The processing of brazing spiral finned tubes is carried out in two steps.
First, the steel strip plane is perpendicular to the pipe axis according to the spiral way winding on the outside surface of the pipe, and the steel strip at both ends of the welded pipe fixed, and then in order to eliminate the gap between the steel strip and the pipe contact, the steel strip and steel pipe are welded together by brazing method. Because of its high cost, this method is often used in another way, the pipe wrapped in the steel belt will be put into the zinc tank for the whole hot galvanizing to replace. The use of overall hot-dip galvanizing Although the plating solution is not necessarily very good seepage between the fins and the steel pipe between the very small gap, but on the outer surface of the fin and the surface of the steel pipe on the outside of the formation of a complete galvanized layer. The use of the overall hot-dip galvanized spiral fin tube, because of the thickness of the galvanized layer (galvanized layer thick, zinc layer firmness is poor, easy to fall off), coupled with zinc liquid can not all penetrate into the gap, so, the bonding rate of fins and steel pipe 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 highly susceptible to corrosion in acids, alkalis and sulphides, so it is not suitable to make air preheater (recovery of waste heat from boiler flue gas) with galvanized spiral finned tube.
