Aluminum Panel finishing - Anodizing

[Magura]

A crate of beer will get you a looong way at the local metal workshop!!!!

Magura

[Philo]

Chad,
I use a $30 siphon "bucket" style blasting rig. I have used it for years and blasted everything from rusty car parts to etching patterns in glass and bathroom tile(looks excellent, by the way, very high SOF). It is one of those tools that I keep finding different ways to use. The bad part is that you need a compressor and will use up some media over time. Some of the media are a little pricey. The poly is $80/30lbs but goes along way. There are ways to conserve it, like blast in a wheelbarrow with some tarp as a 3 sided back drop to keep it from flying off. With just a little practice, you can sand to get most of the scratches out of the AL then do a quick pass with the blast gun with fine silica sand (my primary media) and get a pretty even finish.

[Peter Daniel]

Originally posted by hifiZen
What do you think about the difference between alodine and anodize finishes in terms of durability (scratch and stain resistance)?

I would compare anodizing to applying laquer on wood and alodining to applying sealer. In first case, you have an artificial layer (of some material) sticking to the original surface, in second case (alodine) you don't have that layer. Alodine sort of penetrates the aluminum surface and after applying it you can brush off any excess (of both color and amount of penetration).

Alodine does not protect against scratches and the material is as sensitive as it was before. Anodizing hardens the surface and scratching it is much harder.

If properly applied, alodined aluminum surface looks sort of as stainless steel with deeper tone. Personally I like it, as it preserves the original look. It adds protection against rust and stains, and is very easy to apply; just deep the piece for few seconds and rinse with water, done.

This amp's panels were finished by alodine: http://www.specializedkits.com/patek.html

[hifiZen]

Originally posted by Philo
...I use a $30 siphon "bucket" style blasting rig...

$30, is that it? Hmm. Now where do you get something like that? I was under the impression that blasting equipment cost a lot more than that. I'll have to check into it some more. I have a small compressor and an air tank which I've used for airbrushing in the past, though I'm not sure it'd be powerful enough for any serious blasting work. Maybe just some small, light-duty tasks, which may be enough for my needs.

What grit/grade of blasting material would you recommend? I want to avoid silica, as I've heard that it will embed into the surface of soft metals and can cause inconsistent anodizing / dyeing results. Poly is perhaps a better way to go... ??

Also, has anyone tried a chemical etch such as lye (draino)?

Looks like I've got some experimenting to do here...

[hifiZen]

Originally posted by Peter Daniel
Alodine does not protect against scratches and the material is as sensitive as it was before.

Hrm. That's what I was afraid of. Well, I guess you can't have it all... now the question is whether it's better to have the electrical conductivity or the surface hardness...

Nice Patek amp, btw.

[Magura]

What do you want the electrical conductivity for?

The bolts will take care of the electrical connection the panels in between.

Magura

[Peter Daniel]

With anodizing you only loose surface conductivity. But if you force the screws slightly harder or just taka off some anodizing at the contact area, you still have conductivity.

[hifiZen]

I suppose that's true, though if you wanted to be really picky about RF shielding, it's nice to have a continuous connection which is shorter than your smallest wavelength of interest. I don't think I'd want to tap that many holes though.

Nah, I suppose it's not really such a big deal... just one of those little things which are like icing on the cake. I think RF shielding is an area many people overlook (including myself, in the past), and while I don't build enough equipment to positively demonstrate it's effect for myself (I very rarely build several of the same thing which can be tweaked and compared), I'm reasonably certain that it can play a significant role in extracting the best performance from most audio circuits.

[Philo]

The embedding is caused when you get the nozzle to close to the material and have too much pressure pushing the sand. There are better medias to use for the app. The poly was just an example of the cost. I would use glass beads, which are available in different "screen sizes" or grits. The finer versions produce a more matte finish while the the larger sizes are shinier but have a more "detectable" surface variation. I would say your compressor is to small. A test is if you can pick it up easily, it probably doesn't have the CFM to handle a sandblaster. Although... there are small sandblasting rigs made to work with airbrush compressors. These very small and made for small scale hobbyists (ie, trains). Not really up to what you need. Do you have a friend with a compressor?

[tiroth]

Alodined aluminum is about 1000x better at resisting finger prints etc although certainly not as robust as anodized.

I think it is considerably cheaper and less hazadous to DIY. Neither alodine nor phosphoric acid are as nasty as concentrated sulfuric acid.