The steel structure engineering in daily use has been corroded for a long time. The roof of steel structure workshop is a direct and obvious change part. Corrosion not only destroys the beauty, but also reduces the performance of the overall steel members, and the bearing effectiveness of the structure will also decline.The steel structure roof has serious corrosion and water leakage.Therefore, the anti-corrosion of steel structure is very important, especially in some chemical factories.

 Generally speaking, anticorrosive paint is used as the main anti-corrosion coating for factory buildings. The zinc coated steel which usually needs heavy anti-corrosion coating mainly includes hot-dip galvanized steel and thermal spraying zinc steel.How is the coating system and surface treatment different from bare steel? 

Anti corrosion spraying of steel structure engineering

Zinc is a kind of active metal. The purpose of zinc coating is to provide cathodic protection and rust prevention for steel, which is the same as zinc rich primer. 　　

 Compared with bare steel, the surface of galvanized steel structure has the following differences:

 　　1No matter hot-dip galvanized steel or hot-dip galvanized steel, the surface is usually smooth, and it is impossible to spray clean the steel like bare steel to meet certain roughness requirements; 　　

 　　2Zinc salt will be produced on the surface of active zinc after a period of exposure; 　　

 　　3Active zinc is easy to saponify with fatty acids in some oily paints (such as alkyd, phenolic, etc.) or some active components in other paints; 　　

 　　4Since the zinc metal coating has been provided with protection, the protective coating system of the later coating can be reduced accordingly.

 Therefore, compared with bare steel, the primer for galvanized steel structure has special performance requirements　　

 　　1It is inert to zinc and can not cause adverse reactions; 　　

 　　2It has strong adhesion to smooth zinc surface. 　　

 　　In ISO12944-4 standard, the surface treatment of hot-dip galvanized steel and hot sprayed zinc steel are described, which mainly requires the removal of zinc salts and pollutants.ASTM d2092-2001 surface treatment of galvanized steel for painting is also introduced. 　　

 　　According to iso12944-5 standard, the protective coating system for hot-dip galvanized steel and hot-dip galvanized steel is recommended according to different corrosion grades and durability requirements

 There are two types of primers most commonly recommended by steel structure companies for hot dip galvanized steel and hot sprayed zinc steel surface: 　　

 　　1Ethylene phosphating primer, also known as etching primer and washing primer, is a kind of special paint containing phosphoric acid. The film (8-15 μ m) formed by phosphating primer adheres firmly to the metal surface, playing the role of phosphating and passivation. 　　

 Phosphating primer is rarely used because it contains zinc, chrome yellow and high lead content. It is usually only used when the durability requirement is not high. It is coated with alkyd, phenolic, epoxy ester and other low-grade paints. 　　

 　　2Epoxy universal primer.Some manufacturers also known as epoxy multifunctional primer, is a kind of primer specially designed for smooth non-ferrous metal surface (including galvanized surface), to strengthen the adhesion of the paint to ensure its adhesion strength.At present, this kind of market is the mainstream.