Hot-dip galvanizing is also called hot-dip galvanizing and hot-dip galvanizing: it is an effective way of metal corrosion protection, mainly used in the metal structure facilities of various industries. It is to immerse the steel parts after rust removal into the molten zinc solution melting at about 500 C, so that the surface of the steel components is adhered to zinc layer, so as to achieve the purpose of anti-corrosion. Hot-dip galvanizing process: finished product pickling-washing-adding bath-drying-hanging galvanizing-cooling-medication-cleaning-grinding-hot-dip galvanizing. Hot-dip galvanizing is developed from the older method of hot-dip galvanizing. It has been more than 170 years since France applied hot-dip galvanizing to industry in 1836. In the past 30 years, with the rapid development of cold-rolled strip, hot-dip galvanizing industry has been developed on a large scale.
Hot-dip galvanizing principle: Hot-dip galvanizing, also known as hot-dip galvanizing, is a method of obtaining metal coating by immersing steel components in molten zinc solution. With the rapid development of high-voltage power transmission, transportation and communication, the protection requirements for steel parts are getting higher and higher, and the demand for hot-dip galvanizing is also increasing.
Generally, the thickness of galvanized layer is 5-15 & mu; m, while that of hot-dip galvanized layer is generally 35 & mu; m or above, even up to 200 & mu; M. Hot-dip galvanizing has good covering ability, compact coating and no organic inclusions. It is well known that the anti-atmospheric corrosion mechanism of zinc is mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, zinc layer surface has zinc oxide, zinc (OH) 2 and basic zinc carbonate protective film, which to some extent slows down the corrosion of zinc, and this protective film (also known as white rust) will be damaged and form a new layer.
When the zinc layer is seriously damaged and endangers the iron matrix, zinc produces electrochemical protection. The standard potential of zinc is -0.76V, the standard potential of iron is -0.44V. When zinc and iron form micro-batteries, zinc is dissolved as an anode and iron as a cathode is protected. It is obvious that the atmospheric corrosion resistance of hot-dip galvanizing is better than that of galvanizing.
Formation Process of Galvanized Coating
The formation process of hot-dip galvanizing layer is the process of forming iron-zinc alloy between iron base and the outermost pure zinc layer. The iron-zinc alloy layer is formed on the surface of workpiece during hot-dip galvanizing, which makes the iron and pure zinc layer combine well. The process can be simply described as: when the iron workpiece is immersed in molten zinc solution, first zinc and alpha are formed on the interface; iron (core) solid melt is formed. This is a kind of crystal formed by dissolving zinc atoms in solid state of matrix metal iron. The two metal atoms are fused, and the attraction between atoms is relatively small. Therefore, when zinc saturates in the solid melt, the two elements of zinc and iron atoms diffuse into (or infiltrate into) the iron matrix. The zinc atoms diffuse into (or infiltrate into) the matrix lattice and gradually form alloys with iron. The iron diffused into the molten zinc solution forms intermetallic compounds with zinc and sinks into the bottom of the hot-dip galvanizing pot, which is called zinc slag. When the workpiece is removed from the zinc dipping solution, a pure zinc layer is formed on the surface, which is a hexagonal crystal. Its iron content is less than 0.003%.
The difference between hot galvanizing and cold galvanizing is that the corrosion resistance of hot galvanizing is much higher than that of cold galvanizing (also known as galvanizing). Hot galvanizing will not rust in a few years, cold galvanizing will rust in three months.
Cold galvanizing process is used to protect metals from corrosion. For this reason, zinc filler coatings are used, which are coated on the protected surface by any coating method. After drying, zinc filler coatings are formed, which contain zinc (up to 95%) in the dry coatings. Iron and steel are galvanized on the surface under cooling conditions. Hot-dip galvanizing is a kind of galvanizing on the surface of steel pipes under hot-dip conditions. It has strong adhesion and is not easy to fall off. Although hot-dip galvanized pipes are also corroded, it can meet the technical and sanitary requirements in a long period.