Small tank anodizing

[cameraman]

I anodize in a 6 gallon tank on the back patio. Summer's upon us. I'd resigned myself to the fact that I'll be spending the next 6 or 7 months sweating my petula off, but then some posts by caswellsage, andrewjb, and joebauer08 got me thinking - what about a 1 gallon tank indoors?

I know that theoretically, there should be no difference between anodizing in a 1 gallon tank and a 20 gallon tank, but I'm curious about possible differences in a real-world setup; is there anything that may act just a bit differently, or new issues that need to be addressed?

I kept a close eye on temperature rise during runs when I first started anodizing, but determined that it wasn't significant. I'm thinking that it might become so with the reduced thermal mass of a 1 gal.

Other issues that have occurred to me include exhausting fumes, maintaining minimum distance to cathode plates, agitation in close quarters, and acid concentration (might be more finicky).

Thoughts, or firsthand observations?

[sage]

Good questions just up my alley.
My current tank - until I get the new 6gallon one finished - is about two gallons maybe. I've always done it indoors. I set up a platform to sit on a table (workmate actually) with a back panel. To this I attached a standard range hood - a cheap one from your local Home Depot will do. I put it down to max about a foot above the tank to be sure it attracts the fumes. It works out nice because it has a light as well. I attached a flexible dryer vent hose to it and I send it out the basement window. (works good for small spray painting jobs too)
I can't compare to large anodizing set ups since I've never been there. The largest I've done is maybe 200sqin. I used to anodize at higher currrents than I do know and bath temperature was a problem, but since I keep things down to maybe twice to 3x the LCD settings there have been no problems. The bath gets a fog of small bubbles - hence the range hood. I've nver used automatic agitation. I just carefully move the parts or stir the bath avery 5 minutes or so. I usually try to adjust current to achieve maximum of 120mins (because I'm impatient), but keeping within the 720 rule if you use that method is recommended.
Although I'm not 100% sure of my acid strength I measured specific gravity and it is suspected to be between 2:1 and 3:1 - a bit stronger than LCD.

I put my dye (about 2 quarts) in an enameled kitched pot heated on a single burner electric hot plate in the basement too. The dyeing seems to take about 1/2 hour at 120degF normally and the dye does not ssem to cool too quickly so I remove it from the burner after I put the parts in and use the burner to boil the water while the dying is going on. I manually swish the parts aroundin the dye as well. It's a bit of a juggling act and ocasionally I have to rush up and use the kitched stove becasue the parts are getting to the colour I want and the water isn't boiling yet so I have to get out the big guns.
I always empty the acid tank out after use becasue I don't do it too oftenand I don't like leaving acid out to evaporate near my lathe and milling machne. I put the acid into a 5 gal sealed plastic container - the kind with a pouring spout with the screw cap.

Maybe 15 years now. Never had any problems always had good results.

PS> I'll continue using my bigger tank in the basement in exactly the same fashion. I would expect a bit more circuit resistance and therefore higher required voltage but we'll see. I may have to rebuild my CC (24v) supply for a bit higher voltage output.

Anything I've left out?

Sage

[sage]

I just got a really good idea for a tank agitiator from a friend in the plating business. He doesn't use this idea in his plating tanks but somewhere else in his process )can't remember where he said). He suggested using a paint mixer.
Richards - the company who makes paint supplies like scrapers etc, also make a small paint mixer which is actually a squirrel cage fan about 4" in diameter on the end of a metal rod. You spin it with a drill normally and submerse it in a can of paint. Guaranteed to be the best mixer they say - I agree.
Using a drill I put it in my 6gal tank which is about 24" x 12" x 10" deep. It really moves the liquid - too fast actually so I tried one of those battery screwdrivers which turns at about 180rpm. The round shaft fit snugly in the hex hole on the screwdriver.
Perfect !!! The water was moving qround the tank at a very nice rate. It doesn't take up too much space. All I need now is to make a bracket to hold it over he tank in the middle (where it works best) and maybe connect it to a power supply instead of the batteries.
It has a metal shaft but I don't expect any problems with that as long as it doesn't become part of the electrical circuit. I'll have to see how the plastic squirrel cage hold up in the acid.
So there you go - for $8 a tank agitator.
The reason I didn't go with air (even though I bought all the fittings and pipe) is becasue I wasn't too keen on all the bubbles bursting on the surface causing spattering of the acid. Never actually tried air so it may be a non-issue and also don't like the idea of pumping acid outside the tank especially when I don't need to for cooling or anything.
I'll report on my success with the paint mixer later.

Sage

[sswee]

The main difference I noticed starting out with a 3 gal. and moving up to 15, 20 gal was the amount of heat the tank could handle. I never really noticed anything else. I used aeration up to the 20 gal. The first tank was a square plastic cat food bucket. It worked well, I just outgrew it on the size of parts I was doing. If the parts you do are small enough to go in the tank with enough clearance to the cathode you probably won't notice any differences.
SS

[cameraman]

Originally Posted by caswellsage

Good questions just up my alley.

I figured they were, but now you know why I said 'after you've done a few runs in the big tank'


Range hood's a good idea.
For the mini line I'll probably use microwave to heat the dye - I picked that idea up here and have used it a couple times, works well.
I'll use something that can be sealed for the tank so when it's not in use it's easy to button up.

Instead of traditional agitation, I'm thinking about trying out a couple of wacky ideas (in big tank first) - I want to try attaching some sort of a vibrator to the hanging wires, and I've also been pondering ultrasonic. They make these ultrasonic transducers for creating a fog effect in ponds. My thinking is to encapsulate one against acid exposure and place in bottom of tank, probably not even running it nonstop - 10 seconds per minute possibly (I really don't want 'fog' rolling out the top of the tank). Vibration would probably be more effective, definitely cheaper - but having an ultrasonic anodizing tank is an intriguing idea..

As long as you're keeping 3-6" distance between part and cathode, I don't see any reason you'd experience higher resistance with a bigger tank. I got curious the other day when you mentioned it and measured mine. At 3" it's about 250k and at 6" it's about 450k. I didn't measure tank temp but it was probably about 85° F (no, wasn't anodizing anything!).

I've been using a drill powered blade type mixer to stir up my dye, but never thought of using one as an agitator - I've seen those squirrel cage ones. I dono about that metal shaft, though - you might be a bit optimistic about that. I had to temporarily use my mixer as a hanging bar on a couple of runs and it already started to change color just from the fumes. You might want to give some thought to coating as much of the shaft as you can with some tool dip. Definitely report further - that's a pretty slick idea.

Originally Posted by sswee

If the parts you do are small enough

I've got several that are in the neighborhood of 1x2x2", various little hunks of alum rod and formed sheet. Before hatching this 1 gal idea I'd planned on re-setting up a 3 gal tank.
Have you noticed any difference in fume level between aeration and your current method of agitation?

[sage]

The size of the parts I need to do is the only reason I'm moving up. I have a base plate for a model engine I'm building. It's 13x7" x 1/2 inch thick. It wouldn't fit in the small tank. I'm also crossing my fingers that the temp won't rise too much even in this larger tank. I'll keep the current down to acceptable time.
You could be right about the metal rod on the mixer, but I see the squirrel cage bits can be removed from the rod and I could easily replace the rod with a plastic one. It's really not under much torque stress at the 180rpm of the screwdriver. I consider the whole thing expendable at $8. It works so well it's worth a try though.

You mention 250k for the tank resistance. Something wrong there. From where to where did you measure that. Typically, the resistance is dependant on the size of the part and the resistance of the acid (distance through the acid to the part), but typical running resistance of the tank should be a few ohms or so. I was expecting higher resistance only because if I do a run of my usual small parts and put them in them in the middle of the larger tank the distance would be higher than my small tank. I'll probably fire the whole thing up for a trial tonight.
I also expect to have to replace the cathod really soon. I cobbled it out of aluminum flashing which I thought was thicker when I saw it on the role but it turns out to be only 10thou (.010") thick so it might disappear quickly. Once I'm past the two big parts for this project I can proabably return to my small tank.

Sage

[destroyer125]

Since upgrading from a 2 to 10 gallon tank ive noticed heat will not fluctuate without alot more effort, my old tank some ice would drop the temperature alot, it takes an entire bag of ice to drop it 5-10 degrees now

[cameraman]

Originally Posted by caswellsage

From where to where did you measure that.

I attached short Ti wires to my test leads and stuck them into the bath about 1/8" depth. It was when you'd said something about high resistance of a weak acid solution, so I was curious about the resistance of the solution itself, as opposed to the overall resistance of a part being in the solution. In and of itself I don't think the number is useful for anything; just general curiosity.

I have my plates set up so that I can move them in response to part size.

Originally Posted by destroyer125

upgrading from a 2 to 10 gallon tank ive noticed heat will not fluctuate

So it's looking like going the other direction I may have some problem with temperature but no other surprise issues.

[destroyer125]

I just ran across these http://cgi.ebay.com/Iceprobe-Small-A...QQcmdZViewItem

[luminous]

Originally Posted by destroyer125

I just ran across these http://cgi.ebay.com/Iceprobe-Small-A...QQcmdZViewItem

Hey that's cute... and I might actually have a use for one of those. But I don't think it would be happy in a sulfuric acid solution for very long. It mentions nylon parts, and nylon doesn't like H2SO4 very much, even at 5% strength.
Just my $.02

Steve