In order to improve the boiler thermal efficiency and saves the material cost, large power station boiler water wall tube adopts light tube and flat steel compound. The dimensions of the boiler component proportional to the capacity. A 600MW boiler membrane wall tube panel seam length has more than ten thousand meters. So it must adopt efficient soldering method. In the last century, 90 years ago, domestic boiler manufacturer in most cases, long (6 to 8) submerged arc welding. In the years of actual production found that this approach has a fatal SAW disadvantage that only from one side submerged arc welding, after soldering tube screen will inevitably have serious deflection. The longer tube screen, the greater the distortion, a correction must be funded work processes. Not only improve the production costs, and extend into the production cycle. Therefore it must seek a more reasonable welding method.
The late 1980s, pioneered the development of Japan's Mitsubishi Heavy Industries membrane wall tube panel sided pulsed MAG soldering new welding methods and welding equipment, and successfully applied to welding. Tube panel soldering essentially no deflection. This is a major technological breakthrough. Significant economic benefits. Harbin Boiler Factory a few years later the first company introduced from Japan's Mitsubishi this advanced technology and equipment, MPM main tube panel soldering technology is the key on both sides of the weld must ensure quality, including weld penetration, basically the same shape and dimensions. This requires overhead welding position welding using a special welding process - MAG pulsed arc welding (argon-rich gas mixture).These welding equipment performance and quality of higher quality weld tube panel opposite the more stable, higher pass rate. In fact, the Harbin Boiler plant from the introduction of the original Mitsubishi Heavy Industries. Machine is only equipped with a second generation of pulse thyristor controlled MIG / MAG welding power source, wire feeder isokinetic only traditional wire feeder tube panel opposite the weld pass rate of less than 100%, there is always a certain degree of rework volume, in order to further improve the membrane wall tube panel welding performance MPM, MPM recently made tube panel welder equipped with the third generation of micro-inverter to control the speed pulse welding power source and wire feeder constant feedback, significantly improved the reverse side of the weld pass rate.
Boiler heating surface superheater and reheater pipe fittings part number and thickness, with the boiler capacity increase and multiply, 600MW thermal power plant boiler has reached the maximum wall thickness of 13mm, joint total of more than thousands. The traditional filling cold wire TIG welding efficiency in order to progress in the actual production can not meet the requirements, must be more efficient and ensure joint quality solvent welding method. To this end, Kazakhstan on pots and pans have been introduced from Japan thick-walled tube filaments pulsed MIG automatic tube welding machine, its efficiency than conventional TIG welding increased by 3 to 5 times. Often due to lack of penetration and the roots of crater defects such as sagging and switch back MIG welding TIG welding filling and capping process, improved welding process, while essentially solved the root problem of lack of penetration, but reduces the welding efficiency, increase of equipment investment, but also to complicated procedures. Recently, on the pot, Kazakhstan and from abroad pot of hot wire TIG automatic tube welding machine. The principle of hot wire TIG welding filler wire is fed into the weld pool before by an independent constant AC power. Resistance heated to 650 ~ 800 â,,? high temperature, which greatly accelerated the melting rate of the wire, the deposition rate is close to the same diameter weld deposition rate MTG. However, this should not negate the pulsed MIG welding butt in the small diameter tube wall thickness feasibility of the application. Through a large number of tests have been identified in the thick-walled tube MIG welded butt joints, the root end of more than 90% penetration in ultra-arc segment, and the crater sagging due to continuous multi-layer welding metal bath heat buildup can cause overheating. If the power of the arc welding power source for accurate control, then it could eliminate the formation of defects. However, due to the introduction of automatic pipe welding machine MIG welding power source for the wife of the thyristor pulse power, the procedure can not be achieved arc power control such as switching of the most advanced all-digital control of inverter welding power or pulse waveform control pulse welding power source (computer software control small), you can easily press the welding process requirements of the welding arc for precise power control to ensure the quality of welding joints.
