Large cross section of copper bus TIG welding process Abstract:
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Abstract: Water-cooled TIG welding process, has successfully achieved a large section of copper bus bar welding. Construction and plant operation showed that the process to overcome the traditional old "carbon arc welding" process easy to make welders poisoning, weld and easy carburizing, plastic is poor, the disadvantage of high electrical resistance, with a stable welding quality, easy operation, safety and construction cost lower and so on.

Copper bus bar connected to the power station, metallurgical equipment often encountered, and its connection with clip connection (stud fastening), welding method. Copper bus bar of large cross-section welded to the domestic current data shows that the carbon arc welding, submerged arc welding and Aluminium Welding Electrode of several. Carbon arc welding preheat temperature is higher, must ensure that the weld base metal temperature above 750 ℃, the appearance of the weld shape in general, and high-temperature steam generated Cu2O easy to make welders poisoning, also easy to cause carburizing, plastic lower resistivity than large. SAW preheating temperature lower, about 500 ℃ or so, the quality of more stable, but the current, voltage slightly higher, respectively, 750 A ~ 800 A, 40 V ~ 50 V or so, and the larger amount of flux, solder is not yet there large section, large length of the bus introduction. TIG show from the current national norms, only for δ <12 copper bus bar welding, δ> 12 the single V-groove weld the copper bus bar is not strong guidance.

Shangluo Smelter in the two sets of 15 000 tons / year electrolytic zinc plant, the design requires welding connection method, but not explicitly welding technology and methods. In full consideration to improve the weld quality, based on the work environment, we learn from domestic and foreign experience, the use of conditions in the warm-water-cooled TIG welding process, forming a good weld appearance, internal quality assurance pass grade â…¡ basically solved the ubiquitous copper welding slag, porosity, successfully completed the installation of the project tasks.

1 weldability of copper

Copper is used in the project oxygen copper T1, the total content of 0.05 of its impurities, in which oxygen is 0.02, its physical properties, such as shown in Table 1.

Table 1 The physical properties of oxygen-containing copper table T1

Index Value Index Value Index Index type of face-centered cubic lattice the lattice thermal conductivity of 386.4W / (m · k) the melting point 1083 ℃ linear expansion coefficient of 16.5 × 10-6K-1 boiling point of 2580 ℃ resistivity of 168 × 10-10Ω · m density 8.96kg/cm3

Thermal conductivity of copper at 20 ℃ 7 times than the big iron, 1 000 ℃ more than 11 times when the big, welding, heat conduction out quickly from the heating zones, so that the base metal and filler metal is difficult to fusion, the power shall be used for welding and heat to warm up, easy to form a molten pool when welding.

T1 of the linear expansion coefficient 15% larger than iron, in order to avoid the passage of grain produced near the weld area to ensure the welding gap, so the group should ensure adequate clearance; while its shrinkage rate of 1 times more than the big iron, to prevent pool from the liquid into solid, the temperature difference between layers to form the passage of the larger pattern, it should ensure welding layer temperature.

Copper welding oxygen easily form pores, the main cause of oxygen and water vapor, in which the formation of reactive oxygen pores, pore diffusion of water vapor produced, so the solder powder to be taken measures such as oxygen and slow cooling.

To prevent the rich low melting point of lead or bismuth eutectic rich, moist and should be taken after welding Rapid cold cutting, hammering reduction should be.

To ensure the forming and receiving arc weld root at the joints smooth and reduce heat loss, welding should be prepared graphite plate, baffles and blocking block.

2 welding preparation

2.1 Instruments preparation

1) Production of coke furnace.

2) Prepare the graphite plate.

3) Preparation of graphite baffle and the blocking of the two blocks.

4) The selection of insulation materials, asbestos was.

2.2 Group and preheat

1) The use of planer groove processing, the single V-groove angle of 55 ° ± 5 °, blunt edge of 1 mm, the gap should be preheated before the group was 4 mm ~ 5 mm.

2) group, before treatment with polishing the groove side of the range of 50 mm layer of protection to the exposed metallic luster so far.

? 1 - bus; 2 - graphite plate; 3 - coke ovens;

? 4 - blower; 5 - asbestos was; 6 - baffle

3 Welding

3.1 Selection of welding and welding

1) choose 2 sets Z630 welder welding machine, parallel, the positive connection to ensure smooth current, welding torch is 500 A.

2) The copper wire used Φ6 wire, and sanding before welding, flux selection of gas agent 301.

3.2 Preheating

Continued use of coke oven preheated heated to 350 ℃ ~ 600 ℃ after (far-infrared temperature gun to take the test), was wrapped with asbestos, 400 mm wide on both sides of the weld, the turn off the blower to ensure the heater continues to heat up. At this point, the group due to expansion of the gap reduction is 2mm ~ 3mm, sprinkle evenly in the weld zone 301 gas agent, you can welding. 3.3 The welding parameters

Welding parameters shown in Table 2.

Table 2 Welding parameters

Welding current and voltage tungsten wire layer of argon gas flow rate bottoming 350 A 20 VΦ6 cerium tungsten Φ6 15 ~ 17 (L / min) filling and capping 400 A 20 VΦ6 cerium tungsten Φ6 15 ~ 17 (L / min)

Welding, welding method using left to reduce oxidation, the welding speed should be fast. In order to facilitate observation of molten pool and fill plus wire, welding torch and workpiece angle appropriate for the 75 ℃ ~ 85 ℃, welding wire and welding pieces of angle between 10 ° ~ 20 °, operation torch should be uniform, smooth forward in a straight line, and to maintain a constant arc length, arc length control in general 2mm ~ 4mm, when filled or covered surface, the wire should be placed slightly lateral in the joints filled, gradually lengthen the arc interrupter.

Layer welding, the weld area should continue to ensure that the temperature around 350 ℃ ~ 600 ℃, and should not be too long to stay.

300 × 16 copper plate welding, from the heated to welding is completed, which normally takes about 40 min, welding time is only 10 min.

4 treatment after welding

1) Hydra after welding should be taken to Rapid cold cutting, hammering reduction should be to prevent low melting point eutectic, increasing copper bus toughness.

2) After cooling, the slag with a wire brush to clean up and clear the weld heat affected zone of acid oxide.

3) visual inspection of the weld.

Machinery and equipment 5

Welding equipment for the following.

Welder Z630 2 units in parallel water-cooled TIG welding torch 500 A to a plasma cutting machine Z200 1 1 units of air compressors furnace blower 200ω1 Taiwan Taiwan 400 × 5002 crossing graphite plate δ20 20 / 1 cable car station down chain 8t 1 2t 2 个 infrared temperature gun-proof M130T 1 2 sets of auxiliary fire service labor

6 Labor Organization

Welder 2 riveter two fireman a plasma cutting machine operator 1 technician 1

7 quality standards and inspection

7.1 Quality Standards

Butt joint surface quality by HGJ223-1992 implementation, internal quality implementation JB4730-1994 â…¡ level qualified, to take arms bridge resistivity test method should be consistent with GBJ149-1990.

7.2 Quality assurance measures

1) the welding procedure and weld test by assessing the scene to determine the operating instructions.

2) The training of qualified welders only after induction.

3) and argon welding gas cylinder on the measuring instruments must verify cycle, the instructions accurately.

4) The transfer of strict censorship process, some failed to be treated in order for the next procedure.

8 welding quality

Two for process 300 × 200 test specimens, by visual inspection, color display fusion sound, no defects, the X-ray photography, the test no slag defects, only a hole, according to JB4730-1994 Assessment of grade â…¡ qualified. Then, extraction test, mechanical performance test, test results meet HGJ223-1992 requirements, with double bridge resistivity test method to determine the results of the maximum resistivity 0.015Ωmm2 / m, consistent with GBJ149-1990 requirements.

9 Economic Analysis

After using the welding process, forming a good weld appearance, quality assurance, to avoid the carbon arc welding of high temperature on the strong secondary radiation, and to adapt to more places on the hard place by heating stove with a large heated gas welding torch, welding can also be smooth, while on the bus and the conductive film (fillet weld), the soft bus connection (for joints), and other types of connectors can also be under the guidance of successful welding, applies more broadly.

Compared to carbon arc welding, arc welding resistivity lower weld porosity less quality and more stable; compared to SAW, TIG welder is easier to grasp, and more for the narrow field, large length Bus welding; relative to the original folder then take bus connection, welding less power consumption after the bus, commercial refining a device operation that each of its production of 1 ton of electrolytic zinc power than the original 60 degrees, could be reduced costs about 45 million economic benefit.

10 engineering application

Shanxi Zinc Smelter Company Shangluo 2 sets of 15 000 tons / year electrolytic zinc project in more than 80 tons of copper bus bar, made of T1, cross-section of 300mm × 16mm, 200mm × 12mm, 200mm × 28mm range, single bus up to 17m, and some conductive film (250mm × 12mm, pitch 62mm) and angle of bus connections, embedded access, design requirements for all welding. We use argon welding preheat conditions, forming a good weld appearance, their specimen testing, the inherent quality of joints, mechanical properties and electrical resistivity and other technical indicators are in line with design requirements, duration of each set of Welding Wire is only 25 days fulfill the task ahead to ensure the smooth operation of the plant.

11 Conclusion

1) tungsten arc welding of large cross-section of a copper bus bar is lower preheat temperature, welding quality, easy operation and welding environment better method, δ> 12mm welding of copper and its alloys have a certain the guide. However, prevalence of oxygen in copper welding holes through the use of solder powder, to ensure that the temperature is still difficult to eliminate the interlayer, in theory, by controlling the argon gas and the surrounding environment, hydrogen, nitrogen content to eliminate the pores, but in practice difficult to achieve.

2) the site is mainly produced pores welded joints, the reason for the extinction temperature decreases after the gas too late to cause precipitation. It should take a long rod, each continuous welding finished.

3) on different sections of the copper bus connection angle, the soft connection, embedded connection, the preheating temperature and process parameters is not very different with the docking parameters, should be based on joint cross-section size and type of appropriate warm-up method (such as boat-shaped welding) welding.