Metal finishing Q&As since 1989
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Alodine 600 rinsing question
Alodine rinsing question: At my work the procedure for rinsing parts pulled out of the Alodine 600 tank is to rinse them with a water faucet, which is directly over the Alodine tank as opposed to doing a dip rinse. My question is, wouldn't this remove the Alodine before it sets in? Also wouldn't this cause an excess of contaminates in the Alodine bath? The reason the shop floor does this is they were instructed by our environmental people to reduce the 55 gallons of Alodine rinse water that is disposed of every other week. I believe this was a $250.00 cost to dispose of a 55-gallon drum of Alodine wastewater.
Any suggestions would be appreciated.
- Long Beach, California, USA
2003
A. Hi Steve,
The rinse after chemical treatment is a necessary step, but the conversion coating will not be rinsed off. The coating is being formed when the parts are in the Alodine bath and is deposited on the aluminum surface.
The other part of your question, however, is a bit tricky. Rinsing the parts while they are over the Alodine tank is asking for trouble, IMO. The chemical composition of the bath is set up that way for a reason. Adding water and reaction products back to the bath will, over time, probably compromise the bath's ability to deposit coating effectively. You may be saving money in the short term by not having to deal with disposal of the rinse water. But in the long term, the Alodine bath will probably have to be dumped sooner than normal and the coating that it produces on the parts may be of lower quality.
- Naperville, Illinois
2003
A. Hi, Steve. Situations like you have found yourself in make me want to fall into a primal scream. The world is suffering tens of billions of dollars of needless corrosion every year; landfills and junkyards full of millions of tons of discarded metal scar the earth around the world; and the mines, factories, and transportation systems are overloaded constantly re-manufacturing replacements for metal parts that lasted only a couple of years because they were so poorly finished . . . and yet the pressure is relentless on the few shops who are doing it right, to try to make them stop finishing things right in the name of reducing the effluent by a few milligrams :-)
Chromate conversion tanks are normally unheated or very minimally heated, so the evaporation loss is nearly non-existent. This hose water can therefore cause the chromate conversion tank to overflow, besides contaminating it.
Please go back to doing it the right way. If you can make room for two rinse tanks, you probably will need to dump far less frequently since you don't need to dump until the first gets so contaminated that it continues chromating. If not, do the spraying over the single rinse tank. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003
Q. Thank you for the fast response. So far rinsing parts over our Alodine tank has not caused an overflow problem. Actually it has not appeared to effect the level of the tank at all. However, my gut feeling is that this is not the right thing to do. The pressure I am receiving is from the environmental people due to the fact that they do not want to constantly dispose of rinse water. In the past the procedure was to dump the rinse water every two weeks which to me sounds like overkill. Is there a way I can test the rinse water to insure that I am only disposing of it when absolutely necessary? Again this is the rinse after the Alodine 600 bath.
Steve Shoenberg- Long Beach, California
2003
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