Need opinions on my next tank.

[jtsuttle]

I have came to the milestone in anodizing where tank temp is a real
issue. Yesterday I tried doing some engine mounts for my buddy's
race car. Although I felt that they were to big for my 5 gal setup I
did them anyway. Tank temp and current started rising rapidly but I let
it run just to see what would happen. After 1 hr 15 minutes the tank
temp hit 100 deg F. The fumes were terrible. That's when I chickened
out and pulled the plug. The plan was to do them clear so I don't
know how well they would have taken dye. They do pass the ohm meter
test and look pretty good considering the temp.

I am considering buying a 5 cuft chest freezer to use for a tank.
Now since a freezer would be to cold for type II, I have an external
temp controller with a thermocouple I could drop into the bath. The
controller plugs to 115v and has a 115v outlet where I can plug the
freezer and cut off power at the cord at whatever set point I desire
(-300 to 3000). Its a little over kill but I already have it lying
around. The 5 cuft freezer would be about 37 gal so I would probably
fill it with about 25 gal of electrolyte....

Now this is where I need everyone's opinion. I don't suppose
freezers are designed to be filled with liquid so I'm wondering if
the walls may fail and leave me with 25 gal sulfuric in my basement
floor? The irregular shape of the inside of a small freezer makes it
difficult to put another tank inside it without losing much of the
25 gal volume. I would also hate to step up to a bigger freezer
because of cost and lack of space for a large one. I like the idea
of just using the 5 cuft freezer for the tank but I am a little
apprehensive about it.

What do you all think?

[M_D]

I don't know what type of lining your freezer has, but it would need to be a material that would resist the effects of the anodizing electrolyte. One particular area that may leak even if the lining stood up is the drain, they don't seem very adequate for a water tight seal, let alone acid where the results of leakage would be a big problem.

Have you thought about just setting up a larger tank, as it would take longer to heat it up?

I need to deal with cooling a tank too, I don't know exactly what I'll do yet. I figure I'll need more than a simple heat exchanger cooled with room temperature air and a fan. I may fabricate a titanium heat exchanger and use a small air conditioning unit to control the temperature. The store area of this site has a chiller unit too, and might be a good option.

[Fibergeek]

I'm not thrilled by the freezer idea either. Besides leaking; life might get interesting for the refrigerant compressor, those things are not supposed to be switched on/off that much.

An inline chiller like M_D discussed would be better, you could combined it with an agitation system to deal with this requirement too.

[NeoMoses]

How about a large plastic cooler? I've seen some 100 quart coolers that are fairly inexpensive and would be a good size for anodizing, usually fairly long and somewhat deep. One benefit of a cooler would be resistance to outside temperature influences.

[Easttex]

I'm in line with the other posts on this...nix on the freezer. I'm running about 20 gallons in my tank which is a HDPE sterlite type of tank insulated and sealed in 6 mil plastic. I have ran up to 21 amps (4.5-6 amps/sq'), in my tank for the full 90 minutes with no problems with temp, however, I am heavily agitated with air from a regenerative blower set up. When it comes time for me to upgrade, I'll probably just put in a second tank for volume reasons rather than part size. A second tank would allow me to stagger the runs for custom dye work reasons. If size of the part alone is reason for upgrading coolers or tote tanks should work well. To the best of my knowledge, nitric acid is the only thing that would give you depolymerization issues. You should be safe with any pp,hdpe, or pvc construction.
EasTTeX