Aluminium finishing, blasting, anodising

[GraemeVW]

Wasn't sure if I should put this here or in coatings.
I have a project on the go which involves a few small aluminium pieces, sort of 1"x2" kind of size.
I'd quite like to have a decent finish on these and probably not polished, I was thinking maybe blasted?

I've never done any blasting before, I've always if need it as doing it in any kind of scale needs large equipment. But a little blasting of small parts must be reasonably easy to achieve right? I have a decent compressor. What kind of gun though? Any of the cheapo, hose in a bucket type? What kind of abrasive? Thinking of a nice, fine, smooth satin or mat finish. I can polish first if need be.

And then I was thinking of maybe clear anodising. I've done a fair bit of plating and have lots for zinc, copper, nickel etc. I therefore have tubs, power supply, aluminium wire etc along with the ability to get the parts properly clean.
I think all I'm missing are anodes and acid.
Lead anodes? If so, that should be pretty easy. May even have some. I've read battery acid, I have a few old car batteries, can I drain those?

Usual story, I have a handful of parts to do so want to limit what I spend to as little as possible

 

[brightspark]

its either fine media to leave a finish for painting or bead blasting to leave a smooth satin bare finish .a cheap suction gun will work for smallish reasonably clean parts

 

[GraemeVW]

its either fine media to leave a finish for painting or bead blasting to leave a smooth satin bare finish .a cheap suction gun will work for smallish reasonably clean parts

I think, or at least assume, I'd prefer a bead blasted finish as I guess it would have less texture?
I know nothing about blasting media though.

I've seen guns with little gravity hoppers for the media too. They seem like they could be good for what I need too, but no idea if they are any good.
Are there different nozzle sizes or anything I need to be concerned about?

 

[brightspark]

the cheapo suction guns will run on a 3 hp 14cfm compressor doing small parts but run down on pressure fairly quick . if using beads they are expensive and need to be recovered . best used in cabinets

 

[GraemeVW]

the cheapo suction guns will run on a 3 hp 14cfm compressor doing small parts but run down on pressure fairly quick . if using beads they are expensive and need to be recovered . best used in cabinets

I've been trying to look around and beads not being cheap is about all I've found out so far!

I might be as well just getting the parts done.

 

[GraemeVW]

I've seen airbrush ones, and little pen ones. They have the kind of surface coverage and controllability I'd want, the parts I want to finish are small model sized parts. Not sure if it would have the power to give the surface finish though, they are more for stripping paint of plastic models etc.

 

[Misterg]

And then I was thinking of maybe clear anodising. I've done a fair bit of plating and have lots for zinc, copper, nickel etc. I therefore have tubs, power supply, aluminium wire etc along with the ability to get the parts properly clean.
I think all I'm missing are anodes and acid.
Lead anodes? If so, that should be pretty easy. May even have some. I've read battery acid, I have a few old car batteries, can I drain those?

Lead *cathodes* work fine for me. (The wires are the opposite way around to plating: the parts are connected to +ve. )

Instead of sulphuric acid, I use sodium bisulphate (swimming pool pH down chemical) - it's cheap, no problem getting hold of it, no risk of contamination, and no issues with acid licences, etc.

It has worked brilliantly for me, and is a really tidy way of finishing alloy bits and bobs.

Power supply ~20V max, constant current preferred.
Current 6A per sq. foot of anodising (usually works out as 1 -2 A for the parts I do).
Etch in weak (2%) sodium hydroxide solution for 1 - 2 minutes beforehand.
Rinse with de-ionised water in a spray bottle.
Anodise for 1 - 2 hours (1 hour for a decorative finish. 2 hours is better for taking a dye, and harder wearing, but may discolour the parts more if not dyed).
Rinse with DI water spray again if going into dye, otherwise:
Seal in almost boiling (tap) water for 20 mins afterwards.
I find titanium wires are less hassle than aluminium for 'hanging' the parts (they need to be held pretty tightly to ensure electrical contact).

Keep the chemicals covered and they'll last for ages (12 months +)
Don't let the anodising bath get warm - odd things happen!

(My modest setup)

Last stuff I anodised (the bit on its edge at the back isn't anodised - it's stainless)

 

[GraemeVW]

Lead *cathodes* work fine for me. (The wires are the opposite way around to plating: the parts are connected to +ve. )

Instead of sulphuric acid, I use sodium bisulphate (swimming pool pH down chemical) - it's cheap, no problem getting hold of it, no risk of contamination, and no issues with acid licences, etc.

It has worked brilliantly for me, and is a really tidy way of finishing alloy bits and bobs.

Power supply ~20V max, constant current preferred.
Current 6A per sq. foot of anodising (usually works out as 1 -2 A for the parts I do).
Etch in weak (2%) sodium hydroxide solution for 1 - 2 minutes beforehand.
Rinse with de-ionised water in a spray bottle.
Anodise for 1 - 2 hours (1 hour for a decorative finish. 2 hours is better for taking a dye, and harder wearing, but may discolour the parts more if not dyed).
Rinse with DI water spray again if going into dye, otherwise:
Seal in almost boiling (tap) water for 20 mins afterwards.
I find titanium wires are less hassle than aluminium for 'hanging' the parts (they need to be held pretty tightly to ensure electrical contact).

Keep the chemicals covered and they'll last for ages (12 months +)
Don't let the anodising bath get warm - odd things happen!

(My modest setup)

Last stuff I anodised (the bit on its edge at the back isn't anodised - it's stainless)

Did you put a post on model engineer?
That's all great, thanks.
What are you using for black dye?

 

[MickeyW]

We have a few things hard anodised at work. They mostly are parts with flat surfaces, and we give them a rub with fine wet n dry finish after CNC milling. They come back from the anodisers with a fine satin finish.

 

[Misterg]

What are you using for black dye?

I use commercial black dye - The dye came from ebay - about £12 for 1/4 of a teaspoon full! However it works extremely well. I used about half of it to make up ~2 litres of dye at the maximum concentration, and am still using the same solution ~ 2 years later without it showing any sign of weakening. I still have the other half of the packet. (I used DI water to make up the solution.)

When I first used it, I followed the instructions that came with the dye (30 mins @ 55°C), and the results came out so well that I haven't dared deviate from them. It means that I have to heat the dye bath, which is a minor inconvenience - I really should try it cold. The few colours that I've done have been cold, and good colour has been achieved in a few minutes. (But I don't think they look as classy as a nice, deep black.)

I'd encourage you to give it a go, especially with the sodium bisulphate option.

Ebay black dye

(I make the odd post on ME, but can't take the pedantry for very long! )