Brazed, high-frequency welded spiral finned tube
The processing of brazed spiral finned tubes is carried out in two steps. First, the steel strip is wound on the outer surface of the pipe in a spiral manner with the plane of the steel strip perpendicular to the axis of the pipe, and the two ends of the steel strip are welded to the steel pipe and fixed. Then, in order to eliminate the gap between the steel strip and the steel pipe, the steel strip and the steel pipe are welded together by brazing.
This method is expensive because of its high cost, so another method is commonly used, which is to put the steel strip wrapped tube into the zinc bath for overall hot-dip galvanizing instead. Using integral hot-dip galvanizing, although the plating solution may not well penetrate the very small gap between the fin and the steel pipe, a complete galvanized layer is formed on the outer surface of the fin and the outer surface of the steel pipe. Integral hot-dip galvanized spiral fin tube is used, because it is limited by the thickness of the galvanized layer, and it is impossible for the zinc liquid to penetrate into the gap (when the galvanized layer is thick, the zinc layer is easy to fall off). Therefore, the combination rate of fins and steel pipes is still not high. In addition, the heat transfer coefficient of zinc is smaller than that of steel (about 78% of steel), so the heat transfer capacity is low. Zinc is easily corroded in acids, alkalis, and sulfides. Therefore, the use of galvanized spiral finned tubes is not suitable for making air preheaters (recovering boiler flue gas waste heat).
High frequency welding spiral fin
High-frequency welding spiral finned tube is one of the most widely used spiral finned tubes. Now it is widely used in waste heat recovery in electric power, metallurgy, cement industry and petrochemical industry. The high-frequency welding spiral finned tube uses the skin effect and proximity effect of high-frequency current while the steel strip is wound around the steel tube. Heat the outer surface of the steel strip and steel pipe until it is in a plastic state or melted. The welding is completed under a certain pressure of winding the steel belt. This kind of high frequency welding is actually a solid phase welding. Compared with inlay, brazing (or overall hot-dip galvanizing) and other methods, it is more advanced in terms of product quality (high fin welding rate, up to 95%), productivity and automation .
