Argon arc welding / argon gas shielded welding. It is to pass argon arc protection gas near the arc welding and isolate the air outside the welding area to prevent the oxidation of the welding zone. Argon arc welding is divided into two types: argon arc welding and non melt argon arc welding according to different electrodes.
Working principle and characteristics of 1. non melting polar argon arc welding
Non melted polar argon arc welding is an inert gas (often used in argon) that flows through a non metal chemical reaction in the vicinity of a non melting pole (usually tungsten pole). It forms a protective gas shield to prevent the tungsten extreme head, arc and molten pool and the metal in the high temperature not to contact with the air, and can prevent it from contacting the air. Oxidation and absorption of harmful gases. Thus forming compact welding joint, its mechanical function is very good.
Working principle and characteristics of 2. melting pole argon arc welding
The wire is sent through the wire wheel, the conductive nozzle conducts electricity, and the arc is produced between the parent material and the wire, so that the wire and the material are melted, and the arc and molten metal are protected with inert gas argon. It is different from tungsten arc argon arc welding: one is welding wire as electrode, and it is continuously melted and filled into molten pool and condenses to form weld. The other is to protect gas and follow the technology of melting extreme argon arc welding. The protection gas has been widely used by a single argon gas to develop a variety of mixed gases, such as 80%Ar + CO2 rich argon protection gas . Usually the former is called MIG, and the latter is called MAG. From the way of its manipulation, the most widely used are semi-automatic melting polar argon arc welding and argon rich gas shielded welding, followed by automatic melting polar argon arc welding (the next concrete first).
Compared with tungsten inert gas arc welding, TIG has the following characteristics.
(1) high efficiency because of its high current density, heat concentration, high deposition rate and fast welding speed. In addition, it is easy to lead the arc.
(2) we need to strengthen protection because of strong arc and large smoke, so we need to strengthen protection.
3. protective gas
(1) the most commonly used inert gases are argon. It is a colorless and odorless gas. The content of air is 0.935% (by volume). The boiling point of argon is - - 18. 6 degrees, between the boiling point of oxygen and helium. Argon is a byproduct of oxygen production from liquid air in an oxygen plant.
Bottled argon is used for welding in China, and its filling pressure is 15MPa at room temperature. The cylinder is painted with gray paint and marked with "argon". The chemical composition of pure argon is: Ar > 99.99%; He < 0.01%; O2 < 0.0015%; H2 < 0.0005%; total carbon content is less than 0.001%; water is less than 30mg / m3.
Argon is an ideal protective gas, which is 25% larger than the air density. It is beneficial to protect welding arc during flat welding and reduce the consumption of protective gas. Argon is a very inactive chemical gas. Even at high temperature, it does not react with the metal, so there is no burning loss of the alloy elements and a series of problems resulting from it. Argon is also insoluble in liquid metals, thus causing no porosity. Argon is a monatomic gas, which exists in atomic state. There is no molecular decomposition or heat absorption at high temperature. The specific heat capacity and heat conduction of argon are small, that is, the absorption of the argon itself is small, and the heat transfer to the other is little. The heat in the arc is not easily lost, which makes the welding arc burning and the heat is concentrated, which is beneficial to the welding.
The disadvantage of argon is that the ionization potential is high. When the arc space is full of argon, the ignition of the arc is more difficult, but once the arc is ignited, it will be very undisturbed.
The shortcoming of 4. argon arc welding
(1) due to the large heat affected area of argon arc welding, after repair, the workpiece often causes deformation, hardness reduction, sand eye, local annealing, cracking, pinhole, wear, scratch, bite, or lack of joint force and internal stress damage. Especially, the repair process of small defects in precision forging is protruding on the surface. The cold welding machine can be used to replace argon arc welding in the repair field of precision casting defects, because the cold welding machine has a small heat release and better overcome the shortcomings of the argon arc welding, and make up the setback of the precision casting repair.
Argon arc welding and welding electrode arc welding have a higher degree of injury to the human body. The current density of argon arc welding is large and the light is more intense. The ultraviolet radiation produced by its arc is about 5~30 times that of ordinary electrode arc welding, 1 to 1.5 times the arc welding of welding electrode, and the ozone content is higher in welding. Therefore, try to choose the place where the air flows smoothly and smoothly, otherwise it will do great harm to the body.
Application of 5. argon arc welding
Argon arc welding is used to weld the easily oxidizing nonferrous and alloy steel (currently used mainly by welding of Al, Mg, Ti and their alloys and stainless steel); it is used in single side welding and double-sided forming, such as bottom welding and pipe.