The pretreated strip is sent to the pickling tank for pickling. Pickling methods can be classified into two categories; one is acid leaching, and the other is acid electrolysis. The former is a commonly used method, while the latter is an auxiliary method, most of which are combined with acid leaching. Pickling method: Acids used alone or in combination include nitric acid, hydrofluoric acid, sulfuric acid, etc. Nitric acid is an oxidant that can promote the passivation of stainless steel, but it has no descaling effect when used alone. Hydrofluoric acid is highly corrosive, not only erodes iron scale, but also erodes the base metal, making the surface rough. Therefore, neither of these two acids can act alone, and the mixture of them works best, and a good surface can be obtained in a short time, and the risk of pitting is also small, so no matter what kind of steel, this mixed acid is mostly used. Sulfuric acid has a good pickling effect at higher temperatures, but it is poor at low temperatures, so it is generally only used in the following two situations: One is to improve the descaling performance of chromium steel hot-rolled coils, and sometimes a hot sulfuric acid tank is installed , used in combination with nitric acid and hydrofluoric acid mixed acid tank; the second is on the cold-rolled coil annealing and pickling line, in order to neutralize the alkali carried out on the strip after the alkali tank treatment, set up between the salt bath and the water washing tank Sulfuric acid tank to improve the efficiency of the subsequent pickling tank. When using sulfuric acid pickling, the key is to master the temperature of the acid solution. Stainless steel pickling generally does not use hydrochloric acid. Because hydrochloric acid not only erodes iron scale, but also erodes the metal substrate, even if it is used, it should be mixed with nitric acid, but this mixed acid is still corrosive to the metal substrate, resulting in rough metal surface, so it is rarely used in general stainless steel plants. Pickling electrolysis (also known as electrolytic pickling) Electrolytic pickling is a method to accelerate descaling when it is difficult to completely descale by pickling only. It can be used in combination with pickling to improve pickling efficiency. The characteristics of this method are: due to the effect of electrochemistry, the surface has a good uniform gloss. Nitric acid electrolysis and sulfuric acid electrolysis are usually used in electrolytic pickling, and nitric acid electrolysis is the most used. When nitric acid is used alone as pickling solution, it has no descaling effect, but when current flows through the electrode (silicon cast iron), the oxide film is ionized due to electrochemical action, and pickling can be carried out. However, due to its low corrosion resistance, descaling The ability is small and generally not used alone. The descaling ability of sulfuric acid electrolysis is even worse. In addition, in addition to the electrolysis device, this method also needs a device for recovering waste acid and sulfur oxides in the waste gas, so the equipment cost is relatively high. Strip pickling is carried out continuously, and various pickling methods, including pretreatment, are used in combination in different ways. The combination method is determined according to the steel type, the surface state of the strip steel and the equipment conditions.  

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