Newbie: Powder Vs Anodize

[ianking]

First, great site. I have spent time searching and have read the sticky threads, but now I have a few questions that I hope can be answered.

1. If an anodized finish is dyed it must be Type II as Type III is very difficult to dye due to smaller cell size/higher density of cells.

2. Type II is not as hard as Type III.

3. The hardness that is being measured is using Moh's relative hardness scale.

4. The effectiveness of anodizing is directly related to the Aluminum alloy that is used.

I have an instance where I am looking at two sets of aluminum tubes of different alloys. One is anodized the other is a powdercoated with an epoxy/polyester hybrid. By banging each set of tubes together it appears that the powdercoating flexes and indents without cracking or peeling with no apparent change in coloration. The anodized finish also does not appear to crack or peel, but I am seeing a coloration change almost like a dark scarring. Is this the dye breaking down and the natural coloring poking through?

We are using both powdercoating and anodizing on our frames which are stacked and unstacked frequently, thus the tubes are banging off of each other. After two years in the field the anodized tubes look terrible and the powdercoated tubes look almost brand new. This is counterintuitive to me after reading all of these posts.

Even though anodizing is the hardest is it fair to conclude it is not the most durable dependent on the application?

Your experience and insight is greatly appreciated.

[mcaswell]

1. Type III will accept black I think.
2. But they are so close it's splitting hairs.
3. Not sure of the question
4. Depends what you mean by effectiveness and what you are trying to achieve. Al type will effect the film, but I doubt this is the cause of your troubles.

What I would imagine is happening is that the ano film is more brittle than the more pliable plastic powder coating and is not withstanding the rigors in the same way.

The dye permeates right through the ano film.

Hope this helps

[ianking]

Thank you for the reply.

Yes, the conclusion that I was drawing is that in our application where metal frames are being stacked one on top of the other is that at the points where the frames are contacting metal on metal, that over time the ano is breaking down. This seems to contradict the "hardness" argument. If this is the hardest finish available I would not expect it to break down the way it is.

[mcaswell]

Hardness also means brittleness. An ano film is more glass like than the plastic powdercoat, so any point to point impact would more likely shatter/damage it.

[gbtweedy]

Powdercoat also has much more thickness so in the case of assemblies with close tolerances powdercoating may not be an option.

To create the anodize layers you are creating aluminum oxide on the parts surface. Aluminum oxide is used on most "sand" paper. The layer created is only .5 - 1 mil in most type two applications

[sswee]

ianking,
You're mis-interpreting the terms hardness and durability. Glass is a harder substance than lexan but that doesn't make it more durable to impact. The powder coat is more suited to your application.
SS