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Rinse maintenance

Hey there!

I wish to know some plan of maintenance for the rinse stages on a Zinc Phosphate Pretreatment (5 stages, degrease, rinse (Ti), Zinc Phosphate, Rinse (DI), and organic seal).

Weekly we dump the bath for the stage 2, 4 and 5 (rinse, rinse, seal), and monthly we wash the 3rd stage to remove sludge.

I want to know if the weekly washing on the seal stage it's correct or until we have some parameters of concentration and pH to take the decision to wash the tank.

So, it'll help me if you can recommend me some periods to wash the stage 2, 4 and 5, or some criteria to wash them.

Thanks for your help.

Luis Cárdenas
Automotive Aftermarket - Mexico


The purpose of rinsing is to remove the chemicals from each stage before the work enters the next.
If you are using a rinse tank for a week, the build up of chemicals in the water will be taken into the next tank and contaminate it. For example at the beginning of the week, your first rinse is no longer water but a dilute (and getting stronger daily)solution of the degreaser and you add some of this to the phosphate tank with each load. This will severly limit its life and efficiency.
Worse, your DI rinse is no longer DI after the first load and is wasting your money.
The minimum requirement is that all rinses are running water.
Best practice is to use double counterflow rinses or spray rinses (particularly for the DI)If you only have a small amount og work, use a mains water rinse after phosphating and a final DI rinse from a small garden pressure spray.
The supplier of your phosphating chemicals should have advised you on rinsing. But don,t forget, if you contaminate the bath, they get to sell you the replacement.

geoff smith
Geoff Smith
Hampshire, England

I agree with Geoff that your rinses should be overflowing to minimize the amount of cleaner or phosphatizer that is carried over into the next stage. I also agree that counterflowing is a good practice, too. Remember, water is the cheapest "chemical" in your finishing line.

The rule of thumb I use is this: measure the TDS of your incoming water source and when your rinse tank is twice the TDS of your incoming water source, it's time to start thinking of dumping at least part of the tank and refilling with fresh water.

Clean rinse tanks are as important as any other stage in your line.

Good luck.

Bill Duttlinger
- Naperville, Illinois

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