The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Combining rinse tanks for multiple anodizing tanks?

The company I am working for has tasked me with determining the requirements of adding an in house anodizing line for our parts as well as customer parts. We are in the aerospace industry and are looking specifically at anodizing as it relates to the surface preparation of aluminum for bonding. This line would consist of Chromic Acid Anodizing, Boric-Sulfuric Acid Anodizing and Phosphoric Acid Anodizing. Being new to anodizing I have been reading posts on finishing.com for quite some time but there is something I have not been able to get a definitive answer on. Is it recommended to use a separate rinse tank after each anodizing tank? Can a second rinse tank be combined for all anodizing types? Although most of the parts will remain unsealed, can the sealing tank be combined? Does the type of wastewater management/chemical recovery affect this? I am also assuming that everything upstream (i.e. Alkaline clean, deoxidize, solvent clean, etc...) can be combined for all types, is this a proper assumption?

Thanks,

Andrew Schleif
Engineer - Medford, Oregon, USA
August 31, 2011

My two cents. Keep everything after the chromic acid anodize separate. After adequate rinsing you can use a joint final rinse for the others and you can probably use the same seal-other than the chromic.

James Watts
- Navarre, Florida
First of two simultaneous responses -- September 1, 2011

---

Second of two simultaneous responses -- September 1, 2011

Hello, Andrew.

It is preferable in most cases to have separated rinse tanks following every process tank, but there are exceptions that make sense sometimes, but it is difficult to give a general answer.

For a second rinse it is generally desirable to have a counterflow double rinse after every process solution, but in some cases that is impossible for space reasons. One clean final rinse in that case would be preferable to having only single rinses.

As far as the seal tank, I would certainly want a dedicated rinse, but it may depend on the particular type of seal that you are doing to some extent.

Wastewater management definitely needs to be considered as part of the rinsing system. It is desirable to separate rinses based on the waste treatment that they need. You'll generally have 3 waste streams- chrome rinses, non-chrome acid rinses, and alkaline rinses. The chemical treatment is different for these waste waters, so combining them may not be a good idea. There are exceptions, because there is more than one treatment strategy. The point is that you should consider your rinse system and your treatment system as a marriage.

Sharing rinses does not allow you to consider chemical recovery.

I hope that helps.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri