Sandblasted-like finish?

[kickn]

A quick question here - has anyone ever achieved a bead blasted - type finish without beadblasting? I was thinking a very strong etch might work if I heated the sodium hydroxide fairly high.

Any thoughts?

[M_D]

Yes, you can use an etching solution to achieve a flattened finish. Heating the solution had a profound effect on the speed and intensity the solution will work on aluminum. Also, the ratio it mixed does too.

The biggest trick is to get an even finish, at least that's what I have found. I have the best results with a pretty strong solution, heated to 140-170º F, but it works fast so don't go off and forget or it will eat your parts up. It seems to give a more even finish, compared to a weaker solution at room temperature.

I haven't bead blasted anything, so I can't compare exactly how well the methods match in texure.

[Fibergeek]

In my experience; nothing will produce a totally uniform, grainless matte texture that beadblasting will, or do it as easily.

I have experimented with alkaline (lye) etching at various concentrations and temperatures, but not to the extent M_D has. That said, I favor beadblasting.

If you want to try this, use glass beads only, fine to extra-fine bead size. The beads must not have been previously used on any metal but aluminum (I'm not kidding) they must also be clean and grease free of course.

[kickn]

The biggest trick is to get an even finish, at least that's what I have found. I have the best results with a pretty strong solution, heated to 140-170º F, but it works fast so don't go off and forget or it will eat your parts up. It seems to give a more even finish, compared to a weaker solution at room temperature.

What would you class as a strong/weak solution. My etching bath is based on Sodium Hydroxide right now and its pretty strong (approx 20%).

Thanks

[M_D]

That's a good question, too bad I can't give an exact recipie. We adjust the solution with use, as is gets weaker. I tend to go by time, and if it takes more than a minute or two at most when at 140-150ºF, we add more sodium hydroxide. If I had to guess, we start out with 1-1/2 lbs. per 5 gallons.

I expect most everyone know this, but the parts should cleaned and free of any surface contaminents before etching, otherwise it will be harder to get an even surface.

There are additives that supposedly buffer the sodium hydroxide that I haven't tried. I don't remember exactly what, so I'll see if I can find out and post it here.

[kickn]

You don't have a ph meter you can test your solution with and I can use that for comparison do you?

Thanks

[kickn]

okay - I've been playing with this using sodium hydroxide and can't get a finished that has any texture and doesn't look pitted. The more texture the more pitted. Can you just confirm that that is the result you get?

I think I'll have to go with beadblasting.

Also - on a slightly different topic - is there any home made brightening solution recipe's out there besides the phosphoric acid and nitric acid ones? I'm using nitric acid as part of the process and its a start but I was wondering if there was anything better or is it just easier to go with the bought stuff?

[M_D]

I checked our etching solution and it was 12-13 PH. You probably can't get a texture as distinct and course as bead blasting by etching, without encountering pitting. The sodium hydroxide, like most other alkali or acidic solution, tends to work unevenly on the surface and given enough time it will eat certain areas away noticeably more than others and leave pitted areas.

When we etch it is usually for the purpose of removing the oxide on vibratory tumbled parts, which results in a better quality anodized surface and consequently a deeper and more even dyed color.

On parts that are glossy to begin with, it tends to dull the gloss to an eggshell or flat finish, but the surface still appears smooth. That’s why I said you can’t leave the parts in very long or it will start to eat them up.