Welding can choose AC welding machine or DC welding machine. When using DC welding machine, there are positive and reverse connections. The welding rod, construction equipment and welding quality should be considered.
(1) common structural steel welding
For ordinary structural steel electrode and acid electrode, it can be used for AC and DC. When DC welding machine is used to weld thin plate, DC reverse welding is good. The thick plate welding can generally use direct current connection to obtain a larger depth of melting, of course, DC back connection is also possible, but for the thick plate bottom welding with a slope, the DC back welding is still good. The alkaline electrode usually uses DC reverse connection, which reduces porosity and spatter.
(2) argon arc welding (MIG welding)
Generally, the argon arc welding is direct current reverse welding, not only the arc is not disturbed, but also the oxide film on the surface of the welding piece can be removed when welding aluminum.
(3) tungsten arc welding (TIG welding)
Tungsten pole argon arc welding of steel, nickel and its alloys, copper and their alloys, and their alloys can only be directly connected by direct current. The reason is that the cathode is high, the temperature is high, the temperature of tungsten is high, the tungsten is melted fast, and the tungsten can not be burned for a long time, and the melting tungsten falls into the molten pool, and the tungsten will be cut down. Weld quality.
(4) CO2 gas shielded welding (MAG welding)
In order to keep the arc not messy, weld the weld well and reduce the splash, the CO2 gas shielded welding generally adopts DC back connection, but when the cast iron is surfacing and repairing, it is necessary to improve the metal cladding rate and reduce the heat of the workpiece, and the direct direct connection is used.
(5) stainless steel welding
Stainless steel electrode is preferred by DC reverse connection. If there is no DC welding machine and the quality requirement is not too high, the AC welding machine can be welded with qincao type welding rod.
(6) repair welding of cast iron
Direct direct current inversion is used in the repair welding of cast iron parts. The welding arc is not messy, spatter is small, and the melt is shallow, which coincides with the low dilution rate of cast iron repair welding to reduce the requirement of crack formation.
(7) automatic submerged arc welding
AC or DC power welding can be used in automatic submerged arc welding. According to the requirements of product welding and the selection of the type of soldering agent, such as nickel manganese low silicon solder, it is necessary to use DC power welding to ensure the non chaos of the arc.
(8) the comparison between AC welding and direct current welding
Compared with AC power supply, DC power supply can provide smooth arc and smooth droplet transfer. The arc is ignited, and the DC arc can maintain continuous combustion.
When the AC power welding is used, because of the change of the current and voltage direction, and the electric arc is extinguished and reignited 120 times per second, the arc can not burn continuously.
In the case of low welding current, the DC arc has a good wetting effect on the molten weld metal, and it can standardize the size of the welding path, so it is very suitable for welding thin parts. DC power supply is more suitable for overhead welding and vertical welding than AC power supply, because DC arc is relatively short.
But sometimes the arc blow of DC power supply is a prominent problem. The solution is to transform it into an AC power supply. For AC and DC dual purpose electrodes designed for welding AC power or DC power, most of the welding applications under DC power supply are better.
In manual arc welding, the alternating current welding machine and some additional devices are cheap, which can avoid the harmful effect of arc power as far as possible. But in addition to the lower equipment cost, the effect of using AC power supply is not as good as that of DC power supply.
The arc welding power source (CC) with a steep drop characteristic is most suitable for manual arc welding. The voltage changes corresponding to the current changes indicate that the current gradually decreases as the arc length increases. This characteristic limits the maximum value of the arc current even if the welder controls the size of the weld pool. When the welder moves the electrode along the weldment, it is unavoidable that the arc length is constantly changing, and the arc welding power with the characteristics of steep drop ensures the indisorder of the arc during these changes.