Welding can choose AC welding machine, can also choose DC welding machine. When using a DC welder, there are positive and negative connections, taking into account factors such as the welding rod used, the condition of the construction equipment and the quality of the weld.
Compared with the AC power source, the DC power source can provide a stable arc and a smooth transition of molten drops. -Once the arc is ignited, the DC arc can maintain a continuous burn.
When welding with an AC power source, the arc does not burn continuously and steadily due to the change in current and voltage direction and the fact that the arc has to be extinguished and reignited 120 times per second.
At lower welding currents, the DC arc has a good wetting effect on the molten weld metal and standardizes the weld channel size, so it is ideal for welding thin parts. DC power sources are more suitable for back and standing welds than AC power sources because the DC arc is shorter.
However, sometimes the arc of DC power source is blown is a prominent problem, the solution is to change to AC power source. For AC power source or DC power source welding designed for AC, DC dual-use welding electrodes, the vast majority of welding applications in DC power source conditions better.
(1) ordinary structural steel welding
For ordinary structural steel welding rod, acid welding rod can be AC, DC dual-use, when using a DC welding machine to weld thin plates with DC reverse connection is good.
Thick plate welding can generally use DC positive connection to obtain a larger depth of melt, of course, DC reverse connection can also be, but for the beveled thick plate bottoming welding is still DC reverse connection is better.
Alkaline welding rod generally use DC reverse connection, which can reduce porosity and spatter.
(2) melting electrode argon arc welding (MIG welding)
Fused electrode argon arc welding generally use DC reverse connection, not only arc stability, and welding aluminum can be removed when the surface of the weld oxide film.
(3) tungsten arc welding (TIG welding)
Tungsten arc welding steel, nickel and its alloys, copper and its alloys, Chin and its alloys can only use DC positive connection, the reason is that if the DC reverse connection, tungsten electrode connected to the positive electrode is high temperature, heat, tungsten melting fast, can not make the arc long-term stable combustion, and molten tungsten into the molten pool and will cause tungsten trapping, reducing the quality of the weld.
(4) CO2 gas shielded welding (MAG welding)
CO2 gas shielded welding in order to maintain a stable arc, good weld seam formation, reduce spatter, generally use DC reverse connection, but in the overlay and filler welding cast iron, the need to improve the metal deposition rate and reduce the heat of the workpiece, more DC positive connection.
(5) stainless steel welding
Stainless steel welding rod to DC reverse connection is preferred. If you do not have a DC welding machine, the quality requirements are not too high, you can use calcium Chin type welding rod with AC welding machine.
(6) cast iron welding
Cast iron parts are generally used in the DC reverse welding method, welding arc stability, small spatter, shallow depth of melt, just in line with the cast iron welding needs low dilution rate to reduce the formation of cracks.
(7) Submerged arc automatic welding
Submerged arc automatic welding can be used AC or DC power source welding, according to the product welding requirements and flux type selected such as nickel-manganese low silicon flux, must choose DC power source welding to ensure the stability of the arc; DC reverse connection to reduce porosity, access to a larger depth of melt.
(8) AC welding and DC welding comparison
Compared with AC power source, DC power source can provide a stable arc and a smooth melt drop transition. -Once the arc is ignited, the DC arc can be kept burning continuously.
When welding with an AC power source, the arc does not burn continuously and steadily due to changes in current and voltage direction, and because the arc is extinguished and reignited 120 times per second.
At lower welding currents, the DC arc has a good wetting effect on the molten weld metal and standardizes the weld channel size, so it is ideal for welding thin parts. DC power sources are more suitable for supine and standing welds than AC power sources because the DC arc is shorter.
However, sometimes the arc of DC power source is blown is a prominent problem, the solution is to change to AC power source. For AC power source or DC power source welding designed for AC and DC dual-use welding electrodes, the vast majority of welding applications in the DC power source conditions better.
Manual arc welding, AC welding machine and some of its additional devices are inexpensive and can avoid the harmful effects of arc blowing force as much as possible. However, in addition to the lower cost of equipment, the use of AC power source welding when the effect is not as good as DC power source.
The arc welding power source with steep drop characteristics (CC) is most suitable for manual arc welding. The voltage change corresponding to the current change shows a gradual decrease in current as the arc length increases. This characteristic limits the maximum arc current even if the welder controls the size of the melt pool.
As the welder moves the electrode along the weld, constant changes in arc length are inevitable, and an arc welding power source with steep drop characteristics ensures arc stability during these changes.
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