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12/10/2012

Low Phosphate Coating Weight

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We are getting a low coating weight with an immersion zinc phosphate coating. Could pH be a factor in this issue?

Q. We are getting a low coating weight with an immersion zinc phosphate coating. I cannot locate the recommended pH operating range for this product, even on the Technical Data Sheet. My coating weights are about 300 mg/sq ft, and the free acid is higher than normal at about 6. With a bath temperature of 170ºF, the pH is currently at 2.08. Could pH be a factor in this low-coating-weight issue? D.K.

A. Without the data sheet it is difficult for me to give you a specific answer to your question. However, I can tell you that there are a number of other parameters, including chemical concentration, bath temperature, dwell time, etc., that can affect coating weight. If you are not satisfied with the achieved coating weight, I suggest you contact your local product salesman for guidance. 

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