Anodizing

So I decided to anodize the head.  I took a class at TechShop RDU where they teach you to anodize aluminum in one of their back rooms.  They basically have a large wooden box filled with kitty litter that has a bucket of Sulfuric acid sitting in the middle.  A 2x4 is strapped across the top with a couple aluminum bars with screws in them mounted to the top.  The screws are where you hang your parts from.  The aluminum bars are attached to the positive and negative of a power supply.  There's a bucket of dye also (red or blue).

TechShop RDU Anodizing Rig

First thing i had to do was mask off the critical areas: the spark plug hole and the top of the combustion chamber.  I couldn't just use a SS bolt to plug the spark plug hole.  Apparently sulfuric acid eats SS pretty quickly.  So I fashioned a threaded plastic rod and some nuts together to form an encapsulating assembly.

Masking rod assembly

Then I masked the sealing surfaces with masking tape.

Masking tape on the spark plug hole

Masking on the top of the combustion chamber section

Then added the plastic encapsulating assembly.

Bottom side

Top Side

Next I bead blasted the surface to make sure the surface was even.  Then I had to clean any oil off of the aluminum.  Apparently even oil from your fingers can cause blotchy looking spots in your anodize.  Did this by soaking it in a bucket of warm water with some dish soap for 1/2 hour and then rinsing.

Cleaning the head

The next step was to hang the assembly.  I wrapped 4 wires around the fins on four sides of the head and then wrapped them together so they'd hang off of one of the screws.

Hanging head from 4 aluminum wires and dropping it in the Acid

Then I closed the lid(s) on the top of the bucket and turned the power supply on.  As you can see from the above picture, there are two hanging plates on either side of the bucket.  These are the cathodes.  They're connected to the negative side of the power supply.  The Al wires going to the head are connected to the positive side of the power supply.  The current travels from the PS, down into the head through the haning wires, through the sulfuric acid, and back through the cathode plates.  This causes a reaction at the surface of the aluminum to oxidize it.  Basically rusts it or creates aluminum oxide.  At the same time, the acid eats away at this oxide layer, creating a bunch of craters in the surface of the oxide.  These holes or craters are what allows the dye to hold onto the part later.  Or so I'm told.

Bucket of sulfuric acid with 18A of current running through it

Apparently surface area is pretty critical when anodizing.  First, you need to have equal or greater surface area on your cathode(s) as you do on your anode (part).  To figure out how much surface area I had on my head, I had to model it up in SolidWorks and let it calculate it.  Turns out its about 225 sq. inches.  The cathode plates are about 9x9 so their surface area is around 162 sq. each (front + back) or 320 sq. inches total with both plates, so I was fine there.  The other thing to consider in regards to surface area is current density.  The recommended surface density is 12Amps per square foot per hour.  An hour seems to be the recommeded time, but if you can't reach the current density in an hour, then you just extend the time.  The power supply they have maxes out at 18A, so I cranked it up to that since I have a little over 1.5 sq ft.  Close enough.

Power Supply

I let the head sit in the acid for an hour at 18A.

Soaking in a nice electric acid bath

Another thing to consider is the temperature.  If you let the bath get too hot, the chemical reaction isn't as good and your part doesn't anodize properly.  I noticed that the bucket was getting hot to the touch over the course of the hour, but there was no way to cool it, so I had to live with it.  Some people add cooling elements to their baths which would be a good idea here.  You're supposed to keep the bath around 70 deg. F.  I'm sure mine got higher than that.  It was about 100 degrees outside.

In the mean time, I got the bucket of red dye ready.  I wanted to match the color of the bike, so the red was perfect.

Red dye bath

Apparently, its a good idea to warm up the dye bath to get it to stick to the aluminum, so I warmed it up in the microwave to just below boiling.

After the hour was up, I removed the head and rinsed it off good with water.  I then dunked it in the red dye.

Dunking in red dye bath

After the recommended 20 min in the warmed red dye bath, I pulled it out to see what masterpiece I'd created.

Coming out of dye bath

Looked ok at first, but after rinsing, it looked like this.

Anodized!

Looks like ****!  I was pissed.  I'd spent so much time prepping for this moment and it came out terrible.  I did some reasearch in the books they have on anodizing and found out that cast aluminum doesn't anodize well because it's typically got a bunch of different grades of aluminum mixed in that aren't too pure.  I guess I confirmed that theory.  Other than the junky cast aluminum, the only other thing I can think of that wasn't "as recommended" was the temperature of the bath getting too high.  Not much I could do about that though.

WTF Yo?

 After soaking in the red dye bath, it is recommended to seal it with a sealer.  They didn't have any sealer there, and recommended using a bath of boiling water.  You're supposed to soak the entire part in the bath for 5-10 min.  This apparently seals or locks the die into the part.  I didn't bother with this step because, well, look at it.

So anyway, it was a learning experience at least.  I think I'm just gonna spray paint it black now.  I'll sand blast off whatever anodized surface layer there is on there and get a spray can from HD and call it good.