Characteristics and precautions of argon arc welding
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1. Concept of argon arc welding
Argon arc welding is a welding technology that uses argon as a protective gas. Also called argon gas shielded welding. It is to pass argon protective gas around the arc welding to isolate the air from the welding area and prevent oxidation of the welding area.
Argon arc welding technology is based on the principle of ordinary arc welding, using argon gas to protect metal welding materials, and using high current to melt the welding materials into a liquid state on the base material to be welded to form a molten pool, so that the metal to be welded and the welding material are A welding technology that achieves metallurgical bonding of materials. Since argon gas is continuously supplied during high-temperature molten welding, the welding material cannot come into contact with oxygen in the air, thus preventing the oxidation of the welding material. Therefore, stainless steel and iron hardware metals can be welded .
2. Working principle of argon arc welding
The working principle of argon arc welding in terms of main circuit, auxiliary power supply, drive circuit, protection circuit, etc. is the same as that of manual arc welding. I won’t go into details here, but focus on the unique control functions and arc starting circuit functions of the argon protected welding machine.
3. Classification of argon arc welding
According to different electrodes, TIG welding is divided into two types: melting electrode TIG welding and non-melting electrode TIG welding.
(1) Non-melting pole
Working principle and characteristics: Non-melting electrode argon arc welding is an arc burning between a non-melting electrode (usually a tungsten electrode) and the workpiece. An inert gas (commonly used argon) that does not react chemically with the metal flows around the welding arc. ), forming a protective gas shield so that the high-temperature metal at the tungsten end, arc and molten pool and adjacent heat-affected zone is not in contact with the air, and can prevent oxidation and absorption of harmful gases. This results in a dense welded joint with very good mechanical properties.
(2) Melting pole
Working principle and characteristics: The welding wire is fed through the wire wheel, and the conductive nozzle conducts electricity. An arc is generated between the base material and the welding wire to melt the welding wire and base material. The arc and molten metal are protected by inert gas argon for welding. The difference between it and tungsten arc welding: one is that the welding wire is used as the electrode, and is continuously melted and filled into the molten pool, and condensed to form a weld; the other is the use of shielding gas. With the application of melting arc welding technology, the protection The gas has developed from a single argon gas to a wide range of mixed gas applications. For example, when argon or helium is used as the shielding gas, it is called melting extremely inert gas shielded arc welding (referred to as MIG welding in the world); when using inert gas When a mixed gas with oxidizing gas (O2, CO2) is used as a protective gas, or when CO2 gas or CO2+O2 mixed gas is used as a protective gas, it is collectively called melting active gas shielded arc welding (abbreviated to MAG welding internationally). Judging from its operation mode, the most widely used ones at present are semi-automatic argon protected welding and argon-rich mixed gas shielded welding, followed by automatic argon protected welding.
4. Characteristics of argon arc welding
(1) High efficiency
The current density is large, the heat is concentrated, the deposition rate is high, and the welding speed is fast. In addition, it is easy to strike an arc. Protection needs to be strengthened because the arc light is strong and the smoke is large, so protection must be strengthened.
(2) Protective gas
The most commonly used inert gas is argon. It is a colorless and odorless gas with a content of 0.935% in air (calculated by volume). The boiling point of argon is -186°C, which is between the boiling points of oxygen and helium. Argon is a by-product of oxygen plants fractionating liquid air to produce oxygen.
Bottled argon is used for welding in China, and its filling pressure is 15MPa at room temperature. The cylinder is painted gray and marked “Argon”. The chemical composition requirements of pure argon are: Ar ≥ 99.99%; He ≤ 0.01%; O2 ≤ 0.0015%; H2 ≤ 0.0005%; total carbon content ≤ 0.001%; moisture ≤ 30mg/m2.
Argon is an ideal protective gas, which is 25% denser than air. It is helpful for protecting the welding arc during flat welding and reducing the consumption of protective gas. Argon is a gas with very inactive chemical properties. It does not react chemically with metals even at high temperatures, so there is no oxidation and burning loss of alloy elements and a series of problems caused by it. Argon is also insoluble in liquid metal and will not cause porosity. Argon is a monatomic gas that exists in an atomic state and has no molecular decomposition or atomic endothermy at high temperatures. The specific heat capacity and thermal conductivity of argon are small, that is, the amount of argon absorbed is small and the heat transfer is small. The heat in the arc is not easily lost, which makes the welding arc burn stably and concentrates the heat, which is beneficial to the welding process.
The disadvantage of argon is its higher ionization potential. When the arc space is filled with argon gas, it is more difficult to ignite the arc, but once the arc is ignited, it is very stable.
5. Advantages of argon arc welding
The reason why argon protected welding is so widely used is mainly because of the following advantages.
(1) Argon gas protection can isolate the adverse effects of oxygen, nitrogen, hydrogen, etc. in the air on the arc and molten pool, reduce the burning loss of alloy elements, and obtain dense, spatter-free, and high-quality welding joints;
(2) The arc combustion of argon arc welding is stable, the heat is concentrated, the arc column temperature is high, the welding production efficiency is high, the heat affected zone is narrow, and the stress, deformation, and crack tendency of the welded parts are small;
(3) Argon arc welding is open arc welding, which is easy to operate and observe;
(4) The electrode loss is small, the arc length is easy to maintain, and there is no flux or coating layer during welding, so it is easy to implement mechanization and automation;
(5) Argon arc welding can weld almost all metals, especially some refractory metals and easily oxidized metals, such as magnesium, titanium, molybdenum, zirconium, aluminum, etc. and their alloys;
(6) It is not restricted by the position of the weldment and can be welded in all positions.
6. Disadvantages of argon arc welding
(1) Due to the large heat-affected area of argon arc welding, the workpiece often causes deformation, excessive hardness, blisters, local annealing, cracking, pinholes, wear, scratches, undercuts, or insufficient bonding force and internal defects after repair. Stress damage and other shortcomings. Especially in the repair process of precision castings, small defects are highlighted on the surface. In the field of repairing defects in precision castings, cold welding machines can be used to replace argon arc welding. Since the cold welding machine releases less heat, it can better overcome the shortcomings of argon protected welding and make up for the repair problems of precision castings.
(2) Compared with electrode arc welding, argon arc welding is more harmful to the human body. The current density of argon arc welding is large and the light emitted is relatively strong. The ultraviolet radiation generated by its arc is about 100% compared with ordinary electrode arc welding. 5 to 30 times that of arc welding, and infrared rays are about 1 to 1.5 times that of arc welding. The ozone content produced during welding is higher. Therefore, try to choose a place with good air circulation for construction, otherwise it will cause great harm to the body.
(3) For metals with low melting points and easy evaporation (such as lead, tin, zinc), welding is more difficult.
7. Precautions for argon arc welding
Harmful factors
There are three harmful factors that affect the human body during argon arc welding:
(1) Radioactivity
The thorium in the tungsten electrode is a radioactive element, but the radiation dose of the thorium tungsten electrode during tungsten arc welding is very small, within the allowable range, and does not cause much harm. If radioactive gases or particles enter the human body and serve as internal radiation sources, it will seriously affect health.
(2) High frequency electromagnetic field
When high-frequency arc ignition is used, the intensity of the high-frequency electromagnetic field generated is between 60 and 110V/m, which is several times higher than the reference health standard (20V/m). But because the time is very short, it has little impact on the human body. If arcs are struck frequently, or a high-frequency oscillator is used continuously as an arc stabilizing device during the welding process, the high-frequency electromagnetic field can become one of the harmful factors.
(3) Harmful gases—ozone and nitrogen oxides
During argon arc welding, the arc column temperature is high. The intensity of ultraviolet radiation is much greater than that of ordinary arc welding, so a large amount of ozone and oxygen nitrides will be produced during the welding process; in particular, the concentration of ozone far exceeds the reference health standards. If effective ventilation measures are not taken, these gases will have a great impact on human health and are the main harmful factors in argon arc welding.
Security
(1) Ventilation measures
The argon protected welding work site must have good ventilation devices to discharge harmful gases and smoke. In addition to factory ventilation, several axial flow fans can be installed to exhaust air in places where the welding workload is heavy and welding machines are concentrated.
In addition, local ventilation measures can be used to remove harmful gases around the arc, such as open arc fume exhaust hoods, fume exhaust welding guns, lightweight small fans, etc.
8. Hazards of argon arc welding
(1) Hazards of welding smoke
Argon arc welding is mainly used in the welding of aluminum and aluminum alloys, copper and copper alloys, magnesium and magnesium alloys, titanium and titanium alloys, high temperature alloys, etc., and is widely used in many important industrial sectors. In addition to the same electric shock, burns, and fires as electrode arc welding, argon arc welding also has high-frequency electromagnetic fields, electric shock radioactivity, and arc light damage that is much stronger than arc welding.
(2) Welding smoke purification
①Natural ventilation.
②Cartridge-type mobile welding fume purifier.
③High negative pressure welding fume dust collector.
Natural ventilation has the lowest cost. Pure natural methods are mainly used to reduce the concentration of welding smoke in the workshop by opening windows for ventilation and setting up blinds.
The cartridge-type mobile welding smoke purifier aims the universal suction arm at the point where the welding smoke is generated. Through the negative pressure generated by the system, the dust and toxic and harmful gases generated in the welding smoke are inhaled into the purifier and collected. Cartridge-type mobile welding fume purifiers have a wide range of applications. It is convenient, flexible and easy to move. Can meet various flexible working conditions.
The high negative pressure welding smoke dust collector mainly connects the 50mm diameter hose directly to the welding head. The dust collector works when the welding machine is working, and stops when the welding machine stops. This ensures effective treatment of welding fume while using the minimum air volume. In addition, the high negative pressure welding smoke dust collector can be connected to a hose up to 20m long, and can be effectively connected to automatic welding machine heads. It overcomes the disadvantage that the mobile suction arm needs to be moved manually. Now we have achieved automation, and the network purification effect is remarkable.
9. Applicable scenarios for argon arc welding
TIG welding is a commonly used arc welding method suitable for many different scenarios and applications. The following are some applicable scenarios:
Precision welding: TIG welding can provide highly precise welding and is suitable for jobs that require high-quality, high-precision welding, such as aerospace, automotive manufacturing, and electronic equipment manufacturing.
Butt welding of thin materials: TIG welding is suitable for butt welding of thin materials because it can provide lower heat input and smaller penetration depth, reducing the heat affected area of the material, thereby reducing the possibility of deformation and discoloration.
Stainless steel welding: Argon arc welding has a very good welding effect on stainless steel and can maintain the corrosion resistance and aesthetics of the weld. It is suitable for industries such as food processing and chemical industry that have high requirements on welding quality and appearance.
High temperature alloy welding: Some high temperature alloys such as tungsten, molybdenum, titanium, etc. are difficult to weld, but argon arc welding can effectively weld these materials under the protection of inert gas.
Welded pipes: Argon arc welding is also commonly used in the manufacture and installation of welded pipes, especially stainless steel pipes, aluminum pipes and other pipes, to ensure the quality and reliability of the welds.
Aluminum alloy welding: Argon arc welding is also suitable for the welding of aluminum alloys, and high-quality aluminum alloy welding can be achieved through different gas combinations and welding wire selections.
