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Why so many cascade rinses?

hi, my company wants to set up a new alkaline zinc coating line. I was told to prepare the tech. specs. for the complete facility. while doing some market research, I could not help but wonder "why all the set-ups have so many cascade rinse tanks?". Would not it be easier and cheaper with only two: one to rinse acid contaminated parts, the other for alkaline contaminated parts. I think, with the PLC controlled robot technology, carrying the parts from one tank to another on the line should not be a problem. thanks.

Rafet M. Kircin
Plating workshop engineer, junior - Kirikkale, TURKEY
December 3, 2010

Hi, Rafet. It is worthwhile to question the tank layout, but the large number of rinse tanks may well be justified.

First, if you study the time-motion diagram I think you will find that a higher production rate is achieved with these layouts than with the longer travel distances to common rinses. Second, remember that the contaminating solutions will be dripping from the parts onto and into everything between the process tank and the rinse tank. Third, an effort is usually made to concentrate the process solutions and get back into their tank of origin, which won't work if other contaminants have been rinsed off in them.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 3, 2010

Ted has a white paper on rinsing at this site. Read it.
In short, water and the waste treatment of it cost money. For each additional rinse, you will drop the water use to about a tenth of what you would use for the same level of final rinse contamination.
If you can, look at the addition of a spray rinse, even mists, rinses between the dip rinses. They are highly effective. Not all lines can stand the spray rinses.
Like the old STP Oil Treatment [affil links] ad, you can pay me now or you can pay me later.
Long term, additional rinses are extremely cost effective!

James Watts
- Navarre, Florida
December 3, 2010

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