Passing 240 Hours Salt Spray

Question:

We are currently trying to pass an OEM paint specification. What painting methods (dip, spray, powder, electrocoat or others) will meet 240-hr salt spray resistance? We are currently working with several paint suppliers using a dip process. Parts are weldments from plate steel and are cleaned and phosphated prior to dipping. To date, we have not passed the test. T.P.

Answer:

 Normally, the performance characteristics of the paint material determines its resistance to salt spray and not the application method. As I always say, the paint doesn’t care how it gets on the part. A 240-hr salt spray resistance test is not that severe, and I can’t imagine that you can’t find a paint able to pass, even over phosphated steel. Most good corrosion resistant paints can be applied by several methods. For example, epoxies, which are noted for their adhesion and corrosion resistance, can be applied by dipping, spraying, flow coating, electrocoating and powder coating. I suggest you ask your paint supplier for an epoxy paint. Spraying will apply a more even coating than dipping.

It is also important to note that the surface must be properly prepared. The weldments must be treated to remove contaminants and should be reasonably smooth. Sharp points can be difficult to coat and can become sites for corrosion. This treatment should be done before phosphating. Again, an epoxy paint applied over pretreated steel should withstand 240 hours salt spray.