Li Ying | Tu Du
There are many methods for controlling and protecting metal corrosion, among which the method of preventing corrosion by separating steel and external media through coating is more common in thin plates. These covering coatings are mainly divided into two types: metallic coatings and non-metallic coatings.
(Structure diagram of Tu plated steel products)
The addition of alloy elements such as aluminum zinc alloy and zinc aluminum magnesium alloy with better corrosion resistance to the surface of the steel plate (metal coating) not only improves the service life of the steel plate, but also prolongs the service life of the building. What are the effects of non-metallic coatings on the service life of the steel plate?
01
Factors affecting the failure of coated steel plates
The color coated panels used for building purposes are mainly affected by the harmful substances caused by ultraviolet rays in sunlight, moisture in the air, and industrial pollution, which reduce their service life. The anti-corrosion of architectural color coating products is a combination of coating, pre-treatment film, and coating (primer, topcoat, and back paint). This combination is very important and directly affects its service life.
TIPS: When the content of Zn, Al, and Mg ternary eutectic phases (zinc aluminum magnesium) in the entire coating structure reaches a certain level, the corrosion products are insoluble colloidal substances with low conductivity, which can effectively isolate the transmission of coating and external substances, thus forming a dense and effective protective layer on the surface of the steel plate to prevent corrosion. The cathodic reaction will be effectively suppressed with the appearance of this double-layer structure, significantly improving the corrosion resistance of the coating.
02
Corrosion Failure Process of Coated Steel Plate
The failure process of color coated plates is shown in the following figure, and coating failure, coating failure, and even steel plate perforation are key corrosion processes. Therefore, increasing the thickness of the coating layer and adopting weather and corrosion resistant coating layers are the most effective means to prevent corrosion failure of the color coated plate.
Corrosion Failure Process of Coated Steel Plate
03
Types of coating on coated steel plates
Coating is considered to ensure the durability and corrosion resistance of buildings, and different uses can be met by selecting different coatings, coatings, and thicknesses to meet their service life.
The commonly used topcoat varieties for coil steel coatings now include polyester (PE), silicon modified polyester (SMP), high durability polyester (HDP), and fluorocarbon (PVDF); The varieties of primer and back paint include epoxy (EP), polyester (PE), polyurethane (PU), etc.
Ordinary polyester PE
The product is made by using hot-dip galvanized sheet, hot-dip 55% aluminum zinc sheet, etc. as substrates, after surface pre-treatment, applying one or several layers of paint on the surface, and then baking and curing.
Silicon modified polyester (SMP)
The traditional silicone modified polyester coil coating is modified by cold blending of silicone resin and polyester resin, further improving the weather resistance of the silicone modified polyester resin and achieving outdoor weather resistance of 20 years.
High Durable Polyester (HDP)
High durability polyester (HDP) resin is synthesized using monomers containing cyclohexane structure to achieve a balance between flexibility, weather resistance, and cost. Aromatic free polyols and acids are used to reduce the absorption of UV light by the resin, achieving the high durability of the coating.
Fluorocarbon (PVDF)
PVDF fluoropolymer coatings began in the 1960s and have been proven to have excellent weather resistance after nearly 50 years of practical use. They are currently the best in terms of weather resistance among coil coatings, and fluoropolymers also have extremely high chemical stability.
PVDF resin has excellent UV resistance, preventing the primer from being attacked by UV rays. Therefore, the pigments used must have excellent weather and chemical resistance, and can withstand outdoor exposure for 20-30 years. The chemical properties are relatively stable and suitable for long-term protection.
Weather resistance:
Ordinary polyester PE, silicon modified SMP, high weather resistant HDP, fluorocarbon PVDF
04
How to choose the type of color steel plate coating
Coating is considered to ensure the durability and corrosion resistance of buildings, and different uses can be met by selecting different coatings, coatings, and thicknesses to meet their service life.
Color coating
*The actual service life may vary depending on the product material and environmental impact. Please consult sales personnel for details.
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