About the Zinc Spangles
With beautiful zinc flower is the main characteristic of traditional hot galvanized sheet.The most complete form of zinc crystal is similar to snowflake or hexagonal star. Therefore, the zinc crystal obtained by condensation on the surface of hot plating process is most likely to form snowflake or hexagonal star zinc flower.
Actually, zinc flower just has ornamental value, no practical value, on the contrary, zinc flower in corrosion resistance is not good, surface coating will appear concave uneven.Therefore, household appliances and automobile industry tend to choose small zinc flower (no zinc flower) products, and looks very beautiful with zinc flower products, there is a certain amount of use in the construction industry.
High purity zinc solution will not solidify to form zinc flower when it is cooled, because there is no necessary crystallization nucleus in the zinc solution.In order to obtain a typical zinc flower, it is necessary to add two kinds of alloying elements with different properties in the zinc solution.Another kind of alloying element is soluble in both liquid and solid zinc, such as aluminum, tin, antimony, etc.If only one kind of alloy element is added, the surface state of the zinc layer will change after solidification, but it is not enough to form a typical zinc flower.
Why have Spangles
The way to form zinc flower is to try to form a large number of crystal nuclei as early as possible, reduce the solidification temperature of zinc liquid, in order to extend the growth time of zinc flower crystal, facilitate the growth of zinc flower.
(1) add other elements to the zinc solution
When an alloying element is added to the zinc solution, the crystallization process can be prolonged, and the surface zinc solution will not solidify until its eutectic temperature is reached.
Pure zinc solidifies at 419.5°C, and if tin (less than 0.5%) is added, the tin-zinc eutectoid alloy will not solidify until it is reduced to 198°C.After adding CD, CD zn eutectoid alloy did not decrease to 264.) does not solidify.If pounds (less than 0.3%) is added, the antimony zinc eutectoid alloy will not solidify until it is reduced to 40 °C.When lead is added, the lead-zinc eutectoid alloy will not coagulate until it is reduced to 317°C.
Therefore, the addition of alloy to reduce the melting point of zinc liquid, than the solidification time of pure zinc have different degrees of extension, make the growth time of zinc flower crystal greatly extended, facilitate the growth of zinc flower, so the taste guide the larger zinc flower.
(2) surface blowing
When the zinc layer on the surface is about to solidify, if the vapor or sulfur dioxide flow through the surface, the zinc flower crystal can be jaded to grow, and a larger pattern can be obtained.Another purpose of blowing sulfur dioxide gas flow is to form a dense oxide film and improve the corrosion resistance of galvanized coating.
(3) wire mesh method
This method can only be used on galvanized sheet, which is achieved by making the wire mesh contact the surface of the zinc layer with a magnetic shaft.Because the junction of the wire mesh is cooled at first, the crystallized solid particles are formed at first to form the crystallized nucleus, and the remaining unsolidified zinc liquid starts to expand to form the zinc flower.
(4) water spraying method
The pure zinc solution on the surface of galvanized steel is sprayed with water mist (water and steam or a mixture of water and air) to form the crystallization nucleus before solidification.The unsolidified zinc liquid was dispersed from this point to form zinc flower.
(5) other methods
In addition to the above method, if the surface of the plating can be achieved smooth, galvanized layer is relatively thin, control temperature uniform drop and enough air cooling time, can also obtain a larger zinc flower.