Set of fins
The set of fins process is to process a batch of individual fins with a punch in advance, and then use manual or mechanical methods to set the fins on the outer surface of the pipe by interference at a certain height (fin pitch). It is the earliest method of processing finned tubes. Due to the simple process, the technical requirements are not high, the equipment used is inexpensive, and it is easy to maintain, so many factories are still using it. This process is a labor-intensive process solution, suitable for the capital and technical conditions of general small factories or township enterprises.
Manually set is called manual set. It uses tools to rely on human power to press the fins one by one. In this method, because the pressing force of the fins is limited, the interference amount of the set is small, and the fins are prone to loosening.
Mechanical set fins are performed on a fin set machine. Since the pressing of the fins is by mechanical impact force or liquid pressure, the pressing force is large, so a large interference amount can be used. The bonding strength between the fins and the tube is high and it is not easy to loosen. The mechanical transmission set machine has high productivity, but high noise, poor safety, and poor working conditions for workers. Although the hydraulic transmission does not have the above problems, the equipment is more expensive, requires higher technical requirements for maintenance personnel, and its productivity is lower.
Mosaic spiral fin
The inlay spiral finned tube is a spiral groove with a certain width and depth pre-processed on the steel tube, and then the steel belt is inlaid on the steel tube on the lathe. During the winding process, due to a certain pre-tensioning force, the steel strip will be tightly held in the spiral groove, thereby ensuring a certain contact area between the steel strip and the steel pipe. In order to prevent the steel strip from springing back, both ends of the steel strip must be welded to the steel pipe. In order to facilitate inlaying, there should be a certain backlash between the steel belt and the spiral groove. If the backlash is too small to form an interference, it is difficult for the setting process to proceed smoothly. In addition, the wound steel strip always has a certain rebound, and as a result, the steel strip and the bottom surface of the spiral groove cannot be well joined. Mosaic fins can be carried out on general equipment, the cost is not high, but the production process is complicated and the production efficiency is low.
Brazed spiral finned tube
The processing of the brazed spiral finned tube is performed in two steps. First, the steel strip plane is wound on the outer surface of the pipe in a spiral manner perpendicular to the pipe axis, and the two ends of the steel strip are welded to the steel pipe to fix it. Weld the steel strip and steel pipe together.
This method is expensive, so another method is commonly used, that is, the tube wrapped with steel strip is put into a zinc liquid tank for overall hot-dip galvanizing instead. Although the whole hot-dip galvanizing solution does not seep into 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. The overall hot-dip galvanized spiral finned tube is limited by the thickness of the galvanized layer (when the galvanized layer is thick, the zinc layer has poor firmness and is easy to fall off). In addition, the zinc liquid cannot all penetrate into the gap. The bonding rate of 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 highly susceptible to corrosion in acids, alkalis, and sulfides. Therefore, galvanized spiral finned tubes are not suitable for making air preheaters (recovering boiler flue gas waste heat).