When purchasing hot-dip galvanized seamless tubes, some customers take zinc flower as a judgment mark, and must have zinc flower; while some customers demand "flower-free" galvanized tubes, why?
The crystalline pattern of coated metal appears on the surface of hot dip coating of seamless steel tube during solidification. This crystalline pattern is particularly obvious for galvanized seamless steel tube, showing a beautiful appearance of zinc crystallization, thus becoming an important feature of the appearance of hot dip galvanized seamless tube, which is commonly called "zinc flower". When other metal impurities are contained in the galvanizing bath, zinc flowers are produced. The size and morphology of zinc flower depend on the type and amount of impurities in galvanizing bath. Common impurities are lead, aluminium, antimony, bismuth, tin and other metals.
According to the size of zinc flower diameter, it can be divided into three types:
(1) Big zinc flower
Zinc flowers with diameters larger than 3 mm can be distinguished by naked eyes. They are called large zinc flowers, or normal zinc flowers or natural zinc flowers. The internationally recognized optimum size is 8-12 mm.
(2) Small zinc flower
The zinc flower with a diameter of 1-2 mm is called the small zinc flower. When the hot-dip galvanized seamless tube sprays water mist or zinc powder into the non-solidified zinc layer after it comes out of the galvanizing bath, a water mist drop and a zinc powder particle will form a crystallization center, which will increase the number of zinc flowers per unit area and reduce them. Therefore, the surface of the galvanized seamless tube will form small zinc flowers which can be distinguished by naked eyes. Traditionally, the products produced by this process are called small zinc flowers. Because this process often results in uneven zinc flower, uneven surface color and high production cost, it is not widely used at present.
(3) Zinc-free flower
Zinc flower can not be seen on the tube by naked eyes, which is called zinc-free flower, also known as zero zinc flower. This is accomplished by controlling the chemical composition of zinc liquefaction. In hot-dip galvanizing, zinc-free flower products can be produced by adding only a certain amount of aluminium to the zinc bath without adding lead, antimony and tin. This process does not increase equipment and production cost, and can obtain uniform surface appearance. Therefore, this process has been widely applied all over the world.