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If the zinc coating is good, but in 3% nitric acid when the light, the coating has dark shadow, passivation occurs when the film is brown, may be caused by foreign metal impurities such as copper or lead in the galvanizing liquid. When problems occur in the process of galvanizing large coil galvanized wire, the temperature and current density are checked first, and then the content of zinc and sodium hydroxide in the plating solution is measured and adjusted through the analysis of the plating solution. Whether DPE content is low can be determined by hull cell test.

Industrial rust prevention method: coated with asphalt, iron roof, coated with asphalt, you can prevent rust. Metal coating: Some metal surface will form a dense oxide film, can be coated on the surface of the metal composed of this metal screen. Such as: galvanized iron, tinplate plating, bicycle underwire and some medical equipment are coated with chromium and nickel.