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Application Scopes of Cold Galvanizing

Cold galvanizing spray paint is mainly suitable for two aspects: surface-treated bare steel anti-corrosion and anti-rust primer; hot-dip galvanized layer repair. Its applicable occasions are almost unlimited, including all kinds of bridges, pipelines, mechanical equipment, etc.


Surfaces that cold galvanizing spray paint is suitable for:


As we all know, the quality of surface treatment is the most important factor affecting the quality of the coating film, and the degree of influence reaches 50%. For cold zinc coating, the surface treatment is equally important, and different steel surfaces have different treatment methods and grade levels.


1. New steel surface:


Before spraying cold zinc coating, it is best to choose the method of mechanical derusting (sandblasting, shot blasting, etc.). The surface cleanliness of the steel can reach the Sa2.5 level of ISO8501-1, which is equivalent to the Sa2.5 level of GB8923, which is defined as: "After the steel is mechanically de-rusted, the surface is free of oil, rust, oxide scale and other dirt, or only slight traces are left; 95% of the steel surface is impacted by steel shot (sand), revealing the luster of the metal". For another indicator of surface treatment quality, roughness, different cold-coated zinc materials have different requirements for roughness. In the construction instructions of Zinga, the average roughness Ra=12.5μm is required, that is, the roughness Rz=55~75μm. In the "Strong Zinc" and "Roval" construction instructions, the requirements for roughness are slightly lower, Rz = 40~60μm. 7CF believes that if cold-coated zinc is formed as a film alone, as an anti-corrosion coating, the surface roughness can be controlled to be slightly smaller to ensure the thickness of the coating. In order to ensure the adhesion of the entire coating when recoating heavy anti-corrosion coatings on the cold-coated zinc surface, the surface roughness Rz of the steel should be greater than 60μm.


2. Old steel surface:


It is best to use sandblasting. After removing the old paint film and rust spots, the steel surface still has a certain roughness. If conditions are limited, manual grinding and wind (electric) power tools can also be used to remove rust. It is defined as: the surface should be free of visible grease and dirt, and almost free of loosely attached oxide scale, rust, old coatings and foreign debris. The surface should have the luster of a metallic substrate. Different brands of cold-coated zinc materials have different levels of surface treatment. For example, Belgian Zinga allows a slight corrosion area of about 5% on the steel surface before painting; ROVAL is tested by the China Ship Technology Research Institute when the steel surface is polished to St3 level. The ROVAL coating of 60-80μm D.F.T. The adhesion is excellent, and the pulling method can reach 6.1Mpa.


3. Surface of zinc-coated steel:


Cold-coated zinc-coated materials are generally used for repair or overcoating of old zinc-coated steel sheets or hot-dip zinc-coated steel surfaces. Before spraying cold-coated zinc materials, in addition to removing rust, oil and other dirt, zinc salt (white rust) must be removed at the same time, so as not to affect the adhesion such as ROVAL. Commonly used removal methods of zinc salt include sand sweeping, grinding treatment, and water rinsing, etc., and slight traces are allowed. Similarly, cold-coated zinc materials such as ROVAL are used alone as anti-rust coatings. When repairing and overcoating, the above-mentioned surface treatment method is also used for cold-coated zinc interlayer remelting performance, which is more excellent.


4. Surface treatment of electric welding seam:


As we all know, the electric welding seam is the most easily rusted part of steel structure parts. The practice has proved that after welding and installation of steel components with arc spray zinc (aluminum) and hot dip coating, it is an economical and effective method to repair the weld with cold zinc coating. However, before repairing, the surface of the weld must be carefully removed from splash, slag, grease, weld flaw detector, and other contaminants, and polished to ISO8501-1 St2 level. Apply the first cold-coated zinc immediately after finishing the surface.

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