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Color depth vs. anodizing time

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  • Fibergeek
    replied
    NeoMoses, I now have the eddy current thickness gauge back.

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  • M_D
    replied
    My problem was small cheap aligator clips, apparently they lacked the required spring power. Even after working them on the wire, they didn't seem to work as well as possible.

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  • Fibergeek
    replied
    I'll be looking forward to seeing your dyeing post.

    I use alligator clips too, clear of the electrolyte of course. They work fine if they have teeth to bite into the wire, Wiggling them a little after clipping them on, so that the teeth dig into the wire is a good practice. Using clips with strong springs also helps.

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  • M_D
    replied
    Fibergeek, one of the things I have learned is you are right and that the connection is important. I haven't got a lot of experience, but for the last 6 weeks have been anodizing parts every day almost. When I first got a "real" power supply, I was seeing peak voltages of 13-15 at 4.5 amps per square foot. The area calculations of individual parts are from a CAD program where the parts are modeled in 3D, so that part of the equation is likely pretty good. I thought the connections were good, and questioned your figures and power supply meter accuracy. I was using wires with aligator clips to make the connection to the hanging wire (away from the sollution). When I changed that, the voltage dropped. Then I realized the aligator clips were not making as good of a connection as I had believed.

    Even though it is somewhat related to color depth, I'll start a new post about the dye, I believe I can share some expeience and insights I have learned that may help those having problems.

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  • Fibergeek
    replied
    That wouldn't suprise me either.

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  • Sid03
    replied
    Fibergeek- thats not really what I meant when talking about the dye. I simply have a feeling that even newly mixed red dye wouldnt fall into the range that the manufacturer recommends.

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  • Fibergeek
    replied
    M_D,
    One more comment about connections and then I'll shut up (I promise).

    A peak of 13.8V @ 6A/sq.ft. is a PAR value of 2.3 Ohms/sq.ft. That's within 92% of 2.5A/sq.ft. No connection problems here. People having problems with connections have seen 3.5 Ohms/sq.ft. and up; and lousy results, probably regardless of anodization time.

    Regarding pH of newly mixed dye:

    I'm no dye expert but it seems clear that anodizing dyes are sensitive to pH. It also seems to me that if the dye manufacturer could have made the dye more tolerant of pH, he would have. It's to his business advantage to make his product as easy to use as possible. I've not seen any anodizing dyes available premixed; maybe because even if they were the pH would still be off after some time. The end result is higher costs due to the increased labor and the volume of liquid, and no improvement in pH stability. Pushing the premixing and pH adjustment tasks on anyone else doesn't solve the pH problem, it just raises the dye prices.

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  • Sid03
    replied
    M_D- I'd like to see somebody mix up a new batch of red dye and measure the Ph to see what it is. Something tells me it will be higher then they recommend before you even use it.

    Also, i'd be interested in seeing how all your reds turned out, esp. the ones you did previously before letting the part anodize longer.

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  • M_D
    replied
    I have been wondering about how long the part could go after PAR. Although I have been getting a fairly decent medium red, I was looking for a darker red so did a little test yesterday. I followed the 720 rule, and anodized @6 amps per square foot current density for 120 minutes. It hit a 13.8 V peak at about 30 some minutes, and held until I stopped the anodizing. I didn't have time to record the exact curve, so I don't have that to post like Neomoses' nice chart.

    I was very pleased at how much better the red dye colored, after a few seconds the part had a nice pink hue, a sure sign it was taking the dye well. After 5 minutes or so, it had reached the color my reds had been getting after a 30-60 minute dye period. I left it in the dye for a couple of hours, just to see how dark it would get and it is a nice, deep red.

    I am going to experiment some more at other current densities too.

    Just a related a note about color depth for those having troubles with red: I talked to Lance Caswell to confirm what to use when a red dye PH adjustment is required. He recomended muratic or sulfuric acid to lower, and ammonia to raise the PH. I had done this previously and it helps. The longer anodize time and getting the red PH right makes a world of difference.

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  • bp
    replied
    Your intrpretation of the 720 rule is correct. The formula is used for most commercial anodizers and I cannot see a reason it would not work the same for you.

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  • NeoMoses
    replied
    This is the first I've heard of the 720 rule, so I did a quick google search. Is the following correct?

    Originally posted by finishing.com
    You can get a good estimate of the processing time using the '720 Rule' which states that it takes 720 amp minutes per square foot to produce one mil of oxide. The application of this rule is simple. Take 720 and divide it by your current density in amps per square foot. That will be the time required to produce a coating that is one mil thick. It works fairly well for Type II and Type III coatings and for most wrought alloys. Example - how long to produce one mil at 24 amps per square foot? 720 divided by 24 is 30 minutes. So if you want 12 microns it will require 14.2 minutes. Our experience show that this will get you pretty close, say within 10%. You must use current density control, not voltage control, though.

    Sjon Westre
    METALAST International - Minden, NV, USA

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  • M_D
    replied
    I hope this isn't too off topic for the post, but the mention of different shades and current densities promted me to comment.

    I am getting some pictures sized and will upload them to the album page soon. I have been getting a nice dark blue and black with 4.5 amps per square foot. The red from my setup is not bad at 4.5 amps, but could be better, although it may be the ph which I am also working on. I am about to start testing more at higher amps too, as I need to cut the cycle time down.

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  • bp
    replied
    Just a note on your color variance, understand I am not familiar with dies, only 2 step tin coloring.
    Voltage as you said will play a vital role. Anodized coatings at 10 volts will give you a smaller pore structure but will be more porous, but an anodized coating at 20 volts will be less porous but will have a larger pore diameter.
    We have found that anodizing no greater than 12 amps/sq.ft. will give us the best color uniformity depending on load size. If amp rating on our rectifier is maxed we may run at 18 volts for best color uniformity and adjust our anodize time to the running amps.
    Acid concentration, temperature, air agitation and aluminum content can all play a role in the voltage.
    Voltage will control the pore volume, while the current as a function of time will control film thickness.
    As for your mill thickness issue, we use mill meters that we buy from the Paul Gardner Company or Defalsco. Very easy to use but kind of pricey. (Up to $900.00)
    If your using the 720 rule and all of your anodize parameters are inline, ie: Acid Concentration, aluminum content, temperature, cathode ratio and proper amps/sq.ft. you would have to be very close to the mill spec you are trying to acheive. This will very depending on alloys but should be very close.
    I am also very impressed by your reseach you shared.

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  • NeoMoses
    replied
    the LCD sample pictured was anodized in the 1:3 bath as described in the LCD instructions. The 2 others were anodized in the 1:1 bath, as described above.

    The wire was bought at Home Depot, it's standard aluminum electrical wire, I forget what gage. (10-3, perhaps?)

    The electrical connection on the test pieces is to place the wire through a small 1/8" hole in the part and tighten it thoroughly with a pair of pliers, nearly to to the point of breaking the wire (which happens sometimes. ) The connections are quite tight, even though they are not threaded connections.

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  • Fibergeek
    replied
    Sure!
    I'd be glad to help.
    The gauge is out on loan for the moment, but I can get it back.

    Question:
    The LCD sample in the latest picture, was this one done with 1:1 or 1:3 battery acid/water?

    When convenient, could you post your connection method? The more detailed the better. Please include what the wire is and where you got it.

    I'll be in touch.

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