A bipolar electrode single arc of the basic principles

Two-electrode single arc welding works arc shown in Figure 1. Dual-core single-arc arc welding, the workpiece does not take power, core welding electrodes were connected to two power poles. Between the two welding arc burning core, form a single arc. Arc can be ignited at any point in space and burning. Welding process of heating the base material of the heat from the droplet and the main arc, because the distance between the electrode and the workpiece can be adjusted within a certain space, so the arc of the base metal heat input can be adjusted within a certain range to obtain different than the fusion weld. Smaller fusion weld, the Welding Wire China workpiece deformation and stress less. As the power of the output power is mainly used to heat, melt welding rod, so you can aim to improve welding productivity.
As the single-core arc welding parts as the power pole, there must be active spot area, the heat concentration, the local temperature is high, melting the base material to form the fusion more than the larger pool, more power consumption. Two-electrode arc welding is to use a single electrode double-generated droplet of extreme heat and the Department of arc heat, melt the workpiece and the welding. In addition to the adjusted base metal heat input welding current, welding speed, it can also adjust the distance between the electrode from the workpiece. As the base metal melting less, reducing the fusion ratio, thereby reducing the welding deformation and welding stress.
2 Test Materials and methods
Tests used two-electrode single arc welding electrode as shown in Figure 2 appearance. Two-electrode single arc welding electrode is suppressed using a special mold first half of electrodes, and then bonded to the electrode welding rod, welding core between two parallel and insulated. Welding, welding with a special clamp holding two ends of the core welding, welding clamp jaws were two poles with power connection. Drugs used in skin test type graphite electrode type welding core materials for the H08A, specifications φ4.0mm × 400mm, two welding core spacing 1.2 ~ 2.5mm, the quality factor of the skin electrode drugs was 58.7%.

Because graphite type coating contains a lot of graphite and alloying elements, there is a strong drug leather conductivity, so the solution is dual-core insulation between the focus of the study. Test is performed with mica for insulation agent! Water glass adhesives. Two-electrode welding rod as insulating mica adhesive agent and the mass ratio of 1:0.36 with water glass, the thickness control in the 0.5 ~ 2mm between. After the adhesive to dry at room temperature, 300 ℃ and then dried 1h. To achieve the insulation resistance between the dual-core requirements.
Using the plate method of surfacing welding process performance, dual-electrode welding rod and the end of drug leather sleeve for the distance between the workpiece 5 ~ 10mm, test with the base material is Q235 steel, test board size 250mm × 80mm × 20mm. Before Welding Consumables, the test plate surface with polished wheel clean, to prevent rust, oil affect the welding quality. Electrodes should be subject to 150 ℃ × 1h drying. Test with welding machine ZX7-400S IGBT inverter welding machine, external characteristic band for the constant delay. The no-load voltage 78 ~ 80V, test welding current is 160 ~ 220A. During the experiment, high-speed camera system to observe the arc.
3 results and discussion
3.1 two-wire spacing and the impact resistance of the arc voltage
Arc voltage is a very important parameter, which directly affect the performance of welded joints and weld. Many factors affect the arc voltage, welding conditions in other (drugs leather materials, welding current, arc welding power source, etc.) in certain circumstances, single-core welding electrode welding in a pole piece connected to the supply, mainly by adjusting the electrode and the workpiece The distance between the arc voltage to control the size of the arc, this regulation is implemented in the welding process. Of course, in order to maintain the stability of arc burning, the regulation of this arc there is a certain range, the practical use of arc welding arc voltage is generally 25-37V.
In the two-electrode welding electrode, the arc voltage is also an important parameter affecting weld, experimental studies have shown that two-electrode for surfacing electrode, the resistance between two core a great impact on the arc voltage, resistance increases with the dual-core inter- , the corresponding increase in arc voltage. Under the experimental conditions, dual-core insulation resistance 100 ~ 1000kΩ to meet two-electrode single arc welding electrode welding requirements. For two-electrode graphite electrode, dual-core spacing is also a very important parameter, with the welding pin spacing increases, the resistance between the two welding core increases; it after butt weld rod sleeve shape and have a greater the impact. This test is mainly through the sleeve to determine the shape and weld dual-core spacing, as shown in Table 1.

Seen from Table 1, two welding core spacing is too small, such as dual-core spacing of less than 1.2mm, the base material to absorb heat enough to form a pool, or the formation of amorphous intermittent weld seam, and prone to drug skin electrode short-circuit breakdown phenomena, can not be normal welding. Two welding core spacing is too large, such as dual-core spacing is greater than 2.0mm, easy to partial arc, cathode and anode melting rate is inconsistent, it can not be stable welding. Therefore, in order to ensure weld, solder pin spacing should be a reasonable design. Tests showed that in order to obtain a good weld, two-core spacing of 1.4 ~ 1.7mm appropriate.
3.2 shape of the welding current and arc welding process of impact
For two-electrode single arc welding, use of appropriate size welding current, welding process to make smooth, to ensure the welding quality.
Core with two bipolar electrode spacing of 1.5mm on the Q235 steel welding, steel welding rod and the vertical distance of 5 ~ 10mm. The effects of different welding the weld current, as shown in Table 2.

Shape of the arc welding process of great influence, the main factor is the dual-core spacing and welding current. Using the same welding current I = 200A, respectively, using dual-core spacing of 1.7mm, 2.0mm electrode air burning, high-speed camera system observed arc shape, shown in Figure 3,4.
From Figure 3, Figure 4 shows that when the spacing of 2.0mm arc scattered in the arc of instability; while in 1.7mm pitch, the arc stability and concentration, good weld.
Using the same electrode, the dual-core spacing of 1.7mm, respectively 160A, 200A welding current air burning, high-speed camera system observed arc shape, as shown in Figure 5,6.

It can be seen when the arc welding current at 160A scattered, unstable; in 200A, the arc stability and concentration, good weld.
Seen in the 180 ~ 220A welding current, the spacing between 1.4 to 1.7 to get a good shape and arc weld.
3.3 Chemical composition of deposited metal and mechanical properties
Welding current I = 200A, the use of D618 dual electrode welding electrode production formula, 4-layer surfacing, road between the temperature at 100 ℃. SEM scans the surface of the weld specimens, the surface element w (Fe) 63.94%, w (Cr) 20.51%, w (Mo) 14.08%, w (Si) 1.47%.

Visible, the surface layer of surfacing layer is mainly cellular distribution in the solid solution and intergranular carbide strip or granular form. As the surface layer of the cooling rate faster than the bottom of the cooling, the formation of small solid solution, and the formation of large amount of intergranular carbide, with a strengthening effect on the cladding layer, cladding layer has a high hardness, surface hardness HRC53. 4, with high wear resistance.
4 Conclusion
(1) two-electrode single arc welding, the workpiece does not take power, arc welding electrodes in parallel to each other and double insulated welding two formed the core of the tip can be adjusted in a wider range of heat input, welding parts to be welded to improve thermal cycling.
(2) For two-electrode graphite electrode, dual dual-core spacing between the resistance and is a very important parameter, its electrode welding arc voltage, arc shape and the shape of the sleeve have a major impact, and also with a larger weld the impact.
(3) the quality factor of the skin for drugs was 58.7% of Ñ„4mm dual electrode graphite electrode spacing of the two-core 1.4 ~ 1.7mm, dual-core resistance 100kΩ or more, the welding current is 180 ~ 220A under the welding conditions, availability of good weld, the weld metal chemical composition and mechanical properties can meet the requirements.