Posted: 2/24/2013 1:03:23 PM EDT
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I have wanted to try it for some time.
I am building some fixtures at work using aluminum and figured this would be a good time to try it. This weekend I am experimenting with some scrap parts: Sanding to remove machining marks Polishing Anodizing Coloring Sealing Right now the current in the bath is just beginning to drop. I will post a couple pics a little later when I have a moment. If this works, I'll try it on the real parts in a few days. |
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Well that was an interesting experiment.
The results are inconclusive. All three parts were processed the same except: 1. The Cube was dyed with Red instead of black 2 The "Chocolate" colored one was not polished, just sanded. 
I am leaning towards not cleaning enough properly before anodizing as the cause. 
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Yea you should probably clean again after the polishing. Did you do the water test? ETA:  http://youtu.be/qr-zd6StOOw 12:45 is what I'm talking about. It's got to be really really cleanYes I did, but I can see from that video that I definitely did not clean it enough. Thank you. |
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Before you anodize, you should, "acid etch", material in mild acid to remove any contamination. Dip part in acid for a short time and rinse with distilled water. Experimenting on length of time for acid dip. I read about this but thought I would try degreaser first. Probably the right way to go though. |
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Never seen it done with tinfoil before. Any reason your using it instead of lead? Most of the time when I was anodizing and something didn't take color was from the wire not getting good contact with the part. The tinfoil was something I saw in a video. I was wondering about the wire contact. I am planning to change how I connect parts in the future. |
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Can you tell us where you sourced your equipment from and a brief outline? I've got a shotgun follower I had a buddy machine for me in aluminum and I'd like to anodize it against wear. The DC power supply I got from some auction. The rest I got from: Walmart-RIT dye, distilled water Autozone-Battery acid, degreaser,Turtle wax polishing compound Home Depot-aluminum wire I just researched the process from the Internet. I'll update when I get the process better. |
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I'm assuming that the power supply is set for constant current, and if I'm reading the meter in your picture, it reads about 1.5 amps unless those test pieces are very small. This isn't enough current. You need a minimum of 3amps per sq ft to get decent growth. Voltage should read in the range of 12-19volts.
The reason that the current dropped out on you is because of your connections to the aluminum blocks. Aluminum Oxide (anodization) is an insulator. As the layer increases in thickness, it resistance increases until it reaches the point where it blocks all current. At such a low current (1.5amps) the layer is still very thin and the current can't 'power' through it. In commercial applications, high current is used (60-100amps) so the issue of the layer resistance isn't as much of an issue as it is in lower current applications. It also helps to agitate the electrolyte every few minutes. The anodization process creates heat, and this heat warms the electrolyte around the aluminum causing it to dissolve the aluminum oxide at a faster rate. Agitate helps to dissipate the heat. It also helps to shake any hydrogen bubbles that may be clinging to the aluminum. These bubbles will also prevent anodization and will create non-anodized spots that will not accept the dye, although this doesn't look like your issue, but becomes more of an issue has current levels rise. What is the concentration of your h2so4 bath? High acid levels will also cause the anodization to dissolve as fast as it is created. Low acid levels slow down the anodizaton process. ETA: Corrected 'amps' to 'amps per sq ft' |
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Before you anodize, you should, "acid etch", material in mild acid to remove any contamination. Dip part in acid for a short time and rinse with distilled water. Experimenting on length of time for acid dip. This. Also, if you don't remove ALL factory finish and get to the bare metal, nothing will take and if it does, it won't last long. OP, Why are you wanting to anodize anyways? If it's to keep parts from corrosion, then I would suggest alodine after the acid bath/water rinse for best results. Then of course a good two part fay sealant job for metal to metal contact for best results. Then paint over it. I haven't read the entire post yet, just wanting to add my $ .02 |
| Anything that had a hole in it I always used something to wedge wire tight or if the hole was small enough I used the big aluminum pop rivets. I found that aluminum wire for electric fences worked best for current. It can be bought cheap at tractor supply. I think I paid 40.00 for 1000'. Make sure your anodizing bath stays between 65-70 degrees. Can use small frozen bottles in bath to regulate temperature. It's better to have your bath moving. I used small fish tank pumps to move the bath but they don't last long with the acid. Some use hose or PVC pipe with small holes and a low volume of air to move it that way. |
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I'm assuming that the power supply is set for constant current, and if I'm reading the meter in your picture, it reads about 1.5 amps. This isn't enough current. You need a minimum of 3amps to get decent growth. Voltage should read in the range of 12-19volts. The reason that the current dropped out on you is because of your connections to the aluminum blocks. Aluminum Oxide (anodization) is an insulator. As the layer increases in thickness, it resistance increases until it reaches the point where it blocks all current. At such a low current (1.5amps) the layer is still very thin and the current can't 'power' through it. In commercial applications, high current is used (60-100amps) so the issue of the layer resistance isn't as much of an issue as it is in lower current applications. It also helps to agitate the electrolyte every few minutes. The anodization process creates heat, and this heat warms the electrolyte around the aluminum causing it to dissolve the aluminum oxide at a faster rate. Agitate helps to dissipate the heat. It also helps to shake any hydrogen bubbles that may be clinging to the aluminum. These bubbles will also prevent anodization and will create non-anodized spots that will not accept the dye, although this doesn't look like your issue, but becomes more of an issue has current levels rise. What is the concentration of your h2so4 bath? High acid levels will also cause the anodization to dissolve as fast as it is created. Low acid levels slow down the anodizaton process. This^^^^^^^ I did have the current limit set but the meter is not working properly. I increased current until I saw a "cloud" of bubbles coming from the foil. I will be using a higher voltage (this one maxed at 10v) and higher current supply in the future. Thank you for the great information. |
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Before you anodize, you should, "acid etch", material in mild acid to remove any contamination. Dip part in acid for a short time and rinse with distilled water. Experimenting on length of time for acid dip. This. Also, if you don't remove ALL factory finish and get to the bare metal, nothing will take and if it does, it won't last long. OP, Why are you wanting to anodize anyways? If it's to keep parts from corrosion, then I would suggest alodine after the acid bath/water rinse for best results. Then of course a good two part fay sealant job for metal to metal contact for best results. Then paint over it. I haven't read the entire post yet, just wanting to add my $ .02 Anodizing for the non-conductive surface. |