Plain Finishes
Architects and Specification Writers are increasingly selecting unpainted metallic coated steels for architectural roofing and cladding applications on building exteriors where they want a “Silver” metallic finish.
Resources
Galvanized
The principle reason for Galvanizing is to protect the steel from corrosion. Galvanized coating is essentially pure zinc. Cold rolled steel is dipped into a bath of molten zinc (hence the name Hot-dipped Galvanized). The coating weight is controlled by “air knives” which adjust to produce the desired coating.
The coating thickness chosen will have a direct impact on the life of the material. Agway uses G90 (imperial) or Z275 (metric) coating weight to insure a long life for the product. G90 Coating contributes about 1.6 mils (0.0016 inches) of thickness to the final coated sheet (or 0.0008 inches of zinc to each side of the material).
Zinc provides outstanding anti-corrosion performance for the steel substrate due to a slow oxidation rate and protective sacrificial action, which inhibits corrosion of the steel. The material is passivated and left “dry” or un-oiled. This passivation process provides increased protection to the coating by immersing the material in an acid solution which removes any “free iron” contamination. This contamination can result in premature corrosion of the material. Another result of passivation is the formation of a transparent oxide film that also protects the material from corrosion. The material is then temper rolled to insure a smooth surface.
Galvanized steel conforms to the general requirements of ASTM A-653/653M
Galvanneal / LZC / Satin coat /Wipe coat
After the galvanizing process and while the zinc is still in liquid form, the steel is annealed by passing the material through a furnace. Once the material is annealed, the coating becomes an iron-zinc alloy rather than a free zinc coating as in Galvanized material. This process provides a smoother matt finish, which improves adhesion for painted applications. Many Galvanneal products are painted after fabrication. Galvanneal material offers more corrosion resistance then cold rolled material, and improved spot-weldability over Galvanized material. The baked zinc coating on Galvanneal material is harder than Galvanized material, which makes it extremely scratchresistant. Agway uses ZF75 Coating weight to insure a long life of the product. The cost of Galvanneal material is less then Galvanized material.
Galvanneal material conforms to the general requirements of ASTM A-653/653M
Galvalume Plus®
Galvalume material has approximately 55% aluminum and 45% zinc coating placed onto the steel strip by the hot dip process. The coating is chemically bonded to the steel and has a clear organic resin coating over the aluminum and zinc. This resin is applied to both sides of the material and is then thermally cured. This coating has a high resistance to storage stain. Galvalume material has at least twice the corrosion resistance of Galvanized material with the same coating thickness. Galvalume Plus is ideal for unpainted roofing and siding, the surface is bright with a fine spangle, and has a high heat reflctivity. However, the end user should be aware that plain Galvalume material may display some variations in aesthetic finish quality and a high degree of consistency cannot be guaranteed. There is no need for chemical treatments or vanishing oil; this helps to minimize fingerprints when handling. Agway uses AZ50 (imperial) or AZM150 (metric) for the coating weight to insure a long life of the product.
Galvalume® material conforms to the general requirements of ASTM A792/792M
