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Zinc-phosphate rinsewater is clear but it's tank is green

2007

Hi,

We have an immersion E-coat process with a Zinc Phosphate pre-treatment. The sides of the city water rinse after the zinc stage are green, even though the metal is stainless steel. What is causing this? and what can I do about it besides a complete boil out?

Thanks,
Ben, the curious E-coater

Ben Hill
E-Coat Tech. - Clanton, Alabama

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Probably algae. Maybe work in complete darkness (robotics?) or add algae-eating freshwater snails or fish.

Seriously, ask the E-coat supplier to recommend a compatible biocide. Perhaps a isothiazolinone type such as Acticide.

Beside boiling, some periodically shock treat with hypochlorite or scrub down with hydrogen peroxide solution (using a plastic bristle broom). Clean residue thoroughly before refilling. Try to purge all contaminated tanks at the same time.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007