Current status of fin tube production technology:
1, set of fins
The finning process is to pre-process a batch of individual fins by punching, and then manually or mechanically, according to a certain height (wing distance), the fins are placed on the outer surface of the tube by interference. It is the earliest method of processing finned tubes. Due to the simple process and low technical requirements, the equipment used is inexpensive and easy to maintain, so many factories are still in use. This process is a labor-intensive process solution that is suitable for the capital and technical conditions of a typical small or township enterprise.
The manual method is called a manual suit. It uses tools to rely on human strength to push the fins one by one. In this method, since the pressing force of the fin is limited, the interference of the set is small, and the fin is prone to looseness.
The mechanical set fins are made on a fin kit. Since the fin press-in is caused by mechanical impact or liquid pressure, the press-in force is large, so that a large interference 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 the noise is high, the safety is poor, and the labor conditions of the workers are not good. Although the above problems are not present in the hydraulic transmission, the equipment is expensive, the technical requirements for the maintenance personnel are high, and the productivity is also low.
2, mosaic spiral fins
The inlaid spiral finned tube is a spiral groove of a certain width and depth pre-machined on the steel pipe, and then the steel strip is embedded on the steel pipe on the lathe. During the winding process, due to a certain pre-tightening force, the steel strip will be tightly placed in the spiral groove, thereby ensuring a certain contact area between the steel strip and the steel tube. In order to prevent the steel strip from rebounding, both ends of the steel strip are welded to the steel pipe. In order to facilitate the setting, there should be a certain backlash between the steel strip and the spiral groove. If the backlash is too small and an interference is formed, the inlaying process is difficult to proceed smoothly. In addition, the entangled steel strip always has a certain rebound, which results in a poor joint of the steel strip and the spiral groove bottom surface. Inlaid fins can be carried out on general-purpose equipment at a low cost, but the process is complicated and the production efficiency is low.
3. Brazed spiral finned tube
The processing of the 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 see a good 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 limited 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 zinc liquid cannot penetrate into the gap completely, so the fins and The joint 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 the production of air preheaters (recovery of boiler flue gas waste heat).
4, high frequency welding spiral fins
High-frequency high-frequency welding spiral finned tube is one of the most widely used spiral finned tubes. It is widely used in waste heat recovery in electric power, metallurgy, cement industry and petrochemical industry. The high-frequency welding spiral finned tube is used to wind the steel pipe while using the skin effect and the proximity effect of the high-frequency current to heat the outer surface of the steel strip and the steel pipe until plastic state or melting, and a certain pressure on the steel strip is wound. Finish the welding. This high frequency welding is a solid phase welding. Compared with inlaying, brazing (or integral hot-dip galvanizing), it is more advanced in terms of product quality (high fin weldability, up to 95%), productivity and automation. .
5, three-roller rolling overall spiral finned tube
The production principle of the three-roll cross-rolling integral spiral finned tube is as follows: a mandrel is lined in the light pipe, driven by the rotation of the roll blade, and the seamless steel pipe is processed on the outer surface of the cavity formed by the groove and the core. Finned. 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.
At present, the three-roller-rolled monolithic spiral finned tube technology has been successfully applied to single-fin tube or composite finned tube with copper or aluminum fins, or steel low-fin tube; steel integral finned tube is currently Most of the low finned tubes are found in the market. The overall high finned tubes are made of aluminum, copper, etc., and are generally cold rolled.