Basic knowledge of finned tubes 2

 Basic knowledge of finned tubes

Current situation of fin tube production technology

1.Set fin

The set fin technique is to use a punch to process a single set of fins in advance, and then use the artificial or mechanical method, according to a certain distance high (fin), and the fin is sheathed on the outer surface of the pipe by interference. It is one of the earliest methods to process the fin tube. As the technology is simple, the technical requirements are not high, the equipment is cheap and easy to repair, so, there are still many factories in the use of. This process is a kind of labor - intensive process, which is suitable for the capital and technical conditions of small factories or township enterprises.

The manual method is called hand set. It is the use of tools, relying on the power of the people will be pressed into the fins. This method because of the limited pressure of the fin, the set of a small amount of interference, easy to produce the phenomenon of the fin.

The machine set fin is carried out on the fin set machine. Because the fin is pressed into the mechanical impact force or liquid pressure, the pressure is large, so, can use a large amount of interference. The bonding strength between the fin and tube is high, and is not easy to loosen. Machine set with high productivity, but the noise is big, poor security, poor working conditions of workers. Although the hydraulic transmission does not have the above problem, but the equipment price is more expensive, to use the maintenance personnel's technical request is higher, its productivity is also low.

2. mosaic type spiral fin

The spiral fin tube is a spiral groove with certain width and depth on the steel pipe, and the steel strip is inlaid on the steel pipe. In the winding process, because of certain pre tightening force, strip will tightly buckled in the spiral groove, thus ensuring the strip and tube between the contact area. In order to prevent the steel strip from falling off, both ends of the steel strip should be welded on the steel pipe. In order to facilitate the mosaic, there should be a certain gap between the steel strip and the spiral groove. If the side gap is too small to form a surplus, the mosaic process is difficult to proceed smoothly. In addition, the winding strip always has a certain spring back, and the result is that the steel strip and the bottom surface of the spiral groove can not be well engaged. Mosaic fin can be carried out on general equipment, the cost is not high, but the process of complex production efficiency is low.


3. welding spiral fin tube

Two steps are carried out for the machining of the brazing spiral finned tube. First, strips perpendicular to the plane to the axis of the tube by a spiral wire winding in the outer pipe surface, and the steel welded at both ends is fixed on the steel pipe, and eliminating the gap between the contact strip and tube, brazing method will strip and tube welding together.


This method, because the cost is expensive, so commonly used another method is wrapped around good steel tube into zinc bath in the overall hot-dip galvanizing to replace. The entire hot dip galvanizing, although the bath is not necessarily good to seep into fin and tube between a minimum space, but in the outer surface of the fin surface and the outer tube is the formation of a a complete galvanized layer. The overall hot-dip galvanizing of spiral finned tube, due to the limits of galvanized layer thickness (galvanized layer thickness, Zn solid layer of poor, easy to fall off), coupled with liquid zinc impossible completely infiltrated into the gap, so that the combination of fin and tube rate is not high. In addition, the heat transfer coefficient of zinc is smaller than that of steel (about 78% of steel), so the heat transfer coefficient is low. Zinc is extremely vulnerable to corrosion in acid and alkali and sulfur compounds. Therefore, it is not suitable to make air preheater by using zinc coated spiral fin tube.

4. high frequency welding spiral fin

High frequency and high frequency welding spiral fin tube is one of the most widely used spiral fin tubes. It is widely used in power, metallurgy, cement industry, waste heat recovery, petroleum and chemical industry, etc.. High-frequency welded spiral finned tube is in strip winding pipe at the same time, high frequency current skin effect and proximity effect, the use of the strip and tube outer surface heating, until the plastic state or melting, under certain pressure steel belt winding complete welding. This high frequency welding is a solid state welding. It is compared with that of mosaic, brazing (or whole Galvanized) and other methods, both in product quality (fins welded rate high, up to 95%), or the productivity and automation are more advanced.



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