Finned Tube----Ways to improve the high frequency spiral welded finned tubes and energy saving measures pass rate
Abstract: High-frequency welding spiral finned tube forming process and basic principles. Analysis of the high-frequency welding spiral finning reasons for the low pass rate. Through analysis and testing to prove, to improve the pass rate spiral finning following aspects should be: ① reasonably determine the platen width and groove depth to minimize diversion effect platen; ② adjust the electrode position, improved electrode structure; ③ minimize power loss of high frequency devices; ④ adjust equipment to best match the state; ⑤ minimize high-frequency transformer near ferromagnetic iron loss; ⑥ top forging force increase during welding.
Key words: high-frequency welding; finned tube; skin effect; proximity effect
1.A high frequency spiral fin tube Introduction
Finned tubes (hereinafter referred to as finned tubes) of high frequency welding is the use of a high frequency current characteristics of the metal product strip is welded to the metal pipe is formed. As the finned tube heat transfer area has a large, high efficiency heat transfer, so the gas furnace, oil furnace and radiator mix, its comprehensive heat transfer performance was significantly better than the same size, the same material of ordinary tubes, Studded tube. With finned tube heat exchanger core components in a variety of electric power, chemicals, shipbuilding, civil construction, oil refining unit has been more widely used. Abroad are constantly developed and produced high-frequency spiral fin tubes. According to the data reported, high-frequency welding spiral finned tube passing rate of the U.S. Thermatool company can reach more than 90%, but a few domestic manufacturers of high-frequency spiral welded finned tubes are low passing rate there is a problem. Welding low passing rate mainly as follows:
① between the fins and the pipe did not have "welding", and the edge of the slag produced only strip "stacking" effect, this case for different materials welded steel fins and was particularly prominent; ② fins only standard block factory skill levels are to be further improved. So, as soon as possible to achieve localization AUT equipment is also an important aspect of China to improve the level of pipeline construction.
The center position of the strip only a small part of the welding zone "welding", and the remaining Part of the steel slag heap. For the same kind of finned tube material Welding, through its fins and steel pipe weld microstructure analysis Know, at the junction of the fin and steel as well as a clear dividing line can be cleared Clarity to see both sides of the fin at the bottom weld slag accumulation phenomenon. Therefore, to improve the pass rate is welded finned tube equipment Finned tube manufacturers and manufacturers of common concern.
And electric effects should contact local heating pipe and steel surfaces and Pad, the contact surface can be plastically welding state, while the fin Forging force is applied to the outside of the metal oxide in contact at the local melting Compound and the metal extrusion excess plastic state, the steel pipe member with the fins Part of the question to achieve solid atoms combine to achieve the contact surface Plastic welding. Finning molding shown in Figure 1.
3 high-frequency equipment selection
2 finning forming the basic principles
'In order to improve the high frequency spiral finning pass rate required from
Finned tube according to a certain pitch is considering various factors on the outer seamless steel pipe, which must first consider the high-frequency energy
Winding strip, so the strip perpendicular to the outer surface of the steel pipe to the rational use of high-frequency power. In the high-frequency welding equipment parameters to meet the requirements of
Heat flow for welding using a high frequency current skin effect, the proximity effect is the premise of maximizing the use of the energy in the weld metal zone
Steel electrode strip electrodes
1 finning molding schematics
On welding, to reduce the loss.
The main effects of high frequency finning equipment pass rate is high
The main parameters of frequency power, high-frequency power is the output power and output
Frequency. Ability to determine the output power of the device can be welded, and the output
Determines the frequency of the size of the penetration depth, and determines the quality of the welding
Energy utilization.
Selection should follow the high-frequency power: power to meet the load welding
Requirements for the case, the corresponding increase in the frequency tends to reduce the penetration of
Depth and improve high-frequency welding pass rate. Practical application, should be integrated
Consider selecting a frequency parameter.
Reference to foreign equipment, such as the U.S. company for Thermatool
Production of finned tube high-frequency equipment, the power power of 445 kW,
Frequency of 400kHz. The power supply for the domestic high-frequency equipment
100 ~ 200 kW, the actual output is 60 ~ 120 kW, the frequency of
200 ~ 300kHz. Clearly, domestic support and high-frequency power supply
Output power are relatively small, relatively low frequency.
At present, China is the production of high-frequency welded steel pipe and power are
Design, no welding spiral finned tube dedicated high-frequency power.
Since the impedance ⋯ spiral finning than when welding steel
Large, therefore, the power and load mismatch is a common asked
Problems. Only the best match to get the maximum output power.
To speed welding of high-quality high-frequency spiral fin tube, it must
To improve the existing high-frequency power.
Finned tubes welded steel body is asymmetrical, there is a
The fundamental problem that the current focus on the strip, easy to reach welding temperature
Degrees, while the current pipe on too scattered and not easy to concentrate, steel temperature
Degree is often lower than the strip temperature, welding quality and welding efficiency.
If you do not take advantage of the proximity effect so far focused on the current pipe welds
Place, but with increased electrical power approach to improve the heating of steel
Temperatures often lead to overheating and melting of steel, resulting in broken
Belt. That is, by increasing the output power of the high frequency power supply
Ways to improve the welding pass rate is often not feasible.
Previously, in order ordinary welding stainless steel, stainless steel band
Finned tube stainless steel pipe, had used 200kW, 400 kHz for
High-frequency devices, but tests found that the effect with the use of 100 kW, 400
kHz high-frequency welding equipment out on the quality of the product is not clear
Welded pipe May 2006
Noticeable difference and improvement, because it is.
4 exploratory test work
4.1 preheat pipe using auxiliary power
On the high-frequency welding steel fins, while using an induction loop
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To pipe welding heat to raise the start-temperature high-frequency welding zone
Degrees, so that the high-frequency welding steel and steel "7"-shaped area while melting,
And plastically welded under external force is applied to improve
Weld pass rate.
But preheated thermal expansion and contraction due to the induction coil steel, steel
The outer diameter of the inner diameter will also increase, and when welding on the fins to be cooled
, The tube diameter will shrink, after forming fins on
Will soon fall off, this attempt failed.
4.2 Identification of weld test specimen
In order to obtain high frequency spiral fin tube detects the best thermal resistance
Can take the pipe turning on a lathe layer approach to the table
The surface oxide layer is completely off, and then immediately on to the pipe of high frequency
Welded fins. Under optimum welding parameters to adjust the conditions of welding
Pass rate of more than 80%. Thus the test can be drawn: In addition to steel
Stainless steel thin wall completely and are beneficial to improve the welding pass rate.
Car knife on the outer surface of spiral welded steel pipe online car out of the concave
Tank, increase the melt pipe weld area, thus improving the quality of the welding
Amount. The preferred width of the groove strip thickness, the groove depth as the pipe
Depending on thickness. Steel electrodes located on the groove, high-frequency current is
In the proximity effect and more intensive flow along two ridges groove
Moving, so greatly reducing the high-frequency current in the outer surface of the pipe
Shunt components, can improve the welding efficiency.
5 ways to improve the welding pass rate
5.1 avoid diversion effect platen
The platen should be less than the groove depth in the strip width, the groove width of the platen slightly
Greater than the thickness of the strip, in order to ensure that the high-frequency pressure welding process with
The outer edge of the wheel does not touch the surface of the pipe. If the width of the platen
Much larger than the thickness of the strip, the high-frequency side of the platen welding process
Edge contact with the steel surface, will cause serious diversion, affect the welding
Pass rate, but will soon be the platen edge high-frequency current to burn
Destroyed.
5.2 Adjustment of the strip electrodes and electrode position structural steel electrodes and electrode structure to improve the decision of the two electrodes to maximize the distribution of lands near the welding point. Most manufacturers of existing production lines, steel weld electrode distance 100 mm or more, a serious deviation from welded steel electrode spiral track (see Figure 1), resulting in much lower long 100 mm high-frequency current heating strip edges are bright red line while steel heating zone due to the current shunt and see the bright lines, energy is wasted. High-frequency current through the electrodes and strip steel electrodes were imported steel and steel, but one that is divided into the pipe, and 2 two branches, less than 2. ,, 2 may be the pre-heating of the welding zone play a negligible role, to improve the welding efficiency, must be reasonable to use features to minimize high frequency current, 2, so, increases. Figure 2 is a schematic horizontal feed with welded structures. The platen
Figure 2 levels with welded into the body 'current flowing through the pipe to be welded part. Also very scattered, is presented surface distribution. Generally about l mm strip thickness, weld width does not exceed 2 mm, and, in the steel distribution than its width. If the electrode width of the steel pipe is 5 mm,,. Distribution width than the width of a large steel electrodes. Should be rational use of proximity effect, so do management, mostly concentrated in the weld. Steel electrodes in the best position should be located on the surface of the steel strip pre-welded spiral line, deviate from this position, it will cause unnecessary loss of high frequency energy. Because the weld line is the main heating zone, the only way to make high-frequency current in the surface of the steel pipe welding area is the most reasonable use to make high-frequency current in the pipe surface to effectively pre-weld heat pipe surface area and make it melt. Improved steel electrode position should try to make the high-frequency current to the load matching to achieve maximum power under the conditions of use of proximity effect and improve the welding efficiency. High-frequency welded finned tubes pass rate usually refers to the percentage of fins and integrated welded steel pipe section width and thickness of the strip firmly in the bead width. Weld pass rate increased welding speed can also be increased accordingly.
Figure 3 is a schematic vertical feed with welded structures. In Figure 3, the strip is in close contact with the electrode side of the strip from the strip, and the strip as close to the welding electrode "7" shaped weld zone. Thus, the steel electrodes can be welded to a greater extent near the "7"-shaped weld zone, evaded Figure l steel strip electrodes and electrode welding area near the weld joint and compete for limited space issues. This allows a greater extent to improve the total current, the proportion of the energy waste is minimized.
Figure 3 vertical feed with high frequency welding mechanism can be the most rational use of energy, the welding speed and welding quality finned tubes can be greatly improved at the same time. Welding speed of about 30m/min, welding pass rate increased from about 80% to 90%.
5.3 to minimize current consumption should ensure a high-frequency equipment feeders, secondary feeders diversion area should be large enough to reduce the current loss of the line.
5.4 Adjusting device for the adjustment of the optimal matching state in the best matching state devices to take advantage of the power supply.
5.5 reduction of ferromagnetic material near the high-frequency transformer in order to reduce the iron loss of iron loss, one made using a material of low permeability equipment parts, such as copper or use austenitic stainless steel components, to reduce the high frequency components around the power loss on the weld zone; the second part of the welding transformer is surrounded by "closed" to "open-loop" form, so that the parts can not form the electromotive force induced in the high-frequency current, thereby reducing the induced loss caused.
5.6 increase when upset pressure welding methods can be used to increase the top hydraulic forging force during welding. Only a sufficient role in forging force in order to ensure a true welding molding. Introduction of pneumatic or hydraulic devices are taken to control the top of forging force.
6 Conclusion
High-frequency spiral fin tube has broad application prospects, increase their production welding pass rate is very important. Through the tireless efforts of scientific and technical personnel, both reasonable use of the equipment, save energy, and improve product quality high-frequency spiral fin tube, but also for the development of dissimilar material finned tubes, finned tubes of low permeability, such as stainless steel wing piece carbon steel pipe finned tubes, aluminum fins steel tubes finned tubes, aluminum fin tubes laid the foundation, thus broadening the application field of high frequency spiral fin tube.
