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What Will Affect the Quality of Coated Steel?

There are many factors affecting the quality of color coated steel, such as the base metal, zinc coating, paint types, paint thickness, etc. Also, these factors will influence the price. Let’s have a brief review.

1. Base Metal

When purchasing galvanized steel sheets, choose the steel grades according to the bearing weight, span, and distribution requirements of the building. According to the tensile strength, galvanized steel sheet is divided into 280MPa, 340MPa, 400MPa, 440MPa, 490MPa, 540MPa, and All hard sheets. For example, if the roof panels are usually unloaded, DC51D is suitable; while for parts with large deformation, please choose the materials with better formability, such as DS52D and DC53D. In short, it is important to pay more attention to the mechanical properties of the substrate.

The strength of the color-coated steel depends on the substrate, which also depends on the design requirements, such as yield strength, tensile strength, elongation, and other indicators. Generally, it is recommended to use PPGI steel in acidic environments; While PPGL steel is more suitable for alkaline environments.

Galvanized Iron Coil

Galvanized Iron Coil

Galvalume Coil

Galvalume Coil

2. Coating of Base Metal

The most commonly used base metals for color coated steel include galvanized steel and galvalume steel. In general, coating thickness greatly influences corrosion resistance. The thicker the coating, the better the corrosion resistance. While PPGL coating thickness mainly affects the corrosion performance of the cutting area. Therefore, please pay attention to the coating thickness when purchasing color coated products, which will determine their service life. Appropriate materials can greatly reduce your cost of use. Usually, we recommend that the zinc coating is not less than 120 g/m2, and the AL coating is not less than 100 g/m2.

Service Life of Zinc Coating

Service Life of Zinc Coating

3. Paint Types

The commonly used paints for color steel are: polyester (PE), silicon modified polyester (SMP), high durability polyester (HDP), and polyvinylidene fluoride (PVDF). For the primer, epoxy resin is commonly used for its good adhesion and corrosion resistance; polyurethane is suitable for applications that require better flexibility and UV resistance. For the back coating, if the color-coated steel sheet is used individually, a two-layer-coating structure is better. If it is used in sandwich panels, PE or epoxy resin has better adhesion. Below is a table for your reference.

Paint Types Hardness Bending performance Corrosion resistance Weather resistance Cost
PE Excellent Good Good Great Low
SMP Good Medium Great Excellent Medium
HDP Good Excellent Great Excellent Medium
PVDF Medium Excellent Excellent Excellent High

As shown in the table, PVDF is the most expensive, but its service life is more than 20 years. You can choose according to the use environment and the expected service life.

When choosing the top paint, you need to pay attention to its color, color difference, gloss, hardness, durability, thickness, and other properties. While the back coating is usually determined by the use purposes and use environment. For example, if the pre-painted sheets are used in sandwich panels, choose PE or epoxy resin with good adhesion.

4. Paint Thickness

The paint also plays an anti-corrosion effect. However, because the paint film is porous, the water in the air will still penetrate into the paint and may cause the painting to peel off. For steel sheets, the GI or GL coating has a greater impact on the service life. The recommended top paint thickness is 20 μm or more.

PVDF Coated Steel

PVDF Coated Steel

Pre-painted Coil

Pre-painted Coil

Conclusion

As mentioned, the substrate, coating, and painting greatly influence the quality of pre-painted steel. At the same time, these factors also affect the price. At Wanzhi Steel, we have color coated metal products, such as PPGI, PPGL, color aluminum, etc. Also, there are different paints to choose from. You can choose according to the use environment, expected service life, and budget. Welcome to contact us for more details!

 

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