Colour-coated rolled steel

The consumers of colour-coated steel products include the construction, home appliance, furniture, consumer goods and automotive industries.

Colour-coated coils are most widely used in construction, which consumes more than half of the amount produced worldwide. The coating type directly depends on the exposure conditions. Colour-coated steel is used in various interior finishing work and facade elements.

In the manufacture of appliances and commodities, both standard cold / hot- rolled steel and galvanised steel of various grades meant for bending and deep-drawing are used as feedstock for colour-coating.

In the automotive industry, colour-coating is used for corrosion protection, noise attenuation, and insulation. Such steel is also used to manufacture dashboards and windscreen wipers for cars, etc.

Pre-painted steel manufacturers produce colour-coated coils in various sizes:

• Thickness – 0.25-2.0 mm

• Width – 800-1,800 mm

• Inner diameter – 508 mm, 610 mm

• Length of sheets cut – 1,500-6,000 mm

• Weight of coil – 4-16 tonnes

• Weight of sheet bundles – 4-10 tonnes

Colour-coated steel is produced using galvanised coils of Z100, Z140, Z200, Z225, Z275, Z350 quality and with other metallic coatings in line with EN 10346/ DSTU EN 10346 that are made of such steels as:

• DX51D, DX52D, DX53D, DX54D, DX56D, DX57D for profiling and drawing

• HX160YD, HX180YD, HX180BD, HX220YD, HX300LAD, etc, for cold- forming

• S220GD and S250GD for construction and framing

• Multi-phase steels HDT450F, HCT490X, HDT590X, HCT780X, HCT980X, HCT780T, HDT580X, etc, for cold-forming

Key types of colour-coating include:

• Polyester (PE) – This is based on polyether. Products with this coating are resistant to high air temperature and corrosion; have good colour stability, plasticity and longevity; and are available in different colours at a good price. They are used in roofing and wall structures, particularly for multi-storey residential and industrial buildings in different climates.

• Polyester matt (PEMA) – This is based on polyether, but has a smooth and matte surface with micro-roughness. Such material has a longer life than PE, as well as excellent colour stability and mechanical resistance. Such steel keeps its properties in any climate and can imitate natural materials.

• PVDF – This consists of polyvinyl fluoride (80%) and acryl (20%) and has the highest resistance to any non-mechanical environmental exposure. PVDF is used for wall cladding and roofing; offers excellent resistance to water, snow, acids and alkali; and does not fade over time.

• Plastisol (PVC) – This polymer consists of polyvinyl chloride and plasticisers. Its rather thick coating (0.2 mm) offers good mechanical and weather resistance, but relatively poor heat resistance and colour stability.

• Polyurethane (PU) – This coating is made of polyurethane modified with polyamide and acryl. It has improved resistance to ultraviolet radiation and weather exposure, high strength and longevity. Polyurethane is highly resistant to many acids and chemicals typical in an industrial environment.

Basic standard specifications for continuously organic coated (coil-coated) flat steel products are set forth in BS EN 10169:2010+A1:2012. Basic colours are selected according to the RAL Classic standard.

Galvanised coils are mainly used as feedstock for such products. Paint can be applied on both hot-rolled and cold-rolled coils without a metallic coating; however, in that case, product resistance to atmospheric corrosion is low.

Key steps colour-coated coil production include:

• Paying off the coil

• Pre-cleaning the surface

• Levelling the strip

• Treating with chemicals and de-oiling

• Applying primer (dipping into a bath or using a roll method)

• Curing / drying primer in an oven

• Applying a decorative paint coat (on one or both sides, dipping into a bath or using a roll method)

• Curing / drying paint coat in an oven

• Cooling the strip

• Controlling product quality

• Applying a protective film to prevent mechanical damage to the colour coat (optional)

• Recoiling the colour-coated steel

• Slitting to narrow strip and bands and cross-cutting to sheets (optional)

Buying colour-coated rolled steel from the manufacturer

Metinvest produces colour-coated galvanised steel coils in various sizes and grades in line with international standards. They can be purchased through the global sales network of 38 sales offices in Europe, Asia, Africa and America, as well as 16 metal service centres in Ukraine and authorised dealers.