What is cold galvanizing and hot galvanizing?
Cold galvanizing is also called electrogalvanizing. It is an electrolytic device that removes oil and pickles in a solution containing zinc salt and connects it to the negative electrode of the electrolysis device. A zinc plate is placed on the opposite side of the workpiece to connect it to the electrolysis device. The positive electrode, when the power is turned on and the current moves from the positive electrode to the negative electrode, a layer of zinc is deposited on the workpiece.
Hot dip galvanizing is a method in which steel components are dipped in molten zinc to obtain a metallic coating. The workpiece is degreased, pickled, dipped, dried and dipped in molten zinc. Time, it just goes up.
Main difference between cold galvanized and hot galvanized
Basic principles
Cold galvanizing uses the chemical principle to separate the zinc alloy into zinc ions, which adhere to the surface of the steel. In general, the zinc layer is thin and steel rusts easily in a normal environment. In general, cold galvanizing is used for anti-corrosion of various steel products and structures. The galvanizing amount of cold galvanizing is very small, only 10-50 g per square meter.
It is well known that the anti-atmospheric corrosion mechanism of zinc has mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, there are ZnO, Zn(OH)2 and basic zinc carbonate protective films on the surface of the zinc layer, which slows down the corrosion of zinc to a certain extent. The protective film layer (also called "white oxide") is destroyed and a new film layer is formed.
Principle details:
When the zinc layer is seriously damaged and the iron matrix is compromised, the zinc will electrochemically protect the matrix. The standard potential of zinc is -0.76V, and the standard potential of iron is -0.44V. When zinc and iron form a microbattery, the zinc dissolves as an anode. The iron is protected as a cathode. The hot-dip galvanizing layer forming process is a process of forming an iron-zinc alloy between the iron matrix and the outermost pure zinc layer, and the surface of the workpiece forms an alloy layer iron-zinc during hot plating, which allows between the iron and the pure zinc layer. A good combination, the process can be described simply as: when the iron workpiece is immersed in molten zinc liquid (usually the molten zinc liquid is about 455 degree C), first form a solid solution of zinc and iron alpha in the interface. This is a crystal formed by the dissolution of zinc atoms in the solid state of the base metallic iron. The fusion between the two metal atoms is relatively small.
Therefore, when zinc is saturated in the solid solution, the two elements of zinc and iron diffuse into each other, and the zinc atoms diffused into (or called "infiltrated") the iron matrix migrate in the iron lattice. matrix and are gradually formed with iron. The alloy and iron diffused in the molten zinc liquid form a metal compound FeZn13 with zinc and sinks to the bottom of the hot-dip galvanizing pot, which is zinc slag. When the workpiece is removed from the zinc immersion liquid, a layer of pure zinc is formed on the surface, which is a hexagonal crystal. The iron content is not more than 0.003%, the hot-dip galvanizing coverage is good, the coating layer is fine, and there is no inclusion of organic matter.
