Phosphating that won't remove galvanizing

A. Hi Pedro,

It is difficult to get a high-quality conversion coating on galvanized substrates using an iron phosphate. The fact that you have a three-stage washer makes the problem even tougher.

Are you running your phosphating bath at the correct pH? I believe that your pH is too high, but this is dependent on the chemistry of the bath. I suggest to keep your bath in the range specified by your supplier.

Reducing the pH should have little effect on cleaning ability because this type of phosphating product normally has detergents built into the product to do the cleaning and these will be effective at pH 4-6, which is the range where most iron phosphating baths are run.

I suggest to have your supplier provide you with phosphating options that have better detergency. You could also ask your supplier for a detergent additive that could be added to the bath on an as-needed basis.

A. Hi Pedro. Galvanized surfaces are prepared for powder coating all the time, but with a zinc phosphate process, not with iron phosphate. As George implies, you can't do that in 3 steps, you should have 5 or 7. Good luck.

Regards,

A. Any approved process that uses solvent will remove oil and grease without affecting zinc. Whether you can use it or not depends on many factors which cannot be considered due to your somewhat vague question.