Letter 22074

Maintenance of pH of rinse water [Canada] 

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My concern is the maintenance of our rinse water after anodizing. Can I use sulfuric acid to reduce its pH? The specs required is between 5.5 to 8. How does everyone dealing with anodizing maintain their rinse water pH to its required level?

I appreciate any help or advice I could get.

Thanks,

Nila O. Par
- Winnipeg, Manitoba, Canada

After sulfuric acid anodizing, the pH in the rinse gradually lowers, so you would like to raise it, not reduce it. You could use lye or a similar caustic, but now you are forming sodium sulfate salt in the tank. You do not want to rinse with a "salt" water rinse. If you have multiple rinse tanks, you can let the first one get a rather low pH because later rinses will take care of it. You can NOT leave parts in that rinse tank for any extended time as it will slowly eat the anodizing off. If you only have a single rinse tank, you will use quite a bit of water to keep the pH within limits. If you do not, you will mess up your seal or dye tank pH which IS a problem. Can you add another rinse tank or split the exixting one into 2 cells. Read Ted's article on rinsing.

James Watts
- FL

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