Selection of steel grades and coatings for color coated sheets for construction

      The material requirements of buildings (roof and wall) can be divided into safety performance (impact resistance, wind pressure resistance and fire resistance), residential performance (water resistance, heat insulation and sound insulation), durability (resistance to pollution, weather resistance and appearance retention), production processability (economical, easy to process, easy to maintain and repair). 

        For the owner of the building, safety and service life are paramount. For the design unit, the service life, carrying capacity, and appearance are more important. For the molding manufacturers of building walls and roofing, the processability (surface hardness, wear resistance, shape and steel strength) of the color coated board is the preferred requirement.

Color coated steel performance indicators include:

• Substrate: yield strength, tensile strength, elongation

• Plating: coating weight, bonding strength

• Coating: color difference, gloss, T-bend, impact, hardness, anti-dusting, heat and humidity resistance, etc.

• Surface: visible surface defects, etc.

• Plate shape: tolerance, unevenness, etc.

Steel grade:

      For buildings, the weight of the load (wind load, snow load, construction workers' machinery), the span of the building, the design of the lay length, etc. all depend on the strength of the steel plate. For the building maintenance Structure, the color coated and galvanized sheet are used. Said that there are corresponding standards at home and abroad. Such as China GB/T 12754-2006 ASTM653, ASTM792 in the United States, JISG3302, JISG3321 in Japan, EN10215, EN10147 in Europe , etc. Divided into CQ (common commercial grade), DQ (general stamping), HSS (high-strength structural steel), and FH (fully hard steel) according to the major types of steel.

Coating choice:

      The coating is considered to ensure the durability and corrosion resistance of the building. Different applications can meet the service life by selecting different coatings, coatings and thicknesses.

• Plating, the general coatings for architectural color coatings are hot-dip galvanized and hot-dip aluminum-zinc. For color coating, the application fields of the two substrates are not much different, and in a relatively acidic environment, an aluminum-zinc-plated substrate is a better choice. For wet and alkaline environments, the advantages of the corrosion resistance of the galvanized substrate are reflected.

• Coating, the top coats of commonly used coil coatings are polyester (PE), polyurethane (PU), silicon modified polyester (SMP), fluorocarbon (PVDF), and high weather resistant polyester (HDP).
  

     For gloss, in the outdoor use of color coated panels, loss of light is the earliest phenomenon, especially for high gloss products, the initial loss of light will be very fast. When the gloss is reduced to about 20, it will last for a long time. This phenomenon will occur in a few months of use. Therefore, the color coated panels for outdoor buildings are generally low-light.

      According to the report and related corrosion test results, the front coating layer of 20 μm or more can effectively prevent the intrusion of corrosive media. PVDF products require a thicker coating film. The requirements for the backside coating depend on the application. The sandwich panel requires only one layer of bondable primer. The profiled steel sheet is also required to be coated with two layers due to the indoor corrosive environment and has a thickness of at least 10 μm.