Prepainted Steel Sheet for Construction Use

1. Steel Grades – Base Metal

Steel strength matters in the bearing capacity of buildings, the span, the design of the purlin, etc. There are corresponding standards at home and abroad for color-coated sheets and galvanized sheets for building uses, such as GB/T 12754-2006, ASTM653, JISG3302, EN10215, etc.

The steel sheets are divided into CQ (commercial uses), DQ (general stamping), HSS (high-strength structural steel), and FH (full-hard steel).

CQ is the most commonly used steel grade. For example, the yield strength of DC51 is between 260-320MPa, and its tensile strength is between 350-400MPa. Compared with structural steel, its yield-to-strength ratio is slightly higher.

DQ is mainly used in doors, windows, pipes, and other industries.

HSS: Steel with a yield strength of 280MPa and 345MPa is mostly used, namely S280GD and TS350GD. Compared with CQ steel, HSS steel has some advantages:

1) Due to the relatively low yield strength, HSS has good fire resistance and shock resistance;

2) For thicker steel plates, it can manufacture large-span arched plates;

3) For exterior wall and roof panels, it can be appropriately thinner than CQ material, thereby reducing material consumption.

FH: It is a type of steel that improves yield strength by controlling the annealing temperature. According to the international standard, the yield strength is ≥550MPa, and the tensile strength is ≥570MPa. This type of material has high strength and low elongation.

2. Coating & Paint

The coating and paint aim to improve the durability and corrosion resistance of the building. We should use different coatings, paints, and thicknesses for different uses and design life.

Coating

The commonly used base metals for buildings are hot-dip galvanized steel (pure zinc coating) and galvalume steel (Al-Zn coating). In acidic environments, GL steel is a better choice. For humid and alkaline environments, galvanized steel is better. The coating thickness of HDG for roof panels and exterior wall panels is ≥180g/m2 (about 26 μm) and that of GL is ≥100 g/m2 (about 27 μm). For heavy industrial areas or seaside, the zinc layer thickness is ≥275g/m2 (about 38 μm), and the Al-Zn coating thickness is ≥150 g/m2 (about 40 μm).

Paint

Paint can meet the user’s demand for color and durability. When ordering, it is necessary to specify the type of paint, color and gloss, and coating thickness.

The commonly used top paint are polyester (PE), HDP (high durability polyester), silicon modified polyester (SMP), and PVDF (polyvinylidene fluoride). The primer and back paints are epoxy (EP), polyester (PE), polyurethane (PU), and so on. Below are their features for your reference.

The choice of color is mainly based on the matching with the surroundings and your preference. But the light color has strong heat reflection ability and better color retention. Pre-painted steel sheet for outdoor uses will lose their initial gloss quickly. So the color-coated sheet for outdoor buildings is generally low-gloss.

Notice: Try to use the pre-paint steel from the same supplier in the same building because the powder speed of different paints is different. Even if the color seems to be similar when the building is completed, it may look different after a period of time, which will affect the appearance.

Microscopically, the paint is porous. So water and corrosive media will invade through the weak part of the paint, causing sub-film corrosion, and then the paint will peel off. In addition, even with the same paint thickness, paint twice is denser than a single painting. So the recommended top paint thickness for construction use is more than 20μm. And PVDF-coated steel requires thicker painting.

Prepainted steel sheet is widely used in civil buildings, shopping malls, industrial plants, hotels, resorts, farm buildings, office buildings, and other public buildings. When purchasing color-coated steel for construction use, it is necessary to consider its use environment, use purposes, and expected service life. Then choose the suitable base metal, coating, and paints. XINYONGYUAN Steel has rich experience in manufacturing pre-painted steel and we helped more than 140 clients with their projects. Except for common color coated steel, we also have antibacterial color-coated sheets, nano-coated sheets, and antistatic painted sheets for sale. We are confident to provide you with suitable solutions. If you have any questions, please feel free to contact us.