Thursday, October 28, 2010

Anodizing Aluminum Because You Can!

With Halloween in the air, we need a scary posting.  What is more scary than a bucket of sulfuric acid, a current generator, liberated highly flammable hydrogen gas, and blood-red dye?  Heck, I took my life in my hands for this posting; just to make it more edgy, I even invited a knife thrower from the touring circus to come over and practice on me while anodizing some aluminum bench dogs for fun and definitely not for profit.

I recently ordered custom Qwas dogs from Steve Adams. These are low-profile dogs for planing and they include a 5/16" hole through the center so they could have something attached to them with a 1/4" bolt.  I'm not sure what I'll do with that feature... yet.

Thing is, Steve said "I can make them, but they won't be anodized like the regular ones".  That got me thinking of anodizing them as a test.

I based my procedure on a great article written by Jim Bowes "Anodizing at Home".  Mine will be a photo version of his document along with some observations and tips not present in the article.  Overall, I had good success with some other aluminum dogs, but these from Qwas had been polished with an automotive protectant and I didn't know that first time around.  That said, you'll see some pictures from the first round and second round intermingled.  If a dog has a bit of color when you don't expect it, it is from round two; ignore it... nothing to see here :)  Due to this protectant I wasn't able to 100% remove, a couple Qwas dogs were a bit lackluster.

  • Sulfuric acid, commonly called battery acid; buy it at an automotive supplier in a 6 qt box for next to nothing (I got mine at Car Quest)
  • Manual battery charger.  I initially used an automatic battery charger (regrettably in some pictures); while great for charging a battery, it intelligently determines that the acid bath isn't really a battery and won't work correctly.  The charger should supply 2A at 12V.
  • Roll of aluminum foil; this is the sacrificial stuff.
  • Roll of aluminum un-insulated wire; I found a long spool at Ace Hardware in the picture framing section.
  • Rit Dye commonly available in the laundry section of a grocery store or in great variety at a crafts center.
  • Aluminum angle (not shown).  Get this at the Borg where the angle iron is.  I got 1/2"x1/2".  Cut into two lengths slightly longer than your baking dish (they sit on it).  You will see them in use later; optional but highly recommended.
  • Glass baking dish; (not shown) I used this for the acid bath.
  • Oil drip pan; (not shown) this can hold the baking dish in case of splashes and makes a handy place to tape the leads.
The whole procedure may be a little slow first time out, but then gets really pretty fast.

Start, shall we?

First, googles or at least good eye protection, gloves, and clothes that won't hang into the acid bath are a must.  The battery charger will put 2A through whatever is between the poles... whether that's the acid bath or, say, your heart if you touch the poles with each hand.  The reaction liberates hydrogen so ventilate like you just ate the biggest burrito of your life.  Pay attention.  This is easy, but don't try for a Darwin award.

Okay, really start now...

The parts need to be clean.  The dogs with a loop were 2-3 years old and raw.  They just needed washing with soap and Simple Green.  While I didn't initially know it, the Qwas dogs were polished on the lathe with an automotive protectant and wax.  To clean these, I used 600 grit wet/dry paper then soaked them in acetone overnight.  It wasn't completely cleaned, but I'm okay with it.  While Jim's article recommends a nitric acid wash, I found it too difficult and/or expensive to get here.  Acetone will dissolve nearly any finish or wax.  A sanding with 600 or even 1200 grit wet/dry sand paper will not sand-down the part, but will polish the surface mechanically and remove a lot of grime.  To me this is faster, easier, cheaper than mucking with nitric acid and hazmat fees.

If you haven't yet mixed the dye from previous anodization sessions, mix a full dose of Rit Dye into about 2 cups hot water and mix well.  I used 2 cups of water since that's all I needed to easily cover the parts; if your parts need more, make it more diluted.  I chose red.  You'll re-use this so get a plastic container to hold it between flirting with death, er, anodizing.

Pour the dye mix into a sauce pot large enough to immerse your part.  You want this at room temperature when you finally drop your anodization parts into the dye so if you just mixed it, set the pot in a shallow dish of cold water to cool it faster.

Take a long string of aluminum wire and create a flat paddle of wire turns with an arm of wire reaching out of the pan; you will connect the cathode (negative) pole to this wire.  I ran 2-3 loops up and out of the pan for a better connection to the cathode.

Wrap the paddle portion in a lot of aluminum foil.  The parts (and anode!) will be on the other side of the dish so keep this foil paddle well on its side of the dish.

Using aluminum wire, suspend the parts to anodize on the other side of the baking dish; the anode (positive) pole needs to attach to the wire so bring a decent length outside the dish.  Again, I doubled up on the wire for better contact.

Put the glass baking dish into the oil pan.  Fill the dish with a diluted mix of sulfuric acid by adding 1 cup of water to each 2 cups of acid.  The picture shows how I re-sealed the dispensing tube.  Basically two scraps of wood and a C-clamp pinching the tube shut.  This is more certain than inserting something into the end of the tube and I never use my C-clamps :)  You can re-use the acid mix so you might plan on having a large plastic container with a screw top and plastic funnel for later.

Place the UNPLUGGED battery charger near-by.  Connect the anode (red) clamp to the wire suspending the part.  Connect the cathode (black) clamp to the wire suspending the paddle of foil.  I used blue tape to tape the leads to the oil pan so the wouldn't move.  I also labeled the parts and paddle with positive and negative in the photo for reference.  If you get this backwards, your part becomes the sacrificial media :)

Set the battery charger to 2A at 12V.  Recheck everything.  Plug in and turn on the charger.  You should immediately see bubbles spewing from the sacrificial foil and some from your part.  Set a timer for 15-20 minutes (these dogs were done in 15 easily).

This picture shows my improved setup for the acid bath connections.  The lengths of angle aluminum span the dish.  The foil paddle has its wires come up and loop the aluminum and the cathode clamps over the wires to the bar for a very solid connection.  Similarly, the anode clamps over the wire from the part.  If you had a tall dish, you could easily suspend the part from this setup.  This one is a winner.

While the anodization proceeds, get a plastic dish and fill it halfway with cold water.

Once done, turn off and UNPLUG the battery charger.  Disconnect the clamps and fish out your parts; drop them into the plastic container of cold water to wash away the residual acid.  Fish them out of here and drop them into the pot of dye.

At this point, you could start anodizing other parts.  You need the part to sit in the dye.  Shake the pot a bit, stir it with a plastic spoon, toss the parts around a bit from time to time.  You should be able to pull the part out to inspect them and see that they have taken on a color and may be a colored film.

What has happened to the parts so far is to build a thick surface of oxidation ("rust") on the surface of the parts.  Unlike common ferrous rust, aluminum rust just looks a little pale and doesn't flake off.  The oxidation layer is very porous so the dye will settle into the pores giving the color.  We need to seal the surface to lock in the color.  The rust collapses when subjected to heat like that found in boiling water.  At this point, you could transfer the parts to a pot of boiling water for a few minutes to seal the surface.  Thing is, some of the dye will leach off before the pores seal. What to do!

What I decided to try on my second attempt was to simply put the sauce pan on a burner and get the dye to boiling.  No color could be leached as it is in the color.  The dye is okay with boiling heat as they directions even state that boiling water is the preferred medium for coloring (cloth in this case).  I brought it to a boil and left them there for 15 minutes.

This is the result hot out of the dye.

I cleaned them up with a little light rubbing with 600 grit wet/dry paper to remove some dots of dye that stuck to the dogs including tiny dots you could feel but not see.  Doesn't change the color, but cleans them.  Careful of the edges as those can be sanded lighter.

Some observations:
  • Black dye likely won't make specs like red did in my case; however it is important to note that the specs only happened on the Qwas dogs that had the protectant.  This could be related.
  • The second time I anodized, it took very little time getting to the point of waiting for the process to complete.  While the parts boiled in dye, I put the rest away.  Very fast process dispite the seemingly long instructions :)
  • The un-anodized aluminum sanded easily; I tried sanding an anodized aluminum part and found it very hard by comparison.  Besides beautifying the part, it makes them much more durable.  If you didn't want the color, but wanted the strength, you could do all this with out the dye; just boil in water.