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Zn Coated APGI
Amcan
Prepainted Zn Coated Steel sheet exhibits high corrosion resistance because the
Zn coating on the surface of the base metal plus the double-coat, double-bake
process which consists of two steps of coating and baking following the
pretreatment and chemical coat. The first step is painting and baking of primer
coat, and the second step is painting and baking of finish coat.
Furthermore, the surface of the Zn coating, after it is applied to the base
metal, oxidizes to become Zn oxide, which then reacts with water and the carbon
dioxide in the atmosphere to form a dense basic Zn carbonate film. This series
of chemical reactions minimizes the consumption of Zn by air and water even when
the paints and Zn coated layers are scratched, exposing the base metal, the Zn
melts before the steel does, thereby inhibiting the corrosion of steel by what
is known as 'electrochemical sacrificial action'.
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Galvanic Action APGI
When Zn
and steel are together in the electrolytic solution such as water or sea
water, the Zn melts first because of the difference between their
electro-motive forces. Therefore when the steel base is exposed through a
small scratch in the Zn coating, the steel is protected from corrosion as long
as there is Zn in the adjacent areas.
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Performance APGI
Durability test requirements are stipulated for each class of paint coating.
Three classes of paint coatings are stipulated for prepainted Zn coated sheets
and coils. In terms of ascending durability, these are Class 1, Class 2 and
Class 3.
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Classification |
Symbol |
Durability |
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Class 1 |
1 |
Mainly one coat having durability as specified in the durability test table |
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Class 2 |
2 |
Mainly two coats having durability as specified in the durability test table |
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Class 3 |
3 |
Mainly two coats or more having durability as specified in the durability
test table |
Classification of Durability
of Paint Caotings and Designations
(Abstract from JIS G 3312)
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Classification of durability
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Duration of
salt spray test
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Class 1
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200 hrs.
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Class 2
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500 hrs.
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Class 3
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2000 hrs.
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Durability Test (Abstract from JIS G 3312) |
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