1. Effects of lead
There are always lead and zinc coexisting deposits in nature. In the process of smelting zinc, although it has been rectified many times, there is still a certain amount of lead in the finished zinc of all levels. It should be noted that some lead is
always added to the liquid zinc when hot-dip galvanizing. The dissolution limit of lead in liquid zinc at 450 ℃ is 1.5%. If lead is added beyond this saturation concentration, lead layer will appear at the bottom of zinc pot.
The existence of lead
can also reduce the viscosity and surface tension of liquid zinc, which can increase the wettability of liquid zinc to iron surface. In the process of hot galvanizing, adding lead into the zinc bath can make the surface of the coating obtain beautiful
large zinc flakes, at the same time, it can improve the immersion condition of the molten zinc on the steel plate, so as to shorten the soaking time of the strip steel
2. The influence of iron
When the temperature of liquid zinc is 450 ℃,
the maximum solubility (saturation concentration) of iron in liquid zinc is 0.03%. If the iron content continues to increase, iron will combine with zinc to form iron zinc alloy and sink into the bottom of the pot, which is called bottom slag. In addition,
iron is easy to combine with aluminum to form bottom slag, which can reduce the effective aluminum content, so the adhesion of the coating will be deteriorated. In addition, the existence of iron can increase the viscosity and surface tension of molten
zinc, which will worsen the wetting condition of molten zinc on steel plate and prolong the galvanizing time.
3. The influence of antimony
The beautiful zinc flower can be obtained by adding antimony into the liquid zinc.
of other elements
In addition to the above elements, there are also some other impurity elements, most of which are due to symbiosis with zinc ore, which are not left clean during zinc smelting (such as cadmium, tin, antimony), and some are inevitably
brought into the production process (such as iron).
The content of impurity elements in zinc bath will have some influence on zinc plating, which mainly includes the following aspects:
4.1 affect the properties and structure of the coating. If the dissolution rate of iron in zinc solution (such as cadmium and antimony) is increased or decreased, the iron zinc alloy layer will become thicker or thinner, and the fluidity of liquid
zinc will be increased or the pure zinc layer will be thinned or thickened (such as iron), the brittleness of zinc will be increased, and the coating will become brittle (such as arsenic);