Argon arc welding is an electric arc welding method with inert gas “argon” as the protective gas.
Argon is sprayed from the nozzle to form an inert gas protective layer in the welding area to isolate the invasion of air, so as to protect the arc and molten pool.
This welding method has many advantages:
- Good protection effect, high welding quality, no spatter and beautiful weld formation;
- Small welding deformation, can realize single-sided welding and double-sided forming, ensure root penetration, and can weld at various positions;
- Can weld various metals and alloys;
- Stable arc combustion, open arc operation, no slag, easy to realize automation.
Therefore, it has been widely used in practical production.
However, due to the weak wind resistance of argon arc welding, it is particularly sensitive to rust, water and oil, and has strict requirements on gas purity, groove cleaning and welding process, which is easy to produce pores.
Combined with the production practice, this post analyzes the problem of porosity in argon arc welding and puts forward some treatment methods and precautions.
Influencing factors of stomata
1. Argon is impure
When welding carbon steel, the purity of argon shall not be less than 99.7%, when welding aluminum, it shall not be less than 99.9%, and the purity of argon used for welding titanium and titanium alloy is as high as 99.99%.
Method for detecting argon Purity:
(l) Weld the polished steel plate or pipe without welding wire, and then remelt it on the weld bead for many times. If there are pores, it indicates that argon is impure.
(2) During welding, there is a very small spark around the arc, which also indicates that argon is impure.
(3) Sometimes, when the purity of argon is close to the purity requirements of welding requirements, it can not be detected by the above two detection methods, but when welding welded junctions with gaps, intermittent pores will be generated at the root of the weld, or surface pores will be generated during cover welding, or there is a layer of oxide skin on the surface of the weld bead.
(4) Spot weld a few spots on the nickel plate. If the spot is silver white and the surface is like a mirror, it indicates that the purity of argon is qualified.
2. Argon flow
The argon flow is too small and the anti-wind interference ability is weak;
Too large, the gas flow rate is too large, and the near-wall laminar flow formed when passing through the nozzle is very thin.
After the gas is ejected, it will be disordered quickly, and it is easy to involve the air, which will deteriorate the protection effect of the molten pool.
Therefore, the flow of argon must be appropriate to stabilize the gas flow.
3. Air leakage in air belt
Air leakage at the air belt interface or air belt will cause too small gas flow during welding, and the air will be sucked into the air belt, resulting in poor protection effect.
4. Influence of wind
If the wind is slightly strong, the argon protective layer will form turbulence, resulting in poor protection effect.
Therefore, windproof measures shall be taken when the wind speed is > 2m / S;
When welding pipes, the pipe orifice shall be blocked to avoid ventilation in the pipe.
5. Influence of welding gun nozzle
The nozzle diameter is too small. When the effective protection range of argon around the arc is less than the molten pool area, it will cause poor protection and produce pores.
Especially for field operation and welding of large pipes, larger diameter nozzles shall be used to effectively protect the arc and molten pool.
6. Distance between welding gun nozzle and workpiece
The distance is small and the sensitivity to crosswind is small;
The distance is large and the ability to resist wind interference is weak.
7. The pressure in the cylinder is too small
When the pressure in the gas cylinder is less than 1MPa, it shall be stopped.
8. The welding gun angle is too large
If the angle of the welding gun is too large, on the one hand, the air will be brought into the molten pool, on the other hand, the argon flow on the long arc side will deteriorate the protection effect of the arc and molten pool.
9 . Influence of hydrogen flow meter
Unstable gas outlet of flowmeter, large or small, will affect the protection effect.
10 . Impact of operation
When using the argon arc welding gun with control button, vent gas before welding to avoid excessive pressure in the gas zone, resulting in instantaneous excessive gas flow and air holes during arc striking.
11 . Improper welding gun accessories
The tungsten electrode clamp is not matched, the blocked gas path is not smooth, and the protective gas flows out from one side of the nozzle, which cannot form a complete protective ring.
Influence of welding materials
1 . Influence of welding wire type
Submerged arc welding wire shall not be used to replace manual TIG welding wire, otherwise intermittent or continuous pores will be generated.
2 . The welding wire is not clean
Rust, oil stain and water on the surface of welding wire will directly promote a large number of pores in the weld.
Influence of base metal material
1. Influence of plate or pipe quality
If there is interlayer in the plate or pipe, the impurities in the interlayer will promote the generation of pore defects.
2 . Influence of steel grade
Boiling steel (with high oxygen content and many impurities) cannot be welded by argon arc welding.
Influence of tungsten electrode
1. Influence of tungsten extreme part
The tungsten extreme part is not sharp, the arc drift is unstable, the protective area of argon is destroyed, and the metal in the molten pool is oxidized to produce pores.
2 . Poor protection due to arc climbing during arc striking
When high-frequency arc striking equipment is used, the temperature of the tungsten extreme part is low at the beginning of arc striking, so it does not have sufficient thermal emission electron capacity.
Electrons are easy to be emitted from the place with oxide film and climb along the electrode to find the place with oxide.
At this time, the arc is elongated and the protection effect of argon on the molten pool becomes worse.
When the temperature of the tungsten electrode rises, electrons are emitted from the front end of the tungsten electrode.
The arc length and phase strain are short.
At this time, the oxide on the tungsten electrode surface can be eliminated as long as it is polished clean.
Influence of welding process
1 . Groove cleaning
The groove surface and the range of 10mm on both sides of the groove shall be polished to prevent the magnetic generated by the arc during welding from sucking the rust near the molten pool into the molten pool.
2 . Influence of welding speed
The welding speed is too fast.
Due to the influence of air resistance on the protective gas flow, the argon gas flow will bend and deviate from the electrode center and weld pool, which is not good for weld pool and arc protection.
3 . Influence of arc extinguishing method
During arc extinguishing, the arc extinguishing method of attenuating current or adding welding wire, bringing the arc to the groove side and reducing the arc shall be adopted.
Do not stop the arc suddenly, resulting in the high-temperature molten pool separated from the effective protection of argon gas flow, so as to avoid pores or shrinkage in the arc pit.
4 . Influence of welding current
The welding current is too small, the arc is unstable, and the arc drifts irregularly at the end of the tungsten electrode, damaging the protective zone.
If the welding current is too large, the arc will disturb the air flow and the protection effect will become worse.
5 . Influence of tungsten electrode extension length
If the tungsten electrode extends too long, the protection effect of argon on arc and molten pool becomes worse.
Although there are many factors causing pores in manual TIG welding, as long as we understand the characteristics of argon arc welding, investigate the influencing factors one by one according to the actual situation, and eliminate all factors causing pores in the weld during argon arc welding, we can improve the welding quality in the actual production.