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Hot dip galvanized fluxing agent

Source:    Time: 2016-12-16

   Hot dip galvanizing process requires the help of plating treatment in the workpiece surface to form a smooth activation layer. The main role of the auxiliary plating is to activate the surface of the workpiece after pickling and rinsing to ensure rapid and uniform reaction between the workpiece surface and the molten zinc during dipping. Therefore, the fluxing can be considered as a fine pickling solution.

1. Zncl2, NH4CL double salt to help plating
From the hot-dip galvanized industrial promotion began, from Zncl2, NH4CL composed of mixed salt was used as a fluxing agent. The melting point of ZnCl2 is about 280 ℃, from 280 ℃ to 230 ℃ to reach the so-called first eutectic point E1, E1 at the NH4CL mass fraction of about 12%; at about 180 ℃ when there is a second eutectic point E2, E2 NH4CL mass fraction of 26% -27%. In practice, both eutectic points of the double salt additives are used.

The eutectic point E1 of the mixed salt fluxing agent is characterized by good wetting properties. Eutectic point of the double salt advantage of the salt is below the drying temperature, drying agent, salt film does not absorb moisture; the disadvantage is the poor wetting effect of molten zinc, and because the high content of NH4CL dip coating Soot generation.

In the mechanism, Zncl2, NH4CL double salt bathing aid plating effect based on two aspects: the surface of the workpiece surface treatment in the drying process to form hydroxy chloride zinc acid .which covers the first pickling after the clean surface of the workpiece , Has been stable to 200 ℃ high temperature, which is particularly important in wet hot dip galvanizing. From 200 ° C to a higher temperature, thermal decomposition from the complex salt Zncl2, NH4CL to produce HCL, induced a second pickling, this second pickling in dry hot dip galvanizing is very important, it will So that the zinc bath surface residual Zno dissolved.

Dry hot dip galvanizing and wet hot dip galvanized comparison: dry hot dip galvanized technically easy to operate and analysis and control, it requires the workpiece before the dip to dry well, so the workpiece is suitable for the simple shape of the plating , But may allow the addition of a small amount of AL AL-Zn alloy bath; the formation of zinc ash (or dross) is relatively small. Wet-process hot-dip galvanizing does not require a separate auxili- tation treatment, the workpiece can be wet through the cover layer of the dip coating into the zinc bath, it can be coated with some complex shape of the workpiece (such as hollow parts); zinc bath The addition of a small amount of aluminum is not possible in the wet-process hot dip galvanizing process. Wet galvanized galvanized layer obtained by thicker 、appearance of light, but its control layer of the coating layer control is more complex.