Brief introduction of three-roll cross-rolling integral spiral finned tube and brazed spiral finned tube
The role of the finned tube is simply heat transfer. The lower finned tube is introduced to introduce the three-roll cross-rolling integral spiral finned tube and the brazed spiral finned tube:
1. Three-roller cross-rolling integral spiral finned tube: The production principle of three-roller cross-rolling integral spiral finned tube is shown in Figure 1.8. The light pipe is lined with a mandrel, which is driven by the rotation of the roll blade. The steel tube is machined with fins on its outer surface through a cavity formed by the groove and the core. The fin tube produced by this method has an organic whole due to the base tube and the outer fin, so there is no problem of contact thermal resistance loss, and the heat transfer efficiency is high. Compared with the welding method, the three-roll cross-rolling method has the advantages of high production efficiency, low consumption of raw materials, and high heat exchange rate of the produced finned tubes.
2. Brazed spiral finned tube: The processing of brazed spiral finned tube is carried out in two steps. Firstly, the steel strip plane is wound on the outer surface of the pipe in a spiral manner perpendicular to the axis of the pipe, and the two ends of the steel strip are welded on the steel pipe for fixing, and then the gap between the steel strip and the steel pipe is eliminated, and the brazing method is used. Weld the steel strip and the steel tube together. Because of its high cost, this method is often used in another way. The tube wrapped with steel strip is placed in a zinc bath for integral hot-dip galvanizing instead. The use of integral hot-dip galvanizing, although the plating solution does not necessarily penetrate into the very small gap between the fin and the steel pipe, but 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 with integral hot-dip galvanizing is not limited by the thickness of the galvanized layer, and the zinc liquid cannot be completely infiltrated into the gap. Therefore, the bonding ratio between the fin and the steel tube is still not high. In addition, the heat transfer coefficient of zinc is smaller than that of steel, so the heat transfer capacity is low. Zinc is highly susceptible to corrosion in acids, bases, and sulfides. Therefore, galvanized spiral finned tubes are not suitable for making air preheaters.