Polymer Powder Coatings over Galvanized Steel

[chasan]

Has any one experienced outgassing of galvanized steel during a final cure cycle at temperatures of 325 degrees F resulting in pinholes in the finish cured polymer coating? I am able to correct the problem in some but not all cases by preheating the substrate at a higher temperature prior to the powder coating and would appreciate a different solution if possible.

 

[rembrandt]

This 'Outgassing' May not be from yje Zinc, but from the Flux residue left over on the surface of the galvanizing,
remember the Steel has to pass through the flux on the way into the zinc bath, and on the way out. You could try Degreasing and treating the surface with a Mordant solution, this will only react with the zinc if there is no flux residue on the surface. You have found one way yourself already, by heating the surface prior to coating, you are either heating the flux to such a level that it melts and falls away from the surface or it may be volatiles are vapourised by the temperature,

 

[chasan]

rembrandt,
Thank you for your input. I did not give you a complete picture of the process. A 6 stage cleaning system preceedes the application of the ES powder application which should remove any flux residue. Also, would flux residue be visable?

chasan