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Sheetmetal quotes came in with different coating applications (Zinc Chromate/Iron Phosphate)

My project is a sheet metal medical cart. Made out of mild steel with a powder coat finish. There are areas in which the powder coat does not cover or is masked from. These areas brought up a concern for corrosion. As the sheet metal quotes came in I noticed that the coatings they chose were different. One used a zinc chromate coating and the other used a iron phosphate coating. The piece price is much higher now when they added the zinc phosphate. The iron phosphate just was added without an increase of price. My question is there that much difference in the 2 processes or just the 2 quotes and will the iron phosphate be ideal for my need. Like I said before it is a medical cart that will be shipped over seas. I appreciate any info you can give me.

Kevin Lutkins
Product Designer - Ithaca, NY
October 16, 2009

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It is like a Yugo and a BMW. They will both carry 4 people and go the speed limit. So which is better. No contest, the BMW is, but it costs more, so which is better considering everything including cost. That depends on the use. The zinc phosphate can be a far superior one in corrosion resistance and in paint adhesion. It is more picky to run and normally has more QC done on it. Iron can be good and it can be very poor, depending on who is doing it and the associated QC.
For your parts, I would go for the zinc, based on salt spray or other corrosion tests.

James Watts
- Navarre, Florida
October 19, 2009