Anodizing cathode information required
Q. Hey gang...I have some question which directly relate to the cathodes used in type II anodizing. They are as follows :
1. Using 6061/6063 aluminum sheeting versus lead sheeting - what are the pros and cons?
2. I understand that the cathode:anode ratio should be around 3:1. How critical is this? Can a person utilize a much greater ratio, for example 30:1? What might the result be?
3. I realize it is common practice to remove the cathode(s) from the tank when not in use but I am curious what the cons are to leaving the cathode(s) in the tank full time.
4. When calculating the surface area of a sheet of aluminum which is resting flat against the wall of a tank (or very close to the wall), does one consider both sides of the sheet in the calculation or just the side facing inward to the tank?
The reasons I ask these questions is because I am currently building an anodizing tank. Using 1/2" polypropylene, I have welded up a box with internal dimensions as follows : 30"L x 14"W x 19"H. I was thinking of using 1/16" aluminum sheeting as the cathodes and basically line the inside of the tank. My thoughts were to leave this aluminum in the tank full time.
My thanks goes out to all who reply. Cheers!
A. Aluminum is more conductive, takes less watts, saves on cooling. Lead puts some lead into the waste stream. Purists say use 6063T5, but just recently a shop (who claims no stray current or galvanic current) got less than 6 months. Another shop that I set up got 4 years out of 6061 1/8 inch thick !
For type II the ratio is NOT critical, but 30 to 1 may be a problem. Do not do it. If you are talking a lead lined tank, than use plastic to mask the bottom and ends.
My client that got 4 years with 6061 NEVER removed the cathodes. There was no stray current. The heat exchanger was outside.
Use one side facing the work.
Wow, 1/16 might be a bit thin. But do not line the tank. Have no cathode on the bottom and no cathode on the ends.
Robert H Probert|
Robert H Probert Technical Services
Garner, North Carolina
A. The use of lead in the form of sheet or tubing is both more expensive and less efficient than aluminum. To avoid the aluminum dissolving readily in the anodizing bath the use of 6063t6 mandatory. It is not necessary to remove them when not anodizing. Try to stay as close to a 3 to 1 ratio(3 anode to 1 cathode sq ft) If you have more questions I would be glad to help or you can view my web site.
Drew Nosti CEF
AESF Light Metal Committee
Drew Nosti, CEF|
Ladson, South Carolina
A. Thank you for the input. Drew, you posted that the anode-to-cathode ration is to be in the range of 3:1. That is to say that for every 3 sq.ft of anode, 1 sq.ft. of cathode is required. I have been lead to believe the opposite is true and that for every 1 sq.ft. of anode, 3 sq.ft. of cathode is to be utilized. Perhaps my research is incorrect. Please verify.
I appreciate the help and conclude that : 6063T6, 1/8" thick sheeting will be utilized as cathodes. The sheeting will be fabricated to hang over the sides of the tank in multiple sections thus allowing cathode size manipulation. The cathodes will be removed when not in use, rinsed and hung to dry.
Now is the anode-to-cathode ratio 3:1 or 1:3? Thanks all...Cheers!
A. To answer my own question - a rather basic one I might add. While visiting Mr. Nosti's website (Anodize USA) I have concluded that the anode:cathode ratio is 3:1.
I hope you do not mind Mr. Nosti, I have taken this quote from the Anodize USA website, "...the ratio of 3 sq feet of anode to 1 sq foot of cathode gave the most consistent anodizing.". It should be noted that Mr. Nosti is referring to 6063T6 aluminum cathodes.
Its funny to think, how we grow we sometimes misunderstand stuff. in fact, I feel quite foolish at the moment. For 6 months now I was under the impression that the anode:cathode ratio was to be 1:3. I was anodizing with decent results utilizing this method. I was also using just simply 1/16 aluminum sheeting of an unknown alloy for cathode material. I have currently reversed that theory thanks to Mr. Nosti and finishing.com. My current setup will soon be recalibrated implementing a 3:1 (anode:cathode) ratio while utilizing 6063T6 aluminum cathodes. Just one more step in the right direction. Thanks people! Cheers!
A. Thanks Dan, it is nice to hear that correct information is spreading. Remember it is not a perfect world and in anodizing you can get almost anything to "WORK" .The question is what is the best way. When starting or updating any metalfinishing line try to travel in a direction that will lead to the best technology, even if it is in small steps.Good luck.
Drew Nosti, CEF|
Ladson, South Carolina
A. We have had a member on another anodizing forum try this unusual (to us anyway) 1:3 cathode/anode area. There is definitely something useful here, we will check this out in detail with properly instrumented anodizing experiments this Spring and inform Drew directly (and privately) of our findings.
A. Hello, the ratio from anode : cathode is 3:1 as a minimal ratio in the project of a tank building for a full charge, maximal anode area or rectifier capability that define the greatest area that can be processed.
If you became in any moments a 30:1 ratio, do not problems, make be sure that the rectifier is so adjusted to prevent a burning, in a other ratio ASF (amp per sq ft) that you use conform your bath and Tank construction condition.
I do not remove de cathodes from the Tank, only for cleaning or replacing.
- Blumenau, Santa Catarina, Brazil
February 4, 2013
Q. The anode to cathode calculation is 3:1, this is for maximum load size of the parts? since once we install the cathode of a size then we cannot change for each and every batch.Aijazullah Tajir
- Abu Dhabi, UAE