Spangles Size
According to the European standard EN 10346:2015, the size of hot-dip galvanized zinc spangles can be divided into ordinary spangles and small spangles.
Conventional zinc spangles refers to the size and morphology of zinc grain formed after normal solidification of zinc solution, while the absence of zinc spangles(also known as small zinc flower) is the size and morphology of zinc grain obtained through special control of the solidification process of zinc.If the user needs to specify the size of the zinc spangles, it needs to be negotiated at the time of ordering.
There are many factors that affect the size of the zinc spangles. When the composition of the zinc liquid has the conditions for the formation of the zinc spangles, the following factors affect the size of the zinc spangles:
Raw material: raw material plate thickness, surface roughness is smaller, zinc spanglesis larger.
(2) cooling speed: the faster the cooling speed, the shorter the crystal growth time and the smaller the zinc spangles.
(3) number of crystal nuclei: the size of zinc spanglesis closely related to the number of crystal nuclei of zinc spangles.When the surface of steel base is rough or the surface cleanliness is poor, the zinc spanglesis relatively small.Zinc grain is formed on steel base, the more nucleus, the smaller zinc spangles.
(4) other factors (production environment, etc.).
In order to obtain small zinc spangles, when zinc solution is near the solidification temperature, water droplets with a diameter of less than 0.1mm are immediately sprayed on the surface of galvanized sheet to form a fine and uniform crystal nucleus.In order to obtain smooth zinc spangles, less than 1 % of the press to carry out rolling.Small zinc flower is suitable for painting, light whole zinc flower is suitable for deep stamping.
Big spangles
Normal spangles
Mini spanglesZinc layer adhesion
When the heated steel strip passes through the molten zinc solution (zinc tank), it first forms an iron-zinc alloy layer on the substrate and covers the pure zinc layer outside the alloy layer.The layer thickness of fe-zn alloy is uneven, loose, brittle, poor ductility and easy to crack.
If a certain amount of iron base salt is left on the surface of the steel plate before galvanizing, the resulting iron-zinc alloy will have poor adhesion, poor ductility and easy spalling.When the pure zinc coating contains harmful impurities, such as zinc oxide, zinc slag, cadmium and lead, the formation of large zinc flower, or destroy the continuity of zinc layer, easy to hairline zinc layer small crack.
When the zinc coating is too thick, its bendability is also poor.When aluminum is added to the zinc solution, the aluminum in the zinc solution reacts with the substrate, first forming Fe2AI5 or Fe 2AI3, which thins the iron-zinc bonding layer and improves the adhesion of the zinc layer.
Uneven zinc flower and its influencing factors
Uneven coating surface zinc flower, is a kind of surface defects of hot dip galvanized products, although the use of most products will not produce a great impact, but affect its surface beauty, resulting in the product in the market in some areas of application is limited.Some products with uneven zinc flower also have poor adhesion of zinc layer, which directly affects the use of the product.
The uneven state of zinc flower on the surface of hot galvanized sheet can be summarized as follows:
(1) zinc flower on one side and no zinc flower on the other side.The diameter of the zinc flower with one side of the flower is about 6mm.
(2) along the longitudinal strip, the size of zinc flower fluctuates regularly.
Horizontal along the strip, one side of the zinc flower is large, the other side of the zinc flower is small.
(4) the edge of the strip zinc flower is small, the middle zinc flower is large.
The main factors affecting spangles unevenness of include: the proportion of the two kinds of alloy element in zinc liquid composition, air knife, strip temperature control technology, impurity content in the gas, combustion air, and the strip surface cleanliness and the furnace condition, furnace iron nodules, strip scratches and raw materials on the surface of iron oxide, zinc strip into the pot, most liquid zinc, aiming to have strolled, etc.