Powder coatings on hot-dip galvanized steel provide an excellent corrosion resistant coating. The selection of this duplex system has two major attractions; the duplex system provides a high-grade architectural finish that does not contain any volatile material and the coating is particularly abrasion resistant.
The powder coating is comprised of a polyester thermosetting resin that is applied to a clean galvanized surface and cured at temperatures near 350ºF (180ºC).
Surface Preparation
The surface preparation required to promote good adhesion between the powder coating and the galvanized surface is similar to that of paints. A profiled galvanized surface will provide excellent surface for applying powder coatings.
Applying/Curing the Powder
Due to the equipment required to powdercoat steel, it is usually applied to newly galvanized steel. It is recommended that the galvanized surface be coated within 12 hours of galvanizing. To promote superior adhesion of the powder coating the following should be considered:
- The galvanized steel should not be quenched after it has been galvanized
- The surface of the steel should remain clean
- When transporting the steel be sure to cover loads and keep dry
- If surface contamination has occurred, clean the steel with a proprietary solvent/detergent that is designed for cleaning prior to powder coating
- Maximum adhesion is best achieved by using a zinc phosphate treatment before powder coating the steel. Surface must be entirely clean as this treatment has no cleansing action
- Preheating steel prior to coating
- Use “degassing” grade polyester powder only. Anti-blistering agents, such as polyethylene oxide, can be added to the powder to prevent pinholing and promote good adhesion
