Скачать или смотреть Anodizing aluminum at home, Part 1

DISCLAIMER: DO THIS AT YOUR OWN RISK. I TAKE NO RESPONSIBILITY FOR YOUR ACTIONS AS A RESULT OF THIS VIDEO.

My process:

1.) Surface finish. Sand your part to get rid of scratches etc. I went up to 800 grit. Any imperfections will be enhanced by the anodizing process, not masked. If you want your part to be shiny, now is the time to polish it.

2.) Degrease and wash parts. I use brake parts cleaner in a spray can, then use Simple Green with a scrub brush. I’m not entirely sure if both steps are necessary but it has been working well for me. Parts need to be "surgically clean". Any oils will interfere, so don't touch the part with bare hands beyond this point. You can do a “water break” test to see if part is clean. A stream of water from the faucet should form a uniform sheen on the surface. If the water runs in a thinner stream along the part, there are still contaminants present.

3.) Anodizing: This is “Type II” anodizing, and what’s happening is we are creating an oxide layer that is mostly grown into the surface of the part. This layer is tough, non-conductive, corrosion resistant, and until sealed is also porous -- these microscopic honeycomb-like pores are what holds the dye if you choose to do so. A normal anodize coating is anywhere up to about .001” or .002" thick (a couple of "mil's"), and is difficult to get much thicker than that for this type of anodizing. The sulfuric acid solution needs to be about 15% concentration by weight. The battery acid I bought from the auto parts store is roughly 35% so diluting 50-50 by volume with distilled water will get close. You can use a battery hydrometer to check the specific gravity. You're looking for about 1.1 sg. Look up the MSDS on the acid to be sure what you are buying. (Remember add acid to water, and wear gloves & goggles). For the cathodes, I’m using 2 titanium plates (10cm square) suspended on the sides of the tank using aluminum hooks (Ti plates are supposed to last longer, but you can also use aluminum, or lead). To suspend the part I'm using aluminum rod. Again, you can also use titanium, but remember whatever you use will also get anodized, and if you want to re-use it, you'll need to strip it in lye / caustic soda. Hook up your power supply, + to the part and - to the cathodes. For current, you need to calculate the surface area of the part. The rule is 720 amp minutes per square foot will produce .001" of oxide. In addition, it should be at least 12 amps per square foot. While you can use constant voltage to anodize, you really should try to use constant current and let to voltage do what it needs to, which will result in a more uniform coating and take less time. In my experience the voltage will go anywhere from about 13v to 18v but a lot of factors will determine that. The cathode plates will bubble a lot, which is hydrogen gas being produced. The part will bubble a little too, but not as much – that’s oxygen, and most of the oxygen molecules being generated are attracted to the part, which forms the oxide layer.

4.) Rinse. I dunk the part in cold tap water but then give it a good spray with distilled water to keep from affecting the PH of the dye, which you can re-use many times. I may change this step to 100% distilled water because I think the impurities in the tap water might be interfering with the sealing process later.

5.) Dye (Optional). Mix up dye per manufacturer instructions with distilled water. I used actual anodizing dye from Caswell, mixed in a 2-gallon bucket. For larger parts I siphon it into a pan shown in the video. You can also use Rit, etc. but clothing dye may fade in sunlight and might not be as uniform or consistent in color. Dunk the part and leave it in there for up to 15 minutes. I’ve found that 10 min is usually plenty, and the part won’t take any more dye beyond that. Caswell recommends heating the dye (but not too much, ~140F otherwise you will start sealing early), but I’ve not found that to be necessary. Any color except white can be obtained (white dye molecules are apparently larger than the pores and is problematic.)

6.) Seal. Sealing causes the pore openings in the oxide layer to swell and close, which locks in the color. I’ve been using tap water for this, which has been working fine, but most guides say to use distilled or DI water which I will probably start using, or I may try a nickel acetate sealing solution. I boil the part for 30 minutes. A good long boil will produce a better seal. Some of the dye will leach out at first, so make sure the color starts out slightly darker than you want. Steaming instead of boiling should reduce the color leaching, but can also result in splotches. If you heated the dye bath, the color leaching should be less also. After sealing, rinse the part. Some of the color may still come off when wiped with a towel, but that will eventually stop.