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Reducing the maintenance of zinc phosphate

2006

Hi, we have a 5 stage Zinc Phosphate Pretreatment. The first stage is degreasing the material; we have to wash that stage every 2 weeks; we manage this stage with 2 parameters, free alkalinity and total alkalinity, the reason for these 2 parameters is:
total alkalinity/free alkalinity, if the value of this division is greater than 2, it indicates that we have to change the bath; my question is: How can we improve the control of the bath to minimize the change of the bath?

Thank you all

Luis Cárdenas
Aftermarket Automotive - Mexico

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Hi Luis,
Why do you dump when the total to free ratio equals 2?

What I would do is measure the total to free ratio on a fresh charge and when the ratio is twice that of a fresh charge, I would start to watch the bath more closely. For example, if your ratio on a fresh charge is 1.5:1, I would start watching the bath more closely when the ratio hit 3:1, assuming that your parts are water break free.

If the parts are still water break free clean and you are not using an excessive amount of chemical to keep the concentration where you want it to be, there is no need to dump the bath if your ratio is twice the starting ratio.

Good luck.

Bill Duttlinger
- Naperville, Illinois
2006

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2006

Hi Bill, thank's so much, it'll help us a lot.
I have another doubt, how I can measure the free acid and total acid without titrating; or a equipment to take that parameters more exactly.

Thank you.

Luis Cárdenas
Aftermarket Automotive - Mexico

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Hi Luis,
Titration is the quickest, easiest and cheapest way to determine the concentration in your cleaning bath. Using a buret, you can determine the free and total alkalinity in a matter of two minutes or less.

You can use IC (looking for anions like sulphate, nitrate, etc.) or ICP (looking for cations like calcium, iron, etc.. However, in my opinion, that's overkill for what you want to accomplish. And, getting the equipment to perform those analyses can be quite expensive.

I'd stick with the titration.

Good luck.

Bill Duttlinger
- Naperville, Illinois
2006