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Q&As since 1989


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Static Rinse or Constant Overflow

My question is regarding the rinsing method in a Chemical Conversion coating line. Following immersion in both the alkaline and deox solutions we are currently immersing in a static rinse followed by a spray rinse. The static rinse is tested weekly and usually requires changing about every three weeks. We occasionally have problems with corrosion and adhesion testing and are looking at the static rinse as one of the possible culprits. We would like to find out more about processing with rinse tanks that constantly add fresh water. Is there a general rule of thumb as to the amount of water to be added say per hour. I realize there are a lot of variables, i.e. the amount of processing, size of parts, etc., so if more info is needed I can supply it.

Thanks,

Todd Sjerven
- Sidney, BC, Canada
2002

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Hi Todd,

You are correct, it is difficult to say for certain what a satisfactory overflow rate should be. But anything you do to improve the quality of your rinses will improve the overall quality of your process. IMO, overflowing is a must. Remember, water is your cheapest chemical.

George Gorecki
- Naperville, Illinois
2002

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Any time you run the capacity of a chemical process to exhaustion instead of employing bleed-and-feed, you are adding an unnecessary variable that you need to track. If you are quality conscious, overflowing rinses (bleed & feed) will be less effort in the long run.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

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Somewhere in the archives of this site (letter 13503), there is a graph or chart for quick and easy determination of the extent of rinse water contamination, using amount of carry-over and volume of dilution and flow rates and so on.

It's not my field, but I'm sure I recall someone posting such a chart, and Ted commenting on it.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2002

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At www.metalfinishing.com there is a paper related to how to calculate the overflow required to maintain the rinsing water with low contamination.

Guillermo Castorena
- Mexico
2002

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Ed. note: The Metal Finishing Guidebook is no longer available on line, but follow the link to learn about hard copy.