48. What is the solvent method? What is the purpose of using solvents?

After acid washing and cleaning, or following immersion in dilute hydrochloric acid solution prior to hot-dip galvanizing, steel pipes must first be coated with a layer of concentrated hydrochloric acid, zinc chloride aqueous solution, ammonium chloride aqueous solution, or a compound salt solution of zinc chloride and ammonium chloride, followed by drying. Alternatively, the compound salt solution can be placed directly into a specially designed container on the zinc bath surface, allowing the pipe to pass through the molten compound salt layer before entering the zinc bath. The process of producing galvanized steel pipes using these two coating methods is referred to as the solvent method. The former is called the "dry solvent method" or simply "dry method," while the latter is termed the "wet flux method" or simply "wet method."
The purpose of using solvent is to ensure that the iron matrix on the surface of steel pipe can react with the zinc liquid normally in a short time when the steel pipe is immersed in hot zinc liquid, and to form a complete iron-zinc alloy layer. In the "dry method", the solvent film on the surface of steel pipe can still prevent the metal matrix of steel pipe from being oxidized.