to use on your parts and can tell you specifically it won't, assume it will yellow. This is not a huge deal since lots of folks do clear now, but I found several that claim they "do clear all the time" that don't.
2) The bigger problem - and again it comes down to the skill of the powder coater, is bubbles. My fabulous powder coater told me "all powder coating will form a few bubbles in the oven. It's inherent to the process - some more, some less". Well, I got bubbles alright, and with clear powder coats on polished parts the bubbles stand out like a sore thumb and really wreck the appearance of the finished part - which particularly sucks since I spent hours polishing the parts prior to taking it to the coater...which brings me to 3)
3) Scratches. Scratches ruin the look of the polished aluminum fast, and I've yet to find a powder coater (or anyone actually) that will handle the polished part with the same care I've taken to get it to him scratch-free.
Granted, powder coating can be done really well (ie: door knobs and brass fixtures that don't tarnish in your bathroom) and I obviously got a loser powder coater, but based on my anodizing results, I'm probably done with powder coating.
In anodizing, aluminum oxide is electrochemically formed on the surface by passing a DC current through a solution from the part out to another electrode. The aluminum oxide is then converted to aluminum hydrate, which is extremely hard and protects the part from chips, scratches, and further oxidation. The biggest issue is that anodizing "dulls" the part somewhat.
Bright-dip anodizing is a variation of the process and an obvious one you'd want to employ to achieve bright aluminum trim. In bright-dip anodizing the part is mechanically polished pretty well, then electropolished to an extremely shiny finish, then anodized. As with any anodizing process, the part is dulled somewhat by electrochemically growing a layer of aluminum oxide/hydride on the surface. However, as a rule, the shinier the part is prior to anodizing, the shinier the finished anodized part will be.
I figured I could achieve the same results in a normal anodizing process (as opposed to bright dip) if I polished the part myself to a fine finish (white rouge, etc.) prior to anodizing. Mostly I decided this because I couldn't find anyone locally that offered bright dip anodizing services. So, last week, I polished the part as bright as it will go, then sent it off to a local anodizer. We visited quite a bit and I ask him to put the minimum thickness of oxide on the part to protect it.
Well, the piece came back looking great. If I put it beside a polished piece that has not been anodized I can tell it has a slight haze in the finish now. By itself though, I can hardly tell. The only noteworthy problem is that pits in the metal that were invisible after mechanically polishing (ie: very small pits) enlarged somewhat during the electrochemical treatment. Still though, they are so small I'm probably the only person that will notice - particularly once it's mounted on the truck and driven a bit (or put next to a paint job I've applied
)I had my trial piece done in Spokane, WA at Inland Empire Plating and will send the rest to him when I get done polishing. Let me know if you don't have a local anodizer and want their contact information...
Good luck
