(1) the effective components of hot dip galvanization and optimum workpiece conditions for steel members to dip visco-plating before hot dip galvanization are designed to ensure that the iron matrix on the steel surface reacts normally with the zinc solution in a short period of time to form an iron-zinc alloy layer.: its action mechanism is:
(a) clean the steel surface and remove some iron salts, oxides and other dirt from the surface of the steel after pickling.
(b) purifying the liquid zinc in the zinc liquid to make the steel and liquid zinc rapidly infiltrate and react.
(c) a layer of salt film is deposited on the surface of the steel pieces to isolate them from air and prevent further micro-oxidation.
(d) when the solvent is decomposed by heat (refers to dry method), the surface of the steel can be activated and moist (i.e. reduce the surface tension), so that the zinc solution can be well attached to the steel matrix, and the alloying process can be carried out smoothly.
(e) the air waves generated by the gasification of the solvent when the steel coated with the solvent encountered zinc liquid played a role in removing zinc oxide, aluminum hydroxide and carbon black particles on the zinc liquid.Zncl.2nhci is usually chosen as the assistant plating agent. When the workpiece is immersed in zinc solution, the salt of the assistant plating agent is heated
ecomposition first occurs: the ammonia gas and hydrogen chloride gas released will react with the residual oxides on the surface of the workpiece and zinc oxide formed on the surface of zinc chloride. The coplating solution, which is composed of zinc chloride and ammonium chloride, is a chemical double salt with stable composition, which is easy to crystallize on the surface of steel.
The role of NHCI in the coplating agent is the most fundamental, but NHCI is volatile, so the content cannot be too high to avoid excessive smog in the process of soaking and zinc.ZnC1 ACTS as a coating to reduce the oxidation of the workpiece after pickling and before zinc immersion.At the same time, zncl.2nhci as a mixture of zinc chloride and ammonium chloride formed by the coplating agent has a good automatic drying effect.According to the research report, the mixed ratio of zinc chloride and ammonium chloride is about 0.8 in Europe: in the United States and Japan, trisalt zncl.3nhci or four-salt zncl.4nhc1 solution is usually used, and ammonium zinc ratio is about 1.2-1.6.