Application of nonwhite smoke plating aid in hot dip galvanizing process

The traditional hot galvanizing process includes wet hot dip galvanizing and dry hot galvanizing. Zinc chloride and ammonium chloride or compound brine solution are still used in the plating process as the plating AIDS for steel products. The proportion of ZnCi2:3NH4=3 is generally used (the quality score is low). The low wetting ability of the melting point of this formula has a strong chemical cleaning effect on residual ash on workpiece surface and micro corrosion. In order to prevent excessive chlorination of the surface and air of high-temperature zinc solution in production, zn-aluminum-rare earth alloy is added into the zinc solution to form a dense chlorination film of A1O on the surface of zinc solution, which will reduce the oxidation loss of the surface of zinc solution. Then there is a prominent question, in the process of production, the adhesion with zinc chloride and ammonium chloride film steel parts, encountered 440-450 ℃ in hot dip galvanized zinc liquid temperature will produce larger smoke: actually the decomposition of ammonium chloride in 337.8 ℃ to HCI and NH, namely:

(1) NH4CI HC1 + NH3

Ammonium chloride reacts with aluminum as follows:

(2) 6N H C1+2A1C1+6N H3+3H2 (light blue, white mixed gas)

The reaction between zinc chloride and aluminum in the plating AIDS is as follows:

(3) 3ZnC12+2A1=3Zn+2A1C1 (light blue gas)

The decomposition and release of chlorine and hydrogen chloride reacted as follows with the ferric chloride on the surface of steel parts and zinc chloride on the surface of zinc solution.

(4) FeO + 2 hci + NH3 = FeC1 + H2o

(5) ZnO + 2 hci + NH3 = ZNCI + H2o

It is also proved that the main components of smoke are NH3, HCI, ZnO, etc., and the smoke becomes white. And when molten zinc contains aluminum, there is blue AICI smoke. The two gases combine above the zinc pot to form particulate - or nano-crystalline particles. These gases and particles do not do much harm to human body, but if they are in a large smoke environment for a long time, they will have adverse effects on human body.

With the gradual improvement of people's awareness of environmental protection and the increasingly strict requirements of the state on environmental protection, the traditional zinc-holding zinc plating process of batch hot-dip galvanization cannot meet the requirements of clean and environment-friendly production of hot-dip galvanization industry because of the large amount of exhaust gas and smoke produced by the decomposition of ammonium oxide under high temperature conditions. In this regard, the development of environment-friendly non-white smoke plating AIDS has been the main research and development direction of batch hot dip galvanizing. In order to reduce environmental pollution, researchers and engineers at home and abroad have conducted a series of studies on the composition of plating AIDS and the plating process. Up to now, no new plating AIDS technology can completely replace the