Galvanized steel weathers with a beautiful, protective patina over time, but many architects and designers want their steel to be colorful. Galvanizing steel ensures a long part life, and powder coating gives builders an extensive color palette. But powder coating is not a simple process.
What is Powder Coated Galvanized Steel?
A powder coat can be the second step in producing colorful galvanized steel. The powder coat is applied over hot dip galvanized steel at the galvanizing facility.
The first step in producing powder coated galvanized steel is galvanizing. The steel part is coated with a thin layer of molten zinc. The zinc serves as a barrier against the elements and as a cathode for the electrochemical processes that would otherwise oxidize the iron in the steel. Water and ionic compounds from the environment react with the zinc coating rather than with the steel beneath it. Hot dip galvanizing requires exceptional attention to details and rigorous procedures to ensure the product conforms to ASTM standards. It is important that the steel is not quenched with water or chromate solution.
The second step in producing powder coated galvanized steel is the application of the powder coat to the galvanized part. An even layer of polyester powder coating is applied to the recently galvanized steel and cured in a stove at 180° C.
Powder coatings must be applied within 12 hours of the galvanizing process. All surfaces must be clean and free from grease. Care must be taken in the powder coating process to avoid the formation of pinholes spots and uneven coating.
Advantages of Powder Coating
When powder coated galvanized steel is manufactured properly, it forms an aesthetically pleasing building component with superior longevity and longer time to first maintenance. Zinc and the polyester resin from the powder provide a synergistic protective effect. The polyester topcoat protects the zinc and the zinc protects the steel beneath it. The American Galvanizers Association (AGA) and Society of Protective Coatings (SSPC) tell us that this duplex process potentially increases the service life of the part by as much as two and one-half times the life of the part with either coating alone.
Powder coated galvanized steel helps builders avoid painting costs, since the “painting” is one at the galvanizing facility. Additionally, the U.S. Green Building Council awards LEED credits for using powder coated hot dip galvanized steel including:
- Credit 3.1 – Construction Indoor Air Quality.
- Credit 3.2 – Construction Indoor Air Quality, Before Occupancy.
- Credit 4.2 – Low-Emitting Materials, Paints.
Powder coating hot dip galvanized steel also saves labor and transportation costs.
So, What is the Downside to Powder Coated Hot Dip Galvanized Steel?
The answer to the inevitable question about the downside of using powder coated hot dip galvanized steel is there is none, provided your galvanizing facility has the procedures in place to produce a superior product.
Tiny air bubbles can form under the polyester coating during the curing process in the stove. The outgassing that causes these tiny bubbles is generated by solvents, mold release agents grease, and machine oil that are not removed from the galvanized steel before the polyester resin powder is applied.
Preventing this defect comes down to attention to detail during cleaning. Knowledgeable galvanizers will identify contaminants and remove them before applying the powder. They may have an additional preparation step before the powder coating process to prevent this problem. Depending on the choice of resin, the galvanized steel may be etched with acid or treated with zinc phosphate or a zirconium compound to ensure better adhesion of the polyester powder to the galvanized surface.
Or the part may be prebaked and allowed to cool again before the powder is applied. It may be necessary to use a sealant. But many of these problems can be avoided if your galvanizer simply uses consistent cleaning procedures and knows how much powder to apply.
Get the Best Possible Finish when Galvanizing with Us!
We are ready to provide everything you need for galvanized steel. Our central location allows us to serve the entire United States as the premier provider of hot dip galvanizing services. If you are in need of a galvanizing plant in your area, contact us to see how we can help.