Buildings (roofing panels and exterior wall panels) themselves have material requirements that can be divided into safety performance (impact resistance, wind pressure and fire resistance), residential performance (water resistance, heat insulation and sound insulation), durability (pollution resistance Properties, weatherability and appearance retention), production processability (economy, easy processing, easy maintenance and repair).
For the ultimate owner of the building, safety and service life are paramount. For the design unit, the service life, bearing capacity and appearance are more important. For forming processors of building walls and roofs, the workability (surface hardness, abrasion resistance, plate shape, and steel plate strength) of color coated steel sheets are the first requirements.
Specification and selection of color coated steel sheet for construction
For buildings, the bearing weight (wind load, snow load, construction personnel and machinery), the span of the building, the design of the rubber distance, etc. all depend on the strength of the steel plate. In other words, there are corresponding standards at home and abroad. Such as China’s GB / T12754-2006 in the United States ASTM653, ASTM792, Japan’s JISG3302, JISG3321, European EN10215, EN10147 and so on. According to the steel type, it is divided into CQ (common commercial grade), DQ (for general stamping), HSS (high-strength structural steel), and FH (full hard steel).
It is most commonly used now. For example, TDC51 produced by Baosteel has a yield strength of 260-320Mpa and a tensile strength of 350-400Mpa. Compared with structural steel, its yield ratio is slightly higher.
As general color plates for construction are roll-formed or composite sandwiches, the material’s stamping performance is not high. Therefore, DQ grades are mainly used in door rings, pipes and other industries.
High-strength structural steel: According to the European standard HSS, it can be divided into 4-5 steels with different strengths, but because ordinary CQ grade materials can already replace low-strength HSS steels, the more commonly used in the market are yield strengths of 280Mpa and 345Mpa. The two steel types are TS280GD and TS350GD produced by Baosteel.
Compared with ordinary CQ, HSS steel has several advantages:
1) Due to the relatively low yield strength, the steel has good fire resistance and shock resistance.
2) For thicker steel plates, it can manufacture long-span arched plates.
3) For general exterior wall and roof panel type, it can be appropriately thinner than CQ material, which can save material consumption.
Full hard steel: It is a type of steel that improves the yield strength of steel plates by controlling the annealing temperature. According to international standards, the yield strength is ≥550Mpa and the tensile strength is ≥570Mpa. This type of material has high strength and low elongation, and is suitable for the use of shallow-shaped formed steel plates, which greatly saves the use of materials.
Dimensional accuracy and shape
For color coated rolls, dimensional accuracy includes width accuracy and thickness accuracy.
The delivery precision of steel coils commonly used in countries around the world is a positive tolerance, which is the nominal width of the actual delivery width when ordering. The control of these widths is generally considered during cold rolling of the steel sheet, because the subsequent galvanizing and color coating processes will affect the corrosion resistance of the edges if they are trimmed. However, if the positive tolerance of the steel plate is too large, it will exceed the feeding limit of the forming machine. According to experience, it is more appropriate to control it at 0-5mm.
The meaning of the thickness of the color-coated board varies from factory to factory. Some of the thicknesses marked on the labels of color-coated steel coils are the thickness of the substrate, some are the thickness of the substrate + plating thickness, and some are the thickness of the substrate + plating thickness + coating originality. Baosteel currently uses the thickness of the substrate + the thickness of the coating (excluding color coating). Such a thickness calculation method is suitable for the designer of the building, because the strength of the color coating is low, and design margin and safety are considered Sexual aspects should not be taken into account. For the same reason, Baosteel has always followed the positive tolerances in terms of delivery thickness tolerances. In this way, although the processing area per unit ton of steel is reduced, the safety of the final building is guaranteed. The reduction of the steel sheet must be carried out with an increase in strength.
The shape of the steel plate depends on the shape of the formed steel plate. Generally speaking, the different depth of the profiled plate has different requirements on the shape of the original plate. The shallow shape requires higher unevenness. For the sandwich panel, the shape requirement is higher than that of the profiled steel sheet, especially the uniformity of the performance (internal stress) in the width direction is better, otherwise it will affect the bond strength of the sandwich panel. The more popular flat cores (products that replace glass curtain walls) have extremely high requirements for the unevenness and severity of steel plates.
Selection of coating
The coating is considered to ensure the durability and corrosion resistance of the building. Different applications can meet their service life by choosing different coatings, coatings and thicknesses.
The color coatings currently used for construction are currently hot-dip galvanized and hot-dip galvanized. For color coating, the application areas of the two substrates are not very different. Under relatively acidic environments, aluminized zinc substrates are a better choice. For use in wet, alkaline environments, the advantages of the notch corrosion resistance of galvanized substrates are realized. For the thickness of the coating, the general requirements for roofing panels and exterior wall panels are hot-dip galvanized ≥180g / m2 (about 26um), aluminized zinc ≥100g / m2 (about 27um), in the use environment is in the heavy industry area or the sea At the time, foreign related associations have minimum galvanizing requirements, such as ECCA specifications and Australian standards requiring galvanized layer weight ≥275g / m2 (about 38um), aluminum zinc plating ≥150g / m (about 40um).
The coating should meet the user’s requirements for color and durability. It is also necessary for the processor to satisfy its processing performance. Therefore, when ordering, you need to specify the type of coating, color and gloss, and coating thickness. The functions and selection methods are described below.
(1) Type of coating
The commonly used topcoats of coil steel coatings are polyester (PE), polyurethane (PU), silicon modified polyester (SMP), fluorocarbon (PVDF), high weathering polyester (HDP), primer and back paint. The varieties are epoxy (EP), polyester (PE), polyurethane (PU) and so on.
(2) Color and gloss
The choice of color is mainly based on the matching with the surrounding environment and the owner’s hobby. However, from the perspective of using technology, the light color has strong heat reflection ability and small contrast after powder coating. If it is properly cleaned and maintained, the service life will be long. Will be more beautiful. As for gloss, in the outdoor use of color-coated boards, matting is the earliest phenomenon, especially for high gloss products, the initial matting will be very fast. When the gloss is reduced to about 20, it will remain for a long time. This phenomenon will appear for several months. Therefore, the color coated boards for outdoor buildings are generally low-light. In addition, products from the same color painting factory should be used in the same building. Because color-coated steel sheets from different manufacturers have different coating powdering speeds after a certain number of years of outdoor use, even if the buildings appear to be the same when completed, a visual effect of different colors will appear after a period of time, which will affect the appearance.
(3) Coating thickness
Microscopically, the coating is a porous structure. Water in the air and corrosive media (chlorine ions, etc.) can penetrate through the weak part of the coating, causing corrosion under the film, which causes the coating to foam and peel. In addition, even with the same coating thickness, the secondary coating is denser than the primary coating. According to relevant reports and results of corrosion tests, the front coating must be more than 20um to effectively prevent the intrusion of corrosive media. PVDF products require thicker coatings. The requirements for the back coating depend on the application. The sandwich panel only requires a layer of adhesive primer, and the formed steel panel is also required to be coated with two layers due to the indoor corrosion environment.
This post is also available in: Russian