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topic 3933

Judging quality of a zinc phosphate finish?


We recently received a number of steel parts that we had ordered with a zinc phosphate finish. The finish looked terrible, like cracked and peeling paint. Manufacturing asked me if the parts were acceptable. I honestly couldn't say; I didn't specify the finish and the engineer who did wasn't available. The vendor claimed that this was how zinc phosphate looks.

What does an acceptable zinc phosphate finish look like? If these are unacceptable, what might be the cause of the problem? I would like to give the vendor as much information as possible.

Links to websites with images of zinc phosphate finished parts would be very helpful. In fact, a gallery of different finishes would be a useful addition to this website for layman like me. Thanks, Rob Campbell

Rob Campbell
- Westford, Massachusetts


Sorry, I don't know of any on-line photos of zinc phosphate. If anyone wants to e-mail us some we will be happy to post them. Regards. Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Good zinc phosphate should be a relatively even matte grey to dark grey. If it is not, it probably will fail the salt spray test.

You can get very ugly parts when you try to pickle rather than blast the parts prior to coating. Pickle requires the use of a special additive in the last rinse after the pickle or you will get a very ugly non-uniform coating, and I am not referring to a mottled appearance which is fairly common.

Do a salt spray test. My nickel says it will fail.

James Watts
- Navarre, Florida

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