The mechanical fixed fin is made on the fixed fin machine. Since tableting is based on mechanical shock or liquid pressure, the tableting force is relatively large and large interference can be used. The fin and the pipe joint have high strength and are not easy to loosen. The mechanical transmission unit has high productivity, but the noise is high, and the working conditions of the workers are not good. Although the hydraulic transmission does not have the above problems, the equipment is more expensive, requires higher maintenance personnel, and lower productivity. Due to its high cost, this method is often used in another way, that is, the pipe wrapped with steel tape is placed in a zinc tank for overall hot-dip galvanizing. Using integral hot-dip galvanizing, although there is no good gap between the fin and the steel pipe in the plating solution, a complete galvanized layer is formed on the outer surface of the fin and the outer surface of the steel pipe. The spiral finned tube and the overall hot-dip galvanizing are affected by the thickness of the galvanized layer (when the galvanized layer is thick, the zinc layer is weak and easy to fall off), and the gap between the impermeability of zinc liquid, so the fin and joint rate of the steel pipe is not high . In addition, the heat transfer coefficient of zinc is smaller than that of steel (about 78% of steel), so its heat transfer capacity is low. Zinc is easily corroded in acids, alkalis and sulfides. Therefore, the galvanized spiral fin tube is not suitable for the production of air preheater (boiler flue gas waste heat recovery).
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