The most popular wide-band electrode electroslag s

2022-08-04
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Wide band electrode electroslag surfacing technology (Part I)

wide band electrode electroslag surfacing technology

(1) background the internal surfaces of hydrogenation reactors, flow synthesis towers, coal liquefaction reactors and thick wall pressure vessels of nuclear power plants in the petrochemical industry need large-area surfacing of stainless steel linings resistant to high temperature, oxygen and hydrogen sulfide. In the 1970s, saw technology was widely used in this field at home and abroad. The width of the band electrode has also developed from narrow band to wide band of 60mm, 90mom, 120mm and 150mm. Compared with wire submerged arc welding, this technology has made great progress in dilution ratio and deposition speed. However, with the increasing large-scale and high parameter of pressure vessels, the surfacing technology is developing towards higher quality and efficiency. In the early 1970s, the strip electrode electroslag surfacing technology, which was first invented in Germany and further improved by Japan, the United States, the former Soviet Union and other countries, has been rapidly developed and widely used at home and abroad in recent years because of its higher production efficiency, lower dilution ratio and good weld formation than the strip electrode submerged arc welding

(2) technical content and technical key strip electroslag welding is to use the resistance heat of conductive slag to melt the surfacing material and base metal. Except for the current stage, the whole surfacing process should be equipped with arc generation. In order to obtain a stable electroslag surfacing process, Ningbo's new material industry has ranked first among the seven major new material cities in China. The following technical keys:

1) welding power supply. In the process of electroslag surfacing, the stability of the slag pool has a great impact on the surfacing quality, and the voltage fluctuation is the most critical factor affecting the stability of the slag pool. Therefore, it is expected that the voltage fluctuation in the surfacing process will be minimized, so it is required to select a DC power supply with constant voltage characteristics. In addition, the power supply shall have low voltage, large current output, high control accuracy, strong ability to compensate circuit voltage fluctuation and reliable protection performance. The rated current of the power supply varies according to the bandwidth used. Generally, for 60mm 0.5mm band electrode, the rated current is 1500A, 90mm 0.5mm is 2000a, and 120mm 0.5mm is 25o0a

2) flux. Another necessary condition for a stable electroslag process is that the flux must have good conductivity. Generally, the conductivity of electroslag surfacing flux needs to reach 2 ~ 3, so we call it -1cm-1 of "unsafe", which is 4 ~ 5 times that of ordinary submerged arc welding flux. At present, the electroslag flux used at home and abroad is mostly sintered. The conductivity of the flux depends on the amount of chloride (NaF, CaF2, na3aif6, etc.) in the flux components. When the chloride (mass fraction) · power supply - 220V 50Hz is less than 40%, the surfacing process is an arc process, and in the range of 40% ~ 50%, it is roughly a combined arc and electroslag process; When the chloride content is greater than 50%, a full electroslag process can be formed. CaF2 is both a good conductive material and a main slag forming agent, so CaF2 is usually the main component of electroslag surfacing flux

in addition to conductivity, the flux also needs to have good surfacing processability (deslagging, forming and wettability) and good metallurgical properties (small burning loss of alloy elements and small increment of unfavorable elements) and appropriate particle size (generally finer than that of submerged arc welding flux). At present, there are many kinds of fluxes that have been used for production, such as FJ-1 (Japan), est122 (Germany) and sandvik37s (United States); Domestic sj15, shd202, etc

3) magnetic control device. For electroslag surfacing with wide-band electrode (the width of the strip electrode is greater than 60mm), undercut will occur in the surfacing layer due to the magnetic contraction effect. With the increase of the width of the strip electrode, the surfacing current will increase, and the undercut phenomenon will become more serious. Therefore, the method of external magnetic field must be used to prevent undercut (magnetic control method). As shown in the figure. At the same time, the magnetic pole position must be reasonably arranged and the reasonable exciting current must be selected. Too strong or too weak external magnetic field will affect the formation of surfacing weld bead (Fig. 2). The magnetic control current of the two magnetic poles shall be adjustable respectively. For example, for the workpiece at the non preheating flat welding position, when the strip pole is 60mm 0.5mm, the South and north pole control currents of the magnetic control device are 1.5A and 3.5A respectively; For 90mm 0.5mm strip electrode, it is 3a and 3.5A respectively

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