How to Choose Pre-painted Steel?

Pre-painted steel is a versatile product, which is widely used in construction, home appliances, furniture, and other industries. Also, there are many options in different base metals, paints, finishes, etc. on the market. Please follow Wanzhi Steel to know color coated steel in details.

What Is Pre-painted Steel?

Color-coated steel uses metal coils as substrate, and then is coated with various organic coatings or laminated with plastic films on the surface. The base metal includes cold-rolled steel, hot-dip galvanized steel, galvalume steel, ZAM steel, aluminized sheet, stainless steel, etc. Because it is a coil that has been coated in a metallurgical factory, it is also called pre-painted steel. It is widely used in industrial plants, gymnasiums, airports/stations, partitions, warehouses, elevators, metal curtain walls, etc. The tables below will help you know the product better.

Information Required for Ordering Pre-painted Steel

According to the tables, when purchasing color coated steel, you need to confirm the following information:

1. What product do you need, steel sheet, coil, or steel strip;
2. Product specification and size;
3. Substrate type and zinc layer thickness;
4. Types and colors of top/back paint;
5. Surface finish requirements;
6. Painting structure and functions;
7. Weight (order quantity);
8. Use purposes;
9. Packing method;
10. Inner diameter size (coil);
11. Other requirements.

How to Choose Pre-painted Steel?

Suitable materials can not only meet the requirements of use but also minimize costs. When choosing color coated steel, it refers to choosing mechanical properties, substrate and coating thickness, top and back painting types, and performance. You need to take the following things into consideration, including use purpose, use environment, designed service life, durability, processing method, degree of deformation, etc. If you are still confused, welcome to contact Wanzhi Steel for help.

1. Mechanical Properties

Choosing the mechanical properties mainly depends on the factors such as application, processing method, and degree of deformation. For general uses with low strength requirements and deformation, DC51D and DC52D can be used as substrates. When there is a high requirement for formability, DC53D and DC54D are more suitable. For components with load-bearing requirements, structural steel will be better, such as S280GD, and S350GD.

Codes	Yield Strength (MPa)	Tensile Strength (MPa)	Elongation after Break
DC51D+Z, DC51D+ZAM	240~380	270~500	≧24%
DC51D+AZ	240~380	270~500	≧22%

2. Substrate Type & Coating Thickness

Choosing the substrate type and the coating thickness are mainly based on the application, use environment, and durability. For example, color-coated sheets for construction usually use hot-dip galvanized sheets, ZAM, and galvalume sheets as substrates because of their excellent corrosion resistance. In highly corrosive environments, a thick coating can increase durability and prolong its service life. In addition, when choosing a substrate, please pay attention to the corrosion resistance of cuts.

Below let’s review the corrosion level of the use environment, which can help you choose suitable base metal and paintings.

Corrosion Level	Carbon Steel Loss	Zinc Layer Loss	External environment	Internal environment
Very Low	≤1.3 μm	≤0.1 μm	–	Dry and clean indoor places, such as offices, schools, residences, hotels
Low	>1.3-25 μm	>0.1-0.7 μm	Most rural areas, less polluted cities	Indoor stadiums, supermarkets, theaters
Medium	>25-50 μm	>0.7-2.1 μm	Heavily polluted cities, general industrial areas, low salinity coastal areas	Food processing plants, laundries, wineries, dairy plants, etc.
High	>50-80 μm	>2.1-4.2 μm	Heavily polluted industrial areas, moderately salinity coastal areas	Swimming pools, chemical plants, coastal shipyards
Very High (Industrial)	>80-200 μm	>4.2-8.4 μm	High humidity and corrosive industrial areas	Buildings and areas with high pollution and persistent condensation
Very High (Seaside )	>80-200 μm	>4.2-8.4 μm	High salinity coastal areas	Buildings and areas with high pollution and persistent condensation

3. Top Paint

There are four commonly top paints, including PE, SMP, HDP, and PVDF, which are different in hardness, adhesion, durability, and other properties. PE is currently the most widely used coating, with average durability, good hardness and flexibility, and moderate price. The durability, gloss, and color retention of SMP are better, but its flexibility is slightly poor. HDP has better durability than PE, and it is more cost-effective. PVDF has excellent durability and good flexibility, but it is available in fewer colors and is more expensive. The top coat is mainly determined according to factors such as the use purpose, use environment, designed life, durability, the processing method, etc.

4. Primer & Back Paint

The common primers are epoxy, polyester, and polyurethane. Epoxy has good adhesion and high corrosion resistance, but it is not as flexible as other primers. Polyester has good adhesion and excellent flexibility, but its corrosion resistance is not as good as epoxy. Polyurethane is a primer with relatively good overall performance. The primer is usually selected according to the production process, use purpose, use environment, and the topcoat. While the back paint is usually selected according to the application and use environment. When the use environment is not corrosive, one layer of paint is OK. If it will be pasted with thermal insulation material, the back paint should be with good adhesion.

5. Paint Thickness

The paint thickness is closely related to the corrosion resistance of the color-coated sheet. Generally, the thicker the paint, the better the corrosion resistance. The thickness should be determined based on factors like the corrosiveness of the use environment, the expected life, and durability. While the gloss of the coating mainly depends on the application and preference. For example, low gloss and matt surfaces are better for construction uses, while gloss or high gloss color coated steel is preferred by home appliances.

Tips for Transportation, Storage, Processing

1. During transportation, loading and unloading, storage, and processing, the surface of the color-coated steel should not be damaged and should be stored in a clean and tidy environment, away from the erosion of various corrosive media.
2. Coils should be placed on rubber pads, skids, brackets, and other devices, and the strap locks should be facing upwards.
3. In order to avoid reducing the coating performance, the forming process of the steel sheets and steel strips should be formed at room temperature.
4. The processing performance of the coating will decrease with the prolongation of storage time, so it is recommended to process and use it within one year from the date of completion.
5. For products with polyvinylidene fluoride (PVDF) coating, it is recommended to apply a protective film during processing to prevent the coating from peeling off.
6. During profiling, the rollers, corrugated designs, and steel grades should be properly matched, otherwise it may cause poor deformation of the steel sheets or peeling of the coating after profiling.

Wanzhi Steel has been in the steel industry for about 20 years. We have exported steel products all over the world for more than 11 years and won many regular clients. Pre-painted steel is one of our main products, which is available in different base metals, paint, finishes, sizes, etc. Our annual output of color coated steel is about 300,000 tons. Besides, we also developed some new materials, such as nano coated steel, to better meet your needs. Also, we offer full service, including cutting to size, slitting, profiling, bending, etc. Welcome to contact us for more details!