Hot dip galvanizing technology
What is hot dip galvanizing?
Hot-dip galvanizing, also called hot-dip galvanizing, is a method in which steel components are immersed in molten zinc to obtain a metal coating.
The zinc ingot is melted into a liquid state at high temperature (440°C) and some auxiliary materials are added, and then the pre-treated (degreasing, pickling, aid plating, etc.) metal structural workpiece is immersed in the galvanizing bath: after complex physical and chemical effects Not only is a thicker layer of pure Z2n plated on the steel, but a Zn-Fe alloy layer is also formed.
Formation of hot-dip galvanized layer.
It is generally considered that the hot-dip galvanizing process, the process of forming the galvanized layer is as follows: (the temperature of the Zn molten liquid during hot-dip galvanizing is 430~470C) when the surface-treated steel workpiece enters the Zn molten liquid (the high temperature is about 440C to melt the zinc ingot) , the iron matrix reacts with molten zinc: iron is dissolved to form a solid solution of Zn in a-Fe; mutual diffusion produces Fe-Zn alloy compounds: when the workpiece leaves the zinc melt, pure molten Zn is brought out to cover the alloy layer , forming a pure Zn layer.
What is electro-galvanizing?
Electroplating is an electrochemical process - a redox process.
The cleaned and specially pretreated workpiece to be plated is used as the cathode, and the plated metal Zn is used to make the anode. The two poles are connected to the positive and negative poles of the DC power supply respectively, and are immersed in a plating tank filled with galvanizing liquid (electrolyte). After electrification, the Zn2+ ions in the galvanizing solution move to the cathode (workpiece) under the action of potential difference and are reduced to elemental Zn and deposited on the surface of the workpiece to form a zinc coating; the Zn plating metal on the anode is oxidized into Zn2+ ions and enters the plating layer. Zinc solution to maintain the balance of Zn2+ ion concentration.
Characteristics and applications of electroplated zinc layer
1. The electroplated zinc layer has good uniformity, dense coating and smooth appearance.
2. The thickness of the electroplated zinc layer varies depending on the requirements of the workpiece. The coating is generally no less than 5 um, usually 6"12μm, and only exceeds 20μm under severe environmental conditions. When the thickness of the electroplated zinc layer exceeds a certain value, the adhesion will be greatly reduced.
3. In summary, the electrogalvanizing process is not suitable for use in acid, alkali, and salt spray atmospheric environments: it is suitable for light industry, instrumentation, electromechanical, agricultural machinery, and national defense industries.
