The coating steel plate is manufactured by performing surface treatment (degreasing and chemical treatment) on cold-rolled strip steel and galvanized strip steel (electrogalvanized steel and hot galvanized steel) serving as the base plate on a continuous machine unit, coating one layer or multiple layers of liquid coatings on the base plate by a roll coating method and baking and cooling the coated plate. Due to various different colors of the coating, the coated steel plate is usually called color coated steel plate. Because the coating step is performed before steel plate forming, the coating plate is called precoated steel plate (color plate) for short in foreign countries. The organic coating of the color coated plate plays a role of covering and isolating, prevents the steel plate from rusting and prolongs the service life.
The color coated steel plate is manufactured by performing surface
pretreatment (degreasing, cleaning and chemical transformation treatment) on
cold-rolled steel plate and galvanized steel plate serving as the base plate,
coating the base plate by a continuous coating method (roll coating method),
and baking and cooling the coated plate.
Base plates of color coated plate include cold-rolled base plates, hot
galvanized base plates, electrogalvanized plates and hot aluminized galvanized
base plates. Categories of finish coating of the color coated plate include
PET, SMP, PVDF, HDP, etc. The production process is developed from one time of
coating and one time of baking to two times of coating and two times of baking,
even three times of coating and three times of baking. The surface states of
the color coated plate can be normal coated plates, embossed plates, printed
plates, etc. Main production processes of the common two-coating two-baking
continuous color coating machine unit are:
uncoiling→pretreatment→coating→baking→aftertreatment→reeling.
The coated steel plate has the advantages of light weight, handsome
appearance and high anti-corrosion property and can be processed directly,
being a novel raw material for building industry, automobile manufacturing
industry, home furniture industry, electric industry, etc and has good effects
in substituting wood, performing effective construction, energy conservation
and pollution prevention. The color coated steel plate taking the galvanized
steel plate as the base plate is protected by zinc and is cover and isolated by
the organic coating on the zinc layer, so that rusting of the steel plate can
be prevented and the service life is prolonged by 50% compared with the
galvanized steel plate.
However, in different areas and different using parts, service life of the
color coated plate adopting the same galvanization amount, paint and coating
thickness differs greatly. For example, in industrial areas or coastal areas,
because of the effect of sulfur dioxide or salt in air, the corrosion is
accelerated and the service life is influenced. In rainy season, when soaked by
rainwater for a long time or is exposed in place susceptible to moisture
condensation because of great temperature difference between day and night, the
coating will be corroded quickly and the service life will be shortened.
Buildings and plants manufactured by color coated steel plate have long service
life when washed by rainwater frequently, and otherwise they will be influenced
by sulfur dioxide, salt and dust. Therefore, during design, the larger the
gradient of roof is, the harder the accumulation of dirt such as dust will be
and the longer service life will be achieved; those areas or parts which are
not frequently washed by rainwater should be washed with water regularly.
Color coated steel plate can adopt cold-rolled base plates, hot galvanized base plates and electrogalvanized plates. According to classification of base plates, color coated steel plate can be categories into the following kinds
Color steel plate made from cold-rolled base plate has smooth and handsome appearance and processability of cold-rolled steel plate; however, any tiny scratch on the surface coating will make the cold-rolled base plate exposed in air and the exposed position will become rusty quickly. Therefore, this kind of product can be only applied to temporary isolation facilities with low requirement and serve as indoor material.
Hot galvanized color coated steel plate is obtained by coating organic coating on hot galvanized steel plate. The zinc on the hot galvanized color coated steel plate plays a role of protecting and the organic coating on the surface plays roles of isolating, protecting and preventing rusting, so that the service life of the steel plate is longer than hot galvanized steel plate. The zinc content of hot galvanized base plate generally is 180g/m2 (double-face) and the maximum galvanization amount of hot galvanized base plate for building is 275g/m2.
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