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Spangle is the appearance of crystal grains on galvanized steel. It is formed when the liquid zinc is cooled and solidified during the hot-dipped galvanizing process. The complete spangles look like snowflakes or hexagonal stars. Its size, brightness, and topography depend on a range of factors, such as the composition of the zinc layer, cooling method, etc. Below let’s review the different types of spangles.
According to American Standard (ASTM A653), it can be divided into galvanized steel with normal spangles (N), minimum spangles (M) and zinc-free spangles (F). Chinese standard (GB/T 2518) is similar to ASTM. While according to the European standard (EN10346:2015), the galvanized spangle can be divided into normal spangle (N) and minimized spangle (M). Japanese standard (JIS G3302) is close to the EU standard.
|Standard||Chinese Standard (GB/T 2518)||American Standard (ASTM A653)||European Standard (EN10346:2015)||Japanese Standard (JIS G3302)|
|Code||N (normal spangle)||N (normal spangle)||N (normal spangle)||R (regular spangle)|
|Definition||Do not control the solidification process of the zinc layer to form various sizes of spangles during the natural solidification process.||Spangles are obtained when the zinc coating is naturally solidified. There will be spangles of different sizes and brightness. But the quality of the galvanized layer will not be affected.||Spangles formed during the crystallization and solidification of the zinc layer.|
|Code||M (minimum spangle)||M (minimum spangle)||M (minimized spangle)|
|Definition||Control the solidification process of the zinc layer to obtain relatively uniform and small spangles, which are still visible to the naked eye.||Fine spangles are obtained by controlling the solidification process of the zinc layer in a special way. Usually, the spangles are invisible to the naked eye.|
|Code||F (zinc-free spangle)||F (zinc-free spangle)||Z (zero spangles)|
|Definition||Tiny spangles are invisible to the naked eye by controlling the solidification process of the zinc layer.||To control normal spangle formation to a small value.|
In fact, spangles only offer different surface appearances. But it will not influence the quality of zinc coating. However, as the base metal of PPGI, spangles will influence its painting adhesion and corrosion resistance. Therefore, small or zero spangle products are better for the home appliance and automobile industries. While galvanized steel with normal spangle is often for general purposes and the construction industry. If you have special requirements for spangles, please inform the supplier in advance.
There are many factors that affect the size of the spangle, for example,
(1) Base metal: The thicker the base metal, the smaller the surface roughness and the larger the spangle.
(2) Cooling speed: The faster the cooling speed, the shorter the crystal growth time and the smaller the spangle.
(3) Number of nuclei: The crystal grains are formed on the steel base, the more nuclei, the smaller the spangles.
(4) Other factors (production environment, cooling temperatures, etc.).
When the zinc liquid is close to the solidification temperature, spray water droplets with a diameter of less than 0.1mm onto the surface of the galvanized sheet immediately. Then it will form small and uniform crystalline nuclei, which will help to form small spangles. Then go through skin-pass rolling with a reduction of less than 1% to get smooth spangles. Minimum spangles are suitable for painting purposes, and smooth spangles are suitable for deep drawing.
The shape of the spangle depends on the type of alloy added to the zinc solution. For example, adding lead and antimony will form phoenix-shaped spangles. While adding lead and tin will produce fern-shaped spangles and so on.
The different appearances will influence the processing method. For example, in the case of drawing and deep drawing, the processability of the feather spangle is the best, followed by the fern spangle and the leaf spangle. While during bending and tension processing, the leaf spangle is the best, followed by the feather spangle and the fern spangle.
The uneven spangle is a surface defect of hot-dip galvanized products. Although it will not affect the use of most products, it will impact the appearance of the surface. But sometimes the uneven spangles will cause poor adhesion of the zinc layer, which directly affects the use of galvanized steel. The uneven spangles can be summarized as follows:
(1) There are spangles on one side, and the diameter is about 6mm. While there are no spangles on the other side.
(2) Along the longitudinal direction of the galvanized strip, the size of the spangle shows regular fluctuations.
(3) Along the transverse direction of the strip, the spangles on one side are large, and the spangles on the other side are small.
(4) The spangles on the edge of the strip are small, while the spangles in the middle are large.
Wanzhi Steel is a galvanized steel manufacturer in China, which has 2 hot-dip galvanizing lines at our factory. We offer GI steel coils, sheets and strips with regular spangles, small spangles and zero spangles. Besides, the zinc coating for hot-dip galvanized steel can be 30-275 g/m2. Except for our own quality control system, third-party quality inspection is acceptable. Welcome to contact us for more details.