Common defects in CO2 gas shielded welding are mainly caused by improper operation. There are many common faults in CO2 gas shielded welding, mainly including faults caused by improper adjustment and wear of the mechanical parts of the equipment.
There are many operating defects of CO2 gas shielded welding, mainly including porosity and incomplete penetration.
Before starting CO2 gas shielded welding, the flow rate of the shielding gas must be correctly adjusted so that the shielding gas can evenly and fully protect the welding pool and prevent air from infiltrating. If the protection is poor, pores will appear in the weld. The main reasons for poor protection include the following aspects:
CO2 gas contains a lot of water or nitrogen. Especially when the water content is too high, there will be pores of different sizes on the entire weld.
Water-cooled welding guns are required in many special places during welding. However, there is water leakage inside the welding gun, so pores are most likely to occur during the welding process.
Before welding, due to negligence, the high-pressure valve on the CO2 cylinder was not opened at all or the preheater was not connected to the power supply before starting welding. Due to the lack of protective gas during welding, the entire weld is filled with pores.
When the shielding gas flow rate is appropriate, the wind speed is too high due to the influence of weather and welding environment, so that the shielding gas cannot normally achieve the rated range of protection. The shielding gas is blown away from the molten pool by the rapid wind, and there is no welding process. Effective maximum protection is formed around the seam, or even no protection, causing pores during welding, as shown in Figure-Effect of wind on protective gas.
If the CO2 shielding gas flow rate is too small, the protection range will also be reduced. Due to the reduction of the protection range, the welding pool cannot be completely and reliably protected (Figure-Shielding gas flow-a); however, the CO2 shielding gas flow rate cannot be too large, and the flow rate is too high. The assembly will generate eddy currents and draw air into the protected area (Figure-Shielding gas flow-b), causing protection failure. Therefore, inappropriate gas flow will cause pores in the weld.
Different degrees of spatter may occur during CO2 shielded gas welding. When there is too much spatter, it will block the gas port, causing the gas flow to attenuate and the protected area to become smaller, as shown in Figure-Nozzle clogged by splash. Therefore, during the welding process, if the spatter sprayed onto the nozzle is not removed in time, it will cause the protective gas to generate eddy currents, suck in air, and cause pores in the weld. Therefore, spatter on the nozzle must be frequently removed during the welding process to prevent damage to the surface roughness of the inner circle of the nozzle. In order to facilitate the removal of spatter, it is best to spray a layer of anti-spatter spray or brush a layer of silicone oil on the inner and outer surfaces of the nozzle before welding.
Anti-spatter spray is a high-tech water-based lubricant that is sprayed on the inner and outer surfaces of the nozzle before welding to form a thin film to prevent spatter from adhering to the metal surface during welding and is easy to clean after welding. During the welding process, it can protect the welding tip, welding surface and prevent the welding tip from adhering. Its main features are to prevent welding slag from adhering to and burning the metal surface, preventing carbon deposits on the welding gun, having no flash point or fire point, and a special formula that does not burn. It is suitable for welding all kinds of silicone-free and oil-free mucous membrane materials. No need for welding after welding.Grinding, knocking and smoothing, welding slag is easy to remove, convenient for secondary processing, no solvent-based cleaning agent is required.
Anti-spatter silicone oil is a silicone non-ionic surfactant with unique properties. Various silicone surfactants with different properties can be obtained during production to meet the needs of preventing welding spatter. This product features lower surface tension, better softness and strong antistatic properties, making it suitable for preventing welding spatter.
If the inclination angle of the welding gun is too large during welding (Figure -The inclination angle of the welding gun is too large), air will be sucked in, causing pores in the weld.
When welding, when the extension length of the welding wire is too large or the height of the nozzle is too large, the protective effect of the shielding gas is not good and it is easy to cause pores, as shown in Figure-The welding wire extends too long and the nozzle is too high.
The inner hole of the spring hose is blocked by oxide scale or other dirt, the first half of the sealing plastic tube is broken or the sealing ring at the wire inlet leaks, and the protective gas leaks from the inlet of the welding gun, reducing the flow of protective gas at the nozzle. Small, which is also one of the important reasons for the formation of pores. In this case, you can often hear the “hissing” sound of air leakage at the connection of the wire feeder and welding gun. There are usually pores on the entire weld, and you can also see bubbles in the molten pool during welding. The phenomenon.
In addition, if the oil, rust or oxide scale in the welding area is too thick and has not been cleaned, it is also the reason for the formation of pores in the weld.
Grooving before welding is also an important part of welding. If the bevel angle is too small, the blunt edge is too large, the gap is too small, and the offset amount is too large, it will cause incomplete welding defects, as shown in Figure-Inadequate welding due to improper bevel processing or assembly. In order to prevent lack of fusion, the groove angle is preferably 40°~60°.
During welding, because the weld bead protrusion of the base layer is too high, it is easy to cause lack of fusion, as shown in Figure-Insufficient penetration caused by base layer weld bead. Therefore, when welding the base layer, the swing amplitude of the welding gun should be controlled to ensure that the weld bead of the base layer and the groove surfaces on both sides are well fused, the weld surface is concave, and there should be no grooves on both sides to cover the upper weld.
If the joints are not ground or the arc is struck improperly, the joints can easily become unfused, as shown in Figure-Missing fusion at the interface. In order to ensure that the welding seam is well connected, it is required to grind the joint into a bevel during welding, strike the arc at the highest point, and weld continuously.
During flat welding, if the welding speed is too small, the welding current is too large, the melting number coefficient is too large or the inclination angle a of the welding gun is too large, it will cause incomplete penetration, as shown in Figure-Incomplete penetration caused by inappropriate welding parameters. Therefore, in order to prevent incomplete penetration during the welding process, the welding speed must be adjusted according to the fusion situation to ensure that the arc is located in the front of the molten pool.
When welding, the arc of the welding gun is not aligned with the center of the groove. When the welding gun swings, the arc is biased to one side of the groove. The residence time of the arc on the groove surface is too short, which will cause incomplete welding, as shown in Figure-Insufficient penetration caused by incorrect arc position.
During the welding process, due to the structural limitations of the welding parts, the arc cannot be centered or cannot reach the edge of the groove, which will also lead to incomplete penetration, as shown in Figure-Insufficient penetration caused by welding position restrictions.
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