Dye problems with bead blasted finishes

[Easttex]

I'll try not blasting so hard, and see if that helps. I've been blasting things very thoroughly up until now. Usually, at 90psi, on a 1.5 x 6 piece of bar stock for the tests, I have been going all the way around the perimeter, then the length with back and fourth strokes, followed by diagonal passes going both directions from end to end. Should I be just knocking the smooth surface off the piece or blasting it until I wear out? The dye time on previous tests have been as long as 15-20 minutes at 110* and fried at 4.5-6 amps/sq'.
Thanks,
EasTTex

[Fibergeek]

Only you can determine how matte the matte surface should be on what you are doing. Holding the gun further away from the work will also make the blasting less aggressive.

Your dyeing may be better at 140 deg. F. You should try it.

Since you have two textures that will have different dyeing characteristics on the same piece of metal, you will need to work out some sort of a compromise dyeing scheme.

[Sid03]

sorry to bring up an old post, but I was wondering if anybody could point me towards some decent oil/moisture traps for air compressors?

[Fibergeek]

I'm using a garden variety oil trap from Sears, no complaints. The POS that came with the compressor (also from Sears) is a POS, not the same unit I purchased separately, also from Sears. It cost 20-30 bucks, I don't remember.

[buckeyevs]

I recently anodized some bead blasted parts and mine don't look very black after completion either. They look more dark gray than black. I wetted them with WD40 and they looked very black. Is this just something we must live with or is there a trick to getting a matte black to look black. I'm using the conventional anodizing method powered by a 2amp/6amp battery charger and have been getting pretty nice results with everything not bead blasted. My brother even successfully dyed a key chain hot pink for a present. It turned out great and was very pink. Therefor, I believe my set-up is working just fine and was just wondering if that's just what bead blasted finishes look like. Thanks for any input.

[Fibergeek]

If your parts require some sort of wetting agent (like WD-40) to be the right shade you have a problem, beadblasted or not. Most of my work is beadblasted (for the matte texture) and they look just as they should when they're dry, no wetting agents, no excuses.

What you are describing are the usual symptoms of excessive dissolution. This can be caused by any of the following:

1. Too high an electrolyte temperature.
2. Wrong current density for the electrolyte concentration.
3. Wrong anodization time.
4. Poor cleaning and/or native oxide removal.
5. Bad electrical connections.

What your brother did on a key chain is hardly proof, did these beadblasted parts have the same (or nearly the same) surface area as the keychain? If the answer is no, the keychain is irrelevant.

[buckeyevs]

My latest part was 6061, had roughly 7sq in, the electrolyte was at 70* and was drawing 1 amp. The time shouldn't be the problem because I ran it 3 times before the dye even took(increasing time each trial by 15 min), so I don't think it was in there for too long. I washed it with hot detergent water and a tooth brush, used Caswell Deox/Desmut for 2 minutes. Strait to anodizing after a good rinse. Dye tank for 15-20min.
A connection may have been weak but the amperage was consistent through the time and it seemed on par with what a comparable sized part drawls in my setup. I seem to only have problems with bead blasted parts.

I'm going to connect to the cathodes in a little different manner a.s.a.p. to see if that helps. Now it is alligator clamp connections crimped to aluminum wire (all contacting surfaces cleaned and deoxidized prior to crimping).

[M_D]

Anodizing a 7 square inch part at 1 amp is about 20 amps current density for a smooth part. When they have a rougher texture, it is probably safe to add 15-20%, or maybe more for the actual surface area.

I don't have time to review the whole thread to see what details you have provided so far, but that's too much current unless you have a strong acid concentration. Assuming that you did have the proper electrolyte concentration, 20 amps CD should finish a typical anodizing job in about 20-25 minutes.

With parts that small, you need to be able to accurately control the current, as just a tenth or two error throws it off a lot, percentage wise.