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Dye problems with bead blasted finishes

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  • M_D
    replied
    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.

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  • buckeyevs
    replied
    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).

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  • Fibergeek
    replied
    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.

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  • buckeyevs
    replied
    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.

    Leave a comment:


  • Fibergeek
    replied
    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.

    Leave a comment:


  • Sid03
    replied
    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?

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  • Fibergeek
    replied
    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.

    Leave a comment:


  • Easttex
    replied
    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

    Leave a comment:


  • Fibergeek
    replied
    I'm beginning to wonder if what you are seeing is actually a problem, or the normal visual dyeing differences between matte and polished surfaces.

    The "no change between time steps" makes me consider this; the matte has more surface per unit area than the polished, it will require more time in the dye than polished to get the same shade. If you reduce the PSI and/or use smaller beads; so that the matte surface is somewhat less matte (smoother) do things improve?

    Leave a comment:


  • Easttex
    replied
    Hey,
    I'm still not getting good bead blasted results, a bit better, but not what I expect. I have put in an oil trap right outside of the blast cabinet and changed out the beads. I'm running 200 grit glass at 90 psi, I'm getting a much better peening effect, but still having a very dull gray'ish cast to the parts. I've checked for continuity and all is well. The other side of the test piece, which is polished, seems to be coming out fine. I've done several tests with nearly the same results. The test pieces are always lacking in color saturation. When doing step density tests, there is nearly no difference in the time steps on the blasted side, where as on the polished side the steps are very recognizable and very vivid in color. Any ideas?
    Thanks,
    Easttex

    Leave a comment:


  • Easttex
    replied
    Cool,
    Thanks for the input. I'm on my way out to the shop right now to put in fresh beads and clean out my hose and blast gun. I am putting in a coalescing oil trap on before I run parts tonight. I'll post the results.
    EasTTex

    Leave a comment:


  • M_D
    replied
    I haven't had any experience anodizing bead blasted parts, but all of this sounds a lot like anodizing parts tumbled in ceramic media. Simple cleaning isn't sufficient like it is for smooth machined surfaces. I found that the stripped parts (previously tumbled) did better the second time around. I asked myself why, and the only thing I could think of was they were likely way cleaner and down to pure aluminum alloy after stripping.

    So, I began trying to clean the parts better in the first place. It took a while, but I discovered they needed to soak in 165? + SP cleaner for several minutes at the minimum.

    Things go a lot better when the parts are cleaned in stripper or lye either before or after. Since the lye introduces some level of smut into the equation, they need to be treated in the desmut. Then when they are rinsed of the desmut, they get cleaned a few more minutes in the hot SP cleaner.

    Since the parts are actually clean in the most common sense before starting the cleaning, I am going straight to the lye solution first, desmut second, and cleaner last, with thorough rinsing in between.

    With the aggressive and extended cleaning process, I have eliminated virtually all uncertainty about if the tumbled parts will turn out. I really think Fibergeek is right about the parts being contaminated by dirty beads and/or air, and better cleaning will be the cure.

    Leave a comment:


  • Easttex
    replied
    Hey guys,
    I appreciate the input. The beads I purchased were freshly delivered and in a sealed 50# bag. I am trusting that they were oil free. I am going to install an auxiliary oil trap and moisture collector at my blast cabinet, which is an the other end of a about 40 foot of air line, as well as, putting in some fresh beads. I'll let you know how it comes out. Thanks again,
    EasTTex

    Leave a comment:


  • Fibergeek
    replied
    It still sounds like the beadblasting is contaminating the work, most likely with oil. If this is the case, the oil has been blasted into the now rough surface of the work, its in deep. I doubt simple green, alkaline, or whatever will take it off easily. Elevated temperature and vigorous scrubbing would be in order.

    The oil/moisture trap that came with my compressor was an ineffective POS, I replaced it.

    Since radiator shops aren't noted for their oil-free environment, get your own glass beads from MSC or where ever, you then will know that they're clean. Your blasting cabinet and the gun have to be clean too, are they?

    I'm also assuming you haven't changed anything else besides adding the beadblasting.

    Leave a comment:


  • NeoMoses
    replied
    What happens when you strip the parts and re-anodize them without bead blasting again? Do they turn out as expected?

    I, too, have seen this problem of poor dye absorbtion with colors. Although I haven't determined a root cause, stripping and re-anodizing the parts usually fixes it for me. It's not a good solution, but it is a solution. See if it works for you.

    Leave a comment:

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